| Soy protein has shown great potential to partly replace petroleum-based adhesives for the manufacture of particleboard, plywood, and various composites. The obstacle of applying a soy protein-based adhesive is its relatively poor water resistance. The overall objective of this research was to increase adhesive strength and water resistance of soy protein adhesives.; Laboratory-prepared soy protein isolate (SPI) was used for this study. Effects of chemical and physical modifications were investigated. Cationic detergent, ethanol, glutaraldehyde, and heat were used to modify SPI. Results showed that chemical modification is an effective method to increase adhesive performance of soy protein. Tensile strength of SPI modified with 2.6 mM cationic detergent showed 19.0, 48.5, and 32.6% increases in dry, wet, and soak strengths, respectively, compared with control SPI; and pH had a significant effect on the adhesion of detergent modified soy protein. Esterification rendered protein molecules more hydrophobicity by adding ester groups. At optimum condition, tensile strength of esterified SPI increased 20.4, 61.1, and 35.5% in dry, wet, and soak strengths, respectively, compared with control SPI. Crosslinking induced conformation and structure change in the protein, subsequently affecting its adhesive performance. Dry, wet, and soak strengths increased 31.5, 115, and 29.7%, respectively, by crosslink, compared with unmodified SPI. Heat pretreatment could significantly affect adhesive performance of SPI. Tensile strength of control SPI and esterified SPI increased 27.6 and 2%, 34.8 and 14. 9%, and 14.8 and 7% in wet, dry, and soak strengths, respectively. Heat treatment increased dry and soak strengths of the crosslinked SPI, but not the wet strength.; The increase of setting temperature increased wet, dry, and soak strengths of control and chemical modified SPI. The increased hydrophobic interaction might be the factor that contributed to the tensile strength increase. Moderate structure change is beneficial to adhesive performance, but drastic change is detrimental. |
