Construction and Bio-Based Materials: Properties and Technologies

Table of contents :
Construction and Bio-Based Materials: Properties and Technologies
Preface
Table of Contents
Chapter 1: Steel and Alloys
Effect of Zn/Mg Ratio on Second Phase Dissolution during Solution Treatment of Al-Zn-Mg-Cu Alloys
Second Phase Dissolution Influenced by Simultaneously Enhanced Mg, Cu Contents during Homogenization of As-cast Al-Zn-Mg-Cu Alloys
Second Phase Dissolution and Grain Characteristics of As-Cast Al-Cu-Li Alloys with Different Mg Contents during Homogenization
Exploration of Phase Dissolution during Solution Treatment for a New Al-3.86Cu-0.89Li-0.38Mg-0.28Ag Alloy
Interrelationship of Fracture Mechanism and Microstructure of TC18 Titanium Alloy
Microstructure Evolution and Performance of Laser-Remelted Ti-6Al-4V Alloy
Research Progress on Properties and Application of Titanium Alloy Oil Country Tubular Goods
Effect of Pre-Stretching and Under-Aging Treatment on Fatigue Crack Resistance of Al-Cu-Mg Alloy Casing Pipe
Effect of Secondary Treatment on the Exothermic and Tensile Properties of Vacuum Hot-Pressed Ni/Al Energetic Structural Composites
Laser Cladding of Titanium Alloy Coating on Low Carbon Steel via Cu Interlayer
Corrosion Behavior of 3Cr Steel in Simulated Oilfield CO2 Environment
Chapter 2: Bio-Based Materials and Biorefining Technologies
Preliminary Study of Chemically Pretreated Densification of Juniper Wood for Use in Bone Implants
A Study on Waste Paper Reinforced Recycled Polypropylene Biocomposite
Rheological, Thermal and Mechanical Properties of Wood Plastic Composites (WPCs) Based on Virgin and Recycled Polypropylenes and Birch Plywood Waste
Hemp Shives Mycelium Composites - An Alternative Material for Traditionally Used Plastic Packaging
Potential of some Latvian Industrial Crops Residuals for Conversion to Bio-Based Thermal Insulation Material
Characterization and Evaluation of Water-Based Ecological Paint for Protection of Wood Materials Coated Using Dipping Technique
The Research Landscape of Biorefinery: A Scientometrics Viewpoint
Suberinic Acid Isolation from Birch Outer Bark and their Characterization
Potential of Crude Tall Oil Polyols for Rigid Polyurethane Foam Production and their Comparison with Tall Oil Fatty Acids Polyols
Study of Catalysts for Suberinic Acid-Based Adhesive Polymerization
Constraint Handling and Flow Control in Stirred Tank Bioreactors with Magnetically Coupled Impellers
Cellulose Modification with Maleic Anhydride
Study of a Novel Biorefining Method for Obtaining 2-Furaldehyde, Acetic Acid and Pulp from Birch Wood
Chapter 3: Progressive Building Materials and Technologies
Effect of Modified Starch on Properties of Clay Composites
Preparation of Inorganic Foam Glass-Ceramic with Utilization of Waste Diatomite as a Raw Material
Influence of Microstructure on Physico-Mechanical Properties and Corrosion Resistance of Refractory Forsterite-Spinel Ceramics
Foam Glass Preparation from Waste Diatomite: Assessment of High Temperature Behaviour and Foaming Ability
Corrosion Properties of Castables with Various Calcium Oxide Content
29Si NMR Investigation of the Effect of Acetic and Oxalic Acids on Portland-Limestone Cement Hydration
Keyword Index
Author Index

Citation preview

Construction and Bio-Based Materials: Properties and Technologies

Edited by Dr. Kristine Meile Dr. Ugis Cabulis Dr. Mikelis Kirpluks Prof. Yafang Han Dr. Fenfen Liang Assoc. Prof. Dr. Karel Dvořák Dr. Dominik Gazdič

Construction and Bio-Based Materials: Properties and Technologies

Special topic volume with invited peer-reviewed papers only

Edited by

Dr. Kristine Meile, Dr. Ugis Cabulis, Dr. Mikelis Kirpluks, Prof. Yafang Han, Dr. Fenfen Liang, Assoc. Prof. Dr. Karel Dvořák and Dr. Dominik Gazdič

Copyright  2022 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of the contents of this publication may be reproduced or transmitted in any form or by any means without the written permission of the publisher. Trans Tech Publications Ltd Seestrasse 24c CH-8806 Baech Switzerland https://www.scientific.net

Volume 1071 of Materials Science Forum ISSN print 0255-5476 ISSN web 1662-9752

Full text available online at https://www.scientific.net

Distributed worldwide by Trans Tech Publications Ltd Seestrasse 24c CH-8806 Baech Switzerland Phone: +41 (44) 922 10 22 e-mail: [email protected]

Preface This edition represents the results of scientific investigation and engineering analysis of materials' properties, possible conditions for their applications, and technologies for their synthesis and processing. Readers can find a series of research results on properties and microstructure and the corrosion behaviour of structural steels and alloys. The results of analysis of bio-based materials' properties and technologies of their biorefining will also be interesting to the audience. Wood raw and waste, birch plywood waste, and other cellulose-contained natural materials are regarded as raw materials for biorefinery technologies. The research results on advanced building materials' properties and some technologies for their production are also represented in this edition. This particular topic collection will be helpful not only to engineers but also to academic researchers and students.

Table of Contents Preface

Chapter 1: Steel and Alloys Effect of Zn/Mg Ratio on Second Phase Dissolution during Solution Treatment of Al-ZnMg-Cu Alloys H. Yin, Z.H. Li, K. Wen, Q.H. Wen and Y.N. Li Second Phase Dissolution Influenced by Simultaneously Enhanced Mg, Cu Contents during Homogenization of As-cast Al-Zn-Mg-Cu Alloys W.C. Ren, K. Wen, Y.A. Zhang, H.L. Liu and T.Y. Zhang Second Phase Dissolution and Grain Characteristics of As-Cast Al-Cu-Li Alloys with Different Mg Contents during Homogenization P.C. Chen, X.W. Li, Y. Yao, Z.A. Wang and G. Shi Exploration of Phase Dissolution during Solution Treatment for a New Al-3.86Cu-0.89Li0.38Mg-0.28Ag Alloy T. Wang, B.Q. Xiong, B. Lin, Z.G. Hu and X.W. Li Interrelationship of Fracture Mechanism and Microstructure of TC18 Titanium Alloy X. Ran, Z. Wang, C.C. Liu, P.J. Li and Z.G. Lv Microstructure Evolution and Performance of Laser-Remelted Ti-6Al-4V Alloy K.K. Hu, S.C. Wang, W. Gao, H.Y. Yu and D.B. Sun Research Progress on Properties and Application of Titanium Alloy Oil Country Tubular Goods L.J. Zhu, C. Feng, K. Zhang, F.F. Zhang, W.W. Song, P. Wang and N. Ji Effect of Pre-Stretching and Under-Aging Treatment on Fatigue Crack Resistance of AlCu-Mg Alloy Casing Pipe H.T. Liu, M.F. Zhao, F. Hu, L.J. Zhu, Z.Y. Liu, X.F. Bai and L. He Effect of Secondary Treatment on the Exothermic and Tensile Properties of Vacuum HotPressed Ni/Al Energetic Structural Composites Q.Y. Ding, D. Ma, Y. Tang, X. Li, C.Q. Ma and P. Shen Laser Cladding of Titanium Alloy Coating on Low Carbon Steel via Cu Interlayer W. Gao, S.C. Wang, J. Si, K.K. Hu, H.Y. Yu and D.B. Sun Corrosion Behavior of 3Cr Steel in Simulated Oilfield CO2 Environment N. Ji, X.R. Kuang, K.Q. Ge, P. Wang, Y. Long and C. Feng

3 11 20 30 38 46 56 67 74 80 91

Chapter 2: Bio-Based Materials and Biorefining Technologies Preliminary Study of Chemically Pretreated Densification of Juniper Wood for Use in Bone Implants L. Andze, M. Andzs, M. Skute, V. Nefjodov, M. Kapickis and R. Tupciauskas A Study on Waste Paper Reinforced Recycled Polypropylene Biocomposite J. Jaunslavietis, J. Ozolins, M. Kalnins, G. Shulga, B. Neiberte, A. Verovkins and T. Betkers Rheological, Thermal and Mechanical Properties of Wood Plastic Composites (WPCs) Based on Virgin and Recycled Polypropylenes and Birch Plywood Waste K. Kalnins, J. Kajaks and J. Matvejs Hemp Shives Mycelium Composites - An Alternative Material for Traditionally Used Plastic Packaging G.D. Loris, I. Irbe, M. Skute, I. Filipova, L. Andze and A. Verovkins Potential of some Latvian Industrial Crops Residuals for Conversion to Bio-Based Thermal Insulation Material A. Bērziņš, R. Tupciauskas, M. Andzs and G. Pavlovichs Characterization and Evaluation of Water-Based Ecological Paint for Protection of Wood Materials Coated Using Dipping Technique E. Sansonetti, D. Cīrule, E. Kuka, B. Andersons, I. Andersone and M. Danieks

101 109 117 126 139 147

b

Construction and Bio-Based Materials: Properties and Technologies

The Research Landscape of Biorefinery: A Scientometrics Viewpoint A. Kokorevičs Suberinic Acid Isolation from Birch Outer Bark and their Characterization D. Godina, R. Makars, A. Abolins, A. Paze, M. Kirpluks and J. Rizhikovs Potential of Crude Tall Oil Polyols for Rigid Polyurethane Foam Production and their Comparison with Tall Oil Fatty Acids Polyols E. Kauliņa, A. Abolins, A. Fridrihsone and M. Kirpluks Study of Catalysts for Suberinic Acid-Based Adhesive Polymerization R. Makars, J. Rizhikovs and A. Paze Constraint Handling and Flow Control in Stirred Tank Bioreactors with Magnetically Coupled Impellers A. Buss, A. Suleiko, N. Jekabsons, J. Vanags and D. Loca Cellulose Modification with Maleic Anhydride V. Fridrihsone, J. Zoldners, M. Skute, L. Andze and I. Filipova Study of a Novel Biorefining Method for Obtaining 2-Furaldehyde, Acetic Acid and Pulp from Birch Wood M. Puke, D. Godina, P. Brazdausks and J. Rizhikovs

155 166 174 182 189 197 204

Chapter 3: Progressive Building Materials and Technologies Effect of Modified Starch on Properties of Clay Composites Y. Trambitski, O. Kizinievič and V. Kizinievič Preparation of Inorganic Foam Glass-Ceramic with Utilization of Waste Diatomite as a Raw Material M. Nguyen, M. Sedlačík, R. Sokolař and T. Opravil Influence of Microstructure on Physico-Mechanical Properties and Corrosion Resistance of Refractory Forsterite-Spinel Ceramics M. Nguyen and R. Sokolař Foam Glass Preparation from Waste Diatomite: Assessment of High Temperature Behaviour and Foaming Ability M. Sedlačík, M. Nguyen, T. Opravil and R. Sokolař Corrosion Properties of Castables with Various Calcium Oxide Content D. Zemánek and L. Nevřivová 29Si NMR Investigation of the Effect of Acetic and Oxalic Acids on Portland-Limestone Cement Hydration A.S. Mazur, P.M. Tolstoy and K. Sotiriadis

215 222 229 235 241 247

CHAPTER 1: Steel and Alloys

Materials Science Forum ISSN: 1662-9752, Vol. 1071, pp 3-10 doi:10.4028/p-04ua6p © 2022 Trans Tech Publications Ltd, Switzerland

Submitted: 2022-05-29 Revised: 2022-07-13 Accepted: 2022-07-29 Online: 2022-10-18

Effect of Zn/Mg Ratio on Second Phase Dissolution During Solution Treatment of Al-Zn-Mg-Cu Alloys He Yin1,2,3,a, Zhi-Hui Li1,3,b *, Kai Wen1,2,3 c *, Qing-Hong Wen4,d, Ya-Nan Li1,2,3,e State Key Laboratory of Non-ferrous Metals and Processes, GRINM Group Co., LTD., Beijing 100088, China

1

GRIMAT Engineering Institute Co., LTD., Beijing 101407, China

2

General Research Institute for Nonferrous Metals, Beijing 100088, China

3

Southwest Aluminum (Group) Co., Ltd., Chongqing 401326, China

4

[email protected], [email protected], [email protected], [email protected], e [email protected]

a

Keywords: Al-Zn-Mg-Cu alloy; Zn/Mg Ratio; Solution treatment; Second Phase dissolution

Abstract. The main alloying elements have a decisive influence on the type and quantity of the second phase of the Al-Zn-Mg-Cu alloy, and even on the dissolution of the second phase during solution treatment. The effect of Zn/Mg ratio on second phase dissolution during solution treatment of Al-Zn-Mg-Cu alloys was investigated by means of differential scanning calorimetry (DSC), scanning electron microscope (SEM) and electrical conductivity testing. The results showed that Mg(Zn,Cu,Al)2 phase and Fe-rich phase existed in the as-deformed alloys. In addition, a small amount of Al2CuMg phase was found in the low and medium Zn/Mg ratio alloy. Mg(Zn,Cu,Al)2 phase essentially dissolved into the matrix after solution treatment at 465°C/2h. Increasing the solution treatment temperature and time were both beneficial to the dissolution of the Al2CuMg phase. Conductivity is also a method of assessing the level of dissolution of the second phase. After the second phase was fully dissolved in the alloy, the electrical conductivity gradually increased with the increase of the solution time. Introduction Al–Zn–Mg–Cu age-hardening alloys are widely used in aerospace and transport industries due to their excellent strength and toughness [1-3]. The excellent properties of Al-Zn-Mg-Cu alloys depend largely on the heat treatment process, especially the solution and subsequent aging heat treatment. Among them, solution treatment is a very critical step [4]. Generally speaking, after casting, homogenization treatment, and plastic deformation, a large number of second phases are distributed on the aluminum alloy matrix, and these second phases are the main factor affecting the comprehensive properties of the alloy. The second phases of as-deformed alloys are Mg(Zn,Cu,Al)2 phases [5], Al2CuMg phase [6] and Al7Cu2Fe phase [7], etc. The purpose of the solution treatment process is to dissolve the second phases into the matrix as much as possible, which will increase the supersaturation of the matrix and help the strengthening phase to precipitate more during aging treatment. In the process of solution treatment, the coarse brittle phase that cannot be dissolved into the matrix is the source of cracks in the alloy, which will reduce the fracture toughness and fatigue resistance of the alloy. In recent years, there are many research articles on the solution treatment of Al-Zn-Mg-Cu alloys, including single-stage solution treatment [8], two-stage solution treatment [9, 10], multi-stage solution treatment [11], enhanced solution treatment and high temperature pre-precipitation treatment [12]. Based on economic and industrial production considerations, single-stage solution treatment is still the most practical process. The factors affecting the dissolution of the second phase during the solution treatment of Al-Zn-Mg-Cu alloys include solution temperature, solution time, quenching transfer time, etc. Among them, the temperature and time of solution treatment are the main factors [8]. Liu[13] summarized the increase of solution temperature is of great benefit to the dissolution of dissolvable second phase, the higher main alloying content is, the more effective

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dissolvable second phase dissolution is. Zn and Mg are the main elements that consist of the strengthen phase, and their content has an important influence on the type and quantity of the second phase. The degree of dissolution of the second phase during solution treatment plays a key role in the subsequent aging treatment. However, the effect of Zn/Mg ratio on second phase dissolution during solution treatment was rarely reported. In this paper, the phase characteristics of several Al-Zn-Mg-Cu alloys with various Zn/Mg ratio were investigated and the second phase dissolution of these alloys during solution treatment was analyzed. The effect of Zn/Mg ratio on second phase dissolution during solution treatment of Al-Zn-Mg-Cu alloys was studied. Experimental Al-Zn-Mg-Cu alloys were prepared by the metal mold casting method. The compositions of three alloys with different Zn/Mg ratios are listed in Table 1. The ingots were homogenized to ensure complete dissolution of eutectic phases, and then suffered by deformation processes to plates with a cross-section of 16×65 mm by the forward extruder with an extrusion ratio of 10:1. Specimens were taken from the mid-thickness of the plates. The solution treatment was carried out in the air circulation box furnace with a temperature fluctuation of ±1°C and then quenched in cold water immediately. A JEOL JSM 7001F scanning electron microscope (SEM) attached with Energy Dispersive Spectroscopy (EDS) was used for microstructure observation. Thick sheets with a diameter of 3 mm were cut from the samples for Differential Scanning Calorimetry (DSC) test at a range from room temperature to 580 °C. The heating rate was 10 °C/min. Enthalpy of the endothermic peaks was calculated by the integral of the curve. Conduct conductivity tests on the samples using an eddy current conductivity meter, with three points for each sample Table 1 Nominal chemical compositions of the investigated alloys. Wt. % At. % Alloy number Zn Mg Cu Zr Fe Si Al Zn+Mg Zn/Mg A1 7.27 1.82 2.04 0.1 ＜0.01 ＜0.01 Bal. 6.3 1.5 A2 7.78 1.61 2.02 0.1 ＜0.01 ＜0.01 Bal. 6.3 1.7 A3 8.03 1.42 1.94 0.1 ＜0.01 ＜0.01 Bal. 6.3 2.0 Results and Discussion Microstructure Observation and DSC Analysis of As-deformed Alloys. Fig. 1 shows typical backscattered images of three as-deformed alloys. It can be seen that large amounts of fine white second phases are distributed in the matrix along the extrusion direction. In addition, some spherical or ellipsoidal phases with gray contrast were locally found in A1 and A2 alloys (Fig. 1(a, b)). However, this phase does not appear in A3 alloy. Moreover, a phase distinct from the ubiquitous bright white secondary phase was observed with darker contrast under a high magnification field of view, which was exhibited irregular shapes (the “D” phase in Fig. 1(c)). According to the EDS analysis shown in Table 2, the “A” and “B” phases with gray contrast mainly contain Al, Mg, Cu elements and little Zn element. The atomic ratio of Al, Zn and Mg elements in this phase is close to 2:1:1. Obviously, this phase can be determined as Al2CuMg phase. The “C” phase with bright white contrast contains Al, Zn, Mg and Cu elements, which can be confirmed to be Mg(Zn,Cu,Al)2 phase. The “D” phase contains Fe element, which can be identified as Fe-rich phase. Comparing the microstructure of the three alloys, it can be found that all alloys contain a large amount of Mg(Zn,Cu,Al)2 phases and a small amount of Fe-rich phase. However, Al2CuMg phase exists in A1 and A2 alloys, not in A3 alloy. It can be seen that there are more Mg(Zn,Cu,Al)2 phases in A1 alloy than in the A2 and A3 alloys. This indicates that low-Zn/Mg ratio alloy has more Mg(Zn,Cu,Al)2 phases. This is because the content of Mg(Zn,Cu,Al)2 phase is proportional to the content of Mg element due to the excess of Mg element.

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Fig. 1 SEM micrographs of as-deformed alloys with different Zn/Mg ratios, (a) A1 alloy, (b) A2 alloy, (c) A3 alloy. Table 2 EDS analysis results of second phases in Fig. 2 (at. %) Position

Al

Zn

Mg

Cu

Fe

Phase

A B C D

52.81 49.90 76.43 84.97

2.40 2.52 11.46 2.92

22.93 20.71 6.83 1.43

21.86 26.87 5.27 7.96

2.73

Al2CuMg Al2CuMg AlZnMgCu Fe-rich phase

X-ray diffraction patterns of as-deformed alloys are shown in Fig. 2. The analysis of the XRD diffraction peaks shows that the phase structure consists of α(Al) and η(MgZn2) in as-deformed alloys. The study of Xu [14] declared that the lattice structure of the AlZnMgCu phase is similar to MgZn2 phase. They all exhibit a hexagonal structure. Desolvation and precipitation of Zn and Mg elements occurred forming MgZn2 phase during cooling after homogenization treatment. At the same time, the elements Al and Cu were dissolved into MgZn2 phases, thus forming AlZnMgCu phase. Hence, AlZnMgCu phase and MgZn2 phase have the same structure. AlZnMgCu phase can be written as Mg(Zn, Cu, Al)2. The diffraction peaks of the Al2CuMg phase and Fe-rich phase were not observed in the XRD pattern, probably because these two phases were too small and the diffraction peaks were too weak for the peak shapes to be observed.

Fig. 2 X-ray diffraction patterns of as-deformed alloys. DSC curves of three as-deformed alloys are shown in Fig. 3. It was seen that there were two endothermic peaks at 476 and 483 °C in A1 alloy, respectively. According to the Refs.[15], the endothermic peaks at 476℃ and 483℃ correspond to the dissolution of Mg(Zn,Cu,Al)2 phase and Al2CuMg phase, respectively. There is no endothermic peak was found in A2 and A3 alloy. The

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Construction and Bio-Based Materials: Properties and Technologies

possible reason is that the Mg(Zn,Cu,Al)2 phase is fewer in number and smaller in size of A2 and A3 alloys compared with A1 alloy. Therefore the Mg(Zn,Cu,Al)2 phase dissolves during the heating-up process and does not form an effective endothermic peak.

Fig. 3 DSC curve of three as-deformed alloys.

Fig. 4 SEM images of solution treatment alloys, 465°C/2h: (a, b, c) A1, A2, A3 alloy, 470°C/2h: (d, e, f) A1, A2, A3 alloy, 475°C/2h: (g, h, i) A1, A2, A3 alloy.

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Microstructure Observation after Solution Treatment. Fig. 4 shows the SEM images of A1, A2, A3 alloys after (465, 470, 475°C)/2h solution treatment. It can be seen that the Mg(Zn,Cu,Al)2 phase basically dissolves into the matrix during solution treatment. Al2CuMg phases were found in “A” and “B” positions of A1 and A2 alloys (Table 3), which were aggregated and distributed along the extrusion direction. Only Fe-rich phase was observed in A3 alloy under a high magnification field of view, and it was very small in quantity. It can be concluded that the Mg(Zn,Cu,Al)2 phase dissolved well for three alloys after 465°C/2h solution treatment, leaving Fe-rich phase and Al2CuMg phase that are difficult to dissolve into the matrix. Mg(Zn,Cu,Al)2 phase has completely dissolved into the matrix after 470,475°C/2h solution treatment for three alloys. Al2CuMg phase was still found in A1 and A2 alloys at 470°C/2h, but its amount was reduced and its distribution tended to be dispersed compared with the 465℃/2h solution treatment regime. In addition, there are only a few Al2CuMg phases existed in A1 alloy, and no Al2CuMg phase is found in A2 alloy after solution treatment at 475℃/2h. The above indicates that increasing the solution temperature has a facilitating effect on the dissolution of the Al2CuMg phase. Table 3 EDS analysis results of second phases in Fig. 3 (at. %) Position

Al

Zn

Mg

Cu

Fe

Phase

A B C D

52.62 53.95 87.76 88.65

2.05 1.76 2.41 2.72

22.66 21.80 2.75 2.71

22.67 22.50 5.22 4.27

1.86 1.65

Al2CuMg Al2CuMg Fe-rich phase Fe-rich phase

Fig. 5 Electrical conductivity for the three alloys solution after 465,470,475°C/2h solution treatment. As is known to all, the scattering effect of solid solution atoms on electron conduction is stronger than second phases. Therefore, the more second phases dissolve, the more solid solution atoms existed in the matrix, which results in lower electrical conductivity. Electrical conductivity is also an effective method to evaluate the adequacy of dissolution of the second phase. Fig. 5 shows the electrical conductivity change curves of three alloys under the solution treatment regime of 465,470,475℃/2h. It can be viewed from the curves that the electrical conductivity of three alloys shows a trend of first decreasing and then increasing with the solution treatment temperature from 465℃ to 475℃. It means that the second phase in the alloy is not completely redissolved after 465°C/2h solution treatment. Increasing the temperature to 470°C reduces the electrical conductivity with the dissolution of the second phase. The electrical conductivity decreases with the increase of solution temperature from 470℃ to 475℃, due to the adequate dissolution of the second

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Construction and Bio-Based Materials: Properties and Technologies

phase and the more homogeneous distribution of the elements. Although the Al2CuMg phase remained dissolved during the increase in solution temperature from 470℃ to 475℃ for the A1 and A2 alloys, the amount of the Al2CuMg phase was small and contributed little to the reduction in electrical conductivity. Fig. 6 shows the SEM images of three alloys after 470°C/1,4,6h solution treatment. The Al2CuMg phase was found to be aggregated and distributed in the A1 and A2 alloys after the 470°C/1h solution treatment. However, only a small amount of Al2CuMg phase remained in the A2 alloy after solution treatment at 470°C/4h. Furthermore, no S phase was found in the three alloys at 470°C/6h. Combined with the SEM images of 470°C/2h above, it can be found that the S phase gradually dissolves into the matrix as the solution time increases from 1h to 6h at 470℃. In conclusion, increasing the solution time has a facilitating effect on S phase dissolution. Fig. 7 shows the electrical conductivity change curves of three alloys under the solution treatment regime of 470°C/1,2,4,6h. It can be observed from the curves that the electrical conductivity of the three alloys tends to increase with the increase of the solution time from 1h to 6h at 470℃. This indicates that the continuing extension of solution time with complete dissolution of the second phase results in a more homogeneous distribution of elements within the alloy and an increase in electrical conductivity. However, the decrease in conductivity of A1 alloy at 470°C/2h may be due to the high quantity of second phases in A1 alloy, which are not completely dissolved at 470°C/1h.

Fig. 6 SEM images of solution treatment alloys, 470°C/1h: (a, b, c) A1, A2, A3 alloy, 470°C/4h: (d, e, f) A1, A2, A3 alloy, 470°C/6h: (g, h, i) A1, A2, A3 alloy.

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Fig. 7 Electrical conductivity for the three alloys solution after 470°C/1,2,4,6h solution treatment. Fig. 8 shows area fraction of the second phases of three alloys for different solution regimes. It can be seen that area fraction of the second phases gradually decreases as the solution treatment temperature increases for A1 and A2 alloy (Fig. 8 (a)). From the above SEM analysis result, we can know that reduction of the second phase content is mainly due to the dissolution of Al2CuMg phases. The low content of the second phases in alloy A3 after solution treatment is due to its absence of the S phase. The effect of solution treatment time on the dissolution of the S phases is also evident. The content of the S phase decreases with the increase of time at 470°C, indicating a gradual dissolution of the S phase (Fig. 8 (b)). In conclusion, increasing the solution treatment temperature and time both contribute to S phase dissolution.

Fig. 8 Area fraction of the second phase of the three alloys after solution treatment, (a) 465,470,475°C/2h solution treatment; (b) 470°C/1,2,4,6h solution treatment Conclusions (1) Mg(Zn,Cu,Al)2 phase and Fe-rich phase have been observed in the three as-deformed alloys with different Zn/Mg ratios. A small amount of Al2CuMg phase is found in the low and middle Zn/Mg ratio alloys. As the major phase in the three alloys, the amount of Mg(Zn,Cu,Al)2 phase is inversely proportional to the Zn/Mg ratio. (2) Mg(Zn,Cu,Al)2 phase essentially dissolves into the matrix after solution treatment at 465°C/2h due to its low dissolution temperature. Increasing the solution temperature and time are both beneficial to the dissolution of the Al2CuMg phase.

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(3) Low-Zn/Mg ratio alloy needs more time to dissolve the second phase due to its higher residual phase content. Increasing the solution temperature or time will elevate the electrical conductivity of the alloy while the second phase has been completely dissolved. Acknowledgments This study was financially supported by National Key R&D Program of China (No. 2020YFF0218200) and other related projects. References [1] C. Sigli, F. De Geuser, A. Deschamps, et al. Recent advances in the metallurgy of aluminum alloys. Part II: Age hardening, CR Phys. 19 (2018) 688-709. [2] X. Zhang, Y. Chen, J. Hu, Recent advances in the development of aerospace materials, Prog. Aerosp. Sci. 97 (2018) 22-34. [3] T. Dursun, C. Soutis, Recent developments in advanced aircraft aluminium alloys, Mater. Des. 56 (2014) 862-871. [4] P.A. Rometsch, Y. Zhang, S. Knight, Heat treatment of 7xxx series aluminium alloys—Some recent developments, Trans. Nonferrous Met. Soc. China. 24 (2014) 2003-2017. [5] X. Meng, D. Zhang, W. Zhang, et al. Influence of solution treatment on microstructures and mechanical properties of a naturally-aged Al–27Zn–1.5Mg–1.2Cu–0.08Zr aluminum alloy, Mater Sci Eng. A. 802 (2021) 140623. [6] G. Peng, K. Chen, S. Chen, et al. Evolution of the second phase particles during the heating-up process of solution treatment of Al–Zn–Mg–Cu alloy, Mater Sci Eng. A. 641 (2015) 237-241. [7] X.-l. Zou, H. Yan, X.-h. Chen, Evolution of second phases and mechanical properties of 7075 Al alloy processed by solution heat treatment, Trans. Nonferrous Met. Soc. China. 27 (2017) 2146-2155. [8] J.T. Lu, H. Huang, H. Wu, et al. Effect of Solution Treatment on the Properties and Microstructural Evolution of Al-Zn-Mg-Cu-Er-Zr Alloy, Mater. Sci. Forum. 877 (2017) 303-309. [9] M.A. Azmah Hanim, S. Chang Chung, O. Khang Chuan, Effect of a two-step solution heat treatment on the microstructure and mechanical properties of 332 aluminium silicon cast alloy, Mater. Des. 32 (2011) 2334-2338. [10] S. Kongiang, T. Plookphol, J. Wannasin, et al. Effect of the Two-Step Solution Heat Treatment on the Microstructure of Semisolid Cast 7075 Aluminum Alloy, Adv. Mater. Res. 488-489 (2012) 243-247. [11] X.B. Yang, J.H. Chen, J.Z. Liu, et al. Spherical constituent particles formed by a multistage solution treatment in Al–Zn–Mg–Cu alloys, Mater. Charact. 83 (2013) 79-88. [12] N.M. Han, X.M. Zhang, S.D. Liu, et al. Effect of solution treatment on the strength and fracture toughness of aluminum alloy 7050, J. Alloys Compd. 509 (2011) 4138-4145. [13] H.W. Liu, K. Wen, W.C. Ren, et al. Main Alloying Influence on Second Phase Dissolution during Solution Treatment of Al-Zn-Mg-Cu Alloys, Mater. Sci. Forum. 1035 (2021) 3-9. [14] D. Xu, Z. Li, G. Wang, et al. B. Xiong, Phase transformation and microstructure evolution of an ultra-high strength Al-Zn-Mg-Cu alloy during homogenization, Mater. Charact. 131 (2017) 285-297. [15] C.-s. Zhang, Z.-g. Zhang, M.-f. Liu, et al. Effects of single- and multi-stage solid solution treatments on microstructure and properties of as-extruded AA7055 helical profile, Trans. Nonferrous Met. Soc. China. 31 (2021) 1885-1901.

Materials Science Forum ISSN: 1662-9752, Vol. 1071, pp 11-19 doi:10.4028/p-310n85 © 2022 Trans Tech Publications Ltd, Switzerland

Submitted: 2022-05-29 Revised: 2022-07-06 Accepted: 2022-07-29 Online: 2022-10-18

Second Phase Dissolution Influenced by Simultaneously Enhanced Mg, Cu Contents during Homogenization of As-Cast Al-Zn-Mg-Cu Alloys Wei-Cai Ren1,3,4,a, Kai Wen1,2,3,b *, Yong-An Zhang1,2,3,c*, Hong-Lei Liu4,d, Tian-You Zhang1,2,3,e State Key Laboratory of Non-ferrous Metals and Processes, GRINM Group Co., LTD., Beijing 100088, China

1

GRIMAT Engineering Institute Co., LTD., Beijing 101407, China

2

General Research Institute for Nonferrous Metals, Beijing 100088, China

3

Northeast Light Alloy Co., LTD., Harbin 150060, China

4

[email protected], [email protected], [email protected]

a

[email protected], [email protected]

d

Keywords: Al-Zn-Mg-Cu alloy; Mg and Cu contents; Second phase dissolution; Homogenization

Abstract. The dissolution of second phase with relatively high melting point in as-cast Al-Zn-MgCu alloys was closely related to Mg and Cu contents. In present work, second phases in three Al-ZnMg-Cu alloys with simultaneously enhanced Mg and Cu contents (named by LMC alloy, MMC alloy and HMC alloy as Mg and Cu contents progressively enhanced) were analyzed and the correlated dissolution during homogenization was investigated. The results showed that both Mg(Zn,Cu,Al)2 phase and Cu-rich phase existed in as-cast alloys while HMC alloy possessed more eutectic phases. As homogenized under 470℃/24h, Mg(Zn,Cu,Al)2 phase had dissolved completely, LMC alloy contained little Al2CuMg phase, and the amount of it for the three alloys was arranged as LMC alloy < MMC alloy < HMC alloy. As further homogenized by a second stage at 480℃ for 12h, no endothermic peak for Al2CuMg phase was observed for LMC alloy, and only Fe-rich phase existed. Meanwhile, Al2CuMg phase still remained in MMC and HMC alloy. As the homogenization time prolonged to 36h, Al2CuMg phase in MMC alloy dissolved completely while Al2CuMg phase still existed in HMC alloy. Adding a third stage at 490℃ for HMC alloy, no Al2CuMg phase could be observed for 24h. This give rise to a method by incrementally grading homogenization temperature combined with prolonging soaking time to fulfill the dissolution of second phase for Al-Zn-Mg-Cu alloys with enhanced Mg and Cu contents. Introduction As aerospace and military industry are desperate for weight loss and high performance, Al-ZnMg-Cu alloy has been broadly used in aforesaid fields to fabricate structure components like wings, fuselage skin, stringers, etc. for preferential overall performance combining strength, fracture toughness, stress corrosion crack resistance and light weight [1-3]. Beginning from melting and casting, a series of manufacturing processes are performed from raw materials to final products. Among them, homogenization and solid solution treatments are associated to phase dissolution with a deformation processing gap between them while aging treatment aims to precipitate strengthening phases for obtaining satisfying property [4,5]. Comparing solid solution treatment for simply diminishing second phase formed in deformation part and controlling recrystallization, homogenization plays an important role to dissolve all the dissolvable phases in as-cast alloys and prepare favourable microstructure conditions [6]. If coarse second phases are not eliminated in homogenization, these residual ones can hardly be solved in solid solution treatment and are handed over to final microstructure, significantly deteriorating performances of products. Traditionally, homogenizations have been investigated and explored for various Al-Zn-Mg-Cu alloys by one, two or even three stages to realize second phase dissolution. However, the investigations about dissolution process are not thorough. Especially second phase is directly

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connected to chemical compositions, multiple homogenization treatments are demanded due to the surplus of phases with high melting points. Nevertheless, how to set different homogenization stages and the corresponding effects, there still lack sufficient investigations. Literatures about homogenization treatment have been concentrated on different points. Some focused on the precipitation of dispersoid particles and its effect on recrystallization control [7-10], single or multiple homogenization regimes were just used as processing methods. Some researchers were concentrated on developing new types of dispersoids by adding different rare earth elements [9,11,12] while some investigated the match of homogenization and aging treatments to obtain good property [13]. Still, there were investigations focusing on the dissolution of eutectic phases with or without chemical composition variations [14-16]. But second phase dissolution conditions during different homogenization stages still needs further investigations. In the present work, phase characteristics of three Al-Zn-Mg-Cu alloys with progressively increased Mg and Cu contents were investigated and the second phase dissolution during different homogenization stages was analyzed and its relations with chemical compositions was discussed. Based on these, the preferential homogenization regimes for different alloys were proposed and a method by incrementally grading homogenization temperature combined with prolonging soaking time to fulfill of the dissolution of second phase with relatively high melting points was presented. Experimental Procedure The three alloys were fabricated by direct-chill casting method to ingots with a diameter of 135mm and a length of 250mm and the chemical compositions were shown in Table 1. Considering the alloys with low, medium and high Mg and Cu contents, so they were named as LMC, MMC and HMC alloy, respectively. The ingots were cut from the bottom with a length of 25mm and then cut microstructural observation samples with a cubic size of 10×10×10mm from the position of 1/4R. The DSC samples were cut from the cubic sample with a size of Φ5×1mm. The homogenization treatments were carried out in a ThermConcept KU 70/06/A air circulation box furnace with a temperature fluctuation of 1.5℃ and then quenched in cold water. The samples for optical microstructure (OM) and scanning electron microscope (SEM) observations were delicately grinded on waterproof abrasive paper and then polish on fine polishing cloth assisted with diamond paste. Thereinto, the OM samples needed to be etched by an acid reagent with a matching of 1% HF + 2.5% HNO3 + 1.5% HCl in water (vol.%). The OM samples were performed on an Axiovert 40 MAT metallographic microscope while the SEM samples were observed on an JEOL JSM 7001F scanning electron microscope and the phases were furtherly identified by attached energy dispersive X-ray spectroscopy (EDS). The melting temperature associated with constituent particles was measured by differential scanning calorimetry (DSC) conducted on a NETZSCH STA 409C/CD instrument under argon atmosphere with a heating rate of 10℃/min ranging from room temperature to 550℃, the related endothermic peak enthalpy was calculated by it. Table 1 Chemical composition of Al-Zn-Mg-Cu alloys (wt.%) Alloy number Zn Mg Cu Zr Fe Si LMC alloy 6.3 2.0 1.9 0.11 8×104mg/L), a serve corrosion risk would take to the downhole tubing and casing [8]. At present, S13Cr-110 martensitic stainless steel has been proved to be the most suitable material used in the CO2 environment, but the cost of the material is very high and is not an economic material solution for some oil-gas field which have a low production, thus low-Cr steel, containing up to 5wt% Cr, is a new type of steel developed to handle the contradiction of anti-corrosion and economy of the material used in CO2 environments. Among the low-Cr steels, 3Cr steel has the best combination of cost, being less than 1.5× more expensive than conventional grades of carbon steel, and CO2 corrosion resistance, being approximately 3-10×, or more favorable [9-13]. To date, several research relevant to the corrosion behavior of 3Cr steel in CO2 environment had been carried out. Wang et al. [14] investigated the corrosion behavior and mechanism of 3Cr steel in CO2 environment with various Ca2+ concentration. They found that with an increase in Ca2+

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concentration in the solution, the corrosion rate of 3Cr steel decreased, and Ca2+could enhance the pseudo-passivation of 3Cr steel. Lu et al. [15] focused on the effect of temperature on the 3Cr lowalloyed steel initial corrosion behavior in CO2 solution and indicated that the corrosion potential of this alloy exhibits a negative shift with increasing temperature. Yue et al. [16] investigated the behavior of 3Cr steel at CO2 partial pressures (PCO2) of 2.7/28.5 bar and 200℃, found out that corrosion scales comprise a crystalline FeCO3 outer layer and an inner Fe3O4, FeCr2O4, and Cr(OH)3 at 2.7 bar PCO2. At 28.5 bar PCO2, the inner layer evolves to be a mixture of FeCr2O4 and Cr(OH)3 containing concentrated Cl−ions, and this induces an enhancement of localized corrosion. Zhu et al. [17] revealed the open-circuit voltage (OCP) of 3Cr steel exhibited a tendency to increase over time from -0.67 to -0.48 V. Based on the literature above, the majority of the current research on the corrosion mechanism of 3Cr steel are mainly focused on its electrochemistry process, and the corrosion atmosphere also tend to be very simple. Little information was found in the literature relating to the corrosion behavior in the complicated oilfield service atmosphere, which may be more benefit for the application of the 3Cr tubing and casing. In this article we focused on the corrosion behavior of the 3Cr steel in simulated oilfield CO2 and formation water environment at different temperature and CO2 partial pressure, aiming to make a reference of the material selection for the oil-gas field which use CO2 gas injection flooding. Experimental Material and Solution. The material used here was 3Cr steel with chemical composition (wt%) listed in Table 1, and the metallographic structure of the material was tempered sorbate as shown in Fig. 1. The composition and pH value of the test solution, which simulating an oil field formation water, is shown in Table 2. The solution was made from analytical grade reagents and deionized water at lab. Table 1 Elemental composition of 3Cr steel [wt%]. Material

Element

3Cr steel

C

Si

Mn

P

S

Cr

Mo

Ni

Cu

0.15

0.24

0.59

0.010

0.0017

2.99

0.30

0.028

0.056

Table 2 Composition of the test solution simulating the oilfield formation water [mg/L]. pH

HCO3-

SO42-

Cl-

Ca2+

Mg2+

Na++K+

Fe3+

6.07

330.2

1808.4

125554

10563.5

1630.2

67240.2

6.91

Fig. 1 Metallographic structure of 3Cr steel. Immersion Tests. Fig. 2 shows two views of the test specimen that used for the weight loss tests. The size of the specimen was 40mm×10mm×3mm, and with a hole of Φ5mm on it to fix it in the turntable. Prior to the tests, the specimens were grounded with 200-,400-,800-,1200-grit silicon carbide paper, and then rinsed with deionized water and alcohol, and then dried. The immersion tests were conducted in a 5 L hastelloy dynamic autoclave (shown in Fig. 3) with different temperature

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and CO2 partial pressure as shown in Table 3. The test period was 336 h. Before a specimen was submerged into the solution, the solution was purged with ultrapure N2 for 10 h, and then CO2 for 4 h to deoxygenate. After specimens were immersed into the solution, one more hour of N2 purging was carried out to remove oxygen again after the autoclave was closed and fastened down.

Fig. 2 Size of the test specimen for the immersion tests.

Fig. 3 Schematic of autoclave. Table 3 Parameters of corrosion immersion tests.

T [℃] 60,90,120,140

PCO2 [MPa] 0.05,0.2,0.5,1.0

Ptotal [MPa] 10

T [h] 336

Flow velocity [m/s] 0.23

Prior to conducting immersion tests, the original weight (W0) of each specimen was measured using an analytical balance. After 336 h of immersion, the corroded specimens extracted from the autoclave were immediately rinsed with deionized water and dried. Then the corrosion products were removed through a chemical cleaning procedure in a solution of 10%vol HCL+90%vol distilled water+5g/L C6H12N4 for 5min, rinsed and dried, and then reweighed to obtain the final weight (W1). The corrosion rate (Vc) was reported in mm/a according to the weight loss calculated using Eq. 1. where W0 and W1 are the original and final weight of specimen, g, respectively; t represents the immersion time, d; ρ is steel density, g/cm3; S is exposed surface area, cm2. VC =

36500 ×（W0 − W1 ) ρ tS

(1)

Morphology Observation and Composition Analysis. The morphology and composition of the corrosion products were investigated by a TESCAN VEGA II SEM, a XFORD INCA350 EDS, and a 7000S/L XRD. Experiments Results Immersion Tests. Fig. 4 displays the average corrosion rates of 3Cr steel with different temperature and CO2 partial pressure. The average corrosion rates of 3Cr steel decreased with the increasing of temperature, and increased firstly and then decreased as the CO2 partial pressure rose, and reached its maximum rate at 0.5MPa.

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(a) Corrosion rates changed with temperature, (b) Corrosion rates changed with PCO2 Fig. 4 Immersion test results of 3Cr steel. Corrosion Morphology and Energy Spectrum Analysis. Fig. 5 shows the corrosion macromorphology of 3Cr steel after immersion test at the CO2 partial pressure of 1MPa. The corrosion products were thin and had an uniform distribution at the temperature of 60℃ and 140℃,and when temperature turned to 60℃ and 120℃, the corrosion products were thick and had a maldistribution. After a removal of the corrosion products, as shown in Fig. 6, there were no evident etch pits on the specimen surface, the specimens were all existed as uniform corrosion morphology.

(a) T=60℃

(b)T=90℃

(c)T=120℃

（d）T=140℃

Fig. 5 Macroscopic feature of 3Cr steel after immersion test (corrosion products unremoved).

(a) T=60℃ (b)T=90℃ (c)T=120℃ （d）T=140℃ Fig. 6 Macroscopic feature of 3Cr steel after immersion test (corrosion products removed). Micro-morphology and Energy Spectrum Analysis of Corrosion Products. The micromorphology of the corrosion products changed with the variation of temperature and CO2 partial pressure. Fig. 7 shows the micro-morphology of the corrosion products under different temperature when the CO2 partial pressure was 1MPa. As it’s illustrated in Fig. 7, at 60℃, there were small amounts of corrosion products covered on the specimen surface, and the corrosion products were loose and cracked in some local area. As the temperature rose to 90℃, crystalline substances with triangle cone shape were gradually precipitated and covered on the surface of the specimen. With the increasing of the temperature, more crystalline substance precipitated and its shape were also changed from triangle cone to calcite. Fig. 8 demonstrates the micro-morphology of the corrosion products under different CO2 partial pressure when the temperature was 90℃. As it can be seen that there were

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small amounts of cotton-shaped corrosion products covered on some local area of the material surface when the CO2 partial pressure was 0.05MPa, and as the partial pressure increased to 0.2MPa, there also existed some triangle cone shaped and block-shaped products accompanied with the former existed cotton-shaped corrosion products. Furthermore, when the CO2 partial pressure increased to 0.5MPa, the whole surface of the specimen was covered with the irregular block-shaped corrosion products, and there was a serious cracking among the corrosion products. When the CO2 partial pressure turned to 1MPa, the corrosion products gradually changed to a crystalline substance with a triangle cone, and no corrosion products cracking phenomenon can be seen on the surface of the specimen.

(a) T=60℃ (b) T=90℃ (c) T=120℃ (d) T=140℃ Fig. 7 Microscopic corrosion morphology of material surface under different temperature (PCO2=1MPa).

(a) PCO2=0.05MPa (b) PCO2=0.2MPa (c) PCO2=0.5MPa (d) PCO2=1.0MPa Fig. 8 Microscopic corrosion morphology of material surface under different CO2 partial pressure (T=90℃). Use energy spectrum analysis method to make out the chemical elements composition of the corrosion products with different micro-morphology, as shown in Fig. 9 and Fig. 10. The blockshaped corrosion products were mainly composed of C, O, Cr, Fe, S, Cl, and the crystalline substance were mainly composed of C, O, Ca, Fe.

Fig. 9 Energy spectrum analysis of the block-shaped corrosion product.

Fig. 10 Energy spectrum analysis of the triangle cone shaped corrosion product.

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XRD Analysis of the Corrosion Products. The phase composition of the corrosion products was obtained based on the energy spectrum analysis results of the corrosion products and the X-ray diffractometer, the results were demonstrated in Fig. 11. The results illustrated that the corrosion products were mainly composed of CaCO3, FeCO3, and Cr(OH)3.

(a) PCO2=0.05MPa

(c) PCO2=0.5MPa

(b) PCO2=0.2MPa

(d) PCO2=1.0MPa

Fig. 11 XRD phase analysis of corrosion product at 90℃. Analysis and Discussion The corrosion process of steel in CO2 aqueous solution is very complicated, each reaction rate is largely depended on temperature, pressure, pH value, corrosion product film, and other dissolved ion, this may lead to a more complicated intermediate reaction. As for a naked steel material surface, CO2 corrosion behavior is totally different in cathode and anode. In the anode, the constant dissolution of Fe would lead to a uniform corrosion or localized corrosion, and this would give rise to the speed of the wall thickness reduction or corrosion perforation of the metallic facility. In the cathode, catalytic deoxidizing reaction occurs through the H+ ionized from carbonic would give an acceleration of the carbon steel material’s corrosion process [18]. In practice, as the progress of the CO2 corrosion reaction, the steel surface would be covered by the corrosion product film, the steel’s dissolve rate would be integrated by the structure, thickness, stability and permeability of the film. In this article, besides of the CO2 corrosion products FeCO3, Ca2+ in the high salinity formation water would also react with CO32-, and finally become CaCO3, the reaction equation is as follows: Ca2++ CO32-→CaCO3 And the formation of CaCO3 has a big influence on the corrosion behavior of 3Cr steel. Corrosion Behavior Under Different Temperature. As we had talked above, corrosion rate decreased with the increasing of temperature. How temperature influence the corrosion rate is mainly depend on its impact on the reaction speed and corrosion products film formation mechanism. As for 3Cr steel, Beside of the dissolution of Fe, there also exist the dissolution of Cr in anode reaction [19]: Cr +3H2O→Cr(OH)3+3H++e Cr +H2O→Cr(OH)ads +H+ +e Cr(OH)ads→Cr(OH)+ads +e Cr(OH)+ads +H+→Cr3+ads +H2O +e

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The reaction rate is very slow at 60℃, it is hard for 3Cr steel to form effective corrosion products film on the specimen surface. So the poor quality of the corrosion products film and low fraction of coverage on the specimen surface were all responsible for the high corrosion rate at 60℃. The increasing of the temperature can cause low dissolved CaCO3 level in the formation water, so CaCO3 precipitated from the solution and covered on the surfaced of the 3Cr steel. The quantity and density of CaCO3 are also increased with the rise of the temperature, and this could partly give a contact prevention between 3Cr steel specimen surface and corrosion medium, thus reduce the corrosion rate. Furthermore, some research had also indicated that the corrosion product Cr(OH)3 could make the corrosion products film become anionic selectivity, and this would contribute to a reduction on the anion concentration in the interface between corrosion products film and metallic matrix. The anion concentration reduction would lead to the suppression of the anodic reaction, and finally cause a reduction of the Fe matrix dissolution rate. Therefore it is believed that in the simulated oilfield CO2 and high Ca2+ content formation water corrosion atmosphere, the precipitated mechanism of Ca2+ plays an important role in the corrosion behavior of 3Cr steel at different temperature. Corrosion Behavior Under Different CO2 Partial Pressure. The CO2 corrosion rate of 3Cr steel largely depended on the CO2 content in the solution, namely the CO2 partial pressure. It has long been believed that the content of HCO3-,CO32- in the solution increased with the rising of the CO2 partial pressure, which will give an acceleration of the corrosion reaction. However, just as we had talked above, the average corrosion rate of 3Cr steel increased firstly and then decreased with the rising of the CO2 partial pressure, and reached its maximum rate at 0.5MPa. This phenomenon may be related with the formation mechanism of the corrosion products in high salinity formation water. As had been illustrated in Fig.9, When PCO2≤0.2MPa, the corrosion products composed of mixing pile substance in the bottom layer and columnar calcite substance in the top layer, and this kind of products film did not have a strong protective effect to the 3Cr steel matrix. With the increasing of the CO2 partial pressure, there were a mass formation of FeCO3 and CaCO3, the existence of CaCO3 makes FeCO3 corrosion product layer more easy to fall off, and thus give an increase of the corrosion rate. At 0.5MPa, because of the formation and cracking of Cr(OH)3 product layer, there leave little CaCO3 in the top layer, and this will result in a less protective effect to the 3Cr material matrix. At 1MPa, as the corrosion products of Cr(OH)3 vanished, the corrosion rate was higher than its in PCO2≤0.2MPa, but lower than that in 0.5MPa. Conclusions (1) In the CO2-formation water environment the corrosion rate of 3Cr steel decreases with the increase in temperature, and increases firstly and then decreases as the CO2 partial pressure rose, and reaches its maximum rate at 0.5MPa. (2) The high content of Ca2+ in the formation water make a big influence on the corrosion rate of the 3Cr steel as it can lead to a precipitated of CaCO3 from the solution. Acknowledgement This work is sponsored by Scientific Research and Technology Development Project of CNPC (2021DJ2703) and (2020B-4020). References [1] A. A. Alquriaishi & E. M. El-M. Shokir, Experimental Investigation of Miscible CO2 Flooding, Petroleum Science and Technology, 29 (2011) 2005-2012. [2] Zhang Baoshou, Gu Qiaoyuan, Zhang Haizu, Zhao Qing, Yin Fenglin, Genesis and Study Significance of High CO2 Content in Carbonate Rocks in Tazhong Area,Tarim Basin, Marine Origin Petroleum Geology,3(2010)70-73.

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[3] ROSA M, CUE´LLAR-FRANCA, ADISA A, Carbon capture, storage and utilisation technologies: A critical analysis and comparison of their life cycle environmental impacts, Journal of CO2 utilization, 9(2015)82-102. [4] ZHAO Xue-hui, HE Zhi-wu, LIU Jin-wen, et al. Research status of CCUS corrosion control technology, Petroleum tubular goods and instruments, 3(2017)1-6. [5] ZHANG De-ping, Pilot test of research and application status of CO2 flooding production technology, Science and technology review,29( 2011) 75-79. [6] YANG Sheng-lai, CHEN Hao, FENG Ji-lei, A brief discussion on some scientific issues to improve oil displacement during gas injection Tarim oilfield, Petroleum Geology and Recovery Efficiency,1(2014)40-44+113. [7] LV Xiang-hong, ZHAO Guo-xian, Tubing and Casing material and corrosion prevention, Petroleum industry Press,2015. [8] Xue Yan, Research on Corrosion Behavior of Low Cr Corrosion-resistant Materials in Tarim Oilfield, Xi’an: Xi’an Shiyou University, 2010. [9] Q. Wu, Z. Zhang, X. Dong, J. Yang, Corrosion behavior of low-alloy steel containing 1% chromium in CO2 environments, Corros. Sci. 75 (2013) 400–408. [10] M.N. Zafar, R. Rihan, L. Al-Hadhrami, Evaluation of the corrosion resistance of SA-543 and X65 steels in emulsions containing H2S and CO2 using a novel emulsion flow loop, Corros. Sci. 94 (2015) 275–287. [11] S. Hassani, T.N. Vu, N.R. Rosli, S.N. Esmaeely, Y.-S. Choi, D. Young, S. Nesic, Wellbore integrity and corrosion of low alloy and stainless steels in high pressure CO2 geologic storage environments: An experimental study, Int. J. Greenh. Gas Control 23 (2014) 30–43. [12] S. Guo, L. Xu, W. Chang, M. Lu, Experimental study of CO2 corrosion of 3Cr pipeline steel, Acta Metall. Sin. 47 (2011) 1067–1074. [13] Z. Bai, C. Chen, M. Lu, J. Li, Analysis of EIS characteristics of CO2 corrosion of well tube steels with corrosion scales, Appl. Surf. Sci. 252 (2006) 7578–7584. [14] Bei Wang, Lining Xu, Guozhang Liu, Minxu Lu, Corrosion behavior and mechanism of 3Cr steel in CO2 environment with various Ca2+ concentration, Corros. Sci. 136 (2018) 210–220. [15] Yongxin Lu, Hongyang Jing, Yongdian Han, Lianyong Xu, Effect of temperature on the 3Cr low-alloyed steel initial corrosion behavior in CO2 solution, Materials Chemistry and Physics,178 (2016) 160-172. [16] Yong Hua a, Xiaoqi Yue, Huifeng Liu, et al. The evolution and characterisation of the corrosion scales formed on 3Cr steel in CO2-containing conditions relevant to geothermal energy production, Corros. Sci. 183 (2021) 109342. [17] Jinyang Zhu a, Lining Xu a,Minxu Lu, et al. Essential criterion for evaluating the corrosion resistance of 3Cr steel in CO2 environments: Prepassivation, Corros. Sci. 93 (2015) 336-340. [18] M.B. Kermani, A. Morshed, Carbon dioxide corrosion in oil and gas production-a compendium, Corrosion 59 (2003) 659–683. [19] D.S. Carvalho, C.J.B. Joia, O.R. Mattos, Corrosion rate of iron and iron–chromium alloys in CO2 medium, Corros. Sci. 47 (2005) 2974–2986.

CHAPTER 2: Bio-Based Materials and Biorefining Technologies

Materials Science Forum ISSN: 1662-9752, Vol. 1071, pp 101-108 doi:10.4028/p-r57u45 © 2022 Trans Tech Publications Ltd, Switzerland

Submitted: 2022-06-03 Revised: 2022-07-26 Accepted: 2022-07-27 Online: 2022-10-18

Preliminary Study of Chemically Pretreated Densification of Juniper Wood for Use in Bone Implants Laura Andze1,a,*, Martins Andzs1,b, Marite Skute1,c, Vadim Nefjodov2,d, Martins Kapickis2,e, Ramunas Tupciauskas1,f Latvian State Institute of Wood Chemistry, Dzerbenes street 27, Riga, Latvia, LV-1006

1

Microsurgery Centre of Latvia, Brivibas gatve 410, Riga, Latvia, LV-1024

2

[email protected], [email protected], [email protected], [email protected], e [email protected], [email protected]

a

Keywords: juniper wood, chemical pretreatment, compressed solid wood, wood densification, wood bone implants

Abstract. Kraft cooking of juniper wood with NaOH/Na2S aqueous solution has been used in the study for partial delignification at the temperature of 165oC for different residence time (0-40 minutes) following by thermal compression for densification under a pressure of 5 MPa at 100oC for 24 hours. The densified and natural juniper wood samples were characterized by chemical composition and mechanical properties. The results show that the density of densified juniper wood was increased by 96-127% reaching the value of 1170 kg/m3 that is similar to conventional bone implants (1090 kg/m3). Modulus of rupture and modulus of elasticity of densified juniper wood were increased by 85% and 621%, respectively, demonstrating a high potential of the material to be used as bone implants. Introduction Bone implants have been extensively studied in both material and medicine science for decades. There are thousands of scientific articles on the bone implants. Demand for non-metallic implant materials is growing rapidly, not only because of metal implants damage bone over time due to loosening and biocorrosion, but also because of increased use of modern medical diagnostic systems, e.g., nuclear magnetic resonance (NMR) [1]. Materials such as calcium phosphate, calcium carbonate and calcium sulphate are mainly studied as potential bone substitutes. Materials obtained directly from nature are also being studied, e.g., corals [2]. At the same time, wood as a natural material for bone implants has been studied insufficiently. The main advantage of wood as a bone implant biomaterial is its structural similarity to bone structure. Internal structural similarity also leads to similar properties, e.g. density, anisotropy and fluid transport in cells. Previous studies have shown that wood have a good biocompatibility and osteoconductivity with no toxicity has been observed [3; 4]. The idea of the study is based on two previous investigations - use of Juniperus communis in bone implants by prof. dr. hab. med. E. Ezerietis [5] and a study on the delignification and compaction of wood to produce high-performance materials [6]. The above studies indicate that wood can be used successfully as a bone implant material. However, there are still a number of problems that prevent wood from using in bone implants. The main ones - wood has a variable density and composition depending on age, species and growing conditions; the density of wood is less than that of bone. These problems could be prevented by densification of wood leading to increased density and improved physical-mechanical properties. The first studies on the wood densification have been presented in the early 1900 in the United States when the first patents of wood densification concept were submitted. The initial studies were not complete, they focused on the compression technique without evaluating the plasticization mechanism and the stability of the products. Between 1930 and 1960, research was carried out pretreatment methods of wood densification, for example by using heat treatment or chemical compounds to impregnate the wood filling the porous structure of the cell wall. Recent research on

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Construction and Bio-Based Materials: Properties and Technologies

wood densification has involved the pretreatment of a chemical or enzymatic modification by which chemical components (lignin, hemicelluloses, cellulose) in the cell wall structure are modified and partially destroyed and new covalent bonds are formed [7;8]. Song. et. al. [6] in 2018 initiated a new research direction of wood densification based on partial delignification of wood by chemical pretreatment with alkaline cooking in an aqueous solution of NaOH/Na2SO3 followed by hot-pressing. This method of densification has been used in several latest studies [6;8-11]. As it is known, NaOH/Na2SO3 aqueous solution is widely used in pulping process and is the second most popular method after the Kraft cooking. Kraft cooking results a lower yield of cellulose with stronger fibers for paper materials [8;12]. Based on this fact, our study performs namely Kraft cooking pretreatment using aqueous NaOH/N2S solution by following hot-pressing to obtain improved densified juniper wood. Materials and Methods The research was carried out on samples of solid juniper (Juniperus Communis) wood collected in a forest at Kegums, Vidzeme region, Latvia. Sodium hydroxide (>97%, Sigma-Aldrich), sodium sulfide hydrate (≥60%, Sigma-Aldrich) and deionized water were used for chemical pretreatment of juniper wood. Acetone (>97%, Sigma-Aldrich) and sulfuric acid (>95-98%, Sigma-Aldrich) were used for methods of chemical characterization. Sample preparation. Manually debarked juniper logs 300 mm in length and 50-100 mm in diameter were air-dried for 1 month (Fig. 2 a). Logs were cut into the specimens with a size of 90 mm × 15 mm × 15 mm (longitudinal × tangential × radial). The initial average moisture content of samples was 7.62%. Figure 1 schematically illustrates the research methodology of juniper wood densification and characterization. 4. Chemical characterization: mass loss, Klason lignin , acetone extractives 2. Sulphate cooking: 165oC ; 0, 20 or 40 min 1. Juniper wood

Dry/ wet

3. Densification: 100oC, 5MPa; 24 h

5. Physical-mechanical properties: density, 3 point bending

Figure 1. Schematic illustration of the research. Chemical pretreatment. Typical Kraft cooking aqueous solution was prepared from 1.25M NaOH and 0.25M (calculated to anhydrous substance) Na2S, what is widely used in the pulping industry [12]. Juniper wood specimens where immersed in a 100 ml autoclaves (one sample per autoclave) and fulfilled by the cooking solution for 24 hours. Then autoclaves with specimens were heated up to 165oC in a glycerin bath. The first specimen was removed immediately after reaching 165oC (K0) and other samples where cooked at 165oC for 20 minutes (K20) and 40 minutes (K40). After, the cooked specimens were washed several times with deionized water until stopped coloring and then kept in water. Densification. The chemically pretreated juniper wood specimens were hot-pressed on a radial/tangential direction in a specially designed mold (Fig. 2 b) by a single-stage press JOOS (Type LAP 40, Germany) under a pressure of 5 MPa at 100oC for 24 hours followed by the interrupted heating for another 12 hours. To evaluate the impact of chemical pretreatment, control samples of dry (Control-D) and wet (Control-W) juniper wood were hot-pressed by the same method. The control

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wet specimens were prepared by immersing in a hot (90oC) deionized water for several times until its sunk followed by the hot-pressing. Three specimens per each sample type were produced.

a

b

Figure 2. Sample preparation: a) debarked juniper logs; b) cut specimens in hot-pressing mold. Chemical characterization. Mass loss (ML) of cooked samples was calculated according to Equation (1): 𝑀𝑀1 − 𝑀𝑀𝑀𝑀 𝑀𝑀𝑀𝑀 (%) = 𝑥𝑥100 𝑀𝑀𝑀𝑀

(1)

where Mo, M1 – absolutely dry specimen mass before and after chemical pretreatment, respectively.

Extractives. The wood samples before and after chemical pretreatment were grounded (M20, IKA-WERKE, Germany) and then Soxhlet-extracted with acetone for 8 h to quantify the extractable components gravimetrically (ES 225SM-DR, Precisa, Switzerland) after rotary vacuum-evaporation (PC3001 VARIO, Green Vac, Germany) and expressed as a percentage of the initial wood sample mass (Eq. 2): (2) 𝑀𝑀2 − 𝑀𝑀1 𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸 (%) = 𝑥𝑥100 𝑀𝑀 where M – absolutely dry specimen mass, M1 – mass of absolutely dry round flask, M2 – mass of absolutely dry round flask with specimen extractives.

Klason lignin of the samples was obtained according to TAPPI 222om-98.

Physical-mechanical properties. Density of all densified samples was measured after the conditioning and calculated according to Equation 3: (3) 𝑀𝑀 𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 = 𝑙𝑙 × 𝑤𝑤 × 𝑡𝑡

where M, l, w, t – mass, length, width and thickness of conditioned (25oC; relative humidity 50%) specimen, respectively. Three point bending. The densified juniper samples were evaluated by the modulus of elasticity (MOE) and the modulus of rupture (MOR) in the three-point bending test on a ZWICK/Z100 (Ulm, Germany) universal machine for testing the mechanical resistance of materials. Three specimens per each sample type were determined in the test to calculate the average value property.

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Results and Discussion Visual summary of all obtained juniper wood samples is shown in Figure 3. The wood appearance and color were changed slightly for wet-densified (WD) control specimens (Fig. 3c), while after the chemical treatments the densified specimens contain even surface damages with split fibers (Fig. 3df). These changes are associated to the Kraft cooking process where lignin and hemicelluloses degrade in the wood cell walls and dissolve extractives [13;14]. The reason of chemically pretreated and densified juniper wood color changes could be explained by the chemical degradation of hemicelluloses and lignin that makes new chromophoric groups, as well as termochromatism of the chemicals on the wood surface [9]. The thickness of control samples, which were dry- and wet-densified, decreased by 12% and 47%, while for chemically pretreated and densified samples – in range of 62-73%. a

b Control

d

c Control-DD

e K0D

Control-WD

f K20D

K40D

Figure 3. Visual characteristics of juniper wood samples. Untreated control specimens: a) without densification, b) dry-densified (DD), c) wet-densified (WD); densified specimens after the Kraft cooking: d) removed immediately after reaching 165oC (K0D), e) cooked 20 minutes (K20D) and f) cooked 40 minutes (K40D). The impact of Kraft cooking on juniper wood’s mass loss and contents of lignin and extractives is shown in Table 1. Partial degradation and thermal modification of lignin was performed during Kraft cooking pretreatment and relative content of lignin decreased by 16-23%. Table 1. Chemical characterization of juniper wood before and after chemical treatment.

Control K0 K20 K40

Mass loss, % 0 24 27 32

Lignin, % 34 28.5 29.5 26

Extracts, % 4.8 3.3 3.2 3.9

The significant increase of mass loss after the Kraft cooking could be more explained by the fact of hemicelluloses destruction [13;14] and then by reduction in lignin. Lignin content (34%) in the juniper wood is higher than in other popular softwood [15-16], as example in pine 24-29% [13] and spruce 26-28% [17]. Table 1 shows that the detected lignin content of chemically pretreated juniper

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wood is equivalent to that of pine or spruce and it is good since thermal modified lignin can act as an adhesive in the following densification step by hot-pressing [18].

Density, kg/m3

1400 1050 700 350 0

Control

DD DW K0D control control

K20D K40D

Bone [21;22]

Figure 4. Density of juniper wood depending on pretreatment and densification vs bone. The density of all densified juniper wood increased by 96-127% reaching the value over than 1000 kg/m3 (Fig. 4) which is equivalent to that obtained by other authors [6-7;9-10;19]. The higher density appeared in the densified juniper wood after 20 minutes of Kraft cooking pretreatment. The resulting densified juniper wood density is similar to bone density, which is one of the most important properties for the material to be used in bone implants [20]. The detected bending properties of juniper wood samples are summarized in Fig. 5. Densification of dry control sample was insufficient, while wet-densification resulted to significant increase of both MOE and MOR. Densification of chemically pretreated juniper wood increased even more both MOR and MOE. The highest increase in MOR and MOE was achieved by densified juniper wood after 20 minutes of Kraft cooking pretreatment. Compared to untreated juniper wood, MOE increase is 620% reaching the average value of 12500 MPa while MOR increase is up to 85% reaching the value of 174 MPa. The Kraft cooking after 40 minutes resulted to decrease in bending properties of densified juniper wood meaning that the optimal cooking time was reached after 20 minutes. Therefore, the chemical pretreatment longer than 20 minutes under the given conditions is unreasonable. The MOR and MOE obtained in this study by absolute values are lower than those reported by other authors, however, the percentage increase is comparable [7;9;19]. As shown in the Fig. 5 the MOE and MOR of densified juniper wood samples are equivalent to the bone properties [21-22]. It is known that the wood cell wall is formed of cellulose, hemicelluloses and lignin, and the hemicelluloses and lignin cross-linking cellulose microfibrils. Cellulose chain microfibrils with cross-linked lignin and hemicelluloses function as a skeleton. In the lignocellulosic materials hemicelluloses provides shape stabilization and lignin is responsible for the quasi-elastic recovery mechanism (shape memory effect). Lignin content in the wood has negative correlation with wood elasticity [9-10]. The high lignin content in the juniper wood (Table 1) explains the low MOE value in untreated (control) juniper wood sample [15-16].

Construction and Bio-Based Materials: Properties and Technologies

14000

200

10500

150

7000 3500

MOR, MPa

MOE, MPa

106

0 a

100 50 0

b

Figure 5. Bending properties of juniper wood depending on pretreatment and densification vs bone. However, this is highly related to the wood moisture content. This effect could be compared observing the dry-densified sample which MOE increase is not sufficient, however, wet-densified sample demonstrate significant MOE increase. So, the increase in moisture content helps to form hydrogen bonds during pressing and allows improved densification process by leading to increase in density and simultaneously increase in bending properties. In turn the chemical pretreatment of juniper wood has partially destroyed lignin and hemicelluloses and new covalent bonds are formed what leads to even higher increase of all detected properties suggesting it as an effective remedy for wood improvement comparable to bone properties. In this study, partial degradation and modification of lignin and hemicelluloses of solid juniper wood samples was performed by Kraft cooking pretreatment in combination with the change in the structure of wood cell walls during hot-pressing, provided an increase in density and corresponding increase in MOR and MOE. Summary It is possible to obtain densified juniper wood with similar density and bending properties as bone by Kraft cooking pretreatment and following hot-pressing. Density of pretreated and densified juniper wood increase up to 2.5 times, while MOE and MOR increase up to 7 and 2 times, respectively. The study showed that the detected physical-mechanical properties of densified juniper wood are comparable to the bone suggesting to continue the research on densified wood for bone implants. Acknowledgements Financial support for this research is from Latvian State Institute of Wood Chemistry Bio-economic grant “JunBon” 2022.

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References [1] J. Rekola, A.J. Aho, J. Gunn, J. Matinlinna, J. Hirvonen, P. Viitaniemi, P.K. Vallittu, The effect of heat treatment of wood on osteoconductivity, Acta Biomater, 5 (2009) 1596-1604. DOI: 10.1016/j.actbio.2009.01.018 [2] J. Rekola, L.V.J. Lassila, J. Hirvonen, M. Lahdenpera, R. Grenman, A.J. Aho, P.K. Vallittu, Effects of heat treatment of wood on hydroxylapatite type mineral precipitation and biomechanical properties in vitro, Mater. Sci. Mater. Med., 8 (2014) 2345-2354. DOI: 10.1007/s10856-010-4087-4 [3] A.J. Aho, J. Rekola, J. Matinlinna, J. Gunn, T. Tirri, P. Viitaniemi, P., Vallittu, Natural composite of wood as replacement material for ostechondral bone defects, J. Biomed. Mater. Res. B Appl. Biomater, 83 (2007) 64-71. DOI: 10.1002/jbm.b.30767 [4] K.A. Gross, E. Ezerietis, Juniper wood as a possible implant material, J. Biomed. Mater. Res. A, 64 (2003) 672-683, DOI:10.1002/jbm.a.10437 [5] E. Ezerietis, J. Vetra, J. Gardovskis, K.A. Gross, R. Jupatovs, M. Skudra, J. Krumalis, A. Blauss, LV Patent 11851 (1998). [6] Song et.al., Processing bulk natural wood into a high-performance structural material, Nature, 554 (2018) 224-228, DOI:10.1038/nature25476 [7] J.P. Cabral, B. Kafe, M. Subhani, J. Reiner and M. Ashraf, Densifcation of timber: a review on the process, material properties, and application, J. Wood Sci., 68 (2022) 1-24, DOI:10.1186/s10086022-02028-3 [8] A. Kutnar, M. Sernek, Densification of wood, Zbornik gozdarstva in lesarstva, 82 (2007) 53–62. [9] J. Shi, J. Peng, Q. Huang, L. Cai1, and S.Q. Shi, Fabrication of densifed wood via synergy of chemical pretreatment, hot-pressing and post mechanical fxatio, J. Wood Sci., 66 (2020) 1-9. DOI:10.1186/s10086-020-1853-x [10] P. Mania, M. Wróblewski, A. Wójciak, E. Roszyk and W. Molinski, Hardness of densified wood in relation to changed chemical composition, Forest, 11 (2020) 506-517. DOI:10.3390/f11050506 [11] V. Raman and K.C. Liew, Density of densified paraserianthes falcataria wood pre-treated with alkail, IOP Conf. Ser.: Earth Environ. Sci., 540 (2020) 012030. DOI:10.1088/17551315/549/1/012030 [12] Grant, J. Laboratory handbook of pulp and paper manufacture. Edvard Arnold&Co, Londona; 1944, p 320. [13] I. Sable U. Grinfelds, L. Vikele, L. Rozenberga,M. Zeps, U. Neimane,A. Jansons, Effect of refining on the properties of fibres from young Scots (Pinus Sylvestris) and Lodgepole pines (Pinus Contorta), Baltic Forestry, 23 (2017), 529–533. [14] I. Sable U. Grinfelds, L. Vikele, L. Rozenberga, M. Zeps, D. Lazdina, A. Jansons, Chemical composition and fiber properties of fast-growing species in Latvia and its potential for forest bioindustry, Forestry Studies, 66 (2017) 27-32. [15] K.G. Bogolitsyn, M.A. Gusakova, S.S. Khviyuzov, I.N. Zubov, Physicochemical properties of conifer lignins using Juniperus communis as an e xample, Chem. Nat. Compd., 50 (2014) 337-341. [16] T. Hänninen, P. Tukiainen, K. Svedström, R. Serimaa, P. Saranpää, E. Kontturi, M. Hughes, T. Vuorinen, Ultrastructural evaluation of compression wood-like properties of common juniper (Juniperus communis L.) , Holzforschung, 66 (2012) 389-395. DOI:10.1515/HF.2011.166 [17] J. Wadenback, D. Clapham, G. Gellerstedt, S. von Arnold, Variation in content and composition of lignin in young wood of Norway spruce, Holzforschung 58 (2004) 107-115. DOI:10.1515/HF.2004.015

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[18] R. Tupciauskas, J. Rizhikovs, P. Brazdausks, V. Fridrihsone, M. Andzs, Influence of steam explosion pre-treatment conditions on binder-less boards from hemp shives and wheat straw, Ind. Crop. and Prod. 170 (2021) 113717. DOI:10.1016/j.indcrop.2021.113717 [19] H. Pelit, F. Emiroglu, Density, hardness and strength properties of densified fir and aspen woods pretreated with water repellents, Holzforschung, 75 (2021) 358-367. DOI:10.1515/hf-2020-0075 [20] H.E. Meema, S. Meema, Compact bone mineral density of the normal human radius, Acta Radiol. Oncol. Radiat. Phys. Biol., 17 (1978) 342-352. DOI:10.3109/02841867809127938 [21] L.A. González‐Bárcenas, H. Trejo‐Camacho, I. Suárez‐Estrella, A. Heredia, C. Magaña, L. Bucio, and E. Orozco, Three point bending test of human femoral tissue: An essay in ancient and modern bones. AIP Conference Proceedings 173 (2003) 682, 173, DOI:10.1063/1.1615117 [22] D. Singh, A. Rana, S.K. Jhajhria, B. Garg, P.M. Pandey and D. Kalyanasundaram, Experimental assessment of biomechanical properties in human male elbow bone subjected to bending and compression loads, J. Appl. Biomater. Funct. Mater. (2019) 1-13, DOI:10.1177/2280800018793816

Materials Science Forum ISSN: 1662-9752, Vol. 1071, pp 109-116 doi:10.4028/p-hy2kd0 © 2022 Trans Tech Publications Ltd, Switzerland

Submitted: 2022-05-25 Revised: 2022-06-20 Accepted: 2022-06-26 Online: 2022-10-18

A Study on Waste Paper Reinforced Recycled Polypropylene Biocomposite Jevgenijs Jaunslavietis1,2,a, Jurijs Ozolins2,b, Martins Kalnins2,c, Galia Shulga1,d*, Brigita Neiberte1,e, Anrijs Verovkins1,f and Talrits Betkers1,g Latvian State Institute of Wood Chemistry, Dzerbenes St. 27, LV-1006,Riga, Latvia

1

Riga Technical University, Paula Valdena 3, Riga, Latvia, LV-1048

2

[email protected], [email protected], [email protected], [email protected], e [email protected], [email protected], [email protected]

a

Keywords: recycled waste paper, recycled polypropylene, polymer-based bio-composite

Abstract. The growing global request to make green materials nowadays expresses in reducing environmental problems and obtaining biomaterials with high-performed properties. The use of biomass for obtaining green materials contributes to energy security and climate change mitigation. The aim of the work was to fabricate and study a recycled polypropylene-based composite filled with recycled waste paper obtained by the acid hydrolysis of de-inked newsprint. It has been found that, with increasing the content of the recycled paper microparticles in the bio-composite, its mechanical and wetting properties deteriorated. The presence of maleic anhydride grafted polypropylene as a compatibilizer increased the homogeneity of the structure of the bio-composite, which improved its mechanical properties and decreased its ability to be wetted with water. Introduction Wastes and industrial side streams play a significant role as raw materials in the European bioeconomy. Nowadays, waste biomass research is focusing on its conversion into value-added products. Recycled polyolefins are among the major components of global municipal solid waste, and they present a promising raw material source for producing composites due to their large volume and low cost, compared with neat polymers. The use of recycled synthetic polymers in composites is a promising practice for rational recovering these wastes and reducing their load on the environment [1, 2]. Crystalline cellulosic microparticles can be produced from both wood and non-wood materials as well as from waste paper and cotton waste [3-5]. The obtaining of crystalline cellulose from paper wastes can be regarded as one of the promised options for their recycling. Microcrystalline cellulose obtained by different methods from lignocellulosic materials varies in the values of crystallinity, particle sizes and their distribution, the ability to absorb moisture, etc. There are many isolation technics of crystalline cellulose from lignocellulosic sources such as acid hydrolysis, alkali treatment, extrusion technology, etc. [6]. One of the widely used methods is acid hydrolysis of lignocellulosic materials due to its simplicity and shorter reaction time than other isolation processes [7]. Acid hydrolysis disrupts the amorphous cellulose and leaves its crystalline part. Crystalline cellulose is much stronger and stiffer than amorphous and is often used as a reinforcing filler in bio-composites [8-10]. The growing global request to make green materials nowadays expresses in reducing environmental problems and obtaining bio-composites with high-performed properties. Polymerbased composites filled with cellulosic fibers are characterized by improved physical-mechanical properties such as high strength and stiffness, low density as well as, due to the presence of the natural filler, the ability to biodegrade in a much shorter period of time than synthetic polymers [11]. They

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offer a huge potential in a large variety of applications such as building engineering, packaging, medicine, etc. On the other side, immiscibility between hydrophobic polymer matrix and hydrophilic crystalline cellulosic microparticles is the main drawback of such types of bio-composites [12]. For elimination of this cause, compatibilizers, increasing the interfacial adhesion between a cellulosic filler and a polymer matrix, are applied in bio-composites [13]. Among the interface modifiers, maleic anhydride grafted polypropylene is very popular due to its efficiency [14]. The aim of the research is to obtain and study a new eco-friendly recycled polypropylene-based composite filled with recycled waste paper and to evaluate the effect of a compatibilizer on the mechanical and wetting properties of the bio-composite. Materials and Methods Materials The waste de-inked newspaper served as a source for obtaining the recycled paper-based filler (rPAP). For this purpose, the waste paper was cut into small pieces which were soaked in a 0.05 % hydrochloric acid solution, and after that, they were dried, at first at 60 °C and then at 120 °C according to the developed method [15]. The air-dried treated waste paper pieces were milled in a planetary ball mill (Retsch, Germany) for 10 min at 300 RPM with 15 balls (d = 1 cm). The obtained cellulosic powder was washed until neutral pH and dried again. The dried powder was sieved, using a sieve with a hole size of 200 µm. Recycled polypropylene (rPP) (900 kg/m3, 5.2 g/10 min at 230 °C, and 2.16 kg) was used as a thermoplastic polymer matrix and supplied from a Latvian polymer recycling plant (Nordic Plast Ltd., Latvia). Before blending, it was milled in a knife mill (Retsch, Germany) and was sieved through a sieve with a hole size of 500 µm. Maleic anhydride grafted polypropylene with the trademark Licocene PP MA 7452 produced by Clariant company as a compatibilizer (CL) was used. The composite material samples were obtained, at first, by mixing the powdered rPP with the powder cellulosic filler in the absence and the presence of the compatibilizer for 5 min at room temperature in a vibratory micromill PULVERISETTE 0 (Frisch, Germany). Table 1. Content of recycled polypropylene, recycled waste paper and the compatibilizer in the composite samples Composition rPP, [%] rPAP, [%] CL, [%] rPP 100 0 0 rPP/10 rPAP 90 10 0 rPP/30 rPAP 70 30 0 rPP/50 rPAP 50 50 0 rPP/10 rPAP /CL 87 10 3 rPP/30 rPAP /CL 67 30 3 rPP/50 rPAP /CL 47 50 3 The obtained blends were used for fabricating the samples for tensile and bending tests by the extrusion and molding method using HAAKE MiniLab II and MiniJet II (Thermo Fisher Scientific, Germany) at a temperature of 175 °C, a circulation time in the two-screw extruder of 5 min, the screws rotational speed of 130 rpm, and a molding pressure of 60 MPa at a temperature of 120 °C. The composition of the obtained samples is given in Table 1.

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Methods Mechanical tests. Mechanical properties were determined with a universal machine “Zwick” (Zwick/Roell, Germany) with a load capacity of 0.5 kN at a rate of 50 mm/min and 2 mm/min for tensile and bending tests according to ASTM D638 (2007) and ISO 178 (2010) with the help of the software program (TestXpert I, Zwick/Roell, Germany). Five replicates were made for each mechanical testing, and the standard deviations for the values of tensile and bending strength as well as for tensile and bending modulus and deformations were determined. Wetting properties of WPC samples. The advancing contact angles of the composite samples were measured with a tensiometer Kruss K100M (Kruss, Germany) using the Wilhelmy method. The work of adhesion (WA) was calculated using the Young-Dupre equation: WA = σ (1 + cos ϴ), WA – work of adhesion [mN/m], σ – liquid surface tension [mN/m], ϴ – contact angle [o]. The total surface free energy (SFE) and its dispersive (Lifshitz – Van der Waals interactions) and polar (Lewis acid-base interactions) components were calculated using the Owens-Wendt-RabelKaelble method [16], for which the contact angle values with different liquids: water, dimethyl sulfoxide and diiodomethane were measured. For the calculation of SFE, a special software program (Advance Software Assurance, Kruss, Germany) mounted in the tensiometer was applied. Three replicates were tested for each sample and their arithmetic mean value was calculated. Particle sizes. The size distribution of cellulosic powder particles was measured by a laser granulometer Analysette Nano Tec (Frisch, Germany). Before taking a measurement, powder samples were dispersed in water by an ultrasound probe. Scanning electron microscopy. The morphology of the obtained composite samples was examined using a Tescan Mira/LMU device (Czech Republic). The samples were coated with a 15 nm thick gold layer before analysis by Emitech K550X. Results and Discussion Early [15] it has been shown that rPAP was the cellulosic powder microparticles (Fig. 1) with a crystallinity index of 61% based on the X-ray diffraction spectrum analysis. It was characterised by the following elemental composition: 44.84 % C, 4.47 % H, 50.52 % O, 0.16 % N, and contained 80% of the cellulosic microparticles less than 100 µm.

Fig. 1. SEM image of the rPAP microparticle. It is known that the mechanical properties of polymer composites are critically important for their practical application. Mechanical properties are the most studied material properties due to their importance and ease of testing. The mechanical properties of rPP and the rPP-based composite

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Tensile strength, MPa

samples filled with rPAP having a filling degree from 10 wt% to 50 wt% are shown in Figs. 2 - 5. As shown by the obtained stress-strain dependencies, with increasing the content of the cellulosic filler, the values of the mechanical properties of the composite decrease with the exception of tensile and bending modulus. According to Figs. 2, the drop of the tensile strength at break becomes more pronounced at a high filling degree of 50 wt% which is lower by 27% relative to the polymer matrix. The given results indicate the deterioration of the tensile properties of the composite samples filled with rPAP, compared with the case of rPP, in spite of increasing the values of Young’s modulus of elasticity up to 22-44% (Fig. 3) and decreasing the tensile deformation values up to 29-300 % in the range of 10-50 wt% filling. It is known that the mechanical modules of a composite increase, but the deformations decrease due to mechanical restrictions introduced by filler particles that limit the mobility and deformability of a polymer matrix. The dependences of bending strength and bending modulus on the content of the cellulosic microparticles, presented in Fig. 4 and Fig. 5, have analogical behavior as in the case of the tensile testing. With increasing the content of the filler in the range of 10-50 wt%, the bending strength values at break decreased by 3-29%, but bending modulus values grow by 18-240% in comparison with the rPP sample. The decrease in both the tensile and bending strength of the samples filled with the crystalline cellulosic microparticles confirms the insufficient compatibility between the cellulosic filler and the polymer matrix, which was shown in [16, 17], and may be caused by the prevailing cohesion interaction between the cellulosic microparticles and the formation of their agglomerates. For improving the interface adhesion between the hydrophilic cellulosic filler and the hydrophobic rPP matrix, maleic anhydride grafted polypropylene as a compatibilizer (CL) in the amount of 3 wt% was introduced in the composition of the filled samples. Its addition led to an increase in the mechanical properties of the composite samples. According to Fig. 2 and Fig. 3, the values of tensile strength and modulus of elasticity for the samples with the addition of CL increase from 21.4 MPa to 30.4 MPa and 966 MPa to 1227 MPa, respectively, with growing the content of the filler from 10 wt% to 50 wt% that corresponds to the increase of the tensile strength and the modulus of elasticity by 12–58% and 26–60 %, respectively, compared with the case of recycled PP. The deformation ability drops by almost 5.5 times for the composite sample with CL at a 50% filling relatively the elongation of the polymer matrix. The values of bending strength and bending modulus for the samples with CL (Fig. 4, Fig. 5) enlarge with increasing the filling degree and are higher by 48 % and 2.7 times at the highest filling degree, respectively, but the deflection ability of the samples with CL diminished more than 4 times at this filling in comparison with the case of rPP. The high values of both the mechanical modulеs indicate the increased stiffness of the composite containing the cellulosic microparticles as a filler. Thus, the obtained results show the effectiveness of PP-g-MA as a compatibilizer improving the interfacial adhesion between the cellulosic and the hydrophobic rPP particles. The reinforcement of the interface adhesion in the developed composite samples is connected with the formation of physicochemical bonds between the cellulosic microparticles and rPP due to the interaction of the compatibilizer with both components. This interfacial adhesion enhancement contributes to a more efficient transfer of the load from the polymer matrix to the crystalline cellulosic microparticles. 40

without CL

with CL

30 20 10 0

0

10

30

50

recycled waste paper content, %

Fig. 2. Tensile strength of the filled composite samples with and without the compatibilizer vs cellulosic filler content.

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Young's modulus, MPa

1400

without CL

1200

113

with CL

1000 800 600 400 200 0

0

10

30

50

recycled waste paper content, %

Fig. 3. Tensile modulus of the filled composite samples with and without the compatibilizer vs cellulosic filler content. Bending strength, MPa

40

without CL

with CL

30 20 10 0

0

10

30

50

recycled waste paper content, %

Bending modulus, MPa

Fig. 4. Bending strength of the filled composite samples with and without the compatibilizer vs cellulosic filler content. 3000

without CL

2500

with CL

2000 1500 1000 500 0

0

10

30

50

recycled waste paper content, %

Fig. 5. Bending modulus of the filled composite samples with and without the compatibilizer vs cellulosic filler content. It is known that a major drawback of bio-composites filled with cellulosic fibers is their pronounced water sorption due to the hydrophilic nature of the cellulosic surface as well as its roughness and the presence of a porous system. In recent decades, the studies devoted to surface energetic characteristics have attracted attention due to the enhanced interest in bio-composite materials. The surface energetic characteristics such as a surface free energy and its components - dispersive and polar part could be used to understand and predict the wettability of composites containing a cellulosic filler because the wettability is one of the most important characteristics for determining end-use applications and exploitation conditions. The wettability of the composites to many extents depends on the interface adhesion quality between a polymer and a cellulosic filler. It was found that the larger the interfacial adhesion, the smaller the wettability of the obtained composite [12].

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Table 2. Contact angles and surface energetic characteristics of the samples with 3% CL rPAP content, [%]

Contact angles, [o]

Adhesion work, [mN/m]

102,1 98,1 100,9 99,3

57,3 62,3 58,8 60,3

0 10 30 50

Surface free energy [mN/m] 29,0 27,5 28,5 27,7

SFE dispersive part, [mN/m] 28,96 27,08 28,24 27,10

SFE polar part, [mN/m] 0,04 0,42 0,26 0,30

Table 2 shows the values of contact angles and the energy characteristics of the composite samples with different content of the cellulosic microparticles in the presence of CL. It can be seen that the rPP sample obtained by the extrusion with the followed injection is characterized by the highest value of a contact angle due to its hydrophobic surface. The introduction of only 10% of the cellulosic filler into the polymer matrix leads to a decrease in the wetting angle of the sample by 4 o, which is obviously due to the hydrophilicity of rPAP microparticles and their uneven distribution in the volume of the polymer matrix. In the presence of CL, with increasing the filler content and the uniformity of the crystalline cellulosic microparticles distribution, the contact angles of the samples enhance and reach values of more than 100 o, which may be associated with an increase in the hydrophobicity of the surface samples, and as a sequence, a deterioration in the wettability. Increasing the contact angle values reduces the work of adhesion from 62.3 mN/m to 58.8 mN/m with enlarging the filling degree from 10 to 30 wt%. According to Table 2, rPP has the highest value of surface free energy (SFE) consisting of the dispersed and polar constituents, but the sample with a 10% cellulosic filler has the lowest energy value. However, comparing the values of the dispersed and polar components of surface free energy, it can be seen that the polar part of the rPP sample is almost 10 times smaller than that of the sample with a 10% filler content. The dependence of the SFE polar part of the samples on the content of the crystalline cellulosic microparticles in the absence and the presence of the compatibilizer is shown in Fig. 6. It can be seen that the presence of CL does not have an essential effect on the polar energy of the samples at a low filling degree. However, with an increase in the filler content to 30-50 wt%, the polar energy values of the samples decrease by 2-3 times compared with the values of the SFE polar part for the samples with the same filling in the absence of CL. Therefore, in the given case, the polar part of free surface energy, characterized by the ability of the obtained composite sample to be wetted with water, changes more pronouncedly that the values of the SFE dispersive part. It should be noted that the sample with a 50% filler content has energy parameters comparable to those of the sample containing a 30% filler, which may be due to the presence of some agglomerates of the cellulosic microparticles associated with the insufficient amount of CL at the highest filling.

Polar energy, mN/m

1.2

without CL

0.9

with CL

0.6 0.3 0

rPP

10 30 50 recycled waste paper content, %

Fig. 6. Polar energy of the filled composite samples vs recycled waste paper content.

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The scanning electron microscope images of cross-sections of the composites with the 50% content of rPAP in the presence and absence of CL are given in Fig. 7. The cross-sections were obtained as a result of the rupture of the samples after the tensile test. It can be seen that the low compatibility between the cellulosic microparticles and the rPP matrix in the sample without CL is reflected by the pronounced heterogenic fracture surface that is expressed by the formation of the cellulosic microparticles pull-out, debonding, and the presence of internal voids. No doubt, these a

b

Fig. 7. SEM images of the cross-section of the samples with a 50% filling without (a) and with the compatibilizer (b). defects are the main reason for the reduced mechanical properties of the samples in the absence of CL. On other hand, the surface of the composite sample containing 3% CL was characterized by less heterogeneity The presence of the particle’s pullout and debonding as well as the formation of voids on the cross-section of this sample image is minimal. This may confirm the improved compatibility between the crystalline cellulosic microparticles and the polymer matrix in the presence of CL, which causes the reinforcement of both tensile and bending strength of the composite. Thus, the presence of the compatibilizer plays a crucial role in the performance of the rPP-based composite filled with crystalline cellulosic microparticles. Summary The recycled polypropylene-based composite filled with recycled waste paper in the form of crystalline cellulose microparticles with a different filling degree was obtained. An increase in the content of the crystalline cellulosic filler leads to a noticeable decrease in mechanical properties, with the exception of the values of tensile and bending moduli, and an increase in the polar part of the surface free energy of the composite samples, which indicates a weak interfacial adhesion between the polymer matrix and the filler. The presence of maleic anhydride grafted polypropylene as a compatibilizer improves the compatibility of recycled polypropylene and crystalline cellulosic microparticles in the composite samples, as indicated by an increase in the homogeneity of their structure, an increase in their mechanical properties both in tension and bending, as well as a decrease in the ability of the samples to be wetted by water.

References [1]

S.K. Najafi, Use of recycled plastics in wood plastic composites - A review, Waste Management. 33 (2013) 1898-1905.

[2]

I. Turku, T. Kärki, A. Puurtinen, Durability of wood plastic composites manufactured from recycled plastic, Heliyon. 4(3) (2018) e00559.

[3]

A.M. Adel, Z.H. Abd El-Wahab, A.A. Ibrahim, M.T. Al-Shemy, Characterization of microcrystalline cellulose prepared from lignocellulosic materials. Physicochemical properties, Carbohydrate Polymers. 83(2) (2011) 676-687.

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[4]

M. El-Sakhawy, M.L. Hassan, Physical and mechanical properties of microcrystalline cellulose prepared from agricultural residues, Carbohydrate Polymers. 67(1, 2) (2007) 1-10.

[5]

G. Joshi, S. Naithani, V.K. Varshney, S.S. Bisht, V. Rana, P.K. Gupta, Synthesis and Characterization of Carboxymethyl Cellulose from Office Waste Paper: A Greener Approach Towards Waste Management, Waste Management. 38(1) (2015) 33-40.

[6]

D. Trache, M.H. Hussin, C.T.H. Chuin, S. Sabar, M.R.N. Fazita, O.F.A. Taiwo, T. M. Hassan, M.K.M. Haafiz. Microcrystalline cellulose: Isolation, characterization and bio-composites application - A review. Int J Biol Macromol. 93 (2016) 789-804.

[7]

H. Håkansson, P. Ahlgren, Acid hydrolysis of some industrial pulps: Effect of hydrolysis conditions and raw material, Cellulose. 12(2) (2005) 177-183.

[8]

M. Maskavs, M. Kalnins, M. Laka, S. Chernyavskaya, Physicomechanical Properties of Composites Based on Low-Density Polyethylene and Cellulose-Containing Fillers, Mechanics of Composite Materials. 37(2) (2001) 159-166.

[9]

A. Ashori, A. Nourbakhsh, Performance properties of microcrystalline cellulose as a reinforcing agent in wood-plastic composites, Composites: Part B. 41 (2010) 578-581.

[10] M. Laka, S. Chernyavskaya, G. Shulga, V. Shapovalov, A. Valenkov, M. Tavroginsakya, Use of Cellulose-Containing Fillers in Composites with Polypropylene, Materials Science (Medžiagotyra). 17(2) (2011) 151-154. [11]

A. M. Youssefa, M. S. Hasaninb, M. E. Abd El-Azizc, O. M. Darweshd. Green, economic, and partially biodegradable wood plastic composites via enzymatic surface modification of lignocellulosic fibers. Heliyon, 5 (3), 2019, eO1332.

[12] F.P. La Mantia, M. Morreale, Green composites: A brief review. Composites: Part A: Applied Science and Manufacturing Composites. 42(6) (2011) 579-588. [13] J.Z. Lu, Q. Wu, H.S. McNab, Chemical coupling in wood fiber and polymer composites: a review of coupling agents and treatments, Wood Fiber and Science. 32(1) (2000) 88-104. [14] M.M. Kabir, H. Wang, K. T. Lau, F. Cardona, Chemical treatments on plant-based natural fiber reinforced polymer composites: an overview. Composites: Part B Engineering. 43(7) (2012) 2883-2892. [15] J. Jaunslavietis, J. Ozolins, M. Kalnins, G. Shulga, B. Neiberte, A. Verovkins, Recycled paper additive for wood-polymer composite: preparation and characterization, Key Engineering Materials. 850 (2020) 81-86. [16] Z. Lin, C. Chen, Z. Guan, S. Tan, X. Zhang, A compatibilized composite of recycled polypropylene filled with cellulosic fiber from recycled corrugated paper board: mechanical properties, morphology, and thermal behavior, J Appl Polym Sci. 122 (2011) 2789-2797. [17] X. Zhang, J. Shen, H. Yang, Z. Lin, S. Tan. Mechanical properties, morphology, thermal performance, crystallization behavior, and kinetics of PP/microcrystal cellulose composites compatibilized by two different compatibilizers. J Thermoplast Compos Mater. 24 (2011) 735753.

Materials Science Forum ISSN: 1662-9752, Vol. 1071, pp 117-125 doi:10.4028/p-68xm1n © 2022 Trans Tech Publications Ltd, Switzerland

Submitted: 2022-05-31 Accepted: 2022-08-01 Online: 2022-10-18

Rheological, Thermal and Mechanical Properties of Wood Plastic Composites (WPCs) Based on Virgin and Recycled Polypropylenes and Birch Plywood Waste Karlis Kalnins1,a*, Janis Kajaks1,b, Juris Matvejs2,c 1*

Institute of Polymer Materials, Faculty of Material Science and Applied Chemistry, Riga Technical University, Riga, LV-1048, P.Valdena str.3/7, Latvia Ļatvijas finieris JSC, Riga, LV-1004, Bauskas str.59, Latvia

2

[email protected], [email protected], [email protected]

b

Keywords: composites, virgin, recycled polypropylenes, plywood residues, rheological properties.

Abstract: Article summarizes investigation results of rheological, thermal and some mechanical properties of industrially prepared wood plastic composites (WPCs), based on virgin and recycled polypropylenes (vPP, rPP) and birch plywood production waste product- plywood sanding dust (PSD). Investigated WPCs contain 40 and 50 wt. % PSD different another modifier, such as functional lubricant Struktol TWP-113, antioxidant 1010, thermal stabilizer 168, UV stabilizer 770 and different color pigments. According to our studies, we can conclude that rheological properties studied by capillary rheometry method depends on WPCs composition and experimental parameters: shear stress, shear deformation rate and temperature. The curves of the fluidity indicate to the character of typical pseudo-plasticity of all polymer melts of which viscosity not only depends on temperature, but also decreases with an increase of shear stress and shear deformation rate Pseudoplastic properties confirm also the signed values of fluidity index (n) which for pseudo-plastic liquids always are smaller than one. TGA measurements showed that all systems have the high thermal stability and the weight losses after dynamic heating up to processing temperature 215oC are not more than 5.53 %, but during isothermal heating (1 h) at 215oC only 4.51%. Differential scanning calorimetry (DSC) showed a small changes of melting temperatures, but the beginning of thermal destruction temperature fluctuates between 256.96 and 188.5oC. Density of all composites changes in limits 1.02-1.09 g/cm3, temperatures by Vika 154.4-158.7oC, microhardness 125.1-151.8 MPa and impact strength 7.81-15.39 kJ/m2 Introduction The last 20 years beside WPCs based on virgin polypropylene [1-5] high increasing of interest of scientific community and industry have gained WPCs with recycled polypropylene [6-12}. The use of recycled polypropylene matrix instead of virgin allows to save up fossil resources and successfully to solve ecological problems. At the same time the use of recycled polymer materials allows to decrease of the price of WPCs without essential diminishing of exploitation properties [6-12]. A lot of different, popular products from WPC are produced for the usage in building and car industries. To produce of these products a different processing methods like extrusion and injection molding are utilized. Due to the WPCs are processed from the melt condition the important role play the rheological properties of WPCs melts. Rheological properties of WPCs have not been studied in many works [1, 3, 5, 13-19]. One of the main method of rheological investigations is capillary rheometry at different shear stresses and deformation rates. The rheological tests in the wide range of the shear rates (10-25 1/s up to 5000 1/s) give useful information how will behave WPCs during real processing processes. It was observed that rheological properties vitally depend on the content of wood fibers in polymer matrix [1, 14] and wood fibers during flowing orientate in the flow direction [16]. At the same time at a high shear rates the faster decrease of the shear viscosity is determined [16, 17]. Due to this fact the melt flow behavior is described by power law [17]. Authors [5] have shown the influence of the coupling agents like a maleated polypropylene MAPP (6-7 wt.%) and lubricant Struktol TWP-113 (1-3 wt.%) not only on mechanical properties of WPCs but also on rheological

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behavior of PP composites with saw dust. The melt flow index values of these composites increase 2 times because at the presence of lubricant interfacial interaction on the surface between components is reduced. Melt viscosity of the WPCs also depends on the fibers length. If the length of the fibers is longer the viscosity is lover [1]. Rheological properties and melt flow index values are influenced by crystallization processes in PP matrix at the presence of the wood fibers [3]. Our previous [20-23] studies of rheological properties of industrially produced WPCs based on virgin PP and plywood sanding dust showed a similar results gained by authors [1, 3, 5, 13-19]. The MFI values and rheological characteristics strong depend on composition of WPCs. MFI values of WPCs can diminish up to 3-3.5 times and the fluidity index up to 5-15 times in comparison with the pure PP matrix. The rheological studies showed the decreasing of WPCs melt viscosity with an increase of the shear rate and temperature. The fluidity index values always were smaller than one what confirms the pseudo plasticity of the WPCs melts. TGA measurements revealed a small weight loss of all materials during heating time (10-15 minutes) up to processing temperature (215o C) of WPCs. That indicate to sufficient thermal stability of WPCs during processing processes [22]. The goals of this study were to evaluate the rheological properties of the WPCs based on recycled polypropylene and compare that with virgin PP WP composites. To determine the thermal properties and thermal stability of WPCs and heating higher than a real processing temperatures DSC and TGA methods were used. In additions also some physical-mechanical properties of industrially produced WPCs materials were determined. Materials and Experimental Methods Rheological investigations of the 5 types of the industrially prepared by extrusion process (temperature 215o C) WPCs based on virgin and recycled polypropylenes and plywood sanding dust (PSD) with different composition were made (see Table 1). As a polymer matrix serves polypropylene type Tatren HT 306 with MFI= 3.0 g/10min. (T=230oC, P=2.16 kg) and recycled polypropylene produced by Nordic Plast Latvia with MFI=3.4 g/10 min (T=230oC, P=2.16 kg). but as a reinforcement birch wood plywood production by-product sanding dust with following sizes of the fibers which contain fractions with size more than 500 microns (1.04%), between 250-500 microns (32.16 %) and smaller than 250 microns (66.8%) was used. Composites also contain different additives like lubricant Struktol TWP-113 (blend of an aliphatic carboxylic acid salts and mono and diamides), sterically hindered phenolic antioxidant, thermal (hydrolytically stable phosphite), UV stabilizers-low molecular weight hindered amine light stabilizer (HALS), pigment concentrates based on LDPE. Composition of the composites is given in the Table 1. Fluidity curves of the composites were gained by capillary rheometer type RH7 (T=190, 200 and 215oC, shear deformation rate the limits 50-5000 s-1 and the step 10 s-1). Length of capillary was 16 and 0.25 mm, but diameter 1 mm. Thermal stability of the composite melts was checked with thermal gravimetric analysis (TGA) method what was realized in two steps: heating from 20oC up to 215oC (dynamic heating at the rate 10oC/min.) and standing at the T=215oC, during the time 1 h. Thermal properties were determined by DSC measurements at heating rate 10oC/min (temperature range 20-300oC) in the air. Microhardness of the surface was evaluated by Vikerss M-41 method at a load 200 g. Impact strength was checked on apparatus Zwick 24 (for standard bars EN ISO 179, hammer 2 J) Density was defined corresponding to standard LVS IN ISO 1183:2005 but softening temperature by VIKA (standard LVS EN ISO 306:2014 CE) method A-50 in glycerol. Load 1 kg, heating rate 50oC/h.

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Table 1. Composition of the used WP composites based on virgin and recycled polypropylenes with different additives and plywood sanding dust. Comp.

PSD, cont [%]

1010 antiox. [%]

168 therm. stab.[ %]

770 UV stab. [%]

Pigm. conc.on LDPE, [%]

Type of PP]

40

Struktol TWP113, [%] 3

1-R

0.33

0.33

0.00

0

Recycled black

2-R

40

3

0.33

0.33

0.50

3

Virgin Taren HF-306 yellow

3-R

40

3

0.33

0.33

0.50

2

Recycled green

4-R

40

3

0.33

0.33

0.50

0

Recycled brown

5-R

50

3

0.33

0.33

0.50

2

Recycled green

Results and Discussion As it was shown in our previous investigations [20-23] melt flow index measurements do not give a full information about behavior of the WPCs melts during processing processes. More profound and detailed information on rheological properties of polymer composite melts gives the rheological studies by capillary rheometry in the wide temperatures and shear rate interval. In our case we approbated four recycled PP containing WPCs and one virgin PP WP composite. The chosen temperatures of experiment were 190, 200 and 215o C and the shear rate interval 50-5000 1/s which partially coincide with the temperatures and shear rates of the processing of WPCs with PSD (200215o C and shear rates 100-2000 1/s). Basing on these data we can predict how could behave composites during the real processing processes. As an examples in this work were chosen fluidity curves at 190 o C (Fg.1), shear viscosity-shear deformation rate dependences at 190 o C (Fig.2), fluidity index (n)-shear rate relationship (Fig.3), shear viscosity-shear rate at temperatures 190, 200 and 215o C (Fig.4) for 3-R system and fluidity index-shear rate dependence at 190, 200 and 215o C (Fig.5). From Fig.1 can see that the shear stress grows up slower than shear rate and all curves are rather close located (1-5R) included 2-R based on the virgin PP. The greater differences can observe at low shear rates (50-100 1/s). May be at these conditions expresses viscoelastic nature of polyolefin melts [15, 16]. The fluidity curves indicate to the character of the typical pseudo plastic liquids for that viscosity is not only function of temperature (Fig.4), but depends on the shear rate and shear stress values. Besides viscosity always decreases with an increase of these parameters. (Fig.2). Necessary to sign that the shear viscosity depending on the composition of composites can decrease up to 70 times (from approximately 700 Pa.s till 10 Pa.s) (Fig.2). Resembling as fluidity curves the relationships of shear viscosity-shear rate at 190oC also are more or less equal (Fig.2) The similar sights are observed at 200 and 215o C. Temperature influence on shear viscosity (Fig.4) better are observed at the shear rates more than 1000 1/s when differences of viscosity at 190, 200 and 215oC are greater. Besides at higher shear rates the influence on numerical values of shear viscosity decrease faster. Probably at a lower temperature can appear sliding effect of polymer melts in capillary what arises imaginary shear viscosity decrease.

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Figure 1. Dependences of the shear stress of the composites based on rPP+40 wt.% PSD (1-R, 3-R-4-R), virgin PP (2-R) and rPP+50 wt.% (5-R) with different additives on the shear deformation rate at the temperature 190o C (composites composition are given in the table 1).

Necessary to note that fluidity curves (Fig.1) of systems with rPP (1-R, 3-R, 4-R, 5-R) and virgin PP (2-R) differ a little. Shear viscosity at a low different shear rates of rPP containing WPCs (1-R, 3-R, 4-R, 5-R) also are similar like a virgin PP composite. (Fig 1 2-R). That means that systems with rPP have the same rheological behavior as virgin PP containing materials. Fluidity index (n) shows degree of distinction of the investigated melts from Nuton liquids always is smaller than one (Fig.3 and Fig. 5) and decreases with an increase of the shear rate. That testify of the increasing of influence of the shear rate on degree of non-Nutonian behavior. Different slope of dependences of systems also gives evidence of the influence measure on viscosity. From Fig.3 we can conclude that systems 1-R and 2R are smaller sensitive against changes of shear rate than 3-R, 4-R and 5-R. It is interesting to observe of crossing of relationships at the shear rates 800-9001/s (Fig.3. and Fig.5). Temperature influence on n numerical values increases at lower temperatures (Fig.5). Decreasing of n (Fig.3,5) and viscosity (Fig.2,4) confirms our previous viewpoint of the pseudo-plasticity of all the investigated composite melts. Analyzing temperature influence on shear viscosity (Fig.4, 3-R) are seen that temperature influence on the shear viscosity is quite small and the higher influence expresses only at higher shear rates (800-1000 1/s). Similar character and sight of dependences were gained also for another investigated system. In the aggregate from rheological studies can conclude that all investigated WP composite melts show pseudo-plastic properties and essential differences between of rPP and virgin PP containing WPCs are not observed.

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Figure 2. Dependences of the shear viscosity of the composites based on rPP+40 wt. % PSD (1-R, 3-R, 4-R) and virgin PP (2-R) and rPP+50 wt.% PSD (5-R) with different additives on the shear deformation rate at temperature 190o C.

Figure 3. Depedences of the fluidity index (n) of the composites based on rPP+40 wt. % PSD (1-R, 3-R, 4-R) and virgin PP (2-R) and r+50 wt.% PSD (5-R) with different additives on the shear deformation rate at temperature 190o C.

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Fig.4. Dependences of the fluidity index (n) of the composites based on r PP+40 wt. % PSD (3-R) with different additives on the shear deformation rate at the temperatures 190, 200 and 215o C.

Fig.5. Dependences of the shear viscosity of the composites based on r PP+40 wt. % PSD (3-R) with different additives on the shear deformation rate at the temperatures 190, 200 and 215o C.

DSC and TGA measurements (see Table 2) were done to determine how temperature influences thermal and physical properties of investigated composites. TGA tests showed that the weight losses of the samples during dynamic heating time up to 215o C are not higher than 5.53% (5-R) and fluctuate in the limits 3.87 (4-R)-5.53%, but during isothermal heating at 215oC 1 h is not higher than 4.51% (5-R) and change in limits 2.81%-4.51%. TGA measurements confirm of sufficient thermal stability of all investigated materials. DSC experiments showed that melting temperatures of virgin (2-R) and recycled (1, 3-5 R) PP matrices differ small (about 3.5o C).

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Table 2. Differential scanning calorimetry (DSC) and TGA measurement results Comp.

Composition

Weight of PP, mg

Tm, oC

Destruct. Td , o C

1-R 2-R 3-R 4-R 5-R

rPP+40%PSD vPP+40%PSD rPP+40%PSD rPP+40%PSD rPP+50%PSD

8.98 10.30 10.43 8.03 9.06

167.75 167.97 166.53 164.25 167.33

240.33 188.65 228.27 256.96 247.60

Melting heat ΔHm J/g 59.98 82.03 70.45 63.33 50.40

Degree of crystallinity Xc, % 17.38 23.77 20.42 18.35 14.60

Weight losses, % isothermal heating 3.37 3.17 3.80 2.81 4.51

Weight losses, % dynamic 4.61 4.18 4.70 3.87 5.53

ΔHt=207 J/g melting heat of PP with degree of crystallinity 100%. Source: https://www.netzschthermalanalysis.com The smallest Tm has system 4-R (164.25o C), but the greatest (2-R) virgin PP (167.97o C). The beginning of thermal destruction (oxidation) temperatures differ more. It was interesting to sign that the smallest thermal stability has system with virgin PP (Td=188.65 o C) but Td of composites with rPP changes from 228.27oC (3-R) up to 256.96 o C (4-R). That indicates to the better stability against thermal oxidation processes of recycled PP containing WPCs. In the contrary the melting heat of virgin PP system is the highest 82.03 J/g. That affirms of higher degree of crystallinity (23.77 %) of the sample. The degree of crystallinity of rPP is lower and depending on composition of the WPCs is 14.60% (5-R) and 20.42% (3-R). In the aggregate TGA and DSC tests showed the high thermal stability of all investigated systems and essential differences between recycled and virgin PP containing materials are not observed. That is positive indication for processing processes. So that the investigated composites plan to use as a covers of birch plywood in the plant “Latvijas finieris” JSC then were necessary to exam some additional physical, thermal and mechanical properties especially of the composites based on recycled PP which are important during exploitation of protected plywood. Customers were interested in possibilities of replacing of virgin PP with recycled PP matrix to produce of WPCs sheets. The results of these tests are presented in the Table 3. As can see from the data of table 3, the density values of the composites with 40 wt.% PSD content really is similar. Recycled PP systems have a bit higher density values (1.03-1.05 g/cm3 ) to compare with virgin PP containing WPCs (1.02 g/ cm3 ). Temperatures by VIKA what characterize mechanical properties (behavior) at higher temperatures are equal (in the table 3 are presented results of 2 parallel measurements) and fluctuate between 155.5 o C (1-R) and 158.0 o C (2-R). Microhardness of the surface of the sheets with rPP is a bit (about 17%) smaller than virgin PP WPCs (125.1 MPa 3-R and 151.8 MPa (2-R) respectively. The impact strength also is higher (about 26%) of WP composites with the virgin PP 15.3 kJ/m2 (2-R) versus 11.32 kJ/m2 of rPP containing systems (3-R). Table 3. Some physical, thermal and mechanical properties of the WP composites based on virgin and recycled PP and plywood sanding dust. Parameter Density, g/cm3 Temperature by Vika, oC MH, MPa Impact strength, A, kJ/m2

1-R 1.05 155.5 155.6 145.9 13.40

2-R 1.02 158.6 158.0 151.8 15.39

3-R 1.03 154.4 155.1 125.1 11.32

4-R 1.05 157.6 158.7 135.7 13.33

5-R 1.09 155.8 156.3 127.4 7.81

Summarizing the results of the table 3 can conclude that in the aggregate between properties of WPC with virgin or recycled PP no essential differences what could prevent of utilization of recycled PP matrix instead of virgin PP for producing of WPCs with competed properties. From presented composites with rPP which contains similar content of PSD (40wt%) the most perspective are

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composites 1-R and 4-R These composites have practically the same level of exploitation properties as a virgin WPC (2-R). Due to the less price of rPP and competed properties with virgin PP WPCs based on rPP also could be used for production of WPCs sheets and utilized as a coverings of birch plywood. Conclusions 1. The studies of rheological properties of the WPCs based on virgin and recycled polypropylenes and 40 wt.% PSD with different another additive showed that the fluidity curves of all composites are typical like the pseudo-plastic liquids and the viscosity decreases with the increase of the melt temperature and the shear deformation rate. 2. Differential scanning calorimetry analysis (DSC) and the thermal gravimetric analysis (TGA) of the WP composites affirmed of the high thermal stability of all the investigated systems what allows to process that composites by extrusion at the chosen conditions. 3. Summarizing investigation results of some exploitation properties (density, temperature by Vika, microhardness and impact strength) of WPCs based on recycled and virgin polypropylene matrices can conclude that in our case recycled PP is possible to use instead of virgin PP to prepare WPCs sheets with competed properties and to use that for covering of plywood. Acknowledgements The authors gratefully acknowledge the financial support in accordance with the contract No. 1.2.1.1/18/A/007 between "Advanced Materials and Technologies Competence Centre" Ltd. and the Central Finance and Contracting Agency, concluded on 23rd of April, 2019, the study is conducted by “Troja” LTD with support from the European Regional Development Fund (ERDF) within the framework of the project supervised by " Advanced Materials and Technologies Competence Centre". References [1] L. Xie, T. Guveneberg, L. Stenernagel, G. Ziegmann Influence of particle concentration and type on flow, thermal and mechanical properties of wood-polypropylene composites, J. of Reinforced Plastics and Composites, 29 (13) (2010) 1940-1951. [2] L. Pereira, L. Dos Santos, T. Flores-Sahagun Effect of processing parameters on the properties of polyethylene-sawdust composites, Journal of Composite Materials, 49 (30) (2015) 3727-3740. [3] S. Borysiak, K. Szentner, H. Kasprzuk Crystallization of different polypropylene matrices in the presence of wood fillers, Polymer Composites, 2015, Doi: 10.1002/pc.23088,1813-1818. [4] L.Sobczak, R. Welser, O. Bruggemann Polypropylene based wood polymer composites: Performance of five commercial maleic anhydride grafted PP coupling aģents, Journal of Thermoplastic Composite Materials, 27 (4) (2014) 439-463. [5] S. Bettini, M. Josefovich, P. Mufioz, C. Lotti Effect of lubricant on mechanical properties of compatibilized PP/sawdust composites, Carbohydrate Polymers, 94 (2013) 800-806. [6] Y. Gao, S. Zhu, J. Chen, D. Li Thermal properties of wood-plastics composites with different compositions, Materials,16 (6) (2019) 881. [7] S. Chari, S. Najafi, B. Mohbby, M. Tajvidi Impact strength improvement of wood flour-recycled polypropylene composites, J. of Appl.Pol. Sci. 124 (2) (2012) 1074-1080. [8] A. Kiaeifar, M. Saffari, B. Kord Comparative investigation on the mechanical properties of wood plastic composites made of virgin and recycled plastics, World Applied Science Journal, 14 (5) (2011) 735-738.

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[9] B. Dani, H. Djidjelli, A. Boukerron, et.al. Morphological, mechanical and physical properties of composites made with wood flour reinforced polypropylene/recycled polyethylene terephthalate blends, Polymer Composites, 38 (8) (2017) 1749-1755. [10] S. Hag, R. Srivastava Wood polypropylene (PP) composites manufactured by mango wood waste with origin or recycled PP: mechanical, morphology, melt flow index and crystallization behaviour, J. of Appl. Pol. and Environment, 25 (3) (2017) 640-648. [11] S. Najafi, E. Hamidina, M. Tajvidi Mechanical properties of composites from sawdust and recycled plastics, J. of Appl. Pol. Sci., 100 (2006) 3641-3645. [12] Natural Fibre composites. Materials, Processes and Properties. Ed. By A.Hodzic and R. Shanks 2014. Chapter: Recycled polymers in natural fibres-reinforced polymer composites, pp.103-114. [13] A. Areas, R. Bouza, S. Pardo, et.al. Rheological, mechanical and thermal behaviour of WPC based on recycled polypropylene, Journal of Polymers and Enviroment, 18 (3) (2010) 318-325. [14] S. Maiti, R. Subbarao, M. Ibrahim Effect of wood fibres on rheological properties of i-PP/ wood fiber composites, J. of Appl. Pol. Sci., 91 (1) (2014) 644-650. [15] V. Mazzanti, F. Mollica, N. Kissi Rheological and mechanical characterization of polypropylene-based wood plastic composite, Polymer Composites, 2015, Doi: 10.1002/pc. 232546, 1-15. [16] K. Lewandovski, K. Piszczek, S. Zajchwski, J. Mirowski Rheological properties of wood composites at high shear rates, Polymer Testing, 51 (2016) 58-62 [17] A. Ramzy, A. Moneeb El-Sabbagh, L. Steurnagel, et.al. Rheology of Natural Fibers thermoplastic compounds: Flow length and fiber distribution, J. of Appl. Pol. Sci., 2014, Doi: 10.1002/APP, 39861 [18] V. Mazzanti, F. Mollica, N. Kissi Rheological and thermal properties of PP based WPC/ AIP Conference Proceedings, (2014) 274-277. [19] M. Poletto Influence of coupling agents on rhelogical, thermal expansion and morphological properties of recycled polypropylene wood flour composites, Maderas: Chiencia&Technologia, 20 (4) 2018) a.% 563-570. [20] J. Kajaks, I. Kalnina, K. Kalnins and J. Matvejs Some exploitation properties of wood plastic composites based on polypropylene and birch plywood sanding dust, Proceedings of Estonian Academy of Science, 76 (2) (2018) 117-123. [21] J. Kajaks, K. Kalnins and J. Matvejs Rheological properties of wood plastic composites based on polypropylene and birch wood plywood production residues, 762 (2018) 226-232. [22] J. Kajaks, K. Kalnins and J. Matvejs Mechanical and rheological properties of wood plastic composites based on polypropylene and birch plywood sanding dust, IOP Conference Series: Materials Science and Engineering, 500,(2019), 012001 1-6. [23] J.Kajaks, K. Kalnins and J. Matvejs Rheological properties of WPCs based on polypropylene and plywood sanding dust, Key Engineering Materials, (2021) ( in press).

Materials Science Forum ISSN: 1662-9752, Vol. 1071, pp 126-138 doi:10.4028/p-yl4pa1 © 2022 Trans Tech Publications Ltd, Switzerland

Submitted: 2022-06-10 Revised: 2022-07-26 Accepted: 2022-07-26 Online: 2022-10-18

Hemp Shives Mycelium Composites – An Alternative Material for Traditionally Used Plastic Packaging Gustavs Daniels Loris1,2,a*, Ilze Irbe1,b, Marite Skute1, Inese Filipova1, Laura Andze1, Anrijs Verovkins1 Latvian State Institute of Wood Chemistry

1

University of Latvia

2

[email protected] [email protected] [email protected] [email protected] [email protected] [email protected]

Keywords: Mycelium composites; Hemp shives; Birch bark; Bran; Trametes; Granulometry; Biodegradation; Mold resistance; Compression; Water absorption.

Abstract. Plastic waste is an ever-growing concern, causing harm to many ecological and human health aspects, one of the major contributors to this problem being packaging. Mycelium composites (MC) are ecologically safe materials, well suited for the short-life usage as packaging materials. In our study MC were made using fine and coarse granulometry hemp shives applying them in 3 substrate variants – with added bran, with added bran and birch bark, and as the sole substrate. Material's water absorption and mechanical compression, chemical decomposition, biodegradability, mold resistance and fungal biomass were assessed. Granulometric effect was observed only when using shives as the sole substrate, where larger particle size gave poorer results. Bran did not significantly improve mechanical compression or water uptake. Bark reduced water uptake by ~200 %, but lowered mechanical compression, and provided no benefits to mold resistance which was low for all specimens. Overall, hemp MC showed complete biodegradability after 12 weeks, mechanical compression strength up to 0.235 MPa, compatible with expanded polystyrene, but very high water uptake of up to 1000 %. Future studies are needed to reduce water absorption and improve mold resistance, as well as invent consensus methodology for better cross-study comparison. Introduction Since the beginning of plastic mass production in mid-20th century, its use and production has grown tremendously. It has been estimated that since then its annual production rate has been increasing exponentially by ~8.4 % and in 2017 the global produced plastic amount is said to have been around 8.3 billion tonnes, of which ~40 % comes from packaging [1]. As plastics are not only highly versatile regarding their mechanical properties, one of their greatest advantages is resistance to biological degradation. This is also the biggest downside of it. Virtually all plastics have product lifetime (time period from being sold to discarding) dramatically lower than respective functional lifespan (maximum time period of material's physical capacity); the modelled lifespan of plastic packaging is less than 1 year [2]. However, the degradation rates are very slow, close to none, e.g., polystyrene degradation half-life buried in land is greater than 2500 years [3]. Plastic recycling is a resource demanding and risky process (contamination may lower product quality) of limited possibilities, therefore seldom used [4]. Incineration is also discouraged due to the negative impact of global warming and environmental acidification and pollution [4, 5]. As a consequence, very big amounts of plastic waste every year enter landfills, adding up and making for enormous 79 % of the total ever produced plastic [2]. It has been widely known that plastic waste easily leaches from landfills into the global ocean, where it mechanically disintegrates into micro- and nanoplastic, leading to various direct and indirect major environmental and health risks [6, 7]. On top of all this, 90 % of all plastics production depends on fossil fuels, the unsustainable, non-renewable natural resource [4]. Sustainability is a main development goal of the United Nations as postulated AGENDA 2030, in which points 12 and 14 stand for responsible resource production and consumption, and

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conservation and sustainable use of oceans and seas, respectively [8]. Therefore, solutions for plastic production and waste are needed, and packaging is one of the most important sectors in this context. Mycelium composites (MC) are alternative, ecologically compatible materials that hold great potential for replacing plastic packaging, especially those made from expanded polystyrene (EPS). As its production is based on agricultural waste and biological growth, it does not demand great economical resources [9]. MC is a composite-material that consists of a lignocellulosic substrate and a saprotrophic fungus mycelium. As MC and EPS have compatible density and mechanical properties [10-12], MC is a highly prospective alternative, therefore it is necessary to study this material. Although most studies include information on mechanical properties or water absorption [9-15], little evidence is for mold resistance and biodegradation, and fungal biomass in the material. Nevertheless, presently available data for water absorption is still somewhat scarce and there is not consensus for the standard methodology (also for compression properties), therefore the findings of other studies are hard to compare, unfortunately. As hemp shives is a potentially valorisable agricultural waste product for MC production, and plastic packaging still causing great ecological harm, there is urgency to acquire more, easily reproducible, comparable and appliable data for MC production and properties. In this study hemp shive based MC were produced, using two particle sizes for the shives. In each granulometric group 3 different substrate variants were created: I with added wheat bran, II with added bran and birch bark, and III with hemp shives only. Grown, dried and cut specimens were tested for compression strength and modulus, water uptake and swelling, mold resistance, biodegradation. Chemical analyses for substrate decomposition and fungal biomass assessment in specimen were also performed. The aim of the study was to test, whether 1) hemp shives granulometry affects MC properties; 2) bran affects substrate decomposition and fungal biomass; 3) birch bark affects water absorption and mold resistance; 4) bring more knowledge about hemp shive based MC and provide crucial biodegradation and mold resistance data. Our hypotheses were: 1) MC variants with added bran will result in better fungal growth and mechanical properties; 2) bark will reduce mold growth and water absorption; 3) bigger shives particle size will decrease density and negatively affect mechanical properties and increase water uptake. Materials MC Substrate, Compost. The lignocellulosic substrate used for MC was hemp Cannabis sativa shives from a local construction goods store. Additives for substrate variants were ground birch Betula pendula total bark and wheat bran. Bark was obtained from local plywood factory and bran – from the grocery store. Compost soil was obtained from a local farm, made from cut grass, sawdust, ecological farming litter and enriched with a microbiological consortium of composting microorganisms [16]. Fungus Culture And Microbiological Media. Fungus used in the study was Trametes versicolor (L.) strain Quélet (FPRL 40C). Solid microbiological medium for fungus culturing was MEA (5% malt extract, 3% agar), used for liquid culture inoculation. Liquid cultures were grown in partly synthetic medium with a pH of 6 (15.0 g glucose, 3.0 g peptone, 3.0 yeast extract, 0.8 g NaH2PO4, 0.4 g K2HPO4, 0.5 g MgSO4 on 1 L water). All chemical ingredients utilized in the study were obtained from Sigma-Aldrich (USA). All water used in experiments was distilled water. Methods Fungus Cultivation, Substrate Preparation And Mycelium Composite Production. T. versicolor was cultivated on solid media for 2 weeks at 22 ± 2 oC and RH 70 ± 5 %, then used as inoculate for liquid cultures which were incubated in rotating shaker for 2 weeks at 28 oC and 150

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rpm. Hemp shives were sieved manually, vertically combining and shaking sieves of 3 different sized pore, namely, 15 mm, 7 mm and 3 mm. Granulometric fraction that remained on 7 mm sieve was named B or coarse (7-15 mm), that which remained on 3 mm sieve – A or fine (3-7 mm). Both A and B fractions were used in 3 substrate variants, see Table 1. 43.2 g of substrate (single dose) was equalled to 40 mL of homogenized fungal inoculate. Double dose of substrate was packed into every glass jar and autoclaved at 135 oC for 30 min. When passively cooled to room temperature, inside laminar box, substrate was inoculated with appropriate volume of laboratory mill homogenized liquid culture of T. versicolor. Table 1. Mycelium composite substrate recipes for 40 mL inoculate. Substrate recipe for 40 mL fungal inoculate

I variant shives [g]

bran [g]

II variant water [g]

shives [g]

bark [g]

bran [g]

III variant water [g]

shives [g]

water [g]

A Fine 3-7 mm

40

3.2

32.4

40

12

3.2

32.4

43.2

32.4

B

40

3.2

32.4

40

12

3.2

32.4

43.2

32.4

Coarse 7-15 mm

Inoculated jars were closed and incubated at 20 ± 2 oC and 70 ± 5 % relative humidity in dark for 14 days. On the last day jars were collected, colonized substrate taken out, then dismantled and homogenised. During this step variants that contained bran (namely, I and II) were again supplemented with the same amount of bran as in the beginning. Subsequently, the dismantled substrate was packed into plastic box moulds (16 × 12 × 6 cm), for the second growth phase, separated with a thin plate of organic glass for obtaining bar-shaped specimens (Fig. 1), wrapped with cellophane film and pierced for air exchange. Packed moulds were again incubated in the aforementioned conditions for 7 more days, after which the fully colonized specimens were unmoulded and weighed (m1), dried in room conditions (22 ± 1 oC, RH 30 ± 5%) for 4-5 days, weighed second time (m2) and then dried in laboratory oven at 70 oC for 24 h to inactivate fungal growth, weighed again (m3) and cut with bandsaw into 3 × 3 × 3 cm cubes for material properties analyses. Numbering of the cubes was written onto the specimen side with outer mycelial growth. Relative moisture content was calculated, using mass after unmoulding and mass after oven-drying.

Figure 1. On top, packed mould to be incubated for the second growth phase; below, unmoulded and dried bar-shaped specimens to be cut with bandsaw.

Water Absorption And Mold Resistance. Water absorption tests were carried out according to ASTMD1037: 2012 standard with modifications in specimen size. Before water immersion MC cubes were weighed and manually measured in size in all 3 dimensions [mm] with digital caliper (0150 Inox, Vernier Caliper, Poland). Specimen thickness was considered the dimension perpendicular to the numbered side, while the other two being width and length. Volume [cm3] was calculated from measurements of all dimensions, multiplying them. After the initial measurement specimens were put into plastic trays, weighted down upon and immersed with water, leaving approx. 2 cm surplus layer. After 2h of soaking, specimens were taken out and at first weighed, then measured in size. Following this, specimens were put back into empty

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trays and fresh water added like before. Then after 22 more hours, adding up to 24h of soaking in total, measurement was repeated like before. Water uptake was calculated as the percentual changes in mass, also done similarly for thickness and volumetric swelling. Right after water absorption test specimens were transferred into cylindrical glass trays onto fixed glass sticks to separate specimen from tray's bottom surface, so permitting air exchange, for mold resistance test. Glass lids were put on top of the trays leaving open a thin slit. Specimens were left in indoor conditions (22 ± 2 oC and RH 70 ± 5 %) for 14 days and inspected every 3 or 4 days. Mold growth level was assessed visually in 5 class system: 0 – free from mold infection, 1 – traces of mold growth or discolouration (≤ 5 % surface), 2 – minute growth or discoloration (6 - 25 %), 3 – moderate growth or discoloration (26 - 50 %), 4 – strong growth or discoloration (> 50 %). On days 4, 7 and 14 of mold growth experiment mold was collected with transparent adhesive tape and transferred onto a glass slide, then coloured with lactophenol blue and examined with Leica DMLB (Germany) light microscopy for mold identification at 5×, 10× and for more nuanced morphology at 20× and 40× magnification. Mechanical Compression. All specimens were compressed with the numbered side up, using universal testing device Zwick/Roell Z010. Compression test procedure was carried out according to the modified standard for hard plastic foam ISO 844:2007 in room conditions (21 ± 2 oC, RH 30 %). Mechanical load was gauged at 10 % relative deformation, speed of loading was 10 % def./min and pre-load was 2 N. Before compression test, specimen dimensions were measured in the same way as in water absorption test. Average density for substrate variants were taken from water absorption specimen data. During compression, a stress-strain graph was put out by Zwick/Roell computer program in real-time onto which the elastic modulus (Ed) was determined as the slope of the constructed tangent at the linear (elastic) section of the graph. Compression strength at 10 % deformation (σ10) like elastic modulus was calculated automatically by the software, registering mechanical stress at 10 % deformation. Chemical Analyses And Fungal Biomass. Specimens were first crushed by hand, then ground up using laboratory mill IKA-Werke M20 (Germany). Approximately 7 grams of crushed specimen was ground up for 15 seconds, let to rest, then for 15 more seconds, after which it was poured out onto vibrating sieve shaker Retsch AS200 (Germany) top sieve and sieved for 15 minutes. Sieves of 1000 µm, 600 µm, 400 µm pore size were used to separate mycelium, and substrate fractions for ash, cellulose and lignin analyses, respectively (Fig. S1). Such pore sizes for each wood constituent were chosen due to the preferable fraction for cellulose assay, that is, 0.4 – 0.6 µm. Lignin content was assessed by Klason's method, that is, boiling specimen in 72 % sulphuric acid water solution for 1 hour, after being prior incubated for 2.5 hours with the solution at 24-25 oC. Lignin content in absolute dry specimen was calculated using Eq. 1, where Wlign is lignin content in absolute dry specimen, mlign is dried residue after filtering, and mabs. dry is mass of the absolute dry specimen. Wlign = mlign / mabs. dry * 100%.

(1)

Cellulose content was assessed using Kirschner-Hofer's or nitric acid method, by boiling specimen in concentrated nitric acid and ethanol solution for 1 hour. Ash content was assessed by incinerating specimen in melting pots at 650 oC until mass remained constant, remaining ash collected and weighed. Both cellulose and ash content in absolute dry specimen was calculated with the same formular structure as for lignin. Identical chemical analyses were carried out also for pure substrate components separately – shives, bran and bark. Noteworthy that shives used in these analyses were of complete granulometric fraction, i. e., unsieved. Fungal biomass proportion was assessed grinding up the specimen in the same way as for chemical analyses, and sieved with the same apparatus and method, but using only 1000 µm sieve; what

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remained on top of it was considered mycelium and what fell through – the substrate. The usage of this particular sieve for mycelium separation was decided out of previous empirical experimentation and visual inspection of the outcome. Mycelium and substrate parts were microscopically assessed to discern the level of impurity. Biodegradability. Biodegradation test was carried out according to LVS EN 14045: 2003 standard. MC cubes in 6 replicates were put into natural compost soil of 130 L collective box within 0.5 L separate plastic box compartments to preserve specimen material in a restricted area (Fig. 2). The collective box had drilled holes in the bottom part for excessive moisture to drain off when watering, although that was not necessary. Specimens were kept in 3 layers (bottom, middle, top) in the compost soil and changed every time taken out. This test was carried out for 12 weeks, digging out specimen trays for inspection every week for the first 4 weeks and every second week for the remaining duration. Specimens were taken out the boxes and their content separately probed by hand to check the degree of specimen integrity, then carefully put back into their boxes and into the collective box. Right before the test and each time taking out specimens, ambient temperature and humidity was noted (22.7-26.4 oC, RH 66-73 %) and also for the collective compost box with temperature span of 22.5-24.0 oC and 70-77 % moisture content (one anomaly was in the 10th week – 62.3 %, probably due to incomplete sample sealing) for every 3 soil layers, which was done by collecting ~10 g, drying in laboratory oven and calculating moisture level similar to specimen moisture. After 12 weeks of composting each individual specimen box was taken out, put into laboratory oven and dried for 2-3 days at 40 oC. When dry, boxes’ contents were sieved using 2 mm sieve. Figure 2. Biodegradability test insights. A – specimen in its individual box, B – individual specimen boxes in the collective box. Statistical Analyses. All statistical analyses were carried with RStudio (v. 1.3.1093), except for chemical composition whose data was statistically analysed in part with Microsoft Excel (v. 16.43). Data normality (f: shapiro.test) was assessed for every individual group and skedasticity (f: leveneTest) for individual groups and their combinations, that is, among the whole granulometric fraction and among the total data, too. With the intention of improving homogeneity and skewness, outliers were discarded, using boxplots and removing data points which were outside this interval: IQR ± 1.5*IQR. Nevertheless, the balance of specimen count within groups was also taken into notice, which is why some extreme values still remained in the final data set. Majority of groups after all modifications had 6 or more replicates, only two had 5 replicates and one group had 4. As for chemical analyses, 2 replicates for each variant were obtained. In all groups the results showed low standard errors, therefore statistical analyses were omitted due to low statistical power. For group comparisons parametric ANOVA (f: aov) with Tukey-Kramer (f: TukeyHSD) post-hoc tests were used. Although all groups were distributed normally, two had heteroskedasticity, therefore ANOVA with Welch correction (f: oneway.test) was done and appropriate Games-Howell (f: gamesHowellTest) as post-hoc [17]. When these gave similar results compared with aforementioned regular tests, therefore regular ones were used in the analysis for convenience. Correlations between parameters were carried out using parametric Pearson correlation (f: cor.mtest). For graphs various functions from package ggplot were used (RStudio files in supplementary files folder). All statistical tests were done at the significance level α = 0.05 (p ≤ 0.05).

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Results Moisture Content And Water Absorption. Right after unmoulding grown specimens had moisture levels from 49.5 to 68.3 %. Both in hemp shives A and B granulometric groups lowest moisture was observed in II variant, with added bark (Fig. S3). In I and III variants moisture content was slightly higher for group A than group B, however, only significantly for I variant (Fig. S2). Worthy of mentioning, within group's B III variant specimens there was strong, however insignicant correlation (r=0.78, p=0.068) between dried specimen mass (indicating how packed the mould was) and specimen relative moisture (Fig. S5). In group B the only significant difference was between I and II variants, with II being lower. However, in group A all variants differed significantly (Fig. S4). In water absorption test during the first 2 hours all specimens had taken up more than 90 % of the final water uptake. Within granulometric groups the only differences for this parameter were in II and III variants, where II was highest in A group, and III in B group (Fig. S7). This pattern did not show in volumetric and thickness swelling, as these parameters had bigger inconsistency. After 24h water uptake ranged from 663 to 970 % for group A and from 703 to 1069 % for group B. Even though overall higher water uptake was observed in group B, comparing to group A it differed significantly between III variants only. In both groups lowest water uptake was clearly in II variant – by approximately 200 % lower than the other two variants (ANOVA p < 0.001). Group B had bigger differences between variants, all differed significantly, and the highest uptake in the group was for III Figure 4. Water uptake in groups in all groups after 24h variant (ANOVA p < 0.001), of water immersion. but in group A III variant did not differ from I variant (Fig. 4). Both groups had very strong negative correlations between specimen density and water uptake (r > |–0.93|, p < 0.0001). In group A density had strong negative relationships (p < 0.05) with all of the absorption parameters, however in group B density had negative correlation with water uptake only, as all swelling parameters positively correlated (p < 0.05) with it moderately to strongly (Figs. S9-S11). For swelling in thickness and in volume in group A, the only Figure 5. Swelling (A) in thickness and (B) in volume after variant that differed from the 24h within granulometric groups. rest was II. On the other hand, in group B both mentioned

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parameters differed between all but I and II variants (Fig. 5). Both volumetric swelling and swelling in thickness of group B II variant were always higher than those of II variant of group A, but it was the other way round with III variant whose swelling in thickness and volume were always higher in group A (Figs. 5 and S8). Not surprisingly, in both groups volumetric swelling correlated moderately to strongly positively with swelling in thickness, however only in group A all dimensional swelling parameters had positive correlation with water uptake, whereas group's B water uptake had moderate to strong negative correlation with swelling. (Figs. S9-S11). Density And Mechanical Compression. MC density ranged from 0.085 to 0.118 g/cm3. The only significant difference between groups was in III variants, where that of group B was lower by approximately 0.001 g/cm3 or 11 %. Within groups all variants differed significantly from one another, with II being the highest, then I, and III – the lowest (Fig. 6). As for compression tests, strength values ranged from 0.108 to 0.204 MPa and elastic modulus values from 1.79 to Figure 6. Differences in density between granulometric 3.79 MPa. Within group A groups highest strength was observed in I and III which did not differ significantly, but that of II variant was the lowest. Same pattern was visible in elastic modulus data. For group B all variants differed significantly, with I being the strongest, then II, and III – the weakest. Similar pattern was observed with elastic modulus, but differences between I and II variants were not significant. Comparing the homologous variants between the groups in strength I and II variants had similar values, but III was significantly lower in group B. Elastic modulus did not show significant differences between I Figure 7. Mechanical properties comparison between variants, however, it had higher granulometric groups. values in group B II variant, but A – compression strength at 10% deformation, B – lower in group B III variant (Fig. elastic modulus. 7). Both groups showed significant and strong correlation between strength and modulus (r = 0.9, p < 0.0001), but there were differences in correlations between density and both strength and modulus: group A had strong negative correlations (r = 0.84 and –0.88, resp.) which were significant (p