Preparation And Properties Of Activated Soybean Protein Isolate Modified Urea-formaldehyde Resin Adhesive

In order to improve the bonding properties of urea-formaldehyde resin and reduce the free formaldehyde content,and also for the high value-added utilization of related plant protein raw materials,the soybean protein isolate(SPI)was extracted from soybean meal using alkali solubilization and acid precipitation method,and it was pretreated by activation and used as a modifier to prepare modified UF resin,and the modified UF resin was also used to prepare MDF.The effects of activation pretreatment on the structure and composition of the isolated protein,the differences in the performance of the modified UF resin with SDS/urea pretreatment activated SPI,and the effects of different activation SPI addition processes on various properties of the UF resin were explored.The main research contents and results are as follows:(1)The isolated proteins were prepared by optimizing the alkali-solution-acid deposition process,and the extraction rate of SPI exceeded 60%.The isolated protein was modified by activation with sodium dodecyl sulfate(SDS)and urea,and the chemical groups were characterized by Fourier transform infrared spectroscopy(FTIR).The results showed that the advanced structure of SPI treated with urea activation was opened and more active sites were exposed.Quantitative analysis of the amide I band by Gaussian fitting revealed that the SDS pretreated isolated proteins,in which some of the hydrogen bonds and macromolecular backbone structures were broken,had reduced advanced structures,exposing more secondary structures and active groups,etc.(2)In the SDS or urea pretreatment activated SPI modified UF resin experiments,FTIR,XRD and TG analyses confirmed that the activated SPI modified UF resin had a similar chemical structure,a higher proportion of crystalline regions and slightly lower thermal stability than the pure UF resin.The introduction of highly activated SPI improved the mechanical properties and water resistance of pure UF resin bonded MDF panels,while reducing the formaldehyde emission from MDF panels.The free formaldehyde content of the urea pretreated SPI modified UF resin was 0.13%,and the MDF boards prepared by it reached 45.73 MPa and 4005 MPa for MOR and MOE,respectively,and 0.71 MPa for IB,with a 24hTS of 8.1%and formaldehyde emission of about 5.5 mg/100g.(3)Through the optimization experiment of the preparation process of modified UF resin,it was found that the cross-linking reaction between activated SPI and UF molecules mostly concentrated in the addition reaction stage of the resin,and the addition of activated SPI before the addition reaction significantly improved the mechanical properties and water resistance of modified resin prepared MDF.At the same time,as the amount of activated SPI added increases from 0.5%to 1%,the crosslinking degree between activated SPI and resin molecules decreases,the resin reaction activity decreases,and curing becomes more difficult.The mechanical properties and water resistance of the board are significantly reduced.The best addition node of SPI modifier is before UF resin addition reaction,and the addition amount is 0.5%of the total resin amount.