Study On The Hydrothermal Depolymerization Of Corn Straw Lignin And Its Application In The Modification Of Epoxy Resin

In this paper,the corn straw lignin is raw material,the experiment of its hydrothermal depolymerization was optimized and the optimum synthetic formula of epoxidized lignin was determined,and the curing reaction of epoxidized lignin/epoxy resin-polyamide blend system was investigated,meanwhile,the curing conditions were determined.Based on this curing condition,the performance effect of epoxidized lignin content on epoxy resin/polyethylene glycol/epoxidized lignin-polyamide cement was studied.The details were as follows:The hydrothermal depolymerization of lignin adopts the single variable principle,and the hydroxyl content of the depolymerized product is taken as the evaluation standard.When the heating temperature was 200?,heating time was 100 min,NaOH content was 14%and the ratio of lignin to solvent water was 1:8,the hydroxyl content of depolymerized product was about 1 times higher than that of original lignin.With the help of infrared spectroscopy(FTIR),thermogravimetric analyzer(TG),gel permeation chromatography(GPC)and differential scanning calorimetry(DSC)analysis,the depolymerized lignin and original lignin was characterized.Compared to the original lignin,the depolymerized lignin ether bond was broken,and the hydroxyl content increased,but the aromatic group was not destroyed.After hydrothermal depolymerization,the initial heat resistance temperature was increased,and the final residual mass decreased,meanwhile,the molecular weight distribution became narrower and the molecular weight decreased obviously.The epoxidized lignin was synthesized by the reaction of depolymerized lignin with epichlorohydrin under catalytic agent of tetrabutyl ammonium bromide and NaOH,when the depolymerized lignin reacted with epichlorohydrin in mass ratio of 1:8,the maximum epoxide value of product was 0.164.The obvious vibration peak of epoxide appeared at 911 cm-1 in the FTIR spectra of depolymerized lignin,which indicated that the epoxy group was successfully introduced into the depolymerized lignin.For epoxy resin/epoxidized lignin-polyamide system,the self-catalytic reaction model was suitable to describe the curing kinetics,The curing kinetic equation was as follows da/dt=8.288×107exp(-62760//Rr)?0.6824(1-?)0.8014 The curing conditions were 75? heating for 2 h and 140? heating for 1 h.In the curing process,the epoxidized lignin could also be used in the crosslinking and curing reaction of the epoxy resin,in addition to catalyzing the chemical reaction of the epoxy resin with polyamine.Under the solubilization of polyethylene glycol,the epoxidized lignin had better compatibility with epoxy resin/polyamine system,and could participate in and promote the curing of epoxy resin,and could toughen epoxy resin with polyethylene glycol synergistically.With the increase of the amount of epoxidized lignin added to epoxy resin,the bending strength,impact strength,energy storage modulus and glass transition temperature of epoxy resin curing material increased first and then decreased.When the amount of epoxidized lignin added to epoxy resin was 8%,the mechanical properties and heat resistance of epoxy resin curing material could be improved greatly.