Assessment of soybean protein-based adhesive formulations, prepared by different liquefaction technologies for particleboard applications

Abstract

The development of a feasible and effective method to liquefy soybean protein with the potential to prepare particleboard for wood furniture remains challenging. In this work, different novel liquefaction technologies were proposed to prepare four different soybean protein liquefied products (noted as LSP-Ӏ, LSP-ӀӀ, LSP-ӀӀӀ, LSP-ӀV) that could be used as the matrix of the adhesives to satisfy spraying operation in particleboard industrial production. The effects of different liquefaction techniques on the molecular weight, chemical structure, crystalline degree and physicochemical properties were explored. Moreover, the boiling water-insoluble content, thermal stabilities and bonding properties of soybean protein-based adhesive prepared by LSP and cross-linker epichlorohydrin-modified polyamide (EMPA) were investigated. The results show that the particleboard bond with the “LSP-ӀV + EMPA” adhesive possesses excellent mechanical strength and dimensional stability which meets the industrial requirement of the particleboard according to the GB/T 4897–2015 commercial standard. Moreover, the liquefaction mechanism of the soybean protein solution with high solid content, low viscosity and suitable molecular weight was proposed, as the breaking of the intermolecular interactions by compound modifier effectively unfolded the polypeptide chains, and the polypeptide chains were uniformly and moderately degraded under mild alkaline conditions. Therefore, the “LSP-ӀV + EMPA” adhesive could be uniformly coated on the wood particles by the spraying process, and an effective cross-linking network system was formed during the hot pressing owing to appropriate molecular weight and more active groups of LSP-ӀV. The application prospect of soybean protein-based adhesives would be greatly broadened in the wood composite fields.