Effect of ambient aging during soybean meal storage on the performance of a soybean-based adhesive

Abstract

Ambient aging is a common phenomenon that occurs under ambient conditions during the storage and use of polymeric substances, which may significantly affect the product performance. The aging of soybean meal (SM) during storage and its effects on the structures and properties of both SM and SM-based adhesive were investigated. It is confirmed that the SM powder underwent significant aging in the 4 months after grinding, resulted from the oxidation, decomposition, repolymerization and rearrangement of the SM chains. The carbonyl concentrations on the surface and in the bulk of SM after aged for 6 months increased 31.6% and 20.5, respectively. The physicochemical changes of ambient-aged SM powder affected the SM-based adhesive by increasing wettability but lowering crosslink density. Three-layer plywood, bonded with ambient-aged SM adhesives, exhibited decreased shear strength and water resistance, mainly resulting from the decreased crosslink density of the cured adhesive upon the aging time of the SM powder. The 6-month ambient aging of SM caused dry strength reduced by 52.6% and aged wet strength decreased by 53.8%. As a result, ambient aging and its negative effects should be carefully taken into account by manufacturers and customers to avoid the ineffectiveness and instability of SM and SM-based adhesive.