Study On Graphene Reinforced Soy Protein Adhesive Based On Multi-bond Cooperation

Formaldehyde resin adhesives are widely used in the production of wood-based panels,which have the problems of releasing formaldehyde and other harmful substances from wood-based panel and its products,and the dependence of raw materials on fossil resources.As the continuous improvement of people's awareness of health and sustainable development,the development and application of bio-based wood adhesives has been widely concerned.Plant derived soybean protein is a kind of bulk agricultural and sideline products,which has the advantages of rich source,renewable,low cost,and easy processing.Using it to prepare wood adhesive has the advantages of environmental protection and non-toxic,and can effectively improve the utilization value of agricultural and sideline products.However,the low water-resistant bonding strength,hard and brittle curing layer and poor mildew resistance of common soy protein adhesive seriously limit its large-scale production and application.In this study,soybean powder was used as the main raw material,graphene and nano amino clay were used to strengthen soybean protein-based adhesive.The multiple bonding was constructed through the chemical modification and interface structure design of graphene and nano amino clay to realize the strengthening,toughening,and mildew resistance of soybean protein-based adhesive.This work provided new ideas and new methods for expanding the application of biomass wood adhesives.This work includes the following contents and conclusions:1.Stable aqueous graphene dispersions were prepared by ultrasonic treatment,and selfassembled with multi walled carbon nanotubes(MWNTs)and nanofibrous cellulose(NFC),which was introduced into the protein matrix to construct a non-covalent bond network of multiple hydrogen bonds and ?-? stacking interaction,so as to realize the reinforcement of soybean protein based composite film and adhesive.The introduction of network nanofibers promoted the uniform dispersion of carbon-based materials in protein matrix,and multi nano reinforced phase composite system enhanced the mechanical properties and water resistance of protein film and adhesive.The dry bonding strength of the modified adhesive was 1.67 MPa,which was 52% higher than that of the unmodified soy protein adhesive.The wet strength was 0.61 MPa.The elongation at break of the modified adhesive film was 124.9%.After curing,the total soluble matter and water absorption of the modified adhesive decreased significantly.2.The graphene oxide-enhanced soy protein adhesive and film material were prepared by bionic design.Taking advantanges of the self-polymerization and versatile reaction characteristics of dopamine,the polydopamine layer was attached to the graphene,and covalently cross-linked the soy protein through Michael addition and Schiff base bonds to improve the interface strength between the graphene nanophase and the soy protein to build a strong and tough protein-based adhesive.According to the results,the stress and toughness of the protein film modified with 0.6 wt% graphene increased by 86% and 264%,respectively.The wet bonding strength of modified adhesive was 0.8 MPa.3.Using strong hydrogen bond driven supramolecular self-assembly strategy,phytic acid modified graphene oxide supramolecular complex was prepared and combined with long-chain epoxide neopentyl glycol diglycidyl ether to construct multiple bonding interactions of supramolecular non-covalent bond and covalent bond,so as to improve the wet adhesion strength of graphene reinforced soy adhesive.The results show that the number of internal cracks of the modified adhesive decreased,thus the water resistance of the adhesive was improved.The cured adhesive film was flat and uniform without obvious cracks and holes,suggesting the good toughness.The content of waterinsoluble matter in the cured adhesive increased by 25%,and the water absorption lessened by 41%.The wet bonding strength of the adhesive increased from 0.33 MPa to 1.47 MPa.4.Flake nano amino clay was used as building element to prepare phytic acid-mediated amino clay-based composites through double electrostatic interactions.This constructed a soy protein-based adhesive based on multiple bonding interactions of electrostatic,hydrogen bond and covalent bond,achieving the enhancement of the bonding performance and mildew resistance of the adhesive.According to the results,the surface roughness of the final adhesive increased,the mechanically interlocked force of wood and the adhesive increased,the water absorption of the adhesive lessened,and the water-resistant bonding performance improved.The final adhesive strength(1.19 MPa)exceeded 105% compared with the blank group.The water absorption was 4.26%.There was no obvious mildew on the surface of the modified adhesive,and the anti-mildew performance was enhanced because of the introduction of amino clay.In addition,the adhesive has good biodegradability,biocompatibility and flame retardancy.5.The long-chain alkyl quaternary ammonium salt was grafted onto the surface of amino clay by addition reaction to improve the positivity and mildew resistance of the clay.At the same time,biomineralized nano cellulose was introduced to enhance the bonding performance of soy protein adhesive.The results showed that the bonding network was constructed by electrostatic interaction,covalent bond and metal coordination in the protein system,effectively improving the crosslinking density of the system.At the same time,the bonding network acted as a "sacrificial bond" and can effectively disperse the stress and improve the cohesive strength and toughness of the adhesive.The final wet bonding strength reached 1.8 MPa.The cured adhesive film was uniform and smooth with significantly reduced cracks,and the toughness was improved.At the same time,because the quaternary ammonium modified amino clay has more positive charge,the prepared adhesive had no mold growth or mildew and maintained its original morphological characteristics,suggesting excellent anti mold performance.The diameters of inhibition zones of the final adhesive against Escherichia coli and Staphylococcus aureus were 12.5 mm and 16.3 mm respectively.The antibacterial performance of the adhesive was enhanced.