Polymer Fillers and Stiffening Agents: Applications and Non-traditional Alternatives 9783110669992, 9783110669893

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Chris Defonseka Polymer Fillers and Stiffening Agents

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Chris Defonseka

Polymer Fillers and Stiffening Agents Applications and Non-traditional Alternatives

Author Chris Defonseka Toronto Canada [email protected]

ISBN 978-3-11-066989-3 e-ISBN (PDF) 978-3-11-066999-2 e-ISBN (EPUB) 978-3-11-067010-3 Library of Congress Control Number: 2019954704 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.dnb.de. © 2020 Walter de Gruyter GmbH, Berlin/Boston Cover image: ljubaphoto / iStock / Getty Images Plus Typesetting: Integra Software Services Pvt. Ltd. Printing and binding: CPI books GmbH, Leck www.degruyter.com

Preface Over the years, as global environmental pollution concerns have been increasing, the chemical industry and particularly the plastics industry has had to face some challenges. In order to move away from petroleum-based chemicals as far as possible, research and developers have been able to make some progress in this direction. Additives are important components for the polymer resin industry, first to convert the basic monomers to viable resin compounds and second for processing these polymer resins. This book is a well-researched presentation based on emerging technologies, already in actual practice which shows the immense possibilities of using non-traditional fillers and stiffening agents, which are essential for the plastics industry. With an objective for efficient cost-effective usage of environmentally friendly materials, this book identifies a range of usable non-traditional and non-petro-based fillers and stiffening agents for polymer products. It includes essential basics of polymer chemistry, effective usage of these materials which are abundantly available as renewable biomass, often regarded as waste and also discusses the advantages and cost-effectiveness of the various possibilities of using them singly or in combination. This book also presents practical and innovative methods for manufacturing composite polymer resins which reduces processing costs and thus, costs of the final products. Furthermore, it shows how these biomass materials can be effectively used with formulations and processing methods provided to make excellent substitute products and also new products at reduced costs. Two of these products are alternate products for asbestos/cement roofing sheets, banned in most countries, and polymeric lumber, which is considered by industry as an ideal substitute for natural wood. While this book provides valuable and practical knowledge leading to exciting possibilities for resin manufacturers, plastics processors, and plastics product manufacturers, it will also show researchers and developers the vast possibilities available with the use of these non-traditional fillers and stiffening agents. This book should be of interest to teachers, students and entrepreneurs as well. In conclusion, I wish to thank Lena Stoll – acquisition editor and the staff of De Gruyter – for the excellent support and cooperation extended to me to make this publication possible.

https://doi.org/10.1515/9783110669992-202

Contents Preface

V

1 Basic chemistry 1 1.1 Introduction 1 1.2 Organic chemistry basis 1 1.2.1 Properties 2 1.2.2 Melting and boiling properties 2 1.2.3 Solubility 2 1.2.4 Structural presentation 3 1.2.5 Functional groups 3 1.2.6 Aliphatic compounds 3 1.2.7 Aromatic compounds 4 1.2.8 Polymers 4 1.3 Inorganic chemistry 4 1.3.1 Industrial inorganic chemistry 5 1.3.2 Organometallic compounds 5 1.3.3 Cluster compounds 6 1.3.4 Bio-inorganic chemistry 6 1.4 Basics of analytical chemistry 6 1.4.1 Qualitative analysis 7 1.4.1.1 Flame test 7 1.4.1.2 Gravimetric analysis 7 1.4.1.3 Volumetric analysis 7 1.4.1.4 Electro-chemical analysis 7 1.4.1.5 Microscopy 8 1.5 Industrial chemistry 8 Bibliography 9 2 Polymer chemistry 11 2.1 Introduction 11 2.2 What are polymers? 12 2.3 Monomer structures 13 2.3.1 Polymer microstructures 15 2.3.1.1 Polymer chain lengths 16 2.3.2 Polymer molecular weight 16 2.3.3 Polymer degradation 16 2.3.4 Filled polymers 17 2.3.5 Modified polymers 17 2.3.6 Engineered polymers 17 2.3.7 Properties of plastics 18

VIII

2.3.8 2.3.9 2.3.10 2.3.11 2.3.12 2.3.13 2.3.14 2.3.15 2.3.16 2.3.17 2.4 2.5 2.5.1 2.5.2 2.5.3 2.5.4 2.5.5 2.5.6 2.5.7 2.5.8 2.5.9 2.5.10 2.6 2.6.1 2.6.2 2.6.3 2.6.4

Contents

Compatibility of materials 18 Mechanical properties 19 Friction factor 19 Environmental effects 19 Water absorption 20 Weathering effects 20 Tensile strength 20 Young’s modulus of elasticity 20 Melting point 21 Glass transition temperature 21 Processing of polymers 21 Scope and applications of polymer chemistry Alternative energy 22 Chemical industry 23 Polymers in agriculture 23 Synthetic fibres 23 Coatings 24 Rubber 24 ‘Green’ polymers 25 Adhesives 26 Oil and gas industries 26 Polymers in nanotechnology 27 Speciality polymers 27 Hydrocarbon resins 27 Ethylene vinyl copolymer resins 28 Vitrimer plastics 28 Graphene polymers 29 Bibliography 29

3 Polymer material science 31 3.1 Brief history 31 3.2 What is material science? 31 3.3 Fundamentals of material science 3.3.1 Atomic structures 33 3.3.2 Nanostructures 33 3.3.3 Microstructures 33 3.3.4 Crystallography 34 3.3.5 Chemical bonding 35 3.3.5.1 Covalent bonds 36 3.3.5.2 Polar covalent bonds 36 3.3.5.3 Ionic bonding 36 3.3.5.4 Metallic bonds 36

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Contents

3.3.5.5 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.13.1 3.13.2 3.13.3 3.13.4 3.13.5

Hydrogen bonding 36 Synthesis and processing 37 Thermodynamics 37 Kinetics 37 Nanomaterials 38 Biomaterials 38 Electronic, optical and magnetic materials Ceramics and glass materials 39 Composite materials 39 Polymeric materials 40 Special materials 41 Polylactic acid (PLA) 41 Natural rubber alternative 41 Elastomers 42 New class of polymers 43 Thermoplastic polymers from citrus fruits Bibliography 44

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4 Non-traditional fillers and stiffening agents for polymers 47 4.1 Introduction 47 4.2 Non-traditional fillers and stiffening agents 49 4.2.1 Rice hulls 50 4.2.2 Understanding rice hull ash as fillers for polymers 50 4.2.3 Wheat hulls as a renewable energy/filler source 52 4.2.4 Fly ash 52 4.2.5 Bamboo fibre and flour 53 4.2.6 Properties of eggshell powder as a filler in polymers 56 4.2.7 Coir dust and fly ash composites 57 4.2.8 Graphene – polymer composites 58 4.2.9 Epoxy composites filled with walnut shell powder 60 4.2.10 Expandable polystyrene as filler in rigid polyurethane foams 61 4.2.11 Coconut shell powder as filler in polymers 63 4.2.12 Shellfish shell powder as bio-filler in polymer composites 64 Bibliography 67 5 5.1 5.2 5.2.1 5.2.2 5.2.3

Processing polymers and composite resins Introduction 69 Manufacture of composite resins 70 Concept 70 Manufacturing process in brief 71 Raw materials 72

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5.2.4 5.3 5.4 5.4.1 5.5 5.5.1 5.6 5.7 5.7.1 5.7.2 5.7.3 5.7.4 5.7.5 5.7.6 5.7.7 5.7.8 5.8 5.8.1 5.9 5.10 5.10.1 5.10.2 5.10.3

6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12

Contents

Machinery and equipment 73 Injection moulding 74 Injection moulding with polymer composite resins (PCR) with rice hulls 76 Recommended processing guidelines 78 Injection moulding with polymer resin with eggshell powder 78 Recommended procedure 79 Extrusion process in brief 80 Extrusion of polymeric composite lumber 81 Raw materials 82 Coupling agents 83 Lubricants 84 Heat stabilisers 84 Foaming agents 84 Colourants 85 Manufacture of polymer composite lumber 86 Range of applications 87 Compression moulding 88 Compression moulding with polymeric composite resins 91 Foaming processes 92 Recycling of plastics 92 General standard polymers 93 Bioplastics 93 Biodegradable plastics 94 Bibliography 96 Formulating with non-traditional fillers and stiffening agents 97 Introduction 97 Standard fillers and stiffening agents 97 Non-traditional fillers and stiffening agents 98 Common polymers and additives for formulating 100 Basic properties for composites 104 Calculations, formulations and processing methods for selected manufactures 106 Manufacture of flexible PUR foams 107 Processing method in brief 110 Manufacture of highly filled PUR foams with a combination of NTFSAs 110 Processing method in brief 112 Manufacture of composite polymeric bamboo floor tiles 112 Processing method in brief 113

Contents

6.13 6.14

Manufacture of PVC artificial leather using NTFSAs Processing method in brief 115 Bibliography 116

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Manufacturing special polymeric products with non-traditional fillers and stiffening agents 117 7.1 Introductory presentation 117 7.2 Manufacture of fibre/cement corrugated roofing sheets 118 7.3 Processing method 121 7.4 Manufacture of composite bricks with fly ash 121 7.5 Manufacturing process in brief 123 7.6 Manufacture of bricks with 100% fly ash 123 7.7 Road paving with bitumen, plastic wastes and NTFSAs 125 7.7.1 Raw materials 126 7.7.1.1 Bitumen 126 7.7.1.2 Plastics 127 7.8 Processing method in brief 128 7.9 Manufacture of polymer composite door panels with rice hulls 129 7.9.1 Polymer composite solid doors 130 7.10 Processing method in brief 132 7.11 Manufacture of medium-density fibreboard (MDF) 132 7.11.1 MDF boards from polyvinyl chloride (PVC) 133 7.12 Manufacture of compression moulded parts – thermoset polymer/NTFSA 135 7.13 Processing method in brief 136 Bibliography 137 8

Recommendations for operating efficiency in a manufacturing plant 139 8.1 Introduction 139 8.1.1 Plant design 139 8.1.2 Raw material and storage 141 8.1.3 Machinery and equipment 141 8.1.4 Preventive maintenance 142 8.1.5 Processing systems 143 8.1.6 Quality control/in-house laboratory 143 8.1.6.1 Quality control 143 8.1.6.2 In-house laboratory 144 8.1.7 Process efficiency 145 8.1.7.1 Key factors on a production floor 145 8.1.8 Troubleshooting 146

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Contents

Lean manufacturing 147 Productivity 148 Breakeven point 149 Contribution margin 149 Quick performance indicators 150 A case study: improving operating efficiency Company analysis in brief 151 Assignment parameters 151 Implementation of work plan 152 Addressing concerns 155 Bibliography 157

8.1.9 8.1.10 8.1.10.1 8.1.10.2 8.1.10.3 8.1.11 8.1.11.1 8.1.11.2 8.1.11.3 8.1.11.4

Appendix A

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Appendix B

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Appendix C

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Glossary Index

165 169

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1 Basic chemistry 1.1 Introduction Chemistry is the study of the composition of matter and how it changes. The two broad areas of chemistry are organic and inorganic. Organic chemistry deals with matter that contains the element carbon, whereas inorganic chemistry is the study of matter, mineral in origin. The term ‘organic’ originally meant compounds of plants or animals but now it also includes many synthetic materials that have been developed through research. One such group of synthetic organic materials is called ‘plastics’. Chemical theory is based on the fact that all matter consists of base substances called ‘elements’. Matter is defined as anything that has mass (weight) and occupies space and may exist in the form of a solid, liquid or gas. The structures of matter are composed of small particles called ‘atoms’, which combine to form larger particles called ‘molecules’, and when they combine, they form ‘compounds’. The smallest particle is an atom, and a molecule is formed by two or more atoms. Atoms consist of particles called ‘neutrons’, ‘protons’ and ‘electrons’. The atoms of each element differ in the number of particles they contain. Thus, no two elements will have identical atoms. Neutron is a particle with no electrical charge, whereas protons are positively charged. Both occupy the centre of an atom called the nucleus. Electrons are negatively charged particles and are in orbit around the nucleus. The negative charge of the electrons moving around the nucleus is equal to the positive charge of the protons in the nucleus. Therefore, for all elements, an atom is electrically neutral. If an atom gains an electron, it becomes electronegative (a negative ion) and if an atom loses an electron, it becomes electropositive (a positive ion). An ion is an atom that has gained or lost one or more electrons. Each element has an atomic number, which is the number of protons in the nucleus. The atomic weight of an element is the mass of an atom of that element compared with the mass of an atom of carbon. The molecular weight mass or weight is the total atomic weights of the atoms making up the molecules. The periodic table lists all elements and also shows their atomic and molecular weights. When single elements join together, they form compounds. Some of the most common elements that join together to form plastics are hydrogen, oxygen, nitrogen, chlorine, fluorine, silicone, carbon, and so on.

1.2 Organic chemistry basis Organic chemistry is the study of the structures, properties, compositions, reactions, preparation by synthetic or other means of carbon-based compounds, hydrocarbons, https://doi.org/10.1515/9783110669992-001

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and their derivatives. These compounds may contain any number of other elements, including hydrogen, nitrogen, oxygen, the halogens as well as phosphorous, silicon, and sulphur. Organic compounds are structurally diverse. The range of applications of organic compounds is enormous. They form the basis or of constituents of many products such as plastics, drugs, food, petrochemicals, explosives, paints, and many more.

1.2.1 Properties Physical properties of typical organic compounds of interest include quantitative and qualitative features. Qualitative data includes melting point, boiling point and index of refraction, whereas qualitative properties include door, colour, consistency and solubility.

1.2.2 Melting and boiling properties In contrast to many inorganic compounds, organic materials melt and boil. These properties provide crucial information about the identity and purity of organic compounds. This information correlates with the polarity of the molecules and their molecular weights. Some organic compounds, especially symmetrical ones, undergo sublimation (transition from a solid phase to a gas phase without passing through an intermediate liquid phase). A well-known example of a sublime organic compound of this nature is p-dichlorobenzene, the odiferous constituent of modern-day mothballs. Organic compounds are usually not very stable at temperatures ≥ 300 °C (572 °F), although there are exceptions.

1.2.3 Solubility Neutral organic compounds tend to become hydrophobic, meaning they are less soluble in water than in organic solvents. Exceptions include organic compounds that contain ionisable groups, as well as low molecular weight alcohols, amines and carbolic acids, where hydrogen bonding occurs. Organic compounds tend to dissolve in organic solvents. Solvents can be pure substances such as ether or mixtures. Mixtures can be paraffinic solvents such as the various petroleum or tar fractions obtained by physical separation or by chemical conversion. The degree of solubility in different solvents is dependent upon the solvent type and on the functional groups.

1.2 Organic chemistry basis

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1.2.4 Structural presentation Organic structures can be described by drawings, structural formulae, combinations of drawings and chemical symbols. The line-angle formula is simple and unambiguous. In such a system, the endpoints and intersections of each line represent one carbon atom, and hydrogen atoms can be notated explicitly or assumed to be present as implied by a tetravalent carbon. The depiction of organic compounds with drawings is greatly simplified by the fact that carbon in almost all organic compounds has four bonds, oxygen two, hydrogen one and nitrogen three.

1.2.5 Functional groups The concept of functional groups is central to organic chemistry as a means to classify structures and for predicting properties. A functional group is a molecular model, and the reactivity of that functional group is assumed (within limitations) to be the same in various molecules. Functional groups can have a decisive influence on the chemical and physical properties of organic compounds. Molecules are classified on the basis of their functional groups. For example, alcohols have the sub-unit C-O-H. All alcohols tend to be hydrophilic (usually from esters) and can be converted to the corresponding halides. Most functional groups feature heteroatoms (atoms other than carbon, functional groups and hydrogen). Organic compounds are classified according to their functional groups, alcohols, carbolic acids and amines.

1.2.6 Aliphatic compounds Aliphatic hydrocarbons are sub-divided into three groups of homologous series according to their state of saturation as follows: – Paraffin – which are alkanes without any double or triple bonds. – Olefins and Alkenes – which contain one or more double bonds (e.g. polyolefin). – Alkynes – which have one or more triple bonds. The rest of the groups are classified according to the functional groups present. Such compounds can be straight-chained, branch-chained or cyclic. The degree of branching affects characteristics such as the octane number as in the petroleum industry. Saturated compounds and unsaturated compounds exist as cyclic derivatives. The most stable rings contain five or six carbon atoms but large rings such as macro-cycles, and smaller rings are also common.

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1.2.7 Aromatic compounds Aromatic hydrocarbons contain double bonds. The most important example is benzene, the structure of which was formulated by a chemist who first proposed delocalization (also known as resonance principle) to explain its structure. For conventional cyclic compounds, aromaticity is conferred by delocalized electrons. Particular instability (anti-aromaticity) is conferred by conjugated electrons.

1.2.8 Polymers One important property of carbon is that it forms chains or networks that are linked by carbon–carbon bonds. This linking process is called ‘polymerization’, whereas the chains or networks are called ‘polymers’. The starting source compounds are called ‘monomers’, the basic unit of a plastics being a ‘mer’. There are two main groups of polymers: synthetic and biopolymers. Synthetic polymers are made artificially, and commonly referred to as ‘industrial polymers’, while biopolymers occur within natural environments or with human intervention. Since the invention of the first synthetic polymer product called Bakelite, many others have been invented and continue to be researched and produced to this day. Some common synthetic organic polymers are polyethylene, polystyrene, polypropylene, nylon, poly vinyl chloride, and so on. Synthetic and natural rubbers are also polymers. Varieties of synthetic polymers are specifically made for different products. Changing the conditions at the time of polymerization, alters the chemical structure of the final polymer and its properties. These changes include chain lengths, branching or tacticity. If the product is from a single polymer, it is called a ‘homopolymer’, and if it is from two different polymers, they are called ‘copolymers’. If three different polymers are combined, then the resulting product is called a ‘terpolymer’. When end products are made with these polymers, physical properties such as hardness, density, mechanical or tensile strength, abrasion, heat resistance, transparency, colour, and so on are achieved with a combination of additives to achieve pre-determined end properties.

1.3 Inorganic chemistry Inorganic chemistry is the branch of chemistry dealing with the properties and behaviour of non-carbon compounds. The distinction between organic and inorganic chemistry is far from absolute, and there is much overlap, mostly in the subdisciplines of organometallic chemistry. Many inorganic compounds are ionic compounds of cations (positively charged ions) and anions (negatively charged ions) joined by ionic bonding. Examples of

1.3 Inorganic chemistry

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ionic compounds are salts, such as magnesium chloride, which consists of magnesium cations, and chlorine anions. Another example is sodium oxide, which consists of sodium cations, and oxide anions. In any salt, the proportions of ions are such that the electric charges cancel out, so that the bulk compound is electrically neutral. Ions are described by their oxidation state. Their ease of formation can be inferred by the ionization potential (cations) or from the electron affinity (anions) of the sourcing elements. Important classes of inorganic salts are oxides, carbonates, sulfates, and halides. Many inorganic salts are characterized by high melting points. Inorganic salts are poor conductors in the solid states. Another important feature is their solubility in water and ease of crystallization. Some salts such as sodium chloride are very soluble in water but some others are not. The simplest inorganic reaction is double displacement in the mixing of two salts, the ions are swapped without a change in oxidation state. The net result is an exchange of electrons. Electron exchange can also occur indirectly, for example, in batteries, which is a key concept in electrochemistry. Inorganic compounds are found as minerals. Soil may contain iron sulfide as pyrite or calcium sulfate as gypsum. Inorganic compounds are also found ‘multitasking’ as biochemicals such as electrolytes (sodium chloride) in energy storage or in construction (polyphosphate). The first important man-made inorganic compound was ammonium nitrate for soil fertilization. Inorganic compounds are synthesized for use as catalysts, such as vanadium and titanium chloride or as reagents in organic chemistry, such as lithium aluminium hydride. Subdivisions of chemistry are organometallic chemistry, cluster chemistry and bio-inorganic chemistry. These fields are active areas of research in inorganic chemistry aimed at finding new catalysts, superconductors and therapies.

1.3.1 Industrial inorganic chemistry Inorganic chemistry has traditionally played a major role in the production of industrial chemicals. Some of the most essential inorganic chemicals manufactured in many countries are ammonia, aluminium sulfate, ammonium nitrate, carbon black, chlorine, hydrochloric acid, hydrogen, hydrogen peroxide, nitric acid, nitrogen, oxygen, phosperic acid, sodium carbonate, sodium chlorate, sodium hydroxide, sodium silicate, sodium sulfate, sulphuric acid and titanium dioxide. Manufacture of fertilizers is another major sector of industrial inorganic chemistry.

1.3.2 Organometallic compounds Organometallic chemistry is the study of chemical compounds containing bonds between carbon and metals. They are considered to be a special category, because

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organic ligands (ions or neutral molecules) are sensitive to hydrolysis or oxidation. Thus, organometallic chemistry employs more specialized preparative methods than traditional chemistry. Synthetic methodology, especially manipulating complexes in solvents of low coordinating power, has enabled exploration of very weak coordinating ligands, such as hydrocarbons. Because the ligands are petrochemical in some sense, organometallic chemistry is also very important to industry.

1.3.3 Cluster compounds Clusters can be found in all classes of chemical compounds. According to general theory, a cluster consists of a triangular set of atoms that are bonded directly to each other. Metal–metal bonded di-metallic complexes are highly relevant in this area. Clusters occur in ‘pure’ inorganic systems, organometallic chemistry, main group chemistry and bio-organic chemistry. The distinction between very large clusters and bulk solids are increasingly blurred. This interface is the chemical basis for nanotechnology and arises specifically from the study of quantum size effects in cadmium-selenite clusters. Thus, large clusters can be described as an array of bound atoms, intermediate between a molecule and a solid.

1.3.4 Bio-inorganic chemistry By definition bio-inorganic compounds occur in nature but this sub-class includes anthropogenic series such as pollutants, and drugs. This research area incorporates many aspects of biochemistry, including many types of compounds and metal complexes containing ligands that range from biological macromolecules to the illdefined humic acid. Traditionally, inorganic biochemistry focuses on electron transfer and energy transfer in proteins relevant to respiration. Medical inorganic chemistry includes the study of essential and non-essential elements, with application to diagnoses and therapy.

1.4 Basics of analytical chemistry Analytical chemistry is the study of the separation, identification and quantification of chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the selected sample and also determines the amount of one or more components. The separation of components is often undertaken before analysis. Analytical methods can be separated into ‘classical’ and ‘instrumental’. Classical methods, also known as ‘wet’ chemistry methods, use separation methods such as

1.4 Basics of analytical chemistry

7

precipitation, extraction, distillation and qualitative analysis by colour, door or melting point. Quantitative analysis is achieved by measurement of weights or volume. Instrumental methods use an apparatus to measure the physical quantities of the analyte such as light absorption, fluorescence or conductivity. The separation of materials is accomplished by using chromatography or electrophoresis methods. Analytical analyses have applications in forensics, bio-analysis, clinical analysis, materials analysis and are very important for industrial chemists.

1.4.1 Qualitative analysis A qualitative analysis determines the presence or absence of a particular compound but not the mass or concentration. That is, it is not related to quantity. 1.4.1.1 Flame test An inorganic qualitative analysis refers to a systematic method to confirm the presence of certain (usually aqueous) ions or elements by carrying out a series of reactions that eliminates ranges of possibilities and then confirms the suspected ions with a test. Sometimes, small carbon-containing ions are included in such methods. With modern instrumentation these test are rarely used but can be useful for educational purposes and in situations where state of the art instruments are not available or expedient. 1.4.1.2 Gravimetric analysis Gravimeter is an analysis that involves determining the amount of material present by weighing the selected sample before and after transformation. A common example used for educational purposes is the determination of the amount of water in a hydrate by heating the sample to remove the water such that the difference in weight is due to the loss of water. 1.4.1.3 Volumetric analysis Titration involves the addition of a reactant to a solution being analysed until an equivalent point is reached. Often, the amount of material in the solution being analysed may be determined. Most familiar is an acid–base titration, involving colour changing indication. There are many other types of titration, for example, potentiometric titrations. These may use different types of indicators to reach an equivalent point. 1.4.1.4 Electro-chemical analysis Electro-chemical methods measure the potential (volts), and/or current (amperes) in an electrochemical cell containing the analyte. These methods can be categorized

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according to which aspect of the cell is being controlled and measured. The three main categories are potentiometry (difference in electrode potentials), coulometry (call current measured over time) and voltammetry (cell current is measured while actively altering the cell potential). 1.4.1.5 Microscopy The visualization of single molecules, single cells and nano-materials are an important and highly technical approach in analytical science. Microscopy can be categorized into three main fields: optical, electron and scanning. These fields have seen rapid growth over the years and now highly advanced developments are available due to the advances in computer science and camera technologies. All these branches of analytical chemistry and continuing research and development are important for the field of polymer chemistry, which leads to the formation and manufacture of the all-important plastics resins, and compounds, which have become an essential part of daily human activity.

1.5 Industrial chemistry Industrial chemistry is the branch of chemistry which applies physical and chemical processors to bring about the transformation of raw materials into products that are of benefit to humanity. It involves main disciplines like chemistry, mathematics, physics, engineering and so on. A chemistry graduate is a chemist with knowledge in engineering, chemical processes, economics and industrial management. Polymer chemistry is an extension, and a very important branch in the industrial and manufacturing sector, relevant to the plastics and rubber industries. This field will encompass research, development and conversion of all plastics, generally categorized into two main polymer groups: thermoplastic (softens on heating and can be re-used) and thermosetting (cannot be re-used after moulding). Some of the areas that are benefitted by industrial chemistry are research and development, institutes, production and manufacturing industries, pulp-paper industry, tanning industry, consumer industry, oil and petrochemical refining industries, textile industry, paints and dyes industry, cosmetics industry, cement industry, automobile industry and water purification industry to name a few of the popular ones. With growing climate changes and environmental concerns on a global scale, environment chemistry is playing a leading role in trying to cut down emissions into the atmosphere, with carbon dioxide gas probably the largest contributor towards air pollution. Since air pollution is reaching alarming levels, most countries are now looking to shift away from the use of traditional petro-based products and has been moving towards polymers from natural sources for some time, and this

Bibliography

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presentation is imparting very valuable information of the availability and the possibilities from non-traditional fillers and stiffening agents from natural sources, which are abundantly available in huge volumes in most countries and at lesser costs. These commodities are an essential part and parcel of the polymer industry and directly relevant to the plastics industry. In fact, as can be seen, these items will give better properties in most areas as compared to the traditional petro-based ones and can be processed on normal plastics machinery and equipment but with slightly different moulding parameters with an advantage to the moulders with easier operational conditions and many cost savings. For the benefit of the readers and the plastics industry at large, the author presents detailed information of the vast possibilities with these non-traditional materials to include processes for conversion from raw state, manufacturing methodologies and suitable formulations and projects the important factor of tremendous cost savings, in addition to making a significant contribution towards lessening environment pollutions.

Bibliography [1] [2]

Darell D. Ebbing. (2013) General Chemistry 5th Edition Wayne State University-Publisher Houghton Mifflin Company Boston ISBN: 0-395-74415-6. Defonseka Chris. (2013) Practical Guidelines to Flexible Polyurethanes Apr ISBN: 978-1-84735-974-2-2013. Shawbury, Shropshire, UK: Smithers Rapra UK.

2 Polymer chemistry 2.1 Introduction Information of polymer chemistry is available from books written on this subject. For the benefit of readers, the author takes a different approach in presenting this chapter. Instead of a highly technical text on theory, more ‘commercial’ manufacturing and production methodologies are discussed. This will be more interesting in keeping with the concept of the use of non-traditional fillers and stiffening agents. However, it is also essential that the basics of polymers, their chemistry, formations and structures are understood. Polymer chemistry is a very complex subject, and the information provided here is sufficient for the reader to gain a good understanding of polymers and their chemistry, which is the basis for plastics. In ancient times, people used copper, gold, iron and clay for their daily needs, which were found in their natural forms in the Earth. However, as time passed and technologies advanced, people looked for better goods that were stronger, malleable, durable and practical. Materials that were available could not provide the properties they were looking for, and man in his eternal quest for better products looked for newer materials, which led to synthetic materials. One such group of materials is called ‘plastics’. The word ‘plastics’ is derived from the Greek word ‘plastikos’. In general, a plastic can be defined as a material that is pliable and capable of being shaped by temperature and pressure. Plastics are based on polymers derived from the Greek word ‘polymeros’, with ‘poly’ meaning many, and meros meaning basic units. Polymers are also called resins in the commercial world, which is not really correct because resins are gum-like substances. Polymer chemistry is a multidisciplinary science that deals with chemical synthesis and chemical properties of polymers, which are considered to be macromolecules. Polymer chemists study the large complex molecules (polymers) that are built from smaller (sometimes repeating) units. They study how these smaller building blocks (monomers) were combined to create useful newer materials with specific characteristics. This is done by manipulating the molecular structure of the monomer/polymers used, the composition of the monomer/polymers combination, and applying chemical and processing technology that can, to a large extent, affect the properties of the final product. Polymer chemists are unique within the chemistry and scientific community because of their special knowledge and understanding of the relationships between polymer structures and their properties, spanning from the molecular to the macroscopic state. Although most polymer chemists work on applied research and development of polymers, there are opportunities for fundamental research (mainly in universities, government laboratories, and industrial labs) on theory of polymers in solid and https://doi.org/10.1515/9783110669992-002

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liquid states, on the synthesis of new polymer structures, and also on the mechanical, electronic, optical, biological and other properties of those new polymers are supposed to have. Polymer chemistry and fundamental polymer research are inherently interdisciplinary, spanning chemistry, physics, engineering, economics and even biology.

2.2 What are polymers? A polymer is a large molecule (macromolecule) composed of repeating basic structural units. These subunits are typically connected by covalent chemical bonds. Although the term ‘polymer’ generally refers to plastics, it encompasses a larger class of compounds, comprising natural and synthetic materials with a wide variety of properties. Because of the extraordinary range of polymeric materials, they have essential and vital roles in everyday life of people. They broadly range from the very familiar synthetic plastics and elastomers to natural biopolymers such as nucleic acids and proteins, which are essential for life. Natural polymeric materials such as shellac, amber and natural rubber are used for centuries. Many other natural polymers are the well-known cellulose, nylon, polyvinyl chloride (PVC), polyethylene (PE), polystyrene, polypropylene, silicone and polyurethanes. The most common continuously linked backbone of a polymer used for the manufacture of plastic compounds consists of carbon atoms. A simple example is PE, commonly known as ‘polythene’, whose repeating unit is based on the ethylene monomer, a petroleum by-product. However, other elements such as oxygen and hydrogen are commonly present in the backbone of polymers. Most elements are combinations of two atoms bonded together to form molecules. In plastics technology, bonding patterns are very important because they determine the physical characteristics of the plastic product. Bonds can be divided into primary bonds (ionic or covalent) and secondary bonds called Van der Waal’s forces. All bonds between atoms and elements are electrical in nature. Most elements constantly try to reach a stable state by (a) receiving extra electrons, (b) releasing electrons or (c) sharing electrons. A polymer is made up of many basic units called ‘mers’ repeated in a pattern. If a large number of molecules bond together, a polymer is formed. These basic units are considered to be bifunctional with two reactive bonding sites. Monomers (single units) are the initial basic units that go to form polymers, and in most cases, they are liquids. The chemical reaction or the process that joins these together is called ‘polymerisation’. If a polymer consists of similar repeating units, it is called a ‘homopolymer’ (meaning same type), and if two different types of polymers are polymerised, it is called a ‘copolymer’. If three different types of monomers are polymerised, then the resulting polymer is called a ‘terpolymer’. An ‘elastomer’ is described as any polymer that can be stretched ≥200% of its original length.

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For example: M + M + M. . . . . . . . . . . . . . . . . .= homopolymer M1 + M2 . . . . . . . . . . . . . . . . . . . = copolymer M1 + M2 + M3. . . . . . . . . . . . . . . = terpolymer In general, polymers are classified by systems based on source, light penetration, heat reaction, polymerisation and crystal structure. – Source: polymers from natural sources as well as from modified natural or synthetic sources. – Light penetration: optical properties such as opaque, transparent or luminescent. – Heat reaction: thermoplastic (can be re-used) or thermosetting (cannot be re-used). – Polymerisation: method of joining many basic monomers. – Crystal structure: crystalline (molecules arranged in order) and amorphous (random arrangement of molecules).

2.3 Monomer structures A monomer (basic unit) of a plastic material is the initial molecule used in forming a polymer. If a large number of molecules bond together, a polymer is formed. One of the most important and common monomers is ethylene gas resulting from the refining of crude oil, which is then liquefied. Most monomers are liquids. Figures 2.1 and 2.2 show the basic polymer structures and formation of polymers. Monomers form five basic structures: (a) linear, (b) cross-linked, (c) branched, (d) graft and (e) inter-penetrating. If two different monomers are joined in sequence, it is called co-polymerisation, and the result will be a copolymer. a. Linear structures: there are three basic linear classes – Alternating – ABABABAB. . . . . . . . . . . . . . . . . .. – Random – ABABBAAABBAAA. . . . . . . . .. – Block – AAABBBAAA. . . . . . . . . . . . . . .. b. Cross-linked structures have primary covalent bonds between the molecular chains. c. Branched structures represent three-dimensional branching of the linear chain. d. Graft structures are graft polymers that are similar to cross-linked and branched structured copolymers. The term ‘graft’ is being used to denote a controlled or engineered addition to the main polymer chain. e. Interpenetrating structures: these polymer networks are entangled combinations of two cross-linked polymers that are not bonded to each other. A ‘plastic alloy’ is formed if two or more different polymers are physically mixed together in a melt. The term ‘polyblend’ refers to a plastic material that has been modified by the addition of an elastomer.

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H

H

C

C

H H Ethylene monomer C6H5

H

H

H

H

CL

C

C

C

C

C

C

H

H

H

H

H

H

Polystyrene

n

n

Polyethylene

n Polyvinyl chloride

H

Cl

H

H

H

H

H

C

C

C

C

C

C

C

H

Cl

H

C

H

Cl

H

Monomer H

H

C

C

H

H

Mer where

n

H = hydrogen atom C = carbon atom n = degree of polymerisation [ ] = mer – or I = bond

Figure 2.1: Basic polymer structures.

Polyblends are polymeric materials made by mixing or blending two or more polymers to enhance the physical properties of each individual component. Some common polymer blends include polypropylene/polycarbonate, PVC, acrylonitrile– butadiene–styrene (ABS) and PE/polytetrafluoroethylene. Polymer blending is accomplished by distributing and dispersing a minor or secondary polymer within a major polymer that serves as the matrix. The major component can be thought of as the continuous phase, and the minor components as the distributed or dispersed phase in the form of droplets or filaments. When creating a polymer blend, one must remember that the blend will be re-melted in subsequent processing. For example, a rapidly cooled system, frozen as a homogenous mixture, can separate into phases because of coalescence, when re-heated. For all practical purposes, such a blend cannot be processed. To avoid this problem, compatibilisers are used to ensure compatibility in the boundary layers between the two phases.

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Polymers and copolymers Polymerise

Monomer-A

Mixing Polymer

Polymerise

Monomer-B

Blend of polymers Polymer

Mixing

Polymerise

Monomer-a

Copolymer Monomer-b Figure 2.2: Formation of polymers.

2.3.1 Polymer microstructures The microstructure of a polymer (sometimes called ‘configuration’) relates to the physical arrangement of monomers along the backbone of the chain. These are the elements of polymer structures that require breaking of a covalent bond in order to change. Structures have a strong influence on the properties of a polymer. For example, two samples of natural rubber may exhibit different durabilities, even though their molecules comprise the same monomers. An important microstructural feature of a polymer is its architecture, which relates to the way branch points lead to a deviation from a simple linear chain. A branched polymer molecule is composed of a main chain with one or more substituent side chains or branches. Types of branched polymers include star polymers, comb polymers, brush polymers, dendronised polymers and dendrimers. The architecture of a polymer affects many of its physical properties, including but not limited to solution viscosity, melt viscosity, solubility in various solvents, glass transition temperature and the size of the individual polymer coils in solution. Various methods may be employed for the synthesis of a polymeric material with a different range of architectures.

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2.3.1.1 Polymer chain lengths The physical properties of a polymer are strongly dependent on the size or length of the polymer chain. For example, as chain length is increased, melting and boiling temperatures increase. Impact resistance also tends to increase, as does the viscosity and the resistance to flow of the polymer in its melt state. A common means of expressing the length of a chain is the degree of polymerisation, which quantifies the number of monomers incorporated into the chain. As with other molecules, the size of the polymer may also be expressed in terms of its molecular weight. Synthetic polymerisation methods typically yield a polymer product having a range of molecular weights, so weights are often expressed statistically to describe the distribution of the chain lengths present. Common examples are the number average molecular weight and weight average molecular weight. The ratio of these two values is the polydensity index. A final measurement is contour length, which can be understood as the length of the chain backbone in its fully extended state.

2.3.2 Polymer molecular weight The weight mass of a molecule is determined by adding together the atomic masses of the various atoms making up the molecule. For example, the atomic mass of hydrogen is 1 and that of oxygen is 16. Thus, the molecular mass of a single molecule of water (H2O) = 1 + 1 + 16 = 18. The length (molecular mass) of a polymer chain has a profound effect on processing and properties of a plastic compound. Increasing chain length may increase properties like melt temperature, melt viscosity, toughness, creep and possible polymer degradation.

2.3.3 Polymer degradation Polymer degradation is a change in the properties such as tensile strength, colour, shape or molecular weight of a polymer or polymer-based products under the influence of one or more factors such as heat, light and chemicals. It is often due to a change in the polymer chain bonds via hydrolysis leading to a decrease in molecular mass of the polymer. Although such changes are undesirable in some instances such as biodegradation and recycling, they may have benefits in preventing environmental pollution. Degradation may also be useful in biomedical applications. For example, a copolymer of polylactic acid (PLA), and polyglycolic acid, is employed in hydrolysable stitches that slowly degrade after they are applied to a wound. The susceptibility of a polymer to degrade is dependent on its structure. Epoxies and chains containing aromatic functionalities are especially susceptible to

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degradation by ultraviolet (UV) light, whereas polyesters are susceptible to degradation by hydrolysis, and polymers containing an unsaturated backbone are especially susceptible to ozone cracking. Carbon-based polymers are more susceptible to thermal degradation than inorganic polymers, and are therefore not ideal for most high-temperature applications.

2.3.4 Filled polymers Fillers in general are accepted as being materials that are intentionally incorporated into polymers to change some of their properties, with a main function of making it cheaper. As a rule, any use of fillers will affect the mechanical properties of polymer materials. For example, long fibres will make it stiffer and denser, whereas foaming will make it more compliant and much lighter. Conversely, a filler such as calcium carbonate will decrease the flexibility and toughness of the polymer. Other fillers such as glass fibres or glass spheres will increase the strength. ‘Reinforced plastics’ refer to polymers (matrices) whose properties have been enhanced by introducing reinforcements (fibres) of high stiffness and strength. Such materials are called ‘fibre-reinforced polymers’ or ‘fibre-reinforced composites’.

2.3.5 Modified polymers The properties of thermoplastics can be modified by adding additives. If a plasticising agent is added, the glass transition temperature (Tg) becomes lower, and consequently the shear modulus starts to drop at a much lower temperature. In essence, the plasticiser replaces a temperature rise by ‘wedging’ these low-molecular-weight materials between the polymer’s molecular structures, generating free volume between the chains. This additional free volume is equal to a temperature rise, which consequently lowers the Tg, making a normally brittle and hard material softer and compliant (flexible).

2.3.6 Engineered polymers Engineering plastics are a group of plastic materials that have been ‘engineered’ to supply specific properties in order to meet the requirements of special applications. Each material will usually have a unique combination of properties that makes it the material of choice for a particular high-end application. The term usually refers to thermoplastic materials rather than thermosets. Examples of popular engineered plastic materials are ABS used for automotive bumpers and dashboards; polycarbonates are used for motorcycle helmets; polyamides

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(nylons) are used for skis, ski boots, gear wheels and so on. The general properties required for special applications such as building construction, space travel, automotive applications, transport, machinery and outdoor applications are generally high impact resistance, compressive strength, tensile strength, lightweight, durability, weatherability, strength, flexibility, chemical stability, fire safety and abrasion. These materials being more expensive than others are produced in smaller volumes than standard ones but over the years a tremendous increase in demand is taking place. Engineered plastic materials have replaced many traditional materials such as wood and metal. The advantages have been surpassing them in quality, weight, strength, durability and other properties with aesthetics also playing an important role.

2.3.7 Properties of plastics Some of the important properties of plastics including that of composites, which are key to process them, are: – Compatibility of materials – Mechanical properties – Friction and wear – Environmental properties – Water absorption – Weathering effects – Tensile strength – Compressive strength – Young’s modulus of elasticity – Melting point – Glass transition temperature Some of the other important properties are rheological properties, permeability, electrical properties, optical properties and acoustic properties.

2.3.8 Compatibility of materials In the design and production of composites, material compatibility is the most important aspect for achieving a successful end product and is largely dependent on the combination of materials being used. Testing of materials is a specialized area, and the average producer or processor cannot engage in this activity, because it requires a good knowledge, expertise and equipment to do so. However, a producer of composites can make use of the many databanks available, and also data a raw material supplier will give to design a final product. A producer could also resort to the use of a compatibiliser or a combination of more than one.

2.3 Monomer structures

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Some of the important data required are specific gravity, density, water absorption, melt flow, tensile strength, flexural properties, softening temperature and coefficient of thermal expansion.

2.3.9 Mechanical properties For both thermoplastic and thermosetting compounds, the range of properties is important, and their mechanical properties are of particular importance for designing and production of composites. Mechanical property considerations for designing composites and processing are tensile strength, fatigue, flexural strength, impact resistance, compressive strength, hardness, damping, cold flow, thermal expansion and dimensional stability. Fillers and stiffening agents will enhance some of the important properties of most plastics. A factor often used for the evaluation and selection of materials is the strength-to-mass ratio (i.e., the ratio of the tensile strength to the density of the material). End applications may require a minimum safety factor, depending on the end application, which is called the ‘design factor’.

2.3.10 Friction factor Friction can be defined as the resistance that two surfaces will generate as they slide (or try to slide) against each other. Friction can be between dry surfaces or lubricated surfaces. When dealing with polymers, it could generate enormous amounts of heat and stored near the surfaces due to the low thermal conductivity of the materials. This will be a complication, especially for making composites, multi-layered films, laminations and so on. Temperature influences the coefficient of friction significantly. For example, in the case of PE, the friction first decreases with temperature. At 100 °C, the friction increases because the polymer surface becomes tacky. The friction coefficient drops as the melt temperature is approached, and similarly wear also will vary based on temperature.

2.3.11 Environmental effects The environment in contact with loaded or unloaded polymer materials will play a significant role in its behavioural properties such as durability, brittleness and colour fading . The main environmental problems are exposure to rain, hail, UV radiation, detergents and high- or low-temperature conditions. Any damage or change in a polymeric material is called ‘weathering’. These conditions can be simulated in laboratory tests, and depending on the results, designers of composites or producers can adjust their formulations to improve and make better final products.

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2.3.12 Water absorption All polymers absorb water to some degree or the other but some are sufficiently hydrophilic that they absorb large quantities of water to significantly affect their performance. Water will cause a polymer to swell, serving as a plasticiser, consequently lowering performances, particularly in terms of electrical and mechanical behaviour. Increase in temperature will also result in an increase of the free volume between the molecules, allowing the polymer to absorb more water.

2.3.13 Weathering effects Common problems associated with polymeric composites if exposed to the elements are cracks, warping, brittleness, discolouration and so on due to UV light, moisture and extreme temperatures. These problems will be significantly absent if not exposed to outdoor applications. The location and climate can definitely affect polymeric compounds but the addition of correct additives will lessen or completely protect them. The addition of titanium dioxide or carbon black can prevent colour discolouration. Suitable preventive coatings are also an option. In composites, for example, made with rice hulls, as in composite lumber, the presence of silica in the rice hulls will act as a barrier for moisture, improve compression strength and make the products much stronger, including prevention of formation of mildew.

2.3.14 Tensile strength The tensile strength of a material quantifies how much stress the material will endure before suffering permanent deformation. This property is very important in applications that rely on the physical strength or the durability of a polymer. For example, a rubber band with a higher tensile strength will hold a greater weight load before breaking. Increasing the chain lengths or cross-linking of a polymer will increase its tensile strength.

2.3.15 Young’s modulus of elasticity Young’s modulus quantifies the elasticity of a polymer. It is defined as the ratio of the rate of change of stress to strain. Like tensile strength, this is also highly relevant in polymer applications involving physical properties. The modulus is strongly dependent on temperature. Viscoelasticity describes a complex timedependent elastic response, when the load is removed. Dynamic mechanical analyses

2.4 Processing of polymers

21

are used to measure the complex modulus by oscillating the load sample and measuring the resulting strain as a fraction of time.

2.3.16 Melting point Melting point when applied to polymers suggests not a solid–liquid phase but a transition from a crystalline or semi-crystalline melting temperature. Among synthetic polymers, crystalline melting is discussed only in regard to thermoplastics because thermosetting polymers decompose at high temperatures rather than melt.

2.3.17 Glass transition temperature A parameter of particular interest in the manufacture of synthetic polymers is Tg. This is the temperature at which amorphous polymers undergo a transition from a rubbery viscous liquid to a brittle glassy solid. Tg can be engineered by altering the degree of branching or cross-linking in a polymer or by adding plasticisers. Inclusion of plasticisers tends to lower Tg and increase polymer flexibility. Plasticisers are generally small molecules that are chemically similar to the polymer and create gaps between polymer chains for greater mobility by reducing inter-chain interactions. A good example is PVC. Unplasticised PVC is used for pipe manufacture because it needs to be strong and resistant to heat. Plasticised PVC is used for clothing, artificial leather, sheeting and so on, for which applications the PVC has to be very flexible.

2.4 Processing of polymers This is very important and will be presented under material science chapter, and will cover in detail the processing methodologies for selected important polymers, covering both thermoplastic and thermosetting polymers. For the benefit of readers, the author will include the manufacture of polymeric composite lumber and polymeric composite resins (polymers). This chapter includes the use of non-traditional fillers, stiffening agents, formulations and processing methods for a selected range of final products.

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2.5 Scope and applications of polymer chemistry The plastics industry is heavily dependent on polymer chemists. Without them, there would be no progress in ‘plastics’. Actually, there are three major players who combine their efforts to make the plastic industry a great one: The polymer chemist who works on applied research and development; the producers of the plastics polymers; and the manufacturers/processors of these polymers, which can be generally in the form of pre-pregs, liquids, pellets, powders or others. One may even want to include a fourth player, who designs and builds the necessary machinery, and equipment as required by the vast areas of processing. Since polymer chemistry is a multidisciplinary field, it is essential for polymer chemists to be in constant communication with all players connected to plastics for successful outcomes. Polymer chemists have great scope with a high demand for their services in most spheres of human activity. Whether the work is in universities, industry, personal research, space programs or other valuables, their contributions are highly rated and has become an essential part of daily life. However, a modern concept is developing in which groups of highly educated/qualified professionals are forming group consulting roles to service individual technology needs of very large industrial giants, who think that the human mass at large are capable of providing brilliant and practical solutions to their needs, which will cost less and quicker than their own in-house staffs can provide. For example, take the current global concerns of air pollution by carbon dioxide gas. When put out as a competition cum challenge, they received over 400 responses of possible solutions, albeit most of them were not good enough but among them a few brilliant suggestions were selected for further funded researches. However, the position of polymer chemists is unassailable, and will continue to grow in plastics and other spheres of human activity, and with modern day advanced equipment and instrumentations will make their work that much easier.

2.5.1 Alternative energy The discovery of electrically conducting conjugated polymers some time ago launched efforts to use polymers in electronic applications. The excellent light-harvesting ability of conjugated polymers makes them ideal for use in organic solar cells. There are many different types of coatings that can be used for making solar panels, including dye-sensitised surface coatings, and probably the best results have been obtained with cadmium coatings on glass. However, virtually a new material – graphene – has been discovered to have extraordinary properties like superior thermal conductivity, and strength which gives better results than any material known to date. This newly discovered material when combined with polymers will certainly go beyond solar panels and solar cells, and will also be suitable for light-emitting diodes, transistors, sensors

2.5 Scope and applications of polymer chemistry

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and many other applications. Due to global environmental air pollution concerns, there is a global hunt for alternate energy sources, and the author will present some exciting possibilities later on.

2.5.2 Chemical industry The chemical industry is crucial to modern world economics, and works tirelessly to convert raw materials such as oil, natural gas, air, water, minerals and metals into many products. These base products are then used to make consumer products as well as service manufacturing processes, construction, agriculture and many other industries. A majority of the chemical industry’s output worldwide are polymers, and polymer-related elastomers, rubbers, fibres, plastics, adhesives and coatings. Major industries served include rubber, plastics, textiles, apparel, petroleum products, pulp and paper, and primary metals. Some of the major chemical companies dealing with chemicals and polymer chemistry are BASF, Bayer, Dow, Braskem, Celanese, DuPont, Eastman, Hunstman, Evonik, Mitsui Chemicals, SABIC, Shell Chemicals, Wahua Chemicals to name a few.

2.5.3 Polymers in agriculture Polymers are used in everything from seed coats to enhance germination to container packs for fresh produce in the grocery stores, for mulch films to control weeds and conserve water to plastic pots in greenhouses. Sustainable agriculture has evolved to maximise land use, and also conserve natural resources, and a wide range of polymers in the form of plastics helps to meet these applications. However, the increased use of plastics designed for long-term usage but used for short-term applications creates disposal and environmental issues. Research has always been focused on creating biodegradable plastics, and when using them, research has now been shifted to creating polymers from natural resources like carbohydrates, starch, cellulose, plant proteins and vegetable oils. These serve to replace petroleum-based plastics, as well as designing functional biopolymers that are sensitive to their environment and release agrochemicals on demand in a controlled manner. Some companies involved in this field are Dow Agrosciences, SABIC, DuPont, GE Polymers, Monsnato and Nature Works LLC.

2.5.4 Synthetic fibres Polyester is the predominant class of fibre with the most common specific polymer being polyethylene terephthalate. Polyester is used in a wide range of textiles with

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the largest application area being in everyday clothing. Polyesters are also blended with cotton, and specialised materials are made for sports apparel. The next popular polymer is polyamide, which is commonly known as nylon, and generally used for intimate wear, work wear, industrial fabrics, outdoor apparel and carpets. Probably the two most useful polyamides are polyamide 6.6 and polyamide 6, which are structurally similar and have similar properties. They differ in the monomers used, and the polymerisation procedure causes some tensile thermal property differences. Spandex is a polyurethane–urea thermoplastic elastomer, which imparts elastic recovery when used as a minor component in fabrics with other ‘hard’ fibres such as cotton, polyester or polyamide. Synthetic fibres of polypropylene are used in carpeting, as turfs, nonwovens and some athletic apparel, more commonly in Europe. Polymers are also used as coatings to impart specific treatments for fabrics including oil and strain-resistant applications, wrinkle-resistant treatments for cotton fabrics and hydrophilic treatment that imparts water-absorbing properties.

2.5.5 Coatings Coatings can function as a process to finish a product or also applied to surfaces of many manufactured objects for decorative, functional and protective purposes. The need for end applications are vast, and some of the coatings we encounter today are for automobiles, trains, aircrafts, space travel, infrastructure such as bridges, construction and insulation work, thermal barriers, furniture, food packaging, industrial machinery, pipes, steel rods, containers and many others. In addition to aesthetics, polymeric coatings provide the all-important vital function of protection for any object or product from degradation by environmental factors such as sunlight (UV), moisture or oxidation, including abrasion and wear resistance. Three of the main coating techniques are direct coating (doctor knife), dip coating and spray coating.

2.5.6 Rubber Rubbers are naturally occurring polymers in the form of latex taken from rubber trees. Processing involves incorporation of chemicals to prevent coagulation before being sheeted out. The rubber in latex form can be found on trees, shrubs and other plants, and also can be produced through chemical means (synthetic rubber). A third class of rubber – thermoplastic elastomers – will stretch easily and return to its original shape when tension is removed and will melt at high temperatures. Rubber, often a mixture of polymers, has high resistance to heat, moisture and most other materials, and is a very good insulator. While natural rubber is found in Asia, India, Sri Lanka, Africa, Central and South America, most countries in the world produce

2.5 Scope and applications of polymer chemistry

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synthetic rubber for which there is a great demand, especially in the automotive industry.

2.5.7 ‘Green’ polymers Green polymer chemistry involves the development of green (environment-friendly) polymers. For some time, the plastics industry has been researching and developing new polymers other than from the traditional petrobased sources. Although some of the polymers derived from vegetable oils have potential and can be used successfully, it will take some more time to actually match up with the petrobased ones in some areas as yield, odour, properties and others. Focus is also on more environment-friendly disposable packaging by incorporating biodegradable additives, edible food wrappings, biobased/renewable monomers and processes that minimise the amount of packaging material used. Many suppliers conduct life cycle analyses that consider everything from starting materials to final disposal, including impact on the environment and health. Using starting material, that is, monomers derived from biobased renewable sources such as plants and vegetable oils or replicating polymers already present in nature is a successful strategy for many polymer manufacturers. For the existing synthetic polymers, attempts are being made to decrease the use of organic solvents and increase recycling and re-use. A leading commercially available ‘green’ polymer is PLA. This thermoplastic can be used in packaging and many other applications. As the world looks for more and more versatile polymers, the chemical industry is coming up with new and innovative ideas as sources for polymers. It is true that even today most of the polymers are derived from petroleum oil, and the major portion of the blame for air pollution is put on the bi-products of oil. For sometime now, chemists and researchers have been coming with biodegradable grades of polymers that are limited to a few, and the need and consumption rate is much higher involving many different grades of polymers for a wide range of applications. Since some of these are resourced from food feedstock, it is not a viable solution. To avoid this, chemists are thinking of environment-friendly plastics and develop materials that contain both elements, meaning polymers that are both biobased, and biodegradable, such as PLA or polyhydroxyalkanoates. However, these also have some problems as they are sourced from corn starch, a major food source. According to the reports, researchers from the University of Bayreuth, Germany, have been looking into finding better chemical feedstock for biobased and biodegradable polymers. Their research has come up with a surprise feedstock source – limonene. Limonene is described as a doubly unsaturated terpene and is a biobased nonfood source, which is mainly derived from the peel of citrus fruits. As the major component of orange oil (>90%), it is an abundantly available side product of the

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orange industry. Its versatility as a monomer is rejected by the great variety of polymers that are derived from it. These researchers also claim that the polymer known as PlimC is completely biobased, has a high molecular weight with attractive thermal glass transition temperature Tg = 130 °C, and optical properties with a transmission factor 94%. They also claim that PlimC grades with thermal stability as high as 240 °C could be achieved using appropriate end-capping agents. Some of the other claims are that the transparency is much higher bisphenol-A-carbonate, and has better mechanical properties than many petrobased polymers. Of great interest is the fact that PlimC polymers being an amorphous thermoplastic possesses one double-bond per repeating unit. This suggests a broad range of modifications to adjust and vary the properties in almost any direction, with the exciting possibilities of countless functional materials being derived with the economics of the final resins being a factor to work on.

2.5.8 Adhesives Adhesives are a part of everyday life. They have evolved from the early lower performance glues made from natural products to the versatile high-performance adhesives that are available today. Some of the main areas where adhesives are used are furniture industry, multilayer films used in food packaging, sports equipment and many others. Certain grades of adhesives need to be very flexible for use in labels and tape applications, or to demonstrate high strength and long-term durability to bond different metals and composites in automobiles, aircraft and other industries, engineering and building construction. Some of the popular companies that are in this field are 3M, Bostik, DAP, Henkel, H.B. Fuller and others.

2.5.9 Oil and gas industries Polymeric materials are used throughout the entire gas and oil industry value chain, from upstream oil and gas production activities to midstream and finally downstream refining, and the production of fuels, solvents and speciality chemicals. They are often used in demanding conditions that include high temperatures and high pressures. Solid-state polymers include engineering materials such as plastics, fibres and elastomers for use in oil-well sites and off-shore platforms with applications including construction of structures, such as pipelines, proppant in hydraulic fracturing and coatings as well. Polymeric additives are used in upstream oil production applications as drilling fluids, well stimulants, corrosion inhibitors, scaling inhibitors and viscosity modifiers.

2.6 Speciality polymers

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2.5.10 Polymers in nanotechnology Polymers are really ideally suited for applications in nanotechnology. The size of an individual polymer molecule can be on the nanometre size scale. By exploring this feature, polymers can be used as nano-sized building blocks to create devices with tiny features that are otherwise inaccessible. Constant breakthrough in polymer chemistry permits the synthesis of new materials that can also self-assemble into structures with nano-scale order in solution or bulk. These advanced materials have promising applications in the fields of nanomedicine, electronics, solar energy and many more exciting end uses. Materials at the forefront of this field include carbon-based fibres and carbon nanotubes used in electrical appliances as conductive adhesives, high strength materials and field emitters; in hydrogen and ion storage as chemical and genetic probes; in solar cells and fibres as catalyst supporters, superconductors, fabrics, energy storage, medical applications, films, nanomotors, elastomers and many more.

2.6 Speciality polymers We are all familiar with engineered polymers, which play a very important and essential role in the plastics industry. For the benefit of readers, the author presents here four of the more recent and versatile polymers, researched and being developed by polymer chemists. These special polymers can be classified as polymers with ‘miracle properties’. There are many other emerging new polymers but probably these stand out among them.

2.6.1 Hydrocarbon resins Hydrocarbon resins are low-molecular-weight, amber-coloured thermoplastic resins produced from petroleum-derived monomers with softening point ranges from liquid to 140 °C. They are aromatic hydrocarbons in pellet form and are easy to mix when melted. One of their main uses are when excellent acid and moisture resistance combined with outstanding pigment wetting is vital. Some of their applications are: – Reinforcing agents in rubber components – As binder in protective coatings – Building construction Eastman Chemical Co. among others are the manufacturing leaders of these products. On the subject of road paving, the author will present additional information on how to achieve cost-effective but better road surfaces by using non-traditional

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fillers (biomass) in combination with these grades of polymers. This will also reduce the total bitumen (petro-based content) in a mix.

2.6.2 Ethylene vinyl copolymer resins Fluon PFA resin manufactured by SGC Chemicals America Inc. is a copolymer resin of tetrafluoroethylene, and a perfluorinated vinyl ether can be used over a wide range of temperatures from extreme low (200–260 °C) without losing excellent electrical, mechanical and surface properties. PFA resins maintain many inherent characteristics and similar properties to PTFE and can be processed using conventional thermoplastic processing techniques such as extrusion, injection moulding, blow moulding and electrostatic powder coating. With an oxygen index of 95% or better, these non-combustible resins can be used in various fields, offering outstanding weathering properties with absolutely no reduction or deterioration when exposed to sunlight, wind, rain or exhaust gas. Also characteristics will not change when exposed to outdoors for a long period of time. Main features: – Can be used over a temperature range of 200–260 °C – Low smoke and flame characteristics conforming to standards – High weather and ageing resistance – Chemically stable material and not attacked by most chemicals – Low friction and non-stick properties – Available as pellets Application: – Tubing and pipe – Film and sheets – Valves, fittings and housings – Wire and cable coating – Blow moulded bottles – For chemical processes

2.6.3 Vitrimer plastics A new class of polymers defines the laws of physics. A recent discovery by the French physicist Ludwig Leiber has led to the development of a whole new class of polymer called Vitrimers. Industry has classified them as supramolecular substance, and Vitrimers are a derivative of thermoset plastics that exhibit self-repairing (healing) characteristics.

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The concept of materials that self-repair or do things physically impossible certainly has an awe factor but Vitrimers are just an example. This discovery has certainly opened out a whole new field, and NASA has already started developing more advanced materials in this line. A real benefit in the medical field where Vitrimers are being used in is called ‘organ glue’. This is a self-healing polymer hydrogel that acts as an anti-haemorrhaging wound-healing aqueous solution. Vitrimers also have the ability to form ‘nanobridging’ for these tissues. It can be used in situations when stitches are not practical. If these polymers are used for manufacturing of plastic goods, recycling will be that much easier as these materials can be re-used over and over again, similar to aluminium recycling.

2.6.4 Graphene polymers Graphene is virtually new for the plastic industry, which came into limelight very recently when two scientists were awarded the Nobel Prize for physics for ‘groundbreaking experiments regarding the two-dimensional graphene material’, and since then the industrial world is waiting for it to transform our lives in the same way silicon has done. Although graphene has been around and used for mundane applications, even today with research and development, we are not fully aware of its possibilities. The carbon inter-bonded material has excited scientists and researchers, in that it is supposed to be 100 times stronger than steel, can withstand very high strain, is a million more time electrically conductive than copper, 98% optically transparent, harder than diamonds and virtually impermeable. With these kinds of properties, speculation is rife with applications predicted in everything from foldaway mobile phones, wallpaper, thin lighting panels to the next-generation aircraft. Graphene polymers and graphene composites will be fully presented later.

Bibliography [1] [2] [3] [4] [5] [6] [7]

Jason Ford- news editor-Advanced Materials Magazine- Graphene Takes Center Stage- Article 18th April (2016). AGC Chemicals America Inc.- Fluon PFA Resins- www.globalspec.com Eastman Chemical Co. Hydrocarbon Resins Overview- WA-86 Eastman’s Spectrum of hydrocarbon resins Chris Defonseka. (2014) Introduction to Polymeric Composites with Rice Hulls Smithers. Georgia State University-Hyper physics.phy-astr.gsu.edu/chemical/bond.html Chris Defonseka. (2013) Practical Guide to Flexible Polyurethane Foams. Shawbury, Shropshire, UK: Smithers Rapra. Hillington UK- Hydrocarbon Suppliers- www.gilsonitesuppliers.co.uk

3 Polymer material science 3.1 Brief history The choice of a material or materials of a given era for particular applications is often a defining point. Materials from ancient times and periods such as Stone Age, Bronze Age, Iron Age and Steel Age are great examples. Material science is one of the oldest forms of applied science and engineering. Modern material science evolved directly from metallurgy, which itself has evolved from mining. A major breakthrough in the understanding of materials occurred in the late nineteenth century, when an American scientist demonstrated that the thermodynamic properties related to atomic structures in various phases are related to the physical properties of a material. Gradual understanding and engineering of metals, alloys, silica and carbon materials used in many areas of applications have undergone rapid development, and today some of these materials play a vital role, even in space travel. Material science has driven and is being driven by the development of revolutionary technologies, which are used to produce plastics, semi-conductors and biomaterials. The growth of material science has seen rapid progress over the years because of many research laboratories and development projects initiated by most countries. This field has thus broadened to include university-hosted laboratories to expand the knowledge and training of people in basic research and material sciences. Material science has expanded to include every class of materials, including ceramics, polymers, semi-conductors, magnetic materials, medical implants, biological materials and nanomaterials.

3.2 What is material science? Material science is an interdisciplinary subject spanning the physical and chemical structures of materials in relation to engineering and industrial manufacturing processes. Modern society is heavily dependent on the constant need for more advanced materials. A few examples are lightweight composites for faster and more economical vehicles, optical fibres for easy communication, silicon microchips for information and transmittance and so on. The initial study of material scientists includes structures and properties of a material, and how it is made. They also develop new materials by modification or combination of different materials and device processes for manufacturing them. Material science is vital for development of nanotechnology, quantum computing and medical technologies. This diverse field extends its activities from physics and chemistry bases to mechanical, electrical, magnetic and optical properties, and more, covering materials like metals, alloys, ceramics, polymers, composites and biomaterials. https://doi.org/10.1515/9783110669992-003

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3.3 Fundamentals of material science A material can be defined as a substance made up of matter, generally referred to as a solid but can also be in other forms. There is a myriad of materials around us, and materials can generally be classified into crystalline, semi-crystalline and amorphous. A crystalline material is a substance with its constituent atoms, molecular or ions arranged in an ordered pattern, extending in all three spatial dimensions. Large crystals are generally identified by their macroscopic geometrical shapes. Semi-crystalline substances have structures that have both crystalline and amorphous properties. They are also known as poly-crystalline structures. These structures have true crystal portions mixed with size and orientation. Amorphous structures have little or no crystal properties, and are arranged in random patterns. Common types of amorphous solids include gels, thin films and glass (Figure 3.1).

Crystalline

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Figure 3.1: Atomic arrangements of materials (Source: http://www.doitpoms.ac.uk/tlplib/ atomic-scale-structure/intro.php).

The basis of material science involves studying the structures of materials and their properties. Once a material scientist knows about the structure–property correlation, they can study the relative performance of a material in a certain application. The major determination of the structures of materials, and thus its properties, involves its constituent chemical elements, and the way in which it can be processed into a final desired product. These characteristics taken together, and related through the laws of thermodynamics and kinetics, govern a material’s microstructure and thus its properties. To begin with, structures are one of the most important areas in the field of material science. Material science involves examining the structures of a material from the atomic scale all the way up to the macro scale. Characterisation is a way material scientists examine the structures of materials. This involves techniques such as: diffraction with x-rays, electrons or neutrons analysis, chromatography, electron

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microscopic analysis, thermal analysis and so on. Structures are studied at various levels as follows.

3.3.1 Atomic structures This deals with the study of the atoms of a material, and how they are arranged to form molecules, crystals and so on. Much of the electrical, magnetic and chemical properties of materials arise from the levels of structures. The way in which the atoms and molecules are bonded and arranged is fundamental to studying the properties and behaviour of any material.

3.3.2 Nanostructures Nanostructures deal with objects that are in the 1–100 mm range (1 mm–0.0001 micron). In many materials, atoms or molecules agglomerate together to from objects at the nanoscale. This leads to many interesting electrical, magnetic, optical and mechanical properties. When describing nanostructures, it is necessary to differentiate between the number of dimensions on the nanoscale. Nano-textured surfaces have one dimension, i.e. only the thickness of the surface of an object. Nanotubes have two dimensions on the nanoscale – diameter and length. Spherical nanoparticles will have three dimensions on the nanoscale, i.e. in each spatial dimension. The terms nanoparticles and ultrafine particles (UFP) often are used synonymously, although UFP can reach into the micrometre range. The term ‘nanostructure’ is often used when referring to magnetic technology. Nanoscale nanostructures in biology are often called ultra-structures. Materials whose atoms/molecules form constituents on the nanoscale, meaning they form nanostructures, are called nanomaterials, which are of specific interest to material scientists, because they exhibit unique properties.

3.3.3 Microstructures Microstructures can be defined as structures of materials as revealed by a microscope with high magnification on thin foil of a material. The microstructure of materials are broadly classified as: metallic, polymeric, ceramic, composites, biomaterials and so on, and can strongly influence the physical properties of a material, such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behaviour, wear resistance and other properties. Most of the traditional materials, for example, metals and ceramics are microstructured.

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The manufacture of a perfect crystal of a material is virtually physically impossible. This is because a crystalline material will contain defects such as precipitates, grain boundaries, interstitial atoms, vacancies or substitutional atoms. The microstructures of materials reveal these defects so that they can be studied and analysed. Macrostructures are structures of materials in the scale of millimetres to metres, where the structure of the material can be seen with the naked eye.

3.3.4 Crystallography It is the science that examines the arrangement of atoms in crystalline solids. Crystallography is an important tool for material scientists. In single crystals, the effects of the crystalline arrangement of atoms is often easy to see under a microscope, because the natural shapes of crystals reflect the atomic structure. The understanding of crystal structures is an important prerequisite in understanding of crystallographic defects. Most materials do not occur as a single crystal but in poly-crystalline form, i.e. as an aggregate of small crystals with different orientations. Because of this, the powder diffusion patterns of poly-crystalline samples with a larger number of crystals play an important role in structural determination. Although most materials have a crystalline structure, there are some important materials that do not exhibit regular crystal structures. Polymers display varying degrees of crystallinity, and some are completely non-crystalline (Figure 3.2). For example, glass, some ceramics and many natural materials are amorphous forms of chemical, and do not possess any long-range order in their atomic arrangements. The study of polymers combines elements of chemical and statistical thermodynamics, as well as mechanical descriptions of physical properties.

3.3.5 Chemical bonding Chemical compounds are formed when two or more atoms are joined by chemical bonding. A stable compound occurs when the total energy of the combination has lower energy than the separate atoms. The bonded state implies a net attractive force between them – a chemical bond. The two main types of bonding are: 1) Covalent bonds: bonds in which one or more pairs of electrons are shared by two atoms. 2) Ionic bonds: bonds in which one or more electrons from one atom are removed and attached to another atom, resulting in positive and negative ions, which attract each other.

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Cl Li P N C H

Figure 3.2: Crystallography formation (Source: http://www.utoledo.edu/nsm/ic/instruments/ xray.html).

Other types of bonding include metallic bonding and hydrogen bonding. The attractive forces between molecules in a liquid can be characterised as van der Waals bonds (Figure 3.3). H

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Figure 3.3: Chemical bonding patterns (Source: Introduction to Materials Science – University of Tennessee. https://docs.google.com/viewerng/viewer?url=http://web.utk.edu/~prack/mse201/ Chapter%252015%2520Polymers.pdf).

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3.3.5.1 Covalent bonds Covalent chemical bonds involve the sharing of a pair of valence electrons by two atoms in contrast to the transfer of electrons in ionic bonds. Such bonds lead to stable molecules, if they share electrons in such a way as to create a noble gas configuration for each atom. Hydrogen gas forms the simplest covalent bonds in the diatomic hydrogen molecule. The halogens, such as chlorine, also exist as diatomic gases by forming covalent bonds. Nitrogen and oxygen, which make up the bulk of the atmosphere, also exhibit covalent bonding in forming diatomic molecules. 3.3.5.2 Polar covalent bonds Covalent bonds in which the sharing of the electron pair is unequal with the electrons spending more time around the more non-metallic atom are called polar covalent bonds. In such a bond, there is a charge separation with one atom being slightly more positive, and the other more negative, i.e. the bond will produce a dipole moment. The ability of an atom to attract electrons in the presence of another atom is a measurable property called electronegativity. 3.3.5.3 Ionic bonding In chemical bonds, atoms can either transfer or share their valence electrons. In the extreme case, where one or more atoms lose electrons, and other atoms gain them in order to produce a noble gas electron configuration, the bond is called an ionic bond. 3.3.5.4 Metallic bonds The properties of metals suggest that their atoms possess bonds, yet the ease of conduction of heat and electricity suggest that electrons can move freely in all directions in a metal. The general observations give rise to a picture of ‘positive ions in a sea of electrons’ to describe metallic bonding. The general properties of metals include malleability and ductility, and most are strong and durable. They are good conductors of heat and electricity, their strength indicating that the atoms are difficult to separate but malleability and ductility suggest that it is easy to move electrons in any direction. The electrical conductivity suggests that it is easy to move electrons in any direction in these materials. The thermal conductivity also improves the motion of electrons. All of these properties suggest the nature of metallic bonds between atoms. 3.3.5.5 Hydrogen bonding Hydrogen bonding differs from other bonds, as it is a force of attraction between a hydrogen atom in one molecule, and a small atom of high electronegativity in another molecule. That is, it is an intermolecular force and not an intermolecular bond.

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When hydrogen atoms are joined in a polar covalent bond with a small atom of high electronegativity, such as oxygen, fluorine or nitrogen, the partial positive charge on the hydrogen is highly concentrated because of its small size. If the hydrogen is close to another oxygen, fluorine or nitrogen in another molecule, then there is a force of attraction termed dipole–dipole interaction. This attraction or hydrogen bond can have about 5% to 10% of a covalent bond. Hydrogen bonding has a very significant effect on the properties of water and ice. Hydrogen bonding is also very important in proteins and nucleic acids, and therefore in life processes.

3.4 Synthesis and processing Synthesis and processing involve the study and creation of materials with the desired micro/nanostructures. Even though new materials can be created from an engineering point of view, suitable economical manufacturing methods for them must also be developed. Thus, the processing of materials is very important and part and parcel of the field of material science. Different materials require different processing/synthesis techniques. For example, the processing of metals has historically been very important, and has been studied under the branch of material science known as metallurgy. Chemical and physical techniques are also needed to synthesise other materials such as polymers, ceramics, films and so on. Currently, new techniques are being developed to synthesise nanomaterials such as graphene, which is considered by scientists as the material of the future with vast possibilities.

3.5 Thermodynamics Thermodynamics deals with heat and temperature and its relation with energy and work. The study of thermodynamics is fundamental to material science, and forms the foundation to treat general phenomenon in material science and engineering, including chemical reactions, magnetism, polarisability, and elasticity. Thermodynamics describes the bulk behaviour of the mass, and not the microscopic behaviours of the very large number of its microscopic constituents, such as molecules.

3.6 Kinetics Kinetics is the study of the rates at which systems that are out of equilibrium change under the influence of various forces. When applied to materials science, it deals with how a material changes with time, moving from a non-equilibrium state to an equilibrium state, detailing the rate of processors evolving in materials,

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including shape, size, composition and structure. Diffusion is important in the study of kinetics as this is the most common mechanism by which materials undergo change. Kinetics is essential in processing materials, because among other things, it deals with how the microstructures change with the application of heat.

3.7 Nanomaterials Nanomaterials describe in principle, materials of which a single unit is sized, measured in 1–100 mm. The research on nanomaterials forms a base approach to nanotechnology, leading to advances in materials metrology and synthesis, which have been developed in support of microfabrication research. Materials with structures at the nanoscale level often have unique optical, electronic or mechanical properties. The field of nanomaterials is generally classified like in chemistry, into organic and inorganic nanomaterials.

3.8 Biomaterials Although biomaterial science is not very old, over the past few years many companies have been investing large amounts of money into the development of new products, especially from new sources. Biomaterials can be derived either from nature or synthesised in laboratories, using various chemical and engineering approaches utilising metallic, components, polymers, ceramics, composites or other. Probably the medical field, applications may take precedent but industrial fields among others, are also important sectors.

3.9 Electronic, optical and magnetic materials Semiconductors, metals, ceramics, polymers and other materials are used to form highly complex systems, such as integrated electronics circuits, optoelectronics devices, magnetic and optical storage media and so on. These materials and systems are an essential part of our rapid advancing computer world, and thus are of vital importance. Semiconductors are a traditional example of the use of these materials. These are materials with properties that are intermediate between conductors and insulators. Their electrical conductivities are very sensitive to impurities, and this allows for the use of doping (coating) to achieve desirable end electronic properties. A good example is the doping in the manufacture of solar panels to achieve maximum absorption properties and retention of solar energy on given surfaces. Hence, semiconductors form the basis of the traditional computer.

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This field also includes newer research sectors, such as superconducting materials, spintronics, metamaterials, and so on. One of the latest materials of great interest is graphene. This material has been known for some time but scientists are realising their full value only now. The study of these materials involves knowledge of materials science and solid state physics.

3.10 Ceramics and glass materials The study of brittle materials such as glass and ceramics, especially their structures, is another branch of material science. Bonding in ceramics and glass uses covalent and ionic-covalent types with silica or sand as a fundamental building block. Ceramics are as soft as clay, and when processed are hard as stone or concrete. Usually, they are crystalline in form, and most glass materials contain a metal oxide fused with silica. At high temperatures used to make glass, the material is a viscous liquid. The structure of glass forms into an amorphous state on cooling. Glass can have many end applications from ordinary windowpanes to special ones like eyeglasses to fibres of glass and scratch-resistant. Corning ware, is a good example of scratch-resistant and high heat-tolerant material. The methods used to achieve these special properties is a good example of technology of material science. Engineered ceramics are known for their stiffness, stability under high temperatures, compression and electrical resistance. Alumina, silicon, carbide and tungsten carbide are made from a fine powder of their constituents in a sintering process with a binder. Hot pressing, among others, provides higher density materials, which have many applications in industry.

3.11 Composite materials Another branch of material science in industry is the making of composites. Composite materials are structured materials composed of two or more materials, with one as the matrix, and the other or others acting as reinforcing agents. Applications can range from structural elements such as steel-reinforced concrete to thermally insulative material to composite polymer resins to polymeric composites with biomass fillers, and stiffening agents as composite lumber is an ideal substitute for natural wood. These important products will be presented in more detail under a chapter dealing with non-traditional fillers, and stiffening agents later on. At the high end of applications, the manufacture of thermally insulating materials, which play a key role in NASA’s space travel programs to counter excessive heat on re-entry is a good example of the need for material science technology. One example is the reinforced carbon–carbon light grey material which can withstand re-entry temperatures up to 1,510 °C (2,750 °F), especially used to protect the outer

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wings of a space shuttle. This material is basically made from graphite rayon cloth and impregnated with a phenolic resin (Figure 3.4).

Figure 3.4: Composite extruded decking board (Source: http://www.wisegeek.org/what-arecomposite-materials.htm).

Other examples are: plastic casing of television sets, cell phones and so on. These plastic casings are usually a composite material made up of a thermoplastic matrix such as acrylonitrile butadiene styrene (ABS) in which calcium carbonate, talc, glass fibre or carbon fibres have been added for extra strength, bulk or electrostatic dispersion. These are referred to as reinforcing fibres or dispersants, depending on their purpose.

3.12 Polymeric materials Polymers are also an important part of material science. Polymers are the base raw materials used to make plastics compounds. Plastics are made by a combination of polymers with additives being added to achieve desired properties. These additives, including colours can also be added to raw resins during processing in final products. Some of the most popular, and common polymers are: polyethylene, polypropylene, polystyrene, polyvinyl chloride, nylons, polyesters, polycarbonates, acrylics, polyurethanes, melamines and many others. Polyethylene probably is the most

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widely used polymer resin but polyvinyl chloride (PVC), and polyurethanes (PUR) are also needed in daily life. PVC, inexpensive with large volumes of annual production, lends itself to a vast array of applications, from artificial leather, electrical insulation, packaging, pipes, containers, sheeting and many others. Since this presentation is mainly about polymers, and non-traditional additives, this subject will be discussed later in a separate chapter.

3.13 Special materials Material science technology being under constant research and development provides the materials marketplace with frequent newer materials with speciality polymers among them. What with increased space travel, faster but lighter-weight vehicles, air travel, medical applications, consumer demand and so on, the need for better materials is a constant demand. The following are some of the newer materials with significant importance:

3.13.1 Polylactic acid (PLA) Polylactic acid is one of the significant raw materials used in numerous industrial applications, such as food packaging, medical, automotive, agriculture and others. Polylactic acid is a biodegradable thermosetting polymer, which is produced from lactic acid. It is basically used as an intermediate to manufacture plastics. The packaging sector accounts for a major share of the market. Bio-based packaging is primarily used in food and beverage packaging, medicine packaging and others. These packagings offer better value in terms of functionality, quality, and performance. Agricultural wastes and natural additives are used to manufacture fibres, which in turn are used in biopolymer formulations. These fibres are used for food and beverage packaging as they restrict the growth of the PLA market for these two items, but will certainly be used in other segments in large volumes.

3.13.2 Natural rubber alternative HYSYNAL synthetic rubber sheeting is not made from natural rubber latex, and is a good alternative to applications where latex protein is a concern. These synthetic polyisoprene sheets meet various tests required for medical use and can be sterilised. The primary physical features of HYSYNAL synthetic sheeting are parallel to those of natural rubber sheets. A special formulation of synthetic rubber (polyisoprene) is used to produce this unique powder-free and protein-free sheeting that is

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disposable and cost-effective. HYSYNAL synthetic rubber sheeting can be formulated and manufactured to meet any specific requirements. Some of the special features are: – Excellent resilience – Excellent flexibility – Good abrasion resistance – Low temperature performance – Thickness range: 0.022–0.030 inches ( 0.55–0.76 mm) – Available in different colours – Can be die-cut for use as gaskets, diaphragms, seals and more

3.13.3 Elastomers An elastomer can be defined as a polymer with the property of elasticity. It is a polymer that deforms under stress and returns to its original shape when the stress is removed. Elastomers are amorphous polymers with tremendous segmental motion. Their molecular form is compared often to a spaghetti and meatball-like structure. The meatballs signify cross-link between polymer chains. The polymer chains are made up of many monomer subunits, which consist of carbon, hydrogen and oxygen atoms. Elastomers are not just natural latex but include other polymers such as styrene-butadiene rubber (SBR), and all-purpose rubber composed of a copolymer of styrene and butadiene. SBR has a similar property make-up as natural rubber, and is the highest volume elastomer available. SBR is tough and resistant to heat and flex cracking. Neoprene (CR) is another example, and it is an excellent all-purpose elastomer that is flame-resistant with moderate resistance to oil and gasoline. Neoprene can be classified into two groups – sulphur-modified and mercaptanmodified. Sulphur-modified neoprene has high tear strength and resilience, while mercaptan-modified neoprene has a high resistance to heat and compression- will the speed, efficiency and economy of manufacturing plastic resins. Thermoplastic elastomer (TPE) materials combine the functional performance and properties of thermoset rubbers with the process ability of thermoplastics. TPEs permit fabrication of ‘rubber-like’ articles with the speed, efficiency, and economy of plastics manufacturing. Thermoplastic elastomers are generally low modulus, flexible materials that can be stretched to more than twice their original length, and will return to their original length when the tension is released. Unlike thermosets, thermoplastics can be re-melted and re-moulded. Engineering thermoplastics are a subset of plastics that are used in applications generally requiring higher performance in areas of heat resistance, chemical resistance, impact, fire retardant and mechanical strength. Engineering thermoplastics are often compared to commodity thermoplastics but are more expensive and

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manufactured in smaller production volumes. These thermoplastics are used to make car bumpers, dashboards, motorcycle helmets and more. High-temperature thermoplastics retain their physical properties at higher temperatures and exhibit thermal stability even in the longer run. These thermoplastics have higher heat deflection temperatures and continuous use temperatures. Hightemperature thermoplastics can be used in diverse industries like electrical, medical, automotive, telecommunication and many other specialised fields.

3.13.4 New class of polymers A French physicist Ludwik Leiber with his team at ESPCI Paris Tech has developed a whole new class of plastics called vitrimers. ‘Classified as supramolecular substances, vitrimers are a derivative of thermoset plastics that exhibit self-repairing characteristics’. What is really intriguing about vitrimers is how they do what they do. At their molecular level, the atoms that comprise standard thermosets maintain their crystalline structure through permanent or rigid bonds, the strength of these bonds ultimately determining the material characteristics. Flex, friction and thermal cycles break down these bonds resulting in weakening, which leads to cracks and fractures. Once these bonds are broken, they cannot be repaired. However, the molecular bonds that make up vitrimers are neither permanent or rigid bonds, their state is more akin to a dynamic equilibrium. This means that molecular bonds are forming and breaking simultaneously. Regardless of molecular structure, the number of bonds remains the same. This reaction is thermally activated, allowing vitrimers to go from solid to liquid, and back with no change in crystalline structure. This is known as glass transition. These characteristics in essence are what make vitrimers a self-repairing plastic. The self-repairing qualities of vitrimers are paving the way for a number of impressive innovations, and will lead to many more. One of these is in the medical industry where vitrimers are being used as ‘Organ glue’. This is a self-healing polymer hydrogel that acts as an anti-haemorrhaging wound healing aqueous solution. These materials are also used for making consumer goods, and vitrimers by nature are ideal for recycling because they can be liquefied and solidified over and over again. According to reports, NASA is showing great interest in vitrimers, and working on their special applications.

3.13.5 Thermoplastic polymers from citrus fruits Traditionally, most industrial polymers have been derived from petroleum sources. With growing concerns for climate changes globally due to air pollution caused by these products, the polymer industry has for some time now seeking for polymers and related additives from alternate sources. Fortunately, the chemical

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industry and its research and development sectors have come up with viable solutions periodically. They developed degradable petro-based polymers such as polycaprolactone, polybutylene adipate terephthalate and also bio-based monomers such as biopolyethylene or bio-polyethylene terephthalate. However, they are not 100% satisfactory due to uncertain oil supplies or non-degradability. The chemical industry then researched for planet-friendly polymers that are both bio-based and biodegradable. Some polymers are based on lactose derived from glucose, which in turn is sourced from corn starch, a major food source. Researchers from the University of Bayreuth, Germany are looking into finding a better chemical feedstock for bio-based and bio-degradable polymers, concluding that Limonene is an ideal surprise source. According to the journal Nature, limonene – a doubly unsaturated terpene – is a bio-based non-food resource, which is mainly derived from the peel of citrus fruits. As a major component of orange oil (90%), it is an abundantly available side product of the orange industry, produced in excess of approximately 500 kt per year. Its versatility as a monomer is reflected by the great variety of polymers that can be derived from limonene. According to reports, this research is also discussed in the journal Green Chemistry, which quotes the researchers’ claims that the polymer known as PlimC is completely bio-based, has a high molecular weight with attractive glass transition temperature and good optical properties. PlimC polymers are also supposed to have a high thermal stability of 240 °C when appropriate end-capping agents are used. These polymers are also supposed to be characterised by excellent transparency and hardness. If all these data holds true, then PlimC has the possibility to make a large impact on polymer markets. This will probably mean that the huge global orange production industry will get a sudden boost as a valuable commodity of global importance, and with other bio-feedstocks also being successfully researched, petro-based feedstocks will have to take the second place.

Bibliography [1] [2] [3] [4] [5] [6]

Ashby Michael., Hugh Sherecliff., David Cebon. (2007) Materials: Engineering Science.. Askeland Donald R., Pradeep P. Phule (2005) The science & engineering of materials. (5th. ed.) Thomson-Engineeering ISBN:0-534-55396-6. Callister Jr. William D. (2000) Material Science and Engineering- An Introduction(5th,ed.) John Wiley and Sons.ISBN: 0-471-32013-7. Gaskell David R. (1995)Introduction to the Thermodynamics of Materials (4th.ed.)-Taylor and Francis Publishing. ISBN: 1-56032-992-0. Gonzalez-Vinas W., Mancini H.L. (2004) An Introduction to Material Science. Princeton University Press. ISBN: 0-691-07097-0. Mathews F.L., Rawlings, R.D. (1999) – Composite Materials: Engineering and Science-Boca Raton: CRC Press ISBN: 0-8493-0621-3.

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SPOT-CHEMI article- 21 June (2016) Do Citrus Fruits make the Best Thermoplastic Polymers?. The Industrial Space-article-Sept. (2015) A New Class of Polymer that defies the Laws of Physics. [9] Ford Jason. article 18th April 2016 Graphene takes centre stage. [10] Simpson, John article August (2016) Engineering 360-IEEE Global Spec Automaker Fabricates Vehicle Panels from Graphene.

4 Non-traditional fillers and stiffening agents for polymers 4.1 Introduction The general idea conveyed when the word fillers are used is that they are used to extend a material and also to reduce its cost. However, most of the fillers also act as stiffening agents and as the chemical and plastics industry has been trying to look for alternatives for non-petro-based feedstocks for both polymers and other components, research and development programs have been coming up with some exciting alternatives for both fillers and stiffening agents from freely available biomass sources. Utilising biomass fillers and stiffening agents offers benefits such as reduced material costs, while maintaining and, in some cases, enhancing mechanical properties and a great ‘green’ alternative. These fillers can reduce the cost of polymers by using lowcost biomass in part replacement of expensive base polymers. Working with knowledgeable technical companies and using effective formulating techniques or using composite resins available in the marketplace, resin producers and processors can be more environmentally responsible, while being more profitable at the same time and assist in the phasing out of petro-based feedstocks, which contribute to air pollution. Some of the most common thermoplastic polymers that are being used now or can be used are PP, PE, PLA, ABS, PC, PVC and PS. A multitude of agricultural sources such as flax fibre, wood flour, oat hulls, sugar beet pulp, hemp fibre, sunflower hulls, soybean hulls can be possibly used in addition to the 10 materials chosen that are presented later. Figure 4.1(a) shows biomass, while Figure 4.1(b) shows composite resins. Some of these inexpensive materials such as calcium carbonate, talc, wood flour and so on have been in place for some time now, but this presentation will discuss alternate sources for these as well as present newer materials such as rice hull flour, wheat hull flour, rice hull ash, bamboo flour, shellfish powder, walnut shell powder, coir dust powder, egg-shell powder (calcium carbonate), fly ash, graphene, expanded polystyrene wastes and so on, based on emerging technologies. These can be used directly with polymers as fillers and stiffening agents, while most of them can be used singly or in combination in composites, replacing traditional ones, to give much better properties. For the benefit of the readers, the author will present the sources, properties and the actual uses of some of them in production examples. Considering their higher stiffness compared to the material matrix, they will always modify the mechanical properties of the final filled products or composites. Fillers and stiffening agents can constitute either a major or a minor part of a composite. The structure of filler particles ranges from precise geometrical forms like spheres, hexagonal plates or short fibres to irregular masses. Fillers are generally used for non-decorative purposes, although they may impart colour or opacity to a material. https://doi.org/10.1515/9783110669992-004

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(b)

Figure 4.1: (a) Biomass and (b) composite resins.

Fillers can be classified according to their source, function composition and/or morphology. No single classification is entirely adequate due to the overlap and ambiguity of these categories. Extensive usage of fillers in many commercial polymers is for enhancement in filling, stiffness, strength, dimensional stability, toughness, heat distortion temperature, damping, impermeability and most important cost reduction factor, although not all of these desirable features are found in any single filler. Each of these versatile sources will be discussed in detail, followed by their applications/functions in actual product manufacture with formulations and illustrations as far as possible. The following is a list of manufacturing methods selected for presentation in Chapter 5, which follows: – Manufacture of composite resins – polypropylene/rice hull flour – Injection moulding of these composite resins – Manufacture of composite lumber ― HPPE or polypropylene/rice hull flour or wheat hull flour – PUR foams with EPS foam wastes/calcium carbonate from eggshells – Floor tiles with polymer/bamboo flour – Plastic panels for outdoor sheds with HDPE/recycled polymer/filler/stiffening agent – Road paving with bitumen/fly ash/rice hull ash/polymer wastes Table 4.1 shows some of the uses of biomass wastes: Biomass uses Cellulose biomass waste conversion to value-added products

4.2 Non-traditional fillers and stiffening agents

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Table 4.1: Modified table by author to suit presented subject. Technology

Conversion process Biomass waste

End product

Extrusion/injection . . . . . . Polymer processing Rice hulls, wheat hulls. Composite resins Composite lumber Volumetric expansion

Mixing

Rice hull ash

Industrial products Road paving

Biodiesel production

Chemical

Rice/wheat hull Rapeseed Soybeans

Liquid biodiesel

Direct combustion

Thermochemical

Agri-waste Mixed waste

Heat, steam, electricity

Ethanol product

Biochemical

Agri-waste Wood waste Rice and corn straw

Ethanol

Gasification

Thermochemical

Agri-waste Mixed waste

BTU producing gas

Methanol production

Thermochemical

Agri-waste Mixed waste

Methanol

Pyrolysis

Thermochemical

Agri-waste

Synthetic fuel Charcoal

4.2 Non-traditional fillers and stiffening agents This discussion will be based on 10 materials which the author thinks is best suited for use with polymers in relation to manufacturing products essential for daily life of people. These materials also have potential as fillers and stiffening agents for fields other than polymers, such as cosmetic, food, paper, construction industries and so on, which are also important. – Rice Hulls – Rice Hull Ash – Wheat Hulls – Walnut Shell Powder – Eggshells – Fly Ash – Graphene – Bamboo Flour – Shellfish Powder – Coir Dust EPS – Expandable Polystyrene (EPS)

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4 Non-traditional fillers and stiffening agents for polymers

4.2.1 Rice hulls Rice hulls are unique within nature. This abundant global agricultural waste has all the properties one could expect from some of the best insulating materials and due to constant and diligent research its true potential has emerged and has many possibilities with polymers in the form of a fine powder or flour. The two main product categories are polymeric composite resins and polymeric composite lumber. Rice hulls are the protective coatings/shells of the rice seeds or grains. These hulls comprise a hard material and are unique products of nature. They contain 20% opaline silica in combination with a large amount of a structural polymer called lignin. Tests carried out have shown that rice hulls do not flame or smoulder easily, are highly resistant to moisture penetration and fungal decomposition, do not transfer heat well, are not odorous, do not emit gases, are not corrosive with respect to metals, copper or steel. Rice hulls are very tough and abrasive, consisting of two interlocking halves, encapsulating the tiny space vacated by the milled grain. Rice hulls are freely available in very large volumes in most countries and thanks to the constant research their full potential is emerging only now. They are relatively cheap materials being agri-wastes and can also be used in their natural state as very effective steam boiler fuel. The author having set up three manufacturing units in Sri Lanka and in the Philippines where steam boilers use rice hulls can authenticate this aspect. As compared to diesel oil as a boiler fuel, it is 90% cheaper and the resulting ash can easily be converted to value-added products. Figure 4.2 shows some characteristics of rice hulls.

Rice husk characteristics http://www.knowledgebank.irri.org/rkb/index.php/rice-milling/contributions-and-references-milling/ further-information-byproducts/husk-and-straw-properties

Proximate analysis ‒ comparison of rice husk, rice straw and wood in % (d.b.) Property

Rice husk Rice straw Wood

Volatile matter

64.7

69.7

85

Fixed carbon

5.7 19.6

11.1 19.6

13 2

Ash

Chemical composition of carbon-free rice husk ash in % d.b. Chemial composition

% d.b.

SO2

86‒97.3

K2O

0.58‒2.5

Figure 4.2: Properties comparison of rice husk/rice straw/wood.

4.2.2 Understanding rice hull ash as fillers for polymers The polymer industry has a newfound interest in fillers from industrial by-products and other waste materials having potential recyclability. This new class of fillers

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includes fillers from natural sources, for example natural fibres, agri-waste like wheat and rice hulls, industrial waste like saw dust, coir dust and a recent entry in the form of silica ash and agricultural waste material obtained by burning either rice or wheat hulls. Rice hulls have an unusually high percentage of ‘opaline silica’. Its annual worldwide output is estimated at around 120 million tons, which corresponds to about 4.8 million tons of silica. Silanol groups present on the surface of rice hulls ash can positively influence its reinforcing properties as a filler but being hydrophilic, it will tend to form aggregates due to moisture absorption and probably best results will be obtained when used in combination with another filler material. It is emphasised here that poor understanding of silica ash as a filler is linked to the lack of scientific knowledge of its surface characteristics, since its behaviour is significantly linked to its surface properties. New approaches and studies of silica ash has revealed its true value. The important advantages of using polymeric composites compared to conventional metals is the ease of processing, manufacturing versatility and lower costs. Composites are used in a wide variety of applications ranging from household appliances to aeronautics. The vast potential of these composites are the fillers used either singly or in combination in polymers that modify the resin properties. Rising costs, stringent performance factors and increasing demand has been driving the polymer market to promote numerous studies, attempting to show that the use and performance of natural by-products or industrial wastes are comparable to traditional commercial fillers such as carbon black, precipitated silica, talc and others. Rice hull ash or silica ash, as it is commonly known, is classified as an agricultural waste obtained after burning the rice hulls. This process produces two types of ash – black/coarse and grey/fine with an approximate silica contents ranging from 55%–90% silica, depending on the longevity of the burning. For example, when used as a steam boiler fuel, the initial stages will produce ‘black’ ash, while prolonged heating in the combustion chamber will result in a very fine grey ash high in silica. Although there are limitations in its application as a single filler in thermoplastics, its uses have wide range of applications, depending on its purity and particle size. Precipitated or fumed silica are known to bring improvements in mechanical properties to polymeric composites. Silica ash belonging to the same family has greater potential when used in combination with others as a filler and also a stiffening/strengthening agent in composites. Silica ash is thermally stable and a tough material possessing high specific properties. It is also a readily available low-cost material, which is important to the plastics industry, when considering it as a filler material for thermoplastics. Furthermore, growing environment concerns over landfill has boosted interest in silica ash. Figure 4.3 shows rice hull ash.

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4 Non-traditional fillers and stiffening agents for polymers

Figure 4.3: Rice hull ash (http://generalhorti culture.tamu.edu/h202/labs/lab7/inorganic/ ricehullash.html).

4.2.3 Wheat hulls as a renewable energy/filler source New world trends are showing a great interest to have sustainable agricultural production and that implies utilisation of wastes, which originates from that waste. Large quantities of agricultural crop residues produced every year in the world are not sufficiently used. These wastes, which falls into the category of biomass, can be considered as renewable energy and filler source and can be used for polymer composites as well as for energy generation. Due to continuously increasing growth of populations and rapid development in most sectors and industrialisation, the supply and development of energy sources cannot keep up with the demand. For this reason, research and development projects are aimed at development of technologies, which uses renewable energy sources like biomass, which the world has in plenty. Wheat hull wastes hitherto neglected with little usage is now getting a lot of attention, especially in the polymer industry as ideal filler for polymer composites. Research tests carried out have raised new interests in the hitherto neglected and ignored wheat hull wastes. In their natural state, wheat hulls contain the lignin polymer and also 8%–10% of silica. When fully burnt, the ash will have around 50% silica, similar to rice hulls ash but with lower silica content levels. Trials carried out on pelletising wheat hulls wastes are very promising as compared to wooden pellets, now being used as an alternate fuel for diesel in many countries. The silica content in the hulls generates a higher calorific value as pellets as compared to wood pellets.

4.2.4 Fly ash Fly ash is the naturally occurring residue from the combustion of coal used as a fuel to generate steam or other, for example generation of electricity. It is similar to volcanic ash, which was used thousands of years ago to make concrete, especially during Roman times. Today, when coal is burnt in modern electricity-generating

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plants, temperatures can reach around 2,800 °F and the residue comprises bottom ash and fly ash. This is a light weight aggregate material that falls to the bottom of the combustion chamber and removed periodically as it builds up. The flue gases going up will also contain fly ash and can be carried down through a flute and collected in silos or other. Although there are many applications for fly ash, the most common application is as partial replacement in the manufacture of Portland cement. This filling action can be between 20% and 30% of a total mix or higher depending on the process. Fly ash reacts as a pozzolan with the lime in cement as it hydrates, creating a more binding effect, holding the concrete together. As a result, concrete made with a fly ash content is stronger and more durable than traditional concrete made with only Portland cement, which means it can handle greater loads, is more resilient and lasts longer. Fly ash concrete can withstand harsher service environments and is also less susceptible to chemical attacks like di-icing salts, soil sulphates and others and mitigates the negative impact of deleterious aggregates, especially true when using fly ash in infrastructure projects such as roads, highways and bridges. Fly ash concrete is easier to work with because of its spherical shape and its ability to moderate early concrete set times. The improved flowability, reduced hydration temperatures, additional strength, delayed setting time and reduced costs are some of the main factors that contribute towards the use of fly ash in concrete. The use of fly ash has positive environmental impacts, as it conserves landfill space, reduces energy and water consumption and helps reduce greenhouse gases. According to reports, the production of one ton of Portland cement produces one ton of carbon dioxide gas and the use of fly ash will definitely reduce these harmful gases. Fly ash has similar chemical composition to that of Portland cement, shale and volcanic ash. Like these, fly ash also contains naturally occurring trace elements that are also found in rock and soils. These trace elements are present in parts per million totalling less than 1% of fly ash. The levels of these trace elements in coal are similar in concentration to most naturally occurring soils. When fly ash is incorporated in cement and when hardened, the exposure levels of the trace elements would be far less than open soil and below levels of concern. Figure 4.4 shows fly ash.

4.2.5 Bamboo fibre and flour What is Bamboo? Bamboo is a diverse group of plants with over 1,200 varieties of various sizes. With versatile properties it offers an ecologically viable replacement for wood in many ways. Bamboo is an extremely fast growing plant and has been widely utilised in building construction in China, India, Sri Lanka, Indonesia and South America for centuries. Innovative architects and engineers in the east have

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4 Non-traditional fillers and stiffening agents for polymers

Figure 4.4: Fly ash (http://iizmar.ee/ wp-content/uploads/2014/03/lendtuhk.jpg).

been using bamboo in residential and commercial buildings even to this date, but it is relatively new to the western world. Wood-plastic composites (WPC) is the common term applied for all fibre-filled composites, although wood flours are used more or less exclusively. In the context of this definition, ‘wood’ represents all fibrous materials of plant origin. Today, however, ‘represented’ would be a more precise wording, since some non-wood fibres more actively come into play. A number of Chinese WPC manufacturers that use mostly bamboo as a filler for a composite offers many Bamboo Plastic Composites (BPCs), which in many cases is still referred to as WPCs. Manufacturers that offer either wood flour or bamboo flour as a filler, in most cases, would prefer to use the name WPC for their lumber. There are composite makers who use natural fibres like rice hulls, oil palm and coir dust/fibres in their polymeric composites. These fibres have a combination of functions of real filling and stiffening actions in a composite and bamboo can also be included in upper bracket categories. Manufacturers that market their products as FRP (fibre-reinforced plastics) use thermoset polymers like epoxy, polyether or phenol formaldehyde resins reinforced with fibres such as glass fibre, carbon aramid and others. The market has a fixation on the name FRP and even when bamboo fillers are used, they would still call them FRP, although using a term such as – NFRP (natural fibre-reinforced plastics) would be a better option. Figure 4.5 shows bamboo fibres that can be used for a variety of composite products. Currently, the marketplace is witnessing a gradual trend of utilisation of new names, for example BPC (bamboo), PCRH (rice hulls), PCWH (wheat hulls) and so on, instead of a general use of WPC. Strictly speaking, this is a more accurate description of a product, although the chemical structure and basic compositions may be similar. Moreover, these new composites are capable of better properties and aesthetic values over wood fibre or wood flour and have the right to be called by their individual names, independently of wood.

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Figure 4.5: Bamboo fibres (photo by Composite Materials Group).

Bamboo when planted yields mature materials in 2–3 years where trees for wood will take much longer. According to technical reports, bamboo is stronger in tensile strength, superior to mild steel, can withstand compression loads better than concrete. Some special species of bamboo grow very fast – on a daily basis which is faster than probably any known plant and can grow to heights of 60 ft. Unlike trees, harvesting bamboo does not kill the bamboo forest or create soil erosion. A bamboo forest dose not require replanting. Mature bamboo plants have an extensive deep root system, which keeps on sending up shoots continuously for long years and harvesting actually helps to produce strong yields. Bamboo can grow in almost any type of soil including damaged or degraded lands. Among the best bamboo species, probably the best one is known as Moso. These grow mostly in Zhejang province in the southeast of China, known to the world as the Kingdom of Bamboo. It is harvested when around 5 years old and is known to reach heights of 90 ft with diameters around 5–6 inches. This versatile and beautiful product and also environmentally friendly material offers an alternative to our depleting global supply of timber or natural wood. Bamboo composites using bamboo fibres, powders or flour are emerging as speciality products more cost-effective than most and also much stronger and lighter. For example, bamboo fibres can actually be a stronger reinforcing substitute agent for fibre glass, while bamboo in powder form or as a fine flour will have immense uses in composites as presented later under composite applications. A composite is a synergetic mixture of different materials bound together that makes the combination better than the individual material. Composites are usually stronger, lighter, more weather-resistant and can also be less-costly than what it replaces. We all have composites in our lives – our highways are concrete reinforced with steel, outdoor decks, doors, facades with composite lumber, car body parts, boats and now, the use of bamboo in the form of powder (cosmetics), fibre (reinforcing agent) and bamboo flour (composite resin filler), with all three acting singly or in combination as fillers, reinforcing agents or stiffening agents.

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4 Non-traditional fillers and stiffening agents for polymers

Using bamboo in sealed composites elevates bamboo to new levels, while reducing the problems of mildew, insect infestation or degradation. Properly used, bamboo is a strong natural fibre in any epoxy laminates, such as in fibre glass boats, canoes or surfboards to name a few popular products. The world is now slowly but surely being aware of this versatile and cost-effective ecological friendly natural source, ideally suited for polymeric composites being one of the strongest among natural fibres. Composite manufacturers realising the vast potential of the material are widening their range of applications and have developed process advantages that increase durability and reduce production times of bamboo composites. Such advances and sustained uses of bamboo will create potential great industrial markets for bamboo growers that may someday be a mainstream crop as corn, wheat or rice. Industrial research will be a key factor to promote this unique material, with less erosion of the earth by mining and other methods. Several products already on the market have shown that a bamboo natural fibre composite can be performance competitive when compared to traditionally made composites. Products with great potential with bamboo are surfboards, canoes, boats, snow boards, canoe paddles, decking, fencing, boat hulls, roof tiles, composite lumber, composite polymer resins, railway sleepers to name a few. Bamboo is compatible with both thermoforming and thermoset polymer resins and with suitable processing agents, great products can be made. The processing methods include extrusion, injection moulding, compression moulding, foaming and lamination as the base methodologies.

4.2.6 Properties of eggshell powder as a filler in polymers While many polymers can be filled with non-traditional fillers, polypropylene is one of the most important polyolefins that has a wide range of applications. One may opt to formulate with more than one polymer and also a combination of NTFs, but this presentation is based on a single polypropylene matrix. The use of filled polypropylene in electrical and automotive engineering is on the increase due to its excellent stiffness properties also. Fillers which merely increase the bulk volume and, hence, reduce costs are known as extender fillers, while a filler like eggshell powder, which has both filling and stiffening properties can be classified as reinforcing fillers. If fishbone powder, which is compatible with eggshell powder, is also available, a small percentage addition will yield good results. Several million metric tons of fillers are used annually by the plastics industry. The uses of these fillers and reinforcements are likely to grow rapidly with the constant introduction of improved compounding agents like lubricants, compatibilisers and others which help in the production of polymeric composites. Depending on the end applications, the use of these special additives

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will permit high filler/fillers contents in a polymer matrix, within limits, which can be as high as 80%. Needless to say that this will yield much cheaper products as against the use of traditional fillers and the use of less polymer is certainly a ‘green’ environmental effort. For example, tests and practical usage of composite tiles have shown that this level of filler usage could have a tremendous impact in lowering the usage of petroleum-based plastics. Unlike some TF (traditional filler) and NTF (fly ash), eggshell powder does not form aggregates, which is generally dependent on their surface energy and area. According to research, the properties of filled polymers change with the dispersion state, geometrical shape, surface energy, the surface quality, as well as the particle size of the filler used. The future for filled polypropylene is brighter due to the recent commercial availability of nanosize fillers. Hitherto popular traditional fillers for polypropylene like glass fibre, glass spheres, mica and others may soon be a thing of the past with new NTFSA (non-traditional fillers and stiffening agents) such as eggshell powder, rice hulls, rice hull ash, graphene and so on being used successfully to produce products with even better properties. Figure 4.6 shows eggshell powder.

Figure 4.6: Eggshell powder (https:// ybertaud9.files.wordpress.com/2013/03/ eggshell-powder.jpg).

4.2.7 Coir dust and fly ash composites Coir dust is a by-product of coir fibre production, while fly ash is an industrial waste. Use of coir dust in various forms has been in place for some time now, but the use of fly ash has had only limited applications. However, new emerging research and practices are opening doors to many new exciting and practical applications as composites. A composite material is a combination of two or more materials, used in predetermined proportions whose final characteristics will differ to the individual materials used and also be stronger. For example, a polymer as a matrix that is filled/ reinforced with one or more materials to yield a superior composite material to

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4 Non-traditional fillers and stiffening agents for polymers

meet a specific end application. At present, polymer composites are of great interest because of their versatile and endless possibilities, being superior to traditional composites, with reduced cost factors also playing key role. Natural fibres like jute, flax, rice husks, wheat husks, hemp, cotton can be used as filler/reinforcements as alternatives to traditionally used synthetic fibres like carbon, glass and others, because of low-density, good mechanical properties, abundant availability and biodegradability. Hence, the development of low-cost composites with superior properties using industrial and bio-waste from local resources is of great interest to scientists and researchers. Since a few years ago, studies have been carried out on the mechanical properties of epoxy-based fly ash composites with research attention given to use such materials for capacitor dielectrics, insulation, encapsulation, multilayer ceramic chips, printed circuit boards and so on. Results have shown that fly ash and biofibre based composites exhibit a low dielectric constant and stabilised dielectric loss at high frequency fields and hence are suitable for electronic applications. This presentation is about the development of a novel hybrid polymer composite with coir dust and fly ash as the filler/reinforcing agent. Figure 4.7 shows coir dust.

Figure 4.7: Coir dust (http://creantisworld. com/demo/growgreen/wp-content/uploads/ 2014/03/Coco-Peat-720x640.png).

4.2.8 Graphene – polymer composites Graphene has been around for some time now but its huge potential is dawning on scientists and researchers only now. It had really begun in 2010, when scientists at the Manchester University were rewarded for ‘groundbreaking experiments regarding this two-dimensional material known as graphene’. Since then, the world is being transformed in the same way that silicon did. There is of course, plenty to be excited about according to scientists who claim that graphene is 100 times stronger than steel, can withstand 20% strain, is a million more times electrically conductive than copper and is 98% optically transparent,

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plus it is harder than diamonds and virtually impermeable. Moreover, it is ideal for polymer/graphene filler-based hybrids for energy and electronic applications. The list goes on and on as excited scientists and researchers are paying great attention to this material, predicting its use in applications in everything from foldaway mobile phones, wallpaper-thin lighting to the next-generation aircrafts. According to reports, UK-based Briggs Automotive Company is claiming to be one of the first to develop a car with panels made from composites filled with graphene. Sheets made of graphene composites one atom thick are stronger than standard carbon fibre and also can reduce body weight by 20%, as compared to carbon fibre material. They think that these panels are 200 times stronger than steel. This automaker makes the point that use of graphene in a more wider range will reduce fuel costs, enhance performance and also decrease manufacturing costs. The extraordinary properties of graphene such as its large surface area, outstanding flexibility and transparency, as well as its excellent mechanical, electrical and thermal properties have been researched since 2004, but its true potential in practical applications is being realised only now. Polymer filled/reinforced composites have the potential to be applied to various products such as components of electronic equipment, energy storage media, organic solar cells, heat-conduction composites, film packaging and others. However, restacking occurs frequently during mixing with the polymer matrix due to strong van der Waals forces between the graphene fillers which could result in cracks, pores and pin holes in a composite. These defects could decrease the full beneficial values of graphene-filled polymer composites and a good solvent-free process can overcome this problem by inducing good dispersion of graphene particles in polymer composites for commercial applications. There are three main methods for manufacturing graphene-polymer composites: in-situ polymerisation, solution compounding and melt blending as found out by researchers. Studies carried out on these composites based on a range of polymers including epoxy, poly methacrylate, polypropylene, polyethylene, polystyrene, polyphenylene sulphide, polyamide had shown that in situ polymerisation and solution compounding helped improve the physical properties of these composites by enhancing the dispersion of fillers. However, it has been established that melt-blending process is the most economical technique due to the non-use of a solvent. Thin sheets of polymer filled with graphene can yield lightweight materials which can conduct electricity and can withstand much higher temperatures than the polymer alone. Although polymers can be infused with carbon nanotubes to obtain similar materials, composites with graphene would be much cheaper. Graphene will also raise fewer toxicity concerns than carbon nanotubes. Graphene-polymer composites would be ideal for making lightweight gasoline tanks and plastic containers that can keep food fresh for weeks. They could also be used to make lighter parts for aircrafts, automobiles, as well as strong wind turbines, medical implants and sports equipment. Being excellent electrical conductors and

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with high optical transparency, they could be used to make transparent conductive coatings for solar cells and displays. Advance research is going on to make nanoparticle-embedded polymers. Carbon and glass fibres have traditionally been used to strengthen polymers. Fibre glass/ epoxy composites are a good example. Unlike carbon fibres, a very small amount of graphene nanoparticles – less than 2%, is sufficient to make the polymer stronger and heat resistant. Because less filler is used, the composite can retain the polymer's basic properties like stretchability or transparency. Clay nanoparticles and carbon nanoparticles are strong contenders for use in polymer composites. According to reports, Toyota makes some engine parts from nylon-filled clay composites which are strong and can handle high temperatures than nylon. Carbon-nanotube-infused polymers are used to make baseball bats and golf clubs and they can also be used for car parts, but the high cost of manufacturing carbon nanotubes has limited their use. Figure 4.8 shows graphene-polymer composite resins.

Figure 4.8: Graphene-polymer composite resins (http://creantisworld.com/demo/ growgreen/wp-content/uploads/2014/03/ Coco-Peat-720x640.png).

4.2.9 Epoxy composites filled with walnut shell powder Natural fibres and biomass are abundantly available in nature, and now scientists and researchers are finding the importance of turning to these naturally available resources as ideal, if not, superior filling and reinforcing agents for polymer composites. Most often, they will provide both functions in a single material and the possibilities of using them in combination is also of great importance. The realisation by processors that using polymeric composites is as good as using pure polymers and in most cases yielding superior products, with much less costs, is driving the composite markets forward at a rapid rate. In the more adventurous east, processors are using more and more natural fibres and biomass for making composites backed by great technology. It may be true to say that some of the basic and most important properties in plastic products, like density (light/heavy), tensile strength, compression strength, thermal properties, opacity, aesthetic values

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and so on, can be achieved by today’s composite materials and processors are finding that working with composites filled/reinforced with non-traditional fillers and stiffening materials does not need any deviation from normal processing technology and the fact that new or modified processing equipment is not required is definitely an advantage, when considering the added benefit of reduced costs. Some of the other advantages of using these natural resources include ease of availability, better strength, stiffness, good compatibility, light weight, easily mouldable even for complex parts. There are added advantages because of their distinct characteristics like biodegradability, no odour, no respiratory irritations and being environment friendly. Walnut shells, which may not be so popular in the polymer industry, can play a significant role in the form of powder or flour, especially for combination with thermosetting polymers using compression moulding or layup processes. Walnut-filled composites can produce parts for defence equipment, domestic parts, aerospace structures, sports gear parts, storage systems and many others. Figure 4.9 shows walnut shell powder.

Figure 4.9: Walnut shell powder (http://www. reade.com/media/widgetkit/English_Walnut_ Shell-e0c09233a2713f04543811611759cf2b.jpg).

4.2.10 Expandable polystyrene as filler in rigid polyurethane foams In polymer foams, fillers are generally added to reduce costs, increase density or increase compression strength. Fillers can also influence other material characteristics like optical, surface, electrical conductivity, magnetic properties, mechanical and rheological properties in addition to chemical reactivity, thermal stability, flame retardancy and so on. Fillers are also added to formulations of foams, although their production is very sensitive to changes in composition and parameters of processing. Fillers also could reduce shrinkage and combustibility of polymer foams. Typical traditional fillers used for preparation of rigid polyurethane foams (RPURF) are: aluminium hydroxide, melamine, starch, talc, chalk, borax, calcium carbonate, barium sulphate crystallised silica and nano fillers like bentonite and more recently expanded graphite.

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The quest to find new composites based RPURF and expandable polystyrene by the Crackow University of Technology has yielded interesting results. The filler of RPURF matrix should ideally be a thermoplastic granulate containing a blowing agent, such as EPS beads. This filler should have a softening point below 90 °C. The ideal bead size should be between 0.2 and 4.0 mm while the amount of EPS added to the polyurethane reaction mix could be between 20 and 120 wt.% in relation to polyurethane reagents. The basics of this process are co-expansion of EPS and RPURF with full energy balance. EPS is expanded by the heat generated by the exothermic reaction between the polyol and isocyanate. Of particular interest is the influence of EPS on a composite of RPURF-EPS with regard to properties such as thermal conductivity, compressive strength, core density, and dimensional stability. There is significant increase in the material properties mentioned above and with the addition of EPS as a filler, it is possible to produce foam products that differ in apparent density, thermal conductivity, mechanical properties and dimensional stability. Please see Table 4.2 shown below. Table 4.2: Physical properties of RPURF-EPS composite with 40 wt.% EPS Filler – (author modified figs.). Property of Sample

RPURF

RPURF -EPS

Apparent density kg/cu.m

.

.

Closed cell content %

.

.

Water absorption wt%

.

.

Dimensional stability after  days%

−.

−.

Dimensional stability after  days%

−.

−.

Compressive strength-parallel to rise direction kPa

.

.

Compressive strength-vertical to rise direction kPa

.

.

.

.

Thermal conductivity after  hours mW/(m. K)

The use of EPS beads in composite improves the dimensional stability in comparison to the standard RPURF. All foams, whether they are flexible or rigid will have a certain percentage of closed cells. In the case of EPS filled RPURF, it will have a lower percentage. It is attributed to the addition of EPS which when expanding with the PUR foam destroys the structure of any unopened cells. A relatively high thermal conductivity measured after 24 h in RPURF-EPS composites may be explained by a worse thermal conductivity of expanded EPS beads and lower percentage of closed cells in the composite. Thermal conductivity of foams changes gradually during long ageing. Increasing of thermal conductivity is strongly influenced by the diffusion of the blowing agent

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from the foam. Tests show that after 7 days of ageing, the thermal conductivity of the RPURF-EPS composite increased by about 15%, while the standard RPURF increased only by about 7%. This phenomenon can be explained by the higher content of open cells in the composite material. The diffusion rate of the blowing agent in the standard foam (water) will be stable for all time periods while in the composite it will decrease after 7 days. Therefore, both foamed materials will show about the same heat insulating properties after a long ageing period. As the blowing agent of the standard foam had only carbon dioxide generated by the reaction between water and isocyanate (TDI or MDI), while the composite foam had both carbon dioxide and pentane blowing agent from EPS, after 50 days or more the standard foam will have an increased thermal conductivity factor. This is due to pentane contained in the EPS having a lower diffusion rate than carbon dioxide. Therefore, it is apparent that modification of water-blown RPURF with the addition of a chemical blowing agent in the EPS beads can be carried out successfully to achieve desirable end properties. Rigid polyurethane foams filled with EPS beads show very good mechanical properties and dimensional stability. These filled composites will cost less than pure polyurethane foams and can have several industrial applications. Figure 4.10 shows expandable polystyrene beads.

Figure 4.10: Expandable polystyrene beads (http://media.salvex.com/auction/p/1829597/ 182959669_332068_lp.jpg).

4.2.11 Coconut shell powder as filler in polymers The interest in natural fibre-reinforced polymer composite material is growing rapidly in terms of industrial applications. Researchers are finding that these types of filled composites will yield products with better properties than those made with pure polymers and with significant cost reductions too. They are renewable, cheap, abundantly available, completely recyclable in most cases, low density and biodegradable. Their combination of properties as a filler, stiffening/strengthening agent, solid mechanical properties and others makes them an ideal ecological alternative to traditional fillers and reinforcing agents like glass, carbon and other commercially made fibres used for the manufacturing of composites.

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The natural fibre-containing composites are more environmentally friendly and are used in many end applications like transportation, (automobiles, railway coaches, aerospace) defence applications, packaging, domestic appliances, building construction, industrial applications, indoor/outdoor applications and many others. Coconut shells are available in abundance, especially in tropical countries as a waste product. In rural areas, these shells are used for generating heat for cooking and some enterprises convert them into charcoal and carbon powder. However, waste coconut shells in the form of powder or as a fine powder will have more significant applications in polymeric composites as a filler and stiffening agent. Procurement and processing of waste coconut shells is cost-effective than other artificial fillers and being an agri-waste does not harm the earth, unlike some fillers that have to be mined. They are compatible with most polymers and in composites compatibilisers can be used, if necessary to enhance mixability. It has been found that when polyester was reinforced from 15% to 60% by weight, the composites displayed increases in flexural and tensile strengths, better than unfilled/reinforced polyester. The morphology and the mechanical properties of coconut shell powder-reinforced polyethylene composites have also been evaluated for suitability of using them as a new material for engineering applications. When low density polyethylene as the matrix was reinforced with coconut shell powder with fillings 5%–25%, the results had shown that the hardness of the composite increased but the tensile strength, modulus of elasticity, impact energy and the ductility of the composites decreased with increase in the filler powder. Although these properties decreased slightly, they were within acceptable industrial standards. As the filler loading increased, the poor interfacial bonding between the filler and the polymer matrix caused the decreases in properties due to an increase in the number of micro-voids, causing increase in water absorption levels. With the addition of a compatibiliser the interfacial bonding between the filler and the polymer matrix had improved greatly resulting in improved dimensional stabilities and water absorption behaviour. Figure 4.11 shows coconut shell powder.

4.2.12 Shellfish shell powder as bio-filler in polymer composites Bio-filled polymer composites are gaining wide scope of uses in engineering applications such as naval applications, aerospace structures, spaceship structures, gears because of high modulus and high strength, resistance to corrosion and so on. However, polymeric composites sometimes are susceptible to mechanical damage, when subject to high tensions, compression and flexural loads, resulting in interlayer delamination. Thus, nowadays a lot of research is concentrated on enhancing the mechanical properties of these composites. While injection moulded, extruded or compression moulded composites probably may not experience any mechanical property problems, hand lay-up products such as epoxy/fibre glass for boats

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Figure 4.11: Coconut shell powder (http:// img1.exportersindia.com/product_images/ bc-small/dir_14/406321/coconut-shell-powder -151803.jpg).

and others may be affected. Recent developments in this field is discovering that a good solution is to add secondary reinforcements by way of bio-fillers and shellfish shell powder, which will act in a dual role as both filler and stiffening agent will be ideal. Shellfish shells have a very high content of calcium carbonate and also a significant odour and depending on the end application, a masking agent may have to be used. The shellfish shell powders can be prepared by crushing, grinding and shearing emulsification. Tests have shown that these powders can be used for composite applications with filling ranging from 15%–30% depending on the end applications. A few years ago researchers at the University of Toronto published a paper on the suitability of using shellfish powder as a filler/stiffening agent in polymeric composites to replace metal parts which need high-heat resistance, for example, automobile and motorcycle exhaust systems. Thermoset polymer matrices such as epoxy matrices are widely used as systems due to structural and industrial applications due to its high resistance to corrosion and chemicals, good thermal and mechanical properties. Epoxy (E) resins are increasingly used as matrices in composites. The mechanical properties of a material are those properties that involve a reaction to an applied load. The mechanical properties of a composite determine the range of usefulness of the material and establish the service life that can be expected. The variation in the properties can be due to the change in the microstructure of fibre /filler and matrix reinforcements. Fillers increase load bearing, stiffness, fracture toughness, high temperature loadbearing capability, decrease shrinkage and also improve the appearance of composites. All non-traditional fillers and stiffening agents as presented are highly suitable to be used with standard polymers, either singly or in combination, to produce cost-effective composites for a very wide spectrum of end applications. The following Figure 4.12 shows profiles that are currently being produced by extrusion using polymeric composite resins. Figure 4.13 (a) and (b) shows shellfish shell powders.

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4 Non-traditional fillers and stiffening agents for polymers

Figure 4.12: Profiles extruded with composite resin – polypropylene/rice hulls waste flour. Reproduced with permission from Wuhan Industries Ltd. China.

(a)

(b)

Figure 4.13: (a) Shellfish shells (http://img.weiku.com/photo/9789/978918/product/DRIED_CRAB_ SHELL_MEAL_SCRAB_SHELL_POWDER_SHRIMP_SHELL_LOBSTER_SHELL_SHRIMP_SHELL_POWDER_ 201321913412557.jpg) and (b) Shellfish shell powder (http://g03.s.alicdn.com/kf/ HTB1riPgKFXXXXXZXVXXq6xXFXXXV/Shell-Shrimp-Powder.jpg_350x350.jpg).

Bibliography

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In the East, especially in China, many polymeric composite products like lumber, floor tiles, decking board, furniture, ceilings, roofing sheets, roofing tiles and many others are made with combinations of polymers such as polypropylene, highdensity polyethylene, polyvinyl chloride, while the accent in the West is on decking board, outdoor materials and railway sleepers. Some of these manufactures will be presented in detail in the next Chapter 5, which will present polymer processing methods with different polymers and different non-traditional fillers and stiffening agents as the reinforcing agents.

Bibliography [1] [2] [3]

Patel Prachi. article Graphene-Polymer Composite- May 2008- www.technologyreview.com Article “Bamboo Plastic Composite-BPC or WPC?”-WPC. Asia. Talikoti C.B., Hawal T.T., Kakkamari P.P. Dr. Patil, M.S. Epoxy Composite Reinforced with Walnut Shell Powder- volume 02 -Issue: 05-August 2015. [4] Trujillo Eduardo Jr. (2016) Prof. Ivens, Ian, Dr. Van Vuure, Aart., Polymer Composite Materials Based On Bamboo Fibers CMG Group. [5] Ochi Shinji. “Mechanical Properties Bamboo Fiber/Bamboo Powder Composite Materials” National Institute of Technology, Nihama College-Japan 22 October 2014. [6] Simpson, John- Article “Automaker Fabricates Vehicle Panels from Graphene”-Engineering 360 news- 15th. August 2016. [7] Malewska Elzbieta., Trzyna Marcin., Sabanowska Anna., Proclak Aleksander. (2011) Koniorczyk-“Influence of Expandable Polystyrene Fillers on properties of water blown rigid Polyurethanes Foams”-Crackow University of Technology, Poland. [8] Fillers – Encyclopedia of Polymer Science and Technology. [9] Sutapun Wimontak, Suppakam Nitinat, Pakdeechote Panuwat, Ruksakulpiwat Yupaporn Article “Application of Calcinated Eggshell Powder as Functional Filler for High Density Polyethylene” – Suranee University of Technology, Thailand-August 2013. [10] Igwe Issac O., Onuegbu Genevive C. (2012) – Studies on Properties of Egg Shell and Fish Bone Powder Filled Polypropylene- American Journal of Polymer Science. [11] Singh Alok. Singh Savita. Kumar Aditya- Study of Mechanical Properties of Coconut Shell Powder Epoxy Composites- International Journal of Materials Science and Applications. [12] Defonseka Chris. “Introduction to Polymeric Composites with Rice Hulls”- Smithers Rapra UK-2014.

5 Processing polymers and composite resins 5.1 Introduction Polymers are the backbone of the fascinating world of plastics. Chemical elements combine to form polymers, which can be further processed into various products with the addition of various additives. To meet end applications from simple consumer goods, to automotive to space travel, the need for cost-effective and speciality polymers has resulted in research and development of composite resins and the production of composites. Some of the common general-purpose polymers are polyethylene, polystyrene, polypropylene, polyvinyl chloride, nylon, acrylonitrile butadiene, polyurethanes, melamines, polycarbonates and so on. These comprise both thermoplastic and thermosetting polymers and can basically be in the form of liquids, solids or powders. While composites are a combination of polymers as the matrix with biomass or fibres as the reinforcements, due to global concerns about air pollution based on the large volume use of petro-based polymers, researchers have been coming up with composite resins, which require less polymers. A good example of a composite resin is a combination of polypropylene (40%) and (60%) rice hull powder or wood flour or bamboo flour mixed with additives and pelletised for easy processing. A revolutionary product based on emerging technology – WPC (wood polymer composites), has been in place now for some time. This same product made with rice hull flour/powder, which I will call – PCRH (polymeric composite with rice hulls) has much better proven properties. A good example of a PCRH product is – composite lumber – which is an ideal substitute for natural wood. In this chapter, the author will present in detail the manufacture of composite resins in addition to five polymer processing methods in brief. In research and development of polymers, it is not enough only to produce these polymers but suitable processing methods also have to be worked out. This is where cooperation between researchers, processors, tool makers and machinery manufacturers will pay good dividends. Although most of the processes are listed below, only selected important processes will be presented. The following shows some of the basic methods used to convert polymers into products: – Injection moulding – Extrusion – Blow moulding – Foaming processes – Coating – Compression moulding – Recycling – Vacuum forming https://doi.org/10.1515/9783110669992-005

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– Lamination – Casting – Roto-moulding Of the above six processes, injection moulding, extrusion, blow moulding, compression moulding, foam processing and recycling will be presented in brief as they are the processes that will be used to make polymer composites.

5.2 Manufacture of composite resins Due to growing concerns about air pollution by using petro-based products, the plastics industry in response have been seeking out new alternatives and phasing out the use of these products. Scientists and researchers have been coming up with alternative feedstocks to produce some polymers and other products. The constant uncertainty of resin prices and gradual increases has prompted the plastics industry to greater efforts to find solutions. The use of composite resins made with polymers like polyethylene, polypropylenes, polyvinyl chloride and others including thermosetting polymers combined with wood flour (WPC) was a beginning but now due to emerging technology other non-traditional fillers and stiffening agents like rice hulls, wheat hulls, bamboo powder and a host of others are being successfully used to make composite resins. Two big advantages these resins have are less costs and better properties.

5.2.1 Concept The plastics industry has been dealing with the use of pure virgin polymer resins and also in some cases replacing a part of it with recycled material. The desire to move away from petroleum-based resins has given birth to the concept of polymeric resins and now with non-traditional fillers and stiffening agents. A polymeric composite resin is a combination of a polymer as the matrix and biomass filler with a dual action of filling and being a reinforcing agent. The use of less polymers is an advantage and composite resins made of wood chips and wood flour have been in use for some time now. Although the products made with these resins compare favourably with the traditional ones made with pure virgin and recycled material, some issues such as warping, exposure to weather, water absorption and durability had to be overcome. The advent of polymeric resins with rice hulls (PRRH) has overcome these problems and the products made with them are superior and belongs to a family of emerging technology. While most polymers may be compatible, the most commonly used ones are: low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP),

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polystyrene (PS) and polyvinyl chloride (PVC). Basic additives needed for composite mixes are lubricants, compatibilisers, heat stabilisers and colourants where desired. Additional additives may be used depending on the end applications. The best nontraditional filler for polymeric lumber has been found to be waste rice hulls, which is high in silica content. A combination of different fillers is also feasible to achieve particular end properties. To obtain particular finishes like high gloss, matt, wood veneers and so on, different finishing processes in addition to colours or combinations of colours are available as explained later. The most common processing methods for polymeric composite resins or mixes are: extrusion, injection moulding, compression moulding and lay-up methods. Figure 5.1 shows the general flow of polymeric composite resins with rice hulls to end applications.

5.2.2 Manufacturing process in brief A polymer resin such as a high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC) or other polymers are used as the matrix and mixed with rice hull flour (fine particle size) along with additives such as compatibiliser and a lubricant. Adding a colour is optional. The polymer can be virgin material or a combination with a percentage of recycled material, whereas rice hulls must be moisture free and for good homogenous mixing, the particle size must be reduced to a fine powder. These operations can be done separately before final mixing or can be accomplished online for automatic processing. An automatic extrusion processing line would start with a dryer for the rice hulls, feeding a size reduction equipment, a co-rotating twin extruder, cooling/ take-up downstream to include a pelletising machine with pellet size adjustments and collection to silos. A basic formula would be: 40% polymer, 60% rice hull flour, 1.0% lubricant and 2.0% compatibiliser. Once the extruder is heated and ready, the polymer is introduced into the hopper of the extruder and allowed to get warmed up in the feed zone. The rice hull flour is then added in a stream along with the additives and the heated zones of the barrel along with the heat generated by the rotating screws will produce a homogeneous polymer mass. This mass is pushed forward in the barrel and will go through a breaker plate with a screen pack to remove any foreign matter until extrusion through a pelletising die and the hot polymer strands are cooled on a slowly moving conveyor to reach a pelletising station where the strands are converted to small pellets of predetermined size and auto-fed into large vertical silos for storage, before packing into desired packs for shipping. These composite resins will be (polypropylene/rice hulls) will be a very pale yellow and colourants may be added if desired. Producers may prefer a neutral colour where they can add any colour they desire on the factory floor.

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Figure 5.1: Process flow concept chart designed by the author (photos with permission from Hardy Smith Ltd., India).

5.2.3 Raw materials Basic raw materials will be polypropylene or high density polymer, rice hulls powder, a compatibiliser and lubricant. Since these composite resins tend to be a little heavier than the virgin material, a small quantity, between 0.5% and 1.0% may be added to lighten the final moulded products. For example, hard and heavy products

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will be more suitable for flooring, building construction products, railway sleepers and others but lighter and aesthetically pleasing products will be required for automobile and indoor applications. Polymers can be in the form of granules or powder and free of moisture. If more than one polymer is been explored, mixed and used as the matrix, they should be compatible and here the melt-flows become important. Polymers are generally available in 25 kg bags or in bulk of 400 kg packs (Gaylords). Rice hulls are available in abundance in many countries and the full potential of these humble gifts of nature has not been realised as yet. Unlike wood fibres which are about 6–7 mm in length, rice hulls are about 0.3 mm. Moreover, a substantial part of the silica present is on the outside of the hull. They have an inherent moisture content problem, which can be as high as 15–20% and likely to have small pieces of foreign matter. Therefore, the use of a vibrating sieve before drying and size reduction would be of great help. The ideal allowable moisture content will be ≤1.5% but ≤2.0 will also be acceptable, since the high heat in the extruder barrel will also remove this moisture. Higher moisture contents may result in swelling products of the extrudate and create problems later when moulding. Additives are an essential part of producing composite resins as well as polymeric composite products. Some are needed for assisting in mixing of the hot composite mass, some for producing aesthetically pleasing finishes and some for enhancing one of the common properties of the desired final products. Some of the common additives used are as shown below: – Lubricants – Coupling agents – Stabilisers – Anti-UV agents – Flame retardants – Anti-fungal or microbial agents – Blowing agents – Colourants – Compatibilisers

5.2.4 Machinery and equipment Machinery & equipment- Advanced extrusion systems will combine both operations into one, with the first system having a smaller extrusion system for pellets and a larger more powerful system for the second stage. These systems will depend on the size and volumes of the extrudates to be produced. The second system will have a ‘sizing unit’ to control the dimensions of the extrudate, especially when making wide boards.

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5.3 Injection moulding Injection moulding is a process where a hot polymer is injected into a single cavity or multi-cavity mould made from either steel or aluminium. Generally thermoplastic polymers are used but thermosets are also used, though on a lesser scale. The basic structure of an injection moulding machine is a barrel with power-driven screw inside, connected to a vertical hopper, through which the raw polymer material is fed into the barrel. This barrel is heated well and the solid polymer material is softened by this heat and also by the heat generated by the rotating screw to form a hot melt. At the end of the barrel a small nozzle with an opening is screwed by threads. A solid steel mould is two halves mounted on two platens, one of which is stationary, while the other moves horizontally to open and close. This single cavity or multicavity mould must be well-designed so as to ensure that the molten polymer will travel along the designed paths to fill all the cavities in full. In injection moulding, the mould design is very important and will depend largely on the weight, shapes and features of the parts to be made. The mould will have an internal cooling system and guide pins to align the closing of the two halves properly to prevent material leaks. Here, the clamping force plays an important part in two ways. Firstly, machines are classed, for example as 100 tons, 200 tons, 500 tons and so on and secondly this clamping force is very important as smaller products will need lesser clamping forces and larger ones will require greater clamping forces due the sizes of the moulds. Generally injection moulding machines are either hydraulically or electrically driven and some ‘hybrid’ machines are also available. Due to modern day technology many versions of advanced machines come on the market periodically. Injection moulding machines are also graded on their injection capacity. For example 4 oz., 8 oz., 12 oz and so on but the real effective injection shot capacity is around 75% of the rated one. For controlling the weight per part, during injection of the hot melt, as the screw turns inside the barrel pushing the material forward, the end of the screw will come and stop within a few millimetres from the nozzle opening, which is pre-set by a technician to ensure that only a pre-calculated amount of polymer is injected. This gap will vary with different production runs and is called the ‘cushion’. Thus, an overall basic injection moulding cycle will consist of filling of the hopper with material, producing a hot melt by heat inside the barrel, injection of the melt into a closed mould, the hot melt filling all the cavities, the cooling period (dwell-time), opening of the mould and auto-ejection of moulded parts. The mould is closed and the cycle continues. This operation can be manual, semiauto or fully automatic. General ISO standards for injection moulding can be ISO 9000, ISO 9002 and a special standard as required by the automotive industry QS 9000 and Statistical Process Control (SPC) systems are used. When a customer places an order with an injection moulder in addition to the details, agreed tolerances are discussed and accepted. A customer may supply a mould/moulds which makes it easier and then the moulder will prepare several samples with the QC

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department checking for quality. This stage is called the PPAP (pre-production approval procedure) and the samples approved by the customer before actual production starts. When production commences, each moulding station will be provided with a ‘SPC Chart’ where a machine operator will record the cushion reading at specified intervals on the given SPC chart. This chart will have a median, an upper limit (UCL) and a lower control limit (LCL). The ‘Range’ (the difference between the highest and lowest readings) is also recorded and all must be within the specified limits. If any of the readings are outside the limits, the process is said to be out of control and a technician will then make the necessary adjustments and bring it back into control. For manual or semi-auto operations, each machine will have an ‘open-loop’ system, which means it needs manual correction and auto-operations will have ‘closed-loop’ systems, where auto-corrections will take place. Thermoplastics are the preferred material for injection moulding and are widely used. Generally, this process is used to make large volume solid plastics parts. If a multi-cavity mould is used, the cavities can be identical or some of them can be different and produce products of different geometrics in a single moulding cycle. Moulds are generally made from special tool steels but stainless steel or aluminium can be used for certain products. Depending on the design and the material used, the general lifespan of a mould can be between 30,000 to over 100,000 mouldings with advanced technologies using specially hardened alloys as inside cores which will last longer. Some of the main features of a mould are the ability to withstand high clamping forces to lock the mould before injection, wear and tear of cavities and defamation due to high injection pressure. Metal or other components can also be inserted into the cavities when the mould is open, allowing the injected plastic material to cover it. This process is called insert moulding. This process is often used to make plastic parts with screws and this technique can be also used for in-mould labelling and other variations. For thermosets, typically two different chemical components are injected into the barrel. These chemicals immediately begin an irreversible chemical reaction, which eventually crosslinks the material into a single connected network of molecules. As the chemical reaction occurs, the fluid components permanently transform into a solid. Solidification in the barrel and screw can be problematic, therefore minimising the residual time in the barrel can be achieved by minimising the barrel’s volume capacity and by maximising the cycle times. Some of the common polymers used in injection moulding are: polyethylene, polystyrenes, polycarbonates, polypropylenes, ABS and many others. Injection moulders use self-coloured polymers in the form of granules, powders or pellets and also use masterbatches for achieving an aesthetically pleasing vast range of solid products. In another process called – injection-blow-small hollow containers can be produced. The following Table 5.1 shows some defects of injection moulded parts:

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Table 5.1: Defects of injection moulded parts (compiled by the author). Moulding defect

Defect name

Description

Main cause

Blister

Blistering

Raised or layered zone

Tool/material too hot Insufficient cooling

Burn marks

Air/gas burns

Black/brown burnt marks

Tool lacks venting. Injection speed too high

Colour streaks

Uneven colour

Colour patches

Colour masterbatch not mixed properly

Flash

Excess material

Material sticking on surfaces

Mould over-packed. Gap between mould surfaces

Polymer discolouration Polymer degradation

Excess heat. Dwell time in injection barrel too long.

Water in polymer granules. Excess heat settings. Reduce re-grind.

Sink marks

Sink pockets

Localised depressions on surfaces

Pressure too low. Cooling time too short.

Voids

Air pockets

Empty space within part

Lack of holding pressure. Filling too fast. Mould not fully filled.

Warping

Twisting

Distorted part

Cooling too short.

Splay marks

Silver patches

Moisture in material

Material not dried properly, especially hygroscopic resins

5.4 Injection moulding with polymer composite resins (PCR) with rice hulls When these new materials appeared on the market, injection moulders were cautious in their approach for using these resins but as they got more and more used to it they have realised the advantages of using these materials. With constantly improving material quality of these resins and easier processing technologies, they are now using them with full confidence. Polymer composite resins with rice hulls have opened a whole new frontier based on emerging technology with exciting possibilities.

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Wood fibre blends have already made a name for themselves and have been in use for some years and now PCRs with rice hulls are proving an even better prospect. With growing environmental concerns, rising resin prices, bio-degradable problems and other factors, injection moulders are showing a great interest in these materials. Constant research and development in the manufacturing of these composite resins have significantly improved quality, ease of processing and capability of these materials. In fact, the latest generations of these materials can be efficiently processed on traditional equipment, with minimal adjustments to process settings, with no other physical hardware modification needed. These PCRs can be made with a variety of polymers such as polyethylene, polypropylenes and polystyrenes which will accept rice hulls flour as the filler/reinforcing agent. They can be classified as an emerging family of new materials that can be termed ‘thermoplastic bio-composites’. The fact that they are now available in different grades and properties is a huge advantage for injection moulders. There are many compelling reasons why these composite resins with rice hulls should be used for making products. As they contain at least 50% organic fibres from naturally occurring agri-waste sources they offer injection moulders a ‘green’ factor reduced exposure of injection moulders to fluctuating and rising petroleum prices, reduce energy costs associated with production, while producing products with great properties aesthetically pleasing finishes and highly marketplace-oriented end products for a wide range of applications. To achieve good quality finished products, it is important to use high-quality composite pellets. There are three basic areas vital for selecting these quality pellets as follows: – Moisture content: ideally surface moisture should be less than 1.5%, while the internal pellet moisture content should be less than 1.0%. Increased moisture contents and failure to control the moisture content during processing will result in ‘splay’ (white patches) and excessive brittleness. – Pellet characteristics: Pellets should be clean and relatively consistent in size and shape. There should be no ‘chads’ or ‘streamers’ powdery residues on pellets before usage will indicate the use of non-standard pellet making equipment or poor maintenance on the part of the pellet manufacturer. – Correct grades: one of the benefits of using PCRs with rice hulls is that they can be blended with other pure resins, while maintaining the polymer/rice hulls level. Through blending moulders can achieve different performance characteristics in addition to what is basically offered as: flame retardant, coloured, glossy, extra glossy matt finishes and so on. Thus, moulders have the options of selecting the correct grade or grades as offered by the pellet manufacturers to suit particular end applications.

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5.4.1 Recommended processing guidelines Injection moulding with these resins can follow general moulding techniques but with different operating parameters on standard conventional machines. Finished products when moulded properly, with correct temperature settings, injection speeds and a nonresistance flow path will exhibit minimal stress, smooth surfaces, uniform colour distribution and no evidence of gassing. The two most important principles to remember when moulding with these composite resins is to avoid excessive heat and shear. While some may think that the rice hulls in the composite will act as an inhibitor, tests have shown that actually the reverse is true. For example, rice hullspolypropylene composites flows very quickly at relatively low temperatures and pressures, as a result of which injection moulders can achieve significant energy savings. Added features are shorter cycle times, higher productivity due to reduced filling and cooling times. With reduced polymer content (40%) the dwell time (cooling time) is much less than for virgin materials. Recommended temperature guidelines for injection moulding with polypropylene-rice hulls composite resins are as follows: – Rear zone: 340–370 °F – Front zone: 380–410 °F – Nozzle tip: 390–410 °F Taking these as the basics, moulders will have to adjust these parameters when using different grades to achieve the best results. Moulding pressure will depend on part design as well as the runner system and gate. As a principle, moulding with composite resins will require less temperatures and less pressure than with standard materials. However, moulders should be careful with filling speeds. Because the material will flow quickly, it is important to avoid excessive short fill times as these materials are shear sensitive. If streaking occurs, it can be remedied by simply slowing down the injection rate. Given that lower temperatures are used and polymer content is less, hold times are often lower than for standard materials. The nozzle tip used in processing composite resins should have an orifice as close as possible to the diameter of the sprue to minimise shearing. Smaller orifices may cause increased shearing as well as discolouration caused by overheating of the material as it enters the mould. Injection moulded parts made with composite resins are rather ‘natural’ in colour with a very light brown tone and a uniform grain. However, they can be coloured and high gloss finishes can be easily achieved.

5.5 Injection moulding with polymer resin with eggshell powder This presentation shows the application of eggshell powder as a functional filler for high-density polyethylene (HDPE) composite resins and the method of injection moulding. Particulate mineral fillers such as calcium carbonate, talc and silica have

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been traditionally used as fillers in thermoplastics. Now emerging technologies have made it possible for many non-traditional fillers also to be successfully used. One such filler is eggshell powder with 95% pure calcium carbonate content an ideal filler for thermoplastics. The purpose of adding a filler is to reduce costs by using less polymer resin. These new non-traditional fillers and stiffening agents, although being cheaper than resins will also give much better properties. The ease of processing these new composite resins on standard injection moulding machine without the need for any additional equipment or modifications to existing machines is a big plus. Hen eggshells offer a unique source of renewable mineral fillers. It is available as waste from the food industry and households in substantial quantities and is a calcium carbonate -rich material. According to statistics close to a 10 million tons are widely disposed annually in landfills, of which 96 wt.% were mineral phase of calcium and magnesium. The mineral phase is in phosphate and carbonate form and the other phase is organic matter, including 4 wt.% including carbohydrate and protein. Therefore, the eggshell is an excellent raw material for calcium-based fillers. Eggshell powder has been used as a biofiller for semi-crystalline polymers such as polypropylene (PP), low-density polyethylene (LDPE) and high-density polyethylene (HDPE). This filler helps in improving Young’s Modulus, hardness and heat deflection temperature of the filled polymers.

5.5.1 Recommended procedure Select a HDPE injection moulding grade resin with a melt-flow index of around 2 g/ 10 min and a melting temperature of 136 °C. Wash the eggshells well with normal tap water and dry for 24 hours. Heat them before powdering and allow to cool down at room temperature. Using a ball-mill powder the calcined eggshells (CES) should be ground for about 12 hours or until the desired particle size is achieved. Use a 230 mesh and a 325 mesh sieve which will also remove any foreign material in the powder. Again heat in an oven at about 70 °C to remove any moisture in the powder before mixing with the polymer. Depending on the end application mix 10–40% of the calcined eggshell powder (CESP) in an internal mixer with the addition of small percentages of a lubricant and a compatibiliser and mix thoroughly for about 15 minutes. A standard injection moulding machine can be used with a suitable mould of the part to be moulded, At 40% filling,(CESP:HDPE = 40:60) the recommended moulding parameters are: a melting temperature of 190 °C, a screw speed of 104 rpm, an injection speed of 57–60 mm/sec., a holding pressure of 960–980 kg/sq.cm. and a mould temperature 25–28 °C. Injection moulding procedure is the same as for standard production.

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5.6 Extrusion process in brief Extrusion is a process by which a thoroughly mixed hot melt is forced by the action of a rotating screw or screws, through an orifice or die of pre-determined shape and size This material is called an extrudate. To extrude a thermoplastic or a thermoplastic composite resin, it must first be softened by heat so that it will flow freely to be shaped. Standard extruders will have a single screw or multiple screw and also have three to four heating zones or in special cases, more. The softening process is called ‘plastification’ or ‘thermal softening’ beginning with a feed zone and ending with a metering zone which goes through a set of fine screens contained in a breaker plate through which the hot melt is fed into a die to form an extrudate of different profiles. An extrusion line will have post die downstream equipment beginning with cooling, sizing unit (where necessary), conveyor system, take-up and so on. Since the following presentation is about making polymeric composite lumber, the system should have a vertically moving saw for cutting to desired lengths. Basic parts of an extruder are as follows (Figure 5.2):

SINGLE SCREW EXTRUSION.

gear box & screw bearings

feed hopper

barrel

screw breaker plate heater band

belt drive

d.c. motor

cooling fan

melt pressure transducer

Figure 5.2: A basic polymer extruder (Photo taken from author’s publication: an introduction to plastics extrusion).

5.7 Extrusion of polymeric composite lumber

– – – – – – – – –

81

Barrel Screw/screws Hopper Zonal heaters Motor and drive Control cabinet Cooling systems Extruder head Extruder die

Polymer materials generally in the form of pellets or powders are introduced into the hopper of the extruder and by opening the bottom gate this material will flow into the heated barrel with the slowly rotating screw. Different screw designs and types are used for different materials but universal screws are also available. The designs and lengths are important in order to achieve thorough mixing resulting in an homogenous hot melt. A screw will comprise three zones: the feed zone, compression zone and metering zone and all three combine to produce a well-mixed hot melt for ease of flow through the die. A breaker plate with a screen pack may range zones is important to ensure good mixing and also to prevent material degradation. Extruders are generally classified as 40, 65 and 120 mm with single screw or multiple screws. Screws are identified as: L/D (length to diameter) ratios which may range from 5:1 to 40:1 or other. Single screws between 24:1 and 30:1 are generally ideal for polymer processing. To ensure product quality, the selection of the right screw in relation to the material to be processed is important. Basic screw rotating speeds are generally between 25 and 250 rpm. Most extruders have the option of changing screws for different materials but a universal screw can also be used for simple extrusions. Modern day extrusion systems are far more advanced now and new electro-technologies have made it possible to have ‘closed-loop’ systems where once the desired parameters are set, they will automatically adjust to them during processing These will give much better results than is possible with electro-mechanical open loop operations for temperature, pressure, melt-flow, speeds, measurement and so on, which invariable need checking and adjustments periodically. Some of the products made by extrusion are plastic tubing, water pipes, conduit pipes, electric cables, monofilaments, sheeting, plastic profiles, material compounding, eps insulation boards, plastic pellets, garden hose and many more.

5.7 Extrusion of polymeric composite lumber This discussion is based on extrusion of polymeric composite resins with rice hull flour to manufacture PCR lumber as an ideal substitute for natural wood. This

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filler/reinforcing agent can also be wheat hull flour but rice hulls are preferred due to the higher silica content of 20% against 8% for WH flour. Manufacturers have the option of starting with the ready made composite resins (already presented) or compounding their own polymer/composite batches. These operations can be done separately or on one continuous line from separate raw materials to a finished product. If ready made grades of PCRs are used only one type of finished product can be made, whereas, compounding at site will enable a manufacturer the freedom of formulating to suit different end products. The desired finishes like- gloss, high gloss, matt or wood veneers can be achieved in either case without a problem. Wood chips and wood flour filled polymeric composite resins (WPC) have been popular for some time In order replacing traditionally used virgin polymers. These made great strides due to lesser contents of polymer in a composite resin and the action of wood flour providing the role of filler/reinforcement which resulted in products with much better properties. Initial productions with WPC’s were limited to outdoor decking and other outdoor applications but the advent of PCRs with rice hull flour based on a new family of emerging technology has completely overshadowed the use of WPC resins. This is mainly due to the tremendous all-round improvements of properties, especially, tensile strength, compressive strength, negative water absorption, warp-free, better weatherability and so on plus the advantage of being able to work this lumber with normal standard wood-working tools and techniques. These lumber products have opened out a whole spectrum of end applications as will be shown later. Lower costs and minimal maintenance for outdoor applications are also big advantages. There are a few machinery and equipment manufacturers who specialise in this area of activity and the author mentions here three of them with whom he has had detailed discussions. They are: Cincinnati Milacron (USA), Harden Industries Ltd. (China) and Wuhan Machinery & Equipment Ltd. (China). Please see end of chapter for a list of suppliers for machinery, raw materials and additives. To achieve good final products, the polymer composite mixture for extrusion or the composite resins will need a combination of suitable and compatible additives. When using individual compounding, for extrusion, the process will need efficient control at all stages. These systems will consist of a two-extruder combination in that the first one will be a compounding extruder which will feed the final extrusion system for producing the extrudates.

5.7.1 Raw materials The polymer resin for this presentation will be polypropylene (PP) in the form of granules. A producer may opt for starting with virgin PP or pelletised composite resins on a basis of PP:RH = 40:60. This material should be free of moisture, foreign matter and dust.

5.7 Extrusion of polymeric composite lumber

83

If compounding separately, recommended specifications for the use of rice hull fibres to achieve the best material properties and high production speeds (output rates) are: – Fibre size: 0.11.0 mm ideally 350 µm equal to mesh numbers 35, 40 or 45. Finely ground flour would be best. – Moisture content: < 12% for direct extrusion or < 2% for compounded and pelletised resins. – Other types of fibres can be used with limitations and composite lumber with rice hulls gives the best products. However, when rice hulls are used, specially designed extruder screws are needed due to high abrasion because of the presence of silica in the rice hulls which will shorten the lifespan of a screw. Besides the fibre raw materials, the polymers used as matrices are also significant and important. In general, the most popular and easiest to process composites are based on polyolefin (PP or PE) as matrices for the following reasons: – Higher fibre-filling ratios are possible (≤ 80% natural fibres) – Reduced costs – Final products have a more natural wood-like feel to touch – Recyclability of polyolefin conforms to accepted environmental-friendly regulations.

5.7.2 Coupling agents Coupling agents bond the rice hull fibres to the resin matrix. They boost the flexural strength and stiffness (usually referred to as the modulus of rupture and modulus of elasticity, respectively) which are terms used in the lumber industry. Coupling agents also improve dimensional stability, impact resistance and fibre dispersion, while reducing creep. In structural applications like building construction added strength is important. In outdoor applications such as decking, coupling agents are mainly used to reduce water absorption, where the high content of silica in the rice hulls also greatly helps. Water absorption will result in surface swelling leading to stresses that cause cracking. In the case of WPC’s, a higher percentage of coupling is needed as compared to PCRH to overcome the possible incompatibility between the polar chemistry of wood flour and non-polar resin matrices, especially when they are grades of polyethylene. Chemically modified grafted polyolefin are available. However, newer developments include chemically modified polyolefin that are not made by grafting, long-chain chain chlorinated paraffin and reactive agents suitable for polyvinyl (PVC) composites. Some useful and effective coupling agents are: Polybond3029MP for (HDPE), FusabondMB-226D (PE), MD-353D and Epolene G-2608for polypropylenes.

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5 Processing polymers and composite resins

5.7.3 Lubricants Lubricants facilitate easier mixing at the time of compounding increases throughout and improve the extruded surface finish. Since the composite mixture in this case contains rice hulls flour which is abrasive, the use of a lubricant or a combination of lubricants will enhance a better mixing and also good flow properties for the hot melt. Polymer composites can use standard lubricants such as ethylene bis stearamide, zinc stearate and paraffin waxes. However, there are new alternatives, because metal stearates are known to decouple maleic anhydrous groups of a maleated coupling agent, thus cancelling the effectiveness of the lubricant and the coupling agent. Polymer composites uses nearly as twice as much lubricants as standard plastics. For HDPE composites with a typical filler load of 50%–60% fibre content, the level of lubricant needed would be about 4–5%, whereas, a similar composite with polypropylene (PP) will need only 1–2%. Some of the common lubricants in use are: TPW 104, TPW 113, EBS (AcrawaxC) and Glycolube WP-2200.eat Stabilisers

5.7.4 Heat stabilisers Polymers are a versatile family of materials but with an inherent Achilles heel. Heat is essential to soften a polymer before shaping can take place but excess heat will tend to degrade it. Thermoplastic polymers or plastics can easily be recycled and used again but there is a limit to the number of recycling as the plastic degrades a little at a time and a slight brownish colour indicates degradation. Polymers have to go through two phases of heat challenges. The first is when it is being softened to form a hot melt and then after a finished product has been made, exposure to weather conditions. This is specially so for polymeric composite lumber when used in outdoor applications like decking, railway sleepers, fencing or other. Here, the use of heat stabilisers, UV stabilisers and antioxidants should be considered to counter degradation due to oxidation, atmospheric heat and UV (ultraviolet) rays. Earlier, lead stabilisers in combination with others were used but now newer stabilisers are available like zinc-calcium stabilisers and many others moving away from the use of lead.

5.7.5 Foaming agents Most composites filled with biomass tend to be heavy and there is keen interest in chemical foaming of extruded composites to reduce weight and materials. In this particular case under discussion, both heavy and lighter products are needed. For example, applications like decking, fencing, railway sleepers and so on being heavy is

5.7 Extrusion of polymeric composite lumber

85

better but for applications like automobile parts, indoor ceilings, facades and so on as lighter materials are needed. Foaming is more difficult for crystalline polymers such as PE and for PP than for amorphous polymers such PVC and PS because the latter have better melt strengths. As a general rule, the higher the filler/reinforcing content in a composite, the more difficult it is for foaming on the basis of lesser content of polymer. Clariant brand additives offer a range of CFA (foaming agent), which includes endothermic, exothermic and endo-exothermic blends for most fibre blends, which are ideal for composites with 106 Basic raw materials – Polyol – general purpose – Graft Polyol – cheaper polyol as a filler – TDI – standard isocyanate – Combination of NTFSA fillers – (fine powder form) – Surfactant – Amine catalyst – Tin catalyst – Colorants – optional – Water To make a foam block size 80 inches (203 cm) × 60 inches (152 cm) × 40 inches (102 cm) M = V × D = 203 × 152 × 102 = 111 cu.ft. = 3.14 cu.m × 32 kg/cu.m = 100 kg + 1% =101 kg. Table 6.3 shows a typical formula and weight proportions:

Table 6.3: A guideline formula as compiled by the author. Component

PBW

Proportions

Weight (kg)

Polyol

.

 × . 

.

Graft Polyol

.

 ×  .

.

TDI

.

 × .

.

.

 × .

.

Water

.

 × .

.

Surfactant

.

. × .

.

Amine catalyst

.

. × .

.

Tin catalyst

.

. × .

.

Filler

Total

.

. kg

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6 Formulating with non-traditional fillers and stiffening agents

6.10 Processing method in brief The mould is brought under the bottom opening valve of the large mixing vessel, into which both polyols are put in, and mixed for a few seconds. Colour, if any, is added and mixed for 20 seconds. The filler is then added slowly into this mix and mixed slowly at first, and the speed increased until all the filler has been dissolved fully. During this period, nucleation may be an option, which will help to lessen the thick viscosity of the slurry being formed. Total mixing time may be around 120 seconds, and then add all other components, and mix for another 30 seconds. The TDI is then added and within a few seconds, the whole mix is quickly let into the mould by opening the bottom valve of the mixing vessel. The mixing vessel is then raised above the mould. Creaming time and rise time will be slightly longer than for standard mixtures. After a short time, the foam block can be de-moulded and allowed to cool down and cure fully in a separate area. Due to the high filler content, certain changes in physical properties as compared to conventional foams will take place, which are as follows: – Elongation at tear strength reduced by 20–25% – Tear strength reduced by 5–8% – Increase in compression strength increase by 300%

6.11 Manufacture of composite polymeric bamboo floor tiles Bamboo material as fibres or powders have been found to have excellent properties like compatibility, hardness, highly wear-resistant, good weathering and thus ideal for use as a reinforcing agent in composites. Although, one of the major applications of bamboo fibres could be replacing glass fibre in boat building, surf boards and others, another very interesting and practical application is the use of it to make floor tiles. Some manufacturers of bamboo floor tiles may want to use only bamboo fibres but this is a tedious job as they have to be glued together using adhesives, which may contain chemicals that are not good for the environment. The better and more economical way is using it as a fine powder. Bamboo has to be ‘processed’ before arriving at the form that is required. Firstly, the bamboo has to be steamed to soften it up and then made into strips. From here, either fibres or fine powder can be obtained. The process presented here is making composite floor tiles with polymer matrix, and bamboo powder as the reinforcing agent plus suitable additives. Description Eco-friendly polymer/bamboo floor tiles – natural wood-like quality – looks like and feels like natural wood durable and firm – high density – high degree of UV stability – easy to install – barefoot friendly – anti-slip – no cracking high weather

6.12 Processing method in brief

113

resistance – can be made in aesthetically pleasing colours – reddish brown, grey, black, dark brown and finishes-like wood grain, high gloss and matt finish. The surfaces can be smooth or grooved. Specifications – Nominal size: 300 mm × 300 mm × 25 mm – Density: high density (for load bearing)(density can be lowered by adding small quantity of blowing agent) Raw materials – Polymer matrix: High density polyethylene (HDPE) or grade A recycled HDPE; – Reinforcing agent: Bamboo powder; – Additives: A suitable combination from among anti-UV agents, antioxidants, stabilisers, anti-fungal agents, coupling agents, lubricating agents, melt flow agents and colorants; – Final top clear surface coating of aluminium oxide to enhance wear. Example – To make a batch of 1,000 tiles with a density of 400 kg/cu.m M = V × D = 300 mm × 300 mm × 25 mm × 1,000 × 400 cu.m = 900 kg + 3% waste factor = 927 kg. Using this as a guideline, smaller batches may be worked out convenient to production. Note: There are plenty of suppliers of bamboo powder, especially in the east, who will supply these powders to customer requirements. Table 6.4 shows the formula Guidelines and raw material proportions. Table 6.4: Modified formula by the author. Component

pbw

Proportion

Weight (kg)

HDPE

.

/ × 

.

Bamboo powder

.

/ × 

.

Additives

.

/ × 

.

Total.

.

. kg

6.12 Processing method in brief Here, there are two options available. These floor tiles can be produced by either a compression moulding process using multi-cavity or an extrusion process (faster production volumes). Whatever process is preferred, it is recommended that a twostep process is used, where the polymer (HDPE), bamboo as a fine powder and the

114

6 Formulating with non-traditional fillers and stiffening agents

additives are first thoroughly mixed in an extruder and pelletised and stored in a silo. At this stage, colorants can be added, if desired. Step two will see these readymade pellets either compression moulded or extruded. In the case of the latter, preferably a twin-screw extruder will make a hot melt which is then extruded through a suitable T-die to meet cross-sectional and dimensions required, and the extrudate can be cooled and cut to desired sizes. If a grooved surface or other is required on the tiles, the T-die must have provision for it on the die design. If particular finishes are desired, it is best to do so with additional online equipment, just after drying, and before cutting, rather than trying to do this on individual tiles after cutting.

6.13 Manufacture of PVC artificial leather using NTFSAs Artificial leather is generally made by two methods – direct coating, where a polymer substrate is applied directly and PUR substrate is applied indirectly using a pre-embossed release paper, and then a foamable coat onto which a flexible knitted fabric is laminated. Since the main object is to show the use of NTFSAs in the manufacture of artificial leather, and the manufacture of artificial leather is a vast subject, it is sufficient to discuss only the direct coating method. Direct-coated artificial leather will produce ‘solid’ plastic coatings but very flexible and can be produced in aesthetically pleasing colours and embossed finishes, which include high-gloss and matt surfaces. PUR-coated cloths will be more flexible and naturally foamed PUR-coated cloths will be softer and have a much better texture and are generally used for high-end applications. PVC plastisols are made by a basic polymer, plus a filler polymer (optional), plasticisers, fillers, stabilisers, coating machine with a ‘doctor-knife’ coating station, a long heat-curing oven, an embossing station and take-up of finished cloth. Basic raw materials – PVC polymer in powder form; – Filler polymer in powder form; – Plasticisers – DOP, DIOP; – Fillers- NTFSAs – 1 (egg shell powder); – Thickening agent-NTFSA – 2 (rice hulls/wheat hulls fine powder); – Additives – lubricants, stabilisers; – Colorants – cadmium pigments; – Woven cotton cloth width from 54 to 108 inches (approx. 137–275 cm); The functions of each component is the two polymers will form the PVC base, while the plasticiser will help to mix all components together into a homogenous soft and

6.14 Processing method in brief

115

fluid mass suitable for a coating process. Lubricants will help to create fluidity, while stabilisers will be needed as the coated cloth will be heat-cured. The pigments will colour the PVC mass as desired. Since the woven cloth will be porous, and the substrate will penetrate, two different batches will have to be prepared. The first called the ‘base coat’ will have a ‘thickening agent’ – in this case walnut shell powder – to prevent plastisol penetration, and the second will be standard. Basic formulae Component

pbw

Base coat (kg)

Standard coat (kg)

PVC base

.

.

.

Filler polymer

.

,

–

Plasticiser

.

.

.

NTFSA filler 

.

.

.

NTFSA filler 

.

.

–

Additives

.

.

.

Colorants

.

.

.

.

.

Blowing agent Total

6.14 Processing method in brief A stock batch containing NTFSA-1 (filler), colorants and a little of the plasticiser (wetting) is mixed thoroughly on a three-roll-mill and made into a paste and kept aside. These are generally done in bulk batches, rather than making them per run. This means that a manufacturer will make batches of different colours from which the required quantity can be drawn. The base coat components like polymers, plasticiser is now introduced into a mixer with a large mixing vessel and mixed thoroughly for about 60 seconds. The NTFSA-2 (thickening agent) is then put into this mix and mixed for another 60 seconds. The additives in the form of lubricants, stabilisers or others are then introduced into the mix and mixed for 120 seconds. A correct batch weight is taken from the previously made stock (containing filler and colorants), and put into the main polymer mix and mixed again for 60 seconds. During this time, air bubbles will form in the liquid mix, and if in excess, a de-aeriation process maybe required. This final homogenous liquid plastisol will be used to apply a base coat.

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6 Formulating with non-traditional fillers and stiffening agents

The plastisol for the second and final coat will be made on the same lines but without the NTFSA-2. The base cloth roll (coloured cloth will give better aesthetic finish) is now mounted on the feed end of a coating machine, threaded through the ‘doctor knife’ station, through the heating/curing oven and then threaded to a winding/take-up unit. The machine is started, and as the cloth moves forward slowly, the base plastisol is coated on to the cloth, the pre-set ‘doctor knife’ gap deciding the thickness of the coating. The presence of the thickening agent will prevent the liquid polymer plastisol seeping through the cloth. Common heating elements are: sheathed infrared with adjustable temperatures. The base coat is semi-cured and goes through at a reasonably fast speed and wound up. This is re-wound back and depending on the final thickness of the finished cloth, coats two and three are applied at very slow speeds through the oven which is set at around 200 °C (392 °F). As the cloth emerges at the other end after the final coating, an embossing roller with desired pattern/finish is lowered to sit lightly on the hot PVC surface, and the finish could be of great coated cloth which is wound up. The next chapter will deal with manufactures of speciality products and processes based on polymeric activity, which should have a positive impact on producers as well as consumers. These should be of great interest to many as they are based on emerging technologies and will demonstrate the vast possibilities of using non-traditional fillers and stiffening agents to produce innovative products successfully with the added advantages of cost reduction and also easing environment concerns.

Bibliography [1] [2] [3] [4]

Woodard Chris. article on Bioplastics, and biodegradable plastics- updated July 2015. Article: Functional Fillers, and Speciality Minerals for Plastics-www.Phantomplastics. com/functional-fillers: 16/2/2017. Defonseka Chris. (2013) Book “Practical Guide to Flexible Polyurethane Foams” Smithers Rapra U.K. Defonseka Chris. (2014) Book “Introduction to Polymeric Composites with Rice Hulls” Smithers Rapra U.K.

7 Manufacturing special polymeric products with non-traditional fillers and stiffening agents 7.1 Introductory presentation The use of NTFSAs with polymers can be broadly categorised as: (a) manufacture of composite resins, (b) manufacture of plastics products with these composite resins, and (c) use of them in speciality processes. By now, a reader would have a good knowledge of the vast possibilities of using NTFSAs in combination with polymers. As the plastics industry goes forward, with new developments based on research and development, there is no doubt that newer NTFSAs will be added to the list presented in this book. The three main functions of these NTFSAs are as: reinforcing agents, fillers and stiffening agents in current polymeric activity. According to reports, the real impetus in this area comes from the eastern manufacturers of plastic products, who is not afraid to experiment and try newer NTFSAs in final products. Among the present NTFSAs, wood chips, wood flour, rice hulls, both, fibre, and powder, bamboo fibres, graphene and calcium carbonate from egg shells seems to hold sway. Especially in China, small-to-medium companies have sprung who offer a wide range of non-traditional fillers and stiffening agents in various forms, including made-to order fillers as per customer specifications. Some of the companies in Pakistan, India and some others also offer these in usable forms and in large volumes. The companies in the west and Europe offer more scientific approaches when using these fillers and stiffening agents as they have more advanced and sophisticated engineering and scientific systems. They also have an offer, well-advanced training and product development centres, where polymer products processors can use to design, experiment and develop any production methods in relation to polymeric activity. Due to increasing global environment concerns, the petro-based industries, especially the plastics industry, have been gradually phasing out/reducing the use of petro-based chemicals. Some other concerns like health hazards, plastics wastes in landfills, cost-effectiveness, and so on have prompted the need for remedial solutions, and diligent research are coming up with rewarding answers. For example, most countries have by now banned the use of asbestos fibre due to its proven health hazard (causes cancer) which has/is affecting a definite need in asbestos/ cement roofing sheets in the building sector. Some others are: uncontrollable generation of plastics wastes, the deforestation of our much needed trees for construction/ wood chips to make (WPCs), the large volumes of fly ash generation due to the use of coal and other fuels, the need for cheaper but better materials for construction as an alternative for using natural wood, and alternatives for fillers, dug/refined from under the earth, and also made from hazardous petro-chemicals, and so on. Since, products https://doi.org/10.1515/9783110669992-007

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7 Manufacturing special polymeric products

made from these hitherto acceptable raw materials have been banned or will be banned in the near future, it is imperative that suitable alternatives/solutions will be required. To demonstrate the above categories, the following manufactures are presented in detail, including raw materials, formulations, production methods and properties of final products. Although these manufactures are based on current production information, the author with his long, hands-on experience in industry, and using innovation will present modified formulae/processing methods with NTFSAs for better performance. The following manufactures have been selected for presentation: 1. Manufacture of fibre/cement roofing sheets as an alternative to asbestos/cement sheets 2. Manufacture of composite bricks with fly ash 3. Road paving with plastics wastes and NTFSAs 4. Manufacture polymer composite door panels with rice hulls 5. Manufacture of compression moulded parts – thermoset polymer/NTFSA

7.2 Manufacture of fibre/cement corrugated roofing sheets Until a few years ago, asbestos/cement corrugated roofing sheets were considered a high-end roofing product for houses, buildings and industrial products. However, ever since it was discovered that these fibres contained a serious health hazard, most countries initiated regulations to phase out its use and finally ending in a complete ban. Asbestos is a naturally occurring mineral that was widely accepted for its versatility, tensile strength and insulating properties. It is an ideal material for making speciality products like-fire-proof vests, industrial gloves and make many things better, except it is highly toxic, mostly when in loose fibre form, and today research has revealed that asbestos fibre causes mesothelioma cancer. This has led to more than 50 countries banning its use and others are following. Strangely however, there is no ban for it in the USA, and in some parts of India, large volumes of asbestos/ cement corrugated sheets are being made for roofing. Their argument being that they use only chrysolite (white asbestos fibre) which are less hazardous. There are six types of asbestos: chrysolite, amosite, crocidolite, tremolite, anthophyllites and actinolite. Although, all of these grades are carcinogenic, there are differences in their chemical compositions. In general terms, homes and apartments built earlier often are filled with asbestos, needing only normal wear, and tear with age to dislodge these fibres and make them airborne. Asbestos can be found in roofing, floor tiles, furnace claddings, plumbing, appliances, fireplaces, window caulking, industrial gloves and so on, with great possibilities of exposure in everyday life. Since asbestos have to be mined from the ground, miners and illnesses related

7.2 Manufacture of fibre/cement corrugated roofing sheets

119

to asbestos can be traced to occupational exposures also and beyond when they take these tiny fibres home on their clothes. Therefore, finding adequate alternatives is paramount and fibre/cement corrugated roofing sheets is an ideal solution for those application. With the availability and versatile capabilities of using NTFSAs, better and cheaper corrugated roofing sheets can be made.

Figure 7.1: Roofing sheets with Polymer Composites/Cement. Images of finished corrugated fibre/cement corrugated roofing sheets.

There are a few companies in the west as well as in the east, e.g., who make fibre/ cement roofing sheets as an alternative to asbestos/cement sheets. They are basically available as corrugated sheets or plain sheets of standard industrial sizes, and generally grey in colour but also available in different colours for special applications. In the west, these sheets are made to meet British, American and European industrial standards. Some special features are: – Highly cost-effective weatherproofing – An environmental-friendly asbestos-free product – A unique fibre reinforced cement sheet – Virtually maintenance free – High resistance to chemical attack, rust, rot and corrosion – Non-toxic (fibres used are not toxic) – Available in painted colours – Longevity usage exceeds 25 years

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7 Manufacturing special polymeric products

Research on these manufactures reveals that these roofing alternatives are generally made with a mixture of fibre, cement and a coupling agent plus a hardening agent where necessary. One manufacturer uses strips of polypropylene polymer as stiffening agents but this practice is not necessary if rice hulls fibre (high silica content: 20%), rice hulls ash (silica content: 70% +), fly ash or short bamboo fibre are used, which will automatically provide the function of stiffening. This practice will reduce overall costs as well as being eco-friendly. There are a few important basics to be considered when manufacturing these fibre/cement sheets. A good understanding of the concept, based on achieving the desired end properties will go a long way in producing good products. Some of the important ones are: – Countries/locations – weathering due to extremely cold/extremely hot – Dimensions of standard sheet- length × width × thickness – Density – lightweight/heavyweight/industrial/installed weight – Warping/fracturing/brittleness – Impact resistance/compression strength/breaking strength – Fire hazard/thermal conductivity/thermal transference – Moisture absorption/water absorption/condensation (under) – Effects of chemicals/fungal or microbial activity – Fading of colour/loss of defence surface coat – Durability/life span/maintenance When made in accordance to international standards like BS, DIN, ASTM, SLS, JIS, CE and others, the relative minimum requirements for each category will be specified, and a manufacturer will do well to formulate accordingly and have their products certified for international acceptance. Raw materials – Portland cement – Water – Fibres – long fibre rice hulls, rice hulls ash, short bamboo fibre, paper pulp – (reinforcing) – Quartz sand – binder – Polypropylene powder – for flexibility/stability – Colour (optional) – Defence coat (protective) – as needed Since the main objective of this exercise is to present a suitable alternative for asbestos/cement-corrugated roofing sheets, a detailed manufacturing process will not be discussed but some formulations are given below – refer Table 7.1 to demonstrate how to use the NTFSAs in fibre/cement roofing combinations:

7.4 Manufacture of composite bricks with fly ash

121

Table 7.1: Different combinations for producing fibre/cement sheets as compiled by the author. Component

Form

Formulation 

Formulation 

Formulation 

Cement

Std. Portland

.%

.%

.%

Water

Normal

As needed

As needed

As needed

Rice hulls

Fibre

.%

.%

–

Rice hulls ash

Fine powder

.%

.%

.%

Bamboo fibre

Strands

.%

–

–

Paper pulp

Paper slurry

–

.%

–

Quartz sand

Std. grades

.%

.%

.%

Polypropylene

powder

.%

.%

.%

Note: Use them as guidelines and adjust to meet international standards as desired.

7.3 Processing method The method used is a mixing/calendaring process in a continuous line. The water, sand and cement are mixed to form a slurry and the excess water is drained off. All other components are then put in and mixed thoroughly in a high-load mixer until a smooth paste is reached. If, more than one filler/reinforcing agent is used in combination, it will be necessary to add small quantities of additives to aid in processing. This well-mixed slurry paste is then fed on to a slow-moving conveyer, which runs through two calendaring rollers, where the gap between them can be adjusted. This gap is pre-set and determines the thickness of the final sheet. This slow-moving substrate goes through a hot steam-tunnel for curing and through a corrugating machine and then cut to desired lengths. If coloured roofing sheets are desired, some manufacturers will have an online painting station or some may opt for post-production colour spraying, where one batch can be coloured in different colours. Before this process, sometimes a very light ‘surface sanding’ may be necessary to remove any ‘fines’ (small portions of fibres sticking out). This same process applies for manufacturers who wish to give a defence/protective surface coating, which will help in enhancing weathering.

7.4 Manufacture of composite bricks with fly ash The main source of fly ash generation is from coal, where pulverised coal is used as fuel for thermal power stations. This results in a by-product known as fly ash, which is made up of two types: ash residue collecting at the base of a combustion chamber

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(bottom ash) and also the very light ‘flue ash’ going up a chimney, and collected separately. Both types have considerable pozzolonic activity but will differ in particle size. This versatile resource is being gainfully utilised especially in India for the manufacture of ash-lime bricks and 100% fly ash bricks in Australia, among other countries leading to conservation of natural resources and making a positive contribution towards environment quality. For the benefit of the readers, both manufactures are presented as suitable for use as per their country’s acceptable standards, and one may want to modify the formulations slightly to suit, e.g., North American or European standards. Pulverised fuel fly ash-lime bricks are made from fly ash, lime and an accelerator acting as a catalyst. These fly ash-lime bricks are generally manufactured by blending/mixing the raw materials, then moulded into desired shapes and sizes, and cured using heat and pressure. Sand and rice hulls ash are also materials that can be added to these bricks to make them better. While the sand will give added strength to a brick, the rice hulls will provide a moisture barrier for the final product due to its high silica content. The fly ash will react with the lime in the presence of moisture to form calcium hydrate, which is a good binder. These bricks are suitable for use in masonry work, just like common burnt clay bricks, and will have equally good properties, if not better, than the common burnt clay bricks. It should be mentioned here that fly ash can also be mixed into cement mortar for large size cement bricks, which gives it additional strength and also moisture barriers. The characteristics of fly ash will probably vary from location to location, country to country, and the following data are presented based on Indian locally available fly ash. Physical properties – Specific gravity: 2.54–2.65 g/cc – Bulk density: 1.12 g/cc – Fineness: 350–450 M2/kg Chemical properties Silica 35–59% Alumina 23–33% Calcium oxide 10–16% Sulphur 0.5–1.5% Iron 0.5–2.0% Loss on ignition 12 % Basic raw materials – Fly ash as above. – Gypsum – hydrated calcium sulphate are called gypsum. Minimum purity 35%. – Lime – quick lime or hydrated lime or both can be mixed in the composition. Lime should have a minimum content of 40% calcium oxide. – Sand – river sand can be used but should be clean, and coarse.

7.6 Manufacture of bricks with 100% fly ash

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In India, one advantage in these manufactures is that all these raw materials are readily available in abundance and ready-to-use form from local manufacturers or traders.

7.5 Manufacturing process in brief There are many different types of processing in India, although, the basic raw materials will remain the same. The process described here is a common process being carried out in Chennai (India). Fly ash (70%), lime (10%), gypsum (5%) and sand (15%) are weighed separately, and fed into mixer, where water is added as required for homogenous mixing. The proportions of the raw materials may be varied according to the quality of each component, and also to meet whatever standards the bricks are being made to. The whole batch is mixed thoroughly until a homogenous mass is reached and then fed on to a slowly moving conveyor, feeding this mixture to a brick-making machine, where the bricks (as per pre-set sizes, and shapes) are pressed. Rectangular and conventional sizes are the common productions in keeping the needs of the local building trades. These bricks are then cured in an oven and placed on pallets for a short-period water treatment, which gives them additional strength. In remote rural areas, where all operations are carried out manually, the moulded bricks are put on pallets, kept for 2 days or so and then water-treated before despatch. Advantages of fly ash bricks – High compression strength – Lower water absorption – Dimensional accuracy through uniform shape – High strength-to-weight ratio – Zero efflorescence (whitish patches due to migration from inside) – Consume less mortar in construction – Eco-brick – Solution to coal fuel residue disposal

7.6 Manufacture of bricks with 100% fly ash As the global demand for electrical energy increases, the use of coal as fuel used for steam-powered electrical energy will continue to generate large volumes of fly ash as residues. For a long time, the world utilisation of this material has been minimal, and most of it probably ended up in landfills, contributing environmental pollution. However, the use of fly ash in the manufacture of Portland cement, construction of

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bricks, and so on has eased up this problem, and probably the biggest converter of fly ash is India. Technology from Australia reports that high-performance bricks from 100% fly ash have been made there. The main components are: fly ash (100%), water and a small quantity of an additive. The manufacturing process uses techniques and equipment similar to those used in clay brick factories. These bricks are 28% lighter than standard clay bricks but have compressive strengths higher than 40 MPa, which exceeds some of the best of the load carrying clay bricks by 25%, and could be classed as better than most commercially available clay bricks. Another added advantage is that although the initial formed fly ash brick is grey in colour, after oven curing at high temperatures 1000–1300 °C (1832 °F–2372 °F), it turns a reddish colour similar to clay bricks. Table 7.2 shows some basic processing details.

Table 7.2: Values on an average basis as compiled by the author. Data

Common clay bricks

% FA bricks

Raw material needed per , bricks

– tonnes

. tonnes fly ash

Wastage per , bricks

. tonnes approx.

None

Additives

None

.–. L

Stage  drying

 days

 days

Curing temperature

– °C (– °F)

– °C (– °F)

Firing duration

– days

– h

The properties of bricks play a key role in the final use of it in building construction. When compared to common clay bricks, the fly ash bricks show some interesting property improvements. Table 7.3 shows some of them. When compared to common standard clay bricks, the above shows the tensile strength expressed in the form of the modulus of rupture value nearly three times the value for normal clay bricks. This is important as it shows that fly ash bricks are less prone for cracking. Such cracking caused by differential settlement, excessive loading or salt crystal growth emerging to the surface, has been the major concerns in the building industry. The compressive strength which is about 23% better than clay bricks is also significant in that they can carry bigger loads than allowed for clay bricks and can therefore allow for higher heights. Due to these 100% fly-ash bricks being 28% lighter than clay bricks, significant cost savings can be achieved in building construction. Another advantage is that the clay has to be dug out from the earth and then ‘prepared’ before use, whereas fly ash is more or less readily available.

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Table 7.3: Some basic properties of fly ash bricks as compiled by author. Brick type

Compressive strength

Modulus of rupture

Initial rate of absorption (IRA)

Absorption capacity

Clay bricks

– MPa – MPa (– psi) (– psi)

Range: .–. kg/sq.m/min.

% fly ash bricks

– MPa .–. MPa

.–. kg/sq.m/min.

–%

Average density

– kg/cu.m (– lbs./cu.ft.)

% – kg/cu.m

Av. for best clay bricks

. MPa

. MPa

.–. kg/sq.m/min

–%

 kg/cu.m

Acceptable

 MPa ( psi)

. MPa ( psi)

–

–

 kg/cu.m (min)

Two important properties of building bricks are the initial rate of absorption (IRA) and the absorption capacity. The IRA is of great importance when laying bricks and bonding with mortar. The property of total absorption is also very important for the performance of the bricks. According to the results obtained for the 100% fly ash bricks, indications are excellent performance in laying, bonding and durability.

7.7 Road paving with bitumen, plastic wastes and NTFSAs A few years ago, a town in India was experiencing great difficulties in getting rid of huge volumes of plastics wastes from post-consumer use. The volumes became excessive, and these wastes began to be littered everywhere. The authorities, without any knowledge of chemistry or plastics, hit upon a brilliant idea. Watching the local roads being paved with bitumen, which was being heated to a very temperature before use, they got the idea of mixing these plastics wastes with the bitumen. Knowing that plastics products were made by high heat, this idea seemed reasonable. Initial trials done were hopeful, and with the help of government officials tests carried out, confirmed that the roads paved with bitumen/plastic wastes were far superior, and stood up to weathering much better. As the Indian government approved this method on a national basis and the success was seen by the world community, this method is spreading fast, and places like Vancouver, Rotterdam, Bhutan and many others are already into it. Plastics, a versatile material, having replaced many traditional ones, readily available in many forms, and aesthetically pleasing wide spectrum of colours, qualities and cost-effective too, may be termed as a ‘friend’ to all peoples. This discussion primarily

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refers to consumer products like bags, films, boxes, containers, soft, and hard foams, plates, dishes and so on used by people in daily life. They will be in different colours, shapes, sizes, densities and made from different polymers like: polyethylene, polystyrene, polypropylene, polycarbonate, polyurethanes and among others. Polyvinyl chloride (PVC) is preferably avoided due to hazardous gas. Plastics in general are non-biodegradable, although attempts are being made to include additives for biodegradation. They have very long lifetimes, and putting them into landfills will create land pollution, while the burning of these wastes will lead to serious air pollution. Thus, road paving with a combination of re-cycled plastics wastes and bitumen is a second life application for plastic wastes but temperatures used must be well below the average thermal degradation point. Polymer-modified bitumen is emerging as one of the important construction factors for flexible, durable and cost-effective ways of making paved roads, and also flexible pavements. From its humble beginnings, where about 20% of plastics wastes were directly mixed with 80% heated bitumen for road paving, and the results were found to be amazing – better surfaces and durability than traditional paving, now continuing research is showing ways how to use higher percentages of plastics wastes. An alternate method to use higher percentage of plastics wastes in road paving is by using plastic-coated aggregate (PCA), which is basically the aggregates to be used are coated with the plastics, instead of adding directly to the hot bitumen and blended. The use of NTFSAs in the process of current practices will give better results in enhanced properties and cost savings as explained by the author.

7.7.1 Raw materials The raw materials discussed here are based on current practices on road paving in various places and may vary according to local needs and standards. However, the basic materials are presented, including suitable NTFSAs and basic guideline formulations, explaining the property/function of each component and the overall benefits of the finished processes. 7.7.1.1 Bitumen Bitumen (also known as asphaltum or tar) is a black, oily, viscous material that is petroleum-based, a naturally occurring organic by-product of decomposed organic materials. Bitumen is the thickest form of petroleum, and it is made up of approximately 83% carbon, 10% hydrogen and lesser amounts of nitrogen, sulphur and other elements. It is a natural polymer of low molecular weight. At lower temperatures, it is rigid and brittle, at room temperature it is flexible, and at high temperatures, it flows.

7.7 Road paving with bitumen, plastic wastes and NTFSAs

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Bitumen deposits occur naturally throughout the world but vary widely in chemical composition, and consistency. Bitumen is used for a number of applications such as sealants, adhesives and building mortar. One of the main uses even from ancient times was as a waterproofing material for canoes, boats and light crafts for transport. In current modern times, one of the main uses is for road paving. The method of processing bitumen is nearly universal. Heating the material until the substance condenses the gases within and liquefies, and then adding tempers to tweak the consistency. Minerals such as ochre make it thicker. Grasses and other vegetable matter add stability, while waxy/oily elements such as pine resin or beeswax will make it more viscous. At higher–lower temperatures, it is rigid and brittle, at room temperature it is flexible. 7.7.1.2 Plastics Polymers are substances whose molecules have high molar masses and are composed of a large number of repeating units. There are both naturally occurring, and synthetic polymers. Among naturally occurring polymers are: proteins, starches, cellulose and latex. Synthetic polymers are produced on a very large scale and have a wide variety of properties and uses. Materials known as plastics are all synthetic polymers. Plastic polymers are classified as thermoplastic (softens on heating, and can be reused) and thermosets (hardens on heating, and cannot be reused). This discussion is confined to plastic wastes which are compatible for mixing among themselves, and with bitumen, whether they are thermoforming or thermosets. On a broad base, plastic wastes can be generated from a factory floor, moulding processes, post-moulding rejects and post-consumer wastes. While most plastics wastes can be used in a bitumen mixture, to obtain a smooth homogenous mix, the ideal plastics should have similar or close melting points to each other, and way below their degradation point, which are generally very high. Polyethylene is perhaps the simplest polymer, composed of repeating basic units. It is produced by addition polymerisation of ethylene. The properties of polyethylene depend on the manner in which ethylene is polymerised. When catalysed by organometallic compounds at moderate pressure (15 to 30 atm), the product becomes high-density polyethylene (HDPE). Under these circumstances, the polymer chains grow to very great lengths and molar masses average many hundred thousands. HDPE is hard tough, and resilient. When ethylene is polymerised at high pressure (1000–2000 atm) at elevated temperatures, and catalysed by peroxides, the resulting product is low-density polyethylene (LDPE). LDPE is relatively soft and most of them are used in the production of plastic films. These are the two basic polyethylenes used for a wide variety of plastics products, while some other different grades are also available.

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Polypropylene is produced by the addition polymerisation of propylene. Its molecular structure is similar to that of polyethylene but has a methyl group on alternate carbon atoms of the chain. Polypropylene (PP) is slightly more brittle than polyethylene but softens at temperatures about 40 °C higher. PP is widely used in consumer goods, auto industry, food packaging and its fibres are used in clothing, home furnishing and carpeting. Being one of the important members of the polyolefin family, polypropylene can be processed into many products, and its special properties of toughness, flexibility, lightweight and heat resistance is very useful for plastics processors. Polystyrene is obtained by reacting ethylene with benzene in the presence of aluminium chloride to yield ethylbenzene. The benzene group in this compound is then dehydrogenated to yield phenylethylene or styrene, a clear liquid hydrocarbon. Styrene is polymerised by using free-radical initiators, mainly in bulk, and suspension processes, although solution, and emulsion methods can also be employed. Polystyrene, a hard, stiff brilliantly transparent synthetic resin widely used in the food service industry as rigid trays, containers, disposable packaging and eating utensils, display trays and among many other applications. One of the biggest applications is expandable polystyrene (EPS), which contains a tiny amount of inert gas in each granule, which when heated expands up to 40 to 50 times its original volume, and widely used as lightweight packaging and excellent insulation material for buildings. Polystyrene is also copolymerised with other polymers, lending hardness and rigidity to a number of important plastics and rubber products. Polyurethane is important class of polymers that is formed by the addition polymerisation of an di-isocyanate (whose molecules contain two-NCO groups) and a dialcohol (two-OH groups). Unlike other polymers, polyurethanes do not have a basic monomer as such but they are created by the exothermic (heating giving) reaction between a polyol, and an isocyanate, and the presence of a blowing agent which produces carbon dioxide producing the polyurethane monomer. Polyurethanes are available in many forms such as: flexible, semi-rigid, hard foams, filled foamed, high resilience foams, viscoelastic (memory foam), recycled foams and so on.

7.8 Processing method in brief Different methods may be applied in road paving from location to location and country to country. The basic common components for most processes are: bitumen, aggregates and plastics wastes. The author recommends the use of rice hulls ash and fly ash (NTFSAs), which are highly compatible with these standard mixtures and also provide better durability, lesser wear and tear, better moisture barriers in addition to further cost reduction.

7.9 Manufacture of polymer composite door panels with rice hulls

129

Although the plastics waste will be made up of different products, and also different polymers and colours, it is not necessary to sort them out. However, any foreign matter like wire, stones or others have to be removed before being fed into a shredding machine. Moisture content also should be very low. It is not necessary for the shredded material to contain small pieces but should be reasonably so to facilitate easy mixing and melting. The aggregate mix is then heated to 160–170 °C and transferred to a large mixing chamber, where the shredded plastics waste is added and mixed, giving the aggregates a smooth thin coating. The bitumen, rice hulls ash and the fly ash are then added, and the whole mix is heated to 160 °C (320 °F), and mixed thoroughly. The resulting mix can then be used for road construction. The volume/weight of a batch to be prepared will naturally depend on the length and thickness of the layers to be done. The average road laying temperature could be about 110–120 °C (230–248 °F), and a roller with an eight-ton capacity are used by some. Table 7.4 shows basic formulations that can be used as guidelines.

Table 7.4: Formulation guidelines as compiled by the author. Component

Standard

Modified 

Modified 

Bitumen

%

%

%

Aggregate

As needed

As needed

As needed

Plastic wastes

%

%

%

Rice hull ash

–

%

%

Fly ash

–

%

%

While the presence of plastics will give a smooth surface, flexibility and also act as a moisture barrier, the fly ash will give better strength, the rice hulls ash will act as a filler, and more important a superior moisture barrier due to the high content of silica present.

7.9 Manufacture of polymer composite door panels with rice hulls Sometimes ago when wood polymer composites (WPCs) came on to the market, it created a special type of market. At the beginning, products made mostly were WPC lumber for decking, fencing and outdoor applications. With the ability of these polymer composites material, the producers to come up with equal or superior properties to natural wood, the market demand for this material expanded into

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other applications as well. The appearance of composites with wood-grain effects, and excellent wood veneer finishes, the market was set for greater things. The fact that these were acceptable for building construction work, and being cost-effective, really created an expanding market demand. The advent of other biomass fillers and reinforcing agents (other than wood chips or flour) like rice hulls, wheat hulls, bamboo fibre and so on due to emerging technologies have widened the WPC products market. The possibilities are immense, and the fact that these biomasses are mostly from agri-residues, and will greatly help to reduce earth pollution, is giving the impetus to both researchers and composite producers to constantly look for newer composite products. As the need for new products became thicker and wider, e.g., door panels, decorative boards, machinery designers and manufacturers have been equal to the task, and powerful extrusion systems are non-available. Two of these items are: medium density fibreboards (MDF) for decorative applications like: pantry cupboards, kitchen tops, facades among others and the other is solid door panels cut to desired lengths on the machine. These can be produced in aesthetically pleasing finishes. Hardie Smith of India has complete extrusion systems for production of composite resins, and complete extrusion systems for production of a wide variety of boards, door panels, contoured extrudates and also machinery for customer-ordered finsihes.

7.9.1 Polymer composite solid doors The possibility of making solid or hollow doors in wide widths is a positive boon for wood working and also for the building construction industries. Wood veneers or other decorative finishes are also real cost-savers. Polymer composite doors tend to be a little heavy but this may be an advantage when a heavy solid door is preferred. These can be made in a variety of densities but if a very light door is desired, the addition of a small amount of a blowing agent will produce much lighter products. Product specifications – Door widths: (1,000 mm maximum) – Door length: as per requirement on production line cutting system – Door sizes in mm: 700 × 35 × 2000, 800 × 35 × 2000, 900 × 35 × 2000 (or as desired) – Door colours/Finishes: multiple colours, and finishes – Door thickness range: 15–75 mm – Door density: 650–800 kg/cu.m – Production capacity: 200–300 doors per day

7.9 Manufacture of polymer composite door panels with rice hulls

131

Raw materials Polymer: PVC virgin, and PVC recycled material Natural fibres: rice husks, wood wastes, saw mill wastes, wood powder, Bamboo, coir fibre, cotton stalks, wood flour and bagasse. Machinery – Solid structure – High moisture, and humidity resistance – High tensile strength – Excellent screw holding capacity – Better machinability – Can be processed like natural wood, MDF or any panel processing – Hollow doors have absolute strength These strong and long-lasting polymer composite doors made with PVC, and rice hulls can be produced in superb colours, and finishes. Printing, lamination or protective coatings can be done easily. Figure 7.2 shows some of these doors.

Figure 7.2: Doors made with PVC/rice husks. Reproduced with permission from Hardie Smith Ltd. India

Advantages – Cost-effective – Corrosion resistant – Easy to install – Environment-friendly product – Easy to cut, glued or fit internally – Durability better than natural wood

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7.10 Processing method in brief There are two processing methods. The first will homogenise: PVC (60–70%), rice husks (35–25%) and additives (5%) using an extrusion system connected to a pelletising unit. These hot pellets are cooled and stored in large volume silos. This system will allow a producer the advantage of producing different qualities/densities of polymer composite resins and in different colours also. These resin pellets are then fed into a powerful co-rotating twin screw extruder having a T-die attached to the extrusion head. The extruder will convert these pellets into a smooth homogenous hot mass, and the rotating action will push this hot melt through the T-die. The orifice of this die will determine the width and thickness of the extrudate, while the capacity of the extruder will determine the output rate. The shearing action of the screws will ensure a good homogenous mass, while the movement of the screws will push the hot melt inside through the T-die. Here, a producer may use one or two processing aids to enhance the smooth passage from the extruder barrel to the die. If a blowing agent is incorporated in the mix, extra precaution will be needed as the extrudate will tend to expand as it enters the atmosphere. The extrudate is cooled on a slow moving conveyor and cut to desired lengths. If embossing is desired, it can be done online, when the surface is still warm/hot. Surface finishing – Can be laminated – For patterns, a CNC router can be used – Paper lamination can be done easily – Protective coatings-PU/UV/other – High-resolution printing – Surface can be painted Applications – Perfect replacement for natural wood doors – Internal doors – Kitchen doors/bathroom doors – Cupboard doors/master doors – Lightweight doors for offices – Longer life than natural wood doors

7.11 Manufacture of medium-density fibreboard (MDF) There are different methods in making these MDF boards. They can be called engineered products meaning the final material is end-application-oriented. These boards can be easily produced with great finishes like painted, self-coloured,

7.11 Manufacture of medium-density fibreboard (MDF)

133

laminated with veneers, wood-like effects and many others. MDF boards are generally denser than plywood, much denser than particle board, and are an ideal material for many applications. The following two methods show MDF boards made from a thermoforming polymer (PVC) and a thermoset (urea formaldehyde or melamine formaldehyde).

7.11.1 MDF boards from polyvinyl chloride (PVC) These boards are made with PVC as the polymer matrix, NTFSAs and additives. They are made in standard densities or according to custom orders. Specifications – Panel width: 1,220 mm (maximum) – Panel lengths: as per requirement – Panel sizes: 8 ft (244 cm) × 4 ft (122 cm), 6 ft (183 cm) × 4 ft (122 cm), 4 ft (122 cm) × 4 ft (122 cm) – Panel thickness: 5 mm × 20 mm – Panel density: 650–800 kg/cum. – 300 to 700 boards per day based on 8 ft (244 cm) × 4 ft (122 cm) size (depends on thickness) Raw materials – Natural fibres/NTFSAs: rice hulls, wheat hulls, wood wastes, wood powder, bagasse, bamboo or others – Polymer: PVC/recycled PVC – general specifications: 5 mm × 20 mm – 4 ft (122 cm)), 4 ft (122 cm) × 4 ft (122) flexibility is desired, a small of a plasticiser can be incorporated – Elongation at break – 20–40% – Notch test – 2–5 kJ/sq.m – Glass temperature – 82 °C (180 °F) Figures 7.3 and 7.4 show samples of finished products and the extrusion process. – Melting point – 100–260 °C – Effective heat of combustion – 17.95 kJ/sq.m – Water absorption – 0.04–0.40 Recommended formula – PVC 70% – NTFSA 25% – Additives 5%

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Figure 7.3: Samples of MDF boards (courtesy of Hardie Smith Ltd.).

Figure 7.4: Extrusion process (courtesy of Hardie Smith Ltd.).

Here, the NTFSA content of 25% can be a single fibre or a combination as shown under raw materials. Sometimes it may be necessary to add a compatibiliser but either bamboo powder or rice hulls powder will give good results. A producer may opt to use short fibres which will give better strength, instead of powders or flours. Since, the processing method is similar as described under ‘processing method in brief’ in Section 7.9.1 details of processing is not given here. Moreover, the figure above is self-explanatory and will give the reader a good idea of the extrusion process.

7.12 Manufacture of compression moulded parts – thermoset polymer/NTFSA

135

7.12 Manufacture of compression moulded parts – thermoset polymer/NTFSA Compression moulding is among one of the oldest material processing techniques. Both thermoplastic, and thermoset polymers can be compression moulded but the preferred materials are thermosets in keeping with the end products. This process is suitable for a wide range of industrial, commercial and commercial parts, and products ranging from very small to large automobile body parts. Some of the common resins used are urea formaldehyde, melamine formaldehyde, epoxy, polyester, silicone and some others. In early times, these materials were used in pure virgin forms such as granules, powder followed by sheet moulding compound (SMC), bulk moulding compounds (BMC) and preforms. As technology improved with the idea of using less polymer, the advent for composite resins (polymer/filler/reinforcing agents) became a reality. With rapid developments in composite resins, the market saw composite resins filled with traditional fillers/ reinforcing agents. At the beginning, only small parts like parts for lighting, and electrical needs (wall plates, plug tops, switches) were produced but due to rapid advance in technology, now even very large parts such as automobile body parts, surf boards and others can be compression moulded. Some of the useful thermoset composite resins on the market now are: – Urochem – urea moulding compound from urea formaldehyde resin, cellulose filler, pigments, flow promoter and lubricant. – Melochem – compounded with melamine formaldehyde resin, cellulose filler, pigments, flow promoter and lubricant. – Fenochem – compounded from phenolic resin, cellulose filler, pigments, flow promoter and lubricant. Compression moulding machines are rated by their capacity or maximum clamping force and can be described in simple terms as a ‘heating press’. A mould consists of two halves made of high grade tool steel, with one half fixed to the bottom half of the moulding machine, while the other half will have either a vertical or horizontal movement. Press capacities may range from 100 tons (890 kN) to larger automated machines like 5,000 tons (44,500 kN). A 250 ton (2,200 kN) machine would suffice for making a reasonable range of products, including electrical accessories. Some of the parts that can be made by compression moulding using the thermoset polymer/NTFSA are: electrical plug tops, wall switch plates, bottle caps, circuit breakers, buttons, auto parts, surf boards, pump components, protective helmets, and many others. One of the advantages in compression moulding is that of-insert moulding. As examples, the author would like to highlight the following combinations of thermoset polymers, and NTFSAs: refer Table 7.5.

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Table 7.5: Possible combinations for composite products as compiled by the author. Polymer

NTFSA

Urea formaldehyde

Walnut shell powder

:

.%

Melamine formaldehyde

Calcium from egg shells powder

:

–

Epoxy

Bamboo strands

:

.%

Semi-rigid PUR

Rice hulls flour/shell fish powder

::

.%

– – – –

Ratio

Additive/other

Examples: UF/walnut – Electrical plug tops, wall plates MF/calcium – Melamine dinner plates, cups, saucers Epoxy/bamboo – Surf boards, housings PUR/rice hulls – Autobodies, bumpers, panels

7.13 Processing method in brief The size of the product to be made will determine the platen sizes, and clamping forces needed. Naturally, the dimensions of the platens should be more than the dimensions of the mould to accommodate them for firm clamping. The heating capacities will also differ with each polymer, and since thermosets are used heating temperatures will be higher than for thermoforming polymers. UF, MF will be in powder form, and prone to absorbing moisture from the atmosphere, and will need pre-heating. The moulds are made of tool steel, and can be single (for large parts) or have multi-cavities for smaller parts, and after many mouldings e.g., 30,000 mouldings the cavities may require slight repairs, which will have to be buffed. The process in brief is the opening of the mould halves, and filling the bottom half with the polymer/filler mixture. This can be done manually or through device which can load a pre-set exact amount. If the filling/load is insufficient ‘short-filled’ parts will result, and be rejects. If too much material is loaded, when the material becomes liquid, and flows, it could seep through the clamped mould halves, and thus, flash will result, which will have to be trimmed. Once the material is loaded, the mould halves are clamped tightly, and the heated mould will make the material soft, then into a hot molten state allowing it to flow, and fill the cavity or cavities. Depending on the number of cavities, and the geometrical patterns of the cavities, some moulders may use flow promoters as an additional additive. Colouring can be done as desired. The moulding cycle will include a holding time, and then a cooling period, after which the top mould half is opened. Insufficient cooling times will result is

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warping or also splits. Moulds must be well-designed with easy flow-paths, zero gaps between closed mould halves, good venting, efficient heating, and cooling systems. Safety factors are also very important as the moulds are subject to high heat. Removal of moulded parts can be either manual or auto-ejection. A light coating of a release agent sprayed on to the cavities before filling may be helpful. Functions of the polymer/NTFSA combinations are as follows: – UF/walnut – UF polymer matrix, walnut as a filler/stiffening agent – MF/calcium – MF polymer matrix, calcium as a filler – Epoxy/bamboo – Epoxy polymer matrix, bamboo as a reinforcing agent – PUR/rice hulls – PUR polymer matrix, rice hulls as filler/reinforcing agent, shell fish powder It should be noted that some of the other NTFSAs can also be used singly or in combination so long as they are compatible with the matrices.

Bibliography [1] [2]

Asbestos: An Overview: www.asbestos.com/asbestos Kayali Obada. High Performance Bricks from Fly Ash-school of Aerospace, Civil and Mechanical. [3] Tatara Robert. A.-(2011) Applied Plastics Engineering Handbook- pages 289–309Compression Molding. [4] Steadmans UK – Fibre Cement Sheet Roofing-www.steadmans.co.uk/fibre cement sheet roofing [5] Hardie Smith Ltd. India: http://hardysmith.org/WPC-Flush-Door-lines.html [6] Sreejith P. (2010)-Use of plastic waste in Bitumen Roads-http://sreejithknols.worldpress. com- March. [7] Defonseka Chris. (2014) - Introduction to Polymeric Composites with Rice Hulls-Smithers UK [8] Hirst Kris. K (2014) Bitumen- The Archaelogy and History of Black Goo-Thought Co. -March. [9] Editors of Encyclopaedia Britannica: Polystyrene Chemical Compound: www.britannitmlca. com [10] Thiagarajar College of Engineering: Process for Laying Plastic Roads-www.ice.edu/chemistry/ process.html [11] Sivalingam N. (2011) article on Project Profile on Fly Ash Bricks-MSME-Di, Guindy ChennaiMarch.

8 Recommendations for operating efficiency in a manufacturing plant 8.1 Introduction The operation of manufacturing products, whether they are plastics, rubber, machinery, chemicals auto parts and so on, always creates exciting challenges. In order to be successful, important areas such as research, development, engineering, operating techniques, technology, quality assurance and safety factors must work together. A manufacturing unit can be a small operation, a medium size one or a very large operation. The basics apply to all, irrespective of size but if products are to be made to international standards, then a manufacturer will be called upon to go the extra mile, for quality assurance. From the designing of a plant to layout, engineering services needed raw materials, machinery and equipment, personnel, safety factors, quality control and operating systems, recording, evaluation and overall process control, all these basic areas can be considered important. Although, one might say that all aspects are important on a manufacturing floor, this presentation will only deal with the important areas as relevant to making quality products with polymers, non-traditional fillers and stiffening agents. The following areas are presented as shown below: 1. Plant design 2. Raw material and storage 3. Machinery and equipment 4. Preventive maintenance 5. Processing systems 6. Quality control/in-house lab 7. Process efficiency 8. Troubleshooting 9. Lean manufacturing 10. Productivity 11. A case study in point

8.1.1 Plant design As a first step, designing the plant to suit your intended manufacture is very important, the layout being equally so for easy and smooth production ‘flow’. In this book, several manufactures/processes like injection moulding, compression moulding, extrusion, mixing, coating and so on have been discussed. While injection moulding, compression moulding, mixing and coating will only need reasonable floor space and https://doi.org/10.1515/9783110669992-008

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may even be possible to house some of them together, extrusion processes will need special attention, especially when related to the final product sizes and the NTFSA materials needing large spaces for storage. Perhaps, this will apply to polymers also. The two manufactures that really need floor space are: manufacture of fibre/cement corrugated roofing sheets and polymer composite door panels. Both will need large space, with the accent on length. Since the design for the extrusion of door panels is more complicated than the other, only this will be presented in preference to the others which are simpler. A polymer composite door manufacturer with rice hulls will have a choice of a fully automatic extrusion line or two lines, where first the rice hulls, polymer and additives are mixed, pelletised and then fed into large volume silos for storage. The second line will feed off these silos to produce the wide door panels. The factory floor could be standard concrete and designed to withstand the total weight of machinery, raw materials and other, also keeping in mind the frequent movement of one or two forklifts. Special concrete is not required to counter vibrations of machinery (especially extruders) as modern day ones have very efficient vibrator pads to counter machine vibrations. Due to the nature of the operation, it is best that the receiving of raw materials is done at one side of the factory close to the material preparation area. The polymer raw materials (probably in bags) and additives will not pose any problems for storing space but if the rice hulls are in loose form, then some planning will be needed. If they are supplied in bags, it is much better for easy storage. The following are some of the basic areas to be considered when planning an effective plant layout to ensure a good production ‘flow’. Depending on the volume of planned production, type of machinery and equipment, recommended minimum floor space for manufacture of composite doors would be 100 feet (wide) × 240 feet (length) × 30 feet (high) approximately 31 m × 74 m × 9 m. Wide sliding doors at the front and back of the factory would be standard, along with emergency exists as per local industrial regulations. Keep in mind sufficient working space for a forklift operation. The following are some of the basic areas to be considered when planning an effective plant layout to ensure a good production ‘flow’. – Provision for security – Reception area – Factory office – Staff rest room – Employee rest room – In-house laboratory – Tool/supplies room – Workshop – Engineering control room (power, air, water, other) – Shipping – Quality control/inspection

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– Production area/silos – Raw material storage – Forklift parking/waste disposal

8.1.2 Raw material and storage The polymer resins will generally be available in 25 kg bags or in 200 kg totes (bulk packs), while the additives will be either liquids or solids in smaller packs. Rice hulls directly available from the rice fields (cheapest) will have excess moisture, and also foreign matter. If purchased thus, a manufacturer will have to ‘clean’ it up and dried before pulverising for size reduction. Also, it is possible that the cleaned and dried hulls powder will again gain moisture from the atmosphere if not properly stored. The ideal would be to purchase the rice hulls, cleaned and dried in small packs. Here again, needs caution as hard lumping will take place if too many bags are stacked on top of each other. This is true for bulk purchases from field sources, and more likely to absorb moisture when heaped-up. There are many suppliers of rice hulls in any form (loose, powder, flour) to customised quality and will save a composite producer the trouble of cleaning and size reduction.

8.1.3 Machinery and equipment These depend on the volume of production planned and also the final extrusion machine must have sufficient capacity to extrude these wide profiles of up to 4 feet (1.2 m) required for door panels and MDF boards. The most popular machines for this operation are twin screw co-rotating extruders and one must keep in mind that the actual effective extrusion output is about 10–15% lower than the rated capacity. Modern extrusion systems are well advanced and will have ‘closed loop’ operating systems, meaning that production parameters are pre-set with allowable tolerances and will work within these by limits by self-adjustment due to possible changes in flow of the hot melt. Two of the most common restraints for non-uniform flow are restraints in material feed to the extruder feed zone from the hopper and possible power fluctuations during extrusion. Rice hulls have an inherent abrasive property, which has a significant bearing on the extruder screws due to wear and tear. This is one of the main reasons that the emergence of rice hulls as a special filler and stiffening agent was delayed. At the early stages, extruder manufacturers did not have the technology to overcome the short screw life when rice hulls were used. However, as research and development progressed, this has been overcome but yet the life of a screw dealing with rice hulls is shorter than standard screws.

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Since, electrically operated devices like machines, equipment and others will be on the floor and the chances are that most of them will be started at the same time, electrical power installed should be more than 40% of the estimated requirement.

8.1.4 Preventive maintenance This is an important area for process efficiency. Preventive maintenance is a fundamental planned maintenance activity which can apply to all areas on a factory floor but maintenance of machinery and equipment takes priority. This needs a good knowledge of the workings of all machinery and equipment on the production floor. Effectiveness will go beyond the recommended procedures as given by the manufacturers, which can be used as basic guidelines. A specially trained crew will be an advantage and usually can be part of the workshop personnel. A key phrase should be ‘regular periodic maintenance’. This maintenance includes: – Systematic inspection – Detection – Recording/analysis – Correction – Prevent future failures Due to the varying needs of different types of operations for different manufactures, the types and amounts/frequencies of preventive maintenance will vary, with machinery and equipment taking priority, followed probably by building maintenance and safety factors before others. Preventive maintenance aims to: – Eliminate unnecessary stoppages due to machinery breakdowns – Maximise machinery and equipment life – Prevent accidents due to malfunctioning equipment – Enhance employee safety – Prevent fires and other floor hazards – Eliminate process wastes An ideal preventive maintenance program can drastically reduce errors in day-today operations and also increase the overall preparedness of a plant in case of an emergency. Again, perhaps the most important of them all is to prevent and machinery and equipment failure before it occurs. This is especially so in an extrusion operation and very much so, if it is an automatic operation. Other important aspects are: maintenance of log books, monitoring and availability of ready-to-hand spares.

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8.1.5 Processing systems In this case, the operation involves many different aspects. An overall view would involve material preparation, mixing, extrusion (first stage), pelletising, storing in silos, second stage extrusion of these pellets (final product), cooling, cutting to size, embossing (optional) and finishing. The material preparation operations will involve drying, size reduction as required, while the polymer to be used may also require moisture removal. For ease of hot-melt ‘flow’ inside the barrels of the extruders, a processor may use an additional additive which could be a combination of a special lubricant and flow enhancer. This will also help to lessen the wearing of the screws, thus prolonging its lifespan. Since wide widths are extruded 4 feet (1.2 m) and uniform thicknesses are essential, suitable control devices for both parameters will have to be used. If frequent power failures/ power fluctuations are experienced, then this has to be addressed to cover at least the extrusion operations, as otherwise it will affect product quality. Modern day extrusion systems are well-advanced containing all necessary processing controls for each station, and it is recommended that complete extrusion systems be purchased from one single well-reputed supplier, rather than purchasing individual machinery and equipment, and then making an extrusion system, even though there may be cost advantages.

8.1.6 Quality control/in-house laboratory While some manufacturers may have separate teams for these two important areas of operations, since they are inter-connected, one team could handle both with efficiency. Although, the production of polymeric composite lumber with rice hulls may be easier, the production of polymeric composite doors with rice hulls is a little more complicated due to the sheer width of the profiles, though the raw materials used are more or less the same. Here, maintaining a uniform cross-section during extrusion is important. 8.1.6.1 Quality control Quality control is a procedure or a set of procedures intended to ensure that a manufactured product or performed service adheres to a pre-defined set of quality requirements as specified by a customer or an international standards. Common ones are ASTM (American), BSS (British) and DIN (German), while other international standards are JIS (Japanese), CSA (Canadian), and SLS (Sri Lanka) among others. A customer may have his or her own requirements with different tolerances, depending on a particular product or a localised requirement. QC is similar but not

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identical to QA (quality assurance) and can be defined as guaranteed procedure to ensure a quality product or products. One may even use the expression shown below: Quality assurance = quality control + quality management Quality assurance is also a pre-production requirement, where a manufacturer will produce at least a prototype or a sample of the final product for approval of a customer and comes under the category of PPAP (pre-production approval procedure). In order to implement a QC program, a manufacturer must decide on the standards to be met. To implement a chosen one, there are QC systems like ISO 9000, ISO 9001, ISO 9002 plus others, while QS 9000 is specially designed for the automotive industry. Many manufacturers use the Statistical Process Control (SPC), especially popular among plastics processors. Processing machines such as injection moulding machines and extrusion systems are installed with either open-loop or closed loop controls, with the latter being a self-correcting system based on pre-set parameters. A SPC system will basically have two main charts namely: X-R chart and a Pchart. The former is a very informative document recording the actual operating performance as it happens and contains a media, and an upper control limit (UCL) and a lower control limit (LCL). The X-R chart records the variations of a production process in progress. If the readings recorded are within the limits set, the process is in control, and the products are acceptable. If not, the process is said to be out of control and corrective action will be needed. If the readings are very close or equal to the median, the process is working well and the products are excellent. The P-chart is used after production has taken place on a simple accept/reject principle. Some parts/products may be put on hold. In the case of polymeric composite doors, some reasons for rejects will be: warp, thickness variation, poor surface finish, density variation, dimensional variations or other. Quality control should be carried out by competent personnel, and it is important to receive effective feedbacks from customers which will greatly help. Quality control should apply to all aspects of a process starting with raw materials to final shipping of products. 8.1.6.2 In-house laboratory Most large-scale manufacturers have their own in-house laboratories. When processing polymeric composites with rice hulls or other biomasses, a laboratory will be a great asset. Although, this manufacture will use rice hulls, others singly or in combination are also possible. A manufacturer may want to use some of these other biomass fillers/reinforcing materials which may be more compatible with different polymers being used as the matrices or based on purely economic reasons. Setting up a small in-house lab will be interesting but will need some careful planning, especially about the equipment needed, unlike a standard chemical lab,

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which is fairly straight forward. Some of the basic equipment that will be needed will be: – Small lab-scale extruder plus down-stream equipment – Small pelletising unit (optional) – Suitable dies and accessories – Small dryer and small pulveriser – Mixers – Digital weighing machines – Lab testing machines for tensile/compression/hardness/load bearing tests – Accessories for calculating density, and other important parameters – Other equipment as needed Since, quality control also will be housed under this lab, any extra instruments, measuring devices, monitoring and provision for recording or other should also be provided.

8.1.7 Process efficiency A process efficiency may apply to a small section of an operation or to an overall process, and collectively with other areas finally lead to plant efficiency. In industry, generally an efficiency level of 70% to 80% is probably the norm but higher levels are very difficult to achieve. To achieve efficiency in a manufacturing operation, there are certain basic needs to be put in place. A good, and clean working environment, well-trained and motivated personnel, safety factors, good facilities for employees, high morale are some of the key areas for success. Some factories even go so far as to provide soft pleasant music, which has definitely proven to increase production levels. Some of the factors that affect efficiency are: excess waste, under production, downtime, lack of skills, floor rivalries and so on, just to mention a few. Probably the area that creates the biggest problem is the lack of technology. The following key factors on a production floor will greatly help to raise the level of efficiency: 8.1.7.1 Key factors on a production floor – Mission statement: company objectives, company vision and customer policy – Poster motivation: safety operation, warnings, fire hazards and accident prevention – Machinery: proper installation, operator training, start-up and shutdown procedure – Maintenance: routine, preventive maintenance and spares

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– Quality assurance system: quality, control, monitoring, recording, analysis and action – Process engineering: time, and motion study and constant process improvement – Product development: quality improvement, new products and cost-cutting – Production methods: operating systems, procedure and correct working tools – Workforce: good morale, teamwork, technical skills and good attendance – Productivity: achieving set targets and input/output ratios – Raw materials: quality checks, proper storage and availability – Ventilation: good air quality, efficient exhaust systems and periodic checks – Good management: communication, motivation, decision-making and incentives – Warehouse: layout, proper storing, layout, efficient operation and shipping system – Fire precautions: emergency exits, fire drill and fire extinguishers – Employee facilities: good working environment, lunch room, lockers and washrooms – Tools: proper inventory, issuing system and training for proper use – Production floor committee: key personnel, periodic meetings and trouble shooting – Job rotation: between hard/easy jobs and shift work – Absenteeism: correct selection of personnel and attendance bonus – Rivalries: avoid rivalries between operators and operator/supervisors

8.1.8 Troubleshooting Any business is prone to problems, more so a manufacturing operation. Consider some of the main contributors like raw materials, machinery, and equipment, engineering supplies like-water, electrical power, air supply, personnel and so on that go to a final ending of manufacturing. Trouble can come from any of these important areas. Manufacturing is both an exciting and challenging job, and most manufacturers may really enjoy these challenges, especially when considering the rewards at the end. Monetary gains may motivate some but the majority no doubt will appreciate the opportunity to start, and sustain a manufacturing business, to meet the needs of society, and also shouldering the responsibility of the many employees, and their families. Therefore, a well-organised, smooth running operation with minimal troubleshooting is much desired. Although modern-day manufacturing may have the luxury of well-advanced methodologies, machinery and equipment, still an ideal would be if they occurred only periodically, and not on a daily basis. Just imagine the problem if a fully automatic production line comes to a halt due to a faulty sensor or sensors. The author knows of an incident, for example, a production line consisting of six operators

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assembling industrial ink cartridges at the rate of 2,000 per 8 hour shift, and only on the fifth day, it was discovered the containers were the wrong ones! In this particular manufacture – polymeric composite doors – trouble could come from bad-quality rice hulls (moisture content too high, foreign matter), not using extrusion grade polymer, raw material feed restrictions at the throat of the extruder hopper, power fluctuations, quick wear of screws due to abrasion from rice hulls, pre-set temperature parameters not working properly, excessive moisture in polymer, excessive material waste at start-up time, post production wastes during finishing of extruded products and so on. Extrusion systems generally runs smoothly once they are set up. There will be a certain amount of material waste at start up time, and sometimes due to the hard solidifying nature of this waste, a processor may not attempt to recycle it, due to possible damage to the shredder or granulators. Some operations may have powerful granulators which can easily crush them into reusable material. Assuming that a homogenous free-flow hot melt can be achieved, the emerging extrudate from the extruder head will tend to expand a bit as it enters the atmospheric conditions. This is more so, if a blowing agent is used to reduce the density of the material and the final product. The wide dimensions of the extrudate will also emphasise on the need for proper cross-sectional and surface control coupled with sufficient cooling to have dimensional control within pre-set tolerances. Proper working procedures and awareness will eliminate the need for troubleshooting due to accidents, hazardous spills, possibilities of fires within the factory premises.

8.1.9 Lean manufacturing The term ‘lean’ originated with the Japanese company – Toyota – as a need for improving business practices and therefore enhancing quality and profitability. The core idea is to maximise customer value, while minimising waste. The Japanese idea was simply to create more value for customers with fewer resources, better performance, at lesser costs by eliminating waste. This is a very practical and sensible approach especially for manufacturing operations to produce quality products at higher levels of profit. Businesses, whether manufacturing, services or other knows the value of customers and a lean organisation understands and focuses its key processes to continuously increase it. The ultimate goal is to provide perfect value to the customer, through a perfect value creation based on a reasonable minimal waste factor. In a manufacturing organisation, lean practices are not only confined to the production floor but should start from the very top meaning from management downwards, and throughout the whole organisation. Lean practices are very exciting and challenging, and if tempered with recognition of results with rewards (not necessarily monetary), the effects could be almost magical.

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Waste can apply to many aspects of a manufacturing operation. Although material wastes may be the lead factor, waste of time, downtime, lack of effort, over expenditure and others are also causes for lean thinking and action. Eliminating waste along entire value streams, instead of at isolated points, creates processes that need less human effort, less space, less capital and less time to make products and services at far less costs, and with much fewer defects/rejects, compared with traditional business systems. Manufacturers will be able to respond to changing customer needs or market trends with efficient changes, quality, lower costs and mush higher outputs. A popular misconception is that lean practices are suited only for manufacturing. This is not true. Lean applies to every business activity, from small to big, and will encompass important areas such as finance, marketing, technology and administration. Lean programs are not a tactic or a basic cost reduction program but a process by which overall improvement of activities are achieved.

8.1.10 Productivity Productivity can relate to many areas but in this case, it will refer to manufacturing. Defined simply, productivity is an economic measure of output per unit of input, and in a manufacturing operation, it is best calculated by converting all costs of inputs, for example, raw materials, labour, and other, and comparing the revenue this value has generated during a given period of time. A ratio of 1:1 will indicate no gain, and greater ratios will show revenue, which can be calculated in terms of money or as percentages. Productivity ratios are vital for any business, whether manufacturing or otherwise. Always the target is to achieve more with less inputs. Capital, labour costs and overheads are expensive commodities, and maximising their impacts is a core concern of modern business. Generally, a raw material content in a product may constitute about 50–60% of the costs but in this manufacture because of the use of rice hulls, which is a cheap component, a manufacturer may look for higher return ratios than standard for similar operations. Improving productivity may be done in ‘sections’, meaning breaking down an overall process into individual important areas, monitoring and taking actions to improve them individually, so that the overall result will meet pre-set targets. Here, techniques like time management, technology, operator skills, supervisory skills, waste reduction methodologies and so on will play a key role. A happy and motivated workforce will naturally perform much better than a dissatisfied one. For starters, the working environment should be pleasant. Some factories have soft-piped music, meaningful breaks and good in-house facilities for their employees. According to industrial statistics, productivity can be increased by 15% under these conditions. Other important areas for increasing productivity on a factory floor are: allocating jobs according to the skills and ability of individual

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operators, rotation between hard, and easy jobs, and good interaction between operators. Absenteeism and down time will also affect productivity. Although there is a difference between profitability and productivity, where a manufacturer will consider profitability as an overall factor and productivity as a process efficiency factor, applicable to even section by section, a manufacturer will do well to monitor an on-going operation periodically and take corrective action rather than waiting for analysis from periodic operational statements, which will be too late. The following financial performance indicators may help to monitor and keep an operation on a profitable level: 8.1.10.1 Breakeven point A breakeven calculation will indicate to a manufacturer how much sales are needed to meet total costs, with all sales beyond this point being considered as profits. The breakeven is especially useful in product pricing policy, and also to determine what percentage of a particular market can be targeted. Breakeven values can be expressed in different ways, and as a percentage 60–70% may be an acceptable level, with lower percentages being preferred. A simple way to calculate a B.E. point is as follows: Using formula, BE = FC / (SP – VCUP), where BE = breakeven point, FC = total fixed costs, SP = unit selling price, VCUP = variable cost per unit product. Fixed costs are costs that have to be paid irrespective of whether products are made or not. These are rents, indirect labour, telephone bills and such. Variable costs are costs that vary directly with production such as material costs and direct labour. For example, a polymer composite door manufacturer’s fixed costs for making 10,000 doors are $30,000 per year. Variable cost per door is $70. The selling price per door is $120. Then, applying formula, BE = FC/(SP – VCUP) = 30,000/(120–70) = 600 doors. Therefore, the manufacturer will have to make and sell a minimum of 600 doors before he/she can make a profit. 8.1.10.2 Contribution margin If a manufacturer makes more than one type of door, for example, different sizes, different finishes and after studying sales performance of all and wants to eliminate one or two types to maximise profits, it will be necessary to decide which ones to be

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discontinued from production. To do this, the manufacturer may want to decide based on a contribution factor worked out for each product. A contribution margin is the amount of money each product generates towards meeting overheads and is calculated as: unit sales price minus the unit variable cost of that product. Some products may give better margins than others but have limited sales. On the other hand, some may make lesser contributions towards overheads but have large volumes of sales. Therefore, all these factors will have to be taken into account to arrive at the best combination. 8.1.10.3 Quick performance indicators Some business systems may wait for quarterly or periodic financial statements to see the ‘performance’ of an operation to take corrective action. By this time it will be too late as valuable profit may have been lost. To assist in this, the author recommends two simple strategies shown below which can be analysed on short periods of time as desired. Return per kilogram is the total gross value of sales plus saleable goods versus raw materials consumed during a given period of time. For example, 1,000 doors @ $115 = $115,000 Total raw material consumed = 1200 kg Therefore, the return per kilo = $95.83 per kg Compare to pre-set standards. Cost per kilogram is the total gross costs of operation versus cost of raw material consumed during a given period of time. For example, total costs = ex-factory + administration + marketing + other = $72,000 raw material consumed = 1200 kg. Therefore, cost per kilo = $60 per kg. Compare with pre-set standards.

8.1.11 A case study: improving operating efficiency This presentation is based on an actual assignment carried out by the author for a large manufacturer of PUR foam products to raise the level of operating efficiency to meet pre-set goals. Readers may find the methodologies used interesting in that most of the approaches used can be applied to many plastics products manufacturing operations. Abstract: Foam Company Ltd. (not a real name of the client) was a large manufacturer of flexible polyurethane (PUR) foam products like mattresses, cushions, sheets, slabs, convoluted foam and other products for both the local market and export to the

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neighbouring countries. The factory consisted of over 200,000 square feet (approximately 19,000 m2), employing 300 personnel. The board of directors consisted of a president, technical director, production director supported by a CEO, general manager and other senior staff. The overall organisation was made up of many departments in keeping with the needs of a large foam products manufacturer operating to ISO standards. The main foaming line was fully automatic supported by automatic and semi-autocutting systems. As the company experienced growth and the volume of foam also increased with the addition of new machinery, the company experienced predictable manufacturing problems with regard to quality issues, excessive foam wastes, declining processing efficiency and naturally drop in profits. When the monthly foam wastes became 33% and a drop in sales was experienced due to quality issues, the board decided to seek the services of a consultant. Keywords: PUR foam, excess waste, quality issues, process efficiency, Lean manufacturing, operating efficiency 8.1.11.1 Company analysis in brief Foam Company Ltd. had started as a small single owner operation. Diligent planning at the beginning had made available plenty of land space for expansion. As their brand name established on the local market and sales volumes increased, with additional floor space, and new machines the company had slowly expanded over a period of 20 years. The purchase of a fully automatic continuous foaming line and cutting systems enabled them to really expand their business in keeping with market demands. Due to lack of technology and handling large volumes of foam, from processing conversion to final products, they had to face excessive waste and operating problems. 8.1.11.2 Assignment parameters – Assignment duration: 4 weeks – Assignment period: April 2010 – Assignment targets: a. Waste reduction from 33% to 15% b. Quality issue – load bearing factor (IFD) > 2.0 c. Process efficiency minimum 75% – The team consultant – CEO (main contact) – General manager (working contact) – Project secretary – Project coordinator Communication between the consultant and CEO commenced long before the assignment started. This enabled the consultant to get first-hand information of the

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current operation and prepare a tentative plan of action to be discussed with client and finalised on arrival at the factory. The questionnaire sent to client also helped greatly in preparing this plan. 8.1.11.3 Implementation of work plan Week 1 – Meeting with client, and finalising work plan. Inspection of factory – brief study of current operations – examination and evaluation of company data, recording systems – meeting with directors – meetings with key departmental heads – selection of final action team – Consultant, General Manager, secretary, coordinator, production manager, engineer and technologist. Week 2 – On going study with close observation/recording data of each department in sequence and process flow in general – action flow: 8 am to 1 pm (observation, floor discussions recordings) – 2 pm to 5 pm (training of personnel from different key departments). – Waste reduction: Foaming section, fabrication section, recycling section, postcure section – Quality issues: Marketing foaming section – fabricating section – quality control-engineering – Process efficiency: All sections/departments – Profitability: Production, marketing, finance and planning Training Parameters: basic plastics, and PUR technology – functions of foaming components foaming calculations and formulating techniques – troubleshooting foam defects – quality control systems – monitoring-recording – evaluation – action – statistical process control (SPC) – calculations for load bearing factors (IFD) – density calculations – foam cutting systems- achieving reduction in foam cutting wasteshow to set up a in-house laboratory – ASTM standards – preventive maintenance methods – Lean manufacturing practice – introduction of log books – meeting scheduled targets – safety factors and chemical spill management. Training methodologies: individual and group discussions of problem areas – group lectures – videos – handouts – literature. Week 3: Production flow as observed were: all chemicals are bulk purchases and on arrival are pumped into large holding tanks that are connected to the main foaming line. A crew of five operators with one lead-hand was in charge of the foam production. The modern automatic foaming line (continuous line) needed about one hour to be set up for production. Figure 8.1 shows a production run. The crew came in at 7 am but came to the machine only around 10 am. The lead-hand then studied the production scheduled for the day as issued to them by the production department and was seen discussing it with his team. With the leadhand setting the machine control parameters, the mixing head was activated, and the initial mixture of liquid foam was deposited on to a paper trough moving very

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Figure 8.1: Client’s continuous foaming machine. Photo reproduced with permission from A.S. Enterprises Ltd. India.

slowly on a moving conveyor. This mix was slow to rise, which was normal, and formed part of the inherent initial waste. The requirement for the day was two runs of 700 kg. of foam, and the subsequent flow of foam was good rising to a height of 42 inches (1.07 m) and forming a 1.5 inches (3.8 cm) meniscus on top surface. As the hot foam mass moved forward, it began to ‘cure’ and form one continuous ‘bun’. Down the line, a vertical cutting system cut the foam into standard size blocks and then held in a pre-storage area before transportation to storage for final cure. The entire foaming run lasted only 48 seconds. It was observed that the foam wastes from the start and at the end was sent to the re-cycling section when it was sufficiently cooled. The machine was then cleaned and set up for the second run of a different density, with production parameters reset. It was observed that at the end of each run, the cut foam blocks were marked with the date and density. The crew then went about tidying up the section. The crew returned at 1 pm after lunch and plenty of idling time was observed till 3 pm, when their shift ended. An important observation was that while all the foam blocks made on the first run at 10 am was of ‘good quality’, the foam blocks made during the second run at 11.30 am was of lesser quality. At this time, the atmospheric temperature in the foaming section has increased significantly. Storage The post-production storage area for the foam blocks was very good and clean with efficient ventilation and gas-exhaust systems in place. However, the foam blocks were stored in a random ‘mixed’ pattern for the final 24 hours (minimum) curing time where gas was emitted from the exothermic (heat giving) reactions taking place inside the foam blocks. Hence, the need for good ventilation and exhaust systems. Because of the random storage pattern of foam blocks, if under-cured blocks are taken for fabrication, they would result in rejections. This was observed in some occasions, as the foam blocks taken for fabrication were still ‘wet’ and ‘sticky’, when the curved top surface was cut to remove the rounded meniscus.

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Cutting and fabrication Figure 8.2 shows the cutting and fabrication section. The various colours identify different densities and qualities of foam produced.

Figure 8.2: Foam cutting section reproduced with permission from A.S. Enterprises Ltd. India.

The current practice as observed was the trimming of the top surface with the 1.5 inches (3.8 cm) meniscus and 0.5 inches (1.4 cm) loss on the sides and bottom. Although, this practice was normal, in the current situation where waste was excessive, a change in cutting patterns had to be implemented, starting with elimination or at least reduction of the 1.5 inches (3.8 cm) loss due to the meniscus (rounded top). Moreover, since all the foam blocks were cut to a standard size, when mattresses, cushions, sheets were cut, large slabs of good foam of different sizes were generated and sent to the recycling section. This was unacceptable and on checking the average of all foam wastes generated thus, including the trimmings, it was found to be high and it was concluded that the cutting and fabrication section generated around 20% of the 33% foam wastes experienced by the company. Although, this operation being the ‘pivotal’ action for the overall foam production operation, the quality control steps taken were virtually non-existent. This section should have had daily records of all fabrications activities like blocks fabricated per shift, densities, products, dimensions, time factors, waste records, IFD readings and so on as a daily report to the Production Manager. The result was no attempts made to reduce foam waste from cutting and fabrication, some products with low IFD < 2.0 and also products with dimensional irregularities reaching the shipping section causing problems for marketing. Assembly and finishing This section worked efficiently and different types of foam mattresses were made. Essentially this section comprised of assembly of foam slabs, sheets, padding with soft patterned cloth and trimmings. However, they had two problems. One was variation in foam quality, and the other was that the padding foam (thin sheets) made

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in the factory in the form of rolls of sheet (peeled sheeting) was too coarse and was sticking to the cutting blade of the peeling machine, giving uneven surfaces. After observation and study it was established that the problem lay in the foaming section. 8.1.11.4 Addressing concerns After diligent observation, recordings, discussions and research, it was agreed that the new targets set up could be achieved. Each section to take corrective action separately and then combine them in an overall ‘smooth-flow’ operation to raise the standard of process efficiency. The following recommendations were implemented immediately under the supervision of the consultant: Recommendations/implemented solutions (a) Foaming section – Foaming crew to set up machine for production between 1 pm and 2 pm ready for the next day, instead of waiting for the morning. – The two foam runs to start and be completed between 8 am and 10 30 am, when it is cooler. – The foam runs should be longer. For example, the foam wastes at the beginning and end of a 48 seconds run would be the same as for a 60 seconds run, which will give an additional 175 kg of foam or 350 kg for two runs. This will be a significant reduction in foam wastes, and also reduce the number of foaming days required. – Instead of cutting foam blocks on the machine to a standard size, the blocks to be cut to sizes on a no-waste/minimal waste basis. This will prevent unnecessary wastes later. – Cut blocks to be kept upside down on holding area when they are still warm, to reduce curved surface area. It was found to reduce the meniscus from 1.5 inches (3.8 cm) to 0.5 inches (1.3 cm), which meant a lesser height than the standard 42 inches (1.08 m) could be made, thus saving material. – Each block to be tagged with data like date/ weight/ density/ block dimensions/ other, before being sent to final cure storage. – Introduction of ‘box-test’. A small wooden box-12 inches (30.5 cm) × 12 inches (30.5 cm) × 6 inches (15.2 cm) to be used for batch testing before each time a new formulation is to be run. – To increase the foam load-bearing factor (IFD) from < 2.0 to > 2.0, the filler content of all formulations were raised by 4.0% after a box-test trials of 4.0%, 6.0%, and 8.0%. An increase of 4.0% was found to be sufficient to increase IFD > 2.0. – To solve the problem of foam being coarse for sheeting on the peeling machines and to achieve a ‘fine-celled’ foam, the formula being used was adjusted by increasing air component by 1.0%, and increasing blowing agent by 0.08% which was effective. All other parameters remained the same.

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(b) Storage From the holding area the foam blocks were transported to the final curing area and stored in a random pattern which was not satisfactory. A FIFO (first-in-firstout) system was introduced. This ensured that the foam blocks taken for fabrication were fully cured, and not under-cured. (c) Cutting and fabrication section – As a first step, a quality control system was implemented. Three areas were set up: green (QC passed), yellow (on hold) and red (rejects). – Since the foam volumes were big, the QC inspector to carry out tests on a random selection basis, and then grade with green, yellow or red. – Wooden fixtures were introduced to check dimensions of mattresses and cushions. The IFD could easily be checked with a small hand-held device, while the densities could be checked by weighing and measuring dimensions. – Foam on hold (yellow) to be further cut into cushions, and pads for which there was a good market. From the smaller pieces remaining, sponges could be made which had a ready market. – Since the production schedules were available well in advance, the supervisor to calculate the exact size of blocks required to match the products and advice the foaming section of the required lengths of foam blocks to be cut on the machine. This would minimise or allow zero wastes when blocks are cut. – The cutting and fabrication section experienced a tremendous drop in foam waste with immediate effect. (d) Process efficiency Due to time restraints, it was not possible to really see the final actual maximum overall increase in process efficiency but there appeared to be great improvement in the overall process going on the daily reports coming in. As the recommendations were gradually being implemented, it would take at least three months to reach a maximum level of efficiency. (e) Conclusion With the consultant handing over a final report to the CEO and discussing it with him, a meeting was held with the Board of Directors. The CEO reported an immediate drop in foam waste from 33% to 14% with the possibility of a further reduction of 2%, and that the problem for marketing had been solved and current foam showed good improvement in quality. The assignment ended with the Board thanking the consultant for his efforts and success.

Bibliography

157

Bibliography [1] [2] [3] [4]

Rouse Margaret. article on Quality Control (QC) - http:whatis.techtarget.com/definition/ quality–control. Defonseka Chris. (2013) “Practical Guide to Flexible Polyurethane Foams”. Shawbury, Shropshire: Smithers Rapra UK. Productivity: website: http://www.investopedia.com/terms/p/productivity.asp Defonseka Chris. article on “Researched Solutions for large PUR foam Factory needing Assistance” e-magazine Sri Lanka Institute of Entrepreneurs (SLIE) - Jan/Mar 2013 -www.SLIE. com

Appendix A The following table shows some randomly selected suppliers of biomass fillers and stiffening agents. Since most are manufacturers, customized products can be purchased. Best sources for finding suitable suppliers for additives, dyes, pigments and others are these biomass suppliers who can also recommend the best products to use.

Supplier

Country

Products

Composite Materials Co. Inc. – CT

USA

Wood flour, walnut shell flour, rice hull flour, sisal, and corn cob flour

Hammond Roto Finish – MT

USA

Rice hull flour

Mid-Link International Co. Ltd. European office/Shanghai, China

Germany

Rice hulls ash

Silicon India

India

Rice hull ash, powder and pellets

NK Enterprises

India

Rice hull ash

ADF Asset & Investments

UK

Wheat hulls

Agrilectric Research

USA

Rice hull ash

Tianjin Glory Tang Co., Ltd.

China

Bamboo fibre

Siddhi Vinayak Enterprises

India

Bamboo fibre

Zenco Global Enterprises

Malaysia

Soybean flour and wheat hulls

M M Chemical India

India

Composite polymer powders, HDPE, LDPE, PP, EVA and customized powders

Kanju Industrial (HK) Ltd.

China

Graphite powder for polymers

Rice Hulls Speciality Inc.

USA

Rice hulls and rice hulls powder

This table as compiled by the author shows some key suppliers but many more are available covering a wider range of products.

https://doi.org/10.1515/9783110669992-009

Appendix B The following table shows some suppliers of machinery whose processing systems are suitable for processing polymeric composite materials into final products. These machineries will be available as manual, semi-auto or fully automatic systems. A polymeric composites products manufacturer will also be able to find sources for suppliers of ancillary equipment needed for any process when working closely with a machinery supplier to select the best system/systems for the proposed manufactures. Another important aspect is finding sources for suitable mini versions for laboratory work.

Supplier

Country

Processing systems

Hardy Smith Ltd.

India

Extrusion

Reifenhauser GmbH & Co.

Germany

Extrusion

Harden Industries Ltd.

China

Extrusion

Davis-Standard, LLC

USA

Injection molding/extrusion

Coperion K-Tron

USA

Mixing/drying

Wuhan Plastics Machinery Ltd.

China

Composite polymers

Hennecke GmbH

Germany

PUR foaming

Karunanad Hydropneumatic Controls Pvt. Ltd.

India

Compression molding

HAMRO International Co., Ltd.

Taiwan

Compression molding

This table as compiled by the author shows a few suppliers of relevant machinery for processing composite polymer materials.

https://doi.org/10.1515/9783110669992-010

Appendix C The following table shows some of the popular manufacturers and suppliers of polymers. They will be able to advice processors about good sources for additives, dyes, pigments and others. Polymers are generally available as powders, liquids, granules or pellets, either natural in colour or self-coloured. Basic packs include 25 kg paper bags or in larger 400–500 lb. bulk packs, except for the polymers in liquid form. Countries shown are the main manufacturing sources but their products will be available from their agents/distributors in many countries.

Supplier

Country

Products

Dow Corporation

USA

All

BASF

Germany

All – speciality (EPS)

Bayer AG

Germany

All – speciality (PUR)

Huntsman Corporation

Europe

Speciality PUR

ChemControl Limited

USA

PUR

Isaac Industries, Inc.

USA

PUR

Era Polymers Pty Ltd.

Australia

Two-component PUR systems

BioBased Technologies, LLC

USA

Speciality polymers

Union Carbide Limited

Canada

Polymers

This table as compiled by the author highlights a few major suppliers.

https://doi.org/10.1515/9783110669992-011

Glossary Amorphous Having no ordered arrangement, polymers are amorphous when their chains are tangled up in any old way. Polymers are not amorphous when their chains are lined up in ordered crystals. Anion An atom or molecule which has a negative electrical charge. Cation An atom or molecule which has a positive electrical charge. Complex Two or more molecules which are associated together by some type of interaction of electrons, other than a covalent bond. Copolymer A polymer made from more than one kind of monomer. Covalent bond A joining of two atoms when the two share a pair of electrons. Cross-linking Cross-linking is when individual polymer chains are linked together by covalent bonds to form one giant molecule. Crystal A mass of molecules arranged in a neat and orderly fashion. In polymer crystal, the chains are lined up neatly like new pencils in a package. They are also bound together tightly by secondary interactions. Elastomer Rubber. Hot shot scientists say a rubber or elastomer is any material that can be stretched many times its original length without breaking and will snap back to its original size when it is released. Electrolyte A molecule that separates into a cation and an anion when it is dissolved in a solvent, usually water. For example, salt, NaCl separates into Na+ and Cl– in water. Elongation How long a sample is stretched when it is pulled. Elongation is usually expressed as the length after stretching divided by the original length. Emulsion A mixture in which two immiscible substances, like oil and water, stay mixed together thanks to a third substance called an emulsifier. The emulsifier is usually something like a soap, whose molecules have a water-soluble end and an organic-soluble end. The soap molecules form little balls called micelles in which the water-soluble ends point out into the water, and the organic-soluble ends point into the inside of the ball. The oil is stabilized in the water by hiding in the centre of the micelle. Thus the water and oil stay mixed. Entropy Disorder. Entropy is a measure of the disorder of a system. First order transition A thermal transition that involves both a latent heat and a change in the heat capacity of the material. Free radical An atom or molecule which has at least one electron which is not paired with another electron. Gel A cross-linked polymer which has absorbed a large amount of solvent. Cross-linked polymers usually swell a good deal when they absorb solvents. Gem diol A diol in which both hydroxy groups are on the same carbon. Gem diols are unstable. Why are they called gem diols? It is short for geminal, which means ‘twins’. It is related to the word gemini. Glass transition temperature The temperature at which a polymer changes from hard and brittle to soft and pliable. https://doi.org/10.1515/9783110669992-012

166

Glossary

Heat capacity The amount of heat it takes to raise the temperature of one gram of a material to 1°C. Hydrodynamic volume The volume of a polymer coil when it is in solution. This can vary for a polymer depending on how well it interacts with the solvent and the polymer’s molecular weight. Hydrogen bond A very strong attraction between a hydrogen atom which is attached to an electronegative atom and an electronegative atom which is usually on another molecule. For example, the hydrogen atoms on one water molecule are very strongly attracted to the oxygen atoms on another water molecule. Ion An atom or molecule which has a positive or a negative electrical charge. Latent heat The heat given off or absorbed when a material melts or freezes or boils or condenses. For example, when ice is heated, once the temperature reaches 0 °C, it is temperature will not increase until all the ice is melted. The ice has to absorb heat in order to melt. But even though it’s absorbing heat, it is temperature stays the same until all the ice has melted. The heat required to melt the ice is called the latent heat. The water will give off the same amount of latent heat when you freeze it. Le Chatlier’s principle This principle states that if a system is placed under stress, it will act so as to relieve the stress. Applied to chemical reactions, it means that if product or by-product is removed from the system, the equilibrium will be upset, and the reaction will produce more products to make up for the loss. In polymerizations, this trick is used to make polymerization reactions reach high conversion. Ligand An atom or group of atoms which is associated with a metal atom in a complex. Ligands may be neutral or they may be ions. Living polymerization A polymerization reaction in which there is no termination, and the polymer chains continue to grow as long as there are monomer molecules to add to the growing chain. Matrix In a fibre-reinforced composite, the matrix is the material in which the fibre is embedded, the material that the fibre reinforces. It comes from a Latin word which means ‘mother’, interestingly enough. Modulus The ability of a sample of a material to resist deformation. Modulus is usually expressed as the ratio of stress exerted on the sample to the amount of deformation. For example, tensile modulus is the ration of stress applied to the elongation which results from the stress. Monomer A small molecule which may react chemically to link together with other molecules of the same type to form a large molecule called a polymer. Olefin metathesis A reaction between molecules, both containing carbon–carbon double bonds. In olefin metathesis, the double bond carbon atoms change partners, to create two new molecules, both containing carbon–carbon double bonds. Oligomer A polymer whose molecular weight is too low to really be considered a polymer. Oligomers have molecular weights in the hundreds, but polymers have molecular weights in the thousands or higher. Plasticizer A small molecule that is added to polymer to lower its glass transition temperature. Random coil The shape of a polymer molecule when it is in solution, and it is all tangled up in itself, instead of being stretched out in a line. The random coil only forms when the intermolecular forces between the polymer and the solvent are equal to the forces between the solvent molecules themselves and the forces between polymer chain segments.

Glossary

167

Ring-opening polymerization A polymerization in which cyclic monomer is converted into a polymer which does not contain rings. The monomer rings are opened up and stretched out in the polymer chain. Secondary interaction Interaction between two atoms or molecules other than a covalent bond. Secondary interactions include hydrogen bonding, ionic interaction and dispersion forces. Second-order transition A thermal transition that involves a change in heat capacity, but does not have a latent heat. The glass transition is a second order transition. Soap A molecule in which one end is polar and water-soluble and the other end is non-polar and organic-soluble, such as sodium lauryl sulfate. These form micelles in water, little balls in which the polar ends of the molecules point out into the water, and the non-polar ends point inward, away from the water. Water insoluble dirt can hide inside the micelle, so soapy water washes away dirt that plain water cannot. Strain The amount of deformation a sample undergoes when one puts it under stress. Strain can be elongation, bending, compression or any other type of deformation. Strength The amount of stress an object can receive before it breaks. Stress The amount of force exerted on an object, divided by the cross-sectional area of the object. The cross-sectional area is the area of a cross-section of the object, in a plane perpendicular to the direction of the force. Stress is usually expressed in units of force divided by area, such as N/cm2. Termination In a chain growth polymerization, the reaction which causes the growing chain to stop growing. Termination reactions are reactions in which none of the products may react to make a polymer grow. Thermoplastic a material that can be moulded and shaped when it is heated. Thermal transition A change that takes place in a material when you heat it or cool it, such as melting, crystallization or the glass transition. Thermoset A hard and stiff cross-linked material. Thermosets are different from thermoplastics, which become mouldable when heated. Thermosets are cross-linked, so they do not. Also, they are different from cross-linked elastomers. Thermosets are stiff and do not stretch the way elastomers do. Toughness A measure of the ability of a sample to absorb mechanical energy without breaking, usually defined as the area underneath a stress–strain curve. Transesterification A reaction between an ester and an alcohol in which the OR of the ester and the OR’ group of the alcohol trade places, as shown below.

Index Aliphatic hydrocarbons 3 Amorphous structures 32 Analytical chemistry 6 Aromatic compounds 4 Asbestos 118 Atomic masses 16 Bamboo 53 Biobased renewable 25 Biodegradable plastics 94 Bio-filled polymer 64 Biofiller 79 Biomaterials 38 Bioplastics 93 Bitumen 126 BMC 91 Bonding patterns 12 BPC (bamboo) 54 Breakeven point 149 Chemical bonding 34 Closed loop 141 Cluster 6 Composites 18 Configuration 15 Contribution margin 149 Copolymer 12 Coupling agents 83 Covalent bonds 36 ‘Cream’ time 110 Cross-linking 21 Crystalline material 32 Crystallography 34 Cushion 74 Degradation 16

Flue ash 122 Fly ash 52 Friction 19 Functional fillers 99 Functional group 3 Glass transition temperature 26 Graphene 29, 58 Graphene-polymer composites 59 Green polymer chemistry 25 Homopolymer 12 Hydrocarbon resins 27 Hydrogen bonding 36 Hydrophobic 2 Inorganic 1 Inorganic chemistry 4 Inorganic compounds 5 Ionic bonding 36 Kinetics 37 Lignin polymer 52 Melting point 21 Meniscus 110 ‘Mer’ 4 Metallic bonds 36 Microscopy 8 Microstructures 33 Mixing/calendaring 121 Modified polymers 17 Molar masses 127 Molecular bonds 43 Molecular weight 1 Monomer 13

Elastomer 42 Endothermic 85 Engineered polymers 17 Engineering thermoplastics 42 Exothermic 85

Nanomaterials 38 Nanoparticles 60 Nanostructures 33 Nucleation 112

Fibre-reinforced polymer composite 63 Filled polymers 17, 57 Fines 121

Organic 1 Organic ligand 6 Organometallic compounds 5

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Index

P-chart 144 PCRH (rice hulls) 54 PCWH 54 Plastics 11 Polyblends 14 Polymer 12 Polymer chain 16 Polymeric composites 51 Polymeric materials 12 Polymerisation 4, 12 Polymer-modified bitumen 126 Polymers 4 Qualitative 2 Qualitative analysis 7 Quantitative 2 Quantitative analysis 7

SPC Chart 75 SPC system 144 Synergetic mixture 55 Synthesis 37 Synthetic 4 Synthetic materials 11 Synthetic polymerisation 16 Terpolymer 12 Thermal conductivity 62 Thermodynamics 37 Thermoplastic elastomer 42, 24 Thermoset polymer matrices 65 Unsaturated terpene 25 Vitrimers 28, 43

Rice hulls 50

Weathering effects 20

SMC 91 SPC 74

X-R chart 144