Research On The Preparation Of Plant Protein Adhesive By Sesame Cake And Meal

Sesame cake and meal are new renewable plant protein resources for wood adhesives in the production of plywood because of its brilliant performances,which are non-toxic and harmless to human health.In this work,the main raw materials are dehulled pressed sesame cake and meal.The sesame protein was extracted using an alkali method,the sesame protein adhesive was prepared using urea（U）modification and sodium dodecyl sulfate（SDS）modification,respectively,and the optimal preparation of sesame protein adhesive was obtained through single factor design and orthogonal experiment.The purpose was to select out the optimal single modification method by comparing two modification methods.Based on the optimal single modification,the composite modified sesame protein adhesives were prepared by glyoxal modification that has low toxicity to replace the formaldehyde-based adhesives,which could release formaldehyde in the process of using and harmful to human health.The performance and structure of glyoxal-modified sesame protein adhesives were studied.The composite modified sesame protein adhesives were prepared by zinc oxide based on optimal single modification method according to the mechanism of chelation for produce the environmental protein adhesive.The performance and structure of ZnO-modified sesame protein adhesives were studied.Compared with the performance of glyoxal-modified and ZnO-modified sesame protein adhesive,the optimal composite modified sesame protein adhesive was selected to study the gluing process of plywood,and the purpose of study was to lay the foundation for the application of composite modified protein adhesives in actual production.The major results are summarized as follows:（1）The sesame protein adhesive was prepared using urea modification and SDS modification,respectively.The effects of modifier concentration,modification time,solid-liquid ratio,modification temperature on the plywood boned by adhesive were studied through single factor tests.And the optimum processing technology of urea modified sesame protein adhesive was determined.The results showed that the optimum conditions using urea modification were as follow:urea concentration 3 mol/L,reaction time 4 h,solid-liquid ratio1:8 g/mL,reaction temperature 25°C,and under the optimum conditions,the wet shear strength was 0.75 MPa,which achieved the requirement of type II plywood（≧0.70MPa）in accordance with China National Standard.The optimum conditions using SDS modification were as follow:SDS concentration 3%,reaction time 1 h,solid-liquid ratio 1:8 g/mL,and under the optimum conditions,the wet bonding strength was 0.82 MPa,which achieved the requirement of type II plywood in accordance with China National Standard.Compared to the performance of the two-modified sesame protein adhesive,the viscosity of sesame protein adhesive modified by SDS was too high to be coating on the wood surface,and urea modification was chosen as the best single modification method.（2）The sesame protein adhesives modified by urea in the absence（USP）and presence（GUSP）of glyoxal were prepared.The pH value,solid content,apparent viscosity,bonding strength,formaldehyde emission,infrared spectra,thermal stability and fracture surface of USP and GUSP adhesives were investigated in detail.The results suggested that the pH value of GUSP adhesives decreased,the solid content of GUSP adhesives was basically unchanged,whereas the apparent viscosity of the GUSP adhesives were firstly decreased and then increased when glyoxal was introduced.Moreover,the water resistance improved to some extent when glyoxal was induced.By increasing the content of glyoxal to 12%,the wet shear strength of the GUSP adhesive increased by 38.57%compare to China National Standard and reached a maximum value of 0.97 MPa,which met the requirement of type II grade plywood according to China National Standard.The formaldehyde emission of the plywood prepared by GUSP adhesive was much lower than the limit of 0.5 mg/L of E₀ level required by China National Standard.The FT-IR showed that aldoamine condensation reaction occurred between sesame protein and glyoxal.The TGA showed that the thermal stability of GUSP adhesive could not improve significantly with the addition of glyoxal.The SEM showed that the fracture surface of the GUSP adhesives became more compact and have more glue nails compared to USP adhesive that improved water resistance.（3）The sesame protein adhesives modified by urea in the absence（USP）and presence（ZUSP）of zinc oxide were prepared.The performance and structure of USP/ZUSP adhesives were studied.The results suggested that the pH value and solid content of the ZUSP adhesives increased,whereas the apparent viscosity of the ZUSP adhesives were firstly decreased and then increased when ZnO was introduced.The wet shear strength of the ZUSP adhesives improved remarkably compare to USP adhesive,which achieved the required value of interior use（≥0.70 MPa）in accordance with China National Standard.By increasing the content of ZnO to 8%,the wet shear strength of the ZUSP adhesive increased by 44.29%compare to China National Standard and reached a maximum value of 1.01 MPa.The FTIR showed that a new absorption peak was observed at 2215 cm^-1 in the FTIR spectra of the ZUSP adhesives,which might be attributed to the chelation reaction occurred between sesame protein and ZnO.The thermal stability of the ZUSP adhesives improved remarkably as confirmed by TGA.The SEM showed that the fracture surface of the ZUSP adhesives became more compact compared to USP adhesive that improved water resistance.（4）The gluing process optimization of ZUSP adhesive with 8%ZnO addition was studied.The single factor test was applied to analyze the hot-pressing temperature,hot-pressing time,hot-pressing pressure and coating amount.Because of that,orthogonal test was carried out,the wet bonding strength and compression ratio were taken as indexes.The results showed that the optimum gluing process conditions were as follow:hot pressing temperature 120°C,hot pressing time 10 min,hot pressing pressure 1.2 MPa,coating amount280 g/m²,and under the optimum conditions,the wet bonding strength was 1.10 MPa that increased by 57.14%compare to China National Standard,which achieved the requirement of type II plywood in accordance with China National Standard.The prime cost of ZUSP adhesive with 8%ZnO addition was 2981.3 yuan/ton according to the cost of raw needed for the adhesive,which showed that ZUSP adhesive can be applied to actual production.