Research progress on enzymatic modification and its application in protein-based adhesives
With their advantages of low cost,sustainability,simple production process,and abundant raw materials,protein-based adhesives play a crucial role in addressing the environmental concerns of formaldehyde pollution and dependence on fossil resources caused by aldehyde synthetic resin(urea formaldehyde resin,phenolic resin,and melamine-formaldehyde resin)adhesives in human settlements.Moreover,protein-based adhesives have garnered increased attention within the realm of wood science and technology research and wood-based panel production.Abundantly available sources such as soy protien,peanut protein,and other vegetable oil processing residues are rich in sources and low in cost,being ideal raw materials for making protein-based adhesives.However,the protein-based adhesives have problems such as poor water resistance,high viscosity,poor coating performance,and over-reliance on fossil crosslinkers,weakens the environmental advantages of bio-adhesives,which restrict the industrial application.Enzymatic modification technology has the characteristics of safety,high efficiency,and specificity,which can modify structure and improve functional properties of protein.Moreover,it can effectively reduce the viscosity,release of functional components and active groups,improve the solubility and reactivity of proteins.The appropriate crosslinking agents are used to prepare protein-based adhesives with low cost,low crosslinking agent consumption,high water-resistant bonding strength,and high production efficiency of protein-based adhesives,showing a promising application prospect in protein-based adhesives.This study summarizes the problems and modification targets of protein-based adhesives,including reducing viscosity and improving rheological properties,improving water-resistant bonding strength,enhancing mildew resistant storage and adhesive toughness,accelerating curing and reducing production costs.Then this study analyzes the mechanism of proteases(e.g.,bromelain,papain,trypsin,pepsase,Alcalase,and urease),polysaccharide hydrolase(e.g.,cellulase,xylanase,amylase,lysozyme,chitinase,galactosidase,and pectinase),transglutaminase,tyrosinase,and laccase modifying structure and functional properties of protein,as well as the application progress of enzymatic modification technology in protein-based adhesives to provide reference for the development and performance improvement of protein-based adhesives.The enhanced mechanism of enzymatic modification on the viscosity,toughness of adhesive layer,and water-resistant bonding performance of protein-based adhesives will be clarified,which can provide theoretical and technical support for the large-scale application of protein-based adhesives.
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