| With the increasing awareness of environmental protection and the continuous consumption of non-renewable petrochemical resources,the development of high-quality and environmental-safe adhesives using renewable biomass materials has become a hot spot in the current wood industry.Resource-rich and renewable soybean protein is an ideal resource for the preparation of biomass green adhesives.Aiming at the poor water resistance and high cost of soybean-based adhesive in the current market,this study focused on the following four issues: 1)using soybean protein isolate(SPI)as the raw material,a SPI-based adhesive was formulated and optimized for Type I plywood,and the improvement mechanism on the waterresistance and bond properties were revealed,by which laid the preliminary theoretical foundations for the subsequent development of defatted soybean flour(DSF)based adhesives for Type I plywood;2)using DSF as the raw material,thermal treatment and thermo-chemical treatment were carried out to improve the bond properties of DSF-based adhesive to meet the requirements for Type I plywood,and the improvement mechanism on bond properties by thermal treatment and thermo-chemical treatment was revealed;3)some inorganic filler were applied to improve the bond properties and technological applicability of thermo-chemical treated DSF-based adhesive and reduce its cost,and the improvement mechanism of the optimal inorganic filler on the adhesive performance was revealed;4)the applicable technologies of the optimal DSF-based adhesive were investigated and optimized.Based on above works,some conclusions were drew as follows.1)A SPI-based adhesive for Type I plywood was formulated by the combination of liquefied SPI,thermal treated SPI and crosslinker EMPA solution.A liquefied SPI solution with high solid content but low viscosity was resulted from the combination liquefaction technique in the presence of sodium sulfite,urea,sodium lauryl sulfate and sodium hydroxide.The application of liquefied SPI solution in the formulated SPI-based adhesive resulted in good technological applicability.Thermal treatment led to the dissociation of SPI subunits,thus unfolded the globular structure of SPI and released the embedded active groups that were beneficial for the rearrangement and re-aggregation of the protein molecules.As a result,both the water resistance of SPI itself and its crosslinking activity were improved,by which led SPI-based adhesive excellent bond properties.The optimal thermal treatment condition was keeping SPI at 120 °C for 30 min.The optimal SPI-based adhesive for Type I plywood was formulated from liquefied SPI solution,thermo-treated SPI powder and EMPA solution with mass ratio of 5:5:3,which had a 28h-boiling-dry-boiling wet bond strength of 1.08 MPa.2)The type and amount of modifing agent had important influences on the bond properties of thermo-chemical treated SPI adhesives.The best modified agent was composed of 1%sodium lauryl sulfate and 1% sodium sulfite,with which the thermo-chemical treated SPI adhesive had a 28h-boiling-dry-boiling wet bond strength of 1.22 MPa.The thermo-chemical treatment in the presence of sodium lauryl sulfate and sodium sulfite could effectively unfold the globular structure of SPI and release the embedded active groups,and thus promoted to crosslinking reactions between thermo-chemical treated SPI and crosslinker.Meanwhile,proper self-crosslinking between SPI molecules during thermo-chemical treatment improved the water resistance of SPI itself.As a result,the bond strength and water resistance of SPI adhesive effectively improved.The improvement on the bond properties of thermo-chemical treated SPI adhesive is determined by both the self-crosslinking reaction between protein and protein and the crosslinking reaction between protein and crosslinker.However,the protein-protein crosslinking had much more contributions to the water-resistance improvement thanprotein-protein crosslinking.3)Thermal treatment could destroy the subunits of soybean protein in DSF,unfold its globular structure and release partial embedded active groups,which are beneficial for the self-crosslinking between proteins,Maillard reaction between protein and carbohydrate,and crosslinking between protein and crosslinker.As a result,the cured DSF-based adhesive had a good three-dimensional network structure that improved the water resistance.The thermal-treatment temperature has more influences on the bond properties and water resistance than the thermal-treatment time.The preferable thermal treatment conditions for DSF was at 80 °C for30 min,resulting in a DSF-based adhesive that could withstand 28 h boiling-dry-boiling aging test and had an aged wet bond strength of 0.85 MPa.4)The type and amount of thermo-chemical treatment additives,thermo-chemical treatment temperature and time have important influences on the bond properties of thermo-chemical treated DSF adhesive.Thermo-chemical treatment in the presence of sodium dodecyl sulfate could more effectively destroy the globular structure of soybean protein,and therefore release more reactive groups and inhibit excessive self-crosslinking reaction between unfolded proteins chains.As a result,these changes promoted the Maillard reactions between protein and carbohydrate and the crosslinking reactions between the protein and crosslinker to form a more compact network structure in cured DSF adhesive.Maillard reaction transformed partial soluble carbohydrate into insoluble products that additionally increased the water resistance of DSF adhesive.The optimal thermo-chemical treatment was maintained DSF at 140 °C for 30 min in the presence of 2.5% sodium dodecyl sulfate,which resulted in a thermo-chemical treated DSF adhesive with a 28h-boiling-dry-boiling wet bond strength of 1.21 MPa.5)The addition of inorganic filler could not only reduce the cost of DSF adhesive but also improve its bond properties and technological applicability.The type and amount of inorganic filler have important influences on the bond properties,technological applicability and cost of DSF adhesive.The commercial inorganic filler WSP prepared from montmorillonite clay was an optimal candidate due to its lowest cost,best improvement on water resistance and the mediate improvement on the technological applicability.The enhancement mechanism of the inorganic filler WSP on the water resistance of the thermo-chemical treated DSF adhesive was mainly attributed to the formation of a novel organic-inorganic hybrid structure resulted from the adsorption,hydrogen bonding,electrostatic interaction and chemical bond between active molecules of DSF adhesive and the montmorillonite layers.When formulated DSF adhesive for Type I plywood,the preferable WSP level was 20% on basis of thermo-chemical treated DSF,resulted in an WSP-modified DSF adhesive with a 28h-boiling-dry-boiling wet bond strength of 1.37 MPa and a reduced adhesive cost by 7.05%.6)The effect of the adhesive-formulating factors and hot-press factors(such as DSF species,solid content of crosslinker,WSP/DSF ratio,adhesive consumption,open time,hot-press time,hot-press temperature and hot-press pressure)on the bond properties of the finally-optimized DSF adhesive were investigated.A most economical and effective formulation of DSF adhesive for Type I plywood was obtained as follows: 100 parts of EMPA solution with9wt% solid content blend with 32 parts of thermo-chemically treated DSF and 8 parts of WSP by mechanically stirring at room temperature.The preferable hot-press technologies for Type I plywood was obtained as follows: adhesive consumption of 340g/m2(double bondlines),opentime for 30 minutes after veneer spread DSF adhesive,and hot pressing the plywood at 120 °C and 1.4 MPa for 4.5min.These results about adhesive-formulating and hot-press technologies will provide instructive guidance for commercial application of the final-optimized DSF adhesive in the wood industry. 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