| In order to solve the problems caused by complex four-level structure of soybean protein,such as unstable adhesive bonding and poor water resistance,the structure of soybean protein was regulated by chemical and physical methods using soybean protein isolate as raw material,and then crosslinking agent was added to prepare soybean protein adhesive.On the surface of a particle size of modified soy protein before and after,the hydrophobic index,protein molecular weight,the dispersion as well as to the preparation of the adhesive residue rate,moisture absorption rate,functional group change section morphology,thermal stability,curing adhesives and adhesive bond strength of plywood characterization and analysis of research on soybean protein structure change and the crosslinking agent association effect enhancement effect,establish pretreatment parameters,protein structure,the preparation of the relations between adhesive properties,for regulating the structure of soybean protein to enhance performance of soy protein adhesives to provide theory and practice basis.The main research conclusions are as follows:(1)Urea breaks hydrogen bonds in soybean protein molecules,sodium dodecyl sulfate makes hydrophobic groups inside the protein molecules eversion,and sodium bisulfite breaks disulfide bonds between protein molecules,thus destroying the molecular structure of soybean protein.Compared with the unmodified protein,the surface hydrophobic index increases by 189.92%,76.73% and 158.84%,respectively.The primary structure,leben-helix structure and social-folded structure of the protein molecule were almost intact,and the third and fourth level structures were destroyed.Under the action of denaturation agent,protein hydrophilic groups were exposed,and during the curing process,they reacted with the crosslinking agent to form a closer cross-linking structure.The cross-linking density increased,and the residual rate increased to 91.9%,91.5% and 90.2%,respectively.The water-resistant bonding strength of plywood prepared with urea and crosslinking agent modified adhesives can reach up to 1.07 MPa,which is better than the other two denaturation agents.(2)Ultrasonic cavitation breaks SPI particles,damages the molecular structure of soybean protein and reduces the molecular weight of protein.As the ultrasonic treatment time increased from 10 min to 40 min,the average particle size of SPI decreased by 74.55%,the surface hydrophobic index of soybean protein increased by 484.38%,and the molecular weight of protein decreased.When the ultrasonic treatment was 4 min,the residual rate of the ultrasonic modified soybean protein adhesive was increased by 2.50%,the moisture absorption rate was decreased by 36.40%,and the water-resistant adhesive strength of the prepared plywood was increased by 155.56%.Compared with other soy meal based adhesives reported in the literature,the amount of chemical reagent added was reduced by 650%.(3)Microwave reduced the particle size of SPI particles and made them uniform,damaged the molecular structure of soybean protein,and caused the hydrophobic groups inside to eversion.As the microwave treatment time increased from 1 min to 5 min,the average particle size of SPI decreased by 67.32% and mode by 65.76%.The surface hydrophobic index of the protein increased by 526.04% and the electromotive force of Zeta potential decreased by 22.67%.The active groups of the protein molecules expanded after microwave treatment can react with the epoxy crosslinking agent,and form a more compact crosslinking structure during the curing process,which improves the water-resistant bonding performance of the modified soybean protein adhesive.When microwave treatment was performed for 4 min,the performance of the adhesive was the best.Compared with the unmodified soybean protein adhesive,the residual rate increased by 3.68%,the moisture absorption rate decreased by 41.77%,the water-resistant adhesive strength increased by 160.47%,and the dry adhesive strength increased by 76.79%. |
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