Preparation And Evaluation Of Liquified Dicyandiamide Based On Application For Prepreg

Epoxy resin prepregs are the intermediate materials of composites, whose resin systems exhibit B-stage in curing reaction. Dicyandiamide(DICY) is a latent curing agent and widely used in epoxy resin prepregs. But its poor diepersity and dissolvability in epoxy resin resulting from strongly polar molecule structure lead to aggravate bad disperse state in the cured and affect adversely property of prepregs and composites. In order to increase compatibility between DICY and epoxy resin in prepregs resin system, DICY is commonly liquified modified.In this paper, because of poly ether amine’s good solubility to DICY, liquified dicyandiamide(L-DICY) was prepared by blending polyether amine(PEA) modified by bisphenol A epoxy resins and DICY, and compared amine value, crystalline, stability and dispersity in epoxy resin with DICY and PEA/DICY curing system that was prepared by blending PEA and DICY. The result showed, L-DICY whose primary amine was partly reacted had the least amine value and primary amine content; the crystalline and melting temperature of L-DICY and PEA/DICY were lower than these of DICY; That L-DICY didn’t appear sedimentation in 30 days and the mass of it seldom changed in 5days showed L-DICY had better stability; The dispersion of L-DICY that was improved in epoxy resin was more uniform than DICYand sparser than PEA/DICY.In curing kinetics study, KAS theory was used to analysis the curing activity energy of three resin systems consisting of three curing systems respectively at different curing degree. The result showed, the curing activity energy of PEA/DICY was least and L-DICY of it was similar to DICY, which implied L-DICY had less curing activity to extend the storage life. Malek and SB(m, n) theory was used to stimulate the rate equation of three resin systems at different rates. The rate equation of PEA/DICY and L-DICY could predict the experimental data well. In chemical rheology analysis, dynamic rheology figure showed L-DICY and DICY had longer low viscosity platform, which was benefit for prepregs process. Dual Arrhenius model simulated the isothermal viscosity curves of three resin systems, consistent with the experimental value in the low viscosity area of early stage of curing. Three resin systems were applied to prepregs resin systems and their mechanical property, heat resistance, transparence and dispersity of dicyandiamide of the cured of three resin systems were measured and compared. The mechanical property and heat resistance had little difference among them. The transparence of L-DICY was best, which showed there were few dicyandiamide residue in cured of L-DICY. Many dicyandiamide particles could be seen in the cured of DICY system in microcosmic image, but not be observed in PEA/DICY and L-DICY systems, which better dispersity of PEA/DICY and L-DICY in epoxy resin improved curing reacting.Composites of three system was prepared by prepregs that was prepared by three curing system respectively. The mechanical property, moist heat resistance and dispersity of the composites were measured and compared. Result showed the mechanical property had little difference among three systems. After moist and heat treatment, the mechanical property of L-DICY system fell little,but it of DICY system fell sharply, which demonstrated that L-DICY system had better moist heat resistance. A lot of dicyandiamide particles could be observed in the composites of DICY system in microcosmic image, but not be seen in PEA/DICY and L-DICY systems, which showed moist heat resistance of composites related to residue of DICY.