Designing and Engineering a New Biocomposite Material from Distillers' Grains and Bioplastics

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Designing and Engineering a New Biocomposite Material from

Distillers’ Grains and Bioplastics

Nima Zarrinbakhsh

A Thesis Presented to The University of Guelph

In partial fulfillment of requirements for the degree of Doctor of Philosophy in Engineering

Guelph, Ontario, Canada

ABSTRACT

DESIGNING AND ENGINEERING A NEW BIOCOMPOSITE MATERIAL FROM DISTILLERS’ GRAINS AND BIOPLASTICS

Nima Zarrinbakhsh Co-Advisors: University of Guelph, 2014 Dr. Manjusri Misra Dr. Amar K. Mohanty

In recent years, the expansion of the corn ethanol industry has generated surplus amounts of solid coproducts mainly in the form of dried distillers’ grains with solubles (DDGS). In order to help economic viability and sustainability of the industry, research is being conducted to find new, more profitable applications for this coproduct besides its traditional usage as animal feed.

In the present project, the capabilities of DDGS are evaluated for using as a filler and/or reinforcement in producing green biocomposites with a number of bioplastics. The bioplastics used here are partially originated from renewable resources with end-life biodegradability in compost conditions. The focus of this research is to design and engineer material formulations with balanced performance. Extrusion and injection molding techniques have been employed to produce the biocomposites and the performance of the produced materials was evaluated through several mechanical, thermomechanical and physical properties. The discussions are augmented with thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR).

The results are conclusive in that DDGS is a better filler for polymeric biocomposites when it undergoes a water treatment before processing with polymer melts. The treated DDGS shows a thermal degradation rate four times less than as-received DDGS at 180 °C, the processing temperature of the composite materials. The DDGS biocomposites are produced with a range of biodegradable plastics and the effect of a polymeric isocyanate compatibilizer is evaluated. The compatibilizer improves the interfacial adhesion between DDGS particles and the polymeric matrix, as evidenced by SEM, and thus, enhances the strength and modulus; however,

reduces the impact strength. A high-impact DDGS biocomposite is produced using a combination of compatibilizer and lubricant as additives. The optimization of the material’s formulation is approached statistically based on a full factorial design of experiment (DOE) for additive amounts, followed by a response surface methodology (RSM) for mechanical and physical properties. With this approach, biocomposites of DDGS and bioplastics are successfully designed which exhibit acceptable performance such as tensile strength of more than 20 MPa, flexural modulus of more than 1 GPa, impact strength of more than 100 J/m and melt flow index of more than 5 g/10min.

Dedicated to my priceless gift of God,

Sara M.

Acknowledgements

My sincere acknowledgement is to my co-supervisors, Dr. Manjusri Misra and Dr. Amar K. Mohanty, for providing me with the opportunity of working on this project. Their presence, guidance, support and encouragement throughout the whole program cannot be explained in words. Specifically, I would like to thank them for their trust and belief in me which created a huge self-confidence for my future carrier.

Also, I wish to express my gratitude to my other advisory committee members, Dr. Fantahun M. Defersha, Dr. Gordon Hayward and Dr. Evan Fraser for their time and sincere help towards my research. I benefited, very positively, from their constructive comments and discussions during the course of this project.

I would like to appreciate the Bioproducts Discovery and Development Centre (BDDC) research lab at University of Guelph, Ontario, Canada, for providing research facilities and infrastructure for conducting this project. A great thank you is for my colleagues at BDDC who were always willing to help. I have made invaluable friendships based on kindness and mutual respect.

I am not able to express my feelings towards my parents for their lifelong passion and support that has brought me to this level. During this period of graduate study, I could feel them next to me, every second, even though we were apart by thousands of miles. Also, my extreme appreciation is to my wife, Sara Molladavoodi, who is my true best friend. I cannot imagine accomplishing this PhD without her immense support and love. This is my real pleasure to thank Sara’s parents, too, for encouraging me and loving me endlessly.

I am grateful for the financial support from Ontario Ministry of Agriculture and Food (OMAF) and Ministry of Rural Affairs (MRA), Ontario Ministry of Economic Development and Innovation (MEDI), and Natural Sciences and Engineering Research Council (NSERC). Also, I acknowledge the industrial collaboration of GreenField Specialty Alcohols Inc., Chatham, Ontario, Canada, and Competitive Green Technologies, Leamington, Ontario, Canada. A detailed list of financial supports and industrial collaborations for this project is provided at the end of the thesis.

Table of contents

Acknowledgements ...... v List of tables ...... x List of figures ...... xi List of abbreviations and defined terms ...... xvi List of publications ...... xx

Chapter 1: Introduction ...... 1 1.1. Structure of this thesis ...... 2 1.2. Research problem ...... 3 1.3. Hypothesis...... 4 1.4. Objectives ...... 4 1.5. Significance ...... 5

Chapter 2: Literature Review about the Current Status of Corn-Ethanol Industry and the Research on Distillers’ Grains in the Field of Materials Science and Engineering ...... 6 2.1. Renewable resource-based ethanol scenario ...... 7 2.2. Ethanol production and its coproducts supply in North America ...... 9 2.3. Corn ethanol sustainability: the role of coproducts ...... 14 2.4. Distillers’ grains applications: commercial and potential ...... 16 2.5. Distillers’ grains applications in polymer science and engineering ...... 18 2.5.1 Distillers’ grains-derived novel materials ...... 18 2.5.2 Distillers’ grains polymeric biocomposites ...... 21 2.6. Conclusions and future perspective ...... 39 References ...... 42

Chapter 3: Characterization of Dried Distillers’ Grains with Solubles (DDGS) and Effect of Water-Washing on it for Biocomposite Applications ...... 50 3.1. Introduction ...... 51 3.2. Experimental ...... 53 3.2.1. Materials ...... 53 3.2.2. DDGS waster-washing ...... 53 3.2.3. Composition analyses ...... 54

3.2.4. Thermogravimetric analysis (TGA) ...... 54 3.2.5. Fourier transform infrared (FTIR) spectroscopy ...... 55 3.2.6. Biocomposite fabrication and testing...... 55 3.2.7. Statistical analysis ...... 55 3.3. Results and discussion ...... 56 3.3.1. Thermogravimetric analysis (TGA) ...... 56 3.3.2. The effect of washing time and water amount ...... 58 3.3.3. The effect of heating rate ...... 61 3.3.4. Activation energy of thermal degradation ...... 63 3.3.5. Compositional analysis and infrared spectroscopy ...... 66 3.3.6. Biocomposite processing and testing ...... 69 3.4. Conclusions ...... 72 References ...... 73

Chapter 4: Biodegradable Green Composites from Dried Distillers' Grain with Solubles (DDGS) and Polyhydroxy(butyrate-co-valerate) (PHBV)-Based Bioplastic ...... 79 4.1. Introduction ...... 80 4.2. Experimental ...... 83 4.2.1. Materials ...... 83 4.2.2. DDGS treatment ...... 83 4.2.3. Thermogravimetric analysis (TGA) ...... 83 4.2.4. Sample preparation ...... 84 4.2.5. Mechanical tests ...... 85 4.2.6. Dynamic Mechanical Analysis (DMA) ...... 85 4.2.7. Heat deflection temperature (HDT) ...... 86 4.2.8. Morphological studies ...... 86 4.3. Results and Discussion ...... 87 4.3.1.Thermal stability of DDGS – The effect of water-washing ...... 87 4.3.2. Mechanical properties ...... 91 4.3.3. Fracture surface morphology ...... 96 4.3.4. Thermomechanical properties – HDT and DMA ...... 102 4.4. Conclusion ...... 106 References ...... 107

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Chapter 5: Improving the Interfacial Adhesion in a New Renewable Resource-Based Biocomposites from Biofuel Coproduct and Biodegradable Plastic ...... 109 5.1. Introduction ...... 110 5.2. Experimental ...... 115 5.2.1. Materials ...... 115 5.2.2. DDGS water-washing ...... 116 5.2.3. Biocomposite processing ...... 116 5.2.4. Fourier transform infrared (FTIR) spectroscopy ...... 118 5.2.5. Mechanical tests ...... 118 5.2.6. Melt flow index (MFI) measurements ...... 119 5.2.7. Water absorption measurements ...... 119 5.2.8. Dynamic mechanical analysis (DMA) ...... 120 5.2.9. Morphology studies ...... 120 5.3. Results and discussion ...... 121 5.3.1. Processing curves ...... 121 5.3.2. IR spectroscopy ...... 123 5.3.3. Mechanical properties ...... 127 5.3.4. Melt flow index (MFI) ...... 132 5.3.5. Dynamic mechanical analysis (DMA) ...... 134 5.3.6. Morphology...... 138 5.3.7. Water absorption measurements ...... 143 5.4. Conclusions ...... 145 References ...... 146

Chapter 6: A Statistical Approach to Engineer a Biocomposite Formulation from Biofuel Coproduct with Balanced Properties ...... 150 6.1. Introduction ...... 151 6.2. Experimental ...... 154 6.2.1. Materials ...... 154 6.2.2. Biocomposite processing and characterization ...... 154 6.2.3. Design of experiments ...... 155 6.2.4. Statistical analysis ...... 156 6.3. Results and discussion ...... 157 6.3.1. Effects of compatibilizer and lubricant on mechanical and physical properties ...... 157

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6.3.2. Model development via ANOVA approach ...... 159 6.3.3. Model adequacy check ...... 163 6.3.4. Other residual plots ...... 167 6.3.5. Response surfaces, contour plots and the optimized region ...... 169 6.4. Conclusions ...... 173 References ...... 174

Chapter 7: Overall Conclusions and Future Work ...... 176 7.1. Key outcomes...... 177 7.2. Future work ...... 179 7.3. Overall conclusions of the thesis ...... 182

Financial supports and industrial collaborations ...... 183

List of tables

Table 2-1. Peer-reviewed articles on distillers’ grains biocomposites ...... 23

Table 2-2. Patents and patent applications on distillers’ grains biocomposites ...... 24

Table 3-1. DDGS water-washing conditions ...... 54

Table 3-2. ANOVA table for the effect of washing time and water-to-DDGS ratio on

fractional mass loss (%) at 180 °C ...... 61

Table 3-3. Activation energy values calculated from isoconversional lines and the

respective temperatures for the heating scan of 20 °C min-1 ...... 65

Table 3-4. The mass fraction (%) of DDGS components before and after washing on a

dry basis ...... 66

Table 3-5. Assignment of major peaks in DDGS infrared spectrum ...... 67

Table 4-1. Formulation of all samples prepared in this work ...... 85

Table 4-2. Correlation between HDT and storage modulus values of samples ...... 105

Table 5-1. Biocomposite formulations processed in this work (values based on weight

ratios) ...... 117

Table 6-1. Mechanical and physical properties of different formulations (data adopted

from [12]) ...... 157

Table 6-2. ANOVA table for full model of all studied responses ...... 161

Table 6-3. ANOVA table for reduced model of tensile strength, flexural modulus and impact strength ...... 162

Table 6-4. Regression models and R2 statistic obtained for each response ...... 163

Table 6-5. Experimental and predicted output of responses for the DDGS biocomposite

formulation with 0.75 wt. % of PMDI and 3 wt. % of corn oil ...... 166

Table 6-6. The predicted mechanical and physical properties for the biocomposite formulations specified in Figure 6-7 ...... 172

List of figures

Figure 2-1. The global total ethanol production (in billion litres) and the contribution of coarse grain ethanol towards it...... 8

Figure 2-2. The evolution of renewble feedstock contribution towards global ethanol

production from 2012 to 2022...... 9

Figure 2-3. The world ethanol production by country in 2012...... 10

Figure 2-4. Production distribution of (a) corn cob (tonnes per year) and (b) ethanol

(million gallons per year) in the USA...... 11

Figure 2-5. Schematic of production of ethanol and its coproducts in a dry mill plant.. .. 13

Figure 2-6. Digital image of the yellowish, particulate appearance of dried distillers’ grains with solubles...... 14

Figure 2-7. Distillers’ grains production in the US during 1999-2012...... 14

Figure 2-8. The tensile properties of cyanoethylated DDGS films as a function of

acrylonitrile to DDGS ratio...... 20

Figure 2-9. The tensile strength of plastics from protein and distillers’grain derivetized

with different methods...... 21

Figure 2-10. Mechanical properties of the polyolefin-based DDGS biocomposites; (a)

PP/DDGS and (b) HDPE/DDGS biocomposites...... 25

Figure 2-11. The effect of solvent treatment and compatibilizer on mechanical

performance of the HDPE/25wt.%DDGS...... 27

Figure 2-12. The effect of DDGS amount on tensile properties of phenolic resin/DDGS biocomposites...... 28

Figure 2-13. The effect of MDI compatibilizer on tensile modulus and strength of the

PLA/20wt.%DDGS biocomposite...... 33

Figure 2-14. The effect of water-washing and compatibilization on mechanical

performance of the (PHBV/PBS)/30wt.%DDGS biocomposite...... 35

Figure 2-15. The effect of PMDI compatibilizer and corn oil lubricant on selected

mechanical and physical properties...... 37

Figure 3-1. Thermogravimetric (TG) and derivative thermogravimetric (DTG) curves (20

°C min-1) of DDGS before and after water-washing...... 57

Figure 3-2. The effect of DDGS washing time and water amount...... 60

Figure 3-3. Thermogravimetric (TG) and derivative thermogravimetric (DTG) graphs of

as-received DDGS heated with different heating rates...... 62

Figure 3-4. Thermogravimetric (TG) and derivative thermogravimetric (DTG) graphs of

water-washed DDGS with different heating rates...... 62

Figure 3-5. Isoconversional graphs of (a) as-received and (b) water-washed DDGS...... 65

Figure 3-6. FTIR spectra of as-received and water-washed DDGS...... 67

Figure 3-7. Injected samples of (a) neat PBS, (b) water-washed DDGS biocomposite and

Figure 3-8. Tensile strength and modulus of neat PBS, water-washed DDGS

biocomposite and as-received DDGS biocomposite...... 71

Figure 4-1. Thermogravimetric (TG) graphs of non-washed DDGS, water-washed DDGS

and water-soluble portion of DDGS...... 88

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Figure 4-2. Derivative thermogravimetric (DTG) graphs of non-washed and water-

washed DDGS...... 90

Figure 4-3. Mechanical properties of neat polymers and their blend. Neat PBS had

elongation at break and Izod impact energy of 270% and 140 J/m, respectively...... 93

Figure 4-4. Mechanical properties: (A) polymeric matrix PHBV/30%PBS, (B) non-

washed DDGS green composite, (C) water-washed DDGS green composite, and (D)

water-washed/compatibilized DDGS green composite. All green composites contain 30

wt. % DDGS...... 95

Figure 4-5. Impact fracture surface and fracture mechanism of (a) non-washed DDGS, (b)

water-washed DDGS, and (c) water-washed/compatibilized DDGS green composites. . 98

Figure 4-6. The interface between DDGS and matrix in (a) and (b) non-washed DDGS,

green composites...... 99

Figure 4-7. A schematic of predicted reactions between polymeric matrix, PMDI and

DDGS...... 100

Figure 4-8. Schematic of crack propagation mechanism in green composite with (a) loose

and (b) strong interfacial adhesion between DDGS and matrix...... 101

Figure 4-9. Heat deflection temperature (HDT) of (a) neat polymers and their blend, and

(b) green composites. (A) polymeric matrix PHBV/30%PBS, (B) non-washed DDGS

green composite, (C) water-washed DDGS green composite, and (D) water-

washed/compatibilized DDGS green composite...... 103

Figure 4-10. Storage modulus versus temperature plots for (a) neat polymers and their

blend, and (b) green composites of PHBV-based matrix and 30 wt. % DDGS...... 104

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Figure 5-1. The chemical structure of PHBV, PBAT and PMDI...... 115

Figure 5-2. The axial forces generated during processing of Enmat/w-DDGS (80/20) biocomposites containing different amounts of PMDI/corn oil...... 122

Figure 5-3. FTIR spectra of (a) w-DDGS, PMDI, corn oil, and (b) selected

biocomposites...... 124

Figure 5-4. FTIR spectra of the Enmat and some biocomposites. (a) 4000-2600 cm-1, and

(b) 2200-1300 cm-1...... 126

Figure 5-5. Tensile properties of the biocomposite formulations ...... 129

Figure 5-6. Flexural properties of the biocomposite formulations ...... 130

Figure 5-7. Notched Izod impact strength of the biocomposites formulations; the neat

Enmat matrix showed a non-break behavior in notched Izod impact test...... 132

Figure 5-8. Melt flow index of the biocomposite formulations...... 133

Figure 5-9. Dynamic mechanical analysis (DMA) curves of neat Enmat polymer and

selected biocomposites, (a) storage modulus, and (b) Tan δ...... 136

Figure 5-10. Parameter of interaction, A, between w-DDGS and matrix calculated for selected biocomposite formulations...... 137

Figure 5-11. Scanning electron microscopy (SEM) images of the w-DDGS–Enmat interface. (a) Enmat/w-DDGS (80/20); (b) Enmat/w-DDGS/PMDI (80/20/1); (c)

Enmat/w-DDGS (80/20), higher magnification, and (d) Enmat/w-DDGS/PMDI (80/20/1), higher magnification...... 139

Figure 5-12. Scanning electron microscopy (SEM) images of the PBAT–PHBV interface.

The images show (a) and (b) neat Enmat; (c) and (d) Enmat/w-DDGS (80/20); and (e)

and (f) Enmat/w-DDGS/PMDI (80/20/1) biocomposites...... 141

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Figure 5-13. Schematic presentation of the crosslinking reactions occurring at the w-

DDGS–matrix and PBAT–PHBV interfaces as a result of compatibilization with PMDI

during reactive extrusion ...... 142

Figure 5-14. Water absorption results of neat Enmat polymer and selected w-DDGS

biocomposites...... 144

Figure 6-1. The schematic of the design of experiments in the present work...... 156

Figure 6-2. The main effects plots (left) and interaction plots (right) of the variable

factors for all responses...... 159

Figure 6-3. Normal probability plots of residuals for all responses...... 164

Figure 6-4. Residual plots versus fitted values for all responses...... 167

Figure 6-5. Residual plots versus variable factors...... 169

Figure 6-6. 3-D surface plots and 2-D contour plots of all responses in the studied domain

of the factors...... 171

Figure 6-7. The overlaid contour plots of all responses which highlights the domain of the studied factors to attain the desired response values...... 172

List of abbreviations and defined terms

2-D Two dimensional 3-D Three dimensional α Conversion degree A Pre-exponential factor (in thermogravimetric degradation equation) A Interaction parameter or adhesion parameter (in dynamic mechanical analysis) a Equation constant (in regression model) ABS Acrylonitrile butadiene styrene ADF Acid detergent fiber Adj MS Adjusted mean squares Adj SS Adjusted sums of squares ANOVA Analysis of variance AOAC Association of Official Analytical Chemists AOCS American oil Chemists Society ASTM American Society for Testing and Materials ATR Attenuated total reflection C Carbon C Corn oil (in regression model) CO Carbon monoxide

CO2 Carbon dioxide DDG Dried distillers’ grains DDGS Dried distillers’ grains with solubles DF Degree of freedom DMA Dynamic mechanical analyzer DOE Design of experiments DTG Derivative thermogravimetric E Activation energy

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E' Storage modulus E'' Loss modulus EROI Energy return on (energy) investment EVA Ethylene-vinyl acetate F F-value (statistics) f(α) Reaction model function FAO Food and agriculture organization of the United Nations FM Flexural modulus FTIR Fourier transform infrared g/10min Grams per 10 minutes GPa Giga Pascal GRFA Global Renewable Fuels Alliance HCN Hydrogen cyanide HDPE High-density polyethylene HDT Heat deflection temperature HNCO Isocyanic acid HQP Highly qualified personnel IR Infrared IS Impact strength J/m Joules per meter KV Kilovolts L Litre m Mass MDI Methylene diphenyl diisocyanate MEDI Ontario Ministry of Economic Development and Innovation MFI Melt flow index min Minutes MPa Mega Pascal MRA Ministry of rural affairs N Nitrogen

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N2 Nitrogen gas

N2O Nitrous oxide NaOH Sodium hydroxide NBR Poly(butadiene-co-acrylonitrile) NCE Networks of Centres of Excellence NDF Neutral detergent fiber NSERC Natural Sciences and Engineering Research Council O Oxygen OECD Organisation for Economic Co-operation and Development OMAF Ontario Ministry of Agriculture and Food ORF Ontario Research Fund P PMDI (in regression model) P P-value (in ANOVA table) PBA Potybutylacrylate PBAT Poly(butylene adipate-co-terephthalate) PBS Poly(butylene succinate) PBSA Poly(butylene succinate-co-adipate) PE Polyethylene PECH–EO Poly(epichlorohydrin-co-ethylene oxide) PHA Polyhydroxyalkanoate PHBV Polyhydroxy(butyrate-co-valerate) PLA Poly(lactic acid) PMDI Polymeric methylene diphenyl diisocyanate PP Polypropylene PRESS Prediction error sum of squares PU Polyurethane PUP Polyurethane pre-polymer q Heating rate R Universal gas constant R Response (in regression model)

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R2 R-squared 2 R adj Adjusted R-squared 2 R pred Predicted R-squared RPM Rounds per minute RSM Response surface methodology SEM Scanning electron microscopy Seq SS Sequential sums of squares

SO2 Sulfur dioxide T Temperature Tan δ Loss modulus to storage modulus ratio TG Thermogravimetric Tg Glass transition temperature TGA Thermogravimetric analysis TS Tensile strength US United States USA United States of America UV Ultraviolet v Volume fraction w-DDGS Water-washed dried distillers’ grains with solubles wt Weight ε Error term (in regression model)

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List of publications

Peer-reviewed journal publications

Zarrinbakhsh N, Misra M, Mohanty AK, “Biodegradable Green Composites from Distiller's Dried Grains with Solubles (DDGS) and Polyhydroxy(butyrate- co-valerate) (PHBV)-Based Bioplastic”, Macromolecular Materials and Engineering, 2011; vol 296 (no. 11) pp 1035–1045. Zarrinbakhsh N, Mohanty AK, Misra M, “Fundamental Studies on Water- Washing of the Corn Ethanol Coproduct (DDGS) and Its Characterization for Biocomposite Applications”. Biomass and Bioenergy, 2013; vol 55, pp 251–259. Zarrinbakhsh N, Mohanty AK, Misra M, “Improving the Interfacial Adhesion in a New Renewable Resource-Based Biocomposites from Biofuel Coproduct and Biodegradable Plastic”, Journal of Materials Science, 2013; vol 48 (no. 17) pp 6025–6038. Zarrinbakhsh N, Defersha F.M., Mohanty A.K., Misra M. “A statistical approach to engineer a biocomposite formulation from biofuel coproduct with balanced properties”, Journal of Applied Polymer Science, 2014; vol 131 (no. 13) 40443, doi: 10.1002/app.40443 . Zarrinbakhsh N, Mohanty A.K., Fraser E., Hayward G., Misra M. “Novel Materials from Distillers’ Grains: a New Window for a Sustainable Bioethanol Industry”, Journal of Biobased Materials and Bioenergy, 2014: accepted for publication.

Conference Publications:

Zarrinbakhsh N, Misra M, Mohanty AK, “New Particulate Green Composites from Distiller's Dried Grains with Solubles (DDGS) and Bioplastics”, the 26th ASC Annual Technical Conference (the Second Joint US-Canada Conference on Composites), Montreal, September 26-28, 2011, Paper 1122. Mohanty AK, Zarrinbakhsh N, Misra M, “Green Composites from Co-Products of Biofuel Industries: A New Paradigm towards Value-Added Industrial Uses”,

the 18th International Conference on Composite Materials, Jeju Island, Korea, August 21-26, 2011. Zarrinbakhsh N, Misra M, Mohanty AK, “Biofuel Ethanol Industry Co-Product: New Applications”, Forest and Plant Bioproducts Division, Biobased Materials III: Value-Added Coproducts Session, AIChE annual meeting, October 16-21, 2011, Minneapolis, Minnesota, USA. Paper 566f. Mohanty AK, Vivekanandhan S, Zarrinbakhsh N, Misra M, “Improved Utilization of Co-Products from Biofuel Industries in New Biomaterials Uses: A Move towards Sustainable Biorefinery”, ANTEC SPE conference, April 2-4, 2012, Orlando, Florida, USA. Paper 1261406. Zarrinbakhsh N, Defersha FM, Mohanty AK, Misra M, "A Factorial Design of Distillers' Grains Based Biocomposites: A Path to Sustainability of Corn Ethanol", The 19th International Conference on Composite Materials, July 28- August 2, 2013, Montreal, Quebec, Canada.

Book chapter

Vivekanandhan S, Zarrinbakhsh N, Misra M, Mohanty AK, "Coproducts of Biofuel Industries in Value-Added Biomaterials Uses: A Move Towards a Sustainable Bioeconomy". In: Zhen Fang (ed.), "Liquid, Gaseous and Solid Biofuels - Conversion Techniques", InTech, 2013, Online open access publication, http://dx.doi.org/10.5772/55382.

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Chapter 1: Introduction

Abstract: In this chapter, we briefly review the structure of the thesis and provide a short description of each following chapters. The research problem related to this work is discussed followed by the hypothesis to address it. The objectives that are planned to be accomplished at the end of this work are presented next, and in the end, the significance of this project will be explained.

1.1. Structure of this thesis

This thesis has been prepared in several chapters, each of which presents a

separate but connected study which together make up an entire overarching research project. In the present chapter from the next subsection on, we will discuss the research problem related to the project, the hypothesis to address the research problem, the

objectives and milestones to examine the hypothesis, and finally the significance and

implications to be gained upon successful achievement of the objectives.

Chapter 2 presents a literature review of the current status of the biobased ethanol

industry on a global scale with additional focus on North America. The production of

distillers’ grains is also discussed in more detail followed by the past and present research

on different applications of distillers’ grains in the materials science and engineering

field.

Chapter 3 focuses on the characterization of distillers’ grains and the effect of

water-washing. The results are discussed with respect to compositional analysis,

thermogravimetric analysis and infrared spectroscopy. Also, a preliminary study on the

processing aspects and mechanical performance of biocomposites of as-received and

water-washed distillers’ grains with poly(butylene succinate), PBS, is presented.

Chapter 4 depicts the analysis of biocomposites composed of water-washed

distillers’ grains and a stronger polymeric matrix based on polyhydroxy(butyrate-co-

valerate), PHBV, with a special focus on the effect of compatibilizer on mechanical and

thermomechanical properties. Scanning electron microscopy (SEM) images are included

for additional detail. The low impact strength of the biocomposite produced in this study provided the motivation for conducting the next step of the project.

Chapter 5 reports on an investigation of high-impact strength biocomposites of distillers’ grains with a polymeric matrix based on poly(butylene adipate-co- terephthalate), PBAT. The effects of additives such as compatibilizer and lubricant on mechanical, thermomechanical and physical properties of the biocomposite are examined. The discussion is augmented with infrared spectroscopy and SEM images which illustrate the concepts presented.

Chapter 6 provides an in-depth statistical approach applied to the study of Chapter

5. A design of experiment and the response surface methodology are implemented to optimize the formulation of the high-impact biocomposite for the amount of compatibilizer and lubricant. The optimization is attained with respect to balanced mechanical and physical properties of the biocomposite.

Lastly, we present an overall conclusion for this project in Chapter 7 along with a few ideas for future works in this area.

1.2. Research problem

The purpose of this project is related to the sustainability of the corn ethanol industry. The industry has expanded rapidly in recent years to increase ethanol output that has simultaneously generated surplus amounts of ethanol’s main coproduct, distillers’ grains. However, the outlets of distillers’ grains have not been expanded beyond their traditional usage in animal feed ration and this raises the high possibility of saturation in this market. Long-way transportation or exporting of distillers’ grains are not 3 substantially profitable plus distillers’ grains can spoil quickly in improper storage conditions making it advantageous to consume them locally.

Seeking new applications for distillers’ grains could be threefold beneficial. First, it can address the concern pertaining to the saturation of feed market for distillers’ grains; second, it can reduce the accumulation of distillers’ grains and mitigate the issue of environmental impact of the corn-ethanol industry; and last but not least, it may add value to this ethanol coproduct if high value applications can be created. Thus, economic viability and environmental sustainability of the corn ethanol industry can be addressed through these efforts.

1.3. Hypothesis

It is hypothesized that distillers’ grains have the potential to be found useful in the field of polymer and composite materials. Their functionality will be investigated through utilization as filler/reinforcement in polymeric biocomposites whose performance can be tailored in by optimizing the material’s formulation.

1.4. Objectives

Upon completion of this project, we expect to accomplish:

characterizing distillers’ grains for their physical properties and evaluating their

potential as filler in producing biocomposites,

investigating different green biocomposites of distillers’ grains with bioplastics

which have not been explored so far for their mechanical and physical properties,

producing a green biocomposite of distillers’ grains and bioplastics with

acceptable physical and mechanical performance, and

optimizing the final biocomposite formulation via a statistical approach.

1.5. Significance

Regardless of whether the objectives of this research are met completely or partially in the end, it will help draw a picture of potentials and limitations of distillers’ grains for biocomposite production, providing a more comprehensive knowledge base than what currently exists in the literature. It can also fundamentally be considered as a positive step towards the development of alternative applications of distillers’ grains and hence to the sustainability of the corn ethanol industry.

Moreover, the knowledge gained through this project may be implemented to produce an expanded array of distillers’ grains biocomposites that can be tailored in performance for use in different industries such as consumer products, packaging, automotive, etc., either from biocomposite systems studied directly in this research or from distillers’ grains biocomposites with other bioplastic systems.

Finally, the research conducted seeks to advance the environmental friendliness of plastic materials. Utilizing a biomass such as distillers’ grains in polymeric biocomposites means reducing the usage of plastics and the consequent end-life product waste. Furthermore, the bioplastics used in this project are biodegradable (i.e. compostable) and are partially sourced from renewable resources. These factors all aim to lead to the development of materials that will consume less petroleum, waste less energy, and send less material to landfills.

Chapter 2: Literature Review about the Current Status of Corn- Ethanol Industry and the Research on Distillers’ Grains in the Field of Materials Science and Engineering∗

Abstract: Growing global population, increased energy demand, and depleting petroleum resources; whether these factors pose a challenge for the future depends on the sustainability of today’s small but growing alternative energy industries. In this context, biofuel, but especially the corn-based bioethanol industry, has expanded rapidly in recent years. The industry has passed through several ups and downs and new revenue streams must be sought in order to maintain economic viability. The coproducts of ethanol represent excellent candidates for generating new revenues for alternative energy systems. In particular, the focus of this review is on distillers’ grains, the major coproducts of the bioethanol and the potential they have to create new value added products that may promote a more sustainable bioethanol industry. Several attempts have already been made to develop novel applications for distillers’ grains, alternative to their traditional feed uses, which are discussed briefly herein. More specifically, this review will focus on the role of distillers’ grains within polymer science and engineering. Although this field is still taking shape, there exist several potential opportunities for using distillers’ grains-derived novel materials and distillers’ grains polymeric biocomposites. The purpose of this paper is to critically review these opportunities to provide a clearer insight into the future of this industry.

∗ A version of this chapter has been accepted for publication in: Zarrinbakhsh N, Mohanty A.K., Fraser E., Hayward G., Misra M. “Novel Materials from Distillers’ Grains: a New Window for a Sustainable Bioethanol Industry”, Journal of Biobased Materials and Bioenergy (2014). 6

2.1. Renewable resource-based ethanol scenario

Planet Earth will be hosting 9-10 billion human beings by 2050 [1] and fulfilling the food and energy demand of this population is a major concern. This means that, to be sustainable, agricultural productivity must rise and depleted fossil fuels have to be replaced with renewable ones. Humankind has sought to find the solution to these issues mostly out of one of its most readily available resources, the land. While traditionally land has been used for food and feed production, today our farmland also provides valuable sources of fuel [2]. A key driving force for such a move are governmental policies and mandates across the globe such as in the USA, Brazil, Canada, China,

Argentina, Colombia, the European Union, France, Germany, India, Indonesia, Malaysia,

Thailand and Australia [3].

This, naturally, has raised conflicts and created challenges. Especially regarding corn-based ethanol, biofuel has always been debated critically to justify two main aspects: the government subsidies used for their production, and using food supplies to produce fuel [4]. Additionally, the energy-return-on-investment (EROI) of corn ethanol is lower compared to other renewable sources of energy such as solar and wind, or even sugar-based ethanol [5]. As a result of these factors, further expansion of grain-based ethanol is not predicted to be significant for the current decade though the world total ethanol production is projected to increase rapidly within the same timeframe (Figure

2-1), as published by the OECD–FAO (Organization for Economic Co-Operation and

Development–Food and Agriculture Organization of the United Nations) in the

Agricultural Outlook 2011-2020 [6].

200 (1) Coarse grains ethanol (2) Total 180 160 (2) 140 120 100 80 (1) 60 Production (Bnl) 40 20 0 2010 2012 2014 2016 2018 2020 2022 Year

Figure 2-1. The global total ethanol production (in billion litres) and the contribution of coarse grain ethanol towards it. The graph was drawn by taking data from OECD-FAO Agricultural Outlook 2011-2020 StatLinks (See refernce [7]).

All these issues are driving the use of renewable resource-based ethanol from

first-generation sources (grain and sugar) towards second-generation sources (cellulosic).

Cellulosic matter from wood waste, agriculture residues and perennial grasses as the

source for ethanol production is believed to be a major improvement as it reduces

possible conflicts between “food vs. fuel”, so long as non-food and marginal lands are used to produce the cellulose [8]. Using cellulose also provides a higher EROI than first- generation ethanol [9].

The shift to second generation ethanol is already under way and today and corn ethanol plants are trying to adopt ways of producing ethanol from cellulosic biomass.

However, this transition is challenging. Based on the current status of the bio-based ethanol industry, the grain-based ethanol in North America and the sugar-based ethanol in Brazil are still expected to be the largest source of bio-based ethanol for at least

another decade [10]. As illustrated in Figure 2-2, although the contribution of coarse

grains (mainly corn) to global ethanol production likely to be reduced from 52.3 to 42.9%

in the 2010-2022 period, cellulosic ethanol share is expected to increase to 10.1% of the world’s bioenergy by 2022 [11].

2010-12 2022 13.0% 10.3% 0.2% 10.1% 7.7% 52.3% 42.9% 2.5% 6.5%

2.4%

24.3%

27.9%

Coarse Grains Sugar crops Wheat Molasses Biomass Other

Figure 2-2. The evolution of renewble feedstock contribution towards global ethanol production from 2012 to 2022. The graph was drawn by taking data from OECD-FAO Agricultural Outlook 2013-2022 StatLinks (See reference [11]).

Therefore, adapting the next generation ethanol technology is not going to happen in the near future. Moreover, despite the slowly rising rate of production, ethanol from coarse grains (mainly corn) is still estimated to increase by 21% from 56.26 billion litres in 2011 to 68.19 billion litres in 2020 (See Figure 2-1). This suggests that the sustainability of first-generation ethanol is to be a topic of great importance for many years to come.

2.2. Ethanol production and its coproducts supply in North America

Corn-based ethanol is mostly produced in North America. As reported by the

Alternative Fuels Data Center of the US Department of Energy from the data gathered and published by F.O. Licht, the United States and Canada produced 63.1% of the global ethanol in 2012 [12] (Figure 2-3). More than 95% of the ethanol in the US and 68% in

Canada is produced from corn as the feedstock [13,14]. Also, another 3.9% of ethanol in the US is produced by factories that use corn feedstock along with either sorghum or barley. As a result, ethanol bioenergy plants in the US are concentrated in the central to

the north and north east states where corn production is also concentrated (Figure 2-4).

25.6%

5.4%

2.5% 2.1% 1.8%

3.4% 1.0% 0.3% 61.0% 0.2% 0.1%

USA Brazil Europe China Canada Asia (except China) South America (except Brazil) Australia Africa Mexico & Central America

Figure 2-3. The world ethanol production by country in 2012. The graph was drawn by taking data made available by Alternative Fuels Data Center, a resource of the U.S. Department of Energy's Clean Cities program, at: http://www.afdc.energy.gov/data/ (See reference [12]).

Figure 2-4. Production distribution of (a) corn cob (tonnes per year) and (b) ethanol (million gallons per year) in the USA. Maps were developed and made available by National Renewable Energy Laboratory, a laboratory of U.S. Department of Energy, at: http://maps.nrel.gov/biomass (See reference [15]).

Different coproducts of ethanol are produced based on the production technology.

Originally, wet mill plants were the major ethanol producers in the US. However, with

the development and modification of a “corn dry-grind production process”, dry mill ethanol plants expanded and eventually became the main part of the ethanol production body since they were less expensive to build and yield slightly more ethanol compared to wet mills [16]. As a result, dry mills have grown since 2001 when they produced 36% of

US ethanol to 2010 when they produced 89%. .

Figure 2-5 depicts a schematic of production of ethanol and coproducts in a dry mill plant. Carbon dioxide and distillers’ grains are the main two coproducts that are produced during and after fermentation of the grain’s starch. Distillers’ grains are the yellowish, particulate, non-starchy portion of corn left after the fermentation of the starch

(Figure 2-6). Their composition includes protein, fiber, fat, residual starch, water- solubles, moisture, and ash which provides a good source of nutritious components for livestock diet [17]. They are usually dried and sold at a low cost as “dried distillers’ grains (DDG)” (when contain no water-solubles) and as “dried distillers’ grains with solubles (DDGS)” when they contain water-solubles. In the dry mill plants, producing 1 litre of ethanol generates almost 0.7 kg of DDGS [18]. Thus, as ethanol production has risen in North America, so too has the quantity of DDGS; Figure 2-7 shows how distillers’ grains production in the US has increased almost 6 times from 5.8 million tonnes in 2003 to 34.4 million tonnes in 2012 [18].

Starchy grain Dried grains are ground (mainly corn) Grinding into flour called meal. ¾ Meal is soaked in water. ¾ Chemicals and enzymes are added to reduce Meal Slurrying theviscosity.

Mash is heated between 110-125 Mash Cooking °C for 15 minutes to reduce bacteria levels.

¾Mash is cooled to 85-89 °C Additives such as active dried and held for 45 minutes. yeast, enzymes, antibiotics, urea ¾ Additional enzymes are Liquefaction and Fermentation and antifoams are added and added to reduce the viscosity Saccharification kept at approximately 32 °C for and to break down the starch a period of40 to 75 hours. into simplesugars.

Beer (ethanol CO2 13 vol%, water and grain fibre)

¾Ethanol boils at a lower temperature and rises to thetop ofthedistillation column. Distillation ¾Water and the remaining grain fibre are collected at the bottom of the column. Whole stillage or spent mash (water and grain fibre) Ethanol

Centrifugation

Thin stillage Wet cake or Wet (8% solid) Distillers’ Grains (WDG) (30% solid) Evaporator

Dryer

Syrup or Condensed Distillers’ Solubles Dried Distillers’ Grains (CDS) (35% solid) (DDG) (90% solid) Dryer

Dried Distillers’ Grains with Solubles (DDGS) (90% solid)

Figure 2-5. Schematic of production of ethanol and its coproducts in a dry mill plant. The figure was drawn based on the process description at Canadian Food Inspection Agency website: http://www.inspection.gc.ca/animals/feeds/regulatory-guidance/rg-6/eng/1329275341920/1329275491608 (See reference [19]).

Figure 2-6. Digital image of the yellowish, particulate appearance of dried distillers’ grains with solubles.

45 40 35 30 25 20 15 Million tonnes 10 5 0 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 Year

Figure 2-7. Distillers’ grains production in the US during 1999-2012. The graph was drawn by taking data from Renewable Fuels Association website: http://www.ethanolrfa.org/pages/industry-resources- coproducts (See reference [18]).

2.3. Corn ethanol sustainability: the role of coproducts

The sustainability of corn ethanol has always been debated in different aspects.

Corn ethanol has very much been criticized for its low net energy balance the calculation of which is very sensitive to the allocation of corn ethanol coproducts. As reported by

Hill et al. [20], ethanol from corn exhibits a small positive net energy balance of almost

25 percent more than the input energy used for its production and this energy credit

basically comes from the distillers’ grains, the coproduct of ethanol. Therefore, part of

the input energy to produce ethanol can be counterbalanced by the fact that ethanol’s coproducts, such as distillers’ grains, can replace other products that need energy to be produced, such as corn in animal feed ration [21].

On other hand, corn ethanol is dependent on corn production and price which are affected by irrigation and hence vulnerable to drought. In this regards, the droughts that happened in 2008, 2011 and 2012 illustrate how quickly corn price can skyrocket [22].

This can change the entire logic of ethanol industry and also make it dependent on not only government energy subsidy but also government corn subsidy [22]. The same events have thrown the future of the subsidy system into question, too.

All in all, in order to have a higher net energy gain for corn ethanol, to reduce the vulnerability of this industry to corn production and price, and to decrease the dependence on government subsidies, it is absolutely essential to seek value-added applications for the corn ethanol coproducts, i.e. CO2 and distillers’ grains, and develop

new revenue streams out of them.

Carbon dioxide can be used for the beverage and dry ice markets, as well as some

medical applications. However, the raw CO2 produced in the ethanol plant needs refining

and the additional capital cost for this process is not justified to be done by the ethanol

plant [23]. A new, more effective idea to utilize CO2 from ethanol production involves

injecting it into greenhouses built next to the ethanol plants as a way of stimulating fruit

and vegetable growth. Initiated by GreenField Ethanol in Chatham, Ontario, Canada, the

CO2 along with the waste heat generated by the plant will be used to grow tomatoes in such facilities [24]. While this system shows potential, it is too preliminary to know whether such co-production is economically viable in many places.

With regards to distillers’ grains, there are commercial and potential opportunities

which are going to be specifically discussed in the next section.

2.4. Distillers’ grains applications: commercial and potential

Distillers’ grains have been traditionally used as animal feed and this is as yet the

sole commercial application for it. Although distillers’ grains have been studied for many

species, including dairy cattle [25], beef cattle [26], swine [27], broiler [28], laying hen

[29], turkey [30], lamb [31], catfish [32], tilapia [33], trout [34] and prawn [35], the only

species to which distillers’ grains are practically fed are beef cattle, dairy cattle, swine

and poultry [18]. Distillers’ grains are partially blended with other feeds to make up an

animal’s ration according to federally approved guidelines (e.g. in Canada these

guidelines are set by the Canadian Food Inspection Agency while in the USA it is the

U.S. Department of Agriculture). Normally, animal rations contain no more than 50%

distillers’ grains [19]. However, with the huge expansion of corn ethanol, the domestic

distillers’ grains market in the United States is near saturation [18] and offers bio-

refineries relatively low returns. As such, the bioenergy industry has been searching for

additional uses for distillers’ grains, and with its low cost (~$0.20-0.25 per kg [36]), it has always been considered for new outlets with the aim of value-addition.

One option involves using distillers’ grains as an energy source via combustion or gasification on site at bioenergy plants [37-42]. Using ethanol coproducts to generate heat

and electricity in a dry-mill plant is reported to improve the amount of renewable energy

per unit of input fossil fuel energy three times in comparison with cases where natural gas

is used [41]. In these cases, however, necessary steps need to be taken after distillers’

grains combustion to control and reduce the amount of polluting emissions including CO,

SO2 and more importantly NOx due to high protein content of the coproduct [42].

Distillers’ grains have also been investigated for possible human food applications

such as blended food (distillers’ grains with corn-soy-milk) [43-45], bread and cookies

[46-52], and spaghetti [53]. The studies show that the acceptable inclusion amount of

distillers’ grains is limited up to approximately 20% depending on the product. Increasing

the amount of the ethanol coproduct in the food product involves challenges such as poor or unacceptable quality and darker color [44], fermentation flavor [45], and decline of textural quality and batter elasticity [47,53]. For these undesired outcomes, distillers’ grains have not got into human food market successfully.

Distillers’ grains have shown potential as a soil fertilizer and as an herbicide, too.

It has been reported that distillers’ grains can be good soil amendments since they supply

nutrients and they are no greater a source of N2O emissions than conventional fertilizers

[54]. As such, DDGS has been considered as a good fertilizer for growing corn [55-57]. It

has also reduced the emergence and growth of weeds when blended with the soil of

container-grown ornamental plants [58]. Distillers’ grains have also shown good absorption behavior to disperse oil in the open water or to remove oil from contaminated animals or objects [59]. Moreover, hexane-extracted distillers’ grains have an odor- reducing characteristic and could potentially be used as a biodegradable cat litter [60].

Another emerging application of distillers’ grains is in novel materials and polymeric biocomposites reviewed in the next section.

2.5. Distillers’ grains applications in polymer science and engineering

2.5.1 Distillers’ grains-derived novel materials

Distillers’ grains, with their multi-component chemical composition, offer many opportunities for further enhancement as a whole or as a resource from which to extract useful components. For instance, several reports are available on how fiber [61-64], oil

[65-67] and zein (a variety of protein) [68] can be extracted from distillers’ grains and how these components can be further used to produce thermoplastic films, biodiesel, or binders.

Alternatively, many publications describe distillers’ grains being used as the precursor to produce new materials. A bioadhesive has been produced by reacting dried distillers’ grains with solubles (DDGS) with a base solution [69]. The reaction was performed in a pressure cooker at or above ambient pressure. The reaction products were filtered and the acquired solution was evaporation concentrated to create a dark, viscous adhesive product. The resulting adhesive is specifically suitable as boxboard glue [69].

Yu et al. [70] have produced polyurethane from dried distillers’ grains (DDG) in a three-step method. First, DDG was liquefied in a process with optimized conditions regarding solvent type (ethylene carbonate and ethylene glycol) and amount, time, temperature (150-170 °C) and sulfuric acid catalyst concentration. The resultant of this methodology was biopolyol in the liquefied DDG which was then separated and purified after dilution, pH adjustment, filtration, and evaporation. Finally, the biopolyol formed a

crosslinked network through reaction with diisocyanate and turned into a flexible or rigid polyurethane foam depending on the crosslinking conditions. The product can be used for applications such as packaging or construction isolation.

Xu et al [71] have also reported a liquefaction method for DDGS using petroleum-derived phenol and methanol as solvents in the presence of inorganic catalysts.

The liquefaction has been conducted in a micro reactor under N2-pressurized conditions at high temperatures (200-450 °C). These experiments show that the highest liquefied

DDGS yield (97%) is achieved at around 300 °C in 5 minutes with a phenol/DDGS weight ratio of 2/1.

Hu et al. have produced thermoplastic films from dried distillers’ grains with solubles (DDGS) through two different types of treatments; acetylation [72] and cyanoethylation [73]. In both cases, prior to the treatments, the oil and zein (the main protein in corn) components of DDGS were extracted by ethanol using a Soxhlet apparatus under specific conditions. The extraction of oil and zein was carried out to retrieve these high cost components which can be used for high-value applications. Then, the zein-and-oil-free DDGS was acetylated or cyanoethylated using acetic anhydride or acrylonitrile, respectively, in the presence of solvent and catalyst under optimized time and temperature conditions. The thermoplastic films of treated DDGS were produced by compression molding. The acetylated DDGS films were prepared from the solvent- soluble portion of acetylated DDGS as well as from the total soluble and insoluble portions. Their observations showed that the former makes films of more clarity and transparency with a better thermoplastic behavior due to higher acetyl content. Similarly, thermoplastic films of cyanoethylated DDGS were prepared and evaluated for

mechanical performance in tensile tests. It was observed that by changing the

acrylonitrile to DDGS ratio, the mechanical performance of the film could be tailored. As

it is illustrated in Figure 2-8, by increasing the ratio, the produced thermoplastic film

loses strength but gains flexibility. The modulus of the films shows a similar trend, dropping from 3300 to 60 MPa when the acrylonitrile amount was increased.

750 50 (1) Tensile strength (2) Elongation at break 600 40 (1) (2)

450 30

300 20

150 10 Tensile Strength Strength (MPa) Tensile Elongaion at break (%) break at Elongaion 0 0 123456 Acrylonitrile to DDGS ratio

Figure 2-8. The tensile properties of cyanoethylated DDGS films as a function of acrylonitrile to DDGS ratio. The graph was drawn by taking data from the table reported by Hu et al. [73].

In another attempt, dried distillers’ grains (DDG) were derivatized by several

methods to get it functionalized with carboxylate groups [74]. Then, the derivatized DDG

was mixed with soy protein isolate to form electrostatic bonds and produce a

biodegradable plastic via casting methods. In Figure 2-9, different methods of derivatization of distillers’ grains as well as the tensile strength of samples made from 50 wt. % derivatized distillers’ grains and 50 wt. % soy protein isolate are demonstrated. It is seen that biodegradable plastics have been produced in this way displaying tensile strength of almost 10 MPa.

2 Tensile Strength (MPa) Strength Tensile

Method of derivatization

Figure 2-9. The tensile strength of plastics from protein and distillers’ grains derivetized with different methods. *No pellet suitable for measurements has been formed; **Pellets made of DDG soaked in aqueous NaOH solution (0.l M) before derivatization; ***Pellets made of DDG soaked in aqueous NaOH solution (1 M) before derivatization. The graph was drawn by taking data from the table reported by Schilling et al. [74].

2.5.2 Distillers’ grains polymeric biocomposites

A promising area of value-addition to distillers’ grains is polymeric biocomposites. Biocomposites have nowadays proven their stable and effective existence in a variety of markets from packaging and consumer products to automotive and high- tech products. Key driving forces for these materials are the volatility of petroleum prices and the concerns over petroleum depletion in a few decades. These have created a global move towards utilization of agricultural residues and biomass from renewable resources to completely or partially substitute materials from petroleum resources. This is where the efficiency of biomass has been evaluated and understood not only as filler, but as a reinforcing component.

Distillers’ grains were first thought as a potential filler in polymeric composite

materials because of their low cost. Then, it was realized that it can reinforce the polymer

matrix to some extent due to its fiber content as long as it is processed with polymers at the right temperature or undergoes appropriate pretreatment before processing.

Beneficially, distillers’ grains abundantly contain functional groups suitable for creating chemical bonds during reactive compounding with polymers in the presence of compatibilizers or coupling agents. This means the microstructure and performance of the distillers’ grains biocomposite can be tailored based on the requirements.

Research regarding distillers’ grains composites began less than 15 years ago. The literature available on this subject can be classified based on the polymeric matrix used.

Table 2-1 summarizes different peer-reviewed articles in this area. Also, there have been

several patents and patent applications filed during the last ten years describing material formulations and/or techniques that involve distillers’ grains (Table 2-2). These developments demonstrate the tendency of academia and industry to take distillers’ grains towards material applications.

Table 2-1. Peer-reviewed articles on distillers’ grains biocomposites

Polymeric matrix Article title Production method Ref.

Polyolefins PP and HDPE Mechanical properties of biorenewable Twin-screw [75] fiber/plastic composites extruder/injection molding PP Reinforcing thermoplastics with natural fibers Twin-screw [76] derived from biofuel byproducts extruder/injection molding HDPE Mechanical and thermal properties of high density Twin-screw [77] polyethylene – dried distillers grains with solubles extruder/injection molding composites Engineering plastics ABS Acrylonitrile butadiene styrene Twin-screw [78] (ABS)/lignocellulosic fiber biocomposite: effect of extruder/injection molding artificial weathering on impact properties Thermosets Phenolic resin Compression molding of phenolic resin and corn- Compression molding [79] based DDGS blends Phenolic resin Design properties for molded, corn-based DDGS- Compression molding [80] filled phenolic resin Phenolic-based Properties of distillers grains composites: a Compression molding [81] and wood glue preliminary investigation Polyurethane Renewable resource based biocomposites from Micro extrusion and [82] coproduct of dry milling corn ethanol industry and compression molding castor oil based biopolyurethanes Bioplastics PLA Mechanical and thermal properties of Batch mixing and [83] biocomposites from poly(lactic acid) and DDGS compression molding PLA Tensile strength, elongation, hardness, and tensile Injection molding [84] and flexural moduli of PLA filled with glycerol- plasticized DDGS PHBV/PBS Biodegradable green composites from distiller’s Micro twin-screw [85] blend dried grains with solubles (DDGS) and a extruder/injection molding polyhydroxy(butyrate-co-valerate) (PHBV)-based bioplastic PBS Fundamental studies on water-washing of the corn Micro twin-screw [86] ethanol coproduct (DDGS) and its characterization extruder/injection molding for biocomposite applications PBAT/PHBV Improving the interfacial adhesion in a new Micro twin-screw [87] blend renewable resource-based biocomposites from extruder/injection molding biofuel coproduct and biodegradable plastic PBAT/PHBV A statistical approach to engineer a biocomposite Micro twin-screw [88] blend formulation from biofuel coproduct with balanced extruder/injection molding properties PBAT Biodegradable green composites from bioethanol Micro twin-screw [89] co-product and poly(butylene adipate-co- extruder/injection molding terephthalate) PP: Polyproylene, PE: Polyethylene, HDPE: High density polyethylene, ABS: Acrylonitrile butadiene styrene, PLA: Poly(lactic acid), PHBV: Polyhydroxy(butyrate-co-valerate), PBS: Poly(butylene succinate), PBAT: Poly(butylene adipate-co-terephthalate)

Table 2-2. Patents and patent applications on distillers’ grains biocomposites

Publication No. Patent/application title Ref. US007625961B2 Biopolymer and methods of making it [90] US20050075423Al Biopolymer structures and components including column and rail system [91] US007332119B2 Biopolymer structures and components [92] US20070135536A1 Biobased compositions from distillers’ dried grains with solubles and [93] methods of making those US008299172B2 Biodegradable plastics [94] US20070036958A1 Composite material with grain filler and method of making same [95] US20090110654A1 Bio-plastic composite material, method of making same, and method of [96] using same US20100017347A1 Intelligent pallet [97] US20100210770A1 Elastomeric composite [98] US7786187B1 Mold resistant fiber-filled thermoplastic composites [99]

2.5.2.1 Peer-reviewed articles

2.5.2.1.1 Distillers’ grains biocomposites with polyolefins

Polyolefins were the first matrices into which distillers’ grains were incorporated.

Julson et al. [75] compounded up to 30 wt. % as-received dried distillers’ grains with

solubles (DDGS) with polypropylene (PP) and high density polyethylene (HDPE) and

evaluated the mechanical properties in comparison with similar biocomposites of other

biomasses including big blue stem grass, soybean hulls and pinewood. They used a twin-

screw extruder and an injection molding machine to produce the biocomposite materials.

The mechanical performance of only the polyolefin/DDGS biocomposites are illustrated

in Figure 2-10, based on the data tables reported by Julson et al. [75]. Among all four biomasses studied, DDGS biocomposites showed the least improvement in the tensile and flexural moduli with respect to the neat polyolefin matrix. Moreover, the tensile and

flexural strength of the DDGS biocomposites were less than those from the neat polyolefins. The biocomposites were also evaluated through impact testing. In this case, the addition of DDGS to PP led to a decreased impact strength when compared to neat PP

while the opposite was observed for HDPE-based DDGS biocomposites. Similarly,

DDGS biocomposites from PP and HDPE acted differently in melt flow index (MFI) test.

The PP-based DDGS biocomposites showed higher MFI than the PP control. In contrast, the addition of DDGS to HDPE resulted in a reduced MFI compared to the HDPE matrix.

The overall conclusion of that work indicated that DDGS may not be a suitable filler for polyolefins in the as-received form when no compatibilizer is used.

Tensile Tensile (a) strength (b) strength (MPa) (MPa) 80 50

60 40 30 Impact 40 Tensile Impact Tensile 20 strength 20 modulus strength modulus (J/m) (10×MPa) (J/m) 10 (10×MPa) 0 0

Flexural Flexural Flexural Flexural modulus strength modulus strength (100×MPa) (MPa) (100×MPa) (MPa) ( ) () HDPE( HDPE/20%DDGS) HDPE/30%DDGS() PP PP/20%DDGS PP/30%DDGS HDPE HDPE/20%DDGS HDPE/30%DDGS

Figure 2-10. Mechanical properties of the polyolefin-based DDGS biocomposites; (a) PP/DDGS and (b) HDPE/DDGS biocomposites. The DDGS amounts are on weight basis. Graphs were drawn by taking data from tables reported by Julson et al. [75].

In another work, the effect of two types of compatibilizer in a biocomposite system of 10 wt. % DDGS with PP, produced via twin-screw extruder and injection molding, was studied by Ulven and Fuqua [76]. The compatibilizers were maleated PP

(maleic anhydride grafted PP) and organo-silane. The results showed that the addition of

10 wt. % DDGS does not increase the tensile elastic modulus significantly in both compatibilized and non-compatibilized PP/DDGS biocomposites. Similar to the

previously reviewed work, the biocomposite with as-received DDGS showed lower

tensile strength compared to the neat PP. In the case of compatibilized biocomposites, the organo-silane compatibilizer showed no improvement in terms of strength while the

maleated PP increased it to the strength level of neat PP. The PP/DDGS biocomposites

were also tested for water uptake in boiling water for one hour. No significant change in

the gained weight of all samples with respect to the neat PP was observed.

Tisserat et al. [77] have investigated HDPE as the matrix for DDGS biocomposites. The biocomposite included 25 wt. % DDGS with or without

compatibilization and the compatibilizer used was maleated PE. Moreover, DDGS has

been used in as-received as well as solvent-treated form. Hexane and dichloromethane

were applied to extract oil and polar extractables from DDGS. In general, the solvent-

treated DDGS was better than as-received DDGS in terms of tensile and flexural

properties of the respective biocomposites (Figure 2-11). Additionally, the solvent-treated

DDGS biocomposites showed lower weight gain compared to as-received DDGS

biocomposites in a long term water absorption experiment. As illustrated in Figure 2-11,

this study has also depicted that the solvent treatment and compatibilization together are

very effective at maintaining the mechanical performance of the HDPE/DDGS biocomposites comparable or even superior to the neat HDPE matrix with one exception;

the notched impact strength of all DDGS biocomposites were lower than that of neat

HDPE and neither solvent treatment nor compatibilization created a significant change.

Tensile strength (MPa) 50 40 30 Tensile Impact 20 modulus strength (J/m) 10 (10×MPa) 0

Flexural Flexural modulus strength (100×MPa) (MPa) A B C D E

Figure 2-11. The effect of solvent treatment and compatibilizer on mechanical performance of the HDPE/25wt.%DDGS; A: neat HDPE (matrix), B: as-received DDGS biocomposite, C: compatibilized DDGS biocomposite, D: solvent-treated DDGS biocomposite, and E: solvent-treated and compatibilized DDGS biocomposite. The graph was drawn by taking data from the table reported by Tisserat et al [77].

2.5.2.1.2 Distillers’ grains biocomposites with engineering plastics

Acrylonitrile butadiene styrene is the only engineering plastic reported in the

literature used for distillers’ grains biocomposites [78]. The samples were prepared via

extrusion and injection molding. The study is focused on the impact strength of the

ABS/DDGS biocomposites exposed to artificial weathering (UV/condensation

conditioning). It was found that the impact strength of the ABS/DDGS biocomposites is

far less than neat ABS both before and after weathering conditioning. However, the

ABS/DDGS biocomposite showed higher retention of impact strength than the neat ABS

after exposure to a UV/condensation cycle of 168 hours.

2.5.2.1.3 Distillers’ grains biocomposites with thermosets

The thermoset polymers which have been used so far to produce distillers’ grains biocomposite are phenolic resins and polyurethane. Tatara et al. [79] studied DDGS biocomposites made with a Novolak type of phenolic resin in a wide range of as-received

DDGS content from 10 to 90 wt. %. The biocomposites were prepared through compression molding technique and the material was evaluated under tensile tests. As shown in Figure 2-12, it has been observed that the biocomposites became inferior in tensile yield strength, elongation and modulus as the amount of DDGS increased in the formulation. However, the biocomposites containing 25 to 50 wt. % DDGS showed reasonable mechanical performance. As for example, the phenolic resin-based biocomposite with 25 wt. % of DDGS showed yield strength of 19.4 MPa, Young’s modulus of 2.6 GPa and elongation of 0.8%.

35 3.5 (1) Tensile strength 30 (2) (2) Tensile modulus 3 (3) Elongation at break 25 2.5 20 (1) 2 15 1.5

10 (3) 1 5 0.5 Tensile modulus modulus (GPa) Tensile Tensile strength strength (MPa) Tensile Elongationbreak(%) at 0 0 0 102030405060708090100 DDGS amount (wt. %)

Figure 2-12. The effect of DDGS amount on tensile properties of phenolic resin/DDGS biocomposites. The graph was drawn by taking data from the table reported by Tatara et al. [79].

In Another work, Tatara et al. [80] precisely studied the effect of DDGS amount

and compression molding parameters on the mechanical and physical properties of a phenolic resin/DDGS biocomposite system. It was found that within the investigated range, pressure and temperature of compression molding have minimal effects on the mechanical properties of the studied compression molded biocomposites. However, both mechanical and physical properties were very much affected by DDGS amount from 0 to

75 wt. %. The tensile strength, Young's modulus, and elongation at break were reduced as the DDGS amount was increased while water absorption and biodegradability of the biocomposite increased. The utilization of a coupling agent has been pointed out by the authors as a way to optimize the properties of such a biocomposite system.

Alternatively, DDGS particles were bound together with wood and phenolic resin adhesives to produce biocomposites [81]. The samples were prepared by mixing DDGS and adhesive, spreading them in a Petri dish and finally compressing them with a 5-kg weight placed on them. Some samples were subjected to heat treatment at elevated temperatures. The resulting materials were intended for rapid prototyping applications that involves high adhesive levels and low pressures. DDGS was included as much as 25 and 50 wt. % and in two different particle sizes. The mechanical performance of the produced samples was evaluated in a 3-point bending test. In this case, the DDGS biocomposite with phenolic resin adhesive was easier to prepare and showed higher maximum stress and modulus compared to its counterpart with wood glue. The produced biocomposites were also evaluated for physical properties such as color for aesthetic aspects and water activity for durability aspects to explore more applicability of the new materials.

Thermoset biocomposites of DDGS with polyurethane have also been produced

[82]. The procedure consisted of three steps. Castor oil and isocyanate were stirred at 80

°C to form a polyurethane prepolymer (PUP). The PUP was then mixed with DDGS and

extruded in a micro-extruder at 50 °C to make a premix. The premix was finally

compression molded at 100 °C. The purpose of the study was to overcome the brittle

nature of compressed DDGS by introducing the PUP to the system and making the

biocomposite. Samples containing 25-50 wt. % PUP were produced and tensile properties

were measured. By increasing the PUP content, it was observed that the strength,

modulus and fracture toughness of the biocomposites were increased and the material

shows potential for real world applications.

2.5.2.1.4 Distillers’ grains biocomposites with bioplastics

In recent years, several attempts have been made to engineer sustainable biocomposite formulations from DDGS and bioplastics. Such biocomposites are of great importance for two reasons; either they can be produced almost completely from renewable resources or they can be biodegradable in compost conditions at the end of their life time. In some instances, the biocomposite may have both advantages. For

DDGS biocomposites, a variety of bioplastics have been used including poly(butylene

succinate), PBS [86], poly(lactic acid), PLA [83,84], poly(butylene adipate-co-

terephatalate), PBAT [89], polyhydroxy(butyrate-co-valerate)/poly(butylene succinate),

PHBV/PBS blend [85] and PBAT/PHBV blend [87,88].

DDGS has been characterized through compositional analysis, thermogravimetric

analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) [86]. Such

fundamental studies can be useful for the processing of DDGS with thermoplastics. This

has been investigated in PBS/DDGS biocomposite system [86]. The TGA examines the

thermal stability of DDGS which is of great importance during melt processing with

commodity thermoplastic polymers which is usually performed at temperatures between

160-200 °C. The TGA results indicated that the thermal degradation of DDGS has a multi-step mechanism due to the complex composition of DDGS. The low-molecular weight sugars, fermentation by-products and organic acids in DDGS composition are the first components that start degrading as the temperature increases. These components are usually considered as "solubles" in DDGS composition. Water-washing treatment of

DDGS proved to be an effective method to remove these thermally- less stable components and bring about a more thermally-stable filler for biocomposite applications.

As a result, the thermal degradation rate of water-washed DDGS was one fourth of that of as-received DDGS at 180 °C. Biocomposites of PBS with 30 wt. % DDGS in the as- received and water-washed forms were produced in a micro twin-screw extruder and injection molder. Two different temperatures of 160 and 190 °C were adopted for biocomposite processing. The results were conclusive in that addition of DDGS in either forms reduced the tensile strength, though the reduction in the strength occurred to a lesser extent when water-washed DDGS was used. Moreover, the tensile modulus was improved in both cases with a higher value obtained for water-washed DDGS biocomposite. The difference between mechanical performance of as-received DDGS and water-washed DDGS biocomposites were more prominent after processing at 190 °C. It has also been observed that the as-received DDGS creates excessive smoke during processing at higher temperatures and the respective injected samples had darker

coloration and poor surface quality. FTIR studies also bring more insight to understand the functional groups in DDGS composition. This knowledge can be useful for tracking the chemical bonds created due to either surface modification of DDGS prior to processing or in-situ compatibilization during biocomposite production.

PLA/DDGS biocomposites have been made through batch mixing at 180 °C, grinding and then compression molding again at 180 °C [83]. The effect of DDGS content from 20 to 50 wt. % on tensile properties was studied. Also, the effect of isocyanate compatibilizer (methylene diphenyl diisocyanate, MDI) in this system was investigated. DDGS was used without further treatment except grinding, and similar to previous studies, by increasing the DDGS amount, the tensile strength and modulus were decreased. For example, the tensile strength of the biocomposite of PLA and 20 wt. %

DDGS (PLA/20wt.%DDGS) was less than half of that for the neat PLA. However, the

MDI compatibilizer was found to be effective so that with the addition of 1% (based on the total weight of DDGS and PLA), the PLA/20%DDGS biocomposite showed a strength as large as that of neat PLA with even 25% improvement in modulus. The improved adhesion between DDGS particles and PLA with the addition of MDI compatibilizer was displayed by scanning electron microscopy (SEM) images. As seen in

Figure 2-13, further addition of compatibilizer resulted in reduction in performance again and the 1% MDI amount seemed to be an optimum value for the PLA/20wt.%DDGS biocomposite system being studied.

120 3 (1) Tensile strength (2) Tensile modulus 100 (2) 2.5

80 (1) 2 60

1.5 40 Tensile modulus modulus (GPa) Tensile Tensile strengthTensile (MPa) 20 1 -0.500.511.522.5 MDI amount (wt.%)

Figure 2-13. The effect of MDI compatibilizer on tensile modulus and strength of the PLA/20wt.%DDGS biocomposite. The graph was drawn by taking data from the table reported by Li and Susan Sun [83].

Clarizio and Tatara [84] investigated the possibility of producing PLA/DDGS biocomposite simply though injection molding of a premixture of PLA, DDGS and glycerol as the plasticizer. No coupling agent or compatibilizer was added in the system.

The premix was prepared physically and the goal was to justify whether or not the

extrusion step can be skipped from the production method of such biocomposites. Tensile

and flexural test bars were injected this way containing 20 to 80 wt. % of plasticized

DDGS. The study showed that addition of glycerol did not improve the strength, but

facilitated the injection molding of biocomposites with high level of DDGS filler (80 wt.

%). Addition of any amount of plasticized filler reduced the tensile strength, flexural modulus and surface hardness. All produced biocomposite showed an elongation at break of not more than 3%. This could be because of the brittle nature of the PLA matrix itself.

In addition to evaluating the mechanical performance of the injected biocomposites,

Clarizio and Tatara have demonstrated comparative plots of tensile strength and modulus of the their PLA/DDGS biocomposite as well as PLA biocomposites with other fillers

such as corn and wheat starch, sugar beet pulp or other PLA/DDGS works. The

comparison shows that the mechanical performance of their injected PLA/DDGS

biocomposites are consistent with other works which involve additional processing steps

such as plasticization, extrusion, pelletizing, drying, and/or other costly steps. However,

such steps sound necessary if biocomposites with improved performance are aimed to be

produced through reactive processing method in the presence of a compatibilizer or

coupling agent.

PHBV is another renewable resource-based polymer, which is produced

microbially and exhibits physical and mechanical properties very similar to

polypropylene. Due to the intrinsic brittleness of PHBV, a blend of this biopolymer with

30 wt. % of a tougher biopolymer, PBS has been produced to be used as the matrix for

DDGS biocomposites [85]. DDGS was added in as-received and water-washed form and the biocomposites of PHBV/PBS blend with 30 wt. % DDGS were produced via a micro twin-screw extruder and injection molder. Also, the effect of compatibilizer (polymeric methylene diphenyl diisocyanate, PMDI) in this biocomposite system was studied. The mechanical performance was evaluated in tensile, flexural and impact tests at room temperature and heat deflection temperature (HDT) and storage modulus measurements at elevated temperatures. It has been observed that the strength (tensile and flexural) of the as-received DDGS biocomposite was inferior to that of the neat PHBV/PBS matrix, but it increased when water-washed DDGS was used as the filler; finally upon addition of

PMDI compatibilizer, the strength was quite comparable to that of the neat matrix (Figure

2-14). The modulus of the biocomposites also showed an increasing trend from as- received DDGS to water-washed DDGS and to compatibilized DDGS biocomposite. The

improvement in interfacial adhesion after water-washing and compatibilization was observed under scanning electron microscope. Due to poor adhesion between as-received

DDGS and the matrix, the rigidity (or storage modulus) of the respective biocomposites at high temperatures were lower than that of the matrix and consequently the obtained

HDT values were also less. However, the water-washed DDGS and compatibilized

DDGS biocomposites showed improved storage modulus and HDT compared to the neat matrix. It should be noted that the water-washing and compatibilization applied in this biocomposite system were not so effective in improving the impact strength of the biocomposites and at the highest case (i.e. as-received DDGS biocomposite), not more than 25 J/m for impact strength was obtained. Similarly, the elongation at break was almost 3% for all biocomposites while it was 20% for the neat matrix (Figure 2-14).

70 (1) Flexural strength (2) Impact strength 3.5 (3) Elongation at break (4) Flexural modulus 60 3 50 (1) 40 2.5 (4) 30 2 (2) 20

Impact strength (J/m) strength Impact 1.5 Flexural strength (MPa) strength Flexural Elongation at break (%) break at Elongation 10

(3) (GPa) modulus Flexural 0 1 0 A1 B2 C3 D4 5 Composition

Figure 2-14. The effect of water-washing and compatibilization on mechanical performance of the (PHBV/PBS)/30wt.%DDGS biocomposite; A: neat PHBV/PBS blend (matrix), B: as-received DDGS biocomposite, C: water-washed DDGS biocomposite, and D: water-washed and compatibilized DDGS biocomposite. The graph was drawn by taking data reported by Zarrinbakhsh et al. [85].

As discussed so far, the toughness of the DDGS biocomposites was not the

focused mechanical performance, as much as strength and rigidity, for the newly

developed material such that the resulting biocomposites showed poor elongation at

break and impact strength. In many real world applications, this can be a limiting factor

for the biocomposite.

Therefore, in an attempt to produce a high-impact DDGS biocomposite, a blend

of PHBV with a very tough biodegradable polymer, PBAT, was used for the matrix [87].

The blend was a commercial material that resembles copolymer of polypropylene in

many aspects. Two additives were employed in this biocomposite system; PMDI

compatibilizer to improve the affinity between DDGS and the PBAT/PHBV blend

matrix, and corn oil lubricant as the processing aid and to enhance the melt flow index

(MFI) of the final biocomposite. DDGS in water-washed form was incorporated in the matrix at 20 wt. % level. It was observed that PMDI improves the interfacial adhesion between DDGS and the matrix as well as between PBAT and PHBV within the matrix so that the strength, modulus and impact energy were enhanced all at the same time (Figure

2-15). Although the addition of corn oil alone decreased strength and modulus to some extent, it created a synergism with PMDI helping to improve impact strength; as a result, biocomposites of 20 wt. % DDGS having an impact strength of more than 150 J/m were produced. MFI reduction was a consequence of PMDI addition in this biocomposite system so that an optimum amount of PMDI and corn oil needed to be found to achieve a formulation with a balanced property combination.

MFI (g/10min) 30

10 Tensile Impact strength 0 strength (MPa) (10×J/m)

PMDI/corn oil 0/0 0.5/0 Flexural modulus 0/3 (100×MPa) 0.5/3

Figure 2-15. The effect of PMDI compatibilizer and corn oil lubricant on selected mechanical and physical properties of the (PBAT/PHBV)/20wt.%DDGS biocomposites. The legend shows the percent of PMDI and corn oil based on the total weight of polymeric matrix and DDGS. The graph was drawn by taking data reported by Zarrinbakhsh et al. [87]).

For that, a statistical approach was employed to find such a formulation with

optimum amounts of PMDI and corn oil [88]. The approach consisted of a full factorial

design of experiment (DOE) and regression modeling followed by response surface methodology (RSM). In this approach, 2-D contour plots of tensile strength, flexural modulus, impact strength and melt flow index (MFI) were obtained from 3-D surface plots of the respective properties. Then, the contour plots were overlaid to highlight the formulation region with a desired combination of the aforementioned mechanical and physical properties. Generally, the studied biocomposite system showed balanced properties when PMDI and corn oil were added, respectively, around 0.5 and 3% based on the total weight of the DDGS and the matrix. This approach was found to be useful in predicting several formulations of DDGS biocomposite that potentially can be used in real world applications.

DDGS has also been compounded with PBAT alone [89]. Biocomposites of

PBAT and DDGS (20 and 30 wt. %) were prepared using a micro twin-screw extruder and injection molding machine. DDGS was used as-received as well as washed with water prior to processing. The results again concluded better mechanical and thermal

properties of biocomposites with water-washed DDGS compared to as-received one. The

study also focused on the biodegradability of this biocomposite system and the role of

DDGS in the biodegradation mechanism. The biodegradation experiment was performed

in an aerobic composting condition. The extent of biodegradation was calculated from the

measured CO2 released as a result of the consumption of the biocomposite by the

microorganisms in the compost over a 200-day period. It was observed that DDGS has a

biodegradation behavior very similar to the cellulose (standard reference material) while

PBAT degrades differently with a slower rate. With respect to the DDGS biocomposites,

it has been observed that the biodegradation is very much affected by the addition of

DDGS and the degradation behavior is more comparable to the DDGS than the PBAT

matrix. This suggests that DDGS in biocomposite is the preferred domain for the

microorganisms’ attack. These results indicate the suitability of such biocomposites for

composting after their lifetime.

2.5.2.2 Patents

Several patent applications has been filed explaining the use of coproducts including distillers’ grains in biocomposites. There have been four patents awarded so far in this area, three of which are more relevant to direct utilization of distillers’ grains.

Basically, the patents are not specific to distillers’ grains and involve a broad range of biomass. One example is the method of producing a “biopolymer” composition that is

formulated from a wide range of polymers (thermoplastic or thermoset, petro-based or

bio-based) and a wide range of fermentation coproducts from corn, wheat, sorghum,

barley, oat, rice, rye, etc. [90]. The “biopolymer” described in this patent may contain

0.01 to 95 wt. % of fermentation coproducts and be produced via different methods of

polymer compounding such as thermal kinetic mixer, extruding and high shear mixing

compounding. The compound can be shaped into articles by many methods described in

another patent [92]. Some product examples are lumber replacements, window and door

components, siding assemblies, and other structures.

Another patent describes derivatization methods of distillers’ grains through

several methods to facilitate electrostatic bonds when distillers’ grains are mixed with a

proteineous material [94]. More detail is provided in section 2.5.1 discussing a published

peer-reviewed article of the same work [74].

2.6. Conclusions and future perspective

The sustainability of the first generation ethanol industry is tied with finding new

uses of its coproducts and creating additional revenue streams for the industry. In this

regard, the research on the novel applications of distillers’ grains in polymer science and

engineering realm has already been started but is still in its infancy. So far, the potentials

of this coproduct of ethanol have been identified. Distillers’ grains, with their complex

chemical composition, are excellent low cost sources for obtaining different components

such as fiber, oil and zein that can be used by other industries as raw material. It has also

been treated to extract chemicals such as bioadhesive or biopolyol; the latter can be further crosslinked and turned into a polyurethane foam. Moreover, distillers’ grains have

been functionalized by certain chemical treatments and made more suitable for use in the production of thermoplastic materials.

Several attempts are published in the peer-reviewed literature and patents on utilization of distillers’ grains as low cost filler/reinforcing components in producing polymeric composites. Different polyolefins, engineering plastics, thermosets and biopolymers have been used as matrix materials and mechanical, thermal and physical properties of the resultant biocomposites have been reported. It has been realized that biocomposites of distillers’ grains in the as-received form show mechanical performance inferior to that of the neat matrix. This could be due to thermal degradation of the filler during processing at high temperatures or because of the poor interfacial adhesion between distillers’ grains and the polymeric matrix. Water-washing treatment is one method to remove soluble components and improve the thermal stability of distillers’ grains which can enhance the mechanical performance. However, distillers’ grains can still be worth using in the as-received form as long as the cost reduction benefits counteract the performance loss to an acceptable extent.

Compatibilizers and coupling agents have been implemented successfully to enhance the performance for the distillers’ grains biocomposites. Similar to other natural fiber biocomposites, improving the performance in some aspects may be accompanied by sacrifice in some other properties. Thus, an optimization study is required to develop a material formulation with balanced mechanical and physical properties.

There are also opportunities yet to be further explored. Distillers’ grains as filler/reinforcing components may be enhanced in performance by common surface treatments for natural fibers. These can include acetylation, mercerization, silane

treatment, etc. Such surface treatments may improve the interfacial adhesion between the

filler and the matrix, and/or increase the thermal stability of the filler. However,

implementing such approaches that involve additional steps in biocomposite production

should always be done with appropriate cost considerations. Moreover, with respect to distillers’ grains biocomposites which are biodegradable, it is helpful to study the effect of surface treatments or compatibilizers on the biodegradation of the biocomposite in compost conditions. Also, the literature on distillers’ grains biocomposites still lacks the rheological studies which are of great importance as far as processing and scaled-up production are concerned. Furthermore, suitability of this novel biocomposite to other processing techniques such as vacuum forming or sheet/profile extrusion has not yet been explored.

All these investigations and many others will be helpful in drawing a full picture of the potentials and limitations of novel distillers’ grains-derived materials and their biocomposites. This is a step forward in order to create value-added applications for distillers’ grains and help the sustainability of the corn ethanol industry.

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Chapter 3: Characterization of Dried Distillers’ Grains with Solubles (DDGS) and Effect of Water-Washing on it for Biocomposite Applications∗

Abstract: Dried distillers’ grains with solubles (DDGS), the main coproduct in the dry mill corn ethanol industry, is finding its way towards a reinforcing filler in polymeric composite applications. In such a journey, thermal stability of DDGS is a critical factor affecting both the temperature window of DDGS melt-compounding with polymers and the properties of the final biocomposite material. In this study, DDGS thermal stability was enhanced by washing with water and then used to fabricate biocomposites with poly(1, 4-butanediol succinate) (PBS). The thermal degradation of DDGS, before and after washing, was studied with thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses, showing up to 50 °C improvement in degradation onset temperature of DDGS after washing. Also, the degradation activation energies for water-washed DDGS were smaller than the respective values for as-received DDGS. Compositional analysis and infrared spectroscopy showed that the water-washed DDGS was higher in protein and fiber content compared to as-received DDGS. As a result of improved thermal stability of DDGS after water-washing, the DDGS burning during melt processing was highly prevented and the biocomposites processed at 160 °C and 190 °C showed similar tensile properties. On the other hand, for as-received DDGS biocomposites the tensile properties decreased as the processing temperature increased. Moreover, the increased fiber content of DDGS after water-washing resulted in biocomposites with higher tensile strength and modulus compared to as-received DDGS biocomposites.

∗ A version of this chapter has been published in: Zarrinbakhsh N., Mohanty A.K., Misra M. “Fundamental Studies on Water-Washing of the Corn Ethanol Coproduct (DDGS) and Its Characterization for Biocomposite Applications”, Biomass and Bioenergy. 55 (2013) 251-259. 50

3.1. Introduction

Dried distillers’ grain with solubles (DDGS) is the main coproduct of corn ethanol

from dry mill plants. It is the non-fermentable portion of corn remained after

fermentation and distillation processes. DDGS has a complex composition of nutritious

component including protein, fiber, lipid and solubles and as a result, it has been traditionally used as a low-cost animal feed [1].

DDGS is now attracting attention due to the fact that the corn ethanol industries

have expanded at an unprecedented rate in North America during the last decade and that

DDGS is produced approximately as much as ethanol on a mass basis. Consequently, a

tremendous increase was observed in the DDGS supply in North America in the last 10

years; from 2005 to 2010 alone, DDGS production jumped by 260% [2]. Such a growth

in DDGS production can be the result of the growing demand in ethanol production as well as the shift in corn ethanol production processes from wet to dry mill [3].

As such, it will be crucial to expand DDGS applications in order to help corn

biofuel industry remain economically viable [4]. Such new applications can possibly add

more value to this coproduct and bring benefits to the ethanol industry. In this context,

new areas of research have emerged including DDGS usage for value-added animal feed

[5], human food [6-10], energy production [11, 12], isolation of different components

such as zein [13], cellulose [14] and oil [15, 16], developing new thermoplastics by

acetylation [17], and last but not least, biobased filler in polymeric composite materials

which is reviewed below.

DDGS exhibits several advantages if considered for the biocomposite application.

The low cost of DDGS compared to a polymer matrix can help to reduce the cost of the final product. Additionally, DDGS contains fiber that can reinforce the matrix polymer.

Moreover, DDGS has a density of about 1300 kg m-3 [18] which is lower than inorganic fillers, glass fiber and most natural fibers [19]. This can be a positive point when specific strength and modulus (the ratio of the mechanical property of the composite divided by its density) are concerned. Finally, the DDGS’ complex composition can bring more benefit as far as compatibilization or plasticization is concerned. The chemical composition of major components including protein, fiber and fat are well understood and a wide range of functional groups are available for possible reactions with proper compatibilizers or plasticizers.

The published research on DDGS biocomposites can be categorized based on the matrix polymer used, which includes polyolefins [20], polyurethane [21], phenolic resin

[1, 22, 23] and biobased thermoplastics [24, 25]. Although some attempts reported poor mechanical performance of the studied DDGS biocomposites [1, 20, 22, 23], there are promising points recently reported about improving the mechanical properties of DDGS biocomposites [24, 25].

DDGS starts degradation at a temperature well below the regular processing temperatures for thermoplastics. In the previous work in our lab [25], we have emphasized the importance of thermal stability of DDGS during processing with molten thermoplastic in order to prevent DDGS degradation, obtain better affinity between

DDGS and thermoplastic matrix and apply compatibilizer effectively. In this regard,

DDGS water-washing prior to polymer melt processing was proven to be effective in

enhancing DDGS thermal stability. Following that, we are here studying the effect of

water-washing variables such as time and water amount on the thermal stability and

composition of DDGS with more detailed thermogravimetric and infrared measurements.

3.2. Experimental

3.2.1. Materials

Dried distillers’ grains with solubles (DDGS) from the corn ethanol industry was kindly supplied by GreenField Ethanol Inc., Chatham, Canada. The sample was in

particulate form of an average size of 500 µm with particles larger than 150 µm. The

biopolymer used in this study was Poly(1, 4-butanediol succinate) (PBS) manufactured

by Zhejiang Hangzhou Xinfu Pharmaceutical Co. Ltd. with the melting point of 110-120

°C.

3.2.2. DDGS waster-washing

DDGS was washed with tap water at room temperature. Table 3-1 summarizes the

washing conditions. Washing runs were done in a 0.2 L beaker. Two replicates for each

run were considered. In each run, approximately 10 g of DDGS was stirred in water with

a magnet stirrer. At the end, the beaker content was filtered through a polypropylene

screen with porosity size of 150 µm for easy and fast filtering. The yield after washing

was (73.9 ± 1.5) % compared to the original as-received DDGS weight depending on the

amount of water used for washing. Water-washing of DDGS for biocomposite processing

was performed in a 2 L beaker with 1.5 L water for 100 g of DDGS. Other conditions

were maintained the same.

Table 3-1. DDGS water-washing conditions

Time (min) 5 15 Water-to-DDGS ratio 5 5 (g.g-1) 15 15

3.2.3. Composition analyses

These analyses were performed by Agri-Food Laboratories, Guelph, Canada. The

samples were analyzed for moisture (AOAC 930.15), crude protein (AOAC 990.03), ash

(AOAC 942.05), fat (AOCS Ba 3-38), acid detergent and neutral detergent fibre (forage

analysis procedure of national forage testing association) as well as starch (enzymatic method).

3.2.4. Thermogravimetric analysis (TGA)

TGA experiments were performed by the TGA Q500 from TA Instruments. For each experiment, 15 to 20 mg of DDGS was used. The tests were done in a nitrogen environment with purge flow of 40 mL min-1 and temperature range of 20 to 600 °C. For thermal stability evaluation, non-dried samples were heated with a ramp rate of 20 °C

min-1. Degradation activation energy was obtained by heating with different ramp rates of

10, 20, 30 and 40 °C min-1. The samples for these experiments were dried in a vacuum

oven at 80 °C for 65 hours before TGA. Universal Analysis 2000 software, version 4.5A, from TA Instruments was applied to analyze the results.

3.2.5. Fourier transform infrared (FTIR) spectroscopy

An FTIR instrument from Thermo Scientific, model Nicolet 6700, was used for

infrared spectroscopy measurements. The samples were used in particulate form. The

measurements were done in attenuated total reflection (ATR) mode with 32 scans per

sample and a resolution of 4 cm-1. The results were analyzed using OMNIC Spectra

software from the same company.

3.2.6. Biocomposite fabrication and testing

The biocomposites of PBS and a mass fraction of 30% DDGS (as-received and

water-washed) were prepared by melt extrusion process in a 15-cm3 micro-extruder from

DSM Xplore, Netherlands, followed by injection molding using a micro-injector from the

same company. The mold had the shape of type IV tensile test bars complied with the

ASTM D638. The processing was conducted at two different temperatures of 160 °C and

190 °C. In all cases, the processing included feeding and melting of PBS for 60 sec

followed by feeding and compounding of DDGS for another 90 sec. The baseline

samples were also prepared with neat PBS at both temperatures for the total feeding and

melting period of 150 sec. The injected samples were tested for tensile properties

according to ASTM D638.

3.2.7. Statistical analysis

Analysis of variance (ANOVA) was applied to investigate the effect of the studied variables (time and water-to-DDGS ratio) on the thermal stability of DDGS.

Significance level was considered as 5%.

3.3. Results and discussion

3.3.1. Thermogravimetric analysis (TGA)

Thermogravimetric (TG) graph is well informative on how the material degrades

(loses mass) when heated. Similarly, derivative TG (DTG) graph provides useful

information regarding the degradation rate of different components of the material during

the temperature ramp.

Figure 3-1 shows the TG and DTG curves of DDGS before and after water

washing. The deviation in TG graphs of two samples is clear from approximately 130 °C.

Both DTG curves include the drying stage first (first peak). This stage is typical of the

TG graph of biomass material as also reported for DDGS [26], corn stover [27] and perennial ryegrass [28] and ranges from room temperature to more than 100 °C depending on the heating rate. This peak can also be partially due to volatilization of light

molecule compounds [26, 27].

The second stage is called active pyrolysis [27] or primary combustion [26] when

the test is performed under nitrogen or oxygen, respectively. Rapid mass loss of major

components of DDGS occurs in this stage from more than 100 °C (end of the first stage)

to around 500 °C. These components may include polysaccharides, hemicellulose,

cellulose, residual starch, oil, lignin, some protein components and phenolic acids, as

reviewed in [26].

The third stage of DDGS degradation (more than ~ 500 °C) under nitrogen is a

passive pyrolysis related to the slow mass loss. Such a stage has been reported for corn

stover possibly due to the thermal degradation of lignin or complex high-molecular 56

weight components [27]. We observed no more peaks in derivative TG curve of DDGS

under nitrogen in this stage up to 800 °C (results not shown here). However, the oxidative

degradation peak of lignin, char, some protein components and thermally stable

components like metals occur under oxygen in the third stage (residual combustion stage)

[26].

120 0.1

as-received DDGS ) washed DDGS -1 100 0.08

80 0.06 60 0.04 40 Mass fraction % fraction Mass

First stage 0.02 20 Third stage Second stage Derivative mass fraction % (min fraction mass Derivative 0 0 0 100 200 300 400 500 600 700 Temperature (°C)

Figure 3-1. Thermogravimetric (TG) and derivative thermogravimetric (DTG) curves (20 °C min-1) of DDGS before and after water-washing (washed for 15 min with water-to-DDGS ratio of 15) in nitrogen atmosphere. Different stages of mass loss are shown based on [26, 27].

As shown in Figure 3-1, two major DTG peaks appeared in the second stage for

both as-received and washed DDGS samples related to hemicellulose (lower temperature)

and cellulose (higher temperature) in DDGS. There are two shoulder peaks attached to

the left and right hand side of hemicellulose and cellulose peaks, respectively. As we have also shown elsewhere [25], the shoulder at right hand side of the hemicellulose peak

(120-220 °C) belongs to the degradation of the water-soluble components of DDGS.

These components may include mono- and oligo-saccharides (mainly from glucose and

xylose), fermentation by-products (glycerol and butanediol) and organic acids (lactic acid and succinic acid) [29]. Accordingly, the DTG curve of DDGS water-soluble portion includes several peaks which mainly occur in this shoulder range from 120 to 220 °C

[25]. The other shoulder peak attached to the right of the cellulose peak may be related to degradation of protein and release of HNCO, HCN and CO, as studied by Giuntoli et al.

[30] by TG-FTIR method. The degradation peaks of other components of DDGS such as oil, residual starch and lignin may be covered by the strong peaks for cellulose and hemicellulose.

It was observed that both hemicellulose and cellulose peaks were shifted to the

right, by 5 and 13 °C respectively, as a result of water-washing. This may be due to

dissolution of low-molecular weight xylans and glucans of hemicellulose and cellulose,

respectively, in water.

3.3.2. The effect of washing time and water amount

The main idea of enhancing the thermal stability of DDGS is to make it less

vulnerable to degradation when subject to high temperature of polymer melt processing.

For this, Both TG and DTG graphs are used here to evaluate the effect of the two

variables investigated in this study on the thermal stability of DDGS. As already seen in

Figure 3-1, the water-washing showed significant effect on the degradation onset

temperature and the degradation rate, especially in the temperature range in which

polymer melt processing is typically performed (160 °C to 200 °C) for commodity

thermoplastics such as polypropylene (PP) and polyethylene (PE) as well as biopolymer

thermoplastics such as polyhydroxyalkanoates (PHAs), poly(lactic acid) (PLA) and poly(butanediol succinate) (PBS).

For comparison, the values for the temperature attributed to the fractional mass loss of 5%, and also fractional mass loss (%) at 180 °C and the respective rate versus the washing variables are presented in Figure 3-2a-c. The mass loss values here are reported on a dry basis based on the mass remained after the drying stage (first stage).

It was observed that the water-washing increased the temperature at which fractional mass loss of 5% occurs. From 197 °C for as-received DDGS, this increment was observed to be of more than 40 °C and 50 °C in washed DDGS with water-to-DDGS ratio of 5 and 15, respectively (Figure 3-2a). Similarly, the thermal stability at 180 °C was enhanced after washing comparing the fractional mass loss (%) at this temperature for as-received and water-washed DDGS in Figure 3-2b. Accordingly, the degradation rate at this temperature for water-washed DDGS is approximately 4 times less than that of as-received DDGS as depicted in Figure 3-2c. This suggests that, compared to as- received DDGS, water-washed DDGS is able to withstand the high temperature for a longer time while compounding with molten polymer; or in other words, water-washed

DDGS experiences very less degradation at processing temperature for a given processing time.

Figure 3-2a-c also show the fact that increasing the washing time from 5 to 15 minutes did not change the thermal stability, while the water-to-DDGS ratio affected the

TGA results, statistically significant as analyzed by analysis of variance (ANOVA).

(a) 260 251.6 241.7 240 250.3 240.0 220

200 197.0 180

Temperature of fractional fractional of Temperature 0 5 10 15 20 mass loss ofd. 5 %,b. (°C) Water-to-DDGS ratio (g.g-1)

5 (b) 4 3.28 3

2 1.29 0.94

at 180 °C, d. b. 1 1.17 0.86

Fractional mass loss (%) loss (%) mass Fractional 0 0 5 10 15 20 Water-to-DDGS ratio (g.g-1) ) -1 (c) 2 1.72

1 0.66 0.42 0.63 0.40 0

Rate of fractional mass 0 5 10 15 20 loss (%) at 180 °C (min 180 at (%) loss Water-to-DDGS ratio (g.g-1)

as-recieived DDGS 5 min water-washed 15 min water-washed

Figure 3-2. The effect of DDGS washing time and water amount on (a) temperature of fractional mass loss of 5%, (b) fractional mass loss (%) at 180 °C, and (c) rate of fractional mass loss (%) at 180 °C. The respective values for as-received DDGS are also presented for comparison.

Table 3-2 is the ANOVA summary for the effect of washing time and water-to-DDGS

ratio on fractional mass loss (%) at 180 °C. As observed, the F-value calculated for the effect of water-to-DDGS ratio is greater than the percentage point of the F distribution

related to the assumed significance level (0.05), the numerator degrees of freedom (1)

and the denominator degrees of freedom (4). The opposite is true for the effect of

washing time. Similar results were obtained for the temperature of fractional mass loss of

5% and the rate of fractional mass loss at 180 °C (results not shown here).

However, from the engineering point of view, even washing DDGS with water- to-DDGS ratio equal to just 5 for only 5 min helps significantly enhance the thermal stability of DDGS for polymer melt processing and biocomposite applications.

Table 3-2. ANOVA table for the effect of washing time and water-to-DDGS ratio on fractional mass loss (%) at 180 °C

Source of variation Sum of squares Degree of freedom Mean square F0 F0.05,1,4 Time 0.019 1 0.019 6.25 7.71 Water-to-DDGS 0.221 1 0.221 72.94 7.71 Interaction 0.001 1 0.001 0.23 7.71 Error 0.012 4 0.003 Total 0.253 7

3.3.3. The effect of heating rate

TG and DTG graphs of as-received and water-washed DDGS with different

heating rates are shown in Figure 3-3 and Figure 3-4. Increasing the heating rate shifted the TG curve and DTG peaks to the right. Basically, the higher is the heating rate, the less time the sample has to reach to a uniform temperature which is limited by the heat transfer of the sample and purge gas. Thus, the degradation tends to occur at higher temperatures with higher heating rates. Moreover, as the heating rate increased, the degradation rate also increased. Similar trend in thermogravimetric results has been reported by other researchers [27, 31].

120 0.25 10°C min-1 )

-1 -1 20 °C min 0.2 100 30 °C min-1 -1 40 °C min 0.15 80 0.1 60 Mass fraction % fraction Mass 0.05

40 0 Derivative mass fraction % % (min fraction mass Derivative 20 -0.05 0 100 200 300 400 500 600 700 Temperature (°C)

Figure 3-3. Thermogravimetric (TG) and derivative thermogravimetric (DTG) graphs of as-received DDGS heated with different heating rates.

120 0.25 10 °C min-1 ) -1 20 °C min-1 0.2 100 30 °C min-1 40 °C min-1 0.15 80 0.1 60 0.05 Mass fraction % 40 0 Derivative mass fraction % (min 20 -0.05 0 100 200 300 400 500 600 700 Temperature (°C)

Figure 3-4. Thermogravimetric (TG) and derivative thermogravimetric (DTG) graphs of water-washed DDGS with different heating rates.

However, the total mass loss of both as-received and water-washed DDGS was

independent of heating rate and fixed at an average of (23.2 ± 0.3)% and (24.0 ± 0.3)%

for as-received and water-washed DDGS, respectively.

3.3.4. Activation energy of thermal degradation

The effect of water-washing on thermal degradation of DDGS can be also realized

from the change in degradation activation energy of this multi-component material. In

this study, we have calculated the activation energy based on multiple nonisothermal runs with different heating rates. In such an approach, the rate equation is written as [32]

dα A − E = exp( )dT (3.1) f (α) q RT where α and f(α) are the conversion degree and the reaction model, respectively, A is the

pre-exponential factor and E is the activation energy, q represents the heating rate and R

denotes the universal gas constant. The conversion degree at a given temperature (T) can

be obtained as α = (mi – mT)/(mi – mf), in which mi and mf represent the initial and final

mass, respectively, and mT is the mass at temperature T.

The integral form of the right hand side of equation (1) has no analytical solution.

Knowing the fact that the left hand side of the equation is constant for a given conversion

degree (α) and not dependant on the heating rate (q), Ozawa [33] applies Doyle’s approximation to derive the following simple equation

E log(q) = const −0.4567 (3.2) RT

This means that the plot of log(q) versus T-1 for a given value of α is a straight line, called isoconversional line, the slope of which gives the activation energy. In the isoconversional method, the process kinetics is studied through multiple single-step kinetic equations at different constant conversion degrees (α). Therefore, this method can detect complex multi-step processes when different activation energies are observed at different α values [32]. Such an approach sounds more appropriate for DDGS than single nonisothermal experiment since DDGS consists of several components which degrade at different temperatures with different activation energies and rates.

Using equation (2), we have plotted log(q) versus T-1 of as-received and water-

washed DDGS for a range of conversion degrees (Figure 3-5a and b). It can be seen that

the isoconversional graphs in both cases are well fitted to straight lines. The slope of

these lines changes as the conversion degree changes. This is due to multi-step

degradation of DDGS with multi-component composition.

Applying the linear regression by Microsoft Excel, the slope of the

isoconversional lines and the activation energy for each conversion degree was calculated

and presented in Table 3-3. It was observed that the activation energy values for as-

received DDGS are generally smaller than the respective values for water-washed DDGS,

especially for low conversion degrees which are associated with the temperature range of

polymer processing. For example, the conversion degree of 0.05 for as-received DDGS is

reached at 185 °C with the activation energy of 93 kJ mol-1, while for water-washed

DDGS, the respective values are 242 °C and 158 kJ mol-1.

(a) 1.6

1.4

1.2 log q

1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.15 0.1 0.05 α 0.8 1.30 1.55 1.80 2.05 2.30 1000T-1 (K-1)

(b) 1.6

1.4

log q 1.2

1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.15 0.1 0.05 α 0.8 1.35 1.50 1.65 1.80 1.95 1000T-1 (K-1)

Figure 3-5. Isoconversional graphs of (a) as-received and (b) water-washed DDGS.

Table 3-3. Activation energy values calculated from isoconversional lines and the respective temperatures for the heating scan of 20 °C min-1

α 0.05 0.1 0.15 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 as- E (kJ mol-1) 93 103 127 147 171 204 240 236 213 224 300.0 received T (°C) 185 221 245 259 279 296 319 340 368 399 436 DDGS water- E (kJ mol-1) 158 163 166 169 184 209 227 239 248 263 296 washed T (°C) 242 261 270 278 293 308 326 346 367 397 436 DDGSa a Washed for 15 min with water-to-DDGS ratio of 15.

3.3.5. Compositional analysis and infrared spectroscopy

The composition of DDGS before and after water-washing is presented in Table

3-4. The results clearly showed that DDGS became richer in protein and fibre content after removing water-solubles. Also, it was observed that the water-washing treatment

did not have a significant effect on the fat and starch content. Finally, the ash content of

DDGS was reduced after water-washing.

The structural carbohydrates of DDGS including cellulose and hemicellulose can

be estimated from the fact that NDF generally represents the cellulose, hemicellulose and

lignin contents altogether whereas ADF is a measure of cellulose and lignin [29].

Assuming that the lignin content of DDGS is not abnormally high, the ADF represents

mainly the cellulose content of DDGS which was increased from 19.14% to 28.91% after

water-washing; similarly the hemicellulose has been concentrated from 17.15% to

20.49%.

Table 3-4. The mass fraction (%) of DDGS components before and after washing on a dry basis

Sample As-received DDGS Water-washed DDGS Protein 30.99 35.76 Acid Detergent Fibre (ADF) 19.14 28.91 Neutral Detergent Fibre (NDF) 36.29 49.40 Fat 10.37 10.20 Starch 5.05 5.23 Ash 4.38 2.78

The FTIR spectra of as-received and water-washed DDGS are presented in Figure

3-6. The typical IR spectrum of DDGS consists of several peaks due to several

components composing DDGS including mainly protein, cellulose, hemicellulose, oil and water-solubles. Table 3-5 depicts the assignment of the major peaks in DDGS infrared spectrum.

1105 1631 2924 1027 615

2854 1741 3008 1531 as-rceived DDGS

1155 Absorbance

water-washed DDGS

4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm-1)

Figure 3-6. FTIR spectra of as-received and water-washed DDGS.

Table 3-5. Assignment of major peaks in DDGS infrared spectrum

Wavenumber Assignment range (cm-1)

O–H stretching in cellulosic components and water-solubles, and N–H stretching 3640-3040 in protein Asymmetric and symmetric stretching modes of =C–H and –C–H groups in 3400-2800 different components such as triglyceride of the oil [42] Stretching of the C=O group in triglyceride [42] as well as hemicellulose and 1800-1700 lignin [14, 41] Amide I (1631 cm-1) and amide II (1531 cm-1) bands of protein related to C=O and 1700-1500 C–N stretching and N–H bending absorptions [43-45] C–H and O–H bending, C–C and C–O skeletal vibrations in cellulosic component 1500-1200 [40] or C–O stretching and C–H bending in triglyceride [42] C–O vibrations (1105 cm-1) in organic water-solubles of DDGS. And C–O (C-6 1200-800 skeletal vibrations, 1030 cm-1) in cellulose [40, 41]

The FTIR spectrum of as-received DDGS in the range of 800-1200 cm-1 is very similar to that of polysaccharides as reported by [34] for cellulose, starch, xylan and pectin and also by [35] for different oligomers of glucose. The spectrum in this range mainly consists of two major peaks at 1105 and 1027 cm-1. Since the frequency of 1100

cm-1 is the base absorption value for C–O bonds [36], the major peak at 1105 cm-1 can be ascribed to the respective bond absorption in organic components composing the water- solubles of DDGS such as glycerol [37] glucose oligomers [35], xylans [38] and lactic acid [39]. Moreover, C–O (C-6 skeletal vibrations) in cellulose component is reported to occur at 1030 cm-1 [40, 41].

As far as peak occurrence is concerned, the FTIR spectra of as-received and

water-washed DDGS mainly differ in the region where the peak at about 1100 cm-1 is

removed after washing. Consequently, the low intensity peak appeared at 1155 cm-1 most probably assigned to the C–O asymmetric bridge stretching (C–O–C) in cellulose structure [40, 41]. The spectrum of water-washed DDGS in this range is very similar to that of cellulose extracted from DDGS reported by Xu et al. [14]. Moreover, after comparing the FTIR spectra of as-received and washed DDGS, it was seen that water- soluble portion of DDGS also exhibits another peak in the fingerprint region at 615 cm-1 due to deformations of the soluble molecules.

After water-washing, the relative intensity of the peaks related to the molecular structure of the protein (1500-1700 cm-1), cellulose and hemicellulose (800-1500 cm-1) increased with respect to the major fat-related peak (1740 cm-1). This shows an increase

in the protein and fiber content of DDGS after water-washing compared to its fat content,

as confirmed with the compositional analysis presented above. Thus, it can be mentioned

that no structural component, such as cellulose and hemicellulose, has been removed

from DDGS as a result of the applied washing treatment.

3.3.6. Biocomposite processing and testing

The effect of water-washing of DDGS in biocomposite application is important

from two aspects: feasibility of processing and mechanical properties of the final product.

To investigate the effect of DDGS thermal stability during melt processing, the

processing was performed at two different temperatures of 160 °C and 190 °C. The

biocomposites processed at 160 °C with both as-received and water-washed DDGS had

the brownish color (Figure 3-7), slightly darker for the as-received DDGS biocomposite

due to the higher tendency of it to degrade at this temperature. Such color is normally obtained after melt processing of polymers with proteineous biomass. While processing

at 190 °C, however, the as-received DDGS started to burn, creating excessive char smell and smoke during both extrusion and injection. Consequently, the respective samples were totally black plus that the created smoke caused deficiencies in the injected samples

as sink marks which is illustrated in the enlarged portion of Figure 3-7. The burning of

biomass can create uncertainty in the exact formulation of the biocomposite due to the

mass loss occurring while thermal degradation proceeds.

The tensile properties of the injected samples are shown in Figure 3-8. The

strength of all biocomposites was less than that of neat polymer. This reduction in

strength is caused by the poor adhesion at the polymer-DDGS interface. In case of as-

received DDGS biocomposite, the reduction in strength was more and became worse

with increasing the temperature. The increased rigidity due to the incorporation of DDGS

into the PBS matrix was observed mostly due to the structural components such as cellulose and hemicellulose. As mentioned in the previous section, the water-washed

DDGS contains higher amount of these components which can be the reason of higher modulus of water-washed DDGS biocomposites compared to as-received DDGS biocomposites.

Figure 3-7. Injected samples of (a) neat PBS, (b) water-washed DDGS biocomposite and (c) as-received DDGS biocomposite processed at 160 °C and 190 °C. The enlarged portion shows sink marks on the surface of the sample.

The graphs clearly show how the strength and modulus of the water-washed

DDGS biocomposites remained constant even with 30 °C increment of the processing temperature whereas for the as-received DDGS biocomposites both the strength and the modulus reduced as the processing temperature increased.

40 160 °C 190 °C (a)

20 Tensile strength (MPa) strength Tensile

10 Neat PBS washed DDGS as-received DDGS biocomposite biocomposite

1200 160 °C 190 °C (b) 1000

800

600 Tensile modulus (MPa) modulus Tensile 400 Neat PBS washed DDGS as-received DDGS biocomposite biocomposite

Figure 3-8. Tensile strength and modulus of neat PBS, water-washed DDGS biocomposite and as-received DDGS biocomposite.

3.4. Conclusions

The thermal stability of dried distillers’ grains with solubles (DDGS) was

enhanced by water-washing. The temperature at which fractional mass loss of 5% occurs

was improved from 197 °C for as-received DDGS to 251.6 °C for water-washed DDGS.

Also, the thermal degradation rate at 180 °C was reduced approximately 4 times. The

thermal stability of DDGS was significantly affected by the water-to-DDGS ratio but not

changed by the washing time. The activation energies for the degradation of as-received

DDGS were generally smaller than the respective values for water-washed DDGS. The water-washed DDGS was more concentrated in protein, cellulose and hemicellulose compared to as-received DDGS. The infrared spectrum of water-washed DDGS showed peak removal at 1105 cm-1 and 615 cm-1 due to removing water-soluble portion of DDGS

after washing. The biocomposites prepared from water-washed DDGS were higher in

tensile strength and modulus compared to as-received DDGS biocomposites, but also

more stable in mechanical performance while processed at two different temperatures of

160 °C and 190 °C.

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Chapter 4: Biodegradable Green Composites from Dried Distillers’ Grain with Solubles (DDGS) and Polyhydroxy(butyrate-co- valerate) (PHBV)-Based Bioplastic∗

Abstract: Biodegradable green composites from dried distillers’ grains with solubles (DDGS), a major coproduct of the corn ethanol industry, and a polyhydroxy(butyrate-co- valerate) (PHBV)-based bioplastic were successfully produced. Water-washing of DDGS was performed and thermogravimetric analysis (TGA) showed noticeable improvement in degradation onset temperature of DDGS from 140 °C to 235 °C; this was a key point during melt processing of the composite. Utilizing a compatibilizer improved the adhesion between DDGS and the matrix, which was observed by scanning electron microscopy (SEM), so that the green composite containing treated and compatibilized DDGS showed enhanced modulus (by about 28% from 1.77 to 2.26 GPa) and improved heat deflection temperature (HDT) (by about 21% from 109 °C to 132 °C) compared to the polymeric matrix while having tensile and flexural strengths equal to or greater than the respective properties of the matrix.

∗ A version of this chapter has been published in: Zarrinbakhsh N., Misra M., Mohanty A.K. “Biodegradable Green Composites from Distiller's Dried Grains with Solubles (DDGS) and Polyhydroxy(butyrate-co-valerate) (PHBV)-Based Bioplastic”, Macromolecular Materials and Engineering. 296 (2011) 1035–1045. 79

4.1. Introduction

Dried distillers’ grains with solubles (DDGS) is a low-cost coproduct of the corn ethanol industry in which corn is converted to approximately equal weight of ethanol,

DDGS and carbon dioxide. Specifically, one bushel of corn yields to 10.6 litres of ethanol and more than 7.7 kilograms of DDGS. Since DDGS basically consists of nonfermentable components of corn including protein, fat and fibre, it is mainly used as feed for animals such as dairy, beef, swine and poultry [1, 2].

However, production of DDGS is greater than its limited consumption as animal feed. This is mainly due to the great worldwide interest in finding renewable energy sources, such as biofuel, which has resulted in dramatic growth in ethanol production.

Globally, ethanol production has increased more than five times from 2000 to 2009. As a result, the USA as the largest producer of ethanol has experienced a more than tenfold increase in distillers’ grains production over the 2000 – 2009 period from 2.7 to 30.5 million tonnes [2]. Such an increase makes it is necessary to find alternative uses for

DDGS rather than just as animal feed. Moreover, finding new uses for DDGS can lead to value addition to it and help the viability of biofuel ethanol industry.

It is less than ten years that DDGS has been considered in the literature as a possible biofiller for producing composites [1, 3-6]. One of the very first attempts involved incorporation of DDGS, up to 30 wt. %, into polypropylene (PP) and polyethylene (PE). In comparison with some other biofillers, Julson et al. [3] concluded that DDGS may not be an acceptable filler due to low mechanical properties of

DDGS/thermoplastic composites. In another work, polymerized polyurethane was used

as a binder in compositions having 20 to 90% by weight of DDGS [4]. There are, also, a few works on using phenolic resin as binder between DDGS particles [1, 5, 6]. Tatara et al. [5, 6] blended DDGS with phenolic resin using compression molding. Assessing the mechanical properties of the blends with a wide range of DDGS content from 0 to 90 wt.

%, a decrease in tensile strength, modulus and elongation at yield was observed.

Cheesbrough et al. [1] also studied phenolic resin-based glue composites with DDGS and found that the maximum stress and flexural modulus were improved by DDGS addition.

Such a short review highlights the necessity for more research in order to use

DDGS effectively as a biofiller or, optimally, as a biobased reinforcement in a polymeric matrix for industrial applications. Selecting this polymeric matrix itself is a complex issue in which one must consider several aspects such as material properties, cost and processability.

Polyhydroxy(butyrate-co-valerate) (PHBV) is a semi-crystalline copolymer from the big family of polyhydroxyalkanoates (PHA) made by bacteria. As a biodegradable thermoplastic, PHBV has physical and mechanical properties very similar to polypropylene (PP) and can be considered as a good candidate to substitute this non- biodegradable petroleum-based plastic. However, there are two main obstacles to achieving this: PHBV costs more and is much more brittle compared to PP [7].

Incorporation of natural fibre into PHBV can be a good way to decrease the cost of the final product. Many scientists have studied green composites of PHBV and different natural fibres, such as wheat straw [8], wood fibre [9], cellulose fibre [10], kenaf [11, 12], bamboo and bamboo pulp fibre [13-15]. However, as mentioned before, there are no reports on composites made from PHBV and DDGS. With the current higher price of

PHBV compared to its petroleum-based counterpart, PP, incorporation of low-price

DDGS into PHBV could open new opportunities for industrial application of both

materials.

In this work, we have set out to produce a novel green composite from DDGS and

PHBV. Compounding polymers with natural fibres and rigid particles usually results in a

drastic drop in ductility. Blending thermoplastics of different properties is a common way

to produce a material with tailored properties of each moiety [16]. PHBV, as a brittle thermoplastic, can be blended with two petroleum-based but biodegradable tough polymers, poly(butylene succinate) (PBS) [17] and poly(butylene adipate-co- terephthalate) (PBAT) [18, 19], in order to enhance the toughness without sacrificing its

biodegradability. Since PBS has increased strength and modulus compared to PBAT, it

was selected for use in this work. A blend of PHBV with 30 wt. % PBS was decided as a

rough balance between improvement in toughness and renewable-resourced content of

the polymeric matrix. The miscibility and crystallization behaviour of PHBV/PBS blends

prepared by solution casting has already been studied [17]. However, in this work, we

have applied melt extrusion/injection processing and evaluated mechanical properties.

In the present chapter we have tried to address the challenges involved with

processing DDGS at high temperatures and to find out how successful will be to produce

a green biocomposite out of DDGS. For this purpose, we have applied water-washing and

used compatibilizer. Additionally, both polymers used in this work (PHBV and PBS) are

well-established as biodegradable polymers in the literature and DDGS, as an agricultural

biomass, is also biodegradable [20]. Therefore, their biocomposite is expected to be a

biodegradable material.

4.2. Experimental

4.2.1. Materials

PHBV was obtained from Tianan Biologic Material Co. Ltd, China, in commercial name of Enmat Y1010, with 3 mol% valerate content and melting point of

172 °C. PBS was supplied from Toyo Plastics Co., Ltd, Japan, manufactured by Showa

Highpolymer Co. Ltd, Japan, commercially called Bionolle 1001 which had a melting point of 114 °C. DDGS was kindly provided by GreenField Ethanol Inc., Chatham,

Canada. The compatibilizer used in this study is polymeric methylene diphenyl diisocyanate (PMDI), RUBINATE® M, which has been purchased from Huntsman

Polyurethanes, Canada.

4.2.2. DDGS treatment

For producing green composites, DDGS was used in as-received as well as treated forms. The treatment was washing the as-received DDGS with water in a beaker of 2 litres with a magnet stirrer. 100 grams of as-received DDGS was washed with 1.5 litre of regular water at room temperature for 30 minutes and filtered through a filter paper with particle retention size of 20 micron. Treated DDGS was finally dried overnight at room temperature.

4.2.3. Thermogravimetric analysis (TGA)

A TGA Q500 instrument produced by TA Instruments was used for thermal stability studies. About 15 mg of material was heated from room temperature up to 600

°C with a ramp rate of 20 °C/min. The experiments were performed in nitrogen gas

environment and results were analyzed with Universal Analysis software.

4.2.4. Sample preparation

All materials, except compatibilizer, were dried at 80 °C for at least 24 hours prior

to processing. Samples were processed in a twin-screw micro-extruder, made by DSM

Xplore, the Netherlands, with three heating zones of 175, 180 and 180 °C from top to

bottom, respectively and co-rotating screws of 100 RPM. Blending and compounding

time was maintained 2.5 minutes for all formulations listed in Table 4-1, followed by injecting the sample in a mold at 45 °C by a micro-injection molding machine made by the same company. A 30%-content of DDGS in the green composite formulations was chosen based on our literature survey on natural filler-based biocomposites as a reasonable inclusion value to show the effect of DDGS incorporation into polymeric matrix, its treatment and compatibilization. Also, another idea was to use not less than 30 wt. % of DDGS in order to find out a biobased composite material more cost-competitive as compared to petroleum-based polymer composites.

In case of neat polymers and the blend, polymers were fed into the micro-extruder and melted/blended for 2.5 minutes. For green composites, again both polymers were fed at the beginning and blended for 1.5 minutes. After that, DDGS was fed and all materials were compounded for another 1 minute. This way, the total time during which polymers experienced high temperature and extrusion shear force was 2.5 minutes for all formulations. In case of the formulation containing compatibilized DDGS, PMDI was added to DDGS and mixed manually in the micro-extruder hopper prior to feeding into

the barrel. This method was adopted to reduce, as much as possible, the time that PMDI and DDGS were exposed to the air and moisture prior to feeding.

Table 4-1. Formulation of all samples prepared in this work

Sample PHBV PBS DDGS PMDI (part per hundred (wt. %) (wt. %) (wt. %) composite) Neat polymers Neat PHBV 100 - - - Neat PBS 100 - - PHBV-based blend PHBV/30%PBS 70 30 - - PHBV-based green composites* 49 21 30 - Non-washed DDGS green composite

Water-washed DDGS green 49 21 30 - composite Water-washed/compatibilized DDGS 49 21 30 2 green composite** * The matrix for green composites was PHBV/30%PBS blend. **By using wt. % for showing the PMDI amount, the exact wt. % of PHBV/PBS/DDGS/PMDI would be 48.04/20.59/29.41/1.96 while the 49/21/30 ratio between PHBV/PBS/DDGS is kept constant.

4.2.5. Mechanical tests

Tensile and Flexural samples were tested according to ASTM standard D638 and

D790, respectively, using INSTRON testing machine of model 3382. Also, Izod impact strength of notched samples was carried out as per ASTM D256 by a Testing Machine

Inc. (TMI) instrument. In all mechanical tests, each data is the average of at least 5 measurements. All samples were conditioned for 72 hours at 23 °C and relative humidity of 50%.

4.2.6. Dynamic Mechanical Analysis (DMA)

A DMA Q800 from TA Instruments was used to evaluate the storage modulus of rectangular samples of 3.2×12.5×65 mm. The experiments were performed from -50 to 85

150 °C with a ramp rate of 3 °C/min. A dual cantilever clamp was used at the frequency of 1Hz and oscillating amplitude of 15µm. Universal Analysis 2000 software, version

4.5A, from TA Instruments, was used to do analyze the raw data.

In the DMA tests, the known deflection (strain) was applied on the sample and the resultant response of the test sample was measured by the equipment in terms of (a) the necessary force (stress) to maintain the constant strain, and (b) the phase lag between the applied deflection and the measured force. These two were the essential measurements used by the analysis software to calculate the elastic (storage modulus) component of the viscoelastic response of the material.

4.2.7. Heat deflection temperature (HDT)

The same instrument and samples as for DMA were applied for HDT measurements in three-point bending mode at a constant load of 0.455 MPa. The samples were heated from room temperature to the desired temperature with a ramp rate of 2

°C/min. The HDT was reported as the temperature at which a deflection of 0.25 mm occurs.

4.2.8. Morphological studies

Scanning electron microscopy (SEM) was utilized to investigate the morphology of the composites. The fracture surfaces of impact test specimens were gold-sputtered to gain a coating of about 20 nm prior to characterization. A Hitachi S-570 scanning electron microscopy was applied with a tungsten electron emitter and an accelerating voltage of 10 KV.

4.3. Results and Discussion

4.3.1.Thermal stability of DDGS – The effect of water-washing

Thermogravimetric Analysis (TGA) was applied to investigate the behaviour of

DDGS at high temperatures. During heating in the TGA instrument, DDGS decomposes

and turns into volatiles and ash. According to Morey et al.,[21] DDGS thermal

decomposition occurs in three stages. The first stage (26 – 130 °C) corresponds to moisture loss and volatilization of light molecules such as fatty acids. In the second stage

(130 – 530 °C), degradation of polysaccharides, starch residues from fermentation, hemicellulose, fat/oil and some portions of protein, cellulose and lignin could occur. And finally, some protein components, lignin, char, and thermally stable components such as metals may decompose in the third stage (530 – 775 °C).

Since the melt processing temperature of green composites lies in the second stage of DDGS thermal decomposition, it is important to identify the components of

DDGS which start degrading at these temperatures. Figure 4-1 shows the

thermogravimetry (TG) graphs of non-washed DDGS and water-washed DDGS. When

analysing with the software, a line was plotted tangent to the first portion of TG curve,

before the sudden drop in weight percentage, and deviation from this tangent line was

considered as the onset of DDGS degradation. As it is observed, non-washed-DDGS

started degradation at temperatures about 140 °C while, for water-washed DDGS, it

happened at 235 °C. It suggests that removing water-soluble components of DDGS by

water-washing treatment significantly helps in improving the thermal stability of DDGS.

This can be a key point at melt processing temperatures in order to use DDGS as a

biofiller in producing composites.

As a confirmation, the water-soluble portion of DDGS was isolated by drying the

filtrate solution, after water-washing, at 80 °C for several hours. The corresponding TG

curve in Figure 4-1 admitted the degradation of water-soluble components starting from

120 °C.

100 Water-washed 90 DDGS 80 Non-washed (as- received) DDGS 70 DDGS water- 60 soluble portion

Weight % 50 40 30 20 0 100 200 300 400 500 600 Temperature (°C)

Figure 4-1. Thermogravimetric (TG) graphs of non-washed DDGS, water-washed DDGS and water-soluble portion of DDGS.

Derivative Thermogravimetric (DTG) graph is another useful piece of

information obtained from TGA instrument. It gives the rate at which the material

decomposes as the temperature increases. Since DDGS components degrade at different

rates and different temperatures, each component shows a characteristic peak of a

specific height at a specific temperature in DTG plot. DTG graphs of non-washed DDGS,

water-washed DDGS and water-soluble portion of DDGS are compared in Figure 4-2.

The major peaks in DTG curves of non-washed and water-washed DDGS are typical for materials with lignocellulosic portion, where hemicellulose decomposes at lower temperatures, giving the first peak, followed by cellulose decomposition at higher temperature of the second peak [22]. The difference between DTG curves of non-washed and water-washed DDGS, in this study, is a shoulder attached to the hemicellulose peak in a wide range of temperature approximately from 120 to 220 °C observed in DTG plot of non-washed DDGS. As seen, this shoulder became very small when DDGS was washed with water. This shows that the shoulder can be due to decomposition of water- soluble components of DDGS.

Referring to the DTG curve of water-soluble portion of DDGS in Figure 4-2, this

curve contains several peaks in the temperature range of the shoulder which is attached to

the hemicellulose peak in DTG curve of non-washed DDGS. These peaks are related to

the degradation of what expected to be the water-soluble portion of DDGS. According to

Bootsma et al. [23], hot water treatment of distillers’ grains results in an aqueous stream

which contains dissolved oligosaccharides, basically rich in heteroxylan which is a highly

branched heteropolymer.

12 Water-washed 10 DDGS Non-washed (as- 8 received) DDGS

6 DDGS water- soluble portion 4

2 Derivative Weight Derivative Weight (%/min) 0 0 100 200 300 400 500 600 Temperature (°C)

Figure 4-2. Derivative thermogravimetric (DTG) graphs of non-washed and water-washed DDGS.

Also, there is another peak in DTG curve of water-soluble portion which appears in the temperature range of hemicellulose DTG peak. Such observation suggests that the hemicellulose is also passed partially through filter paper after DDGS washing. This is possible to happen due to the type of filter paper used in this study which allowed the particles, less than 20 micron, to pass through. However, such phenomenon is not

expected to happen dramatically as a result of water-washing treatment. Usually,

hemicellulose removal is occurred due to delignification of the lignocellulosic materials

in an alkali solution such as sodium hydroxide [24] or by hydrothermal treatment of

cellulose-containing materials in hot water [25], while the washing medium used in this

work was regular water at room temperature. As also seen in Figure 4-2, DTG curve of

water-soluble portion shows no cellulose peak. All these observations suggest that no

significant structural fibre was being lost in the treatment. This conclusion is also

consistent with mechanical properties data of water-washed DDGS green composite compared to non-washed DDGS composite, presented in the following sections.

Similar to what Giuntoli et al. have reported [22], small irregularity appears between hemicellulose and cellulose peaks in our work that can be due to residual starch.

However, any changes in residual starch content during water-washing can be considered negligible. This is mainly because starch is water-insoluble, and also that DTG curves of both non-washed and washed DDGS samples showed this starch-related irregularity.

Another note to point out is the shift of the second cellulose peak in the DTG plot.

It is observed that when different components exist in the material, they may affect thermal degradation of each other as they have chemical and physical interaction with each other. Seemingly, those components with lesser thermal stability tend to promote the thermal degradation of those components with higher thermal stability. Such observations gave additional information besides our main purpose of the study, i.e. successfully producing DDGS-containing green composite with acceptable properties, and suggest that covering whole aspects about DDGS treatment may need a more focused and separate study/publication.

4.3.2. Mechanical properties

4.3.2.1. Neat polymers and the PHBV/PBS blend

The mechanical properties – tensile, flexural and impact – of neat polymers and their blend of 30 wt. % PBS are shown in Figure 4-3. As it is observed in Figure 4-3a, the modulus of blend lied in between the moduli of neat polymers. Tensile yield stresses of

neat polymers and their blend were more or less in a same level (Figure 4-3b) which can

be due to small difference between the values for neat PHBV and neat PBS. It should be

noted that neat PHBV and its blend with PBS did not show necking phenomenon and

cold-draw region in tensile test and broke after yielding at a stress level less than their yield stress. Thus, the yield stress is considered as maximum tensile stress.

However, there was a large difference between maximum flexural stresses of neat

PHBV and PBS. Essentially, this difference arises from the fact that neither of these

materials yield or break during flexural test up to standard 5% of strain. In such cases, the

modulus of the material determines the final value of the flexural stress. The more the

flexural modulus, the more the maximum flexural stress when material does not yield or break within 5% of strain.

As in Figure 4-3c, the elongation at break for PHBV blend with 30 wt. % PBS was higher than that of neat PHBV by a factor of 2.7. Similarly, impact strength was increased by 35% as a result of blending with 30 wt. % PBS. This happened while neat

PBS had shown an elongation at break of around 270% and impact energy of about 140

J/m.

Considering a balance between mechanical properties of neat polymers and the blend, and improved ductility of PHBV/30wt. %PBS blend compared to neat PHBV led us to prepare green composites of this blend with non-washed DDGS, water-washed and water-washed/compatibilized DDGS.

5 a Tensile Modulus (GPa) 4 Flexural Modulus (GPa)

0 PHBV PHBV/PBS PBS (70/30)

100 b Tensile Yield Stress (MPa) Maximum Flexural Stress (MPa) 80

0 PHBV PHBV/PBS PBS (70/30)

35 c %Elongation @ Break 30 Impact Energy (J/m)

0 PHBV PHBV/PBS (70/30)

Figure 4-3. Mechanical properties of neat polymers and their blend. Neat PBS had elongation at break and Izod impact energy of 270% and 140 J/m, respectively.

4.3.2.2. DDGS green composites

The mechanical properties of the green composites, containing 30 wt. % DDGS,

are illustrated in Figure 4-4. As mentioned earlier, the polymeric matrix used for green

composites in this study was PHBV/30%PBS. Both tensile and flexural moduli of matrix

and green composites have an increasing trend from matrix to green composites of non-

washed, water-washed and water-washed/compatibilized DDGS (Figure 4-4a). On the other hand, addition of non-washed DDGS resulted in a drastically decreased tensile and flexural strengths of green composite compared to the matrix (Figure 4-4b). This

behaviour has already been reported by other authors for composites of DDGS and other

matrices [1, 5, 6]. It was observed that by water-washing the DDGS, tensile and flexural

strengths were improved compared to non-washed DDGS green composite. Moreover,

the highest improvement level in these properties was achieved when water-washed

DDGS and compatibilizer were applied together, i.e. in water-washed/compatibilized

DDGS green composite.

When a polymeric matrix is filled with rigid particles, the initial modulus of

elasticity is higher than that of matrix and this depends on the degree of adhesion between particles and matrix; the better the interfacial adhesion, the more the improvement in modulus due to load transfer from matrix to rigid particles. However, particle-matrix debonding occurs with increasing load [26]. When there is no adhesion

between matrix and filler, it is just the matrix that carries the load under tensile condition.

According to Nicolais and Narkis [27] model, the strength of the composite is less than

that of matrix by a factor of (1 – aφ2/3) where φ is the volume fraction and a is a shape

factor of filler particles, e.g. a = 1.21 for spherical particles.

3.5 a Tensile Modulus (GPa) 3 Flexural Modulus (GPa)

2.5

1.5

0.5

0 ABCD

70 b Tensile Strength (MPa) 60 Flexural Strength (MPa)

0 ABCD

35 c %Elongation @ Break 30 Impact Energy (J/m)

0 ABCD

Figure 4-4. Mechanical properties: (A) polymeric matrix PHBV/30%PBS, (B) non-washed DDGS green composite, (C) water-washed DDGS green composite, and (D) water-washed/compatibilized DDGS green composite. All green composites contain 30 wt. % DDGS.

Thus, according to modulus and strength of different green composites, it was

predictable that water-washed DDGS particles would have better adhesion to the matrix

than non-washed DDGS. Moreover, utilizing compatibilizer would further improve the

interfacial adhesion so that the strength of water-washed/compatibilized DDGS green

composite was very close to or even exceeded the strength of polymeric matrix.

Such a change in adhesion bonds between two phases may cause a change in

fracture mechanism in impact test [14]. As seen in Figure 4-4c, the green composite of

water-washed/compatibilized DDGS showed the least energy absorbed during impact

fracture while non-washed DDGS green composite had a higher average impact energy.

This is to be more discussed when presenting the scanning electron microscopy images of the fracture surfaces.

In case of ductility, compounding the DDGS with polymeric PHBV/30%PBS matrix resulted in a decreased maximum elongation in comparison with that of the matrix. However, regardless of the degree of adhesion between DDGS and matrix, all

DDGS green composite showed a similar value of elongation at break of about 3%.

4.3.3. Fracture surface morphology

Figure 4-5 demonstrates the impact fracture surface and fracture mechanism of

green composites. The interface between two phases is more focused in Figure 4-6. As in

Figure 4-5a, several holes and rough fracture surface with non-washed DDGS particles show that DDGS pullout was a prevalent phenomenon in impact fracture of this green composite rather than fracture of DDGS particles. This can be as a result of poor interfacial adhesion between DDGS and matrix. As a biomass, DDGS possesses a lot of

hydroxyl groups that can form hydrogen bonding with hydroxyl groups of polyesters in

the matrix. However, due to DDGS decomposition during melt processing, produced volatiles may prevent proper adhesion between DDGS and matrix. This was observed as

a gap between DDGS and matrix in fracture surface images of non-washed DDGS green

composite. The gap between DDGS particles and polymeric matrix is more focused in

Figure 4-6a and b for this composite.

As mentioned earlier, water-washing had a promising effect on thermal stability

of DDGS so that the majority of its mass, in thermogravimetric test, was unaffected at

higher temperatures. This can lead to a relatively better interfacial adhesion between

DDGS and matrix. However, DDGS pullout still occurs as shown in Figure 4-5b. A closer look at how DDGS and matrix are connected in this case is presented in Figure

4-6c and d. It was observed that interfacial gap still exists between DDGS particles and

the matrix.

A better interfacial adhesion was even achieved by using PMDI as the

compatibilizer. The SEM image of water-washed/compatibilized DDGS green composite

in Figure 4-5c shows a smooth fracture surface. DDGS particles are so embedded by the

matrix that almost no pullout of DDGS particles has occurred. This can lead to fracture of

DDGS particle during impact test. Figure 4-6e and f also show a strong adhesion with no

gap between phases. PMDI effect on improving the interfacial bonds between PHBV and

bamboo pulp fibre has already been observed [14].

Figure 4-5. Impact fracture surface and fracture mechanism of (a) non-washed DDGS, (b) water-washed DDGS, and (c) water-washed/compatibilized DDGS green composites.

Figure 4-6. The interface between DDGS and matrix in (a) and (b) non-washed DDGS, (c) and (d) water- washed DDGS, and (e) and (f) water-washed/compatibilized DDGS green composites. The figures on the right side are enlarged images of rectangular portion shown in the left-hand side images.

The reactions of PMDI with DDGS and matrix which can lead to a better

adhesion between phases are schematically presented in Figure 4-7. It is predicted that covalent bonds between DDGS-PMDI-matrix account for the better adhesion compared to the condition that weaker hydrogen bonds exist between DDGS-matrix.

Figure 4-7. A schematic of predicted reactions between polymeric matrix, PMDI and DDGS.

As mentioned, such a change in interfacial adhesion results in the change in

fracture mechanism. When the crack tip in impact test approaches a DDGS particle

loosely attached to the matrix, it is easier for crack to change its path of propagation

around the particle rather than breaking the particle, thus increasing the surface area of

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fracture. This produces a pulled-out DDGS particle and finally, several DDGS pullouts cause a rough fracture surface. Such a mechanism absorbs more energy compared to when DDGS particles are strongly embedded by the matrix. In this situation, crack must break the particle in order to propagate which leads to a smooth fracture surface of the green composite. Figure 4-8 represents a schematic of this hypothesis.

Figure 4-8. Schematic of crack propagation mechanism in green composite with (a) loose and (b) strong interfacial adhesion between DDGS and matrix.

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4.3.4. Thermomechanical properties – HDT and DMA

Heat deflection temperature (HDT) is of great importance since it is considered as the maximum temperature up to which a polymeric material can be used as a rigid material. The HDT values for neat polymers, their blend and DDGS green composite in this study are presented in Figure 4-9. As in Figure 4-9a, the HDT of PHBV/PBS blend

lies between the HDT of neat polymers, i.e. blending PHBV with 30 wt. % PBS reduced

its HDT by 39 °C from 148 to 109 °C.

In case of green composites of this matrix (PHBV/30%PBS) with 30 wt. %

DDGS in Figure 4-9b, improvement in HDT occurred only when there was a good adhesion between DDGS and matrix. In other words, the maximum improvement in HDT was observed in water-washed/compatibilized DDGS green composite by 21% from 109

to 132 °C. On the other hand, non-washed DDGS green composite showed a decreased

HDT compared to the matrix. In order to better understand the behaviour of sample at

higher temperatures, storage modulus measurement was conducted by DMA.

Storage modulus (E΄) from DMA test gives useful information on how elastic (or

rigid) the material is at different temperatures. This represents the in-phase component of

material’s response to the oscillating applied strain and is related to the amount of energy

that sample stores and gives back in each cycle of deformation [28]. The storage modulus

curves of neat polymers, their blend and green composites are depicted in Figure 4-10.

Blending PHBV with PBS decreases its storage modulus which was expectable as a result of lower E΄ value for neat PBS (Figure 4-10a). The storage modulus of

PHBV/30%PBS matrix was improved by incorporation of water-washed DDGS, as

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illustrated in Figure 4-10b. Also, using compatibilizer resulted in more improvement in storage modulus as for water-washed/compatibilized DDGS green composite. However, the decreased value of E΄ observed in non-washed DDGS green composite can be due to promoted debonding between DDGS and matrix as a result of oscillating applied strain in

DMA test. Such an effect can also be more promoted when temperature increases.

180 a 150

120 C) ˚ 90 HDT ( 60

0 neat PHBV PHBV/PBS (70/30) neat PBS

140 b 120

100 C)

˚ 80

60 HDT ( 40

0 ABCD

Figure 4-9. Heat deflection temperature (HDT) of (a) neat polymers and their blend, and (b) green composites. (A) polymeric matrix PHBV/30%PBS, (B) non-washed DDGS green composite, (C) water- washed DDGS green composite, and (D) water-washed/compatibilized DDGS green composite. All green composites contain 30 wt. % DDGS.

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6 a 5

4 PHBV/PBS 100/0 3 70/30 0/100 2

1 Storage modulus Storage modulus (GPa) 0 -50 0 50 100 150 Temperature (˚C)

5 b Water-washed/compatibilized DDGS green composite 4

...... Water-washed 3 DDGS green composite

2 polymeric matrix (PHBV/30%PBS) 1 non-washed DDGS

Storage modulus Storage modulus (GPa) green composite 0 -50 0 50 100 150 Temperature (˚C)

Figure 4-10. Storage modulus versus temperature plots for (a) neat polymers and their blend, and (b) green composites of PHBV-based matrix and 30 wt. % DDGS.

It is mentioned that in semicrystalline polymers, HDT increases by increasing the degree of crystallinity, change in crystalline morphology or relieving built-in stresses in the amorphous phase. At the same time, there is a correlation between modulus- temperature behaviour of the material and its HDT [29]. In fact, it can be said that the

104

change in the other factors such as crystallinity or crosslink density affects the modulus of the material.

The correlation between HDT values of samples and their storage modulus at some selected temperatures is presented in Table 4-2. The more the storage modulus

(rigidity) of the material at high temperature, the more its resistance to deflection and consequently, the more the temperature to deflect it up to a given value. Similar correlation between HDT and storage modulus has also been reported for PHBV/wood fibre [9] and PHBV/recycled cellulose fibers [30] composites.

Table 4-2. Correlation between HDT and storage modulus values of samples

HDT Storage modulus (GPa) (°C) Sample 80 °C 100 °C 120 °C Neat polymers Neat PBS 109 0.23 0.20 - Neat PHBV 148 1.48 1.08 0.75 PHBV-based blend PHBV/30%PBS 109 1.06 0.67 0.28 PHBV-based green composites* Non-washed DDGS green 86 0.69 0.40 0.17 composite Water-washed DDGS green 113 1.13 0.78 0.34 composite Water-washed/compatibilized 132 1.20 0.83 0.40 DDGS green composite * The matrix for green composites was PHBV/30%PBS blend.

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4.4. Conclusion

Dried distillers’ grains with solubles (DDGS) was used successfully as a biofiller in producing green composites via melt processing. Such type of researches can help the development of value-added usages for DDGS. The polymeric matrix was a blend of

PHBV and 30 wt. % PBS with improved ductility compared to neat PHBV. The thermal stability of DDGS was improved by water-washing, which is essential in preventing

DDGS decomposition during melt processing. Accordingly, three types of green composites of non-washed, water-washed and water-washed/compatibilized DDGS with

PHBV-based matrix were studied. Improved thermal stability of the water-washed DDGS resulted in a better interfacial adhesion between DDGS and PHBV-based matrix, as confirmed by SEM studies. Also, compatibilizer was effectively utilized to further improve the adhesion between DDGS and matrix. Applying both approaches, i.e. DDGS water-washing and compatibilizer, led to a green composite with superior properties such as tensile modulus, flexural strength and flexural modulus compared to its matrix. DDGS water-washing, more effectively together with compatibilizer, compensated the drastic drop in tensile strength of non-washed DDGS green composite. Also, water-washed and water-washed/compatibilized DDGS green composites showed improved heat deflection temperature (HDT) in comparison with matrix. A strong correlation between storage modulus of material at higher temperatures and its HDT value was observed. As a summary, the results of this study show the potential of DDGS to be effectively used for producing a type of biodegradable green composite that can be utilized for applications necessitating more rigidity and higher temperature performance, but less ductility compared to the polymeric matrix itself.

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Chapter 5: Improving the Interfacial Adhesion in a New Renewable Resource-Based Biocomposites from Biofuel Coproduct and Biodegradable Plastic∗

Biocomposites of a biopolymer and a coproduct of corn bioethanol industry, dried distillers’ grains with solubles (DDGS), were produced by reactive melt extrusion and injection molding. The biopolymer matrix was a blend of polyhydroxy(butyrate-co- valrerate),PHBV, and poly(butylene adipate-co-terphthalate), PBAT. The effect of compatibilizer, polymeric methylene diphenyl diisocyanate (PMDI), and corn oil lubricant was studied. The change in melt processing force suggested the occurrence of chemical reactions during the processing. This hypothesis was further investigated by infrared spectroscopy by which the formation of urethane and urea bonds between DDGS and polymeric matrix was approved. Dynamic mechanical analysis (DMA) confirmed the occurrence of crosslinks at PBAT–PHBV interface showing that the Tan δ curves for PBAT and PHBV of the matrix shifted slightly towards each other. Moreover, the calculated parameter of interaction, A, from Tan δ curves admitted the stronger bond at the DDGS–matrix interface as a result of addition of PMDI compatibilizer. Also, scanning electron microscopy (SEM) images revealed improved interfacial adhesion at the DDGS–matrix interface as well as PBAT–PHBV interface within the matrix itself. The obtained crosslinked interfaces resulted in improvement in the strength, modulus and elongation at break of biocomposites. Moreover, a synergism of PMDI and corn oil effects led to a dramatic improvement in impact strength of this biocomposite system so that the respective value for the prepared DDGS biocomposite increased from 75 J/m to 212 J/m with addition of 1% of PMDI and 3% of corn oil.

∗ A version of this chapter has been published in: Zarrinbakhsh N., Mohanty A.K., Misra M. “Improving the Interfacial Adhesion in a New Renewable Resource-Based Biocomposites from Biofuel Coproduct and Biodegradable Plastic”, Journal of Materials Science. 48 (2013) 6025–6038. 109

5.1. Introduction

The growing global population has recently highlighted the critical need for sustainable development. Materials science as a technology enabler have a crucial role in this development such that it can mitigate the problems with fossil fuel, provide an efficient use of available material resources and reduce undesirable environmental impacts from technology and economic growth (pollution and waste) [1].

Petroleum-based plastics have been traditionally used in polymeric composite industries. Recently, major concerns over depleting petroleum resources and the non- biodegradability of the majority of petroleum-derived plastics have spurred researchers and industries to seek more sustainable alternatives. Such sustainability can be achieved by finding new plastics and composites from renewable resources with end-of-life biodegradability and of course economic viability [2-5]. Considering these concepts, we have set out to develop a green biocomposite by bringing several aspects into one picture:

(a) using materials from renewable resources (more than 50 wt. % of the biocomposite content), (b) using almost 100% biodegradable (compostable) materials, (c) developing a value-adding usage for the corn ethanol industry’s main coproduct and (d) applying green modification on the filler.

Polyhydroxy(butyrate-co-valrerate), PHBV, is a renewable resourced-based co- polyester made through bacterial fermentation [6]. PHBV exhibits physical and mechanical properties mostly resembling polypropylene (PP) and has the potential for substituting PP in many applications. This biopolymer has been commercially available since the 1980’s; however, its growth in industrial applications has been obstructed by

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two main drawbacks: low toughness and high cost [7]. PHBV is too brittle and most of the commercially available grades show an elongation at break of less than 10% after a

week or so [8]. Also, the current production volume of PHBV is so limited compared to

PP that the cost-performance balance is still in favor of PP.

Blending brittle PHBV with tougher polymers can be a practical way to obtain a

material with tailored properties. Physical and mechanical properties of PHBV blends

with elastomers or relatively tough thermoplastics have been studied extensively. Some

studied elastomers blended with PHBV include epoxidized natural rubber [9], ethylene- vinyl acetate (EVA) [10], poly(epichlorohydrin-co-ethylene oxide) (PECH–EO) [11],

potybutylacrylate (PBA) [12], poly(butadiene-co-acrylonitrile) (NBR) [13] and tough

thermoplastics blended with PHBV are poly(butylene succinate) (PBS) [14] and

Poly(butylene succinate-co-adipate) (PBSA) [15].

Recently, the blend of PHBV and poly(butylene adipate-co-terphthalate), PBAT,

has attracted interests in the research. PBAT is a biodegradable thermoplastic with low

modulus, high flexibility and very high impact strength [16, 17] so that the blend of

PHBV and PBAT would provide an excellent combination of mechanical properties of each moiety. Javadi et al. [18] have studied the crystallinity, morphology, and mechanical and thermomechanical properties of PHBV/PBAT blends available in the market with different ratios and compared with the microcellular injection-molded samples of the same blend. Moreover, Gallo and colleagues [19] have tried to improve the flame-

retardancy of such blend by compounding with phosphorus-based additives and metal

oxides. However, the industrial application of this blend is restricted to a large extent by

its high cost. To the best of our knowledge, there are only two published articles to date

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that have investigated the incorporation of low-cost biomass into PHBV/PBAT blend to produce less expensive biocomposites [20, 21].

Incorporation of low-cost biomass into polymeric matrix could be a solution to reduce the cost, but also has other added advantages such as improving the rigidity and increasing the biobased content [7]. However, the low impact strength is a key drawback

of natural fiber composites [22]. This disadvantage may offset the advantages of

biocomposites in many practical cases were high toughness is required.

Dried distillers’ grains with solubles (DDGS) is an inexpensive coproduct from bioethanol industry. In a dry-mill ethanol plant, the original corn mass gives almost equal weight of ethanol, carbon dioxide and coproducts, which are nonfermentable components, mostly in the form of DDGS. DDGS composition consists of protein, fat, fiber and other carbohydrates and is used as animal feed; however, it exhibits promising potential as filler in biocomposite applications. At the same time for the corn bioethanol industry to be economically viable, it is strongly critical to find novel applications for its coproduct [23, 24] since the rapid expansion of the corn ethanol industry during recent

years has created large amounts of DDGS coproduct which exceed its consumption as

animal feed. In this context, a tremendous increase has been observed in the DDGS

supply in North America, especially in US, during the last five years from 12 to 32.5

million metric tons; almost a 170 percent increase [25].

DDGS is an attractive filler for biocomposite production due to its low cost. It can

also be considered for reinforcement as it contains fiber. In the last 10 years, DDGS has

been used as a filler in producing biocomposites with different polymeric matrices

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including polyolefins [26, 27], polyurethane [28], phenolic resin [29-31], engineering plastic [32] and biobased thermoplastics [33, 34]. Reviewing the literature shows that this novel utilization of DDGS in the as-received form is not quite satisfactory as far as mechanical properties are concerned. However, utilizing a compatibilizer as well as treatment of DDGS before processing improves the mechanical performance of the

DDGS-biocomposites to a great extent [27, 33, 34].

In our previous work, we have shown that the processability, strength and modulus of DDGS biocomposite with poly(butylene succinate), PBS, are enhanced by

DDGS water-washing prior to processing [35]. We had already observed that implementing the isocyanate compatibilizer, polymeric methylene diphenyl diisocyanate

(PMDI) efficiently improves the interfacial adhesion between water-washed DDGS and a polymeric matrix, which was a blend of biodegradable polyesters, PHBV and PBS [34].

However, the low impact strength (~ 15 J/m) and elongation at break (~ 3%) of that biocomposite remained as a challenge. At the same time, our preliminary studies showed that addition of the isocyanate compatibilizer increases the extrusion compounding torque

(i.e. viscosity) while processing and reduces the melt flow index (MFI) of the biocomposite. Thus, we decided to utilize a lubricant for the ease of processing and possible improvement of MFI. As a lubricant, corn oil was chosen since it is renewable resource-based and also already exists in DDGS particles to some extent and is compatible with it.

The most significant objective in the present work was to engineer a novel biocomposite from DDGS and PHBV/PBAT blend for the first time via reactive extrusion that has a high impact strength while exhibiting acceptable modulus, strength

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and processability. In this regards, the extrusion mixing torque and the adhesion at different interfaces within the biocomposite material were focused on and studied.

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5.2. Experimental

5.2.1. Materials

Dried distillers’ grains with solubles (DDGS) from corn ethanol industry was kindly supplied by GreenField Ethanol Inc., Chatham, Canada. The sample consisted of particles roughly larger than 150 µm and an average size of 500 µm. The biopolymer

thermoplastic was purchased from TianAn Biologic Materials Co., Ltd. This product is a

PHBV/PBAT (45/55) blend commercially named as Enmat Y5010P to which we refer

shortly as Enmat hereinafter. The compatibilizer we used was polymeric methylene

diphenyl diisocyanate (PMDI), RUBINATE® M, purchased from Huntsman

Polyurethanes, Canada. Commercial 100% pure corn oil, available in the grocery market,

was used as a lubricant. The chemical structure of PHBV, PBAT and PMDI are

illustrated in Figure 5-1.

CH 3 CH2 CH2 O CH3 O CH2 HCHO CH2 C OCHCH2 C OH n N N N n m C C C O O O PHBV PMDI

O O O O

H O C C O CH2 O C CH2 C O CH2 OH 4 4 m 4 n

PBAT

Figure 5-1. The chemical structure of PHBV, PBAT and PMDI.

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5.2.2. DDGS water-washing

DDGS was washed with tap water at room temperature for 15 minutes prior to biocomposite processing. This was performed to increase the thermal stability of DDGS for polymer melt processing [34]. Washing was done in a 2 L beaker. 100 g of DDGS was stirred in 1.5 L water with a magnet stirrer. At the end, the beaker content was passed

through a kitchen screen at once for fast separation of the water. The washed DDGS (w-

DDGS) remained on top of the screen was collected and dried at room temperature for at least 48 hours. The yield after washing was about 70% of the original as-received DDGS.

The water-washing was done to remove the water-soluble portion of DDGS such as mono- and oligo-saccharides, fermentation by-products and organic acids. Moreover, the neutral detergent fiber (NDF) content of DDGS increases as a result of water-washing.

The characterization of DDGS before and after water-washing has been presented in

Chapter 3 and reported elsewhere from our lab [35].

5.2.3. Biocomposite processing

The biopolymer (Enmat) and water-washed DDGS (w-DDGS) were dried at 80

°C for at least 8 hours prior to processing in a hot-air oven. A twin-screw micro-extruder

from DSM Xplore was used to process the biocomposites. This micro-extruder consists

of a 15 cm3 vertical barrel with three heating zones, which were set at 175, 180 and again

180 °C from top (feeding zone) to the bottom (die zone), respectively. The co-rotating

screw configuration at 100 rpm was utilized. Each time about 13 g of materials was fed

into the extruder to produce one test bar. In each cycle when feeding completed, the

feeder and hopper were replaced by a stopper to push the remaining material in the

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feeding section into the barrel and to close the barrel so that the materials inside the barrel

be circulated up and down and compounded properly.

Total compounding time was maintained constant for all formulations listed in

Table 5-1. First, the biopolymer was fed and melted for 80-90 seconds and then w-DDGS was added and compounded for another 70-75 seconds. At the end of compounding, the

material was allowed to be extruded through the die opening at the bottom of the barrel and collected inside a cylinder-piston part pre-heated to 180 °C. A micro-injection molding machine, made by the same company, was used immediately to inject the cylinder content into a mold preheated at 45 °C.

In all formulations containing lubricant and/or compatibilizer, corn oil was added along with biopolymer while PMDI was mixed and fed with w-DDGS. The mixing was done manually in the micro-extruder hopper before feeding into the barrel.

Table 5-1. Biocomposite formulations processed in this work (values based on weight ratios)

Sample Enmat/w-DDGS PMDI (%) Corn oil (%)

1 80/20 0 0 2 80/20 0.5 0 3 80/20 1 0 4 80/20 0 3 5 80/20 0 6 6 80/20 0.5 3 7 80/20 1 3 8 80/20 0.5 6 9 80/20 1 6

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In this work, the w-DDGS concentration was kept constant at 20 wt. % as shown in Table 5-1 since our preliminary experiments showed a huge reduction in mechanical

performance, especially the tensile strength, of the w-DDGS biocomposite with 40 and

60 wt. % of w-DDGS without compatibilizer. More discussion in this regard is provided

in section 5.3.3.

5.2.4. Fourier transform infrared (FTIR) spectroscopy

A Thermo Scientific FTIR instrument, model Nicolet 6700, was used for infrared

spectroscopy measurements in attenuated total reflection (ATR) mode. The samples were

manually ground and used in powder form. The measurements were done with 32 scans

per sample and a resolution of 4 cm-1. The results were analyzed using OMNIC Spectra

software from the same company.

5.2.5. Mechanical tests

An INSTRON testing machine, model 3382, was implemented to perform tensile

and flexural tests according to ASTM D638 and D790, respectively with 5 replicates.

Test bars of type IV were used for tensile tests with a speed of 20 mm/min. Neat Enmat polymer was tested for tensile properties at 50 mm/min. Izod impact strength of notched

samples was measured by a Testing Machine Inc. (TMI) instrument complied with

ASTM D256 with 6 replicates. The samples were notched with a motorized notching

machine also made by TMI. All mechanical test samples were kept at room temperature

for 72 hours before mechanical measurements.

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5.2.6. Melt flow index (MFI) measurements

MFI test was performed using a melt flow indexer machine, complied with the

ASTM D1238, manufactured by Qualitest International Inc, model MFI-2000A. To

prepare MFI test samples, extruded strands of each formulation were prepared using the same micro-extruder explained above and then pelletized into small granules. These granules were dried prior to MFI test in the same way mentioned in section 2.3. For each

formulation, 6 g ± 0.1 g of dried pelletized granules were fed into the MFI heating

cylinder preheated to 190 °C ± 0.1 °C. The applied load was 2.16 Kg. The samples were

cut 7 min ± 0.1 min after charging the granules with a 30 sec interval, automatically by

the instrument. The samples with an MFI less than 3.5 g/10min were cut every 2 min to

obtain sample large enough for weighing. The first three cuts were used for weight

measurement and MFI calculation. In case of formulations with MFI of more than 25

g/10min, two cuts were possible to be done due to high flow of the molten material.

5.2.7. Water absorption measurements

The experiments were performed according to the ASTM D570. For each tested

material, three injection molded rectangular bars were dried at 50 °C under vacuum for

24 hrs. Samples were then cooled in a desiccator, weighed to the nearest 0.001 g

immediately, and immersed in distilled water at room temperature. Periodic weight

measurements were done after blotting the samples with paper towel to remove excess

surface water. The percentage of water absorption was calculated based on the gained

weight after immersion compared to the dried sample weight.

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5.2.8. Dynamic mechanical analysis (DMA)

Rectangular injected samples of 3.2 mm ×12.5 mm ×65 mm were used for storage

modulus and Tan δ measurements by DMA Q800 from TA Instruments. The experiments were performed from -50 to 80 °C with a ramp rate of 3 °C/min. The dual cantilever

mode was used. A frequency of 1Hz and a strain of 0.02% were applied. Universal

Analysis 2000 software, version 4.5A from TA Instruments, was used to do analyze the raw data.

It this study, force (stress) and phase lag responses of the tested samples, measured by the DMA equipment, was used by the analysis software to calculate the elastic (storage modulus) and viscous (loss modulus) components of the viscoelastic

response of the material. The ratio of the loss modulus to storage modulus was then

calculated by the software to give Tan δ values.

5.2.9. Morphology studies

A Hitachi S-570 scanning electron microscope (SEM) with an accelerating

voltage of 10 KV and a tungsten electron emitter was implemented to study the

morphology of the fractured surfaces from impact test. Gold-sputtering was performed on

the test specimens before SEM for an approximate coating of 20 nm.

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5.3. Results and discussion

5.3.1. Processing curves

The vertical micro-compounder used in this study was capable of measuring and

recording the axial force necessary to push the material downward while processing.

This force is a good indication of the viscosity of the system, especially when used to

compare relative melt viscosity between samples and represents the occurrence of

degradation or crosslinking during the process.

The axial forces generated during processing of some of the formulations are

shown in Figure 5-2 for comparison. The curves show the feeding sequences of the

biopolymer and w-DDGS as explained in experimental section. The force dropped

suddenly at the end of each compounding cycle when the compound material was

allowed to be extruded out of the barrel from the die opening.

The last 60 sec of the processing curve (distinguished roughly by vertical dashed

lines in Figure 5-2) represents the axial force while compounding all components together. As compared with the Enmat/w-DDGS (80/20) formulation (PMDI/corn oil

0/0), the processing force (as a measure of melt viscosity) increased by the addition of

PMDI (compatibilizer) whereas corn oil (lubricant) reduced the force. The respective curve of the formulation containing both PMDI and corn oil lay in between. This indicates that PMDI increased the viscosity of formulations and corn oil decreased it, respectively.

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While compounding, studying the change in the processing force over the time is

also informative as far as mixing uniformity, degradation or crosslinking are concerned.

It was observed that compounding of w-DDGS with Enmat alone showed a gradual decrease in the force during the compounding period which can be mostly due to the

breakage of the w-DDGS particles and reaching mixing uniformity. Addition of PMDI to

this system created an increasing trend in the processing force after a first drop which is

suggesting the occurrence of the crosslinking between w-DDGS particles and the

polymeric matrix. Such a reaction is also possible between the polymer chains itself

which will be discussed later on. The addition of only corn oil to the Enmat/w-DDGS

system resulted in a relatively constant force value while compounding. However, with

the formulation containing both PMDI and corn oil a constant increase in the force was

occurring during processing which reached almost to a plateau state. This in fact

suggested that corn oil influences the crosslinking phenomenon in this system.

9000 Enmat/w-DDGS/ 8000 PMDI/corn oil 7000 80/20/ 1/0 6000

5000 80/20/ 0/0 4000

Force (N) Force 3000 80/20/ 1/3 2000

1000 80/20/ 0/3 0 0 50 100 150 200 Time (sec)

Figure 5-2. The axial forces generated during processing of Enmat/w-DDGS (80/20) biocomposites containing different amounts of PMDI/corn oil.

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5.3.2. IR spectroscopy

To verify the crosslinking reactions, the FTIR spectra of biocomposites and their

individual components were studied which are shown in Figure 5-3 and Figure 5-4. As

observed in Figure 5-3a, the strong characteristic peak of PMDI pertaining to its

isocyanate (–N=C=O) vibrations is occurring at 2240 cm-1. Regarding corn oil and w-

DDGS spectra, the peak at 1741 cm-1 corresponds to the carbonyl (–C=O) stretching in

pure corn oil and the same oil naturally present in w-DDGS. Moreover, the symmetric

and asymmetric stretching of –C–H bonds of CH2 group in corn oil showed peaks in

2853 cm-1 and 2922 cm-1, respectively. In w-DDGS spectrum, the amide I and amide II

bands of w-DDGS protein emerged as two peaks at 1628 cm-1 and 1517 cm-1, related to

the C=O and C–N stretching (amide I band) and N–H bending (amide II band)

absorptions. Finally, the broad peak occurring in the range of 3040 cm-1 to 3670 cm-1 is due to stretching of O–H and N–H groups abundantly available in w-DDGS carbohydrates and protein.

The infrared spectrum of Enmat (PHBV/PBAT blend) illustrated in Figure 5-3b consists of several peaks. The infrared spectra of PHBV and PBAT have been reviewed by other researchers [17, 36]. The absence of the sharp characteristic peak of isocyanate group of PMDI suggested that no unreacted PMDI was present in the biocomposite formulations containing PMDI.

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a 2240

1628 1517 w-DDGS

2922 2853 1741

Corn oil Absorbance

PMDI

4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm-1)

Enmat/w-DDGS/PMDI/Corn oil

80/20/1/3

80/20/1/0

80/20/0/0 Absorbance

100/0/0/0

4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm-1)

Figure 5-3. FTIR spectra of (a) w-DDGS, PMDI, corn oil, and (b) selected biocomposites.

The difference between the Enmat spectrum and the biocomposites’ can be studied in two regions enlarged in Figure 5-4. The spectra in the range 2800 – 3700 cm-1

(Figure 5-4a) mostly confirms the presence of components other than Enmat in the

biocomposite. The narrow peak at around 3440 cm-1 in Enmat spectrum occurs due to O–

H stretching in polyester backbone terminals which was covered by the broad peak of O–

H and N–H vibrations of w-DDGS in the biocomposite formulations. The symmetric CH2 stretching of the polyester matrix had a peak at 2876 cm-1 to which a small shoulder was

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added at 2854 cm-1 after addition of w-DDGS. This shoulder could be attributed to the

symmetric CH2 stretching in the oil content of w-DDGS [37], as mentioned before, which

became stronger when corn oil was added to the formulation. Similarly, the asymmetric

-1 CH2 stretching absorbance of the polyester matrix (2936 cm ) became stronger and was

-1 shifted to the asymmetric CH2 stretching peak of the corn oil (2922 cm ) in the biocomposite samples.

The spectra of biocomposites also differ from that of the polyester matrix (Enmat) in the range 1500 – 1660 cm-1, depicted in Figure 5-4b. After addition of w-DDGS to the

Enmat matrix, the amide I band absorption in the range 1570 – 1660 cm-1 emerged as a

slight shoulder to the base of the carbonyl stretching vibration (~ 1740 cm-1) of the polyester matrix. Similarly, the amide II absorption was observed in the range 1510 –

1530 cm-1. As PMDI was added to the biocomposite formulation, the intensity of these

bands, especially the latter, increased.

The chemical reaction of monomeric MDI with DDGS and polyester matrix have

been proposed in the literature [28, 33]. The reactions between the –N=C=O groups of

MDI and O–H groups in DDGS and polyester as well as N–H groups in DDGS yield

urethane (–NH–CO–O–) and urea (–NH–CO–NH–) groups acting as the links between

different components.

The resulted urethane groups generally show an N–H bending and stretching absorption at 1530 cm-1 and 3400 cm-1, respectively [38]. The former was observed in our biocomposites formulations containing PMDI (Figure 5-4b, solid arrow). The latter peak

contributes to the absorptions at more than 3000 cm-1 and seemed to be overlapped with

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O–H stretching absorptions. This might be the reason why the intensity of the peaks in this region was maintained even after consumption of O–H and N–H groups by PMDI.

Also, it has been reported that the N–H bending absorption in pure urea occurs at

1599 cm-1 and 1628 cm-1 [39]. Finding such absorptions was hard in IR spectra of our samples due to overlapping with amide I absorption in w-DDGS and the strong carbonyl absorption of the polyester matrix (Figure 5-4b, dashed arrow).

a 2931 2876

2854 2936 Enmat/w-DDGS/PMDI/Corn oil

80/20/1/3

80/20/1/0

Absorbance 80/20/0/0

100/0/0/0

4000 3800 3600 3400 3200 3000 2800 2600 Wavenumber (cm-1)

Enmat/w-DDGS/PMDI/Corn oil 80/20/1/3

80/20/1/0 Absorbance

80/20/0/0

100/0/0/0

2200 2100 2000 1900 1800 1700 1600 1500 1400 1300 Wavenumber (cm-1)

Figure 5-4. FTIR spectra of the Enmat and some biocomposites. (a) 4000-2600 cm-1, and (b) 2200-1300 cm-1. 126

5.3.3. Mechanical properties

5.3.3.1. Tensile

The results of the tensile yield strength and modulus are depicted in Figure 5-5a

and b. For all samples during tensile test, the maximum stress in the stress-strain curve

occurred at yield point, thus the tensile strength of the biocomposites were equal to their

yield stress.

The yield strength and modulus are strongly affected by the interfacial adhesion

of the two phases and the increased tensile strength and modulus is a qualitative

representation of a better adhesion due to the load transfer happening at the interface

[40]. In this regard, the addition of w-DDGS with no compatibilizer resulted in a reducing trend of tensile strength from 16.3 MPa for the biocomposite of Enmat/w-

DDGS (80/20) to less than 10 and 5 MPa for the biocomposites of 40/60 and 60/40, respectively. Similar trend was observed for other mechanical properties including modulus and impact strength (data not shown here). This suggested a poor adhesion exists between DDGS particles and the matrix when no compatibilizer is added. For this reason, the biocomposite of Enmat/w-DDGS (80/20) was focused for further formulation optimization with compatibilizer and lubricant.

It is clear from Figure 5-5 that PMDI was effectively acting as a compatibilizer

since addition of PMDI led to a higher strength and modulus for a given amount of corn

oil. For example, the average tensile strength of Enmat/w-DDGS biocomposite was

increased from 16.3 MPa to 22.7 MPa after addition of 0.5% PMDI. Similarly, the modulus was improved from 0.97 GPa to 1.2 GPa for the same amount of PMDI. This

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was expected based on our previous study showing the PMDI compatibilization effect in a biocomposite of DDGS and another biopolymer system [34]. However, increasing the amount of PMDI from 0.5 to 1% did not influence these mechanical properties significantly which suggests that an optimum value of the PMDI amount for the interfacial adhesion improvement would be around 0.5%.

The elongation at break was also changed by the addition of PMDI. Generally when the particle-matrix bond is poor, it can behave as an inherent flaw that produces a cavity of its size [41]. The possibility of growing and merging these internal flaws during tensile test and transforming to a crack with a critical length can be increased with increasing the number of the flaws. Thus, the improved interfacial adhesion at w-DDGS– matrix interface as a result of PMDI compatibilization could help in preventing the formation of such internal cavity at the interface and delay the fracture in the sample while tensile test. In a similar way, the possible crosslinks occurring at the PBAT–PHBV interface could improve the interfacial adhesion within the matrix and consequently the elongation at break.

Unlike PMDI, addition of corn oil resulted in the decreased strength and modulus of the biocomposites. The processing force graphs reviewed in the section 5.3.1 also showed this behaviour of corn oil as a lubricant in this biocomposite system which can ease the mobility of the polymer molecular chains and reduce the internal friction between them. However, addition of corn oil reduced the elongation at break only when

PMDI was not added to the formulation. Interestingly, a synergistic effect of corn oil and

PMDI on the elongation at break was seen in the biocomposites containing both components. In other words, while addition of corn oil alone resulted in a reduced

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elongation at break, its inclusion along with PMDI created an increasing trend in the average elongation at break, unlike tensile strength and modulus (Figure 5-5c).

30 a PMDI (%) 25 0 0.5 1.0

Yield strength strength (MPa) Yield 5

0 036 Corn oil (%)

1400 b PMDI (%) 1300 0 0.5 1.0

1200

1100

1000

900

Tensile modulus (MPa) 800

700 036 Corn oil (%)

60 c PMDI (%) 50 0 0.5 1.0

% Elongation% breakat 10

0 036 Corn oil (%)

Figure 5-5. Tensile properties of the biocomposite formulations; tensile properties for the neat Enmat matrix were measured as: yield strength (24.5 ± 0.4 MPa), modulus (1170 ± 20 MPa) and % elongation at break (290 ± 30).

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5.3.3.2. Flexural

Figure 5-6a and b illustrate the measured flexural ultimate stress and modulus of the biocomposites. Basically, similar behaviour in these properties was observed with addition of PMDI and corn oil compared to tensile properties, i.e. the properties increased after addition of PMDI whereas a decreasing trend was obtained by amount of corn oil.

Similar to tensile properties, no significant change was observed in flexural ultimate stress when PMDI amount was increased from 0.5% to 1.0%.

40 a PMDI (%) 35 0 0.5 1.0 30

5 Flexural ultimate stress (MPa)

0 036 Corn oil (%)

1400 b PMDI (%) 1300 0 0.5 1.0

1200

1100

1000

900

Flexural modulus Flexural modulus (MPa) 800

700 036 Corn oil (%)

Figure 5-6. Flexural properties of the biocomposite formulations; the flexural ultimate stress and modulus for the neat Enmat matrix were measured as: (34.1 ± 0.5 MPa) and (1110 ± 20 MPa), respectively.

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5.3.3.3. Impact strength

The effect of PMDI and corn oil on the impact strength is presented in Figure 5-7.

PMDI was found to be very effective in improving the notched Izod impact strength

while corn oil alone showed an opposite effect.

A surprising improvement in the impact strength was obtained when both corn oil

and PMDI were added. This synergism can be more clear considering, for example, that

the average impact strength of Enmat/w-DDGS biocomposite was increased from 75 J/m

to 139 J/m with the addition of 1% of PMDI alone, and reduced to 68 J/m with the

addition of 3% of corn oil alone, while addition of the same amount of PMDI and corn oil together resulted in an average impact strength of 212 J/m.

Our observation regarding the improving effect of PMDI on the impact strength is different from the other works using PMDI as the compatibilizer. It has been reported that the improved adhesion at the interface of PLA-sugar beet pulp [42] and PHBV- bamboo pulp fiber [43] as a result of PMDI compatibilization prevented the fiber pull-out mechanism which has a significant contribution in energy absorption in impact test.

Previously, we had also observed similar behavior to these two works in a biocomposite of a PHBV-based blend and DDGS filler [34]. However, PMDI might have also a different influence in the present work since there is a possibility of crosslinking happening in the polymeric matrix between the two polyester components, i.e. PHBV and

PBAT, besides the interface of matrix-filler. Zhang et al. [44] have reported the increased

impact strength of the PLA/PBAT blend as a result of compatibilization with glycidyl

methacrylate. Their proposed mechanism for crosslinking exhibits the compatibilization

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reaction involving the hydroxyl group of polyester at the backbone terminals of

molecular chain. Also, similar result has been reported for PLA/PBS blend

compatibilized with isocyanate coupling agents [45].

The fact that the improvement in impact strength is more prominent in the

presence of corn oil along with PMDI might be due to the lubricating effect of corn oil while processing which can help increase the mobility of the polymer chains and availability of more sites for crosslinking reaction by PMDI.

300 PMDI (%) 250 0 0.5 1.0

200

150

100 Impact strength (J/m) 50

0 036 Corn oil (%)

Figure 5-7. Notched Izod impact strength of the biocomposites formulations; the neat Enmat matrix showed a non-break behavior in notched Izod impact test.

5.3.4. Melt flow index (MFI)

As mentioned in section 5.3.1, the crosslinking reaction during extrusion affected

the processing force obtained by the micro-extruder which was a measure of the

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viscosity. Since such biocomposites are targeted for injection molding application, their viscosity at molten state is of great importance. We have measured the MFI of the biocomposite formulations as a property very much affected by the viscosity. The results are depicted in Figure 5-8. The Enmat/w-DDGS biocomposite with no PMDI and corn oil exhibit a relatively high MFI value of about 21 g/10min which is suitable for injection molding applications. It is clear from the graph that the addition of corn oil as the lubricant alone increased the MFI, while PMDI reduced it drastically even at 0.5%. This can be another outcome of the strong effect of PMDI as compatibilizer in this biocomposite system that reduced the mobility of the polymer chains due to the crosslinking reactions. Addition of corn oil along with PMDI had no significant effect on the MFI values, thus the biocomposite formulations containing 0.5% of PMDI showed an average MFI of 5 g/10min and it reduced to less than 1 g/10min with increasing the

PMDI amount to 1%.

35 PMDI (%) 30 0 0.5 1.0

MFI (g/10min) MFI 10

0 036 Corn oil (%)

Figure 5-8. Melt flow index of the biocomposite formulations.

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5.3.5. Dynamic mechanical analysis (DMA)

5.3.5.1. Storage modulus

The dynamic mechanical properties of neat Enmat polymer and a selected number

of biocomposite formulations were studied over a broad range of temperature. The

storage modulus curves are shown in Figure 5-9a. This property is the elastic component of the viscoelastic response of the sample when dynamic strain is applied, thus represents the rigidity of the sample at a specific temperature. The curves illustrate that the storage modulus increased as w-DDGS was added to Enmat and it was further improved by addition of PMDI compatibilizer. This can be due to the improved interfacial adhesion between filler and matrix. This trend in storage modulus is in agreement with tensile and flexural moduli results discussed before. Also, the lubricating effect of corn oil in this biocomposite system can be deduced here from the decreased storage modulus of the biocomposites containing corn oil as compared to their counterparts without corn oil.

The first sudden reduction in the storage modulus observed in all curves attributes to the glass transition temperature of PBAT content in the Enmat matrix. Below this temperature, all matrix polymer chains, including PHBV chains, are completely immobile and rigid. An interesting observation was obtained when comparing the storage modulus curve of the biocomposite without compatibilizer and lubricant (80/20/0/0) to that of the biocomposite with compatibilizer and lubricant (80/20/1/3). The storage modulus response was found to be controlled by the lubricating effect of corn oil at temperatures where the matrix molecular chains are too “frozen” to be mobile (below Tg of PBAT). On the other side, the storage modulus response of the biocomposite was

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governed by the improvement in the interfacial adhesion as a result of PMDI

compatibilizer only when the polymer chains gained enough heat energy to start mobility

(above Tg of PBAT). The switchover point between these lubricant and compatibilizer

effects is depicted as point “S” in Figure 5-9a.

5.3.5.2. Tan δ

The mechanical loss factor, Tan δ, curves are demonstrated in Figure 5-9b. All curves show a major peak at lower temperatures and a small or shoulder peak at higher temperatures which correspond to glass transition of PBAT and PHBV, respectively. No such peak was observed for the w-DDGS protein probably due to the low content of it in the formulation. The maximum peak values represent the glass transition temperature

(Tg) of matrix polymers in the tested biocomposite formulations. The occurrence of two

distinct Tg for PBAT and PHBV states the immiscibility of the two polymers. As observed, these peaks are affected by addition of w-DDGS, corn oil and PMDI. The dashed lines in Figure 5-9b are used to track the peak shifts with respect to the Tg of

PBAT and PHBV of the neat polymer sample. It is clear from the figure that addition of corn oil reduced the Tg of PBAT, so did addition of w-DDGS possibly due to its oil content. However, the Tg values of PBAT in PMDI-compatibilized biocomposites were

higher than the respective in neat polymer. Studying the PHBV glass transition peaks, on

the other hand, shows that the Tg values of PHBV were affected by w-DDGS and corn oil

in the same way as for PBAT. But interestingly, the PMDI-compatibilized biocomposites

had lower Tg values for PHBV than that in the neat polymer sample. The shift of Tg

values of PBAT and PHBV towards each other in the PMDI-compatibilized

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biocomposites suggests that compatibilization and crosslinking reaction may have

happened at the PBAT–PHBV interface.

3500 a Enmat/w-DDGS/PMDI/Corn oil 3000 S (A) 100/0/0/0 2500 (B) 80/20/0/0 (C) 80/20/0/3 2000 (D) 80/20/1/0 (E) 80/20/1/3 1500 (E) (D) (C) (B) 1000 (A)

Storage Modulus (MPa) Modulus Storage 500

0 -50 -25 0 25 50 75 100 Temperature (°C)

0.16 b 0.14 Enmat/w-DDGS/PMDI/Corn oil (A) 100/0/0/0 0.12 (A) (B) 80/20/0/0 (C) 80/20/0/3 0.1 (D) 80/20/1/0 δ (E) 80/20/1/3 0.08 Tan 0.06 (B) (C) 0.04

0.02 PBAT glass PHBV glass (D) transition (E) transition 0 -50 0 50 100 Temperature (°C)

Figure 5-9. Dynamic mechanical analysis (DMA) curves of neat Enmat polymer and selected biocomposites, (a) Storage modulus, and (b) Tan δ.

To compare and quantify the effect of corn oil and PMDI on the state of adhesion between the w-DDGS and the Enmat polymer matrix, we have calculated the parameter

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of interaction (or adhesion parameter), A, from the following equation [46]:

1 tanδ A = c −1 (5.1) 1− v tanδ f m in which vf is the filler volume fraction and c and m subscriptions denote the composite and matrix, respectively. The polymer chain mobility at the interface of the filler and matrix is largely affected by the interaction level between two phases. The stronger is the interfacial adhesion, the lower would be the Tan δ of the composite and consequently the parameter A value. Thus, lower A values reflect stronger interfacial adhesion.

The calculated parameter A values for the biocomposites at selected temperatures are depicted in Figure 5-10. Basically, addition of corn oil slightly increased the A values compared to Enmat/w-DDGS (80/20). Moreover, PMDI-compatibilized biocomposites showed smaller A values almost for the whole range. This also admits the strong interaction at the interface of w-DDGS and matrix as a result of PMDI compatibilization.

0.35 (B) 0.25 (A)

0.15

0.05 (D) A -0.05 (C) Enmat/w-DDGS/PMDI/Corn oil -0.15 (A) 80/20/0/0 (B) 80/20/0/3 -0.25 (C) 80/20/1/0 (D) 80/20/1/3 -0.35 -40-200 20406080 Temperature (°C)

Figure 5-10. Parameter of interaction, A, between w-DDGS and matrix calculated for selected biocomposite formulations.

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5.3.6. Morphology

The morphology of the neat Enmat polymer and biocomposites were studied through impact-fractured surfaces. Two aspects were intended to investigate including interactions at DDGS–matrix interface as well as at PBAT–PHBV interface in the matrix itself. Figure 5-11 shows the SEM images of uncompatibilized and compatibilized

biocomposites. The uncompatibilized sample exhibited a rough fracture surface (Figure

5-11a) because of several pulled-out w-DDGS particles or the respective holes due to the

same mechanism of pulling-out occurred on the other surface of fracture. On the other

hand, the compatibilized biocomposite had a very smoother fracture surface throughout

the whole surface with much fewer pulled-out w-DDGS particles (Figure 5-11b). This

observation admitted the improvement in interfacial adhesion after addition of PMDI

compatibilizer. The high resolution implemented by SEM helped in better understanding

of such improvement when observing individual w-DDGS particles at higher

magnifications. As presented in Figure 5-11c and d, the w-DDGS particles in the

uncompatibilized biocomposite were mostly detached and raised from the matrix with a

gap between them whereas in the compatibilized biocomposite, the w-DDGS particles

were embedded and covered by the matrix that made it hard to distinguish between the

two phases.

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Figure 5-11. Scanning electron microscopy (SEM) images of the w-DDGS–Enmat interface. (a) Enmat/w- DDGS (80/20); (b) Enmat/w-DDGS/PMDI (80/20/1); (c) Enmat/w-DDGS (80/20), higher magnification, and (d) Enmat/w-DDGS/PMDI (80/20/1), higher magnification.

The images related to the PBAT–PHBV interaction within the matrix are shown in Figure 5-12 at higher magnifications. In the neat Enmat polymer, the morphology consisted of PBAT phase as the continuous matrix with dispersed PHBV phase in it. The

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gap between these two phases of the matrix was clearly observed along with several holes on the surface due to the detachment of PHBV phase (Figure 5-12a and b). Similar observations were made for the uncompatibilized biocomposite when focusing on the interface of PBAT and PHBV as observed in Figure 5-12c and d. However, different morphology was obtained after addition of PMDI compatibilizer. The dispersed PHBV phase in the compatibilized biocomposite was covered by the PBAT continuous phase and PHBV detachment from the PBAT phase was rarely observed (Figure 5-12e and f).

140

a b

30 µm 8.6 µm

c d

30 µm 8.6 µm

e f

30 µm 8.6 µm

Figure 5-12. Scanning electron microscopy (SEM) images of the PBAT–PHBV interface. The images show (a) and (b) neat Enmat; (c) and (d) Enmat/w-DDGS (80/20); and (e) and (f) Enmat/w-DDGS/PMDI (80/20/1) biocomposites.

141

Based on the mechanical and physical properties presented before and the SEM observations explained here, the reactions at the interfaces of w-DDGS–matrix and

PBAT–PHBV in presence of PMDI compatibilizer can be presented schematically as in

Figure 5-13. Occurrence of such crosslinking phenomenon at different interfaces could be the reason of the significant improvement in mechanical performance, especially impact strength, of the w-DDGS biocomposite after addition of PMDI compatibilizer.

HO OH PHBV O=C=N N=C=O HO NH2 HO OH + DDGS + PMDI HO OH O=C=N N=C=O H2N OH PBAT HO OH

Reactive extrusion

HO OH

O PHBV O C O O C NH NH N=C=O O=C=N O PMDI O PMDI O NH C O HN C NH N=C=O HO O C NH DDGS O PBAT O O O C NH N=C=O HO O C NH HN C NH PMDI O PMDI O O NH C O OH O=C=N NH C O O C NH O PBAT O PHBV O O C NH NH C O N=C=O HO O C NH PMDI O O PMDI N=C=O O=C=N NH C O HN C NH DDGS

H2N OH

Figure 5-13. Schematic presentation of the crosslinking reactions occurring at the w-DDGS–matrix and PBAT–PHBV interfaces as a result of compatibilization with PMDI during reactive extrusion.

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Due to this effective mechanism of crosslinking proposed for the studied

compatibilizer and lubricant system, it is anticipated that the biocomposites of Enmat/w-

DDGS with w-DDGS concentrations of more than 20 wt. % would exhibit almost the same level of tensile strength with improved modulus due to the higher w-DDGS fiber

content in the biocomposite formulation. However, the elongation-at-break might be

reduced as a result of the replacement of the flexible matrix (Enmat) by the rigid w-

DDGS particles in the formulation. Same is expected for MFI results. A separate

systematic research is recommended for a deeper understanding and optimization of

compatibilizer and lubricant amount when higher w-DDGS concentrations are used.

It is expected that other reactive compatibilizers that generate the same

mechanism of extensive covalent bonds between the matrix and O-H and N-H groups of

DDGS particles as well as between the O-H groups of the polymer chains within the

matrix, would create similar effect on the mechanical and physical properties of DDGS

biocomposite. Therefore, compatibilizers such as other di- or tri-isocyanates are expected

to improve the mechanical performance and be more effective in presence of corn oil or

other lubricants that are compatible with DDGS and bioplastics.

5.3.7. Water absorption measurements

The water absorption measurements for the neat Enmat polymer and some

biocomposite formulations were studied over long time and are shown in Figure 5-14.

Generally, DDGS incorporation into the Enmat matrix resulted in higher moisture uptake.

DDGS is a hydrophilic material compared to the Enmat polymer due to the higher

amount of O–H and N–H groups which are favorable for hydrogen bonding with water

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molecules. The neat Enmat polymer reached the water absorption saturated point at less

than 1% after almost 25 days. However, all the biocomposite formulations did not show

the saturation even after 300 day. This behavior has also been reported for biocomposites of PLA–sugar beet pulp compatibilized with PMDI after 200 days [42]. Similar to that work, we observed that the initial rate of water absorption was reduced by the addition of

PMDI, irrespective of corn oil addition, but gradually reached the absorption level of uncompatibilized formulation. The initial improved resistance to water absorption might be due to the consumption of hydroxyl groups of DDGS in the crosslinking reaction.

However as mentioned in the previous sections, the crosslinking reaction could result in new N–H groups after formation of urethane and urea bonds between Enmat or DDGS and PMDI. These N–H groups could also create hydrogen bond with water molecules similar to O–H groups but weaker due to lower electronegativity of nitrogen compared to oxygen.

5 Enmat/w-DDGS/PMDI/corn oil 4 80/20/0/0 80/20/1/3 3 80/20/1/0 2 100/0/0/0 Water absorption (%) absorption Water 1

0 0 50 100 150 200 250 300 350 400 days after immersion

Figure 5-14. Water absorption results of neat Enmat polymer and selected w-DDGS biocomposites.

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5.4. Conclusions

A biocomposite of DDGS and PBAT/PHBV blend was produced by reactive melt

extrusion and injection molding. The effect of compatibilizer (PMDI) and corn oil

lubricant on different properties were studied. Occurrence of crosslinking reaction after

compatibilization was admitted by FTIR spectra of biocomposites. PMDI and corn oil

showed a synergized improving effect on elongation at break and impact strength of the biocomposite so that an inclusion combination of 1% PMDI and 3% corn oil resulted in

impact strength of more than 200 J/m. The crosslinking effect of PMDI resulted in the

reduced MFI of the biocomposites. The water absorption of biocomposites was higher

than that of the matrix, but PMDI addition reduced the initial absorption rate to some

extent. Dynamic mechanical analysis (DMA) showed an increase in storage modulus of

the matrix polymer after incorporation of DDGS. Further addition of PMDI and corn oil

resulted in the increment and decrement of storage modulus of the biocomposites,

respectively. The calculated parameter of interaction, A, from Tan δ curves admitted stronger bonds at the DDGS–matrix interface after PMDI compatibilization. Moreover, the glass transition peaks pertaining to PBAT and PHBV of the matrix shifted slightly towards each other which suggested occurrence of crosslinking at the PBAT–PHBV interface as well. The improved interfacial adhesion of at DDGS–matrix and PBAT–

PHBV interfaces was justified by the SEM observations.

145

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Chapter 6: A Statistical Approach to Engineer a Biocomposite Formulation from Biofuel Coproduct with Balanced Properties∗

Abstract: A 32-full factorial design of experiment (DOE) and regression modeling were implemented together as a practical approach to develop a distillers’ grains-filled biocomposite with balanced mechanical and physical properties. The effects of compatibilizer and lubricant on tensile strength, flexural modulus, impact strength and melt flow index of the biocomposites were studied. Analysis of variance (ANOVA) was implemented to develop least square regression models containing statistically significant main effects (linear and quadratic) and interaction effect. The developed models showed good predictability for the new measurements. The statistical approach adopted in this work including overlaying contour plots of the response surfaces in the studied level domain was effective in highlighting an optimized region that leads to balanced mechanical and physical properties.

∗ A version of this chapter has been published in: Zarrinbakhsh N., Defersha F.M., Mohanty A.K., Misra M. “A statistical approach to engineer a biocomposite formulation from biofuel coproduct with balanced properties”, Journal of Applied Polymer Science. 131 (2014) 40443, doi: 10.1002/app.40443. 150

6.1. Introduction

More than 10 billion people are expected to inhabit the globe in less than 40 years

[1]. With this, the sustainability of the current depleting petroleum resources is a huge concern for satisfying the energy demand of the growing population. Thus for today’s and the future generations, the energy resources have to be renewable in a reasonable period of time. The transportation sector is a main petroleum consumer. Biodiesel and biobased ethanol are two candidates from renewable resources for substituting the petroleum-based fuels and the aim is to gradually reduce the contribution of the petroleum in transportation fuels [2].

Corn and sugar are currently the major precursors for producing biobased ethanol.

Having a higher energy return on investment (EROI) value, lignocellulosic resources have recently been considered as future feedstock for the second generation of biobased ethanol [3]. However, it is projected that by 2020 the lignocellulosic matter will only contribute a 4% share to the total biobased ethanol production whereas corn and sugar

will still contribute the most (78%) [4]. Therefore, the future of this industry is highly

affected by the sustainability of the current first generation of biobased ethanol.

With the recent expansion in dry mill plants and corn ethanol production, the

sustainability of this industry is critically tied with finding new revenue streams for it,

especially from its coproducts, CO2 and distillers’ grains. These coproducts are produced

as much as ethanol on a weight basis [5]; however, it is a challenge now to maximize the

revenue from selling these coproducts. The raw CO2 from corn ethanol plants cannot be utilized for the beverage and dry ice markets unless further refining steps of CO2 are

151

adopted [6]. Distillers’ grains only known use is as a low cost feed partially blended in

livestock diet [5].

With the low cost of distillers’ grains, there is a great motivation to seek new

applications for it with the aim of value addition. In this regard, distillers’ grains have been compounded with several thermoset [7, 8] and thermoplastic [9, 10] polymers. The first few studies suggested that biocomposites of as-received distillers’ grains are not satisfactory so far as the mechanical properties are concerned. Therefore, pretreatment and/or compatibilization are two methods that may serve to enhance performance. For performing these methods, the composition of distillers’ grains needs to be investigated.

Dried distillers’ grains with solubles (DDGS) mainly consist of protein, fiber (cellulose and hemicellulose), lipid (oil), water-solubles and residual starch. The water-solubles need to be washed out for improved thermal stability of the biomass during composite melt processing [11]. The rigid fiber component of DDGS can contribute to modulus improvement while the protein and oil components may create a plasticized phase which decreases the final material stiffness. Notably, the complex composition of DDGS contains several functional groups of O-H and N-H which are capable of chemical reaction with proper compatibilization [12]. By choosing a reactive compatibilizer, crosslinks can form at the matrix-filler interface which can improve the mechanical properties significantly.

Aiming at an eco-friendly and biodegradable biocomposites, it was shown in

Chapter 4 that DDGS is a promising filler with utilization of a compatibilizer. Although

the produced DDGS biocomposite had strength as high as that for the biodegradable

matrix along with higher modulus, the impact strength and elongation of the material was

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drastically reduced [13]. In Chapter 5, a high-impact DDGS biocomposite was developed

with improved modulus compared to the biodegradable matrix and a tensile strength very close to that of the matrix [12]. A bio-based lubricant was added to enhance the processability of the biocomposite together with the compatibilizer to enhance its mechanical performance. A synergistic effect of compatibilizer and lubricant on the

impact strength was observed, while tensile properties were affected by compatibilizer

and lubricant in different ways. On the other hand, the melt flow of the produced material

was highly influenced by the compatibilizer only. The effects of compatibilizer and

lubricant on different mechanical and physical properties were so complex that a more in-

depth statistical approach seemed to be useful to draw an optimum region of the

material’s formulation and to identify the materials behavior for more practical

applications.

For most engineering applications, such as automotive interior parts, the

polymeric material needs to satisfy specific requirements of mechanical performance

including rigidity, strength and toughness. At the same time, the physical properties such

as flowability of the melt are important for manufacturing aspects. Therefore, in the

present work, we are trying to find the optimized formulation of the high-impact DDGS

biocomposite with balanced rigidity, strength and melt flow properties. The interaction

between the factors (compatibilizer and lubricant) is also examined with respect to

different material properties. The approach here is a full factorial design of experiments

(DOE) followed by statistical analysis of response surface methodology (RSM) using

Minitab® software.

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6.2. Experimental

6.2.1. Materials

The bioplastic matrix used in this research was a commercial biodegradable polymer marketed as Enmat Y5010P from TianAn Biologic Materials Co., Ltd., China.

The polymer was a blend of polyhydroxy(butyrate-co-valerate), PHBV, and poly(butylene adipate-co-terephthalate), PBAT. Dried distillers’ grains with solubles

(DDGS) was supplied by GreenField Ethanol Inc., Chatham, Canada. Polymeric methylene diphenyl diisocyanate (PMDI) was used as the compatibilizer commercially named as RUBINATE® M from Huntsman Polyurethanes, Canada. Corn oil was purchased from the market and used as the processing aid lubricant for biocomposite processing.

6.2.2. Biocomposite processing and characterization

DDGS biocomposites with constant ratio of DDGS to bioplastic (hereinafter mentioned as Enmat), 20 to 80 (weight basis), with different levels of compatibilizer and lubricant were produced. The biocomposite processing was performed in a micro twin- screw extruder followed by injection molding in a micro injection molding machine, both from DSM Xplore. The processing conditions were kept constant for all samples. The processed biocomposites were characterized for their tensile strength, flexural modulus, impact strength and melt flow index (MFI). Detailed information about processing conditions and characterization method has been published in our previous work [12].

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6.2.3. Design of experiments

The experiments were designed to investigate the effects of two variable factors

on four measured responses. The variable factors are PMDI compatibilizer and corn oil

lubricant amounts and the measured responses are tensile strength, flexural modulus,

impact strength and melt flow index of the biocomposites. The amount of PMDI compatibilizer was kept limited up to 1 wt. % since higher amounts could result in occurrence of excessive crosslinking of the matrix and inhibit the flow of the molten

material completely. Also, the excessive crosslinking in the matrix can make the

microbial break-down of molecular chains more difficult which has an adverse effect on

biodegradability of the final biocomposite [14]. The amount of corn oil was kept, by

experience, not more than 6 wt. % since higher amounts resulted in improper mixing of

the corn oil with the polymer matrix and DDGS filler.

Response surface methodology has been implemented here to find an optimized

level of the independent variables (factors), PMDI and corn oil, while keeping a balance

between mechanical properties and MFI as the measured responses. Response surface

methodology is usually coupled with a central composite design of experiment as an ideal

design to study the curvature of the response function. However, a 32 full factorial design

of two factors with 3 levels was adopted here due to the limitations on the levels of PMDI

and corn oil and ease of processing. Such a design is also certainly a possible choice to

investigate the curvature in response surfaces [15]. The schematic of the design is shown

in Figure 6-1. The levels of both PMDI and corn oil are the ratio of the weight of each additive to the weight of the composite’s load-bearing components (biopolymer plus

DDGS).

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3 Corn oil Corn %) (wt. 0 0 0.5 1.0 PMDI (wt. %)

Figure 6-1. The schematic of the design of experiments in the present work.

6.2.4. Statistical analysis

Minitab® statistical software, version 16, was used to analyze the significance of the effects of the factors via ANOVA. This approach is used to: (1) generate the quadratic regression model for each response with least square method, (2) check the model adequacy using residual analysis, (3) plot the response surfaces and the respective contours, and (4) overlap the contour plots of different responses to find the optimized formulation region. A significance level of 0.05 was considered in this study.

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6.3. Results and discussion

6.3.1. Effects of compatibilizer and lubricant on mechanical and physical properties

Mechanical and physical properties of the different formulations investigated in this study are presented in Table 6-1. These properties were selected for optimization analysis since tensile strength and flexural modulus are good measures of strength and rigidity of the resulting material, respectively. Moreover, impact strength and melt flow index (MFI) of a material represent its toughness and flowability/processability. These are typical properties of a commercial product for injection molding applications that are usually reported in materials’ technical datasheet. Thus, the optimization of the formulation based on these criteria is adopted in our investigation to obtain a material with balanced mechanical performance and processability.

Table 6-1. Mechanical and physical properties of different formulations (data adopted from [12])

Corn oil PMDI Tensile strength Flexural modulus Impact strength MFI (wt. %) (wt. %) (MPa) (MPa) (J/m) (g/10min) 0 16.3 ± 0.4 1090 ± 30 75 ± 6 20.9 ± 2.1 0 0.5 22.7 ± 0.5 1350 ± 10 126 ± 8 3.9 ± 0.5 1.0 22.7 ± 0.4 1250 ± 40 139 ± 21 0.4 ± 0.2 0 12.5 ± 0.7 930 ± 40 68 ± 5 26.3 ± 3.1 3 0.5 20.3 ± 0.5 1080 ± 20 159 ± 15 7.5 ± 1.4 1.0 20.5 ± 0.7 1110 ± 20 212 ± 13 0.5 ± 0.2 0 10.5 ± 0.3 820 ± 20 63 ± 7 27.7 ± 3.0 6 0.5 17.5 ± 0.3 1020 ± 30 129 ± 6 3.8 ± 0.5 1.0 18.0 ± 0.6 930 ± 50 200 ± 60 0.1 ± 0.0

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In Figure 6-2, the main effect plots (left hand side) and interaction plots (right

hand side) of the two variable factors, compatibilizer (PMDI) and lubricant (corn oil), are

illustrated. As also reported in our previous work [12], PMDI had been used as the

compatibilizer to enhance the mechanical performance of the DDGS biocomposite. Its

positive effects on tensile strength, flexural modulus and impact strength can be observed

by looking at the main effect plots as well as the interaction plots with constant corn oil and varying PMDI amounts in Figure 6-2. On the other hand, it is obvious that the

addition of PMDI drastically reduced the MFI. Moreover, we observed an increment of

the mixing force with the addition of PMDI during processing of the biocomposites.

Therefore, corn oil was introduced to this biocomposite system as the lubricant for the

ease of processing and to increase the MFI of the final biocomposite. The interaction plot for MFI in Figure 6-2 shows enhancement of this measured response with the addition of

corn oil alone (when PMDI level is zero).

It is also observed in Figure 6-2 that the two factors, PMDI and corn oil, affect the

tensile strength in two different ways; same is observed for flexural modulus. No

interaction between PMDI and corn oil is seen for tensile strength and flexural modulus.

However, an interaction between the variable factors possibly exists with respect to the

impact strength. This can be realized from the interaction plot for impact strength which

shows a change in the plot’s slope (from negative to positive slope) with the addition of

PMDI within the 0-3 wt. % of corn oil. Moreover, Figure 6-2 demonstrates that the MFI response is more influenced by PMDI factor than by corn oil. The complex effects the two factors and their interaction are studied in the following sections more in-depth.

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(Response is Tensile Strength (MPa)) (wt. %) 24 PMDI(wt. (phr) %) Corn oil (phr) 22 0.0 21 20 0.5 19 18 1.0 16 17 PMDI

Mean 14 Mean 15 12 (wt. %) 10 13 0 3 6 0.0 0.5 1.0 0 3 6 Corn oil (wt. %)

(Response is Flexural Modulus (MPa)) 1400 PMDI (wt.(phr) %) Corn oil(wt. (phr) %) 0.0 1300 0.5 1200 1200 1.0 1100 1100 PMDI 1000 Mean Mean 1000 900 (wt. %) 800 900 0 3 6 0.0 0.5 1.0 0 3 6 Corn oil (wt. %)

(Response is Impact Strength (J/m)) 225 PMDI (wt.(phr) %) Corn oil(wt. (phr) %) 200 0.0 180 175 0.5 160 150 1.0 140 125 PMDI 120 Mean 100

Mean (wt. %) 100 75 50 80 0 3 6 60 0.0 0.5 1.0 0 3 6 Corn oil (wt. %)

(Response is MFI (g/10min)) 30 PMDI (wt.(phr) %)Corn oil (wt.(phr) %) 0.0 25 25 0.5 20 1.0 20 15 15 10 PMDI Mean

Mean 10 5 (wt. %) 5 0 0 0 3 6 0.0 0.5 1.0 0 3 6 Corn oil (wt. %)

Figure 6-2. The main effects plots (left) and interaction plots (right) of the variable factors for all responses.

6.3.2. Model development via ANOVA approach

The analysis of variance (ANOVA) is a useful tool to evaluate the significance of a factor and, in case of more than one factor, the interactions between the factors with respect to a specific response. The factors can be studied in two or more levels and the predictive capability of the regression model developed by ANOVA is dependent upon the number of levels chosen for the factors. In most preliminary studies, a linear model suits the requirements by changing the factors in two levels only (low and high levels).

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For more thorough investigations, the factors can be studied in more than two levels so

that a regression of higher order can be developed, the factor interactions of higher

degree can be evaluated and the curvature in the response plot can also be considered

[15].

In this work, a two-way ANOVA is implemented as two factors are studied. The

factors were changed in three levels and a quadratic regression model is developed

including the interaction of the two factors. The general format of the regression model

for each response (R) would be:

2 2 R = a0 + a1P + a2C + a3P + a4C + a5P×C + ε (6.1)

where P and C denote the PMDI and corn oil amounts in wt. %, respectively, and ai are

equation constant and coefficients to be estimated by least square regression, and ε is the

error term of the model.

Table 6-2 shows the ANOVA tables obtained for the all responses considering full

model. The P-values for individual factor effects of first and second order as well as and their interaction are listed. This P-value is an indication of whether the specific studied term is statistically significant or not. For the significance level of 5%, the P-values of less than 0.05 indicate a statistically significant effect that has to be considered in the least square regression model. Referring to Table 6-2, the quadratic corn oil effect on

tensile strength, the PMDI-corn oil interaction effect on flexural modulus and the

quadratic PMDI effect on impact strength are not statistically significant. Therefore, these

effects were eliminated in generating the regression model of the respective responses.

The ANOVA table for the reduced model of these three responses are presented in Table

6-3.

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Table 6-2. ANOVA table for full model of all studied responses

Analysis Variance of for Flexural Modulus

adjusted sums of squares, Adj MS: adjusted squaresmean

sequential sums of squares, Adj SS:

Analysis of Variance for Tensile Strength Tensile for Variance of Analysis Strength Impact for Variance of Analysis Index Melt Flow for Variance of Analysis DF: Degree of freedom, Seq SS: Source DF Seq SS Adj SS Adj MS F P Source DF Seq SS Adj SS DF Adj MS Seq SS Adj SS F Adj MS P F P DF Seq SS Adj SS Adj MS F P

Total 44 737.432 44 1146344 0.000 177.00 509.594 1146344 2547.97 44 2547.97 5 0.000 47.20 Regression Linear PMDI 27552.0 oil Corn Square 5 PMDI*PMDI 505.67 0.000 145.246 726.230 726.230 5 737.432 oil oil*Corn Corn 216498 132.23 1082489 0.000 1082489 Interaction 137760 2 oil PMDI*Corn 1 1 1 1 Error Residual 603.936 Lack-of-Fit 401.136 202.800 2 120.409 0.144 256.471 1 Error Pure 219.568 120.409 20.334 137760 128.236 44 Total 1 120.553 219.568 0.144 120.409 446.45 1.741 39 120.553 20.334 764.42 419.20 1.741 0.000 0.144 3 60.276 0.000 70.79 11.202 1.741 0.000 5 Regression 36 2 209.85 1.741 0.000 0.50 Linear 11.202 1 2.970 1 1.741 0.000 PMDI 8.232 902873 0.483 1.741 1 oil 0.287 Corn 174041 2.970 160360 6.06 2.879 2 382699 Square 8.232 54.70 241193 1 728833 6.06 583.7 PMDI*PMDI 160360 54.70 0.018 191350 0.990 176736 19 oil oil*Corn Corn 28019 241193 Error 104555 0.229 160360 0.018 116.87 16376 28019 Interaction 176736 1 147.31 4.33 2 104555 48 97.94 0.000 oil PMDI*Corn 1 1 1 1 1 0.000 16376 88368 Residual 63.86 0.011 0.000 121263 2602.67 2880 Lack-of-Fit 118393 2 6728 16376 53.97 0.000 2880 1 2869 Error Pure 1729 12353 3 24 39 Total 1 2880 9869 0.000 10.00 6176.3 8456 6728 2880 3581 8041 1729 28674 165779 0.003 9869.3 63855 10.58 2880 8041 6727.6 3 3581.2 1728.8 8456 28674 16.91 36 2880 8041 63855 53 45 0.000 11.53 1.76 8041 6.13 4228.2 2.96 4868 0.000 35181 8041.0 9558 1.76 23151 1637 0.001 2 0.192 8041.0 7.24 0.017 0.092 13.78 1 35181 0.192 4868 9.78 23151 2183.24 1 13.78 0.002 1 0.001 1 2173.28 1622.7 0.000 839.36 514.5 977 0.001 23.62 771.84 2 1 419.680 309.91 3.15 9.96 1 771.839 145.77 21.47 323.66 333.53 31.20 0.034 268.08 0.000 51.84 323.663 31.20 21.472 0.000 341.79 3 31.20 112.42 51.839 170.895 7.46 31.20 0.000 31.196 18.01 59.36 22.51 0.013 31.196 0.000 10.84 0.000 16 22.51 10.84 0.004 32.20 0.004 7.502 32.20 3.73 2.012 0.033

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Table 6-3. ANOVA table for reduced model of tensile strength, flexural modulus and impact strength

Analysis of Variance for Tensile Strength Source DF Seq SS Adj SS Adj MS F P Regression 4 726.086 726.086 181.521 639.94 0.000 Linear 2 603.936 420.270 210.135 740.81 0.000 PMDI 1 401.136 219.568 219.568 774.07 0.000 Corn oil 1 202.800 100.572 100.572 354.56 0.000 Square 1 120.409 120.409 120.409 424.49 0.000 PMDI*PMDI 1 120.409 120.409 120.409 424.49 0.000 Interaction 1 1.741 1.741 1.741 6.14 0.018 PMDI*Corn oil 1 1.741 1.741 1.741 6.14 0.018 Residual Error 40 11.346 11.346 0.284 Lack-of-Fit 4 3.114 3.114 0.779 3.40 0.018 Pure Error 36 8.232 8.232 0.229 Total 44 737.432 Analysis of Variance for Flexural Modulus DF Seq SS Adj SS Adj MS F P Regression 4 1079609 1079609 269902 161.78 0.000 Linear 2 902873 379847 189924 113.84 0.000 PMDI 1 174041 250445 250445 150.11 0.000 Corn oil 1 728833 129402 129402 77.56 0.000 Square 2 176736 176736 88368 52.97 0.000 PMDI*PMDI 1 160360 160360 160360 96.12 0.000 Corn oil*Corn oil 1 16376 16376 16376 9.82 0.003 Residual Error 40 66735 66735 1668 Lack-of-Fit 4 31554 31554 7888 8.07 0.000 Pure Error 36 35181 35181 977 Total 44 1146344 Analysis of Variance for Impact Strength DF Seq SS Adj SS Adj MS F P Regression 4 136031 136031 34007.8 56.02 0.000 Linear 2 121263 22511 11255.7 18.54 0.000 PMDI 1 118393 21951 21950.8 36.16 0.000 Corn oil 1 2869 3581 3581.2 5.90 0.019 Square 1 6728 6728 6727.6 11.08 0.002 Corn oil*Corn oil 1 6728 6728 6727.6 11.08 0.002 Interaction 1 8041 8041 8041.0 13.25 0.001 PMDI*Corn oil 1 8041 8041 8041.0 13.25 0.001 Residual Error 49 29748 29748 607.1 Lack-of-Fit 4 6597 6597 1649.2 3.21 0.021 Pure Error 45 23151 23151 514.5 Total 53 165779 DF: Degree of freedom, Seq SS: sequential sums of squares, Adj SS: adjusted sums of squares, Adj MS: adjusted mean squares

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The least square regression models developed from the three-level factorial design

and (reduced) ANOVA tables are listed in Table 6-4. The models will be used to plot the

response surfaces and find the optimized region with desired combination of response

values. The R2 statistics for the developed models are also presented. The results of the lack-of-fit test in Table 6-3 and R2 statistic in Table 6-4 are discussed in the following

section.

Table 6-4. Regression models and R2 statistic obtained for each response

Response Regression model R2 statistic R2= 98.46% Tensile strength R2 = 98.31% TS = 16.0017 + 20.6033P - 0.9650C -13.8800P2 + 0.1967PC adj (MPa) PRESS = 14.0084 2 R pred = 98.10% R2= 94.18% Flexural R2 = 93.60% FM = 1114.89 + 658.87P - 78.93C -506.53P2 + 4.50C2 adj Modulus (MPa) PRESS = 84461.2 2 R pred = 92.63% R2= 82.06% Impact strength R2 = 80.59% IS = 73.901 + 78.086P + 12.660C + 12.203PC - 2.631C2 adj (J/m) PRESS = 37728.5 2 R pred = 77.24% R2= 97.90% MFI = 21.4923 - 51.3187P + 2.2377C - 1.1350PC + 30.1490P2 - R2 = 97.35% MFI (g/10min) adj 0.2213C2 PRESS = 101.570 2 R pred = 96.10%

6.3.3. Model adequacy check

The developed regression models with ANOVA approach needs adequacy check

for at least three aspects, (i) the validity of assumption made in ANOVA about normal

distribution of the errors, (ii) the lack-of-fit tests for the fitted model, and (iii) the R2 statistic for variability in the data explained by the model.

The normal distribution assumption for the errors has been checked by illustrating the normal probability plots for the residuals resulted from each developed model. Figure

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6-3 presents these plots. It is observed that all residual plots follow a straight line and confirm the validity of normal distribution assumption. In this method, the more emphasis is put on the middle part of the plot rather than the two extremes and small deviation from normality at these end points are of little concern [15].

(response is Tensile Strength (MPa)) (response is Flexural Modulus (MPa)) 99 99

95 95

80 80 60 60 40 40 20 20

5 5 Normal % probability Normal % probability Normal 1 1 -1.5 -1.0 -0.5 0.0 0.5 1.0 -100 -50 0 50 100 Residual Residual

(response is Impact Strength (J/m)) (response is MFI (g/10min)) 99 99 95 95

80 80 60 60 40 40 20 20

5 5 Normal %probability Normal %probability 1 1 -75 -50 -25 0 25 50 -4 -3 -2 -1 0 1 2 3 4 Residual Residual

Figure 6-3. Normal probability plots of residuals for all responses.

When replicates exist in the data points, the lack-of-fit test in ANOVA is one of the ways to check whether the developed model including the existing terms of effects

(main effects and interaction) is fitting well the experimental data. In this test, the contribution of sum of squares for lack-of-fit towards the sum of squares of residual error is separated from the sum of squares of pure error. The lack-of-fit statistic is then calculated by dividing the mean square of lack-of-fit by that of pure error [15].

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The ANOVA results already presented in Table 6-2 and Table 6-3 show that the

lack-of-fit test statistic is significant in all cases. Several possibilities need to be

considered here. Firstly, it may suggest that the experimental data points are better

described by a regression model with higher order, i.e. a 42 full-factorial design needs to

be performed to obtain a more accurately fitted model. It may also be the result of

occurrence of several data points with unusually large residual that cannot be explained

by the existing fitted model. Moreover, it can also be partly because the mean square of

the pure error is so significantly low that leads to a significantly high lack-of-fit statistic

and this can sometimes happen as a result of precise measurements. Thus, it is recommended to consider the result from the lack-of-fit test along with R2 statistic. The

R2 statistic is another informative approach to evaluate the applicability of the developed

model. This information basically represents the variation about the mean values

explained by the model and indicates an overall measure of the obtained fit.

2 2 The calculated values of the R and R adj show that the models reasonably fit the

experimental data. Moreover, the PRESS (prediction error sum of squares) can measure

how capable the model is to predict the responses in a new experiment, and alternatively,

2 2 R pred (R for prediction) can be calculated from the PRESS for the same purpose. The

2 R pred in Table 6-4 indicate that the models can very well predict responses for new

observations.

With these contradictory conclusions from lack-of-fit test and R2 statistic, it is

worth to note that when a large amount of data are involved, a partially deficient model

could be, nevertheless, applicable and sufficient to be used with proper caution [16].

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Therefore, a new data point was experimentally tested. The DDGS biocomposite was formulated again from DDGS/bioplastic (Enmat), 20/80 (weight basis), and 0.75 wt.

% of PMDI and 3 wt. % of corn oil. The experimentally measured physical and mechanical properties of this formulation are listed in Table 6-5. The respective calculated values from the fitted model are also presented. The comparison between these two sets of data shows that there was a fairly good compliance between experimental and predicted values. The absolute difference between the predicted values and the experimental ones in worst case was not more than 7.1%. An important point to mention is that the pattern of the difference between predicted and experimental results among the responses does not follow the pattern of significance of the lack-of-fit statistic among them. Referring to Table 6-2 and Table 6-3, the lack-of-fit is the most significant for the

flexural modulus > tensile strength > impact strength > MFI, while the absolute

difference between predicted and experimental outputs is the higher for tensile strength >

impact strength > MFI > flexural modulus (Table 6-5). This confirms that both lack-of-fit

statistic and R2 statistic should be taken into account in order to examine the applicability

of the fitted models.

Table 6-5. Experimental and predicted output of responses for the DDGS biocomposite formulation with 0.75 wt. % of PMDI and 3 wt. % of corn oil

Tensile Flexural Impact MFI Source strength Modulus strength (g/10min) (MPa) (MPa) (J/m) Experiment 19.8 ± 1.1 1090 ± 20 166 ± 13 2.2 ± 0.3 Regression model 21.2 1130 174 2.1 Deviation of predicted value from experimental value (%) + 7.1 + 3.7 + 4.8 - 4.6

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6.3.4. Other residual plots

Apart from normal probability plot of residuals, other plots can be illustrated to

obtain other useful information. By plotting the residuals versus fitted values, one can

again check the normality assumption and/or whether the residuals follow any pattern with respect to a specific variable. Figure 6-4 shows the residual plots against the fitted

values for all responses. Generally, the residual plots are structureless with respect to the

fitted values except for the impact strength that shows large residuals at the extreme right

hand side of the plot. This behavior is too mild to be considered as a heteroscedastic

behavior for the residuals, especially that it is very outstanding only at fitted values of

more than 200 J/m. This behavior can usually occur when the error of the experiment is a

percentage of the magnitude of the response value [15].

(response is Tensile Strength (MPa)) (response is Flexural Modulus (MPa)) 1.0 50 0.5

0.0 0

-0.5 Residual Residual -50 -1.0

-1.5 -100 10 12 14 16 18 20 22 24 800 900 1000 1100 1200 1300 Fitted Value Fitted Value

(response is Impact Strength (J/m)) (response is MFI (g/10min)) 3 50 2 25 1 0 0 -25 Residual Residual -1

-50 -2

-75 -3 50 75 100 125 150 175 200 225 0 5 10 15 20 25 30 Fitted Value Fitted Value

Figure 6-4. Residual plots versus fitted values for all responses.

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Moreover for impact strength, we found a correlation between the magnitude of

the residual and the level of the variable factors (PMDI and corn oil). As illustrated in

Figure 6-5, the residuals are the largest when PMDI and corn oil at their highest level.

Such an obvious pattern was not observed for other responses. This suggest that extra

caution needs to be considered when predicting the impact strength of formulations with

PMDI and corn oil simultaneously close to their highest level (1 and 6 wt. %,

respectively), when using the developed regression model. As the level of PMDI and

corn oil increases, their contribution towards the material formulation gets more

prominent. In this case, it may be better to consider a mixture design of experiment in

order to obtain a regression model with higher precision.

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(Response is Tensile Strength (MPa)) 1.0 1.0 0.5 0.5 0.0 0.0 -0.5 -0.5

Residual -1.0 -1.0 -1.5 -1.5 0 3 6 0.0 0.5 1.0 Corn oil (wt. %) PMDI (wt. %) (Response is Flexural Modulus (MPa)) 50 50 0 0 -50 -50 Residual -100 -100 0 3 6 0.0 0.5 1.0 Corn oil (wt. %) PMDI (wt. %)

(Response is Impact Strength (J/m)) 50 50 25 25 0 0 -25 -25 -50 -50 Residual -75 -75 0 3 6 0.0 0.5 1.0 Corn oil (wt. %) PMDI (wt. %) (Response is MFI (g/10min)) 3 3 2 2 1 1 0 0 -1 -1

Residual -2 -2 -3 -3 0 3 6 0.0 0.5 1.0 Corn oil (wt. %) PMDI (wt. %)

Figure 6-5. Residual plots versus variable factors.

6.3.5. Response surfaces, contour plots and the optimized region

After developing regression models and analyzing strength and weakness points of them, a graphical method is a useful tool to find a region with desired properties within the studied level range of the variable factors. For this, the 3-D surface plots of all responses have been demonstrated in terms of the factors in Figure 6-6. The 2-D

169

projections of the surfaces or the contour plots are also presented. The contour plots are

more practical graphs to realize the pattern of the responses in the studied domain of

factors. In Figure 6-6, it can be clearly observed that different patterns of responses are generated by the factors in the studied region. In this regard, finding a formulation with desired properties would be easier if taking advantage of these plots.

Given the desired values for responses, contour plot overlay method was adopted to find a formulation with balanced mechanical and physical properties. In the example in

Figure 6-7, we have found an optimized formulation region where the tensile strength, flexural modulus and impact strength are at least 20 MPa, 1 GPa and 100 J/m, respectively. This combination of mechanical properties gives acceptable tensile strength and flexural modulus balanced with a good impact strength which is normally expected to be achieved for a thermoplastic material in consumer products, automotive interior parts, etc. The MFI is the material property affecting the injection molding process and is usually decided by the size of the part. In this example, an MFI value of at least 5 g/10min is specified for a medium to small size part. The domain of the factor levels that leads to the desired properties is highlighted in white color in Figure 6-7. The plot suggests that for such a combination of mechanical properties, flexural modulus is not a concern and it will be fulfilled as long as other three responses are met. Some examples points are specified in Figure 6-7 within the highlighted region for which the predicted

responses are listed in Table 6-6. The values showed that a wide range of impact strength

(from 100 to 150 J/m) and MFI (from 5 to 10.9 g/10min) is achievable within the white

feasible region of PMDI and corn oil levels in this example.

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Tensile Strength (MPa) 6 Tensile 5 Strength (MPa) 4 25 < 14 3 14– 16 20 TS (MPa) 16– 18 2 18– 20 15 6 Corn oil (wt. %) (wt. oil Corn 20– 22 1 10 3 > 22 0.0 Corn oil (wt. %) 0.5 0 0 1.0 0.0 0.2 0.4 0.6 0.8 1.0 PMDI (wt. %) PMDI (wt. %)

Flexural Modulus (MPa) 6 Flexural 5 Modulus (MPa) 4 1400 < 900 3 900– 1000 1200 FM (MPa) 1000– 1100 2 1000 1100– 1200 6 Corn oil (wt. %) (wt. oil Corn 1200– 1300 1 800 3 > 1300 0.0 Corn oil (wt. %) 0 0.5 0 0.0 0.2 0.4 0.6 0.8 1.0 1.0 PMDI (wt. %) PMDI (wt. %)

Impact Strength (J/m) 6 Impact 5 Strength (J/m) 4 < 75 200 75– 100 3 IS (J/m) 150 100– 125 2 125– 150 100 6 Corn oil (wt. %) 150– 175 1 > 175 50 3 Corn oil (wt. %) 0..0 0 0.5 0 0.0 0.2 0.4 0.6 0.8 1.0 1.0 PMDI (wt. %) PMDI (wt. %)

Melt Flow Index (g/10min) 6 MFI 5 (g/10min) < 1 4 30 15– 59– 3 20 MFI (g/10min) 913– 2 13– 17 10 6 Corn oil (wt. %) oil Corn > 17 0 1 3 Corn oil (wt. %) 000.0 0.5 0 0 1.0 0.0 0.2 0.4 0.6 0.8 1.0 PMDI (wt. %) PMDI (wt. %)

Figure 6-6. 3-D surface plots and 2-D contour plots of all responses in the studied domain of the factors.

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6 Impact Strength: 5 100 J/m

4 Flexural Modulus:

7 1000 MPa 3 6 Tensile Strength:

2 4 5 20 MPa

Corn oil (wt. %) (wt. oil Corn 1 3 MFI:

1 2 5 g/10min 0 0.0 0.2 0.4 0.6 0.8 1.0 PMDI (wt. %)

Figure 6-7. The overlaid contour plots of all responses which highlights the domain of the studied factors to attain the desired response values.

Table 6-6. The predicted mechanical and physical properties for the biocomposite formulations specified in Figure 6-7

Tensile Flexural Impact PMDI Corn oil MFI Formulation no. in Figure 6-7 strength Modulus strength (wt. %) (wt. %) (g/10min) (MPa) (MPa) (J/m) 1 0.26 0.4 20.1 1220 100 10.9 2 0.4 0.4 21.7 1270 112 6.5 3 0.4 1.2 21.0 1210 122 7.6 4 0.4 2 20.2 1160 130 8.5 5 0.53 2 21.3 1180 143 5.1 6 0.53 2.7 20.7 1140 148 5.6 7 0.53 3.5 20.0 1110 150 5.8

At the end, it should be noted that in addition to the mechanical and physical properties studied here, the product development would be the next step that involves process engineering and scale-up investigations. These investigations are necessary for understanding the melt behavior of the biocomposite for large scale extrusion as well as part manufacturing via industrial methods such as injection molding. In this regard, the rheological studies can create useful information about the viscosity and other melt properties of the developed biocomposites.

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6.4. Conclusions

The combination of a 32-full factorial design of experiment (DOE) and analysis of variance (ANOVA) was implemented to predict the mechanical and physical properties of a DDGS-filled polymeric biocomposite. Tensile strength, flexural modulus, impact strength and melt flow index were the measured responses after incorporation of compatibilizer and lubricant at low weight percentage levels in the material’s formulation. Least square regression models were developed for each response to fit the data. The normal probability plot of residual admitted the validity of the normality assumption of the ANOVA. The R2 statistic of the models demonstrated a good predictability of them. This approach was found to be very practical in the studied level domain of the factors. However as analyzed with the residual plots versus the factors, it was noted that extra caution needs to be considered for predicting impact strength when the level of the factors increases simultaneously. The graphical methodology of the contour plots effectively helped in finding a level domain of the factors to obtain a formulation with balanced mechanical and physical performance.

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Chapter 7: Overall Conclusions and Future Work

Abstract: This final chapter briefly presents key outcomes of each research study from previous chapters. Also, some ideas are suggested for future investigations on distillers’ grains biocomposites to follow this work. At last, this chapter ends with an overall conclusion of the project.

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7.1. Key outcomes

This project was an attempt to realize the opportunities and limitations of

distillers’ grains, the main coproduct of corn ethanol, in a novel area of application. Here,

the aim was the utilization of distillers’ grains as filler/reinforcement in polymeric

biocomposites involving biobased and/or biodegradable (i.e. compostable) bioplastic

matrices. The formulation of the distillers’ grains biocomposite was the point of focus so

as to be able to tailor the mechanical and physical performance of the produced material.

In the first step, dried distillers’ grains with solubles (DDGS) was characterized

through thermogravimetric analysis and infrared spectroscopy considering the

requirements of melt processing with polymers. The first point to evaluate was the

thermal stability of distillers’ grains at high processing temperatures. It was observed that

a water-washing step prior to the melt processing improves the onset of thermal

degradation and reduces the rate of degradation significantly. In regards to melt

processing, the extrusion and injection molding of biocomposites with as-received DDGS

resulted in excessive smoke, dark appearance of the injected samples and a rough finish

of the injected sample surfaces unlike the biocomposite processing with water-washed

DDGS. The results of this step suggest that for extrusion and injection molding with

thermoplastics, water-washed DDGS or as-received DDG (dried distillers’ grains without

solubles) are better candidates. Also, the mechanical properties showed that the tensile

strength is reduced compared to the neat biopolymer matrix if distillers’ grains are added with no compatibilizer.

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In the second step of the project, an isocyanate type of compatibilizer proved to be very effective at producing a biocomposite of water-washed DDGS with a PHBV- based biopolymer that exhibits strength and rigidity of comparable to commodity plastics and displays good thermomechanical behavior. The limitation of the resulting biocomposite in this step was that toughness and ductility were reduced with the increase in strength and rigidity.

Thus in the next step, biocomposites of water-washed DDGS and a PBAT-based biopolymer were produced with different amounts of compatibilizer and lubricant seeking a formulation with balanced mechanical and physical properties. It was observed that both additives act synergistically in improving the toughness and ductility while the strength and rigidity of the biocomposites remained almost unchanged. Such a success in mechanical performance of the biocomposite was, however, accompanied by the sacrifice of melt flow of the biocomposite.

A statistical approach consisting of a full-factorial design of experiment (DOE) and the response surface methodology (RSM) was successfully adopted to analyze the behavior of the biocomposite from previous study, mathematically model the selected properties and predict an optimized range of formulations with balanced strength, rigidity, impact and melt flow properties. Biocomposites with such formulations can be good candidates for manufacturing packaging or consumer products of medium to small sizes.

This research was conducted with distillers’ grains produced by one corn ethanol plant. Due to the variability in the fermentation process of corn from one ethanol plant to

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another, or even within one ethanol plant from one batch to another, the variability in the chemical composition of the DDGS sample is expected based on its source and date of production. This may have an influence on the mechanical and physical properties of the resulting DDGS biocomposite. The fundamental knowledge gained throughout this research about the effect of water-washing on DDGS thermal stability and the influence of the studied compatibilizer and lubricant system in tailoring the properties of the biocomposite can be extended to biocomposites of DDGS from different sources.

However, a systematic research is recommended to develop a correlation between the

DDGS composition (or the source) and the performance of the final biocomposite.

7.2. Future work

In addition to the last point, just discussed above, about the investigation of the effect of DDGS source, there are still several aspects related to the present work for further investigation that were beyond the scope of this project. Some examples are as follows:

Evaluation of other compatibilizer and lubricant systems will generate a

deeper understanding of different mechanisms that can improve the

mechanical and physical performance of the biocomposites.

Even though the biodegradation and compostability of distillers’ grains

biocomposites have been studied in the literature and already reviewed in

Chapter 2, the effect of other additives such as compatibilizer and

lubricant on this behavior could be further investigated. In a related work,

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the recyclability studies are also suggested to determine the life time of such biocomposites.

Though this project was aimed at green biocomposite of distillers’ grains with bioplastics from renewable resources and end-life biodegradability, it is worth studying distillers’ grains biocomposites with commodity plastics since these plastics are still much cheaper than most bioplastics and the market for them and their biocomposites has already been established for a long time. Therefore with moderate adjustments, distillers’ grains biocomposites with commodity plastics may enter more easily into the marketplace until the time that cost-competitiveness of bioplastics with commodity plastics is achieved.

The next step after a formulation optimization study (such as the present thesis) is a process optimization study in which the optimized formulation will be used to optimize the parameters involved in a desired processing method through which the biocomposite will be shaped into a product. For this purpose, there are several characterization methods by which more information about the physical properties of the distillers’ grains biocomposite can be obtained that have not been employed in this project.

In this regard, the rheological experiments are suggested for understanding the viscosity and other melt properties of the produced biocomposite. The effect of temperature, time and shear rate on the melt behavior of the biocomposites gives useful information for process engineering and product development.

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This research was focused on the processing method involving extrusion and injection molding which is the most common way in industries for producing biocomposites. However, compression molding can be another option. This method may be less harsh to thermally sensitive biomasses such as distillers’ grains although it is not as versatile as injection molding with respect to the shape complexity of the final product.

Due to high protein content, distillers’ grains may be considered for

plasticization with additives such as glycerol and blending with other

plastics. This, of course, needs preliminary study to validate the

effectiveness of the plasticization since the fiber content of distillers’

grains may lead to adverse effects in this case.

There are several questions about the distillers’ grains biocomposites

outside the field of materials science. Some questions include:

Is recycling a better option than biodegradation

(composting) at the end of life time?

How does this new application add value to distillers’

grains?

How does such a value addition affect distillers’ grains’

place in the animal feed market?

Comprehensive analyses such as a life cycle assessment (LCA) or an

economic feasibility study are suggested to address these and other similar

questions.

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7.3. Overall conclusions of the thesis

With the completion of this thesis, a clearer insight about the potentials and

restrictions of distillers’ grains for the production of biocomposites has been attained.

This knowledge is essential to identify achievable markets and to manufacture

commercial products out of distillers’ grains. In this context, materials science and

engineering is found to be an excellent platform for developing value-added applications of a corn ethanol coproduct.

Finally, a great deal of success would be reached if this work is able to encourage the generation of new ideas for future and further works with distillers’ grains and similar under-valued but highly advantageous biomasses. This research is an example of the contribution of “materials science and engineering” field of research to the sustainable development. Interdisciplinary works between materials scientists, agriculture specialists, biofuel experts, etc. is a must to build a greener society with minimum impact on the environment of the future generations.

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Financial supports and industrial collaborations

This project was carried out using the financial supports from:

(1) Highly Qualified Personnel (HQP) scholarship program, from Ontario

Ministry of Agriculture and Food (OMAF) and Ministry of Rural Affairs

(MRA), Canada.

(2) ARF+ research program, from Ontario Ministry of Agriculture and Food

(OMAF) and Ministry of Rural Affairs (MRA), Canada.

(3) Ontario Research Fund, Research Excellence, Round-4 (ORF RE04) from

Ontario Ministry of Economic Development and Innovation (MEDI),

Canada.

(4) Discovery Grant from Natural Sciences and Engineering Research Council

(NSERC), Canada.

(5) Networks of Centres of Excellence (NCE) AUTO21 project from NSERC,

Canada.

(6) Leaders Opportunity Fund (LOF) from Canada Foundation for Innovation

(CFI), for equipment support to carry out this research.

(7) Federal Economic Development Agency for Southern Ontario (FedDev

Ontario), Canada, for infrastructure support in this project.

Also, the in-kind supply of distillers’ grains samples by GreenField Specialty

Alcohols, Chatham, Ontario, Canada, is appreciated. Additionally, the collaboration of

Competitive Green Technologies, Leamington, Ontario, Canada, is acknowledged for providing an internship opportunity for Nima Zarrinbakhsh during Winter, 2014.

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