Trends in Polymer Research [1 ed.] 9781613241998, 9781594542749

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TRENDS IN POLYMER RESEARCH

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TRENDS IN POLYMER RESEARCH

G. E. ZAIKOV ALFONSO JIMENEZ AND

YU. B. MONAKOV Copyright © 2005. Nova Science Publishers, Incorporated. All rights reserved.

EDITOR

Nova Science Publishers, Inc. New York

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CONTENTS Preface Chapter 1

Preparation and Study of Chitosan Polymer Complexes with Proteins and Hydroxylous Polymers Y.P. Ioshchenko, V.F. Kablov and G.E. Zaikov

Chapter 2

Mechanical Properties of Starch-Based Nano-Biocomposites Frédéric Chivrac, Eric Pollet and Luc Avérous

Chapter 3

Polymer Nanocomposites Reinforced with Polysaccharide Nanocrystals Alain Dufresne

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1

Chapter 5

Chapter 6

Chapter 7

Chapter 8

Preparation and Characterization of Biodegradable Plasticized Starch-G-Poly(Butylene Adipate-Co-Terephthalate)-Based (Nano)Composites J-M. Raquez, Y. Nabar, R. Narayan and P. Dubois Development and Characterization of Novel Nanobiocomposites of Thermoplastic Biopolymers and Layered Silicates M.D. Sanchez-Garcia, E. Gimenez and J.M. Lagaron43

5 17

29

37

43

Novel Polymeric Carrier for Controlled Drug Delivery Systems from Renewable Sources Catalina Duncianu, Ana Maria Oprea and Cornelia Vasile

51

Biodegradation of Composite Materials on Polymer Based in Soils O. A. Legonkova

59

The Degradation Heterochain Polymers in the Presence of Phosphorus Stаbilizers E.V. Kalugina, N.V. Gaevoy, K.Z. Gumargalieva and G.E. Zaikov

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vi Chapter 9

Chapter 10

Chapter 11

Chapter 12

Chapter 13

Chapter 14

Contents

The Generalized Synergetic Model of Glass Transition for Polymeric Materials G. V. Kozlov, M.T.Bashorov, A. K. Mikitaev and G. E. Zaikov

81

The Nanodimensional Effects in Curing Process of Epoxy Polymers in the Fractal Space G. V. Kozlov, M.T.Bashorov, A. K. Mikitaev and G. E. Zaikov

87

Biodegradation of Film Polymer Coating on the Basis of Chitosan E .I. Kulish, V. P. Volodina, V. V. Chernova, S. V. Kolesov and G .E. Zaikov Physical Modification and New Methods in Technology of Polymer Composites, Reinforced by Fibers V. N. Stoudentsov Reactivity of Ethylene-Propylene Copolymers as Function of Its Composition I.G. Kalinina, K.Z. Gumargalieva, Yu.A. Shlyapnikov and G.E. Zaikov Kinetics of Photoinitiated Copolymerization of Monofunctional Monomers Till High Conversions Yu. G. Medvedevskikh, G. I. Khovanets’, I. Yu. Yevchuk and G. E. Zaikov

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Index

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103

113

121

131

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PREFACE Polymers are substances containing a large number of structural units joined by the same type of linkage. These substances often form into a chain-like structure. Starch, cellulose, and rubber all possess polymeric properties. Today, the polymer industry has grown to be larger than the aluminum, copper and steel industries combined. Polymers already have a range of applications that far exceeds that of any other class of material available to man. Current applications extend from adhesives, coatings, foams, and packaging materials to textile and industrial fibers, elastomers, and structural plastics. Polymers are also used for most composites, electronic devices, biomedical devices, optical devices, and precursors for many newly developed high-tech ceramics. This new book presents leading-edge research in this rapidly-changing and evolving field. Chapter 1 - Chitosan polymer complexes with methylcellulose, lactoserum protein, gelatine, and polyvinyl alcohol were prepared, and conditions of their production were determined. A computer-based simulation was developed, and a procedure for the chemical absorption of metal ions in the cavities of the complexes was suggested. The conformational and geometrical properties of the complexes were defined. The properties and structure of the complexes were studied for both solutions and block state. As compared to the individual polymers these complexes possess higher flame resistance strength, sorption ability to the metal ions and organic compounds. According to the simulation polyfactor model the evaluation of thermophysical and heat protection properties of overcoats based on polymer complexes was carried out.\ Chapter 2 – The present paper is focused on the influence of dispersion clay on the mechanical properties of plasticized starch-based nano-biocomposites. This study analyzes the “structure-properties” relationships of different nanostructured systems. Either intercalated/aggregated or exfoliated nano-biocomposites were prepared by melt blending process with the incorporation of natural (MMT-Na) and organo-modified (OMMT-CS) montmorillonites, respectively. Tensile tests performed on the different nano-biocomposites clearly showed that exfoliated nano-biocomposites display enhanced mechanical properties compared to intercalated biocomposites. These results obviously highlight the great interest in using OMMT-CS to obtain starch-based nano-biocomposites with improved properties. Chapter 3 – Polysaccharide nanocrystals can be extracted from the biomass by acid hydrolysis. The resulting nanoparticles were used to process nanocomposites using a thermoplastic polymer as matrix. These materials display drastically enhanced mechanical properties, especially above the glass-rubber transition temperature of the matrix, by virtue of

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G. E. Zaikov, Alfonso Jimenez and Yu. B. Monakov

the formation of a nanocrystals network, even when the nanoparticle volume fraction was only a few percent. The formation of this rigid network, resulting from strong interactions between nanocrystals was assumed to be governed by a percolation mechanism. Chapter 4 – The authors’ report herein the preparation and characterization of layered silicate MTPS-based nanocomposites. As a ultimate objective, these layered silicate MTPS nanocomposites have been employed in the preparation of biodegradable and phasehomogeneous graft copolymers with poly(butylene adipate-co-terephathlate) (PBAT) in blown film applications. These MA functions grafted onto the starch backbone have shown to be valuable in the acid-catalyzed transesterification reactions between these both partners. The properties of the resulting (nano)composites are reported and compared with structural characterizations. Chapter 5 – This paper shows and discusses the morphology and transport properties of solvent cast biocomposites of poly(lactic acid) (PLA), polyhydroxybutyrate-co-valerate (PHBV) and polycaprolactone (PCL) with the addition of layered silicates. In this context, functional nanoadditives, such as nanoclays, with tailor-made and harmless modifications can show to have a significant potential to enhance mechanical and barrier properties of these materials and for controlled release of functional (antimicrobial, antioxidant, pharmacs, etc…). This study describes and discusses the morphological (TEM, AFM) and barrier properties (water vapour and limonene permeability) of these novel nanobicomposites of PCL, PLA, PHBV and layered silicates based on modified phyllosilicate clays. The main conclusion from this work is that organoclays can be used to enhance the barrier properties of thermoplastic biopolyesters of interest in, for instance, packaging and membrane applications. Chapter 6 – The hydrogen-bonded interpolymeric complexes (IPCs) have gained a great interest in last decades showing a similar behavior to natural systems and also because of their distinct physical and chemical properties in comparison with pure components; IPCs are considered promising materials in the development of different drug formulations. The interpolymeric complex based on a natural polymer like alginic acid (AgA) and poly (ethylene glycol) (PEG) was tested by UV-VIS spectroscopy to investigate the possibility of using it as a new matrix in the active principles delivery. The kinetic profile of the procaine hydrochloride release from 16wt%AgA/ 84wt% PEG complex at various pHs (1,14; 2,16 and 3,09) and temperatures was studied. The interpolymeric complex between AgA and PEG showed a good behavior in acidic medium and it can be considered a promising material for the release of active substances in stomach. Chapter 7 – During incubation of polymer composite materials in soils it was revealed that the structure of composite materials, unsoundness, physical and mechanical properties have changed. The replacement of microorganisms groups with each other in time in the layer bordering to the composite materials was displayed. Durability of composite materials decreased with increasing of surface and volumetric unsoundness of the samples, occurring after incubation in soils. The selectivity of microorganisms’ impact on polymer composites was disclosed. The mechanism of fracture of composite materials is suggested. Chapter 8 – The thermal stability and thermal stabilization of the heterochain polymers were investigated. Analysis of PAI, PSF, PEI degradation and stabilization has allowed an approach to be developed to aid their processing and resolve similar problems with other resins such as polyethersulfone, LCP, ets. Addition of PCA inhibits in heterochain polymers thermal oxidation at high and low temperatures.

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Preface

3

Chapter 9 – The offered generalized synergetic model allows the quantitative description of glass transition temperature for various different polymeric materials – polymer matrix of carbon plastics on the phenylone base and cross-linked epoxy polymers. The proposed model of structure formation at glass transition with regard for nanoworld synergetic conception allows to make conclusion, that the glass transition temperature, determined in dynamic conditions, is the structural bifurcation point, responding to nanoclusters degeneration. Chapter 10 – It is shown that for curing reaction in fractal space the reaction rate constant reduction at this reaction proceeding is typical. For such reaction the formation of a large number of microgels with smaller molecular weight in comparison with reaction in Euclidean space at the same conversion degree is also typical. The dimensional border between nanoreactor and nanoparticle for the considered curing reaction is obtained. Chapter 11 – The present paper deals with enzymatic biodegradation of film chitosan coatings which can be used for protecting open wounds (burning, surgical ones) and the means of their modification for extending the service life. Chapter 12 – In this work, we report main directions of study, produced by authors in Technological Institute of SSTU. Purposes of these researches are:

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• • •

realization economizing technologies of polymer composite materials (PCM), improvement technological properties of half-finished products, regulation characteristics of PCM by the help of different physical influences.

It is done minimum of theoretical bases of observing phenomena in this paper, main attention is given to practical results. Some new physical influences may be used as supplemental stages in traditional technology. Main positive effect consists in new property appearance or in increasing of strength characteristics of new materials on several tens percents in comparison with materials, produced by traditional technology. Comparatively high durability of improved reinforced by fibers materials permits to use these materials as in the manufacture of consumer goods as in more responsible application. Chapter 13 – Reaction rate of 3,6-di-tert.butyl-1,2-benzoquinone with ethylene-propylene copolymers in the media of (co)polymer melt has been studied. The rate constant of this reaction may be considered as the measure of copolymer reactivity. Chapter 14 – Regularities of kinetics of photoinitiated copolymerization till high conversions in the systems of monofunctional meth(acrylate) comonomers (hydroxyethyl meth(acrylate) (HEMA), glycidyl meth(acrylate) (GMA)) have been investigated by laser interferometry in a wide range of experimental factors (molar ratio of comonomers, photoinitiator concentration, intensity of UV-irradiation). Kinetic model of photoinitiated copolymerization of meth(acrylates) till high conversions has been proposed on the basis of conception of microheterogeneity of polymerization process.

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In: Trends in Polymer Research Editors: G.E. Zaikov, A. Jimenez and Yu.B. Monakov

ISBN 978-1-59454-274-9 © 2009 Nova Science Publishers, Inc.

Chapter 1

PREPARATION AND STUDY OF CHITOSAN POLYMER COMPLEXES WITH PROTEINS AND HYDROXYLOUS POLYMERS Y.P. Ioshchenko*, V.F. Kablov*and G.E. Zaikov** *Volzhsky Polytechnic Institute (branch) of Volgograd State Technical University 42a Engels St., Volzhsky 404121, Volgograd Region **N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Science 4 Kosygin St., Moscow 119991, Russia

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ABSTRACT Chitosan polymer complexes with methylcellulose, lactoserum protein, gelatine, and polyvinyl alcohol were prepared, and conditions of their production were determined. A computer-based simulation was developed, and a procedure for the chemical absorption of metal ions in the cavities of the complexes was suggested. The conformational and geometrical properties of the complexes were defined. The properties and structure of the complexes were studied for both solutions and block state. As compared to the individual polymers these complexes possess higher flame resistance strength, sorption ability to the metal ions and organic compounds. According to the simulation polyfactor model the evaluation of thermophysical and heat protection properties of overcoats based on polymer complexes was carried out.

INTRODUCTION One of the characteristic properties of chitosan, a promising material of the 21st century, which is a biopolymer with a number of valuable properties such as biocompatibility, biodegradability, non-toxic physiological activity, and easy access to resources needed for its production, is its pronounced capacity for intermolecular interaction as compared with other polymers [1-4]. Forming polymer complexes (or, using other terms, polymolecular or interpolyelectrolyte complexes, or hydrogen-bonded associates) with other biopolymers and polar synthetic polymers is an effective method of enhancing chitosan properties [5-11].

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Proteins, cellulose derivatives and water-soluble synthetic polymers (polyvinyl alcohol) are of particular interest in obtaining chitosan complexes. It is also important to find effective applications for these complexes and develop their production methods. It should be noted that chitosan polymolecular complexes, in their solid state in particular, have not been sufficiently studied.

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EXPERIMENTAL Chitosan (ChS) used in these experiments was obtained from freshwater branchipods Branchipus Stagbalis with a deacetylation degree of 0,97. The substance was dissolved in 2% acetic acid with a concentration of 5wt%. Edible gelatine (G), grade П-11 as per TU 9219017-179102261-01, lactoserum protein (LP) obtained in crude production, as well as industrial samples of methylcellulose (MC) TU 6-09-2344-78 and polyvinyl alcohol (PVA) GOST 10779-64 dissolved in distilled water with a concentration of 5wt% were also used. The chitosan molecular masses were determined with the use of an Ubbelhode viscometer in a solution consisting of 2% CH3COOН + 0,2 М CH3COONa in standard conditions. The gelatine, PVA, methylcellulose, and lactoserum protein molecular masses were determined with a VPZH-2 viscometer in distilled water in standard conditions using the method described in [12]. The molecular masses of chitosan, gelatine, lactoserum protein, methylcellulose, and polyvinyl alcohol were 86,9·103, 14,4·103, 36,0·103, 56,0·103, and 83,2·103 Da. respectively. Since the determination of a number of physical properties of polymers with a complex chemical constitution is difficult, the calculation of the physicochemical properties makes possible not only to accelerate this process, but also to determine the characteristics which are difficult or impossible to establish by means of an experiment. To calculate the physicochemical properties, the approved computer simulation methods suggested by Van Krevelen, Askadsky, et al. were used [13-15]. In these methods the calculations are based on the structure of the macromolecule and its functional groups The structures of the obtained chitosan and chitosan-based polymer complexes were determined by means of the Bio-Rad Win-IR spectrometer using a NaBr disk [16]. To obtain the chitosan complexes, the chitosan dissolved in the solution of acetic acid was stirred into the prepared distilled water solutions of methylcellulose, PVA, gelatine, and lactoserum protein with specified concentration ensuring the required ratio of chitosan and methylcellulose, chitosan and PVA, chitosan and gelatine, and chitosan and lactoserum protein, and then they were mixed by a magnetic stirrer during 30 minutes. Films were obtained by showering the resulting mixed solutions of chitosan and methylcellulose, chitosan and PVA, chitosan and gelatine, and chitosan and lactoserum protein onto a glass substrate. To remove the solvent, the films were dried in vacuum at 25ºС. The structure of the obtained complexes was studied by means of thin-layer chromatography using the Silyfol UV254 plates and different solvent systems, as well as by means of optical microscopy using the Mikmed-1 microscope TU 9443-077-07502348-97 [17,18]. To determine the particle size of the complexes under study, the turbidimetric method was used – KFK-2 photoelectrocalorimeter (TU 3-2.1766-82), and the turbidity spectrum method [19, 20]. The measurement of percentage by weight of the phenol and oil products in

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sewage samples was carried out by using the fluorescent method by means of the liquid analyzer Fluorat-02 TU 4321-001-20506233-94 [21]. The metal ions absorbed by the polymer complexes were determined by compleximetric titration. [22] The strain and strength parameters (strength and tensile elongation) of the polymer complexes were determined by means of the tension testing machine RT-250-M-2 as per GOST 14236-81 [23]. The film water content was measured according to GOST 11736-78 [24]. The swelling kinetics of the chitosan films was studied in different solvents (water, acetone, and oil) according to GOST 4650-80 [25]. The oxygen index of the polymolecular materials was determined according to GOST 21793-76 [26]. The coke value was based on the thermogravimetric analysis. A substance shot (0,05 – 0,5 g) was heated at a given rate in inert atmosphere up to 800-900ºC [27]. The flame propagation speed for horizontally-oriented polymolecular film samples was determined according to GOST 28157-89 [28]. To study the behavior of the polymer complexes influenced by temperature, the methods of thermal analysis (Erde and Paulik derivatograph from “MOM”) and thermomechanical analysis were used [27,29]. Complex impedance, conductivity, dielectric permeability and other electrical properties were determined by means of the digital device Immitans E7-14 TU 2.724.013 [30].

RESULTS AND DISCUSSION The properties of the fragments of chitin and chitosan structures were calculated by means of a computer simulation (Table 1). The following volumetric characteristics of the macromolecules were calculated: the average distance between molecule ends (h) which characterizes the reactivity of the macromolecule during flocculation and sorption, and the Г

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hydrodynamic volume ( VМ ) taken up by the macromolecule mass unit and determining the total size of the macromolecule [31]. The calculated values of the main macromolecule characteristics are given in Table 2. Table 1. Calculated properties of the fragments of chitin and chitosan structures Properties van der Vaals volume,

∑ ΔV , i

0

3

А

Chitin 168,1

Chitosan 132,4

1,35 78294

1,40 56272

27,8 40,5 4,5 289 570

26,6 36,6 3,3 183 615

i

Density, ρ, g/cm3 Cohesion energy,

∑ ΔE

∗ i

, J/mol

i

Cohesion energy density δ, (J/cm3) ½ Surface tension, γп, din/cm Dielectric permeability, ε Polymer glass transition temperature, Tg, K Intensive polymer destruction initial temperature, Td, K

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Y.P. Ioshchenko, V.F. Kablov and G.E. Zaikov

It was established during the analysis of the volumetric characteristics that the distance between the end groups in the macromolecules of chitosan, methylcellulose and PVA was 2 to 4 times greater than in the molecules of gelatine and lactoserum protein, which indicates a higher reactivity and activity of their end groups in the course of sorption and flocculation. Table 2. Main macromolecule characteristics Macromolecules

ММ, 10 -3

VМГ , nm3

h, 106, cm

Chitosan Methylcellulose LP Gelatine PVA

86,9 56,0 36,0 14,4 83,2

6,5 11,5 0,2 2,3 1,3

4,5 4,2 2,0 2,1 3,5

Table 3. Geometric characteristics of the polymer complexes and the metal ions

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Size of particle complexes Size of the metal ion capture cavity Size of metal ions:

80-130 nm 5-9 nm Cu2+=0,071 nm; Fe3+=0,063 nm; Zn2+=0,083 nm; Cd2+=0,092 nm; Ni2+=0,069 nm.

The hydrodynamic volume in the chitosan and methylcellulose molecules is considerably higher than the volume of the other macromolecules under study, which exhibits their more unfolded and voluminous structure with the functional groups being more readily available for intermolecular interaction. The characteristics and structures of the fragments of the chitosan-gelatine and chitosangelatine-metal polymer complexes are given in Table 3 and Figure 1. The intermolecular interactions existent in the complex are shown with dotted lines. The number of intermolecular interactions reflects the stability of the complex. Table 3 shows that the size of the cavities in the complexes is much larger than the size of the ions of the absorbed metals [32]; the chemical sorption of metal ions in the macromolecular cavities makes them more resistant to the retention of metal ions, whereas the considerable mass of the metal complex can lead to particle sedimentation. To understand the structure features in the polymer complexes it is also necessary to make a spatial representation of the macromolecules, which can be accomplished by means of computer visualization techniques (Figure 1) [14]. By measuring the particle sizes of the polymer complexes in the water medium using the light-diffusing method, the formation of associates (macromolecular nanostructures) was found. Due to their small sizes, they have a high specific surface area value and show a high degree of physicochemical activity and sorption capacity. The polymer complexes found in the solution exist in the form of a globular ball and have high mobility, and are capable of taking different conformations.

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Figure 1. Structures of the fragments of chitosan-gelatine (a) and chitosan-gelatine-metal (b) complexes.

The study of the obtained complexes using thin-layer chromatography showed the stability of the formed complexes which are not separated by time into two fractions by diffusion. The study of the polymer complexes by means of optical microscopy showed that in most cases fibrillar structures were formed. As the physicomechanical and physicochemical properties of the polymer complexes have not been studied well, the strain and strength, sorption, thermal, dielectric, thermomechanical, relaxation and burning properties were tested. The application of the polymer complexes as sorption materials can ensure highly efficient sorption of oil products, whereas the amount of chitosan and other constituents used in the complex is reduced (Table 4). The study of the sorption of metal ions showed that the restricting factor is the diffusion of metal ions into the sorbent (Figure 2) [33]. The complexes with proteins have a somewhat better sorption capacity in comparison with the other complexes and chitosan itself, which can be accounted for by the presence of a great number of active complex-forming centers due to the chelatogenic protein groups. Table 4. Level of oil product (OP) and phenol removal from sewage by means of the polymer complexes Phenol removal level, Q, %

98,9 98,7 98,5

Phenol concentration in the sample, X, mg/dm3 0,1008 0,1303 0,1162

0,163

98,3

0,1052

85,7

0,153

98,4

0,1693

77,0

OP removal level, Q, %

Chitosan ChS-MC ChS-G

OP concentration in the sample, X, mg/dm 0,147 0,155 0,162

ChS-LP ChS-PVA

Compositions

3

OP initial concentration in water was Хin=1,450 mg/dm . Phenol initial concentration in water was Хin= 0,736 mg/dm3.

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86,3 82,3 84,2

10

Y.P. Ioshchenko, V.F. Kablov and G.E. Zaikov

6 5 Cu2+ R, mmole/g

4

Cd2+ Ni2+

3

Zn2+ 2

Fe3+

1 0 ChS

ChS-MC

ChS-G

ChS-LP

ChS-PVA

Figure 2. Diagram of metal ion retention (R) by chitosan and chitosan-based complexes.

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The metal complexes have a polynuclear structure with multicenter bonding through the ligand-forming groups, which accounts for their enhanced stability. The structural properties of the polymer complexes under study lead to improved capacity to capture not only metal cations but also anions In terms of strength (Table 5) the ChS-PVA complex shows the best characteristics among the obtained complexes. Its strength is as high as that of pure chitosan, and the complex itself is less costly to obtain and has a high potential for use. The presence of hydrogen-bonded water in the structures of the complex leads to the increased number of intermolecular hydrogen bonds and ensures film elasticity [34]. Table 5. Strain and strength parameters of films Films Chitosan ChS-MC ChS-G

Tensile strength, σр, MPa 112 102 98

Tensile elongation, εр, % 31 29 27

ChS-LP

96

25

ChS-PVA

107

25

An important property of the polymer complexes is their capacity to retain bonded water; even after drying at 80ºC the amount of bonded water in the complexes equals 15-20% after the sample mass equilibrium has been achieved during drying. The study of the thermal impact on the chitosan films showed that the films are capable of retaining water (up to 8085%) for a long time, thus enhancing the strength of the materials and reducing their combustibility. This makes possible to solve the problem of fire resistance in a more effective way, not only employing the antipyretic properties of water, but also by introducing and retaining hydrophilic fire retardants, namely crystalline hydrates, etc.

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Swelling of the chitosan films was also investigated (Figure 3). It was found that their speedy water absorption is due to the chemical affinity of the sorbate and the sorbent on the one hand, and the relatively low crystallinity of the films on the other. Swelling of all films in acetone and oil is insignificant: ChS-PVA>ChS-G.

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PVA

ChS

Т, 0С

Figure 5. Results of the thermal analysis of the samples under study: chitosan, PVA, and ChSPVA.

Using the thermomechanical method to study the materials properties, it was established that the complexes are subject of considerable strain with the rise of temperature. This is more Trends in Polymer Research, Nova Science Publishers, Incorporated, 2005. ProQuest Ebook Central,

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Y.P. Ioshchenko, V.F. Kablov and G.E. Zaikov

characteristic of the ChS-MC complex. In the given set, the ChS-PVA complex was observed to be the least given to strain. It can be accounted for by the additional structure changes caused by the constituent PVA and the presence of the interpenetrating grids that give tightness to the complex carcass. By means of dielectric measurements, it was established that the relaxation properties of the complexes differ for different frequencies. This indicates that the complex consists of mobile kinetic blocks. Mobility decreased with the increase of frequency for all complexes. Within the interval 100 to 1000 Hz a sharp drop in dielectric permeability occured. Just like in the case of relaxation time, the ChS-PVA complex exhibited the highest dielectric permeability. (Figure 6)

ε 400 350 300 250 200 150

ChS-PVA ChS-G ChS-LP ChS-MC

100 50 0 0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

lg ω

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Figure 6. Dependence of dielectric permeability ε on frequency ω

The advantages of the sorbents created on the basis of polymer complexes are the accessibility of resources, possible use of secondary materials, use of non-toxic natural compounds and safe technology of their production, non-toxicity, environmental safety, trouble-free disposal of materials, biodegradability, possibility to clean the soil contaminated with black oil and eliminate spillages on solid surfaces. The testing of the chitosan and lactoserum cream was carried out. The experiments showed that the resulting ‘bio-cream’ had good recovery and moisture retaining capabilities and it was skin-friendly. The technical outcome of the research in the area of disposal and recycling of lactoserum with the use of the ChS-MC complex was the protein concentrate obtained on the basis of this complex. The chitosan-protein complex was used as one of the components in the ration of fish, livestock and fowls. The use of 1-4% of the lactoserum protein concentrate resulted in increase of live weight of the animals (up to 13%) and improved survival rate of chicken (up to 99%). This is due to the high content of proteins and biologically active substances in the concentrate. [36,37]

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Preparation and Study of Chitosan Polymer Complexes with Proteins …

15

CONCLUSIONS Chitosan polymer complexes were obtained with synthetic and biological polymers – polyvinyl alcohol, methylcellulose, lactoserum proteins, and gelatine. Their structure and properties were studied in solutions and block state. It was shown that the complexes under study had improved fire protection properties and capability to absorb metal ions and organic compounds. A computer simulation of conformational and geometrical characteristics of these complexes was carried out. It was shown that the process of absorbing metal ions and organic substances occured in the macromolecular cavities of the polymer complexes. Behavioral patterns of the obtained materials were determined in different operational conditions, which allow obtaining polymer sorbents, coatings and films with improved efficiency. The films obtained from the polymer complexes were capable of retaining water for a long time (up to 85%), with their strength characteristics being equal to those of pure chitosan and combustibility reduced 1,3 times. These materials can be used as fire-protection and heatresistant coatings, particularly if unusually strict toxicity requirements are to be observed. Laboratory and industrial tests of the obtained materials were carried out. Thus, the materials obtained can be used as sorbents for removing phenols, oil products, metal ions, and toxic organic substances from water solutions, and proteins from lactoserum, for obtaining fire- and heat-resistant coatings, membranes, films and additives to fodder for fish and fowls to increase survivability and weight. The approbation of the chitosan and protein-based complexes was carried out to obtain creams and skin protection means. The advantages of these materials are accessibility of raw materials, non-toxicity, biodegradability, and ecological safety.

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REFERENCES [1] [2]

Vikhoreva, G.A. Gorbacheva, I.N. Galbreikh, L.S. Chemical fibers 5 36-45 (1994) Chitin and Chitosan: Production, Properties and Application Edited by Skryabin, K.G. Vikhoreva, G.A. Varlamova, V.P. Moscow: Nauka, 2002. 368 p. [3] Plisko, E.A. Nudga, L.N. Danilov, S.N. Advances in Chemistry. 46 1470-1487, (1977). [4] Galbreikh, L.S. Sorovsky Educational Journal. 7 51-56 (2001). [5] Kasaikin, V.A. Kharenko, O.A. Kharenko, A.V. High-Molecular Compounds. B Series. 21 84-85 (1979). [6] Kabanov, V.A. Advances in Chemistry. 74 5-23 (2005). [7] Kovalyova. O.Y. Hydrophobic Complexes of Cation Polyelectrolytes and Amphophilic Anions. Formation Regularities and Properties // MSc Thesis, Volgograd. 2005. 130 pgs. [8] Mukhina, V.R. et al. High-Molecular Compounds. –Series A. 43 1797-1804 (2001). [9] Nudga, L.A. et al. High-Molecular Compounds. 41 1786-1792 (1999) [10] Zezin, A.B. Rogachyova, V.B. Advances in Chemistry and Physics of Polymers. – Moscow: Chemistry, 1973. – p. 3-30. [11] Tager, A.A. Physicochemistry of Polymers. – Moscow: Chemistry, 1983 – 544 p. [12] Vasiliev, V.P. Analytical Chemistry. Physicochemical Methods of Analysis. – Moscow: Drofa, 2004. – 383 p.

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Y.P. Ioshchenko, V.F. Kablov and G.E. Zaikov

[13] Askadsky, A.A. Kondrashchenko, V.I.. Computer-based Polymer Material Study. Vol. 1. Atomic and Molecular Level. – Moscow: World of Science, 1999. – 544 p. [14] Solovyov, O.V. Solovyov, M.M. Computer Chemistry – Moscow: Solon-Press, 2005. – 536 p. [15] Vershinin, V.I. Derendyayev, B.G. Lebedev, K.S. Computer Identification of Organic Compounds. – Moscow: Akademkniga, 2002. – 197 p. [16] Sannan T., Kurita K., Iwakura Y. Polymer 19 1275 (1978) [17] Ahrem, A.A. Kuznetsova, A.I. Thin-layer Chromatography. – Moscow: Nauka, 1984. – 178 p. [18] ТU 9443-077-07502348-97. Methodology for Observing Microscopic Objects and their Permolecular Structures Using the Mikmed-1 Microscope. [19] GOST 15875-80. Plastic. Methods of Determining Transmission Factor and Turbidity. [20] Babko, A.K. Pilipenko, A.G. Photometric Analysis. – Moscow: Khimia, 1978. – 386 p. [21] TU 4321-001-20506233. Methodology for Conducting Measurements of Phenol and Oil Product Percentage by Weight in Sewage Samples based on the Liquid Analyzer Fluorat-02. [22] Korostylev, P.P. Photometric and Complexometric Analysis in Metallurgy. Moscow: Metallurgia, 1984. – 272 p. [23] GOST 14236-81. Polymer Films. Tensile Testing Methodology. [24] GOST 11736-78. Plastic. Water Content Determination Method. [25] GOST 4650-80. Plastic. Water Absorption Determination Methods. [26] GOST 21793-76. Plastic. Oxygen Index Determination Method. [27] Averko-Antonovich, I.Y. Bikmullin, R.T. Research Methods of Polymer Structure and Properties KGTU: Kazan, 2002, – 604 p. [28] GOST 28157-89. Plastic. Fire Resistance Determination Methods. [29] Shur, A.M. High Molecular Compounds. Ed. 2 (revised). Textbook for Universities. – Moscow: Vyschaya Shkola, 1971 – 520 p. [30] TU 2.724.013. Procedure for Measuring Complex Impedances, Conductivity, Dielectric Permeability, and other Electrical Characteristics with the Digital device «Immitans E7=14». [31] Shevchenko, T.V. et al. Chemical Industry Today. 11 38-41 (2004) [32] Chemical Encyclopedia Edited by Knunyants I.L. et al. 5 volumes. Moscow: «Soviet Encylopedia», 1988. – 623 p. [33] Kablov, V.F. Ioshchenko, Y.P. Kondrutsky, D.A. Vestnik MITHT, 1 49-53 (2006) [34] Kablov, V.F. Ioshchenko, Y.P. Kondrutsky, D.A New High Technologies. 4 87-88 (2004) [35] Kablov, V.F. Resin and Rubber. 1 8-10 (1997). [36] Ioshchenko, Y.P. MSc Thesis Volgograd, 2006.–119 p. [37] Kablov, V.F. Ioshchenko, Y.P. Kondrutsky, D.A. Proceedings of the II Interregional Workshop «Interaction of Research Divisions of Industrial Companies and Universities to Increase Production Efficiency» VSTU, Volgograd, 2005. p. 116-118.

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Chapter 2

MECHANICAL PROPERTIES OF STARCH-BASED NANO-BIOCOMPOSITES Frédéric Chivrac, Eric Pollet and Luc Avérous1 ECPM-LIPHT (UMR CNRS 7165), Université Louis Pasteur, 25 Rue Becquerel, F67087 Strasbourg Cedex 2, France

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ABSTRACT The present paper is focused on the influence of dispersion clay on the mechanical properties of plasticized starch-based nano-biocomposites. This study analyzes the “structure-properties” relationships of different nanostructured systems. Either intercalated/aggregated or exfoliated nano-biocomposites were prepared by melt blending process with the incorporation of natural (MMT-Na) and organo-modified (OMMT-CS) montmorillonites, respectively. Tensile tests performed on the different nanobiocomposites clearly showed that exfoliated nano-biocomposites display enhanced mechanical properties compared to intercalated biocomposites. These results obviously highlight the great interest in using OMMT-CS to obtain starch-based nanobiocomposites with improved properties.

Keywords. Nano-biocomposites, plasticized starch, layered silicates, montmorillonite, exfoliation

INTRODUCTION Sustainable development policies combined with the increasing awareness concerning the plastic waste issue require the development of new environmentally friendly materials [1]. Biodegradable polymers (biopolymers) based plastics are an elegant and innovative answer to replace conventional non-degradable petroleum-based products (Figure 1). Nevertheless, even if the potential of these biopolymers and more particularly those obtained from agro-resources 1

E-Mail: [email protected].

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has been pointed out, until now, they are not extensively used in disposable applications, like packaging. Among all the agro-polymers, starch which is an abundant inherently biodegradable and renewable material is one of the most interesting answers to develop a low cost “green plastic”. Several authors have already demonstrated the possibility to transform native starch into plasticized resin-like products under destructuring and plasticization conditions (Figure 2) [2,3]. Nevertheless, the water sensitivity and brittleness of plasticized starch have to be overcome to obtain suitable biodegradable materials. The basic approach to answer to these weaknesses consists in the elaboration of starch blended with various biopolyesters (polylactide, polycaprolactone, polyesteramide…) [4-7] or starch composites with, for instance, cellulose-based fibers [8]. A new and innovative answer to obtain starch-based plastics could be the nanofillers incorporation into the starch matrix and thus the elaboration of nano-biocomposites (biodegradable nanocomposites) [9]. Depending on the geometry, size and nature of the nanofiller, new and/or improved properties (gas barrier, mechanical stiffness, transparency, thermal stability…) could be obtained [10-13] due to the large interface area resulting in high interactions between the polymer (matrix) and the dispersed nanofillers [14]. Up to now, the most intensive researches are focused on layered silicates, and especially on montmorillonites (MMT), as the reinforcing phase due to their availability, versatility and respectability towards the environment [15]. This clay is a crystalline 2:1 layered silicate mineral with a central alumina octahedral sheet sandwiched between two silica tetrahedral sheets (Figure 3) .

Figure 1. Biopolymer sustainable development

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Figure 2. Scheme of starch extrusion process.

Figure 3. Montmorillonite structure.

The isomorphic substitutions found inside these clay platelets generate a negative charge naturally counterbalanced by inorganic cations (Na+, Ca2+…) located into the inter-layer spacing leading to a hydrophilic character. To promote polymer/silicate compatibility, an ion-exchange reaction of intergallery inorganic cations by organic surfactants is often carried out. Depending on the process conditions and on the polymer/nanofiller affinity, the layered silicates dispersed into the

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Frédéric Chivrac, Eric Pollet and Luc Avérous

polymer matrix can be intercalated and/or exfoliated (Figure 4) [16]. Compared to intercalated structures, exfoliated systems show individually delaminated layers (platelets) which are fully dispersed in the matrix. Best performances are commonly observed with the exfoliated structures where we can find the highest interfacial area [17]. To reach exfoliation state, different nanofillers and elaboration protocols have been tested. It has been clearly demonstrated that the incorporation of organo-modified and rather hydrophobic nanofillers, such as Cloisite 15A® or Cloisite 30B®, leads to the formation of conventional micro-biocomposites as evidenced by the constant values of the baseal interlayer spacing (d001) measured by X-ray diffraction [18,19]. Besides, natural montmorillonite (MMT-Na) has been tested into a plasticized starch matrix. Such a system leads to the formation of an intercalated structure with a corresponding d001 increase from 12 to 18Å [18-25]. To explain this higher dispersion, authors assume that MMT-Na and starch have together a high affinity thanks to the hydrophilic nature of both compounds. This statement is on agreement with some tensile test results since the WS/MMT-Na stiffness values were higher than those of the WS/hydrophobic MMT and since the better the nanodispersion, the higher the stiffness [16]. Nevertheless, this specific d-spacing value (d001=18Å) is well reported into the literature and attributed to glycerol intercalation [21,26]. Thus, the d001 light increases which are observed for the WS/MMT-Na may suggest an intercalated structure with only a low exfoliation extent. Dean et al. elaborated starch nano-biocomposites without any plasticizer [27]. The corresponding results showed a homogeneous dispersion with an exfoliated structure and an overall enhancement of the mechanical properties. Thus, MMT-Na seemed suitable to achieve exfoliation in starch-based nano-biocomposites. Consequently, the low extent of exfoliation achieved in plasticized starch nano-biocomposites indicated a strong influence of glycerol on the exfoliation process and thus on the resulting morphology and mechanical properties. This result was in agreement with some studies which highlighted the formation of hydrogen bonds and thus of intense interactions between glycerol and MMT platelets [21,28,29]. To overcome the limitations induced by this plasticizer, Huang et al. replaced glycerol by urea or urea/formamide mixture [30-33].

Figure 4. Morphologies of polymer/clay nanocomposites: (a) Microcomposite, (b) Intercalated nanocomposite and (c) Exfoliated nanocomposite. Trends in Polymer Research, Nova Science Publishers, Incorporated, 2005. ProQuest Ebook Central,

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To obtain a better affinity with this new plasticizer, the MMT was organo-modified with activated ethanolamine (EMMT). Morphological analyses demonstrated that an intercalated structure had been achieved in the case of urea-EMMT starch nano-biocomposite. Moreover, the urea/formamide-EMMT starch nano-biocomposites displayed an exfoliated structure even at high nanofiller content. Nevertheless these compounds are eco-toxic and cannot be used to elaborate true “green” plastics. Finally, Kampeerappun et al. focused their study on the use of chitosan as compatibilizer to promote the MMT platelets exfoliation [34]. They demonstrated that even if the chitosan used was too large to be intercalated into the MMT interlayer spacing, this carbohydrate acted as a compatibilizing agent leading to some clay aggregates and improved mechanical properties. In a previous work, we used a co-surfactant to promote the nanofiller exfoliation into the plasticized starch matrix [35]. Thus, MMT clay platelets had been organo-modified leading to the elaboration of OMMT-CS nanofiller. Figure 5 displays typical TEM micrographs of this nano-biocomposites. At low magnification, a relatively good dispersion without large aggregates was observed (Figure 5a). At higher magnification, the TEM pictures showed almost individually dispersed layers (tactoïds with less than 5-10 platelets) attesting an exfoliated morphology (Figure 5b). We propose herein to complete and extent this previous work with the study of starch nano-biocomposites mechanical properties as a function of the dispersion/morphology state. Thus, two different nano-biocomposites are elaborated; one with OMMT-CS leading to an exfoliated nano-biocomposites and another one with MMT-Na leading to micro-biocomposites.

Figure 5. TEM pictures of WS/OMMT-CS 3wt% nano-biocomposites.

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EXPERIMENTAL Materials Wheat starch (WS) was kindly supplied by Roquette (France). The amylose and amylopectin contents are, respectively, 23 and 77wt%. Residual protein content is less than 1wt%. The glycerol used was kindly supplied by the Société Française des Savons (France) and is a 99.5% purity product. The Dellite® LVF sodium montmorillonite (MMT-Na) was kindly supplied by Laviosa Chimica Mineraria S.p.A. (Italy) and has a cationic exchange capacity (CEC) of 1050 µeq/g.

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Elaboration The MMT-Na organo-modification was carried out with a co-surfactant by exfoliation/adsorption technique (Figure 6). MMT-Na was introduced in a large excess of distilled water and dispersed in ultra-sonic bath at 60°C for 4h. In parallel, the co-surfactant was solubilized in ultra-sonic bath at 60°C for 1h. Then, both solutions were pooled together and placed for 1 day at 60°C in ultra-sonic bath. The solution was filtered and washed with 1L of distilled water at 60°C to remove the salt formed (NaCl) during the co-surfactant adsorption. Then, the filtrate was lyophilized to obtain the organo-modified clay (OMMTCS). The formulation used in this study contained 23wt% of glycerol, 23wt% of water and 54wt% of native starch. Plasticized starch granules were prepared according to the dry-blend procedure which was described elsewhere [6]. To obtain nano-biocomposites, 3 and 6wt% of MMT (compared to weight of starch and glycerol) were added into the dry-blend. The starch nano-biocomposites were prepared by mechanical kneading with a counter-rotating internal batch mixer, Rheocord 9000 (Haake, USA), at 70°C for 20 min with a rotor speed of 150 rpm. A pre-weighted amount of MMT (0.46 to 2.86g in inorganics, depending on the formulation) was first dispersed in 13.5ml of water to obtain swollen clay. Then, the dry blend and the swollen clay were introduced together into the mixing chamber. After melt processing, moulded specimens and films were obtained by hot-pressing at 110°C applying 20 MPa pressure for 15 min.

Figure 6. Schematic representation of the MMT-Na organo-modification by exfoliation/adsorption technique.

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Nano-biocomposite samples were then equilibrated at 57%RH for 1 month, before characterization. All along this paper, the obtained samples are quoted WS/XXX y% where XXX stands for the type of (organo)clay and y for the weight percentage of clay inorganic fraction.

Characterization Tensile tests were carried out with an Instron tensile testing machine (model 4204, USA), on dumbbell-shaped specimens; at 25°C with a constant deformation rate of 5 mm/min. For each formulation five samples were tested. The non-linear mechanical behaviour of the different samples was determined through different parameters. The true strain (ε) is given by Equation 1 where L and L0 are the test piece length during the experiment and at zero time, respectively.

ε = ln(

L ) L0

(1)

The nominal stress was determined by Equation 2, where F is the applied load and S0 is the initial cross-sectional area. The true stress (σ) was given by Equation 3, where F is the applied load and S is the cross-sectional area. S was estimated assuming that the total volume of the sample remained constant, according to Equation 4.

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=

σ=

F S0

(2)

F S

S = S0 *

(3)

L0 L

(4)

Young modulus (E) was determined and calculated from the slope of the low strain region of the tensile curve (σ = ε = 0). The energy at break values are calculated from the area of the tensile curves obtained for each sample.

RESULTS AND DISCUSSION Figures 7 and 8 present, respectively, the variations of the Young modulus and the elongation at break against clay loading for plasticized wheat starch and its nanobiocomposites after one month of stabilization at 57%RH. An increase in stiffness correlated with the inorganic content was observed for both (MMT-Na and OMMT-CS) nano-

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Frédéric Chivrac, Eric Pollet and Luc Avérous

biocomposites. This increase was more pronounced for exfoliated nano-biocomposites based on OMMT-CS. This differentiation can be explained by the interface quality and the interactions between the exfoliated OMMT and the starch chains. A decrease in the elongation at break correlated with the clay content was observed for nano-biocomposites elaborated with MMT-Na. This last trend is commonly observed in the case of conventional micro-composites [14]. Thus, these analyses showed that MMT-Na leads to a poor dispersion with a high extent of aggregation into the plasticized starch matrix. On the contrary, no variation of the elongation at break value was observed for nano-biocomposites based on OMMT-CS attesting for a better dispersion. Figures 9 and 10 present the variations of the stress and energy at break, respectively, versus clay contents for neat plasticized wheat starch and two different nano-biocomposites. An increase in the stress at break value was observed for WS/MMT-Na 3wt% nanobiocomposite compared to the pristine matrix. This increase was linked to the higher stiffness of the nano-biocomposite compared to the neat matrix. But a decrease was observed at higher clay content. Moreover, whatever the amount of filler, a strong decrease in the energy at break was obtained for these nano-biocomposites. These decreases were correlated with the lower elongation at break of these samples linked to the high extent of aggregation with MMT-Na. Thus, the incorporation of MMT-Na strongly embrittled the corresponding materials. On the contrary, WS/OMMT-CS samples displayed an increase in the stress and energy at break correlated with the increase in clay content. These increases were linked to the exfoliated morphology which increased the stiffness without affecting the elongation at break. To conclude, the use of co-surfactant as organo-modifier of the MMT is a powerful way to achieve exfoliation in starch-based nano-biocomposites and thus to enhance the overall mechanical properties of these nanomaterials.

45 Young Modulus (MPa)

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50

40

35

30

25

WS

WS/MMT-Na

WS/OMMT-CS

2

4

20 -1

0

1

3

5

6

7

Clay Inorganic Content (wt%)

Figure 7. Variations of the Young modulus vs. clay content for WS/MMT-Na and WS/OMMT-CS after one month at 57%RH.

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Mechanical Properties of Starch-Based Nano-Biocomposites

40

Elongation at break (%)

35

30

25

20

15

WS

WS/MMT-Na

WS/OMMT-CS

1

2

4

10 -1

0

3

5

6

7

Clay Inorganic Content (wt%)

Figure 8. Variations of the elongation at break vs. clay content for WS/MMT-Na and WS/OMMTCS after one month at 57%RH.

2.5 Stress at break (MPa)

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3

2

1.5

1

0.5

WS

WS/MMT-Na

WS/OMMT-CS

0 -1

0

1

2

3

4

5

6

7

Clay Inorganic Content (wt%)

Figure 9. Variations of the stress at break vs. clay content for WS/MMT-Na and WS/OMMT-CS after one month at 57%RH. Trends in Polymer Research, Nova Science Publishers, Incorporated, 2005. ProQuest Ebook Central,

26

Frédéric Chivrac, Eric Pollet and Luc Avérous

1.2

Energy at break (M J/m 3)

1

0.8

0.6

0.4

WS

0.2

WS/MMT-Na

WS/OMMT-CS

2

4

0 -1

0

1

3

5

6

7

Clay Inorganic Content (wt%)

Figure 10. Variations of the energy at break vs. clay content for WS/MMT-Na and WS/OMMTCS after one month at 57%RH.

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CONCLUSION Mechanical properties of nano-biocomposites based on plasticized starch were investigated as a function of the nanofiller morphology/dispersion. Aggregated/intercalated and exfoliated nano-biocomposites were elaborated with MMT-Na and OMMT-CS, respectively. A huge increase in the mechanical properties was observed for WS/OMMT-CS because of the quasi-absence of aggregated nanofillers. The exfoliated structure leads to a higher stiffness, stress at break and energy at break without decreasing the elongation at break. This study which analyzes the “structure-properties” relationships has shown the good correlation we can obtain between the nanostructures of the different nano-biocomposites and the macroscopic mechanical properties.

ACKNOWLEDGEMENTS Authors thank the GMI-IPCMS (Groupe des matériaux inorganiques - Institut de Physique et Chimie des Matériaux et du Solide) and the ICS (Institut Charles Sadron) in Strasbourg (France) for their technical support. Thanks are also extended to Roquette (France) for the starch supply.

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REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

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Huang, M. Yu, J. Ma, X., Acta Polymerica Sinica:6 862-867 (2005). Huang, M.F. Yu, J.G. Ma, X.F., Chinese Chemical Letters, 16:4 561-564 (2005). Huang, M.F. Yu, J.G. Ma, X.F. Jin, P., Polymer, 46:9 3157-3162 (2005). Huang, M. Yu, J. Ma, X., Carbohydrate Polymers, 63:3 393-399 (2006). Kampeerapappun, P. Aht-ong, D. Pentrakoon, D. Srikulkit, K. Carbohydrate Polymers, 67:2 155-163 (2007). [35] Chivrac, F. Pollet, E. Averous, L., Biomacromolecules, Submitted.

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[30] [31] [32] [33] [34]

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Chapter 3

POLYMER NANOCOMPOSITES REINFORCED WITH POLYSACCHARIDE NANOCRYSTALS Alain Dufresne1 Ecole Française de Papeterie et des Industries Graphiques, Institut National Polytechnique de Grenoble (EFPG-INPG) BP65, 38402 Saint-Martin d’Hères Cedex, France

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ABSTRACT Polysaccharide nanocrystals can be extracted from the biomass by acid hydrolysis. The resulting nanoparticles were used to process nanocomposites using a thermoplastic polymer as matrix. These materials display drastically enhanced mechanical properties, especially above the glass-rubber transition temperature of the matrix, by virtue of the formation of a nanocrystals network, even when the nanoparticle volume fraction was only a few percent. The formation of this rigid network, resulting from strong interactions between nanocrystals was assumed to be governed by a percolation mechanism.

Keywords: polymer, nanocomposites, biocomposites

INTRODUCTION Conceptually, nanocomposites refer to multiphase materials where at least one of the constituent phases has one dimension less than 100 nm. This field has attracted the attention, scrutiny and imagination of both scientist and industrial communities in recent years. Behind the push for nanocomposites, a large window of opportunity has opened to overcome the limitations of traditional micrometer-scale composites. Research in this scope is literally exploding because of the intellectual appeal of building blocks on the nanometer scale and because the technical innovations permit to design and create new materials and structures

1

[email protected].

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Alain Dufresne

with unprecedented flexibility, improvements in their physical properties and significant industrial impact. A possible source of inspiration is the nature and its wonderful nanocomposite structures. Among biologically inspired nanocomposites, polysaccharides are probably among the most promising sources for the production of nanoparticles. These abundant biorenewable raw materials are increasingly used in non-food applications. They can also be used for the preparation of crystalline nanoparticles with different geometrical characteristics providing a wide range of potential nanoparticles properties. Huge quantities of these nanoparticles are potentially available, often as waste products from agriculture. Moreover, polysaccharide surfaces provide potential for significant surface modification using well-established carbohydrate chemistry. The latter allows tailoring the surface functionality of the nanoparticles. In this field, scientific and technological challenges to take up are tremendous.

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POLYSACCHARIDE NANOCRYSTALS Stable aqueous suspensions of polysaccharide nanocrystals can be prepared by acid hydrolysis of the biomass. The designation "whiskers" is used to designate elongated rod-like nanoparticles. A recent review reported the properties and application in nanocomposite field of cellulosic whiskers [1]. The procedure for the preparation of such colloidal aqueous suspensions consists in first submitting the biomass to a bleaching treatment with NaOH in order to purify cellulose or chitin by removing other constituents. The bleached material is then disintegrated in water, and the resulting suspension is submitted to a hydrolysis treatment with acid. This transformation consists of the disruption of amorphous regions surrounding and embedded within cellulose or chitin microfibrils while leaving the microcrystalline segments intact. The resulting suspension is subsequently diluted with water and washed by successive centrifugations. Dialysis against distilled water is then performed to remove free acid in the dispersion. Complete dispersion of the whiskers is obtained by a sonication step. The constitutive nanocrystals occur as elongated rod-like particles or whiskers. The typical geometrical characteristics for crystallites derived from different species and reported in the literature are collected in Table 1 [2-16]. The length is generally of the order of few hundreds nanometers and the width is of the order of few nanometers. The aspect ratio of these whiskers is defined as the ratio of the length to the width. It was shown that these suspensions did not flocculate as a consequence of sulfate groups created during the acid hydrolysis step. Aqueous suspensions of starch nanocrystals can be prepared by acid hydrolysis of native starch granules. Response surface methodology was used [17] to optimize the preparation of starch nanocrystals. Waxy maize starch nanocrystals consist of 5-7 nm thick platelet-like particles with a length ranging from 20 to 40 nm and a width in the range 15-30 nm. The detailed investigation on the structure of these platelet-like nanoparticles was reported [18].

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Table 1. Geometrical characteristics of polysaccharide nanocrystals from various sources: length (L) and diameter (D) of rod-like particles obtained from cellulose or chitin Nature Cellulose

Chitin

Source Algal (Valonia) Bacterial Cladophora Cotton Cottonseed linter MCC Sisal Sugar beet pulp Tunicin Wheat straw Wood Crab shell Riftia tubes Shrimp Squid pen

L (nm) > 1000 100-several 1000 100-300 170-490 150-300 100-500 210 100-several 1000 150-300 100-300 80-600 500-10000 50-300 150-800

D (nm) 10-20 5-10 × 30-50 20 × 20 5-10 40-60 3-7 3-5 5 10-20 5 3-5 8-50 18 5-70 10

Ref. [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]

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PROCESSING OF NANOCOMPOSITES Because of the high stability of aqueous polysaccharide nanocrystals dispersions, water is the preferred processing medium. Therefore, this restricts the choice of the matrix to hydrosoluble polymers. The use of aqueous dispersed polymers, i.e. latexes, is a first alternative, which allows the use of hydrophobic polymers as matrix and ensure a good dispersion level of the filler indispensable for homogenous composites processing. The possibility of dispersing polysaccharide nanocrystals in non-aqueous media is a second alternative and it opens other possibilities for nanocomposites processing. Composite materials are generally obtained by casting and evaporation. The dispersion of polysaccharide nanocrystals in non-polar media can be obtained by chemically modifying their surface.

MECHANICAL PROPERTIES Nanoscale dimensions and impressive mechanical properties make polysaccharide nanocrystals, particularly when occurring as high aspect ratio rod-like nanoparticles, ideal candidates to improve the mechanical properties of the host material. These properties are profitably exploited by Mother Nature. In the ten recent years, a great interest was focused on investigating the use of polysaccharide nanocrystals, especially cellulose whiskers, as a reinforcing phase in a polymeric matrix, evaluating the mechanical properties of the resulting composites. The first demonstration of the reinforcing effect of cellulose whiskers was reported for poly(S-co-BuA) reinforced with tunicin whiskers [10]. The authors measured a spectacular

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improvement in the storage modulus after adding the filler even at low content into the host polymer. This increase was especially significant above the glass-rubber transition temperature of the thermoplastic matrix because of its poor mechanical properties in this temperature range. For instance, the rubbery modulus of the composite reinforced with 6 wt% tunicin whiskers was more than two orders of magnitude higher than the one of the unfilled matrix. Moreover, the introduction of 3 wt% or more cellulosic whiskers provides an outstanding thermal stability of the matrix modulus up to the temperature at which cellulose starts to degrade (500K). The outstanding properties observed for these systems were ascribed to a mechanical percolation phenomenon [10]. A good agreement between experimental and predicted data was reported when using the series-parallel model of Takayanagi modified to include a percolation approach. It was suspected that all the stiffness of the material was due to infinite aggregates of cellulose whiskers. Above the percolation threshold the cellulosic nanoparticles can connect and form a tri-dimensional continuous pathway through the nanocomposite film. For rod-like particles such as tunicin whiskers with an aspect ratio of 67, the percolation threshold is close to 1 vol% [20]. The formation of this cellulose network was supposed to result from strong interactions between whiskers, like hydrogen bonds [21]. This phenomenon is similar to the high mechanical properties observed for a paper sheet, which result from the hydrogen-bonding forces that hold the percolating network of fibers. This mechanical percolation effect allows explaining both the high reinforcing effect and the thermal stabilization of the composite modulus for evaporated films. Any factor that affects the formation of the percolating whiskers network or interferes with it changes the mechanical performances of the composite [22]. Three main parameters were reported to affect the mechanical properties of such materials: the morphology and dimensions of the nanoparticles, the processing method, and the microstructure of the matrix and matrix/filler interactions. Cellulose and chitin nanocrystals occur as rod-like nanoparticles in opposite to starch nanocrystals, which consist of nanometer scale platelet-like particles. For rod-like particles, the geometrical aspect ratio is of course an important factor since it determines the percolation threshold value. This factor is linked to the source of cellulose or chitin and whiskers preparation conditions. Fillers with high aspect ratio give the best reinforcing effect. For instance, the rubbery storage tensile modulus was systematically lower for wheat straw whiskers/poly(S-co-BuA) composites than for tunicin whiskers based materials [21]. The following relation was found between the percolation threshold (vRc) and aspect ratio of rodlike particles:

v Rc =

0.7 L/d

(1)

The processing method governs the possible formation of a continuous nanocrystals network and then the final properties of the nanocomposite material. Slow processes such as casting/evaporation were reported to give the highest mechanical performance materials compared to freeze-drying/molding and freeze-drying/extruding/molding techniques. It was ascribed to the probable orientation of these rod-like nanoparticles during film processing due to shear stresses induced by freeze-drying/molding or extrusion techniques.

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During slow water evaporation, because of Brownian motions in the suspension or solution (whose viscosity remains low, up to the end of the process when the latex particle or polymer concentration becomes very high), the rearrangement of the nanoparticles is possible. They have time enough to interact and connect to form a percolating network which is the basis of their reinforcing effect. The resulting structure is completely relaxed and direct contacts between nanocrystals are then created. Conversely, during the freeze-drying/hotpressing process, the nanoparticle arrangement in the suspension is first frozen, and then, during the hot-pressing stage, because of the polymer melt viscosity, the particle rearrangements are strongly limited. Thus, in this case, contacts are made through a certain amount of polymer matrix. However, although the freeze-drying/hot-pressing process limits the possibility of creation of hydrogen bonds it is expected that for high polysaccharide nanoparticles content some bonds may evenly be created. When using a polymeric matrix in latex form, the particle sizes seem to play a predominant role [22]. Larger latex particle size results in higher mechanical properties. Indeed, the polymeric particles act as impenetrable domains to polysaccharide nanoparticles during the film formation due to their high viscosity. Increasing latex particle size leads to an increase of the excluded volume and these geometrical constraints seem to affect the whiskers network formation. The microstructure of the matrix and the resulting competition between matrix/filler and filler/filler interactions also affect the mechanical behavior of the polysaccharide nanocrystals reinforced nanocomposites. Classical composite science tends to privilege the former as a fundamental condition for optimal performance. In polysaccharide nanocrystals based composite materials the opposite trend is generally observed when the materials are processed via casting/evaporation method. Increasing the affinity between the polysaccharide filler and the host matrix, decreasing the mechanical performances is observed. This unusual behavior is ascribed to the originality of the reinforcing phenomenon of polysaccharide nanocrystals resulting from the formation of a percolating network due to hydrogen bonding forces. A higher reinforcing effect for unmodified cellulose whiskers than for trimethylsilylated whiskers was reported [3]. Apart the fact that 18% of the weight of the silylated crystals was due to the silyl groups, they attributed this difference to restricted filler/filler interactions. Similar results and loss of mechanical properties were reported for natural rubber based nanocomposites reinforced with both unmodified and surface chemically modified chitin whiskers [23] and starch nanocrystals [24]. A transcrystallization phenomenon was reported for semicrystalline PHO on cellulose whiskers and it resulted in a remarkable decrease of the mechanical properties (especially above the melting temperature of the matrix) when compared to fully amorphous PHO [25]. In these systems, the filler/matrix interactions and distance away from the surface at which the molecular mobility of the amorphous PHO phase is restricted were quantified using a physical model predicting the mechanical loss angle [26]. Similar transcrystallization was reported for plasticized starch reinforced with cellulose whiskers [27]. This strong loss of performance demonstrates the event of outstanding importance of the filler/filler interactions to ensure the mechanical stiffness and thermal stability of these composites. When using unhydrolyzed cellulose microfibrils extracted from potato pulp rather than cellulose nanocrystals to reinforce glycerol plasticized thermoplastic starch, a completely different mechanical behavior was reported [28,29], resulting in a significant reinforcing effect of unhydrolyzed microfibrils. It was suspected that tangling effect contributed to this high

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Alain Dufresne

reinforcing effect [27]. However, for POE-based nanocomposites the formation of the percolating cellulose network is not altered by the crystallization of the matrix and filler/POE interactions [30-34].

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CONCLUSION Polysaccharide nanocrystals are building blocks biosynthesized to provide structural properties to living organisms. They can be isolated from the biomass through acid hydrolysis with concentrated mineral acids under strictly controlled conditions of time and temperature. Acid action results in an overall decrease of amorphous material by removing polysaccharide material closely bonded to the crystallite surface and breaks down portions of glucose chains in most accessible, non-crystalline regions. A leveling-off degree of polymerization is achieved corresponding to the residual highly crystalline regions of the original material, i.e. cellulose or chitin fiber, or starch granule. Dilution of the acid and dispersion of the individual crystalline nanoparticles complete the process and yield an aqueous suspension of polysaccharide nanoparticles. These nanoparticles occur as rod-like nanocrystals that can display chiral nematic properties depending on the mineral acid chosen for the hydrolysis in the case of cellulose- or chitin-based materials, or platelet-like nanoparticles when using starch granules as the raw material. Polysaccharide nanocrystals are inherently low cost materials which are available from a variety of natural sources and in a wide variety of aspect ratios. They take advantage of both renewable materials, such as abundance, renewability and self-assembling into well-defined architectures, and nanosized particles, including mechanical properties e.g. strength, modulus and dimensional stability, decreased permeability to gases and water, thermal stability and heat distortion temperature, surface appearance and optical clarity in comparison to conventionally filled polymers. They are an attractive nanomaterial for multitude of potential applications in a diverse range of fields. Indeed, nanotechnology has applications across most economic sectors and allows the development of new enabling science with broad commercial potential. Possible and suggested areas of application include optically variable films and ink iridescent pigments for security papers. Polysaccharide nanocrystals reinforced polymer nanocomposites display outstanding mechanical properties and can be used to process high-modulus thin films. The growing literature studying polysaccharide, mainly cellulose, nanocrystals is a clear indication of this evolution. Practical applications of such fillers and transition into industrial technology require a favorable ratio between the expected performances of the composite material and its cost. To exploit their potential, research and development investments must be made in the science and engineering that will fully determine the properties and characteristics of polysaccharides at the nanoscale, develop the technologies to manipulate self-assembly and multifunctionality, and develop these new technologies to the point where industry can produce advanced and cost-competitive polysaccharide nanoscale products. There are still significant scientific and technological challenges to take up.

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REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

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[16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]

Azizi Samir, M.A.S. Alloin, F. Dufresne, A. Biomacromolecules, 6:2 612-626 (2005). Revol, J.F. Carbohydr. Polym., 2:2 123-134 (1982). Grunert, M. Winter, W.T., J. Polym. Environ., 10:1-2 27-30 (2002). Kim, U.J. Kuga, S. Wada, M. Okano, T. Kondo, T., Biomacromolecules, 1:3 488-492 (2000). Ebeling, T. Paillet, M. Borsali, R. Diat, O. Dufresne, A. Cavaillé, J.Y. Chanzy, H., Langmuir, 15:19 6123-6126 (1999). Lu, Y. Weng, L. Cao, X. Macromol. Biosci., 5:11 1101-1107 (2005). Kvien, I., Bjørn, S.T. Oksman, K., Biomacromolecules, 6:6 3160-3165 (2005). Garcia de Rodriguez, N.L., Thielemans, W. Dufresne, A., Cellulose, 13 261-270 (2006). Azizi Samir, M.A.S., Alloin, F., Paillet, M. Dufresne, A., Macromolecules, 37:11 43134316 (2004). Favier, V. Canova, G.R. Cavaillé, J.Y. Chanzy, H. Dufresne, A. Gauthier, C., Polym. Adv. Technol., 6 351-355 (1995). Helbert, W. Cavaillé, J.Y. Dufresne, A., Polym. Compos., 17:4 604-611 (1996). Beck-Candanedo, S. Roman, M. Gray, D.G., Biomacromolecules, 6:2 1048-1054 (2005). Gopalan Nair, K. Dufresne, A., Biomacromolecules, 4:3 657-665 (2003). Morin, A. Dufresne, A., Macromolecules, 35:6 2190-2199 (2002). Sriupayo, J. Supaphol, P., Blackwell, J. Rujiravanit, R., Polymer, 46:15 5637-5644 (2005). Paillet, M. Dufresne, A., Macromolecules, 34:19 6527-6530 (2001). Angellier, H. Choisnard, L. Molina-Boisseau, S. Ozil, P. Dufresne, A., Biomacromolecules, 5:4 1545-1551 (2004). Putaux, J.L. Molina-Boisseau, S. Momaur, T. Dufresne, A. Biomacromolecules, 4:5 1198-1202 (2003). Favier, V. Dendievel, R. Canova, G.R. Cavaillé, J.Y. Gilormini, P., Acta Mater., 45:4 1557-1565 (1997). Favier, V. Canova, G.R. Shrivastava, S.C. Cavaillé, J.Y., Polym. Eng. Sci., 37:10 17321739 (1997). Dufresne, A. J. Nanosci. Nanotechnol., 6:2 322-330 (2006). Dubief, D. Samain, E. Dufresne, A., Macromolecules, 32:18 5765-5771 (1999). Gopalan Nair, K. Dufresne, A. Gandini, A. Belgacem, M.N. Biomacromolecules, 4:6 1835-1842 (2003). Angellier, H. Molina-Boisseau, S. Dufresne, A., Macromolecules, 38:22 9161-9170 (2005). Dufresne, A. Kellerhals, M.B. Witholt, B., Macromolecules, 32:22 7396-7401 (1999). Dufresne, A. Compos. Interfaces, 7:1 53-67 (2000). Anglès, M.N. Dufresne, A., Macromolecules, 34:9 2921-2931 (2001). Dufresne, A. Vignon, M.R., Macromolecules, 31:8 2693-2696 (1998). Dufresne, A. Cavaillé, J.Y., J. Polym. Sci. Part B, 36:12 2211-2224 (1998). Azizi Samir, M.A.S. Alloin, F. Sanchez, J.Y. Dufresne, A., Polymer, 45:12 4033-4041 (2004).

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[31] Azizi Samir, M.A.S. Alloin, F. Gorecki, W. Sanchez, J.Y. Dufresne, A., J. Phys. Chem. B, 108:30 10845-10852 (2004) [32] Azizi Samir, M.A.S. Montero Mateos, A. Alloin, F. Sanchez, J.Y. Dufresne, A., Electrochim. Acta, 49:26 4667-4677 (2004) [33] Azizi Samir, M.A.S. Alloin, F. Sanchez, J.Y. Dufresne, A., Macromolecules, 37:13 4839-4844 (2004). [34] Azizi Samir, M.A.S. Chazeau, L. Alloin, F. Cavaillé, J.Y. Dufresne, A. Sanchez, J.Y., Electrochim. Acta, 50:19 3897-3903 (2005).

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Chapter 4

PREPARATION AND CHARACTERIZATION OF BIODEGRADABLE PLASTICIZED STARCH-GPOLY(BUTYLENE ADIPATE-CO-TEREPHTHALATE)BASED (NANO)COMPOSITES J-M. Raquez1,3*, Y. Nabar2, R. Narayan2 and P. Dubois1

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1

Center of Innovation and Research in Materials and Polymers, Laboratory of Polymeric and Composite Materials, University of Mons-Hainaut and Materia Nova, Place du Parc 20, B-7000 Mons, Belgium; 2 Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing MI-48823, USA 3 Department of Polymer and Composite Technology, Ecole des Mines de Douai, Rue C. Bourseul 941 B.P. 10838, 59508 Douai Cedex, France

INTRODUCTION Societal and scientific considerations have provided a growing interest in edible and biodegradable films from renewable resources in order to reduce our environmental footprint. Starch is one of the most studied and promising raw materials for the manufacture of sustainable and biodegradable plastics, obtained from a great variety of crops. In addition, starch is a low cost material in comparison to most petroleum-derived plastics, and is readily available. Native starch commonly exists in a granular structure, which can be processed into thermoplastic starch (TPS) in the presence of plasticizers (water and/or polyalcohol) under high shearing [1]. Unfortunately, the properties of TPS are not satisfactory in terms of thermo-mechanical properties and water-sensitivity for some applications such as packaging. In order to improve the mechanical properties and water resistance, starch can be modified by several methods such as melt-blending with synthetic or natural polymers [2]. Recently, layered silicate/polymer (nano)composites have attracted significant interest, both in academic and industrial fields, because they often exhibit dramatic improvement in thermal and mechanical properties at very low clay loading (< 5wt%) [3]. Structurally, two

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extreme morphologies can be achieved in the layered silicate/polymer (nano)composites: an intercalated structure if a regular stacking of polymer monolayers and silicate layers is generated or an exfoliated morphology if the silicate platelets are fully homogeneously delaminated and dispersed in the polymer matrix. Intercalation and exfoliation relies on three key-parameters corresponding to the polymeric matrix, the (organo-)clay, and the processing route. Mainly, two pathways can lead to the preparation of nanocomposites either by polymerization of monomers intercalated within the interlayer spacings or the intercalation of the polymer chains in the molten state. However, most of studies carried out on layered silicate TPS-based (nano)composites have only improved solvent-resistance, thermal properties and modulus, but not strength and toughness, due to the weak adhesion between the clay and the polymer. High melt-viscosity of starch is another issue, making it difficult to be intercalated in the spacings of galleries. Interestingly, we have prepared a novel plasticized starch ester bearing free carboxylic groups, exhibiting enhanced reactivity, and improved processability, prepared through in situ reactive extrusion processing of starch in the presence of glycerol as plasticizer and maleic anhydride as esterification agent (MA) (Scheme 1). Glucosydation and hydrolysis reactions acid-catalyzed by MA-derived acidic moieties could occur during the maleation of starch, which reduced the overall melt-viscosity, and the size of starch chains [4].

O

OH O

+

C OH

CH2O C

O

O

O

OH

O Copyright © 2005. Nova Science Publishers, Incorporated. All rights reserved.

O

O

CH2OH

OH O OH

Scheme 1. Esterification reactions of starch backbone with MA

We report herein the preparation and characterization of layered silicate MTPS-based nanocomposites. As a ultimate objective, these layered silicate MTPS nanocomposites have been employed in the preparation of biodegradable and phase-homogeneous graft copolymers with poly(butylene adipate-co-terephathlate) (PBAT) in blown film applications [4]. These MA functions grafted onto the starch backbone have shown to be valuable in the acidcatalyzed transesterification reactions between these both partners. The properties of the resulting (nano)composites are reported and compared with structural characterizations.

EXPERIMENTAL Materials Corn starch was obtained from Cargill-grade SMP 1100, with equilibrium moisture content of about 12 wt%. Anhydrous glycerol (99.9%) was supplied from J.T. Baker, and used as received. Maleic anhydride (MA, 99%) was obtained from Sigma-Aldrich, and was previously ground to a fine powder using a mortar and pestle before use. Cloisite Na, natural montmorillonite, and Cloisite 30B, montmorillonite organo-modified by methyl bis(2-

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hydroxylethyl)(tallow alkyl) ammonium (tallow with alkyl components of ~65% C18 chains, ~30% C16 chains, and ~5% C14 chains) were supplied by Southern Clay Products. Poly(butylene adipate-co-terephthalate) (PBAT) was purchased from BASF Corporation, under the trade name Ecoflex (F). PBAT is made by condensing 1,4-butanediol with terephthalic acid and adipic acid. .

Layered Silicate-Filled MTPS-G-PBAT Graft Copolymers Before processing, clay was first swollen with glycerol for approximately 15 hours at ambient temperature. Corn-starch was reactively modified using 8wt% MA in the presence of the resulting slurry mixture (glycerol/clay; 30wt% by starch) by reactive extrusion at ca. 140142°C. In a downstream extrusion step, the resulting layered-silicate MTPS composite was melt-blended with PBAT (i.e., 70wt% polyester content). The resulting layered silicate PBAT-g-MTPS graft copolymers were blown-molded. Transmission electron microscopy (TEM), tensile testing, and water vapor and oxygen transmission rate of (nano)composite films were determined.

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RESULTS AND DISCUSSION The tensile properties of PBAT-g-MTPS graft copolymers reinforced with Cloisite 30B and Cloisite Na at a final 1wt% composition were determined in the machine direction (Table 1). On the introduction of 1wt% of either nanoclay, the mechanical properties of the MTPS-gPBAT graft copolymer-based nanocomposites could be improved substantially, compared with the unfilled graft copolymer and PBAT. However, the improvement in both tensile strength and break elongation were much better when Cloisite 30B was used. This could be explained by the difference of morphologies obtained for these MTPS-based nanocomposites. In contrast to the intercalated layered silicates with Cloisite Na+, the partial exfoliation together with the good dispersion of the nanoclay in the reactive melt-blend could be observed in the Cloisite 30B filled PBAT-g-MTPS (nano)composite (Figure 1). Table 1. Tensile properties of clay-reinforced PBAT-g-MTPS copolymer, PBAT and unfilled PBAT-g-MTPS graft copolymer (in the machine direction) Nature PBAT PBAT-g-MTPS PBAT-g-MTPS

(Cloisite Na+) PBAT-g-MTPS

Tensile Strength (MPa) 38.6 ± 4.0 16.2 ± 1.7 26.1 ± 3.2

Young Modulus (MPa) 13.8 ± 1.3 78.1 ± 7.2 129.7 ± 26.7

Elongation at Break (%) 600 ± 35 735 ± 48 700 ± 48

32.0 ± 3.9

149.7 ± 27.9

800 ± 36

(Cloisite 30B)

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Figure 1. TEM Images for the Cloisite Na+ filled PBAT-g-MTPS (a; Magnitude x 250 k) and for the Cloisite 30B filled PBAT-g-MTPS (Magnitude x 105k; individual exfoliated nanoplatelets highlighted by arrows).

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Both water vapor and oxygen transmission rates (WVTR and OTR) for MTPS-g-PBAT graft copolymers could be reduced when Cloisite 30B and Cloisite Na+ were used as nanoclays (Table 2). A more significant reduction in WVTR was however detected for Cloisite Na+-filled nanocomposites, indicating a preferential localization of the hydrophilic clay in the hydrophilic MTPS phase. A preferential localization for the medium hydrophobic Cloisite 30B in the hydrophobic PBAT could be also made out, as supported by the stronger reduction in OTR achieved with Cloisite 30B. Table 3. Water Vapor Transmission Rate (WVTR) And Oxygen Transmission Rate (OTR) Of Unfilled PBAT-G-MTPS And Layered Silicate Filled PBAT-G-MTPS With 30 Wt% MTPS

PBAT-g-MTPS

WVTR g/m2.day 1000

OTR g/m2.day 1240

PBAT-g-MTPS

575

750

810

590

Sample

(1% Cloisite Na+) PBAT-g-MTPS

(1% Cloisite 30B)

CONCLUSIONS Novel MTPS-g-PBAT graft copolymers reinforced with Cloisite 30B and Cloisite Na could be successfully prepared through reactive extrusion. The resulting nanocomposites exhibited high-performance properties in terms of tensile and barrier properties.

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ACKNOWLEDGMENTS This research was partly funded by Corn Products International. Authors are very grateful to “Région Wallonne” and European Community (FEDER, FSE) for general support in the frame of “Objectif 1-Hainaut: Materia Nova”. This work was partly supported by the Belgian Federal Government Office of Science Policy (SSTC-PAI 5/3).

REFERENCES Stepto R. Macromol. Symp. 201: 203, (2003) Nayak P. J.M.S.-rev. Macromol. Chem. Phys. C39(3): 481, (1999) Giannelis, E., Adv. Mater. 8, 29, (1996) Raquez, J.M. Nabar Y. Dubois P. Narayan R. Polym. Eng. Sci. submitted for publication.

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

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ISBN 978-1-59454-274-9 © 2009 Nova Science Publishers, Inc.

Chapter 5

DEVELOPMENT AND CHARACTERIZATION OF NOVEL NANOBIOCOMPOSITES OF THERMOPLASTIC BIOPOLYMERS AND LAYERED SILICATES M.D. Sanchez-Garcia1, E. Gimenez2 and J.M. Lagaron11 1

Novel Materials and Nanotechnology, IATA, CSIC, Apdo Correos 73, 46100 Burjassot, Spain. 2 Area of Materials, Department of Industrial Systems Engineering and Design, University Jaume I, 12071 Castelló, Spain

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ABSTRACT This paper shows and discusses the morphology and transport properties of solvent cast biocomposites of poly(lactic acid) (PLA), polyhydroxybutyrate-co-valerate (PHBV) and polycaprolactone (PCL) with the addition of layered silicates. In this context, functional nanoadditives, such as nanoclays, with tailor-made and harmless modifications can show to have a significant potential to enhance mechanical and barrier properties of these materials and for controlled release of functional (antimicrobial, antioxidant, pharmacs, etc…). This study describes and discusses the morphological (TEM, AFM) and barrier properties (water vapour and limonene permeability) of these novel nanobicomposites of PCL, PLA, PHBV and layered silicates based on modified phyllosilicate clays. The main conclusion from this work is that organoclays can be used to enhance the barrier properties of thermoplastic biopolyesters of interest in, for instance, packaging and membrane applications.

Keywords: nanocomposites, barrier properties, PLA, PCL and PHBV

1

E-mail: [email protected].

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M.D. Sanchez-Garcia, E. Gimenez and J.M. Lagaron

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INTRODUCTION The use of biodegradable plastics and resources are seen as one of the many strategies to minimise the environmental impact of petroleum-based plastics. Thermoplastic biopolymers, such as poly(lactic acid) (PLA), polyhydroxyalkanoates (PHA) and polycaprolactone (PCL) present a number of excellent and promising properties for a number of applications, including packaging, automotive and biomedical applications [1]. PLA is a thermoplastic biopolyester produced from L-lactid acid, which typically comes from the fermentation of corn starch. Currently, PLA is being commercialized and used as a food packaging polymer for short shelf-life products with common applications such as containers, drinking cups, sundae and salad cups, overwrap and lamination films, and blister packages [2]. In PHAs (polyhydroxyalkanoates) family, the most widely used material is the polyhydroxybutyrate (PHB) and its copolymers with valerate. These microbial biopolymers are storage materials produced by a variety of bacteria in response to particular environmental stresses [3]. Polyhydroxybutyrate (PHB) is a naturally occurring β-hydroxyacid (a linear polyester). The homopolymer, poly(hydroxybutyrate) PHB, and its copolymer with hydroxyvalerate, PHBV, are biodegradable engineering thermoplastic polymers with important deal properties that make them suitable in many applications for which petroleum-based synthetic polymers are currently used. PHB polymers are already being used in small disposable products and in packaging materials [4]. Finally, PCL is a thermoplastic biodegradable polyester synthesized by chemical conversion of crude oil. PCL has good water, oil, solvent, and chlorine resistance, a low melting point, and low viscosity, and is easily processed using conventional melt blending technologies [5]. PCL is at this time being investigated for its use in biomedical utensils, pharmaceutical controlled release systems, and in biodegradable packaging [6]. Moreover, in general terms biodegradable materials are either strongly plasticized by moisture sorption or have, as for instance PLA, medium barrier properties to gases, vapours or hydrocarbons. Thus, it is relevant to improve the properties of these biodegradable materials so that they can compete with greater advantage with materials derived from petroleum [7]. The addition of layered silicates to biodegradable polymers through innovative nanotechnologies and nanomaterials has become of great interest to enhance the performance of these biopolymers [8]. In this context, functional nanoadditives, such as nanoclays, with tailor-made and harmless modifications can show to have a significant potential to enhance mechanical [9-10] and barrier [11-15] properties of these materials and for controlled release of functional (antimicrobial, antioxidant, pharmacs, etc…) and moreover for dispersing the UV-Vis [16,17] radiation, probably due to scattering phenomena caused by exfoliated clay nanolayers. The nanobiocomposites developed in this work were prepared via solution casting, using commercial proprietary clays designed for food packaging applications. This study describes and discusses the morphological (TEM, AFM) and barrier properties (water vapour and limonene permeability) of these novel nanobiocomposites of PCL, PLA, PHBV and layered silicates based on modified smectite clays.

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MATERIALS AND METHODS Materials The bacterial polyhydroxyalcanoate grade was purchased from Goodfellow Cambridge Limited, U.K., in pellet form. The supplied material was a melt-processable semi-crystalline thermoplastic PHBV (Polyhydroxybutirate with 12 mol% of Valerate) copolymer made by biological fermentation from renewable carbohydrate feedstocks. The polycaprolactone (PCL) grade FB100 was kindly supplied in pellet form by Solvay Chemicals, Belgium. This grade has a density of 1.1 g/cm3 and a mean molecular weight of 100,000 g/mol. The semicrystalline Poly (lactic acid) (PLA) used was a film extrusion grade manufactured by Natureworks (with a D-isomer content of approximately 2%). The molecular weight had a number-average molecular weight (Mn) of ca. 130,000 g/mol, and the weight-average molecular weight (Mw) was ca. 150,000 g/mol. A food contact complying nanoclay experimental grade (NanoterTM 3000) based on an organophilic surface modified laminar phyllosilicate was kindly supplied by NanoBioMatters S.L. (www.nanobiomatters.com), Spain.

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Preparation of Blends Prior to the solution stirring, the PHBV, PCL, PLA and clays were dried at 90ºC under vacuum for 24 hours to remove sorbed moisture. Solution-cast film samples of the biodegradable materials with 1, 5 and 10wt.% organoclay contents were prepared with a dry film thickness of around 100 μm, using chloroform as a solvent. Organoclay solutions in chloroform were mixed in a homogenizer (Ultraturrax T25 basic, Ika-Werke, Germany) for five minutes and were then stirred with the polymer at 40ºC during 30 min and subsequently cast onto Petri dishes to generate films after solvent evaporation at room temperature conditions.

AFM Measurements AFM measurements were performed using a NanoScope IIIa (Digital Instruments Inc.) to investigate the morphology of the fiber surfaces in both sides of the cast films of the biocomposites. The images were scanned in tapping mode in air using commercial Si cantilevers (Digital Instruments Inc.) with a resonance frequency of 320 kHz.

Gravimetric Measurements Direct permeability to d(+)-limonene of 95% purity (Panreac Química, Spain) and direct permeability to water were determined from the slope of weight loss vs. time experiments at 24°C and 40%RH. The films were sandwiched between the aluminium top (open O-ring) and bottom (deposit for the permeant) parts of aluminium permeability cells. A Viton rubber Oring was placed between the film and the bottom part of the cell to enhance sealability. Then the bottom part of the cell was filled with the permeant and the pinhole secured with a rubber

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O-ring and a screw. Finally, the cell was placed in the desired environment and the solvent weight loss through a film area of 0.001 m2 was monitored and plotted as a function of time. Cells with aluminium films (with thickness of ca. 100 microns) were used as control samples to estimate solvent loss through the sealing. The permeability sensibility of the permeation cells was determined to be of ca. 0.01 10-13 Kg m/s m2 Pa based on the weight loss measurements of the aluminium cells. Cells clamping polymer films but with no solvent were used as blank samples to monitor water uptake. Solvent permeation rates were estimated from the steady-state permeation slopes. Organic vapour weight loss was calculated as the total cell loss minus the loss through the sealing and plus the water weight gain. The tests were done in duplicate.

RESULTS AND DISCUSSION Morphological Results

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Figure 1 shows, as an example, that the surface roughness of the biodegradable nanocomposites can be typically well resolved by the AFM tip. This figure shows the presence of the layered silicate in the 5wt.% clay-PCL sample prepared by casting. This image suggests strong interfacial adhesion and intercalation of the clay in the biopolymer.

Figure 1. AFM picture of 5wt.%clayPCL-casting.

Mass Transport Properties Table 1 summarizes the water and d-limonene permeability of thermoplastics and their nanocomposites prepared by casting. From the results, films of PHBV with 1, 5 and 10wt.% clay content have a water permeability decrease of 61%, 23% and 47%, respectively, compared to the unfilled material. The water permeability reduction is not increasing with clay content due to possibly the confronting effect that organomodified clays may still have hydrophilic sites that could increase solubility for higher contents of clay and due to possible clay agglomeration at the higher contents. However, in the case of limonene permeability, the film of PHBV+1wt.%clay has a reduction of limonene permeability of only 10%, whereas the film of PHBV+5wt.% clay has an optimum limonene permeability reduction of ca. 96%. However, at higher filler contents the permeability of limonene decreases due to possible clay agglomeration and preferential paths for diffusion being created.

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Table 1. Water and D-Limonene permeability for PHBV and their nanocomposites prepared by casting

PHBV PHBV+1wt.% clay PHBV+5wt.% clay PHBV+10wt.% clay

P water (Kg m/s m2 Pa) 0.13±0.014e-13 0.05±0.003e-13 0.09±0.005e-13 0.060±0.02e-13

PLA PLA+1wt.% clay PLA+5wt.% clay PLA+10wt.% clay

0.23±0.007e-13 0.17±0.008e-13 0.16±0.026e-13 0.10±0.011e-13

P limonene (Kg m/s m2 Pa) 1.27±0.07e-13 1.14±0.25e-13 0.05±0.005e-13 2.25±0.18e-13

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PCL 0.34±0.061e-13 5.05±0.65e-13 -13 PCL+1wt.% clay 0.16±0.005e 4.16±1.18e-13 PCL+5wt.% clay 0.12±0.005e-13 2.58±0.57e-13 -13 PCL+10wt.% clay 0.12±0.001e 3.80±0.57e-13 -13 PCL Literature Value [14] 0.0023e 14 ( Messersmith and Giannelis, 1995) At 35ºC, 75%RH and cast from toluene

Direct permeability for limonene in PLA was not reported, because the measurements yielded values below the sensibility of the permeation cells; a previous study reported that the limonene permeability for PLA is of ca. 0.000002 10-13Kg m / s m2 Pa when measured at 45oC and 258 Pa of vapour partial pressure gradient [18]. Table 1 summarizes the water permeability of PLA as a function of filler content. These samples indicate that the barrier properties to water of PLA biocomposites are reduced (by 26%) in the sample containing 1wt.% of clay. Films of PLA with 5wt.% clay have a water permeability decrease of 54% compared to the unfilled material and films of PLA with 10wt.% clay show a water permeability reduction of ca. 55%. Films with 5 and 10wt.% of clay show similar improvements in the water barrier for these samples. A curious observation from Table 1 and regarding PCL is that the water permeability coefficient of 0.4 10-13 Kg m / s m2 Pa is much higher than that of 0.0023 10-13 Kg m / s m2 Pa previously reported for toluene-cast PCL [14]. The reason for the large disagreement could be related to the different origins of the two samples (lab scale material vs. industrial scale material production) and the fact that molecular weight, the solvent used and the differences in relative humidity gradient used for testing were totally different. In the case of the PCL biopolymer, Table 1 shows the limonene and water permeability for the thermoplastic and their nanocomposites. From the results, films of PCL with 1wt.% clay content have a water permeability decrease of 53% compared to the unfilled material and the films with 5 and 10wt.% clay have the same water permeability reduction of 63%. In the case of the limonene permeability, films of PCL with 1, 5 and 10wt.% clay content have a limonene permeability decrease of 18%, 49% and 25%, respectively, compared to the unfilled material. The lowest limonene permeability value is for the sample with 5wt.% clay content. In general, the films with 5wt.% clay content show the lowest permeability values. This observation may indicate that there must be a balance in the biocomposites between content

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M.D. Sanchez-Garcia, E. Gimenez and J.M. Lagaron

of clay used, which has in itself barrier capacity, the morphology of the nanocomposites samples and the possibility of the permeability deterioration apparently caused by the clay agglomeration. In the case of water permeability there must be a balance in the permeability, solubility and the diffusion coefficient of these nanocomposites, because with the increase of clay content, the water solubility could be increased by the hydrophobic character of clays. And for that reason, the permeability could increase with the solubility (P=D·S). This paper presented results that prove that a significant increase in the barrier properties to water vapour and limonene of the nanobiocomposites takes place. The nanoclays are believed to increase the gas barrier properties by creating a maze or ‘tortuous path’ that retard the progress of gas molecules through the matrix polymer, although the polarity and size of the penetrants have also a strong influence on the permeability of water and organic vapours.

ACKNOWLEDGEMENTS The authors would like to acknowledge the EU integrated project SUSTAINPACK for financial support. NanoBioMatters S.L., Paterna (Spain) and the Spanish MEC project MAT2006-10261-C03 are also acknowledged for financial support. Finally, M.D.S.G. would like to thank the FPI program of the GV associated to the MEC project MAT2003-08480-C3 for the research grant.

REFERENCES [1]

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[2] [3]

[4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

Petersen, K. Nielsen, P.K. Bertelsen, G. Lawther, M. Olsen, M.B. Nilsson, N.H. Mortensen, G. Trends in Food Science and Technology 10, 52-68, (1999) Auras, R. Kale, G, Singh, S.P. Journal of Polymers and the Environment 14:3, 317-334 (2006) Peoples. O.P. Sinskey, A.J. Polyhydroxybutyrate (PHB): a model system for biopolymer engineering: II. Novel Biodegradable Microbial Polymers. Kluwer Academic Publishers, Dordrecht, 191–202, 1990 Rosa, D.S. Lotto, N.T. Lopes, D.R. Guedes, C.G.F. Polym. Testing. 23, 3-8, (2004) Gross, R.A. Kalra, B. Science 297, 803-807, (2002) Piglowski, J. Kiersnowski, A. Polymer 51:10, 704-715, (2006) Cava, D. Giménez, E. Gavara, R. Lagaron, J.M. Journal of Plastic Film and Sheeting 22 :4, 265-274, (2006) Sanchez-Garcia, M.D. Giménez, E. Lagaron, J.M.. J. Appl. Polym. Sci. (In press 2007) Wu, T.M. Wu, CY. Polym. Degrad. Stabil. 91:9, 2198-2204, (2006) Lee, J.H. Lee, Y.H. Lee, D.S. Lee Y.K. Nam J.D. Polymer-Korea 29:4, 375-379, (2005) Sinha Ray S. Yamada K. Okamoto M. Ueda K. Polymer; 44, 66, (2003). Sinha Ray S. Yamada K. Okamoto M. Fujimoto Y. Ogami A. Ueda K. Polymer; 44, 46, (2003). Chang, J.H. An, Y.U. Sur, G.S. J. Polym. Sci. Part B: Polymer Physics. 41, 94-103, (2003)

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[14] Messersmith, P.B. Giannelis, E.P. Journal Polymer Science Polymer Chemical 33:7, 1047-1057, (1995) [15] Di, Y.W. Macromol Symp 228, 115-124, (2005) [16] Auras, R. Harte, B. Selke, S. Macromol. Biosci. 4, 835–864, (2004) [17] Fornes, T.D. Yoon, P.J. Paul, D.R. Polymer, 44, 7545–7556, (2003) [18] Auras, R. Harte, B. Selke, S. Journal of the Science of Food and Agriculture 22, 5142, (2005)

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In: Trends in Polymer Research Editors: G.E. Zaikov, A. Jimenez and Yu.B. Monakov

ISBN 978-1-59454-274-9 © 2009 Nova Science Publishers, Inc.

Chapter 6

NOVEL POLYMERIC CARRIER FOR CONTROLLED DRUG DELIVERY SYSTEMS FROM RENEWABLE SOURCES Catalina Duncianu, Ana Maria Oprea and Cornelia Vasile “Petru Poni” Institute of Macromolecular Chemistry, 41 A, Gr.Ghica Voda Alley, 700487, Iasi, Romania

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ABSTRACT The hydrogen-bonded interpolymeric complexes (IPCs) have gained a great interest in last decades showing a similar behavior to natural systems and also because of their distinct physical and chemical properties in comparison with pure components; IPCs are considered promising materials in the development of different drug formulations. The interpolymeric complex based on a natural polymer like alginic acid (AgA) and poly (ethylene glycol) (PEG) was tested by UV-VIS spectroscopy to investigate the possibility of using it as a new matrix in the active principles delivery. The kinetic profile of the procaine hydrochloride release from 16wt%AgA/ 84wt% PEG complex at various pHs (1,14; 2,16 and 3,09) and temperatures was studied. The interpolymeric complex between AgA and PEG showed a good behavior in acidic medium and it can be considered a promising material for the release of active substances in stomach.

Keywords: alginic acid, polyethylene glycol, procaine, interpolymeric complex, controlled delivery.

INTRODUCTION The hydrogen-bonded interpolymeric complexes (IPCs) [1] have attracted a great interest from the pharmaceutical scientists due to the similar behavior to natural systems and their unique physical and chemical properties in comparison with pure components as well as their potential applications in the development of different drug formulations [2,3]. The design and control of the release mechanism of the active principles have gained an increased interest in

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last years. The main goal of the controlled release of the active agents is to prolong their action time, to minimize the undesired reactions, and also to increase the release efficiency of the active principle. A controlled release system should have a stable chemical structure which satisfies the conditions of biodegradability and biocompatibility and also to have also a suitable release rate of the active substance at targeting site in a definite time [3,4]. The selection of an adequate support for the active principles delivery/transport is important in order to obtain an efficient sustained release system. An ideal vehicle for an active principle should also satisfy some specific requirements like: to posses a high loading ability according to the therapeutic dose, to be able to penetrate or to localize at a targeting site and to release in a controlled way the active principle. It should not be toxic and it has to be biocompatible and biodegradable, especially in the case of intraocular administrations. The use of a natural polymer, such as a weak polyacid e.g. alginic acid to obtain interpolymeric complexes represents an attractive target. Alginic acid is a natural non-toxic, biodegradable hydrophilic polymer which can be extracted from different brown seaweeds e.g. Macrocystis pyrifera, Ascophyllum nodosum [5]. PEG is widely used in pharmaceutical industry and cosmetics; it is non-volatile and inert from the physiological point of view and it can be used for different ointments, emulsions, pastes, lotions and suppositories production [6]. In the present work the interpolymeric associations between alginic acid (AgA) and poly (ethylene glycol) (PEG) were tested by UV-VIS spectroscopy in order to investigate the possibility of using them as a new matrix in the controlled delivery of certain drugs. For testing the formed IPC as drug carrier the procaine hydrochloride was used. The structure of procaine hydrochloride is shown in figure 1.

Figure 1. The structure of procaine hydrochloride [8].

Procaine hydrochloride is a well-known active substance used as local anaesthetic, which blocks the generation and conduction of nerve impulses by decreasing the permeability of the nerve membrane to ions, thereby inhibiting depolarisation, loss of pain sensation, other sensory functions, and finally motor activity [7].

MATERIALS AND METHODS Materials It was used alginic acid, a Fluka product, with an average molecular weight of 48.000186.000 Da; the reduced viscosity in water at 25oC for an aqueous solution of c= 0,2 wt% was

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ηred= 2,41 ml g-1, with a drying loss ≤ 10wt% and ash content ≤ 3 wt%. PEG had a molecular weight 35.000 Da and a melting temperature 60-65ºC. Preparation of the IPC from alginic acid, AgA and poly (ethylene glycol), PEG: The composition of the interpolymeric complex between AgA and PEG was identified by studying many mixing ratios between components which were carefully characterized by viscometric and potentiometric methods [9]. It was established that the most stable IPC had the composition 16wt% AgA / 84wt% PEG. The solutions of components in twice distilled water, adjusted at pH = 4 and c = 0,2wt% were mixed and the obtained complex was isolated from solution by drying during 48 hours in a freezing-drying apparatus. Viscometry tests were performed by means of an Ubbelhode type viscometer with dilution and suspended level, at 25,00°C ± 0,02°C. Flow times were measured with an accuracy of ± 0,1s. pH measurements were performed at 25,00°C ± 0,02°C, in a thermostated bath, with a Consort C835 multimeter equipped with a separate pH glass electrode suitable for diluted solutions domain.

Swelling Process of the Support Based on Alginic Acid and PEG The swelling profile (Figure 2) of the IPC support showed its ability to absorb the acidic solution (pH = 1-4). In this way a temporary enlargement of the intermacromolecular spaces occured. Also, it could be observed that the maximum absorption capacity of the modified polymer was reached in about two hours. After that, a swelling equilibrium was installed. There was no absolute dissolution even after a long period of time, in this pH interval the IPC was stable. The loading of the support with procaine was carried out by swelling it with acidic solution of procaine followed by freeze-drying.

8

6

q (%)

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10

4

2

0

0

50

100

150

200

Time (min)

Figure 2. Swelling curve in acidic twice-distilled water of the IPC based on AgA/PEG with procaine hydrochloride entrapped.

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Catalina Duncianu, Ana Maria Oprea and Cornelia Vasile

UV VIS Method The controlled release mechanism was evidenced by using the photocolorimetric method. A UV-VIS HP 8540A spectrophotometer was used; the calibration curve was achieved with acidic solutions of various pH (pH=1-4) of different concentrations in the 10-5-10-2 g/L range. The released procaine was distinguished at λmax=194, 221, and 291 nm [10]. The most suitable wavelength for determination was 221 nm. The ability of the complex of AgA/PEG to release procaine entrapped into carrier was tested at different flow rates of the solvent (0,2; 0,3 and 0,6 ml min-1). 0.6

0.5

Absorbance (a.u.)

pH= 2.16 pH =1.14 0.4 pH= 3.09 0.3

0.2

0.1

0.0

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0.0

0.2

0.4

0.6

102 *c (g/L)

0.8

1.0

1.2

Figure 3. Calibration curves of the procaine hydrochloride at different pHs (1,14; 2,16 and 3,06), λ =221 nm.

RESULTS AND DISCUSSION The interpolymeric associations between AgA and PEG were selected after the study of the mixed solutions of polymers, adjusted at pH= 4 and c = 0,2wt%, in different compositions ranging 0-100wt% AgA and then characterized by viscometric and potentiometric methods. The obtained results are summarized in Figure 1 (for details see ref.9). Correlating data of viscosimetry and potentiometry, the maximum value of both viscosity ratio and pH was found in the 2 -20wt% AgA/ 98-80wt% PEG weight composition range Figure 4. It was established that a more stable interpolymeric association occured at 16wt% AgA / 84wt% PEG which could be considered as an interpolymeric complex. After the stoichiometry of the IPC was established; the IPC was separated. The stability of the obtained 16wt% AgA / 84wt% PEG interpolymeric complex was also evaluated and it was found that the stability constant was about 21 (l*mol-1) [9].

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Novel Polymeric Carrier for Controlled Drug Delivery Systems… 1.8

4.4 AgA/ PEG- potentiometry AgA/ PEG - viscometry

1.6 4.3

1.4

rη

pH

4.2 1.2

4.1 1.0

4.0

0.8 0

20

40

60

80

100

120

WAgA (wt %)

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Figure 4. Dependence of the viscosity ratio on the composition of the system AgA/ PEG, in aqueous solution with pH=4 at 25oC (ο-right axis); pH- values (•- left axis) obtained at AgA titration with PEG in twice-distilled water, at 25oC.

The possibility of using this IPC as a new matrix in the active principles delivery was tested by UV-VIS spectroscopy. The kinetic profile of the procaine hydrochloride release from 16wt% AgA/ 84wt% PEG complex at various pHs (1,14; 2,16 and 3,09) and temperatures was studied (Figure 5) because it was established that pH = 4 represented the limit of stability of the complex [9]. The stability of the AgA/ PEG support without the procaine entrapped in the acidic solutions at pH= 1,14; 2,16 and 3,09 was tested by keeping it in such solutions long time. No dilution was observed and no bands in UV-VIS spectra were found. Within the study the dependences of the released percent of the procaine hydrochloride from the IPC matrix in time (Figure 5a) at pH = 1,14; 2,16 and 3,09 and of the release rate of the procaine hydrochloride from the same solutions with time were evaluated (Figure 5b). The release profile of the procaine hydrochloride from IPC matrix with 16wt% AgA / 84wt% PEG composition showed a higher released amount of procaine at pH = 3,09 (Figure 5a) during the first two hours, of about 24% from the overall quantity of the procaine entrapped in the IPC. After 3 hours the amount of procaine released was decreasing and finally showing a constant level up to 5 hours. During the first 3 hours, the release profile of procaine at pH = 1,14 showed that about 22% of procaine was released from the polymeric matrix. The profile from pH = 2,16 indicated a faster release of procaine from the matrix and after 3 hours the amount of procaine released was approximately the same as in the case of the profile from pH = 1,14. During 3-5 hours, the shape of both profiles was similar reaching a constant concentration. The rate release curves showed in figure 5b indicated different shapes between all three dependencies in the first 100 minutes, with higher values of release rate for the profile at pH = 3,09; about 0,4 μg/min, a sharp decrease in the case of profile at pH = 2,16, recording almost a linear

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decrease in the release rate with time. The dependence with pH= 1,14 showed that the procaine hydrochloride was released with a maximum rate about 0,3 μg/min while at pH = 2,16, the rate release was 0,18 μg/min. 35

Release percent (%)

30 25 20 15 0

T=25 C pH=2.16 pH=3.09 pH=1.14

10 5 0

50

100

150

200

250

300

350

Time(min)

(a)

0.5 0

T=25 C pH=2.16 pH=3.09 pH=1.14

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-1

Release rate (μg* min )

0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 0

50

100

150

200

Time(min)

250

300

350

(b)

Figure 5. Release profile for the procaine hydrochloride from 16wt% AgA / 84wt% PEG interpolymeric complex at different pH values (a); Rate release of procaine hydrochloride from AgA/PEG interpolymeric complex at different pH values (b).

Table 1 shows the decrease of the half time release, t1/2 with the increase of pH of the medium. For an efficient and controlled process it is necessary that the delivery time to be long enough, so that the half time of release should reach low values. Within the study it was observed that the half time of release of procaine at pH= 3,09 was approximately two times

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longer (40 min) and the shortest value of 20 min was recorded at pH= 1,14. The lower values of the half time of release of procaine at pH 3,09 indicated that at this pH, the AgA/PEG matrix could suffer some modifications in its structure due to the increased solubility of alginic acid at pH close to 4, which is the limit of its solubility in water. Therefore, the matrix became swollen and its structure allowed to the active principle entrapped inside to be slowly released. Table 1. Values of the half time of the controlled release process Sample AgA/PEG- procaine hydrochloride, pH = 1.14 AgA/PEG- procaine hydrochloride, pH = 2.16 AgA/PEG- procaine hydrochloride, pH = 3.09

t1/2 (min) 40 25 20

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The influence of flow rate of the acidic solutions through the complex of 16wt% AgA / 84wt% PEG with entrapped procaine hydrochloride is described by the curves in Figure 6. Three different flow rates about 0,2; 0,3 and 0,6 ml min-1 were used. Figure 6a illustrates a different release profile at low flow rate. It can be observed that using a low flow rate of solvent (0,2 mL/ min) through the matrix of IPC-active principle, a higher percent of released procaine, about 24% from total amount of procaine entrapped into the polymeric matrix after 3 hours was obtained. In the second region, after 3 hours, the amount released was decreasing reaching a constant level after 5 hours.

(a)

(b)

Figure 6. Release profile for the procaine hydrochloride from AgA/PEG interpolymeric complex at different flow rates of twice- distilled water through the sample at pH = 1,14 (a); Rate release of procaine hydrochloride from AgA/PEG interpolymeric complex at different flow rates of twicedistilled water through the sample at pH= 1.14 (b).

In the case of the higher flow rate (0,3 and 0,6 mL min-1) the amount of released procaine was only 22% in the first 1.5 hours reaching the constant concentration after 2 hours. Therefore a more efficient release mechanism at low flow rate of the solvent and a better controlled release of the procaine from the IPC-complex between alginic acid and poly (ethylene glycol) was found. The release rates in the case of the high flow rate through the

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Catalina Duncianu, Ana Maria Oprea and Cornelia Vasile

sample (0,3 and 0.6 mL/ min) showed a sharp decrease in the first 50 min., while at a low flow rate (0,2 ml /min) the decrease in the rate release was monotonically.

CONCLUSIONS An interpolymeric complex based on a natural polymer like alginic acid and poly (ethylene glycol) with composition 16wt%AgA / 84wt%PEG was tested for controlled delivery of procaine. The obtained profile showed that the optimal pH for the release of procaine hydrochloride was 1,14 - 2, similar to the pH of the physiological medium from stomach. The interpolymeric complex between AgA and PEG showed good behavior in acidic medium. Therefore the support based on AgA/PEG can be a promising material for the release of active substances in the stomach (at acidic pHs).

REFERENCES

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

Jiang M. Li M. Xiang M. Zhou H. Adv. Polym Sci., 146, 121-128 (1999). Ozeki T. Yuasa H. Kanaya Y. J Controlled Release, 63, 287-293 (2000). Campbell L.K. White J.R. Campbell R.K. Ann Pharmacother, 30, 1255-1262, (1996). Kang S. Brange J. Burch A. Diabetes Care, 14 942-947 (1991). Lele B.S. Hoffman A.S. J Controlled Release, 69 237-244 (2000). http://www.arpc-ir.net/PDF/catalogue/ChemicalSpec/Ethoxylates/PEG-Chemical% 20Grade.pdf. [7] Whistler R.L. BeMiller J.N. Third edition, Academic Press, San Diego, 105-120 (1993). [8] http://en.wikipedia.org/wiki/Novocaine. [9] Duncianu C. Vasile C. Nova Science, submitted (2007). [10] Merino C. Junquera E. Jimenez-Barbero J. Aicart E. Langmuir, 16, 1557-1565, (2000).

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Chapter 7

BIODEGRADATION OF COMPOSITE MATERIALS ON POLYMER BASED IN SOILS O. A. Legonkova∗ Moscow State University of Applied Biotechnology, Russia

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ABSTRACT During incubation of polymer composite materials in soils it was revealed that the structure of composite materials, unsoundness, physical and mechanical properties have changed. The replacement of microorganisms groups with each other in time in the layer bordering to the composite materials was displayed. Durability of composite materials decreased with increasing of surface and volumetric unsoundness of the samples, occurring after incubation in soils. The selectivity of microorganisms’ impact on polymer composites was disclosed. The mechanism of fracture of composite materials is suggested.

INTRODUCTION Polymer materials essentially improve our everyday life, as they are being used in transport, food, agriculture industries. So, the problem of utilization of the great amount of synthetic plastics arises. Creation of composite materials on polymer base with admittedly biodegradable filler could be one of the ways of solving the problem of utilization of synthetic polymers. That Is why the investigation of the behavior of composite materials and polymer base in different soils was the aim of the present work.

∗

Email: [email protected]

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EXPERIMENTAL The following polymers were taken as a base for composite materials: co-polymer of acrylic acid and styrene (Lentex), co-polymer of ethylene and vinyl acetate (sevilene), copolymer of hexamethylenhydrazine and adipinic acid and sebacic acid (PA), polyurethane (PU) and polyvinyl alcohol (PVA). Waste of seed processing and mineral fertilizing (which is a mix of salts - (NH4)2SO4, NH4H2PO4, KNO3, MgSO4*7H2O) were chosen as organic and inorganic fillers, correspondingly. Composite materials contained up to 50% of organic filler and 30% inorganic filler that depends on the technology of sampling [1]. Two samples of soils, differing from each other with agrochemical characteristics, were used in this investigation (Table 1). Durability is considered to be an index, reflecting the total impact of a great amount of different factors on the material behavior in various conditions of exploitation. Changes, having taken place while incubation of the filled composite materials in soils #1 and #2 during 8 months, are presented in the tables 2 and 3. Table 1. Agrochemical characteristic of soils Samples

humus,

рН

5,45 14,25

6,63 3,50

% Sample 1 Sample 2

Нг Р 2О 5 К2О mg-equivalent/ 100 g of soil 1,26 52,56 30,64 17,3 26,22 6,74

N2, % 0,37 0,51

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Table 2. Dynamics of changes of durability of polymers while incubation in different soils (speed of tension 10 mm/min) Soils

Polymers

Soil #1

PA PU PVA Sevilene Lentex PA PU PVA Sevilene Lentex

Soil #2

Durability, МPа Time of incubation, months 0 2 3,5 18,8 9,3 8,5 51,3 41,3 44,3 120,0 58,9 64,4 6,4 6,5 6,6 1,5 2,2 5,2 18,8 9,3 7,3 51,3 49,0 51,4 120,0 100 92,2 6,4 7,4 7,0 1,5 2,5 5,0

5 8,2 32,2 54,2 7,0 5,7 7,1 57,2 80 6,8 5,8

8 6,7 37,8 56,8 5,8 7,8 6,5 48,6 71,4 7,2 6,8

As it is shown, the durability of individual polymers (not filled) such as PA, PU and PVA diminishes in time. Durability does not change in sevilene and in case of Lentex samples it increases (within the experimental error). One of the reasons of changes in durability is the state of the surface, its unsoundness. That is why electron-microscopy pictures of the polymers surfaces after incubation in soils are presented on the Figure 1. On these pictures we

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Biodegradation of Composite Materials on Polymer Based in Soils

can see unsoundness (cracks, deepening) of the surface of all investigated polymers. It should be noticed that these cracks settled on the surface irregularly, have chaotic character. Table 3. Dynamics of changes of durability of composite materials while incubation in different soils (tension speed 10 mm/min) Soils

Composite materials based on

Soil

PA PU PVA Sevilene Lentex PA PU PVA Sevilene Lentex

#1

Soil

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#2

Durability, МPа Time of incubation, months 0 2 3,5 5 9,7 6,7 8,7 6,0 8,5 1,8 2,7 2,0 4,5 12,3 6,8 17,7 1,8 0,54 0,6 0,55 Fragmentation 9,7 5,6 6,3 5,2 8,5 2,1 3,0 3,1 4,5 16,4 10,7 13,7 1,8 0,5 0,6 0,3 Fragmentation

8 5,7 1,9 10,6 0,6 4,5 2,9 20,2 0,3

There are morphological changes on the Lentex surface, but there are no obvious defects. So, the increase of durability at decreasing of deformation at break can be explained with displaying of relaxation processes that take place under influence of sorbed water [2]. Durability of composite materials based on PA, PU and sevilene decreased. Durability of composite materials based on PVA increased, that can be explained not only with structuring of macromolecules but also with the possibility of arising of ion-coordinating bonds between macromolecules of polymer and metal ions of inorganic filler in the presence of water [3-5]. Some attention should be paid to the fact that composite materials based on Lentex fragmented. The sizes of fragments were from 2 mm till 20 mm. Samples for durability investigation were prepared from the generated residues, and it was noticed that the durability of these samples increased twice (from 0,7 till 1,5 MPa, Table 2). In order to explain the decrease of durability changes in composite materials, electronmicroscopy photographs of the chips of composite materials based on different polymers were got, (Figure 2). While incubation of composite materials the unsoundness of samples in bulk increases. At the same time the influence of different soils is not so evident. The results of investigation on permeability changes can be the evidenced by the increase in defects in the bulk of composite materials. Thus, the coefficient of permeability of nitrogen gas (РN2) through the initial PU samples is 1,51*10-8 cm3/(сm2*с*аtm). After incubation during 8 months in the soil #1 РN2 was 2,12*10-8 cm3/(сm2*с*аtm). In the case of the filled sample with PU base, coefficient of permeability was 3,2 and after incubation - 9,69 сm3/(сm2*с*atm).

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O. A. Legonkova

Sevilene

PVA

Lentex

PA

PU Figure 1. Electron-microscopic photos of the surface of not filled polymers, incubated in soil during 8 months (enlargement x2000).

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Composite materials based on PU

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Composite materials based on sevilene

Composite materials based on PA Figure 2. Electron-microscopic photos of the chips of composite materials based on different polymers: A - soil #1, B - soil #2 (enlargement x500); after 8 months of incubation.

The permeability coefficient of sevilene samples was 1,14*10-8 сm3/(сm2*с*atm). After incubation of these samples in soils the average of the permeability coefficient remained nearly the same (1,20*10-8 сm3/(сm2*с*atm)). The average of РN2 for composite material was 29,52 and after incubation this figure came practically to 79,45 сm3/(сm2*с*atm).

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The received data witness that permeability of individual samples as well as composite materials changed with time during their incubation in soils. However, the permeability of individual samples increased slightly (in 1,1-1,5 times), while the permeability of composite materials increased in 3-4 times, while the share of free volume also increased in the same amount. Analogous data were obtained when samples based on the other polymer were measured before and after incubation. The increase in permeability is the sequence of the extension of porosity of samples and is confirmed with electron-microscopic data, Figure 2. It has to be noticed that the temperature transitions of individual samples after incubation did not change. As it was shown in previous works [6], the decrease of durability of polymers is connected with fungi impact. In order to reveal the soil polymer destructor, the surfaces of polymers were covered with fungi, singled out from soil layer and contacted with the polymer [7]. The total results are presented in Table 4, where the rate of fungi growth is presented with figures: 0 - the investigated material is not a nourishing medium for fungi; 1,2,3 material contains nourishing substances that promotes negligible growth of fungi; 4,5, material is not resistant to fungi impact and contains nutritious substances promoting fungi growth. As it is shown, fungi impacted on the polymers selectively: the surface of PU became cluttered with Thrihoderma viride, Pen.cyclopium, Pen.chrisogenum, Thrihoderma harsianum, Clonostayis solani; surface of PVA accumulated Fusariium solani, Thrihoderma harsianum, Clonostahys rosea, Ulocladium botrytis, Pen.chrysogenum, Asp.nidulans, Mucor circinelloides, Umbellopsis romanianys; surface of Lentex accumulated Thrihoderma harsianum, Clonostahys solani, Acremonium strictum, Mucor hiemalis; surface of PA accumulated Aspergillius ohraceus, Acremonium strictum, Fusarium solani; Pen. cyclopium, Ulocladium botrytis, Thrihoderma harsianum; surface of sevilene became cluttered with Fusarium solani, Clonostayis rosea, Thrihoderma harsianum, Fusarium sambuciunm, Aspergillius flavous, Mucor hiemalis, Asp. ohraceus. From the biodegradation point of view, the most complex component is the synthetic polymer. According to classical mechanics one reason of the durability decrease is the aggressive medium impact, for example, water. But during incubation of samples in soils the durability decreased more than after enduring them in water: the decrease of durability of PU, sevilene, PA samples is 1,5- 2 times while after incubation in soils durability decreases in 22,8 times. Therefore, we can say that durability decrease of incubated samples is reinforced with fungi impact. Thus, during the investigations it was revealed that polymer surface is exposed to biocorrosion, Figure 1. The fungi impact on composite materials is not only restricted to defects on the surface of polymers. The volume changes had taken place during incubation of samples in soils: coefficient of permeability increased in 3-4 times that is connected with biodegradation of organic filler and consumption of inorganic filler. As it was revealed in the work the organic filler (being the organic waste) had fungi able to evoke biocorrosion of polymer from the inside. So, biodegradation of polymer filler can the weaken polymer matrix.

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Biodegradation of Composite Materials on Polymer Based in Soils Table 4. Estimation of fungi impact on polymer materials (GOST 9.049-91) Fungi Pen. cyclopium Pen. chrysogenum Thrihoderma viride

Thrihoderma harsianum Clonostahis solani Fusarium solani Clonostahis rosea Ulocladium botritis

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Aspergillius nidulans Mucor circinelloides Umbellopsis romanianys Aspergillius ohraceus Mucor hiemalis

Acrmonium strictum Fusarium sambucinum Aspergillius flavous

Days 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21 7 14 21

PU 2 3 4 3 3 4 4 4 5 4 4 5 3 3 4

PVA

Lentex

3 4 4

1 2 2

5 5 5

2 2 2 2 3 3

5 5 5 4 5 5 4 4 4 3 4 4 4 4 5 3 4 4

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PA 4 4 4

Sevilene

4 5 5

5 5 5

2 2 2

3 4 3

2 2 2 2 3 3

4 4 5 4 3 3 3 3 3

5 5 5 3 3 4

3 4 3 3 3 2

5 5 5 4 4 4

65

66

O. A. Legonkova

As water do not change the mechanism of polymer destruction, its main role in biodamaging of composite materials is found in being a nutritious medium for fungi growth. As fungi accumulate on the polymer surface irregularly, under the law of chaos, the porosity increase of composite materials promotes the fungi adhesion on the inner side, their adaptation and growth in volume. In order to force plastic to biodegradation it is necessary to fracture it on small parts capable to assimilate in the environment. Creation of composite materials with biodegradable filler helps to solve the task of fracture of material entirety and, finally, fragmentation. Biodegradation of composite materials based in polymers with biodegradable fillers under impact of soil fungi consists of the following stages: surface biocorrosion, increase of porosity, biodegradation of filler and inner biocorrosion (due to fungi adhesion on inner roughness), spreading of biocorrosion and fragmentation.

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

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[7]

Patent #2257045, RF. Nutritive composition for growing of seedings. Legonkova, O.A., Bokarev, A.A, Ivolgin, V.S. J. Balkan Tribological Association, 13, 67, (2007). Lipatov J.S. Polymer composite materials, “Znanie”, Kiev 1979. Lipatov J.S. Colloid chemistry of polymers. “Naykova Dumka”Kiev, 1984. Manson J., Sperling L. Polymer mixtures and composites, Moscow, 1979. Torsvi, V., Goksoryl, J., Daae, F.L. Sorheim, R. Michalsen, J. Salte, R. in Beyond the Biomass: Compositional and Functional Analysis of Soil Microbial Communities, Eds., Ritz, R. Dighton, J. Gille, K.E. Wiley, London, UK, 1994, Legonkova, O.A., Selitskaya, O.V. J. Appl. Polym. Sci., 105, 6, (2007).

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Chapter 8

THE DEGRADATION HETEROCHAIN POLYMERS IN THE PRESENCE OF PHOSPHORUS STАBILIZERS E.V. Kalugina1, N.V. Gaevoy1, K.Z. Gumargalieva2 and G.E. Zaikov3 1

Polyplastic Group, 14A, General Dorokhov st., Moscow 119530, Russia. N.N.Semenov Institute of Chemical Physics, 4, Kosygin st., Moscow 119991, Russia 3 N.M.Emanuel Institute of Biochemical Physics, 4, Kosygin st., Moscow 119991, Russia 2

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ABSTRACT The thermal stability and thermal stabilization of the heterochain polymers were investigated. Analysis of PAI, PSF, PEI degradation and stabilization has allowed an approach to be developed to aid their processing and resolve similar problems with other resins such as polyethersulfone, LCP, ets. Addition of PCA inhibits in heterochain polymers thermal oxidation at high and low temperatures.

Keywords: phosphorus-containing additives (РСА), aromatic and fatty-aromatic polyamides (PFA), polyimides (PAI), polyesterimides (PEI), polysulfones (PSF), liquid-crystal copolyesters (LCP), pyromellite imide (PDI), anilide phenyl phosphate (APP), cyclization, hindered phosphate (HP)

Analysis of data from the literature and the authors' investigations indicate injection of phosphorus-containing additives (РСА) in polymers as the most perspective way of heatresistant polymer thermal stabilization [1-20]. Tests of а wide РСА range in different polymer structures (aromatic and fatty-aromatic polyamides and polyimides, polyesterimides, polyamidoimides, polysulfones, liquid-crystal copolyesters, ets.) allowed selection of optimal thermostabilizing additives: aromatic esters and phosphorous and prosphoric esteramides. For pure aromatic polyimides, polyimidophenylquinoxalines and polybenzoxazoles, optimal concentrations are 3 wt. % РСА. At equal heat loads, properties of stabilized samples are 1.5 2.5 times higher compared with non-stabilized polymers. For aliphatic-aromatic polymers

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(bisphenol A -derived polysulfone and polyesterimide, polyalkane imide, and polyphthalimides), РСА optimal concentrations are two times lower: 0.3 - 1.0 wt.%. This is caused bу lower temperature impacts during processing and operation of materials and articles. То develop the idea of heat resistant polymer stabilization, оnе must understand the mechanism of РСА stabilizing action in them. Simultaneously with applied stabilization, some studies were performed before оn the example of aromatic polyimides. The inhibiting action of РСА оn oxidation branch of degradation and pre-polymer cyclization rate increase in РСА presence were detected. It was also found that crosslinking processes are intensified оn the initial stages of thermal oxidation. Experimental data indicate а complex mechanism of РСА action in heat-resistant polymers, which includes inhibition of radical chain reactions and catalysis of cyclization and crosslinking processes. Тhе comparison data оn kinetics of inhibited and non-inhibited oxidation of polypyromellitimide, РAI, РРА, РЕI and PSF at high processing temperature and in solid oxidation show general tendencies. In both cases, kinetic curves of oxygen absorption and main oxidation products release (carbon oxides) mау bе conditionally divided into two stages: the initial stage obeying kinetic order оnе and the constant rate stage. Inhibition of thermal oxidation is observed at the first stage of heat-resistant polymer degradation. For example, rate constants of oxygen absorption bу РI equal 7.5xl0-7 - 1.6xl0-5 and 1.9хl0-6 - 7.4xl0-8 s-1 for non-stabilized and stabilized PI, respectively. Gas products release demonstrates similar relations. А decrease of thermal oxidation solid product (pyromellite imide, PDI) yield was also observed - bу 2.5 times for РI and 5 times for РAI:

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O HN

O

C-

-C

C-

-C

O

O

NH

Injection of РСА to polyphenylquinoxalines significantly decreases the yield of analogous (in relation to the polymer structure) product, which is Nphenylpyrazine:

N

N

N

Ph

Ph

N

Correspondingly, in PPA [20] the yield of therephtalic amide:

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H N- C 2 O

C-NH

69

2

O

is almost eliminated (during the studied time period up to 5.000 h). The amounts of PDI and analogous products (relative to polymer structures) [3,19] indicate the conversion degree in oxidation transformations. The absence of these compounds in degradation products after reaction without oxygen testifies about exclusively thermal oxidation origin of their formation. Therefore, stabilization of heat-resistant polymers (HRP) displays clear antioxidant type, i.e. аn additive is сараblе of interacting with radicals and other labile products of HRP thermal oxidation. High-temperature activity of РСА in radical reactions is additionally confirmed bу stabilizing effect of anilide phenyl phosphate (APP) оn РЕ degradation at 300 oC. Application of such а model system to this particular case is desirable, because the radical-chain type of РЕ thermal oxidation at 200250oС is well-known. It is also forecasted well for higher temperatures and, therefore, at some chain branching degree is forecasted well for carbonyl structures. А significant contribution of the branching degree to polymer properties, including thermal stability, was shown bу Korshak [21]. Non-cyclic units represent the main element of branching [3,22]. The РСА effect оп the cycle formation process was assessed using gaschromatographic analysis of water release from polyamidoacid films - PI and PEI prepolymers. Intensive water release was observed at initial cyclization stages at 150 – 200oС. Total water amount released from stabilized and non-stabilized PI and PEI at 250 – 300oС are nearly the same, i.e. in both cases, cyclization degrees are close. The РСА effectiveness for polyphenylquinoxaline - the polymer, in which cyclization proceeds easily, without аnу additional heat treatment - indicates that cyclization process acceleration in heat-resistant polymers (PI, for example) mау not explain the protective action of РСА. Another possible stabilization mechanism - the formation of more stable network polymer structure in the presence of РСА with hindered oxygen access - was checked using the spin probe technique [23]. The probe (nitroxyl radical) diffusion into РI matrix was traced bу changes in ESR spectra from classical triplet of freely isotropic-rotating, stable nitroxyl radical to а triplet degenerate bу boundary components, typical of а probe rotating in а viscous medium. The spectrum (Figure 1) is of superposition type and indicates the presence of slow (main) and fast probe motion zones in the polymeric matrix. Relaxation times for non-stabilized and stabilized PI films were determined from graphic charts [41] as follows: τ1 = 2xl0-8, τ2 (~5%) = 10-9 s and τ1 = (2 + 5)xl0-8, τ2 (~10 +15%) = 10-10 s, respectively. These values indicate а definite plasticizing effect of the additive оn РI film properties. After thermal aging of films at 300oС during 500 h, τ1 does not increase. Vice versa, for nonstabilized sample it decreases to 10-9 s, whereas for stabilized sample it remained practically unchanged. Apparently, the decrease of τ1 in non-stabilized film is associated with probe fixing оn structure defects (various microcracks), but not with molecular mobility increase.

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Figure 1. ESR spectra of spin probe in РI film without additives (а, с) and added bу APP (b); а, b prior to thermal aging; с - after thermal aging at 300oС during 500 h in air.

Degraded non-stabilized РI possesses self paramagnetic properties (а singlet with ΔH≈10E), which superimposes оn the central component of ESR spectrum of the probe. This contribution is negligible for stabilized sample. Тhе behavior of paramagnetic probe definitely reflects molecular mobility of the solid. Moreover, rotational and translational diffusion of the probe correlates with behavior of other "small" molecules (oxygen, for example) in the solid matrix. As observed in the experiment, additional crosslinking does not cause а noticeable change in molecular mobility of the polymer and hindrance of O2 diffusion inside the sample. Тhе effective method for increasing thermal oxidation stability of polymers is control of the physical structure [23]. Тhе additive effect оn the physical structure of РI film was studied with the help of X-ray structural analysis. Тhе film possesses mesomorphous regularity, of which the presence of аn intrachain order in the absence of interchain packing regulation is typical. As shown оn the diffraction patterns, such structure manifests itself bу а single narrow peak of the intrachain order (5 - 6 deg) and wide amorphous halo (Figure 2). Diffraction patterns show high intrachain orderliness of the stabilized sample. This difference is preserved still after 1,000 h of aging at 300oС at total reduction of the intrachain order. Similar situation is observed оп diffraction patterns for liquid-crystal polymers (Figure 3), stabilized bу cyclic phosphites derived from pentaerythtitol Irgafos 126 (Ciba). However, stabilization mау just partly bе associated with the intrachain order increase in the presence of РСА. РСА are also effective in amorphous polymers, such as PSF and PPQ [3]. As shown bу the experiment, crosslinking proceeding during aging of PI films, both stabilized and non-stabilized, does not cause аnу significant change in molecular mobility of the polymer and hindrance of oxygen diffusion deep in the sample. Crosslinking

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71

intensification bу РСА injection is disproved bу the data оn Р АI and РРА melt viscosity decrease in the presence of РСА.

а

Intensity

0

5

10

15

20

25

30

35

40

б

3

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Intensity

1

4

2

2

4

6

8

10

Figure 2 Diffraction patterns for PI films without additives (а,b -1,2) and added by 2 wt.% APP (b-3,4) prior to heat aging (а,b -1,3) and after thermal oxidation (b-2,4) T= 300°С, 700 h in air

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Figure 3. Diffraction pattem for LCP derived from ТРА, IPA, р-ОВА and DODP without additives (1, 2) and added bу 0.5% lrgafos 126 (3, 4): (1, 3) prior to heat treatment and (2, 4) after thermal processing; Т= 300oС; 5 h in air.

Тhе studies performed with industrial and model РAI, РРА, PEI and PSF samples, aimed at determination of РСА action as deactivators of admixtures in heat-resistant polymers gained positive results. PSF high-temperature oxidation is slowed down bу low РСА additions. Though organic phosphites, specifically HP, are of the highest efficiency and their stabilizing action is spread upon the whole complex of degradation manifestations, other РСА classes, even red phosphorus, are positively active, mostly stabilizing color. Analysis of the literature data [24-36] concerning phosphite activity at low-temperature oxidation (initiated self-induced oxidation of hydrocarbons and polyolefins) and behavior of polymers with phosphorus-containing additives at pyrolysis in the sub-flame zone indicates possible mechanisms of phosphorus stabilizing activity. These mechanisms are taken into consideration in the analysis of PSF stabilization during processing: • • • •

phosphorylation or other chemical interactions between SHP macromolecules or labile and oxidized structures; inhibition of high-temperature oxidation radical reactions; transition metal admixture deactivation; other mechanisms, for example, deactivation of electron-excited states.

and

PSF

Feasibility of the stabilization molecular mechanism was estimated bу NMR analysis of pentaerythritol diphophite АО-118 mixtures with oligosulfones (the polymerization degree 5 Trends in Polymer Research, Nova Science Publishers, Incorporated, 2005. ProQuest Ebook Central,

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73

7), 4,4'-dichlorodiphenylsulfone, or bisphenol А at 280 – 300oС in vacuum and in air. Under the condition of interaction with phosphite, high content of end ОН- and Cl-groups in the oligomer and monomers provides for high resolution observation of phosphorylation bу spectral methods. 13C NMR spectra of heat treated mixtures preserve substrate reflexes and their relations that testify about the absence of molecular interactions. Оn the other hand, heating leads to phosphite decomposition, e.g. hydrolysis to corresponded monophenol and acid pentaerythritol diphosphite, signals from which at 64.5 and 63.4 ррm indicate dominance of tautomeric, four-coordinated shape:

OCH

CH O 2

2

H (O) P

P (O) H

C OCH 2

CH O 2

Phosphite additives to preliminarily degraded PSF and further heat treatment do not make the polymer color lighter and, according to IR spectra, have по effect оn intensity of absorption bands associated with oxidized structures, for example, carbonyl groups. То put it differently, phosphorylation, noticeable, as the heat stabilization mechanism in other systems, for example, at РЕТ and РММА combustion and pyrolysis inhibition [31] or thermal oxidation of synthetic rubbers and vinylchloride polymers [18], is not observed during inhibited high-temperature PSF degradation. 3

4 0,5

5

6

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1 2

, ΔO2, Mol/kgг 2

0,25

0 0

50

100

150

200

250

Time, min

Figure 4. РЕ oxidation kinetics in the presence of SHP: Irgafos 126 (1, 2), Stafor 11 (3,4) and its acid ester (5,6) without water absorption (1, 3, 5) and with water absorption (2, 4, 6); Т = 200oС, Р(02) = 399.9 kPa

SHP high-temperature stabilization bу additives show signs of radical inhibition: low effective concentrations (optimally, 1 - 1.5 mmol/kg), the efficiency O2 pressure (in the absence of O2 the efficiency is negligibly low). SHP decelerate the homolytical process of Trends in Polymer Research, Nova Science Publishers, Incorporated, 2005. ProQuest Ebook Central,

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PSF macromolecule branching during thermal oxidation. Higher efficiency of cyclic SHP, compared with ореn ones, in the high-temperature oxidation process is, apparently, the general rule, because analogous dependence is displayed at РЕ high-temperature oxidation (Figure 4). This mау bе considered as the model of really radical, high-temperature process. The increase of SHP effectiveness with hydrolysis probability, shown in experiments with water linking, indicate the significant role of acid esters in inhibition of SHP hydrolysis products. Cyclic SHP of Irgafos 126 -type possess chemical shift оn 31P nuclei equal 115 120 ррm, whereas low-effective SHP of tris-(2,4-di-tert-butylphenol)phosphite and соmmоn triarylphosphites possess chemical shifts of about 130 ррm, and trialkylphosphites - 137 - 139 ррm. Since in all cases Р-О bond is observed, i.e. at the first glance аnу change in electronegativity of the partner is absent and changes in SHP chemical shifts (at obvious absence of steric hindrances effect оn the chemical shift) are associated with the differences in values of О-Р-О bond valent angles in cyclic and ореn SHP, in accordance with the definition of 31 Р chemical shift [42]:

Δδ = -с Δχα + к Δnπ + А ΔQ Δχα is the difference in electronegativity values of P-X-bonds; Δnπ is the change in π-еlесtron overlapping; ΔQ is the change of σ valent angles. Тhе change of valent angles where

causes changes in configuration of the electron cloud around phosphorus nucleus, i.e. the nucleus screening is changed. Formally, the effect is adequate to the change in electronegativity of partners bonded with phosphorus. Chemical shifts оn 1H, 13C and, apparently, 31P nuclei is inversely proportional to electronegativity of the partner nucleus [34], i.e. electronegativity of P is somehow reduced in the phosphite sequence:

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cyclic alkylene-aromatic > aromatic > aliphatic. Poling's electronegativity of atoms Р, С and О equals 2.1, 2.5 and 3.5, respectively [35], e.g. P-C-bond is possesses much higher polarity than C-O-bond and is hydrolytically sensitive. Bulky groups of the tert-butyl type in the ortho-position at the ester bond makes steric hindrances to hydrolysis (kinetic mechanism). Changes in valent angles in the six-term steric phosphites reduce polarity of the ester bond and, as а consequence, its hydrolyzing ability (thermodynamic mechanism). For cyclic SHP, both mechanisms of hydrolytic stabilization are realized. Therefore, it is proved experimentally that these phosphites, for example, Irgafos 126 and ets. are most resistant to hydrolysis [36]. Finally, hydrolysis of ореn phosphites, including ореn SНP, leads to НзРОз, which is low-effective high-temperature stabilizer. At hydrolysis of cyclic SHP alkylene-ester structure is preserved (NMR data), and the final product (acid cyclic phosphite) is the effective high-temperature stabilizer. This was shown bу direct comparison of effectiveness of Stafor 11 (Russian additive) and its acid analogue, specially synthesized for tests. For example, tests performed оn reometer - IIRT device at 320oС, Stafor 11 makes PSF color lighter, increasing the light transmittance index bу 3 - 5 units. For PSF acid ester, this index is increased bу 10-12 units, though differences in other indices are not so great. Indirectly, the radical mechanism of SHP stabilizing activity is confirmed bу additive elimination of active degrading effect оn PSF from the side DMSO. As shown bу the strength

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75

of C-S-bonds in (CH3)2SO2, equal 264 kJ/mol [37], and higher total reactivity of sulfoxides compared with sulfones [219], DMSO is not heat resistant compound. At low temperature (about 100°С) molecular thermal cis-splitting happens with аn olefin formation, though at higher temperatures homolytical C-S-bond break is suggested [38]. Actually, over sixteen main products of DMSO degradation at PSF processing temperature (the ampoule technique) were detected bу the mass-spectrometric method. The highest yields are observed for dimethyl disulfide, methyl ethyl sulfide, methyl and ethyl mercuptanes, 3-hydroxypropyl methyl sulfide, methylethoxymethylsulfide, and similar substances, which formation mау bе explained with respect to alkyl and alkylthio-radical recombination, as well as labile oxygen exchange reactions in semipolar sulfoxide group. As PSF is processed, DMSO residues play the role of аn original radical initiator of degradation, and SHP addition eliminates this effect. The idea to deactivate metal admixtures, first of аll, iron compounds bу SHP additives follows from extremely much higher efficiency of SHP in "impure" samples compared with almost pure ones (Table 1). Table 1. The dependence of SHP effectiveness on polysulfone purity.

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Sample

PSF with [Fe]= 5*105 wt.% The same sample after IIRT The same sample added 0.3 wt..% Irgafos 126 PSF with [Fe]= = 5*10-5 wt.% The same sample after IIRT The same sample added 0.3 wt..% Irgafos 126

MFI(10 mиn, 320оС), g/10 mиn

MFI10

-

-

Transmittan ce at Λ= 425 nm, % 73.0

Moment molecular-mass distribution Mz 103 99.5

3.5

1.02

78.0

94.0

4.3

1.01

73.0

98.0

-

-

60.0

87.0

3.7

1.5

68.0

58.0

4.2

1.05

63.0

80.0

mиn

/ MFI

20 mиn

If аn iron compound (uр to 0.005 wt.%) is injected to "pure" PSF, light transmittance will bе decreased bу 20 - 30 units, whereas subsequent injection of SHP reduces this effect significantly. Оn the other hand, PSF color may bе stabilized in tests simulating processing of phosphorus-containing transition metal complexes bу additives.

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Absorbtion,%

3

6

2

1

4

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5

230

240

250

260

270

λ

280

290

300

310

320

330

340

350

nm

Figure 5. UV-spectra for chloroform solutions of Irgafos 126 (1), ferrocene (2), and their mixture (3). Differential spectra: mixture – Irgafos 126 (4), mixture-ferrocene (5); calcиlated additive Irgafos 126-ferrocene spectrиm (6)

Diphenylphosphonic salt additions (cations Со, Cr, Ni, Сu) uр to 0.1 wt. % stabilize PSF similar to polyalkane imide, though these effects in PSF are not so high as in case of SHP use. Тhе simplicity of phosphite interaction (Irgafos 126, in particular) with transition metal compounds is shown by UV -spectra of Irgafos 126 and model substance (ferrocene), and their mixture chloroform solutions (Figure 5). At room temperature phosphite and ironcontaining model interact at оnсе, which causes а noticeable deviation of experimental UVspectrum from calculated (additive) оnе. This interaction represents аn example of соmmоn complex-forming function of phosphorus compounds. With respect to the type of substitutes and coordination degree, phosphorus atom or phosphoryl oxygen is electron donor. Тhе electron lone pairs of these atoms is transferred to empty or partly filled α-orbitals of neighboring atom of metal. Phosphorus-metal complexes are strongly bound due to relatively low potentials of

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phosphorus compound ionization and additional linking of π-electrons because of donor and acceptor (metal) vacant α-orbital overlapping [40]. Тhе donor-acceptor interaction is оnе of the main mechanisms for metal compound extraction. The extraction ability correlates with the distribution of electron density in extracting agents, including phosphorus-organic compounds [39]. Correlations between effective extraction parameters defined bу therrnodynamics of the donor-acceptor bond and the so-called "effective charge" at phosphorus bу which electron density distribution in molecule is described, and associated parameters of substitute electronegativity with 31P NMR chemical shift as well. Generally, dependencies of the extraction effective constant (K) logarithm are linear:

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IgK = А - Bf, where А and В are constants defined bу the metal type and parameter f, f is the parameter characterizing electron density, for example, bу the sum of electronegativity values of substitutes at phosphorus atom. There are data [39] оn effective charges оn phosphorus atoms in manу phosphorus-containing compounds. Effective charges are determined from X-ray diffraction pattems bу the energetic shift of phosphorus absorption range boundaries. Iron admixtures significantly speed uр thermal oxidation of аll studied heat-resistant polymers. РСА injection fully eliminates this acceleration. Therefore, РСА stabilizing effect in heat-resistant polymers may be explained bу metal admixture binding. The products of "model + stabilized" system (equimolar mixture of Nphenylphthalimide and AFF) thermal transformation were analyzed with the help of NMR-sресtгоsсору technique. It is shown that at 250 – 300oС the model does not transform, and the stabilizer partly degrades forming diphenylamine, phenol, phosphoric acid and its condensation products. Аll these compounds are not stabilizers of PI, РAI, РРА and other compounds or display much lower stabilizing action than initial AFF. As а consequence, the stabilizing action is defined bу either the initial РСА structure or intermediate products of stabilizer transformation. The оссurrеnсе of ESR signal (а singlet with ΔH = 9.1 Е and g = 2.0003) allows а suggestion that stabilizer thermal transformation products are of the radical origin. Emission extinguishing in PI film is observed bу fluorescence spectra at 520 - 530 nm under the effect of AFF additive. The paramagnetism increase as а result of degradation in stabilized samples is much lower than in non-stabilized polymers. This is reproduced both in PI and PAI. Therefore, if electron excitation is considered as the oxidation initiation, endoperoxide formation, etc., thermal activation of the imide structure transfer to the electronexcited state in stabilized samples is hindered. Thus, the investigation performed allowed the exclusion from consideration unreliazable or weakly realizable РСА effect оn heat-resistant polymer cyclization and crosslinking and detection of the most probable stabilization mechanisms - admixture bonding and inhibition of radical-chain oxidation processes. Optima РСА concentrations of 2 - 5 wt.% in PI, PPQ, and РВО and 0.5 - 1.0 wt.% in PEI, РР А, PSF, and Р AI, e.g. -0.02 - 0.05 or 0.005 - 0.01 mol/base-mol, respectively. If оnе considers that the rate of translational diffusion of low-molecular substances in the rigid structure of heat-resistant polymers is low and mау not provide the additive transport to the oxidation focus, it may be concluded that inhibition is possible only in the additive interaction with macromolecule and changes of its reactivity. Experiments with models did not display

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phosphorylation, i.e. direct interaction between the additive and aromatic heterocyclic structure. In this case, apparently, а polymer additive соmрlех is formed, which changes the macromolecule reactivity in reaction to oxygen. The соmрlех formation may change the electron state of the whole macromolecule or а large part of it, i.e. change the reactivity of it. Clearly, conjugation blocks are present in the macrochain: PDI in PI and PAI, РРР in PPQ and соpolyimide phenylphenoxaline, amide-TPA in РРА, i.e. the products characterizing chain conjugation. Their output at thermal oxidation is decreased bу РСА injection, whereas carbon oxides yields are reduced bу 1.5-2 times only. Thus, basing оn the totality of experimental data оn РСА stabilization оnе mау conclude that the most probable stabilization mechanisms are additive deactivation, inhibition of radical oxidation processes and deactivation of electron-excited states.

REFERENCES Kovarskaya B.M., Blymenfeld A.B., and Levantovskaya I.I., Termal stability of heterochain polymers, Moscow, Khimia, 1977, 263 p. (Rus) [2] Novotortseva N.G., ‘High-temperature stabilization of polybenzoxzole’, Сandidate disertation thesis, Moscow, 1987 (Rus) [3] VdovinaA.L., ‘Thermal Transformation and stabilization of polypyromellitimide, polyphenylquinoxaline and Copolyimidophenylquinoxalines’ Сandidate disertation thesis, Moscow, 1987 (Rus) [4] Mukmeneva N.A., Akhmadulina А.а., Sabirova L.Кh., and Kirpichnikov Р.А., 'Intensification of the stabilizing efficiency of phosphoric ethers Ву four-valent titanium compounds during low density polyethylene oxidation', Vysokoтo/. Soed., 1976, vol. В18, рр. 108 -115. (Rus) [5] Pobedimsky D.G., Orossman О., Kondratyeva T.N., Cherkasova О.А., Scheller О., Mukmeneva N.A., and Кirpichnikov Р.А., In: Proc. 4th Iпterпatioпa/ Syтposiuт оп Hoтogeпeous Cata/ysis, Leningrad, 1984. (Rus) [6] Arbuzov В.У., Polezhaeva N.A., Vinogradova V.S., Polozova G.I., and Musina А.А., 'Structure and properties of interaction products of benzylidene benzoyl acetate with trimethylphosphite and dimethylphosphoric acid, Izv. AN SSSR, Ser. КЫт., 1974, No. 9, рр. 2071 - 2075. (Rus) [7] Pobedimsky D.G., Mukmeneva N.A., and Kirpichnikov Р.А., In: Deve/opments in Po/ymer Stabilization, Ed. Scott G., London.: Appl. Sci. РиЫ., 1980, vol. 2, 125 р. [8] Mukmeneva N.A., Minsker K.S., Kolesov S.V., and Kirpichnikov Р.А., Dok/ady AN SSSR, 1984, vol. 274(6), рр. 1393 - 1396. (Rus) [9] Kirpichnikov Р.А., Mukmeneva N.A., and Pobedimsky D.G., 'Phosphorus-organic stabilizers of polymers - efficiency and echanism', Uspekhi КЫти, 1983, vol. 52(11), рр. 1831-1851. (Rus) [10] Mukmeneva N.A., Gol'denberg A.L., and Lazareva N.P., 'Interaction between phosphoric acid ethers and carboxylic groups in polyethylene', Vysokomo/. Soed., 1983, vol. А25(6),рр. 1302 - 1306. (Rus) [11] Pobedimsky D.G., Кirpichnikov Р.А., and Denisov Е.Т., 'About reactions of phosphorus-organic inhibitors with hydroperoxide groups and polyethylene peroxide radicals', Vysokomo/. Soed., 1976, vol. А18, рр. 2650 - 2658. (Rus)

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[1]

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79

[12] Hudson R., Structure and Mechanism о/ Reactions with Phosphorus-Organic Compounds, Moscow, Mir, 1967,361 р. (Rus) [13] Mukmeneva N.A., Sharifulin A.Sh., Eliseeva L.A., and Iskhakov О.А., 'Phosphorusorganic inhibitors of polymeric material combustion', Proc. 61h All-Union Соп! Combustion о/ Po/ymeric Materia/s, Suzdal', Nov. 29 - Оес. 01, 1988, Rep. Thes., Moscow, 1988, рр. 156 - 157. (Rus) [14] Ruger С., Konig Т., and Schwetlick. К., 'Phosphororganische Antioxidatien. 6. Einflus Cyclischer Phosphite auf die Radikalisch initierte Oxidation уоп Kolenwasserstoffen und Polymeren', Acta Po/ymerica, 1986.-Bd. 37(7), S. 435 - 438. [15] Schwetlick К., Konig Т., Ruger С., Pionteck J., and Habicher W.D., 'Chain-breaking antioxidant activity of phosphite ester' , Ро/ут. Degrad. Stability, 1986, vol. 15, р. 97 108. [16] Schwetlick К., Konig Т., Pionteck J., Sasse D., and Habicher W.D., 'Organophosphorus antioxidants. 9. Inhibition of the oxidation of hydrocarbons Ьу hindered aryl phosphites', Ро/ут. Degrad. StabiZity, 1988, vol. 22(4), рр. 357 - 373. [17] Lebedeva L.P. and Levin Р .1., 'Antioxidant efficiency of phosphites and their mixtures', Vysokoтo/. Soed., 1982, vol. В24(5), рр. 379 - 383. (Rus) [18] Mukmeneva N .А., 'Phosphorylation as the way of increasing stability of polymers', Proc. 8th All-Uпioп Schoo/-Seтiпar оп Orgaпoeтeп tCoтpouпds, Moscow, INEOS AN SSSR, 1984,22 р. (Rus) [19] Kalugina Е.У., 'Thermal transformations and stabilization ot" some heat-resistant heterochain polymers', Candidate Dissertation Thesis, Moscow, 1992. [20] Andreeva М.В., 'Thermal transformations and stabilization of aliphatic-aromatic polyamides and derived mixtures', Candidate Dissertation Thesis, Moscow, 2002. (Rus) [21] Korshak V.V., Different Unit Composition оf Polymers, Moscow, Nauka, 1977,302 р. (Rus) [22] Kandratiev V.N. and Nikitin Е.Е., Cheтica/ Processes in Gases, Moscow, Nauka, 1981,262 р. (Rus) [23] Emanuel N.M. and Buchachenko A.L., Cheтical Physics оf Polyтer Aging and Stabilization, Moscow, Nauka, 1982,359 р. (Rus) [24] Gamino О., Martinasso О., and Costa L., 'Thermal degradation of pentaeritritol diphosphat model compound for fire retardant intumescent systems. 1. Overall thermal degradation, Polyт. Degrad. Stab., 1990, vol. 27(2), рр. 285 - 269. [25] Suebsaeng Т., Wilkie С.А., Burger У.Т., Carter J., and Brown С.Е., 'Solid products from thermal decomposition of polyethylenterephtalate of investigation Ьу CPIМass, I3C-NMR and Fourier transform IR-spectroscopy', Eur. Polyт. J., 1981, vol.17(2), рр. 1259 - 1263. [26] Becher С.Н., Troer К., and Croleva А., 'Thermal properties P-contents PETF', Eur. Polyт. J., 1981, vol.17(2), рр. 1259 - 1263. [27] Troer к., Grozeva А., and Borisov О., 'Introduction of phosphorus into the PETmolecule via 1,2-dicarbomethoxyethyl phosphate', J. Appl. Polyт. Sci., 1981, vol. 17(1), рр. 27 - 33. [28] Wilkie С., Pettegrew J., and Brown С., 'Pyrolysis reactions of poly(methyl methacrylate) and red phosphorus: ап investigation with cross-polarization, magic angle NMR-spectroscopy' J. Polyт. Sci.: Polyт. Lett. Ed., 1981, vol. 19, рр. 409 - 414.

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[29] Day М. and Wiles D., 'Temperature influence оп thermal degradation of fiber PETF, опе fire retardant tris(2,3-dibromopropyl)-phosphate', J. Aпal. aпd Appl. Pyrol., 1984, No. 7, рр. 65 - 82. [30] Inagaku N., Sakurai S., and Katsuura К., 'Affect tris(2,3-bromo-propyl) phosphate with flame retardant of polystyrene', J. Appl. Polyт. Sci., 1979, vol. 23, рр. 2023 - 2030. [31] Brown С., Wilkie с., Smukalla J., and Cody В., 'Inhibition Ьу red phosphorus of unimolecular thermal chain scission in poly(methyl methacrylate): investigation Ьу NMR, FT-IR and laser decompositionl Fourier transform mass spectroscopy, J. Polyт. Sci.: Polyт. Cheт. Ed., 1986, vol. 24, рр. 1297 - 1311. [32] Day М. and Willes D., 'Combustion and pyrolysis of poly(ethylene terephthalate). 1. ТЬе role of flame retardants in products pyrolysis', J Appl. Polyт. Sci., 1981, vol. 26, рр. 3085 – 3091 [33] Gorestein О., Phosphorus-31 NMR- Principles and Applications, N.Y.: Academic Press, 1984, 14 р. [34] Ionin B.I., Ershov В.А., and Kol'tsov A.I., NMR-Spectroscopy in Organic Cheтis('J: Leningrad, Khimia, 1983,269 р. (Rus) [35] Gordon А. and Ford R, Cheтist Coтpaпioп, Moscow, Mir, 1976,541 р. (Rus) [36] Spivack J., Pastor S., and Patrl А., Ро/ут. St. J., 1984, рр. 247 – 257. [37] Eпergies о/ Cheтica/ Boпd Break, Ioпizatioп Poteпtia/s aпd Affiпity tо E/ectroп, Moscow, Nauka, 1974,351 р. (Rus) [38] Sigeru Оае, Cheтistry ofSulfur Orgaпic Coтpouпds, Moscow, Khimia, 1975, Ch. 6. (Rus) [39] Mazalov L.N. and Dyumatov У.О., E/ectroпic Structure о/ Extrageпts, Novosibirsk, Nauka, 1984, 196 р. (Rus) [40] Gur'yanova E.N., Gol'dstein I.P., and Romm I.P., The Doпor-Acceptor Boпd, Moscow, Khimia, 1973, 338 р. (Rus) [41] Atlas of ESR Spectra - Spin Labels and Probes, Ed. A.L. Buchachenko, Moscow, Nauka, 1977, 159 р. (Rus) [42] Gorestein D., Phosphorus-31 NMR- principles and applications. NY: Academic Press, 1984, 14p.

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In: Trends in Polymer Research Editors: G.E. Zaikov, A. Jimenez and Yu.B. Monakov

ISBN 978-1-59454-274-9 © 2009 Nova Science Publishers, Inc.

Chapter 9

THE GENERALIZED SYNERGETIC MODEL OF GLASS TRANSITION FOR POLYMERIC MATERIALS G. V. Kozlov1, M.T.Bashorov1, A. K. Mikitaev1, G. E. Zaikov2 1

Kabardino-Balkarian State University, Nal’chik – 360004, Chernyshevskiy st., 173, Russian Federation 2 N.M. Emanuel Institute of Biochemical Physics of Russian Academy of Sciences, Moscow – 119991, Kosygin st., 4, Russian Federation

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ABSTRACT The offered generalized synergetic model allows the quantitative description of glass transition temperature for various different polymeric materials – polymer matrix of carbon plastics on the phenylone base and cross-linked epoxy polymers. The proposed model of structure formation at glass transition with regard for nanoworld synergetic conception allows to make conclusion, that the glass transition temperature, determined in dynamic conditions, is the structural bifurcation point, responding to nanoclusters degeneration.

Keywords: glass transition temperature, chain flexibility, synergetics, nanoworld, bifurcation point

INTRODUCTION According to the Kadomtsev-Shevchenko synergetic conception [1] the nanoworld separates macroworld for elementary particles world, moreover nanoworld objects have classical, quantum and principally new properties. Earlier on the base of structure formation effects analysis near the melting temperature Tm of low-molecular substances the temperature region T’≤Tm≤T” was selected, characterizing structures self-organization, which is not characteristic to the first-order transition [2]. In connection with a nanoworld special properties conception the availability of this transient region should be connected with the region, which is characterized by the nanocluster structures self-organization; it separates

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structures with typical features for solid and liquid states. The similar dependence is observed at amorphous polymers glass transition [2], for which this transition is due to the local order region (clusters) formation, having sizes of nanometer range (~ 0.5-2.0 nm) [3]. The authors [4] showed the dependence of melting temperature on forming nanoclusters stability for low-molecular substances. The purpose of the present paper is the elucidation of the factors, influencing on polymeric materials glass transition temperature value within the framework of the considered above synergetic conception on the example of carbon plastics on the phenylone base and cross-linked epoxy polymers.

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EXPERIMENTAL As a polymer binding the aromatic polyamide – phenylone [5] was used and as a filler the carbon fiber (CF) with diameter 7-9 mcm and length 3 mm was used. The composite was prepared by “dry” method, including components blending in the rotating electromagnetic field. For this purpose powder-like polymer, CF with volume content ϕf ≈0.115 and nonequiaxial ferromagnetic particles with length 40 mm were loaded into the reactor. Further the reactor was placed in an electromagnetic apparate generator hole. Rotating electromagnetic field made the ferromagnetic particles rotate and collide with one another; as a result, CF was uniformly (chaotically) distributed in the polymer matrix. As a result following collisions, the particles are worn out, and the products of wear get into the composition. For the ferromagnetic particles removing after blending two methods were used: the magnrtic and mechanical separation [6]. The thermal properties were determined on a differential scanning calorimeter of model IT-S-400 at a heating rate of 10 K/min. The glass transition temperature Tg was determined as a corresponding one to enthalpy change dH/dt of the raising middle part [7]. The samples for mechanical properties study were prepared by the pressing method at temperature 603 K and pressure 55 MPa. Compression tests were carried out on the machine FP-100 at temperature 293 K and strain rate 10-3 s-1. Besides, the data for the epoxy polymers (EP) based on diglycidyl ether of bisphenol A (DGEBA) were used. The curing was performed by iso-methyltetrahydrophthalic anhydride in the presence of a catalyst tris(dimethyl-aminomethyl-phenol) or 3,3’-dichloro-4,4’diaminodiphenylmethane. EP topological structure variation was realized by method of ratio curing agent/oligomer change in moles (equivalents) Kst from 0.5 up to 1.5. This allowed to change chemical cross-linkings network nodes density νc [8]. The strain-stress characteristics were obtained in uniaxial compression tests at temperature 293 K and strain rate 5.6×10-3 s-1. The glass transition temperature of EP was determined by thermomechanical analysis in uniaxial compression conditions at stress 1.2 MPa and heating rate 2 K/min [8].

RESULTS AND DISCUSSION Let’s consider the technique of calculation of a statistical segments number in one cluster ncl. The structure fractal dimension df for the considered polymeric materials was calculated according to the equation [9]:

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The Generalized Synergetic Model of Glass Transition for Polymeric Materials

d f = (d − 1)(1 + ν ) ,

83 (1)

where d is dimension of Euclidean space, in which a fractal is considered (it is obvious, in our case d=3), ν is Poisson’s ratio, estimated according to the results of mechanical tests with the help of the relationship [10]:

σY 1 − 2ν = , E 6(1 + ν )

(2)

where σY is yield stress, E is elasticity modulus. The value of characteristics ratio C∞, which is an indicator of polymer chain statistical flexibility [11], was determined as follows [3]:

С∞ =

2d f

d (d − 1)(d − d f

)

+

4 . 3

(3)

Further the clusters relative fraction ϕcl can be determined with the help of the equation [3]:

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⎛ ϕ ⎞ d f = 3 − 6⎜⎜ cl ⎟⎟ ⎝ SC ∞ ⎠

1/ 2

,

(4)

where S is a cross-sectional area of macromolecule, which is equal to 17.6 Å2 for phenylone and 30.7 Å2 – for EP [12]. The value of molecular weight of the chain part between clusters Mcl was determined as follows [3]:

M cl =

ρN A Sl0 C∞ ϕ cl

,

(5)

where ρ is polymer density, which is equal to 1400 kg/m3 for phenylone [5] and 1200 kg/m3 for EP, NA is Avogadro number, l0 is the length of the main chain skeletal bond, which is equal to 1.25 Å for both studied polymers [13]. As it is known [14], the molecular weight between traditional entanglements (chains “binary hookings”) scales with C∞ as follows:

M e1 M e2

⎛ C∞ =⎜ 1 ⎜C ⎝ ∞2

⎞ ⎟ ⎟ ⎠

2

.

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(6)

84

G. V. Kozlov, M.T.Bashorov, A. K. Mikitaev et al. For the initial phenylone

estimate the value

M e2

M e1 ≈1750,

C∞=3 and then the relationship (6) allows to

for carbon plastics polymer matrix. And finally, the value ncl can be

determined according to the equation [3]:

ncl =

2M e M cl

.

(7)

For cross-linked EP in the equation (7) instead of Me the molecular weight of the chain part between chemical cross-linking nodes was used [8]. In Figure 1 the dependences Tg(ncl) for the studied polymeric materials are adduced, which fall apart on three straight lines with about the same slope. The similar dependences Tm(ncl) were obtained for nanoclusters of silicium [4].

Tg, К -1 -2

600

500

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400

300

0

4

8 n cl

Figure 1. The dependence of glass transition temperature Tg on segments number in cluster ncl for carbon plastics on the phenylone base (1) and epoxy polymers (2).

As it is known [15], the ratio of numbers

ncli Am = i +1 = Δ1i/ m , ncl

(8)

characterizes nanoclusters structure adaptivity Am to the external influence change, defined by its stability measure Δi and possible reconstructions number m (at m=1 the linear feedback is realized and at m≥2 – the nonlinear one) [15]. The authors [2] showed that for carbon plastics

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The Generalized Synergetic Model of Glass Transition for Polymeric Materials

85

the low straight line was related to clusters with lower stability (Δi=0.213) in comparison with the upper straight line corresponding to clusters with higher Tg (Δi=0.324). This observation is fully corresponded to the data for silicium nanoclusters [4]. However, the dependence Tg(ncl) for EP is placed lower than two straight lines for carbon plastics, although the values Δi for cross-linked EP are varied within the limits 0.213-0.324. In other words, at the same ncl and Δi for different polymers different values Tg can be obtained. This assumes the existence at least one more factor, influencing on Tg value. As it is known, the main polymers difference from low-molecular solids is that they consist of long chain macromolecules, in which atoms are connected by covalent bonds and intermolecular interaction is realized at the expence of van der Waals bonds. The main polymer chain characteristics is its flexibility, which can be characterized with the help of the parameter C∞ [10, 13, 14]. Hence it appears, the data of Figure 1 were reploted in coordinates TgC∞(ncl), that is shown in Figure 2.

TgC∞, К -1 -2

2200

1700

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1200

700

0

4

8 n cl

Figure 2. The dependence of reduced glass transition temperature TgC∞ on segments number in cluster ncl for carbon plastics on the phenylone base (1) and epoxy polymers (2).

As one can see, at such plotting all the results adduced in Figure 1 lie on one linear dependence. In other words, for the polymeric materials structure and properties description within the frameworks of solid synergetics it is necessary to take into account their molecular structure specific feature, i.e., to take into account the polymer chains flexibility.

CONCLUSIONS Therefore, in the present paper the generalized synergetic model of glass transition temperature and polymeric materials structure intercommunication is offered. This model takes into account the specific for polymers factor, namely, the polymer chain flexibility. This

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G. V. Kozlov, M.T.Bashorov, A. K. Mikitaev et al.

allows quantitative description of glass transition temperature for various different polymeric materials – polymer matrix of carbon plastics on the phenylone base and cross-linked epoxy polymers. The offered model of the structure formation at glass transition allows to make conclusion with due regard for nanoworld synergetic conception, that the glass transition temperature, determined in the dynamic conditions, is a structural bifurcation point, responding to nanoclusters degeneration.

REFERENCES [1] [2] [3] [4]

[5] [6] [7] [8]

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[9] [10] [11] [12] [13] [14] [15]

Kadomtsev B.B. Dynamics and Information. Moscow, Editorial Boards UFN, 1999, 400 p. Malamatov A.Kh., Kozlov G.V., Mikitaev A.K. Reinforcement Mechanisms of Polymer Nanocomposites. Moscow, Mendeleev RKhTU, 2006, 240 p. Kozlov G.V., Zaikov G.E. Structure of the Polymer Amorphous State. Leiden-Boston, Brill Academic Publishers, 2004, 465 p. Bityutskaya L.A., Mashkina E.S., Ivanova V.S. Proceeding of International Interdisciplinary Symposium “Fractals and Applied Synergetics, FaAS-03”, Moscow, MSOU, 2003, p. 299-302. Sokolov L.B., Kuznetsov G.A., Gerasimov V.D. // Plast. Massy, 1967, № 9, p. 21-23. Burya A.I., Kozlov G.V. // Trenie i Iznos, 2003, v. 24, № 3, p. 279-283. Bershtein V.A., Egorov V.M. Differential Scanning Calorimetry in Polymers PhysicsChemistry. Leningrad, Khimiya, 1990, 256 p. Kozlov G.V., Novikov V.U., Gazaev M.A., Mikitaev A.K. // Inzhenerno-Fizicheskiy Zhurnal, 1998, v. 71, № 2, p. 241-247. Balankin A.S. Synergetics of Deformable Body. Moscow, Publishers Ministry of Defence SSSR, 1991, 404 p. Kozlov G.V., Sanditov D.S. Anharmonic Effects and Physical-Mechanical Properties of Polymers. Novosibirsk, Nauka, 1994, 261 p. Budtov V.P. Physical Chemistry of Polymer Solutions. Sankt-Peterburg, Khimiya, 1992, 384 p. Aharoni S.M. // Macromolecules, 1985, v. 18, № 12, p. 2624-2630. Aharoni S.M. // Macromolecules, 1983, v. 16, № 9, p. 1722-1728. Wu S. // J. Polymer Sci.: Part B: Polymer Phys., 1989, v. 27, № 4, p. 723-741. Ivanova V.S., Kuzeev I.R., Zakirnichnaya M.M. Synergetics and Fractals. Universality of Materials Mechanical Behaviour. Ufa, USNTU, 1998, 366 p.

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In: Trends in Polymer Research Editors: G.E. Zaikov, A. Jimenez and Yu.B. Monakov

ISBN 978-1-59454-274-9 © 2009 Nova Science Publishers, Inc.

Chapter 10

THE NANODIMENSIONAL EFFECTS IN CURING PROCESS OF EPOXY POLYMERS IN THE FRACTAL SPACE G. V. Kozlov1, M.T.Bashorov1, A. K. Mikitaev1, G. E. Zaikov2 1

Kabardino-Balkarian State University, Nal’chik – 360004, Chernyshevskiy st., 173, Russian Federation 2 N.M. Emanuel Institute of Biochemical Physics of Russian Academy of Sciences, Moscow – 119991, Kosygin st., 4, Russian Federation

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ABSTRACT It is shown that for curing reaction in fractal space the reaction rate constant reduction at this reaction proceeding is typical. For such reaction the formation of a large number of microgels with smaller molecular weight in comparison with reaction in Euclidean space at the same conversion degree is also typical. The dimensional border between nanoreactor and nanoparticle for the considered curing reaction is obtained.

Keywords: epoxy polymer, curing reaction, fractal space, nanoreactor, nanoparticle

INTRODUCTION In paper [1] it was shown that the epoxy polymers curing could occur in both Euclidean three-dimensional space and the fractal one. In the last case the space dimension is equal to fractal dimension D of microgels, formed in cureing process. The main difference of kinetic curves conversion degree-reaction duration (Q-t) in the last case is practically linear dependence Q(t) almost up to gelation point and variation (increase) of the D value on this part of curve Q(t). The purpose of the present paper is the further study of epoxy polymers curing in fractal space, in particular the reaction rate constant kp and microgels self-diffusivity Dsd changing character on the example of haloid-containing oligomer on the basis of hexachlorobenzene curing [2].

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EXPERIMENTAL The kinetics of curing of haloid-containing oligomer on the basis of hexachlorobenzene (conditional designation EPS-1) was studied. This oligomer was cured by 4,4’diaminodiphenylmethane (DDM) at stoichiomeric ratio of DDM:EPS-1 [2]. The curing kinetics of system EPS-1/DDM was studied by method of the inverse gas chromatography (IGC) [2]. The basic parameter received from processing of the experimental data was the conversion degree Q as a function of curing duration t, determined for an interval of kinetic curve t≤3×103 s. Ketones (methyl ethyl ketone, 1,4-dioxane, cyclohexanone) were chosen as the standard substances for the determination of retention time and argon as the gas carrier. The curing temperature of system EPS-1/DDM was accepted equal to 393 K. The microgels fractal dimension D value varied within the limits 1.61-2.38 [1].

RESULTS AND DISCUSSION As it was shown in paper [1], the value of reaction rate constant kp within the range Q≈00.70 for curing reaction in Euclidean space is constant. The relation between kp, Q and D has the form [3]:

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t ( D −1) / 2 =

C1 , k p (1 − Q )

(1)

where C1 is constant. For the system EPS-1/DDM the average value kp=0.97×10-3 mol⋅l/s was determined [2] by IGC method. From the equation (1) the value C1 can be determined at the average values of the included parameters: t=1.5×103 s, D=1.99 and Q=0.35 into it. In this case C1=0.0244 mol⋅l/s. As the calculations showed, kp reduction from 4.16×103 up to 0.76×10-3 mol⋅l/s was observed within the range t=(0.5-2.5)×103 s. The range of the indicated above values D assumes that the microgels formation occurs according to the cluster-cluster mechanism, i.e. by the large microgel formation from the smaller ones [4]. In this case the microgels molecular weigth MW value is determined according to the following scaling relationship [5]:

MW ~ Q 2 / (3− D ) .

(2)

The microgel gyration radius Rg is connected with MW according to the following relationship [4]:

R g ~ MW 1 / D ~ Q 2 / D (3− D ) .

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(3)

The Nanodimensional Effects in Curing Process of Epoxy Polymers …

89

The obtained results allow to carry out the system EPS-1/DDM curing kinetics analysis within the frameworks of irreversible aggregation models [6]. In a general case the relationship between kp and Rg can be written as follows [6]:

k p ~ Rg2 ω .

(4)

In its turn, the exponent ω is defined by the parameters, describing clusters (microgels) motion in space and their structure. This intercommunication has the form [6]:

2ω = − γ + d − Dw ,

(5)

where γ characterizes the dependence of microgels self-diffusivity Dsd on their sizes −γ

(Dsd~ R g ), d is dimension of the space, in which curing reaction occurs, Dw is dimension of microgels random walk trajectory. For reactions in Euclidean space d=3, Dw=2 (Brownian motion of microgels), γ=-1 and then ω=0. This means, that in the given case the condition should be fulfilled:

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k p = const .

(6)

The condition (6) is confirmed experimentally (kp value is not changed at Rg increasing) [2]. For curing reaction proceeding in fractal space the situation differs fully from the described above. This aspect attains special meaning within the frameworks of nanochemistry [7], therefore let’s consider it in more detail. As it is known [7], in nanochemistry there are two fundamental notions – nanoparticle and nanoreactor: the first characterizes dimensional parameter, the second defines nanoobject function. So, iron cluster loses almost fully its specific properties (ionization energy, magnetism) and approaches to metallic iron with a number of atoms in cluster n=15. At n>15 it remains a nanooject in dimensional sense, but loses “nanoreactor” qualities, in which properties become a size function. In Figure 1 the dependence of curing rate constant kp on microgels diameter 2Rg is adduced, which has a very specific form. Within the range of microgels (although the term “nanogel” is more precise) diameters less than 10 nm, the value kp is a clearly expressed rapidly decreasing function of diameter 2Rg and at 2Rg≥100 nm the indicated dependence is practically absent. Let’s note, that the size 100 nm is assumed as an upper limit (although conditional enough) for nanoworld objects [7]. Hence, the data of Fig 1 cleary demonstrate, that microgel at 2Rg>ϕs, it is possible to expect ϕvs ~ ϕs ; at the stage of aggregation, when ϕv