Crosslinking Modification Of Protein-based Adhesives And Mechanism

Bonding performance and water resistance of protein-based adhesives wre closely related to its cross-linker. To study the mechanism of protein-based adhesives with cross-linker, amino acids and dipeptide as model compounds of protein were creative in this study. The mechanisms of protein-based adhesives modified by cross-linker formaldehyde, phenol formaldehyde resin and epoxy resin were reflected by their reaction with model compounds amino acids and dipeptide by FT-1R, 13C-NMR and ESI-MS. Curing performance and heat-resistant quality of soy protein-based adhesive and Jatropha curcas L. protein-based adhesive crosslinked by formaldehyde, phenol formaldehyde resin and epoxy resin were studied by DSC, TG and DMA. To discuss the mutual relation between crosslinking mechanism of protein-based adhesives and practical applation, preparation process of soy protein-based adhesive and Jatropha curcas L. protein-based adhesive was optimized by testing performance of plywood and particleboard. The main conclusions are summarized as follows:(1) Keeping some macromolecule structures of protein helped to improve the bonding strength and water resistance of protein-based adhesives. Protein treated with alkali destroyed the macromolecular structure of protein, decreased the cohesive strength of the protein.(2) Protein contained acylamino and aliphatic amino. Acylamino and aliphatic amino had hydroxyl methylation reaction with formaldehyde under the alkaline condition. Under the acid condition, easy protonation of aliphatic amine resulted to activity reduce or lose completely and the reaction with formaldehyde was not obvious. But acylamino still had hydroxyl methylation reaction with formaldehyde. The other hand, the degree of degradation of soy protein under the alkaline condition was higher than the acid, resulted to exposure of the more active functional groups. The both leading to the performance of plywood of the alkaline soy protein-based adhesive was better than the acid, but curing temperature was lower than the acid. Before crosslinking modification of soy-based adhesive, it could get better bonding performance when it was transferred to alkaline condition.(3) Phenol formaldehyde resin reacted with protein in the form of quinone structure under alkaline condition. And para hydroxyl methyl of quinone structure of phenol formaldehyde resin reacted with protein. Increasing the hydroxymethyl content of phenol formaldehyde resin could improve the bonding performance, water resistance, operating performance, and reduce the curing temperature of soy protein-based adhesive crosslinked by phenol formaldehyde resin. Improving the toughness of phenol formaldehyde resin could improve the bonding performance and water resistance of protein-based adhesives.(4) The main products between epoxy resin and amino group were given priority to replacing amino N-1. Epoxy resin could increase the cohesive strength and crosslinking density of protein-based adhesives, lead to the better bonding strength, water resistance and thermal stability of protein-based adhesive.(5) Degradation of Jatropha curcas L. protein under alkali was not satisfied, and its storage stability was poor. Mixed with other protein could promote Jatropha curcas L. protein hydrolysis. The ultimate degradation degree of Jatropha curcas L. protein depended on what kind of the adding protein.(6) Soy protein was charged into the first preparation stages of "alkali-acid-alkali" of UF and MUF resin, the products had good thermal mechanical properties, high strength and low free formaldehyde for dihydroxy methyl branch and methylene bridge bonds increasing.