Comparative Study Of The Properties Of Three Protein-based Wood Adhesives

The traditional formaldehyde system of thermosetting synthetic resin adhesives in the production and use of man-made panels have varying degrees of formaldehyde release problems,and the main raw materials for the production of formaldehyde,urea,phenol,etc.are non-renewable resources.As people’s awareness of environmental protection increases,the importance of renewable resources is becoming more and more prominent.Environmentally friendly bio-based adhesives made from renewable resources have become a current research hotspot.Agricultural production residues of plant protein meal is a class of protein-rich biomass resources,currently mainly used for animal feed,the annual output is huge.If plant protein meal can be effectively used as raw materials for wood adhesives,it can reduce the production cost of adhesives,improve the environmental performance of panels,reduce environmental pollution,and help promote the rational development and use of renewable resources.In this study,three common vegetable protein meals(cottonseed meal,soybean meal and peanut meal)were used as the main raw materials for the preparation of three protein-based adhesives,and by comparing the performance of the three adhesives,the most suitable vegetable protein meals and the best overall performance of the protein-based adhesives were studied and screened as raw materials for wood adhesives,providing a certain theoretical basis for the production and application of renewable protein-based adhesives The study will provide a theoretical basis and technical guidance for the production and application of renewable protein-based adhesives.The main research contents are:(1)Prepare three unmodified protein-based adhesives and compare the basic properties and bonding strength of the three unmodified protein-based adhesives;(2)Prepare three protein-based adhesives modified with urea and compare the basic properties,bonding strength,infrared structure,thermal stability and microscopic morphology of the three protein-based adhesives;(3)Prepare three protein-based adhesives modified with urea and modifiers and compare the basic properties,bonding strength,infrared structure,thermal stability and microscopic morphology of the three protein-based adhesives.The basic properties,bonding strength,infrared structure,thermal stability and post-curing microscopic morphology of the three protein-based adhesives were investigated;(4)to determine the best protein-based adhesive in terms of basic properties,wet bonding strength and raw material cost.The main findings of the study are as follows:(1)The dry bonding strength and wet bonding strength of the three protein-based adhesive glued plywoods prepared without modification did not reach the standard of Class II panels of the National Standard;(2)The dry bonding strength of the three protein-based adhesive glued plywoods prepared with urea modification was improved,but the wet bonding strength was not significantly improved and still did not meet the national standard for Class II panels;(3)The dry bonding strength and wet bonding strength of the three protein-based adhesive glued plywoods prepared by the composite modification of urea and modifier were significantly increased.When the modifier was added at 20%,the dry bonding strength of the composite modified soy protein adhesive glued plywood was the highest(1.817 MPa).The highest wet bonding strength(0.972 MPa)was achieved when the modifier was added at 25%of the compound modified cottonseed protein adhesive.The reaction between the modifier and the protein molecules changed the structure of the composite modified protein adhesive,but the difference in IR structure between the adhesives of different protein raw materials was small.Among the three compound-modified protein-based adhesives,the composite modified cottonseed protein adhesive had relatively good thermal stability.The addition of modifiers improved the surface structure of the cured adhesive layer and the cottonseed protein adhesive had a flatter and denser adhesive layer cross-section;(4)Considering the basic performance of the adhesive,wet bonding strength and raw material cost,the cottonseed protein adhesive modified by the modifier and urea compound has relatively good physical and chemical properties,and is the adhesive with the best overall performance among the three kinds of vegetable protein meal prepared adhesives.