| Soy-based adhesive inherently possesses poor water resistance,high viscosity,difficulty in coating and high brittleness of solidified adhesive layer,futhermore,many modification methods have high cost which limit their application on plywood fabrication.In this paper,defatted soybean meal was used as the main raw material,polyamide epoxy resin(PAE)was used as the cross-linking agent,soybean meal-based adhesives were prepared by the combination of soybean protein isolate residue and rapeseed meal defatted and soybean meal,and the adhesive was further strengthened and toughened by carboxyl styrene butadiene latex to prepare low cost soybean meal-based adhesive with low viscosity,easy sizing,good water resistance and high toughness.The bonding properties of the modified adhesives were characterized by preparing plywood and testing the bonding strength,The adhesive properties of the modified adhesives were characterized by preparing plywood and testing the adhesive strength.Rheometer and XRD were used the viscosity,cross-linking density,functional group,thermal stability and cross-section morphology of the modified adhesive were characterized by analyzer,FTIR,TGA and SEM.The strengthening and toughening mechanism of the modified adhesives were clarified,which provided theoretical and technical support for the modification and industrial application of soybean meal-based adhesive.The main conclusions are as follows:(1)Soybean meal-based adhesive with low cost,low viscosity and high water resistance could be prepared by compounding soybean residue with soybean meal.Soybean residues were dispersed uniformly in the soybean meal-based adhesive,and the microphase separation system was formed by hydrogen bond between the soybean residue and the adhesive system,so as to improve the bonding performance of soybean meal-based adhesive and the bonding strength of plywood.The modified adhesive system showed the best comprehensive performance with 5% soybean residue,compared with the adhesive without soybean residue,the viscosity was reduced by 22.4%,the water-resistant adhesive strength was increased by 35.2%,up to 1.19 MPa,which met the use requirements of class II plywood(≥ 0.7MPa).(2)Carboxylated styrene-butadiene rubber latex could strengthen and toughen soybean dregs / soybean meal composite protein adhesive.Carboxybutylbenzene flexible long chain could form interpenetrating network with soybean dregs / soybean meal composite protein adhesive crosslinking system,effectively buffer and transfer external force,improve the toughness and bonding performance of the adhesive.Adding 10 g carboxylated styrene butadiene latex modified adhesive,the cured adhesive film showed the characteristics of toughness,flat and compact structure,which effectively improved the waterresistant bonding strength and toughness of the soybean residue / soybean meal composite adhesive,and the bonding strength of plywood increased by 12.6%,up to 1.34 MPa.(3)Rapeseed meal could improve the strength and toughness of soybean meal-based adhesive and reduce the cost of soybean meal-based adhesive.Rapeseed protein could participate in the protein adhesive system to play a bonding role;rapeseed fiber could play a better loading role in the soybean meal-based adhesive system,resist external stress,and achieve the effect of strengthening and toughening the modified adhesive system showed the best comprehensive performance with 15% rapeseed meal.Compared with the soybean meal-based adhesive without rapeseed meal,the viscosity decreased by 31.7%,the bonding strength of plywood increased by 63.6%,up to 1.44 MPa,and the dry adhesive strength reached 2.42 MPa. |
