Technical Paper - Environmental pollution has prompted an interest in and a need for bio-based wood adhesives. Modified soy protein has shown adhesion properties similar to those of formaldehyde based adhesives. The objective of this research was to investigate the compatibility of a modified soy protein (MSP) with six commercial synthetic latex adhesives (SLAs). Four different blending ratios of MSP and SLAs were studied. Adhesion, structural change, and rheological, thermal and morphological properties of the MSP/SLAs blends were characterized. Dry adhesion strength of MSP, SLAs and their blends were all similar with 100% wood cohesive failure. Water resistance of all six SLAs was improved by blending with MSP in terms of the wet adhesion strength. The wet adhesion strength of MSP/PBG (40/60) blends was 6.416 MPa, as compared to 4.66 MPa of pure PBG (press bond glue, urea formaldehyde based resin). Viscosity of MSP/SLAs blends was reduced significantly and reached the lowest value at 40–60% MSP. Infrared spectra, thermal properties, and morphological images indicated that chemical reactions occurred between soy protein and PBG molecules. The MSP provided some functional groups, such as carboxylic (–COOH), hydroxyl (–OH) and amino groups (–NH2), that cross-linked with hydroxymethyl groups (–CH2–OH) of PBG, and also acted as an acidic catalyst for the self-polymerization of urea formaldehyde based resin.

Source : Qi, G. and Sun, X.S., “Soy Protein Adhesive Blends with Synthetic Latex on Wood Veneer”, J. of the American Oil Chemists’ Society, Vol. 88, No. 2, 2011.

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