Physicochemical properties of soy protein adhesives modified by 2-octen-1-ylsuccinic anhydride

Soy protein adhesives (SPA) with high solid content display great potential as alternatives to petroleum-based adhesives. This study investigated the adhesive properties of SPA as modified by 2-octen-1-ylsuccinic anhydride (OSA) at different concentrations. Physicochemical properties including electrophoresis profile and turbidity and thermal and rheological properties also were characterized in detail. OSA was grafted to some soy protein molecules through a reaction between amine, hydroxyl groups of protein, and anhydride groups as confirmed by Fourier transform infrared spectroscopy (FTIR). The conformation of OSA-modified SPA was unfolded as indicated by the absence of high molecular weight protein bands in reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and by the decrease in thermal stability detected by Differential Scanning Calorimetry (DSC). The turbidity of OSA-modified SPA decreased at pH basic to isoelectrical point (IP) but increased at pH acidic to IP. The wet strength of SPA applied on two ply plywood increased to 3.2 MPa at 3.5% OSA concentration compared to 1.8 MPa for the control; then the strength leveled off as OSA concentration increased further. SPA modified with 3.5% OSA worked better on maple wood veneer than yellow poplar wood veneer when three ply plywood was made. Wood cohesive failure (WCF) was observed for both soaked maple and yellow poplar plywood specimens: 60% WCF for the former and 5% WCF for the latter. The oily nature and hydrophobic long alkyl chains are the main reasons to improve the adhesion performance of SPA.

► A new soy protein adhesive system with high solid content, good flow-ability and good water resistance was investigated in this study.
► 2-octen-1-ylsuccinic anhydride (OSA) with the oily nature and long hydrophobic alkyl chains was chose to modify soy protein adhesive.
► The wet adhesion strength of soy protein was greatly improved by using up to 3.5% OSA, and leveled off as OSA concentration further increased.
► Physicochemical properties including electrophoresis profile and turbidity and thermal and rheological properties also were characterized in detail.