The Research Of Soybean Protein Adhesive Modified By Water-soluble Epoxy Polymer

The increasingly stringent requirements of living environment put forward more stringent requirements for the environmental protection of indoor wood-based panels,so it is imperative to develop environment-friendly biomass adhesives.Soybean protein adhesive as a kind of biomass adhesive is prepared by rich resources and renewable soybean protein,which can fudamentally solve the formaldehyde pollution problem caused by aldehyde resin.However,soybean protein adhesives have the disadvantages of poor water resistance and low adhesive strength,which limit their wide application in the field of wood-based panels.In order to overcome the above shortcomings,this paper adopts the water-soluble epoxy resin and epoxied lignin polymer as the crosslinking agent to modify soybean protein adhesives and carried out the following three aspects of research content:1)With soybean protein isolated(SPI)as raw materials,constructing the system of soybean protein adhesives modified by water-soluble epoxy resin(EPOXY),and clearing the water-resistant structure form mechanism of modified soybean protein adhesives;2)Synthesizing epoxied lignin polymer(EPL)with industrial lignin and ethylene glycidyl ether and optimizing the EPL synthesis process,constructing the system of modified soybean protein adhesive prepared with SPI and EPL.The lignin is demethylated by the method of microwave heating for improving its reactivity,and it is used to synthesis the epoxied demethylated-lignin polymer(EPDL).Analyzing the effect of demethylation modification of EPDL on improving bonding strength of soybean protein adhesive,and revealing the mechanism of improving the bonding performance of modified soybean protein adhesives.Which can provide technical parameters and theoretical basis for the preparation of water-resistant soybean meal adhesives from defatted soybean meal(SM);3)With SM as the main raw material,the high-performance modified soybean meal adhesive is optimized by comparing the modification effects of EPOXY,EPL and their compounds on soybean meal adhesive.Meanwhile,the hot-pressing process conditions of plywood prepared with modified soybean meal adhesive are optimized.The main results from this study can be summarized as follows:(1)The epoxy group on EPOXY molecule can react with active hydroxyl,amino on SPI molecules and amide group on PAM forming water-resistant chemical structure and increase the bonding strength of soy protein adhesive;When the dosage of EPOXY is 4%,non-ionic PAM concentration is 0.05%,the initial viscosity of modified SPI adhesive is 1075 m Pa.s,and potlife more than 5 h,bond strength reach 1.16 m Pa,which meet the bond strength requirement according to the China National Standard(GB/T 9846-2015).(2)The optimal synthesis conditions of EPL are as follows:EGDE/L mass ratio is 5:1,reaction temperature is 30℃,reaction time is 3.5 h,the concentration of Na OH solution is 1%,number of EGDE drops is 3 times,the epoxy value of EPL is 0.292 mol/100g;Demethylation modification can obviously increase the hydroxyl content of lignin and the degree of epoxidation reaction between lignin and EGDE by the method of Microwave heating,the epoxy value of EPDL increases by nearly 20%comparing with EPL as the same preparation method.(3)The water-resistant modified soy protein adhesive(EPL-SPI,EPDL-SPI adhesives)are prepared with EPL and EPDL as the crosslinking agent respectively.When 5%EPL is added,the bonding strength of EPL-SPI adhesive reaches the maximum value of 0.99 MPa;while7.5%EPDL is added the bonding strength of EPDL-SPI adhesive reaches the maximum value of 1.17 MPa.Demethylation modification can obviously increase the bonding strength of soy protein adhesive modified by epoxied lignin polymer.(4)EPL can obviously improve the bond strength of modified soybean meal adhesive(EPL-SM adhesive),when the dosage of EPL is 8%,the bonding strength of EPL-SM adhesive reach maximum value 1.05 MPa;The hot pressing process parameters as follows:hot pressing temperature 120℃,hot pressing time 6.5 min(75 s/mm),hot pressing pressure 0.9 MPa,sizing amount 180 g/m~2.