Synthesis And Curing Kinetics Of Epoxy Resin Tough Curing Agent

Epoxy resin is widely used in many fields such as composite material, coating and adhesive because of its superior mechanical, adhesive, electrical, water-resistant and chemical-resistant property, et al. However, its application is greatly limited due to the low toughness and poor crack resistance. Therefore, the toughness of epoxy resin has been developing one of the research hotspots. Many methods have been developed. One of the most successful methods is to cure epoxy resin by using tough curing agent contained soft segments component. This method can mostly hold the superior mechanical properties of epoxy resin, with simple and convenient process.Two kinds of tough curing agents were respectively prepared by using epoxy-oleic methyl ester and epoxy-oleic capryl ester as termination agents of epoxy-amine adduct (G-oligomer). The structure of the agent was characterized, the mechanical ability of curing material was tested and the morphology of fracture surface was observed. The results indicated that the oxirane group of epoxy-oleic ester reacted with the primary amine group of G-oligomer, the extension at break of the material respectively cured by G-methyl ester and G-capryl ester was increased, the brittle fracture surface of the material was represented toughness breakage. The effect of G-methyl ester on material toughness is better than G-capryl ester, which suggested that the length of the ester carbochain has a little effect on material toughness. The side carbochain in molecular structure of the curing agent made a primary contribution to the toughness. The DSC exothermic curves of G-oligomer,G-methyl ester and G-capryl ester with epoxy resin were determined respectively by differential scanning calorimetry (DSC) measurements at different heating rates. The curing temperature was confirmed, and the curing kinetics of the three non-isothermal curing processes was studied by KAS method,Friedman method and FWO method. The results showed that the order of the curing peak temperature was G-methyl ester>G-capryl ester> G-oligomer; the order of apparent activation energy and frequency factor analyzed by KAS method and Friedman method was G-methyl ester > G-capryl ester > G-oligomer; the reaction order suggested that the curing process was complicated; the kinetic model of the curing process was self-catalyzed reaction.The isothermal curing reaction process of G-oligomer and G-capryl ester with epoxy resin was also observed respectively by Fourier transform infrared (FT-IR) spectroscopy at four different temperatures. The effect of curing temperature and time on curing fractional conversion and reaction rate was discussed; the curing kinetics of the isothermal initial curing reaction was also studied. The results demonstrated that the fractional conversion and reaction rate were rapidly increased in the initial curing reaction. The higher the curing temperature, the higher the fractional conversion and reaction rate was. With increasing of the curing temperature and time, the fractional conversion and reaction rate decreased and became constantly. The initial curing reaction was a first order reaction. The apparent activation energy and frequency factor of curing reaction used G- capryl ester was bigger than that of used G-oligomer. It has a high degree of correspondence with the KAS and Friedman analyses in DSC method.