Study On Disruption And Modified By Crosslinker Of Soy Protein-based Adhesive

The use of natural adhesives have thousands of years, because of thedefects of their own performance, leading to many restrictions in application. Lately,there has been a considerable industrial interest in the development of natural andrenewable adhesives, such as soy protein-based adhesive becoming a hot topic whichis one of the most promising natural adhesive and has attracted considerable attentionfor its abundance and acceptable performances. Poor water resistance and bondingstrength are the both bottlenecks limiting its development. Till now, the problem ofthe water resistance of soy protein-based adhesive is still not totally resolved. Themain work on soy adhesive of today could be divided into two sides. One is theapplication of soy adhesives and the other is how to improve its water resistance.Withthe continue futher study, good performance of soy protein-based adhesive comingwill gradually rise in the application proportion in wood industry, to substitutetraditional synthetic resins such as urea formaldehyde resin, phenol formaldehyderesin, and melamine formaldehyde resin as adhesives for wood panels, because of theenvironmental pressure worldwide.Nowadays, there are main two methods in modifying soy protein, one ischemical modifying and the other is cross-linker modifying. Alkaline treatment is themost commonly used method to modify soy protein and NaOH is the mainalkali.Study on soy protein-based adhesive is rather late in China. According to thelately literature, the dry shear strength and wet shear strength of soy protein-basedadhesive plywood have met the requirement of GB/T9846.3-2004class Ⅱplywood.`The following is the main study contents in this paper:1. To modify soy protein-based adhesive, not only to ensure a certainhydrolysis degree, but also to ensure that the adhesive has a certain bondingstrength properties. Meanwhile, we need to consider the viscosity ofadhesive to ensure the operability of adhesive. On the above basis, Alkali(NaOH) was used for the disruption of soy flour in this paper. Influences of the addition amount of NaOH, sodium dodecyl benzene sulfonate(SDBS),solid content of soy flour, treating time and treating temperature onhydrolysis degree and viscosity of soy protein were studied. Choosing thebest conditions, wish to provide a reference for the subsequent study basedon alkaline degradation of modified soy protein;2. On the above study based on disruption of soy protein by NaOH, instead tochoose mixed alkalis, namely Ca(OH)2and NaOH, were used to disrupt soyprotein in this study. Influences of the weight ratio of Ca(OH)2/NaOH on dryshear strength, wet shear strength, water resistance of soy protein-basedahesive were studied. The structure characteristics and thermal properties ofsoy protein treated by Ca(OH)2and NaOH were studied by FT-IR and DSC, wishto provide a reference for the subsequent study based on mixed alkalisdegradation of modified soy protein;3. Based on disruption of soy protein by Ca(OH)2/NaOH and NaOH alone, wechoose chemical modified reagent(SDBS) and cross-linker(formaldehyde) tocontinue the modifying process;4. On the above study, homemade cross-linkers were used mixed withdisrupted soy protein, not only be able to retain the protein macromoleculeand bring in the good performance of synthetic resin in water resistance, butalso to take full advantage soy protein side chain reactive groups. Thatguarantees the simplicity of the preparation process of soy protein adhesive,and optimizes the ratio of cross-linkers by orthogonal test;5. On the above all studies, hot-pressing process of cross-linker modified soyprotein-based adhesive is studied. The curing mechanism of cross-linkermodified soy protein-based adhesive is studied by FT-IR13、C-NM and1H-NMR, wish to provide a reference for the industrial application of soyprotein-based adhesive.Through the above five aspects of the study, we have a deeper understanding ofthe modified soy protein-based adhesive and draw the following five conclusions:1. In the present experimental range, when treating soy protein with NaOH alone, the optimium conditions would be: addition amount of NaOH7%onsolid content of soy protein, SDBS1%, treating3h, treating temperature90℃and solid content of30%. Then, the hydrolysis degree and viscosity ofsoy flour would be up to1.5Pa s and45%;2. The results showed that soy protein adhesive treated by Ca(OH)2/NaOH had betterdry shear strength, wet shear strength and water resistance than those of soyprotein with NaOH alone. However, the effect for the improvement on waterresistance caused by Ca(OH)2was limited. That was partly proved by results ofFT-IR. DSC results indicated that the optimal weight ratio of mixed alkalis mCa(OH)2:mNaOH=2:1;3. Soy protein treated by mixed alkalis Ca(OH)2/NaOH than those of soy proteinwith NaOH alone, whether on cross-linker (formaldehyde) crosslinkingmodification, or on chemical modified reagent (SDBS) modification,modified soy protein-based adhesives have higher dry shear strength withrelatively stable, and the wet shear strength and water resistance have goodperformance;4. In the present study range, the optimal cross-linkers conditions optimized byorthogonal test would be:6%X1(homemade cross-linker),3%melamineformaldehyde resin(MF),8%X2(homemade cross-linker). Then, in thiscondition, the dry shear strength(D), the wet shear strength(W2) and shearstrength(W1) would be up to1.682Mpa,1.139Mpa and1.63Mpa;5. In the present experimental range, the optimal hot-pressing process would be:160℃hot-pressing temperature,1.5Mpa hot-pressing pressure,8min hot-pressingtime, and380g/m2two sides sizing. Then, the dry shear strength and wet shearstrength of soy protein-based adhesive modified by cross-linker based on soyprotein adhesive treated by Ca(OH)2/NaOH have met the requirement of GB/T9846.3-2004class I plywood. The wet shear strength is very stable, and don’tchange with the rising time of boiling water. The reduction of the hydrophilicgroups and the cure systems highly crosslinking are the key to the good performance of wet shear strength and water resistance proved by FT-IR、13C-NMR and1H-NMR. In the present study range,changing the relevantparameters, the results are still meeting the requirement of GB/T9846.3-2004class I plywood, and the cost is3,000yuan/ton. The cost of soy protein-basedadhesive modified by cross-linker is high. At the same time, high viscosityand low solid content are still its defects. To reduce the amount ofcross-linker agent and expanding its application in plywood or otherwood-based panels varieties yet to be strengthened.