Preparation,Properties And Mechanism Of Soybean Based Biomass Materials

There is an urgent need to develop biodegradable polymer composites based on renewable agricultural and biomass feedstock due to severe environmental pollution caused by petroleum-based synthetic polymer materials.Soybeans are rich in soybean protein and soybean oil,and offer advantages of abundant resource,low price,and easy availablility.Therefore,soybeans are considered to be ideal resources to develop biomass materials.In this thesis,soybean protein and soybean oil were chosen as raw materials to prepare sustainable biomass materials,and the preparation techniques and application mechanisms were systematically studied,by which achieving effective utilization of soybean resources in the field of biomass materials,and this is in consistent with the concept of sustainable development.This thesis mainly includes three parts:First,soybean proteins were used as raw materials to develop water-resistant soybean protein based wood adhesives,the preparation and modification techniques were investigated,and the improvement mechanism of water-resistance and technical processability were revealed;Second,soybean protein and wood flour were employed as raw materials to develop fully biodegradable wood flour/soybean protein composites which can be applied in agriculture,packaging industry and decoration industry,moreover,the processing and property tailoring technology were systematically studied,and the balance mechanism of its mechanical stability and biodegradability was revealed.Third,bio-based thermosetting resins based on MAESO(maleinated acrylated epoxidized soybean oil)and renewable reactive diluents were prepared,the preparation of methacrylated vanillyl alcohol and methacrylated eugenol was investigated,and the crosslinking modification behavior with MAESO resin was analyzed.The detailed research contents and results are shown as following:(1)Soybean protein was thermally degraded under strong alkali conditions,under such conditions,not only the technical applicalibility was improved,but also the number of reactive sites within soybean protein was increased,and the resulting thermal-caustic degraded soybean protein solutions(DSP)had high solid content(36.7%-38.2%),low viscosity(325-872 cP)and long work life,which is acceptable to prepare soybean protein based adhesives.The crosslinking behaviors between DSP and each crosslinker(glyoxal,glutaraldehyde and PMDI)were investigated,and the effect of crosslinking on the properties of soybean protein based adhesives were evaluated.PMDI could react with both the reactive groups of DSP and the hydroxyl groups of wood to form solid chemical bonds.Therefore,PMDI exhibited better crosslinking efficiency with DSP than that of glyoxal and glutaraldehyde.The water resistance of soybean protein based adhesives improved with the increasing of PMDI loading,but the work life is just 20-30 min.Soybean protein adhesive modified by the combination of MMT with polyisocyanate exhibited an improved work life of 2-3 h,and an increased water resistance,indicating a water-resistant soybean protein adhesive which can bear 28 h boiling-dry cycled treatment was successfully developed.(2)In order to understand the improvement mechanism of water resistance and work life of MMT modified soybean protein based adhesives,a variety of modern analytical methods combined with conventional chemical analysis have been used to reveal the nano-scale blocking mechanism of MMT,the results showed that after intercalating treatment soybean protein with MMT,some reactive groups within soybean protein interact with MMT by hydrogen bonds and electrostatic bonds,and thus not only reduced the concentration of reactive groups in soybean proteins but also increased the steric hindrance for the active groups in soybean proteins that react with PMDI,and thus decreasing the reaction rate between soybean protein and PMDI,and effectively prolonging the pot life of adhesive.Moreover,MMT modification can also increase the chemical crosslinking reaction of PMDI with soybean protein and wood flour during hot pressing,by which further improve the water resistance of adhesive.Therefore,a novel approach to prepare water-resistant soybean protein adhesive has been reported,and a nano-scale blocking mechanism was proposed.(3)Wood flour/soybean protein composites were developted by using modified soybean protein and wood flour as raw materials,the moisture content and molding conditions(in terms of hot pressing temperature,hot pressing time and hot pressing pressure)of wood flour/soybean protein composites were optimized.The property tailoring technology of wood flour/soybean protein composites was obtained by evaluating the crosslinker types and different modified soybean protein on the properties of composites.The effects of molding technology on the properties of composites indicated that when the moisture content of the mixed material maintained at about 20%,the optimum molding conditions are 120 ?,7.5 MPa and 5.5 min.The effects of five crosslinkers on the properties of the wood flour/soybean protein composites were shown as follows:the order of the improvement of the mechanical properties of five composites was C-TSP-MPA>C-TSP-PMDI/GO>C-TSP-PMDI>C-TSP-WE>C-TSP-GO.Among the five evaluated crosslinkers,modified polyamide prepared composites exhibited the best mechanical stability with dry state tensile strength of 32.77 MPa and accelerated aging tensile strength of 19.61 MPa.Moreover,thermal-acid treatment could effectively improve the water resistance of soybean protein,and the composite prepared with TSP had better properties than that prepared with DSP.(4)The biodegradation behavior and the mechanical property evolution of wood flour/soybean protein composites were systematically investigated through soil burial biodegradation and laboratory microbial degradation test.Some of the soybean protein and wood flour component within the composite were continuously consumed as the nutrients of the microorganism with increasing degradation time,the weight of the composite sample was continuously reduced,the interface bonding of the composite was disrupted,and the mechanical properties were continuously decreased.The balance of mechanical stability and biodegradability of wood flour/soybean protein composites can be achieved by tailoring protein-crosslinker-protein and protein-crosslinker-wood chemical linkages to proper chemical crosslinking efficiency.When the crosslinking efficiency of the composites increased,the mechanical stability of the materials increased and the biodegradability decreased;when the crosslinking efficiency decreased,the mechanical stability of the composites decreased and the biodegradability accelerated,revealing the balance mechanism of mechanical stability and biodegradability of wood flour/soybean protein composites.(5)A novel,bio-based monomer,methacrylated vanillyl alcohol(MVA)with reactive carbon-carbon double bonds was synthesized using renewable vanillyl alcohol and methacrylic anhydride by esterification reaction.The resulting MVA was used to crosslinking MAESO resin to prepare novel thermosets.With the increasing of MVA loadings from 0 to 40%,the viscosity of the MAESO resin system was siginificantly decreased,the gelation time and the elongation at break were shortened,the curing reaction rate,the curing degree,the tensile strength and tensile modulus were increased,furthermore,the glass transition temperature and storage modulus of the resulting MAESO-MVA resin exhibited a certain degree of improvement.Therefore,MVA can replace toxic styrene as a reactive diluent for MAESO resin.(6)A low volatility,low toxicity and low viscosity methacrylated eugenol(ME)was prepared by Steglich esterification reaction using renewable eugenol as raw material in the absence of solvents.The resulting ME was firstly used as a reactive diluent of MAESO resin to produce novel thermosets via free radical polymerization.With the increase of ME loadings from 0 to 100%,the viscosity of MAESO resin system was significantly decreased.The combination of MAESO homopolymerization,ME homopolymerization and MAESO-ME copolymerization accelerated the crosslinking reaction.The curing degree was increased gradually,and the thermal stability was improved;the resulting ME can crosslink with MAESO resin and effectively increase the storage modulus and glass transition temperature of the cured resin,which can used as an effectice reactive diluent for MAESO resin to replace toxic styrene.Compared with MVA,ME monomer improved the mechanical properties and processability of MAESO resin to a higher extent.