Modification Of Defatted Soybean Flour Adhesive By Low-cost Inorganic Fillers And Its Mechanisms

Due to the low solid content,high viscosity,insufficient water resistance,and the higher cost than formaldehyde-based adhesives commonly used in the wood industry,traditional soybean-based adhesives had inferior market competitiveness and their applications in wood industry are highly limited.Based on the current industrial production model of soybean-based adhesives(mechanically blending crosslinker solution and defatted soybean flour at normal temperature),low-cost inorganic fillers were used to modify soybean protein adhesives with attempt to reduce the cost of defatted soybean flour(DSF)adhesive and improve its bond properties and technological applicability in this study.The preferable filler species and filler amount were determined,and the modification mechanism of inorganic fillers on the structure and performance of the DSF adhesive were determined by various analyses and testing methods.The following main conclusions were drawn:(1)Five low-cost and chemically stable inorganic fillers,namely montmorillonite(MM),kaolin(KL),light calcium carbonate(LCC),heavy calcium carbonate(HCC)and talcum powder(TC),were selected to modify DSF adhesive.Inorganic fillers can partially replace defatted soybean flour(DSF)and effectively improve technological applicability of DSF adhesive by reducing the viscosity of the adhesive,relieving shear thinning,and reducing adhesive cost by 7.6%-9.5%.Montmorillonite and kaolin were suitable for the modification of DSF adhesives,especially for exterior-use plywood as significantly improved water resistance up to 58.9%and 46.6%.These improvements were attributing to the penetration of crosslinker/DSF chains into the interlayers of the silicates via intercalation,stable chemical bonds between the fillers and crosslinker,and excellent compatibility between the filler particles and DSF adhesive.(2)Influences of the type and amount of kaolin on the structure and performance of DSF adhesive was investigated due to the good modification effect of Kaolin on DSF adhesive and different Kaolin composition structures.The reactivity order of the three types of kaolins is:GC<GB<GA.The type ? wet strengths of the three kaolin-modified DSF adhesives met the performance requirement of the Chinese standard for Type ? plywood(?1.0 MPa),which were all higher than that of Con-DSF(without fillers).The water resistance order of the three kaolin-modified DSF adhesives is:DSF-GA>DSF-GB>DSF-GC.Only DSF-GA could meet the performance requirement of the Chinese standard for Type ? plywood(?1.0 MPa),in terms of type ? wet strength of 1.05 MPa.Adhesives DSF-GA,DSF-GB,and DSF-GC reduced their costs by 7.1%,8.1%,and 10.0%compared to Con-DSF,respectively.(3)Three industrial kaolins could improve the water resistance of DSF adhesives to various degrees due to following interactions.These kaolin could be uniformly dispersed in the soy protein adhesive,and interact with other components of adhesive via chemical cross-linking between EMPA and the hydrogen bonds between the kaolin layers,unfolded soy protein molecular chains and EMPA molecules penetrated into the kaolin interlayers through intercalation to form intercalation complexes,resulting in increased crosslinking density and water resistance.However,the different reactivity of three types of kaolin with the DSF adhesive system resulted in various water resistances of the modified DSF adhesives.(4)Combination of filler GA that had the greatest influence on the water resistance of DSF adhesives and filler GC that reduced the most adhesive cost,and the addition level of combination kaolin were evaluated for further formulation optimization using the optimal combination ratio(GA:GC=1:1).The results showed that the optimal amount of combination kaolin for indoor use was 45%in terms of the DSF-adhesive viscosity of 5256 mPa.s,the dry strength of 3.64 MPa,the type ? wet strength of 1.37 MPa and the type ? wet strength of 1.1 MPa,confirming that adhesive Kaolin45 could not only improve the water resistance of DSF adhesive but also reduce the cost of DSF adhesive by 12.8%.The optimal amount of combination kaolin for outdoor use or structural use was 30%,in terms of the DSF-adhesive viscosity of 5688 mPa.s,the dry strength of 3.05 MPa,the type ? wet strength of 1.41 MPa and the type ? wet strength of 1.16 MPa,confirming that Kaolin30 could not only improve the water resistance of DSF adhesive but also reduce the cost of DSF adhesive by 8.5%.(5)The potting time of Kaolin-modified DSF adhesive since formulated has a certain impact on its application performance.With the increasing potting time,the wet strength of the adhesive DSF-GA gradually increased,the adhesive system became gradually stable,and the solubility of the adhesive gradually improved.