Faculty of Engineering
Reinforced Bamboo Nanocomposites using Stabilized Polymers:
Characterizations and Optimization
Muhammad Adamu
Doctor of Philosophy 2021
Reinforced Bamboo Nanocomposites using Stabilized Polymers:
Characterizations and Optimization
Muhammad Adamu
A thesis submitted
In fulfillment of the requirements for the degree of Doctor of Philosophy (Chemical Engineering)
Faculty of Engineering
UNIVERSITI MALAYSIA SARAWAK 2021
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DECLARATION
I declare that the work in this thesis was carried out in accordance with the regulations of Universiti Malaysia Sarawak. Except where due acknowledgements have been made, the work is that of the author alone. The thesis has not been accepted for any degree and is not concurrently submitted in candidature of any other degree.
……… Signature
Name: Muhammad Adamu
Matric No.: 16010166
Faculty of Engineering Universiti Malaysia Sarawak Date :
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DEDICATION
I dedicate this thesis to my children; Fatima, Musa, Muhammad-Anwar, Asma’u and Ummu Kulthum.
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ACKNOWLEDGEMENT
Firstly, I would like to express my sincere gratitude to main advisor Dr. Rezaur Rahman for the continuous support of my PhD study and related research, for his patience, motivation, and immense knowledge. His guidance has helped me in all the time of the research and writing of this thesis. I could not have imagined having a better advisor and mentor for my PhD study.
Besides my advisor, I would like to thank the rest of my sipervisory committee Prof. Sinin Hamdan and Associate Prof. Khairudin Sanaullah for their insightful comments and encouragement.
My sincere thanks also go to Dr Haji Alhaji, Dr. Muhammad Khusairy Bin Bakri, Dr. Hakeem Amuda, Dr Adamu Babale and all the rest of my colleagues in UNIMAS for contributing in one way or the other towards successful completion of my research.
To my parents, brothers, sisters and family at large, I say a big thank you for your prayers and encouragement over the years. I am particularly grateful to my friends Adamu Yusuf, Usman Hamidu, Ahmed Haske, Adullahi Moriki, Abdullahi Muhammed, Bashir Mohammed, Uztaz Iliyasu. May Allah reward you all. My gratitude also goes to my colleagues in Nigerian National Petroleum Corporation, for their support and assistance whenever I requested. I remain eternally grateful.
My special thanks to my wives Saadatu Ahmed, Fatima Adamu and my kids Fatima, Musa, Muhammad and Asma’u for their patience, prayers, support and understanding. May we live long to reap the fruit of this labour.
iv ABSTRACT
Bamboo is an abundant natural resource in Malaysia that has prospect to substitute wood in many engineering applications. However, there are drawbacks such as poor physico-mechanical properties, susceptibility to damage, frequent costly maintenance, deterioration of physical and mechanical properties due to environmental variation. In this work, the effects of montmorillonite nanoclay and combination of stabilized polymers such as poly(ethylene-alt-maleic anhydride) (PEA), polyvinyl alcohol (PVA), polyvinyl alcohol-co-acrylonitrile, and polyvinyl alcohol-co-styrene on formulation of bamboo nanocomposites were investigated and optimized using response surface methodology. When poly(ethylene-alt-maleic anhydride) was used, functional groups in the raw bamboo and nanocomposites were identified using Fourier transform infrared spectroscopy (FTIR). X-ray diffraction XRD) plots showed the prominent peak intensity at a diffraction angle of 73° due to the transformation of the amorphous structure to a crystalline structure in the prepared nanocomposite. The morphologies of the raw bamboo and the nanocomposites were compared using scanning electron microscopy (SEM) analysis. There was an increase in the modulus of elasticity (MOE) from 7.82 GPa to 18.96 GPa and a corresponding increase in the modulus of rupture (MOR) from 68.67 MPa to 121.48 MPa of the raw bamboo to the nanocomposites, respectively. There was also improvement in the thermal properties from the differential scanning calometry (DSC) and thermogravimetric (TGA) results. Similarly, for PVA formulated bamboo nanocomposites, The FTIR spectra of the nanocomposites indicated incorporation of the polymer and nanoclay in the structure and diffractograms from XRD also indicated higher crystallinity of the prepared nanocomposites compared to raw bamboo. The SEM image revealed that of the lumens of the raw bamboo were filled by the polymer and nanoclay after formation of the nanocomposites.
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Improved mechanical properties were observed in the prepared nanocomposites compared to the raw bamboo with the MOE increased from 7.82 GPa to 17.32 GPa MOR increased from 68.67 MPa to 118.74 MPa. Optimal values were found to be 15.082 GPa for MOE and 96.879 MPa for MOR with R2 of 0.9999. Better thermal properties were observed in the developed nanocomposites compared to the raw bamboo as revealed by both the DSC and TGA results. In the same vain, PVA/acrylonitrile formulated nanocomposites, models were developed to predict modulus of elasticity and modulus of rupture of the nanocomposites. Optimized values of MOE and MOR were 12.82 GPa and 105.52 MPa respectively at 10 wt% clay loading, 15 wt% PVA/acrylonitrile loading and modification time of 5 min. The melting and decomposition temperature of the nanocomposites have shown high improvement compared to the raw bamboo. Nanocomposites produced using PVA-co-styrene showed dispersion of nanoclay into the bamboo matrix was confirmed by the compositional analysis. The XRD results showed that the degree of crystallinity was slightly improved upon impregnation with PVA-co-styrene while reduction in the hydroxyl groups was observed using the FTIR and the SEM showed tightly filled up cell cavities of the bamboo matrix. The thermal stability of the formed nanocomposites was found be slightly less stable than the raw bamboo with the DSC showing low glass transition temperature and the TGA showed lower decomposition temperatures for the nanocomposites compared to raw bamboo as a result of plastic property of the styrene. The MOE and MOR were found to be have significantly increased after formation of the nanocomposites indicating improvement of mechanical properties of the bamboo.
Keywords: Bamboo, optimization, nanocomposite, response surface methodology,
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Nanokomposit Buluh Bertetulang Menggunakan Polimer Stabil: Pencirian dan Pengoptimuman
ABSTRAK
Buluh merupakan salah satu sumber semula jadi yang terbanyak terdapat di Malaysia yang mempunyai prospek untuk menggantikan kayu dalam banyak aplikasi kejuruteraan. Walau bagaimanapun, terdapat beberapa kelemahan kegunaan buluh seperti sifat fizik-mekanikalnya yang lemah, kerentanan terhadap kerosakan, penyelenggaraan yang kerap memakan kos, kemerosotan sifat fizikal dan mekanikal kerana perubahan persekitaran. Dalam kajian ini, kesan daripada tanah liat montmorilonite bersaiz nano dan gabungan penstabil polimer seperti poli(etilena-alt-maleik anhidrida) (PEA), polivinil alkohol (PVA), polivinil alkohol-co-akrilonitrida, polivinyl alkohol-co-stirena, dan formulasi nanokomposit buluh diselidiki dan dioptimumkan menggunakan metodologi tindak balas permukaan. Apabila poli(etilena-alt-maleik anhidrida) digunakan, kumpulan fungsional dalam buluh mentah dan nanokomposit dikenalpasti menggunakan spektroskopi infrated transformasi Fourier (FTIR). Plot sinar-X difraksi (XRD) menunjukkan intensiti puncak yang menonjol pada sudut difraksi sebanyak 73° kerana transformasi struktur amorf kepada struktur kristal dalam nanokomposit yang disediakan. Morfologi buluh mentah dan nanokomposit dibandingkan menggunakan analisis mikroskop elektron imbasan (SEM). Terdapat peningkatan dalam modulus keanjalan (MOE) dari 7.82 GPa kepada 18.96 GPa dan peningkatan yang sesuai dalam modulus pecahan (MOR) dari 68.67 MPa kepada 121.48 MPa buluh mentah kepada nanokomposit, masing-masing. Terdapat juga peningkatan sifat termal dari pengimbas perbezaan kalori (DSC) dan termogravimetrik (TGA). Begitu juga, untuk nanokomposit buluh yang diforumulasikan dengan PVA, spektrum FTIR nanokomposit menunjukkan penggabungan polimer dan tanah liat bersaiz nano dalam
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struktur dan difraktogram dari XRD juga menunjukkan kristalografi yang lebih tinggi dari nanokomposit yang disiapkan berbanding buluh mentah. Imej SEM mendedahkan bahawa lumen buluh mentah diisi oleh polimer dan tanah liat bersaiz nano selepas pembentukan nanokomposit. Sifat mekanikal yang lebih baik diperhatikan pada nanokomposit yang disediakan berbanding dengan buluh mentah dengan MOE meningkat dari 7.82 GPa kepada 17.32 Gpa dan MOR meningkat dari 68.67 MPa kepada 118.74 MPa. Nilai optimum didapati adalah 15.082 GPa untuk MOE dan 96.879 MPa untuk MOR dengan R2 daripada 0.9999. Sifat terma yang lebih baik diperhatikan pada nanokomposit yang dikembangkan berbanding dengan buluh mentah seperti yang ditunjukkan oleh hasil DSC dan TGA. Dalam masa yang sama, PVA/akrilonitril nanokomposit dirumuskan dan model dikembangkan untuk meramalkan modulus keanjalan dan modulus pecahan nanokomposit. Nilai dioptimumkan MOE dan MOR masing-masing ialah 12.82 GPa dan 105.52 MPa pada pemuatan tanah liat bersaiz nano 10 wt%, muatan 15 wt% PVA/akrilonitril dan masa pengubahsuaian 5 minit. Hasil XRD menunjukkan bahawa tahap kekristinaliti sedikit bertambah baik semasa impregnasi dengan PVA-co-stirena sementara pengurangan kumpulan hidroksil diperhatikan menggunakan FTIR dan SEM menunjukkan rongga sel matrik buluh yang terisi rapat. Kestabilan termal nanokomposit yang dibentuk didapati sedikit kurang stabil daripada buluh mentah dengan DSC menunjukkan suhu peralihan kaca yang rendah dan TGA menunjukkan suhu penguraian yang lebih rendah untuk nanokomposit berbanding buluh mentah akibat daripada sifat plastik styrene. MOE dan MOR didapati telah meningkat dengan ketara selepas pembentukan nanokompoit yang menunjukkan peningkatan sifat mekanik buluh.
Kata kunci: Buluh, pengoptimuman, nanokomposit, metodologi tindak balas permukaan, sifat mekanik.
viii TABLE OF CONTENTS Page DECLARATION i DEDICATION ii ACKNOWLEDGEMENT iii ABSTRACT iv ABSTRAK vi
TABLE OF CONTENTS viii
LIST OF TABLES xv
LIST OF FIGURES xvii
LIST OF ABBREVIATIONS xx CHAPTER 1: ` INTRODUCTION 1 1.1 Research Background 1 1.2 Bamboo Composites 3 1.3 Problem Statements 5 1.4 Research Gap 7 1.5 Research Hypothesis 7 1.6 Research Objectives 8 1.7 Research Scope 8
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CHAPTER 2: LITERATURE REVIEW 11
2.1 Introduction 11
2.2 Polymer Matrix 11
2.3 Composite Materials 13
2.4 Natural Fibers 14
2.5 Features of Bamboo and bamboo composites 17
2.6 Distribution of Bamboo 18
2.7 Anatomy of bamboo 20
2.8 Chemical Composition of Bamboo 22
2.9 Surface Modification Processes and Nanocomposites fabrication 23
2.9.1 Salinization Treatment 23 2.9.2 Acetylation Treatment 23 2.9.3 Benzoylation Treatment 24 2.9.4 Maleisation Treatment 24 2.9.5 Isocyanate Treatment 24 2.9.6 Peroxide Treatment 25 2.9.7 Enzymatic Treatment 25
2.9.8 Corona, Cold Plasma Treatment 25
2.10 Vacuum impreganation 26
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2.12 Montmorillonite for Nanocomposites 27
2.13 Polymer Screening Criteria 31
2.14 Bamboo Nanocomposites 31
2.15 Polymers in Nanocomposite 33
2.16 Response Surface Methodology 35
2.17 Characeterization 37
2.18 Summary 39
CHAPTER 3: RESEARCH METHODOLOGY 41
3.1 Introduction 41
3.2 Materials 41
3.3 Bamboo Samples Preparation 41
3.4 Formlation of nanocomposites 42
3.5 Polymerization and curing 44
3.6 Mechanical Testing 44
3.6.1 Three-Point Bending Test 44
3.7 Characterization for Physico-Chemical and Morphology 45
3.7.1 FTIR Spectroscopy 45
3.7.2 X-ray Diffraction (XRD) 45
3.7.3 Scanning Electron Microscopy (SEM) 46
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3.8.1 Differential Scanning Calorimetry (DSC) 46
3.8.2 Thermogravimetric Analysis (TGA) 47
3.9 Modification using PEA 47
3.10 Design of Experiment for Treatment with PVA 48
3.11 Design of Experiment for Treatment with PVA and Acrylonitrile 50 3.12 Design of Experiment for Treatment with PVA And Styrene 51
3.13 Summary 54
CHAPTER 4: POLY (ETHYLENE-ALT-MALEIC ANHYDRIDE) BAMBOO
NANOCOMPOSITES 55 4.1 Introduction 55 4.2 Compositional Analysis 55 4.2.1 FTIR Analysis 55 4.2.2 XRD Analysis 57 4.3 Morphological Properties 58 4.4 Mechanical Properties 60 4.5 Thermal Properties 61 4.5.1 DSC Analysis 61 4.5.2 Thermogravimetric Analysis 62 4.6 Summary 65
CHAPTER 5: BAMBOO/POLYVINYL ALCOHOL NANOCOMPOSITES 66
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5.2 Analysis of Variance (ANOVA) on effect on MOE and MOR 66
5.3 Prediction of Optimal Conditions 71
5.4 Sample selection for characterisation 73
5.5 Compositional Properties 73 5.5.1 FTIR Analysis 73 5.5.2 XRD Analysis 74 5.6 Morphological Properties 75 5.7 Thermal Properties 76 5.7.1 DSC Analysis 76
5.7.2 Thermogravimetric Analysis (TGA) 78
5.8 Summary 79
CHAPTER 6: POLYVINYL ALCOHOL /ACRYLONITRILE BAMBOO
NANOCOMPOSITES 80
6.1 Introduction 80
6.2 Model Fitting and Optimization 80
6.3 Analysis of response surfaces 83
6.4 Determination of Optimal Values 86
6.5 Characterization of bamboo nanocomposite 88
6.6 Compositional Properties 88
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6.6.2 XRD analysis 90
6.7 Morphological Properties 91
6.8 Thermal Properties 93
6.8.1 DSC Analysis 93
6.8.2 Thermogravimetric Analysis (TGA) 94
6.9 Summary 97
CHAPTER 7: BAMBOO/PVA/STYRENE NANOCOMPOSITES 99
7.1 Introduction 99
7.2 Analysis of Variance (ANOVA) on effect on MOE and MOR 99
7.3 Prediction of Optimal Conditions 106
7.4 Compositional analysis 108
7.4.1 X-Ray Diffraction Analysis (XRD) 108
7.4.2 Fourier Transform Infrared Spectroscopy (FTIR) 109
7.5 Morphological Analysis 111
7.6 Thermal Analysis 113
7.6.1 Differential Scanning Calorimetry (DSC) 113
7.6.2 Thermogravimetry Analysis (TGA) 114
7.7 Summary 115
CHAPTER 8: CONCLUSION AND RECOMMENDATIONS 117
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8.2 Research Findings 117
8.3 Recommendations for Future Study 119
REFERENCES 121
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LIST OF TABLES
Page
Table 2.1 Bamboo regions along with countries 19
Table 3.1 Bamboo Impregnation at different pH levels 47
Table 3.2 Variables for use in the design of the experiment 48
Table 3.3 Design of xperiment values from design expert 11 49
Table 3.4 Variable for experimental design 51
Table 3.5 Variables for use in the design of the experiment 51
Table 3.6 Experimental design from design expert 11 53
Table 4.1 MOE and MOR of RB and nanocomposites 60
Table 4.2 Result of TGA for RB and nanocomposites 64
Table 5.1 ANOVA results for MOE 66
Table 5.2 Comparison of the experimental and predicted results 69
Table 5.3 Selected runs for characterizations 73
Table 6.1 Experimental design and results 81
Table 6.2 Selected runs for characterization 88
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Table 6.4 TGA results of treated bamboo samples 96
Table 7.1 ANOVA results for MOE 101
Table 7.2 ANOVA results for MOR 102
Table 7.3 Comparison of results the experimental and model predicted values 104
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LIST OF FIGURES
Page
Figure 2.1 Classification of natural fibers 16
Figure 2.2 (a) Bamboo culm (b) Cross-section of bamboo culm (c) Vascular bundles, (d) Fiber strand (e) Elementary fibers (f) Model of poly
lamellae structure of bamboo 21
Figure 2.3 (a) Vascular bundle of bamboo (b) Elementary fiber 10–20 µm (c)
Nanofibril 1–10 µm involves lignin and hemicellulose 21
Figure 2.4 Chemical constituents of bamboo Fiber 22
Figure 3.1 Flow chart for the experimental procedure 43
Figure 4.1 FTIR spectra of RB and nanocomposites 57
Figure 4.2 XRD diffractograms of RB and PEA1, PEA2, PEA3, PEA4 and PEA5
nanocomposites 58
Figure 4.3 SEM images (1500×) of: (a) raw bamboo (b) PEA1 (c) PEA2 (d)
PEA3 (e) PEA4 and (f) PEA5 59
Figure 4.4 DSC thermogram of (a) RB (b) PEA1 (c) PEA2 (d) PEA3 (e) PEA4
and (f) PEA5 62
Figure 4.5 TGA of (a) RB (b) PEA1 (c) PEA2 (d) PEA3 (e) PEA4 and (f) PEA5 63
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Figure 5.2 Surface plot for optimization of MOE 72
Figure 5.3 Surface plot for optimization of MOR 72
Figure 5.4 FTIR spectra of RB and bamboo nanocomposites 74
Figure 5.5 XRD diffractograms of RB and nanocomposites 75
Figure 5.6 SEM micrographs of (1500x) (a) RB (b) PVA1 (c) PVA2 (d) PVA3
(e) PVA4 and (f) PVA5 76
Figure 5.7 Differential scanning calorimetry (DSC) thermogram of (a) RB (b)
PVA1 (c) PVA2 (d) PVA3 (e) PVA4 and (f) PVA5 77
Figure 5.8 Thermogravimetric analysis (TGA) plots of (a) RB (b) PVA1 (c)
PVA2 (d) PVA3 (e) PVA4 and (f) PVA5 78
Figure 6.1 Residual normal probability plot for MOE 82
Figure 6.2 Residual normal probability plot for MOR 82
Figure 6.3 MOE 3D surface plot (a) Time constant (b) PVA/Acryloniterile
constant, (c) Clay constant 84
Figure 6.4 MOR 3D surface plot (a) Time constant (b) PVA/Acryloniterile
constant, (c) Clay constant 85
Figure 6.5 Surface plot for optimization of MOE 87
Figure 6.6 Surface plot for optimization of MOR 87
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Figure 6.8 XRD diffractograms of raw bamboo and nanocomposites 90
Figure 6.9 SEM images of (a) RB (b) BNC1 (c) BNC2 (d) BNC3 and (e)BNC 92
Figure 6.10 Differential scanning calorimetry (DSC) thermograms of (a) Raw
bamboo (b) BNC1 (c) BNC2 (d) BNC3 and (e) BNC4 93
Figure 6.11 TGA plots of (a) Raw bamboo (b) BNC1 (c) BNC2 (d) BNC3 and (e)
BNC4 95
Figure 7.1 Residual plots of the predicted and experimental values for (a) MOE
(b) MOR 106
Figure 7.2 Surface plot for optimization of MOE 107
Figure 7.3 Surface plot for optimization of MOR 107
Figure 7.4 XRD diffractograms for RB; NC1, NC2, NC3, NC4 and NC5
nanocomposites 108
Figure 7.5 FTIR spectra of RB and nanocomposites 110
Figure 7.6 SEM of (a) RB (b) NC1 (c) NC2 (d) NC3 (e) NC4 and (f) NC5 112
Figure 7.7 DSC thermogram of (a) RB (b) NC1 (c) NC2 (d) NC3 (e) NC4 and (f)
NC5 113
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LIST OF ABBREVIATIONS
ANOVA Analysis of Variance BNC CMM DSC FTIR MMT MOE MOR NC OBFM PEA PP PVA RB RMM RSM SEM TGA VMT XRD Bamboo Nanocomposite
Compression Moulding Method Differential Scanning Calorimetry Fourier Transform Infrared
Montmorillonite Modulus of Elasticity Modulus of Rupture Nanocomposite
Oriented Bamboo Fiber Mat Poly (ethylene maleic anhydride) Polypropylene
Ply Vinyl Alcohol Raw Bamboo
Roller Moulding Method Response Surface Methodology Scanning Electron Microscopy Thermogravimetric analysis Vermiculate
1
CHAPTER 1 `
INTRODUCTION
1.1 Research Background
Bamboo is a natural lignocellulosic-based composite material, which is abundant in the Asian Pacific region (Khalil et al., 2015). Malaysia is a heavily forested country, and forest products including bamboo are important sources of income. While bamboo has been an important resource, widely and easily available, it has remained a poor man's crop compared to timber and other non-timber crops like rattan. However, the potential for growth of the bamboo industry is tremendous. This has been recognized by researchers. In the last decade or so, Forest Research Institute Malaysia (FRIM) has given very high priority for bamboo development, both in terms of growth and the manufacturing aspects. Malaysia has about 70 species of bamboo: 50 in Peninsular Malaysia, 30 in Sabah and 20 in Sarawak (Wong, 1989). The 10 available genera are Bambusa, Chusquea, Dendrocalamus,
Dinochloa, Gigantochloa, Phyllostachys, Racemobambos, Schizostachyum, Thyrsostachys and Yushania (Wong, 1989). There are 12 bamboo species commonly
exploited for commercial purposes (Azmy and Abd. Razak 1991). The most common species extracted are Gigantochloa scortechinii, G. levis, G. ligulata, Dendrocalamus asper,
Bambusa blumeana, Schizostachyum grande and S. zollingeri. The export of bamboo
increased from 329 tonnes in 1991 to 7348 tonnes in 1995 (valued at RM 193 019). The import value increased from 2097 tonnes in 1991-94 426 tons in 1995 (valued at RM 2 586 188) (Kovac & Streit, 1996). The main buyers for Malaysian bamboos were Singapore and Vietnam. Malaysia also imported finished bamboo products such as chopsticks from Taiwan (Bahari & Krause, 2016). Malaysia exported RM9.9 million worth of bamboo products last
2
year. Primary Industries Minister Teresa Kok said the economic contribution of the Malaysian bamboo industry was still low compared with the US$68.8 billion (RM288.2 billion) global bamboo market (Savacool & Valantine, 2011). Bamboo is synonymous with the Malaysian community, with its handicraft products and for other daily uses. Various innovations and novelty products made from bamboo such as furniture, lamination boards, floors and fabrics have been widely used. It grows faster than any other kind of wood species and can mature within 3 to 8 years (Clark et al., 2015). Bamboo has been traditionally used to construct village houses as a structural material because of its light weight and high mechanical strength, and since then, the industrial development of bamboo has broadened in its application areas (Chaowana & Barbu, 2017). A lignocellulosic resource contains cellulose, hemicellulose, and lignin. There are some very basic properties that must be looked at, when preparing bamboo and other natural fibers as engineering materials (Lau et al., 2018). Some of these properties include the hygroscopic nature and the wet environment for most of their applications (Sanal, 2016). They are affected mainly by natural actions be they fungal attack, heat, aqueous media, photo-chemical induced reactions, direct chemicals, or entirely mechanical degradations. They swell and shrink as a result of changes in the cell wall moisture content, burns easily, decay, and susceptible to attacks by different bases, acids and radiation (Liu et al., 2012). To halt this resultant dimensional instability, researchers are modifying natural composites with various chemicals and materials that are nano-sized to tailor their mechanical properties for engineering materials development (May-Pat et al., 2013; Saw et al., 2014; Thakur et al., 2014). Another area of interest is getting the right composite materials that are compatible and can improve the strength of the formed nanocomposite and still maintain good ductility (Oksman et al., 2016).
