| Preparing environmentally friendly soy-based adhesives using defatted soy flour and improving its water resistance via different types of modification techniques of soy protein were extensively investigated. However, in addition to protein, defatted soy flour also consists of40%(w/w) carbohydrate, which negatively affects the properties of soy-based adhesives. Modification and utilization of these components were rarely reported previously. In this Dessertation, the relationship between contents of soy protein, carbohydrate, sucrose and glucose in soy-based adhesives and its water resistance were determined. Viscozyme L enzymolysis conditions of carbohydrate in defatted soy flour (DSF) were investigated, and combination of acid, salt and alkali was then apply to modify the structure of soy protein in the DSF to expose its active functional groups. Then the epoxides or styrene were grafted into components of DSF to obtain boiling-water-resistant soy-based adhesives. The results showed that:(1) The amount of hydrophilic groups (e.g., hydroxyl groups) in the soy-based adhesives decreased as the carbohydrate content decreased or sucrose and glucose content increased. The cross-linking and hydrophobicities of cured soy-based adhesives were enhanced by Maillard reactions between soy protein and sucrose and glucose. Soy-based adhesives prepared with soy protein isolated and DSF had the lowest and highest water absorptions, respectively. The highest bonding strength of poplar and masson pine plywood were0.73MPa and0.76MPa, for a glucose content of carbohydrate in the soy-based adhesive of71wt%and100wt%, respectively. The lowest bonding strength was observed in a cured soy-based adhesive prepared from DSF. A reduced carbohydrate content, or increased sucrose and glucose fractions in the carbohydrate, decreased the hydrophilicity and increased the bonding strength of the cured SBA.(2) The suitable Viscozyme L enzymolysis conditions of carbohydrate in DSF are as follows:pH5.2, temperature50℃, and time20min, the additive amount of Viscozyme L depended on the acturelly needed. Under this conditions, the soy-based adhesives with higher1H NMR chemical shift of β-xylose(δ4.65ppm), β-D-glucose(δ4.70ppm), a-lyxose(δ5.08ppm) and lower1H NMR chemical shift of arabinogalactan (δ5.29ppm). Reducing sugar and glucose content was increase, whereas sucrose and coarse fibre content was decrease. The contents of insoluble substances in soy-based adhesives were lower than control, and its water resistance after curing higher than control.(3) Positive correlationship between reducing sugar content and bonding strength of soy-based adhesives was significance. The effects of treatment temperature and pH on bonding strength were significance, but insignificance on reducing sugar content; the effects of Viscozyme L treatment time were the smallest. The optimized preparation conditions of Viscozyme L treatment soy-based adhsive was treatment temperature54℃, treatment time20min, pH=5.1. Under this condition, the contents of reducing sugar, glucose, sucrose, coarse fibre and bonding strength of soy-based adhesives were2.93%,1.020%,0.42%,1.15%and0.62MPa, respectively. XRD and1NMR indicated that during DSF was treated by Viscozyme L with combination of acid, salt, and alkali, the carbohydrate and soy protein of DSF were hydrolysis; and the order degree of soy protein decrease, but the order structure had no variation. The soy-based adhesives contain more active functional groups and with better water resistance after curing, but bonding strength haven’t met the requirement of GB/T9846-2004for plywood type I.(4) The suitable grafting conditions of Epichlorohydrin (ECH) on the components in DSF were as follows:pH6.2, temperature70℃, and time30min. The effects of additive amounts of ECH on viscosity of soy-based adhesives is significance than epoxy resin, the additive amounts of ECH and epoxy resin were25%and50%, viscosity of soy-based adhesives enhancement were2889.5%and12.6%, respectively. Solid content and bonding strength of soy-based adhesives increase with the additive amounts of ECH and epoxy resin. All bonding strength met the requirement of GB/T9846-2004for plywood type I when the additive amounts of ECH and epoxy resin were10%and30%, respectively. FTIR,1HMNR, TG, and DSC indicated that ECH modified soy-based adhesives were grafted epoxy groups, and FTIR absorption peaks of carboxylic ester and ether structure in ECH modified soy-based adhesives enhancement, meanwhile, the absorption peaks of hydroxyl decrease. During epoxy resin blend with soy-based adhesives, partly epoxy groups react with amino groups immediately; and majority epoxy groups react with hydroxyl in the process of curing. The heat resistance of curing soy-based adhesives was increased.(5) The suitable grafting conditions of N-methylol acrylamide (NMAM) on components in DSF were as follows:pH5.2, temperature70℃, and time30min; And the additive amounts of NMAM was15wt%of DSF."Viscosity, solid content, and monomer percent conversion increase with the additive amounts of styrene. The viscosity, solid content, monomer percent conversion, pH value, formaldehyde content, residual monomer, working life, and shelf life of styrene modified soy-based adhesive were4.939Pa.s,22.6%,72.3%,7.53,0,0.28%,4.6h, and47days, respectively, when the additive amounts of styrene was30wt%of DSF. Its bonding strength could meet the requirement of GB/T9846-2004for weathering plywood. FTIR,1HMNR, TG, and DSC indicated that NMAM was grafted into the component of soy-based adhesive, and styrene monomer copolymerization with NMAM. Hydrophilic groups of styrene grafted soy-based adhesives were further removed during blend with PMDI. The curing adhesives with hydroxyl group content decrease, vinyl disappearance, benzene ring percentage increase; finally, its water resistance was improved further.(6) Ageing ability of masson pine and eucalyptus grandis plywood were employed to evaluate the properties of styrene grafted soy-based adhesive. The decreased dry and wet strength of masson pine or eucalyptus grandis plywood were range from51.2%to69%,67%to70.9%,26.9%to55.0%, and37.6%to39.1%, respectively; and wood fail percentage was almost zero when accelerated ageing time was2160h. The decreased dry and wet strength of masson pine or eucalyptus grandis plywood were range from3.5%to19.9%,10.0%to16.1%,3.8%to24.6%, and9.8%to12.9%, respectively; and wood fail percentage of dry samples were no veriation, but wood fail percentage of wet samples were decrease when natural ageing time was 225days. The decreased dry and wet strength of masson pine or eucalyptus grandis plywood were range from37.4%to41.8%,48.2%to53.6%,57.7%to61.1%, and59.1%to69.6%, respectively; and wood fail percentage of dry masson pine samples were range from95%to100%, but wood fail percentage of wet masson pine samples were zero; all the wood fail percentage of eucalyptus grandis samples were almost100%when soil burial time was225days. The properties reduction of masson pine plywood during accelerated ageing test was higher than natural ageing or soil burial test, and soil burial test was higher than natural ageing test. The properties reduction of eucalyptus grandis plywood during natural ageing test was lower than accelerated ageing or soil burial test, and during45days of soil burial and accelerated ageing test, the properties reduction was similarly. The effects of accelerated ageing test or soil burial test on gluability of styrene grafted soy-based adhesive was severer than natural ageing test. Under the experimental scope, there are no significant correlations of the three kinds of ageing methods on gluability of soy-based adhesive. SEM indicated that combination of veneers in control samples were tight and bonding layers not clearly. All bonding layers of samples were almost damaged and veneers were delaminated during accelerated ageing test. There are no veneers of samples were delaminated during natural ageing test, but bonding layers were clearly. Also no veneers of samples were delaminated during soil burial test, but veneers were severe rotten. |
PDF Full Text Request