MODIFIED SOY PROTEIN BASED ADHESIVES AND THEIR PHYSICOCHEMICAL PROPERTIES by GUANGYAN QI B.S., Henan University of Technology, P. R. China, 2004 M.S., Henan University of Technology, P. R. China, 2007 -------------------------- AN ABSTRACT OF A DISSERTATION Submitted in partial fulfillment of the requirements for the degree DOCTOR OF PHILOSOPHY Department of Grain Science and Industry College of Agriculture KANSAS STATE UNIVERSITY Manhattan, Kansas 2011 ABSTRACT Soy protein is one of the most promising bio-degradable adhesives, with great potential as alternatives synthetic petroleum based adhesives for wood composite industries. However, its intrinsic drawbacks such as low water resistance, high viscosity, and short shelf life still limit its broad application. In this research, soy protein was further modified and characterized to improve adhesion properties, flow-ability, water resistance, and long shelf life, which could facilitate the industrialization of soy protein based adhesives. In this study, we exploited the in situ sodium bisulfite (NaHSO ) modification on soy 3 protein in soy flour-water extracts, and then the modified soy protein was obtained through acid precipitation. First, different concentrations of NaHSO were used to modify soy flour 3 slurry, then glycinin-rich and β-conglycinin-rich fractions were precipitated at pH 5.4 (SP 5.4) and pH 4.5 (SP 4.5), respectively. Unmodified sample SP 5.4 and SP 4.5 showed clay-like properties and viscoelastic properties, respectively; whereas with addition of NaHSO in 3 range of 2-8 g/L, both SP 5.4 and SP 4.5 had the viscous cohesive phase with good hand- ability and flow-ability. The overall adhesion performance of SP 4.5 was better than SP 5.4; the wet strength of these two fractions was in the range of 2.5-3.2 MPa compared to 1.6 MPa of control soy protein isolate. Then soy protein with various β-conglycinin/glycinin (7S/11S) ratios were extracted from soy flour slurry and characterized for adhesion properties based on the different solubility of 7S and 11S globulins. Seven glycinin-rich soy protein fractions and six β- conglycinin-rich soy protein fractions were obtained. According to the morphology, viscosity, and particle size results, we proposed that proper protein-protein interaction, hydration capacity (glycinin-rich fractions), and certain 7S/11S ratios (β-conglycinin-rich fractions) in modified soy protein are crucial to continuous protein phase formation. The viscous cohesive samples were stable for up to several months without phase separation at room temperature, with the wet adhesion strength of 2.0-2.8 MPa. The soy protein modified with NaHSO showed good compatibility with commercial 3 glues applied on plywood and paper labeling fields. The modified soy protein made some functional groups, carboxylic (-COOH), hydroxyl (-OH) and amino groups (-NH ) available, 2 which cross-linked with hydroxymethyl groups (-CH -OH) from urea formaldehyde (UF) 2 wood glue. The modified soy protein (MSP) with pH 4.8 also acted as an acidic catalyst for the self-polymerization of UF based resin. The wet adhesion strength of MSP/UF blends (40/60) was 6.4 MPa with 100% wood cohesive failure, as compared to 4.66 MPa of UF. As to the paper labeling application, peel strength of MSP on glass substrate increased rapidly, with curing time much shorter than commercial polyvinyl acetate based adhesives (PVAc). And the MSP/ PVAc blends showed shorter curing time, higher water resistance and lower viscosity than pure PVAc. Chemical modification could also enhance the adhesion strength of MSP. 2-octen-1- ylsuccinic anhydride (OSA) was proved to be grafted on soy protein through reaction between amine, hydroxyl groups of protein and anhydride groups. The oily nature and hydrophobic long alkyl chains of OSA mainly contributed to the significant water resistance improvement of MSP. MODIFIED SOY PROTEIN BASED ADHESIVES AND THEIR PHYSICOCHEMICAL PROPERTIES by GUANGYAN QI B.S., Henan University of Technology, P. R. China, 2004 M.S., Henan University of Technology, P. R. China, 2007 -------------------------- A DISSERTATION Submitted in partial fulfillment of the requirements for the degree DOCTOR OF PHILOSOPHY Department of Grain Science and Industry College of Agriculture KANSAS STATE UNIVERSITY Manhattan, Kansas 2011 Approved by: Major Professor Xiuzhi Susan Sun Copyright GUANGYAN QI 2011 ABSTRACT Soy protein is one of the most promising bio-degradable adhesives, with great potential as alternatives synthetic petroleum based adhesives for wood composite industries. However, its intrinsic drawbacks such as low water resistance, high viscosity, and short shelf life still limit its broad application. In this research, soy protein was further modified and characterized to improve adhesion properties, flow-ability, water resistance, and long shelf life, which could facilitate the industrialization of soy protein based adhesives. In this study, we exploited the in situ sodium bisulfite (NaHSO ) modification on soy 3 protein in soy flour-water extracts, and then the modified soy protein was obtained through acid precipitation. First, different concentrations of NaHSO were used to modify soy flour 3 slurry, then glycinin-rich and β-conglycinin-rich fractions were precipitated at pH 5.4 (SP 5.4) and pH 4.5 (SP 4.5), respectively. Unmodified sample SP 5.4 and SP 4.5 showed clay-like properties and viscoelastic properties, respectively; whereas with addition of NaHSO in 3 range of 2-8 g/L, both SP 5.4 and SP 4.5 had the viscous cohesive phase with good hand- ability and flow-ability. The overall adhesion performance of SP 4.5 was better than SP 5.4; the wet strength of these two fractions was in the range of 2.5-3.2 MPa compared to 1.6 MPa of control soy protein isolate. Then soy protein with various β-conglycinin/glycinin (7S/11S) ratios were extracted from soy flour slurry and characterized for adhesion properties based on the different solubility of 7S and 11S globulins. Seven glycinin-rich soy protein fractions and six β- conglycinin-rich soy protein fractions were obtained. According to the morphology, viscosity, and particle size results, we proposed that proper protein-protein interaction, hydration capacity (glycinin-rich fractions), and certain 7S/11S ratios (β-conglycinin-rich fractions) in modified soy protein are crucial to continuous protein phase formation. The viscous cohesive samples were stable for up to several months without phase separation at room temperature, with the wet adhesion strength of 2.0-2.8 MPa. The soy protein modified with NaHSO showed good compatibility with commercial 3 glues applied on plywood and paper labeling fields. The modified soy protein made some functional groups, carboxylic (-COOH), hydroxyl (-OH) and amino groups (-NH ) available, 2 which cross-linked with hydroxymethyl groups (-CH -OH) from urea formaldehyde (UF) 2 wood glue. The modified soy protein (MSP) with pH 4.8 also acted as an acidic catalyst for the self-polymerization of UF based resin. The wet adhesion strength of MSP/UF blends (40/60) was 6.4 MPa with 100% wood cohesive failure, as compared to 4.66 MPa of UF. As to the paper labeling application, peel strength of MSP on glass substrate increased rapidly, with curing time much shorter than commercial polyvinyl acetate based adhesives (PVAc). And the MSP/ PVAc blends showed shorter curing time, higher water resistance and lower viscosity than pure PVAc. Chemical modification could also enhance the adhesion strength of MSP. 2-octen-1- ylsuccinic anhydride (OSA) was proved to be grafted on soy protein through reaction between amine, hydroxyl groups of protein and anhydride groups. The oily nature and hydrophobic long alkyl chains of OSA mainly contributed to the significant water resistance improvement of MSP. TABLE OF CONTENTS TABLE OF CONTENTS ....................................................................................................... viii  LIST OF FIGURES ............................................................................................................... xiii  LIST OF TABLES ................................................................................................................. xvi  ACKNOWLEDGMENTS ................................................................................................... xviii  Chapter 1 - INTRODUCTION ................................................................................................. 1  1.1. GENERAL BACKGROUND ........................................................................................ 1  1.2. OBJECTIVES ................................................................................................................ 4  1.3. REFERENCES .............................................................................................................. 8  Chapter 2 - LITERATURE REVIEW .................................................................................... 10  2.1. ADHESION MECHANISUM ..................................................................................... 10  2.2. WOOD ADHESIVES .................................................................................................. 10  2.3. SOYBEAN AND SOY PROTEIN CHEMISTRY ...................................................... 12  2.3.1. Soybeans ............................................................................................................... 13  2.3.2. Soy protein chemistry ........................................................................................... 13  2.4. FUNCTIONALITY OF 7S AND 11S ......................................................................... 16  2.5. FRACTIONATION OF SOY PROTEIN .................................................................... 17  2.6. PROTEIN STRUCTURE AND STABILIZATION ................................................... 18  2.7. SOY PROTEIN ADHEIVES AND ITS MODIFICATION ........................................ 19  2.7.1. Chemical modification .......................................................................................... 19  2.7.2. “Short cut method” adhesive blending ................................................................. 23  2.7.3. Nano technology ................................................................................................... 23  2.8. REFERENCES ............................................................................................................ 28  Chapter 3 - ADHESION AND PHYSOCOCHEMICAL PRPOPERTIES OF SOY PROTEIN ADHESIVES MODIFIED BY SODIUM BISULFITE .................................................. 35  3.1 ABSTRACT .................................................................................................................. 35  3.2. INTRODUCTION ....................................................................................................... 35  3.3. MATERIALS AND METHODS ................................................................................. 37  3.3.1 Materials ................................................................................................................. 37  3.3.2. Soy protein adhesive preparation .......................................................................... 37  viii 3.3.3. SDS-Polyacrylamide Gel Electrophoresis ............................................................ 38  3.3.4. Determination of Solubility .................................................................................. 38  3.3.5. Rheological properties .......................................................................................... 38  3.3.6. Thermal properties ................................................................................................ 39  3.3.7. Morphological properties ...................................................................................... 39  3.3.8. Wood specimen preparation .................................................................................. 39  3.3.4. Shear strength measurements ................................................................................ 39  3.4. RESULTS ANDDISCUSSION ................................................................................... 40  3.4.1. Soy protein fraction yield ...................................................................................... 40  3.4.2. SDS-PAGE analysis .............................................................................................. 40  3.4.3. Solubility ............................................................................................................... 42  3.4.4. Rheological properties .......................................................................................... 43  3.4.5. Thermal properties ................................................................................................ 44  3.4.6. Morphological properties ...................................................................................... 45  3.4.7. Mechanical properties ........................................................................................... 46  3.5. CONCLUSIONS ......................................................................................................... 47  3.6. REFERENCES ............................................................................................................ 60  Chapter 4 - PHYSICOCHEMICAL CHARACTERIZATION OF SOY PROTEIN ADHESIVES OBTAINED BY IN SITU SODIUM BISULFITE MODIFICATION DURING ACID PRECIPITATION ................................................................................ 63  4.1. ABSTRACT ................................................................................................................. 63  4.2. INTRODUCTION ....................................................................................................... 64  4.3. MATERIALS AND METHODS ................................................................................. 65  4.3.1. Materials................................................................................................................ 65  4.3.2. Soy protein adhesive preparation .......................................................................... 65  4.3.3. Electrophoresis (SDS-PAGE) ............................................................................... 66  4.3.4. Particle size analysis of protein precipitates aggregates ....................................... 66  4.3.5. Determination of protein solubility ....................................................................... 66  4.3.6. Rheological properties .......................................................................................... 67  4.3.7. Thermal properties ................................................................................................ 67  4.3.8. Morphological properties ...................................................................................... 67  ix 4.3.9. Wood specimen preparation .................................................................................. 68  4.3.10. Shear strength measurements .............................................................................. 68  4.4. RESULTS AND DISCUSSION .................................................................................. 68  4.4.1. NaHSO -modified soy protein samples ................................................................ 68  3 4.4.2. SDS-PAGE ............................................................................................................ 69  4.4.3. Apparent viscosity ................................................................................................. 71  4.4.4. Solubility of soy protein in different reagents ...................................................... 72  4.4.5. Thermal properties ................................................................................................ 73  4.4.6. Morphology properties .......................................................................................... 74  4.4.7. Shear adhesion strength ........................................................................................ 75  4.5. CONCLUSIONS ......................................................................................................... 76  4.6. REFERENCES ............................................................................................................ 91  Chapter 5 - SOY PROTEIN ADHESIVE BLENDS WITH SYNTHETIC LATEX ON WOOD VENEER ............................................................................................................ 94  5.1. ABSTRACT ................................................................................................................. 94  5.2. INTRODUCTION ....................................................................................................... 94  5.3. MATERIALS AND METHODS ................................................................................. 96  5.3.1. Materials................................................................................................................ 96  5.3.2. Adhesive preparation ............................................................................................ 97  5.3.4. Apparent viscosity ................................................................................................. 97  5.3.5. Spread rates ........................................................................................................... 97  5.3.6. Wood specimen preparation .................................................................................. 97  5.3.7. Shear adhesion strength ........................................................................................ 98  5.3.8. Water resistance .................................................................................................... 98  5.3.9. Infrared spectroscopy ............................................................................................ 98  5.3.10. Transmission electron microscopy ...................................................................... 99  5.3.11. Dynamic viscoelastic measurement .................................................................... 99  5.3.12. Scanning electron microscopy ............................................................................ 99  5.3.13. Differential scanning calorimetry ....................................................................... 99  5.3.14. Thermogravimetric analysis .............................................................................. 100  5.4. RESULTS AND DISCUSSION ................................................................................ 100  x