Synthesis Of Lignin-based Epoxy Resin In Ionic Liquid [BMIm]Cl And Characterization

Though lignin is a renewable biomass resource derives from a wealth of source, the utilization efficiency of it is still insufficient. The fact that large quantity of industrial lignins were wasted as garbage every year, along with environmental pollution problems, had caused people’s attention. The application of lignins has become a hot research topic in recent years.Based on the structural properties of lignins and the research situation about the usage of lignins in the synthesis of materials, the lignin-based epoxy resin(LGEP) was synthesized using the industrial alkali lignin(LG) as raw material in this paper. The ionic liquid [BMIm]Cl, a kind of green solvent, was employed instead of traditional organic solvents to dissolve the LG, and p-cresol was selected as phenolic agent to phenolate LG. Then more active phenolic lignin(PLG) was achieved. The PLG then involved in the epoxidation reaction with epoxy chloropropane (ECH) obtaining the lignin-based epoxy resin (LGEP).Firstly, the LG, which had been purified, was phenolated by the method of sulfuric acid-p-cresol to obtain PLG. The results of FT-IR spectrum analysis and determination of phenolic hydroxyl content showed that the lignin molecule is grafted successfully phenolic hydroxyl, which improved the active of LG effectively. Through the L9(34) orthogonal experiments, with the phenolic hydroxyl content of PLG as the response value, investigated the dosage of p-cresol(mL/g), the amount of60wt%sulfuric acid(10mL/g), modification temperature and modification time effect on the phenolic hydroxyl content of LGEP. The optimum process conditions of phenol modification was explored as follows:the dosage of p-cresol was10ml/g, and the amount of60wt%sulfuric acid as the catalyst was lOmL/g, with the modification temperature was80℃and the modification time was3h. The phenolic hydroxyl content of PLG under the optimum process conditions was1.45mmol/g. The results provided certain reference for the synthesis of LGEP.Secondly, referencing the one-step synthesis principle of Bisphenol-A epoxy resin, LGEP was synthesized by the epoxidation reaction of PLG with ECH under alkaline condition.The results of FT-IR spectrum analysis show that lignin successfully partakes in the synthesis of epoxy resin. Moreover, through the L9(34) orthogonal experiments, with the epoxy value of LGEP as the response value, investigated the effect of the pH of system, n(ECH):n(phenolic hydroxyl), reaction temperature and reaction time on the epoxy value. The optimum process conditions of synthesis of LGEP was explored as follows:pH was9, and molar ratio of ECH to phenolic hydroxyl group was2.5, with the reaction temperature was90oC and the reaction time was5h. The epoxy value under the optimum process conditions was0.43.Finally, LGEP was modified by phthalic anhydride as curing agent and triethylamine as accelerant. The modification progress was estimated that the LGEP systen with95%curing degree was53.7minutes and the curing time of the LGEP systen with99%curing degree was124.4minutes at the curing temperature482.66K. Referencing the result, the curing time was set as125min.