Foaming properties of soybean protein-based plywood adhesives

A study was conducted to evaluate the potential of soy protein-based plywood glues for foam extrusion. Foaming properties were the first criterion used to screen several soy protein sources. Foaming capacities and stabilities of glue mixes containing animal blood (control) or soy products (meals, flours, concentrates, and isolates) were compared and correlated with molecular weights and surface hydrophobicity indices (S-O) in an attempt to identify structure/function relationships. The blood-based glue mix produced more foam than any of the soy-based glues. Soy flours and concentrates generally produced greater foam Volumes and more stable foams than soy meal and isolates. Differences in foaming properties could not be explained by solubility profiles or S-O. However, results of gel electrophoresis indicated that soy products with poor foaming properties had extensive structure modifications or contained considerably lesser amounts of protein available for foaming reactions. Glue mixes containing the soy flours ISU-CCUR, Honeysoy 90, Nutrisoy 7B, and defatted Soyafluff and the soy concentrates Arcon F, ISU-CCUR, and Procon 2000 demonstrated the desired mixing and foaming properties for foam extrusion.