Research On Novel Curing Agents For Epoxy Resin And The Carbon Nanotube Composites

Epoxy resin is one of the most important thermosetting polymers, widely used in the fields of aeronautics, astronautics, machine and electronics due to its excellent mechanical and electrical properties, high heat distortion temperature and good chemical resistance. However, there are some shotcomings of the"two-pot"resin composites with curing agent as well as the cured epoxy is brittle, which affect the properties of epoxy resin. The effect of curing agent and reinforcement on the properties of epoxy resin were investigated in this paper.In order to accomplish this work, firstly, the curing agents and the resin composites were prepared, and then the mechanics properties and the dielectric properties of the composites along with the cure kinetic of the resin systems were studied by experimental and theoretical methods. There are mainly two parts in the research as following.1) The research on epoxy resin/microcapsule mold-curing agent system.To obtain a"one-pot"latent curing agent of epoxy resin, 2-ethyl-4-methyl imidazole (EMI-2,4) was imployed to prepare the microcapsule curing agent, which can improve the storage stability of resin system.The contents in our research include the preparation and optimization of the microcapsule agent, as well as curing kinetic and the mechanics of the resin composites.The EMI-2,4 was modified by an epoxide ring opening from the second-type ring nitrogen of EMI with the large molecule of butyl glycidyl ether (BGE). The product EMI-g-BGE can be an effective latent curing agent of epoxy resin and can reduce the hydrophilicity of the products. Elemental analysis, FTIR spectroscopy, and 1HNMR spectroscopy have been used to characterize EMI-g-BGE.EMI-g-BGE was encapsulated by evaporation emulsion method and with Polyether Imide thermoplastic resin (PEI) as the shell material. The surface morphology of microcapsules with the SEM photograph and particle size distribution along with the encapsulation efficiency has been investigated. The experimental results showed that the optimal microcapsules can be obtained with the ratio of core to shell being 1:1, the concentration of the dispersion agent 8%, the stirring speed 700rpm and the temperature 36℃.There are more than 10 months of storage time in room temperature of epoxy resin composites with microcapsule curing agent. The curing kinetic of epoxy resin with EMI-g-BGE or microcapsule curing agent as curing agent was studied by non-isothermal DSC technique at different heating rates. The Kissinger and Ozawa methods were adopted to calculate the kinetic parameters of the two systems, with which results showed that they were both the same complex reaction and the kinetic model was a two-parameter (m, n) autocatalytic model. The apparent activation energy Ea had increased from 72.61kJ/mol to 89.55kJ/mol, which indicated the shell material of the microcapsule curing agent prevented the activation of the curing reaction.The impact strength of the epoxy cured with microcapsule increased over one time more than that with EMI-2,4 curing agent, and the tensile strength and the flexural strength have not decreased. Thermogravimetic analysis (TGA) showed that the heat stability of the epoxy cured with microcapsules had not been affected.2) The research on epoxy resin/carbon nanotubes compositesThe mulltiwalled carbon nanotubes (MWNT) were introduced to improve the mechanical and electrical properties of epoxy resin. In our study, MWNT was modified with a mixture of H₂SO₄/HNO₃, and then the carboxylated MWNT (a-MWNT)was stirred using chloride. The obtained acyl chlorination MWNT was reacted with epoxy curing agent triethylene-tetramine (TETA). Finally, TETA-MWNT was obtained. The modified MWNT was testified by FTIR,Ramon analysis, and the titration test and the elemental analysis showed the reaction ratio from–COOH to–NH2 was 46.55%.MWNT/EP composites were prepared by ultrasonicated dispersion method. The mechanical test showed that the composites of TETA-MWNT/EP had excellent properties than MWNT/EP and a-MWNT/EP composites. TEM graphs showed the dispersion of TETA-MWNT in epoxy matrix had been better than MWNT or a-MWNT, meanwhile, the morphology of fractured compositions showed the compatibility of TETA-MWNT in epoxy matrix improved greatly. IR analysis showed the reaction of amido group in TETA-MWNT with epoxy, which explained the good property of TETA-MWNT/EP composites.Mechanical test with different contents of TETA-MWNT showed that the best content was about 0.75 percent.The dielectric properties of epoxy resin with different contents MWNT were researched according to the scaling law, with the theoretical percolation threshold of epoxy resin composites filled with TETA-MWNTs was 4.20%. The value of the relative dielectric constant of resin composites was as high as 421 with the TETA-MWNT content of 4.14vol% at 1kHz, which was almost 60 times higher than that of epoxy matrix and the dielectric loss was 0.80. The relative dielectric constant of MWNT/EP and a-MWNT/EP were 391 and 120, while the dielectric loss was 2.51 and 0.88 with the same MWNT contents as TETA-MWNT/EP. The results showed that the dielectric properties of TETA-MWNT/EP were well.TGA tests of the composites indicated that the TETA-MWNT/EP composites had more heat stability than the pure resin. Comparing with the pure epoxy resin, the starting decomponded temperature of the composites increased 20℃, and the maximal decomponded temperature increased 30℃. The curing kinetic of TETA-MWNT/EP/EMI-2,4 system was studied with non-isothermal DSC technique at different heating rates. The results showed that there was a small peak in the DSC curve due to the reaction of TETA-MWNT with epoxy group. The kinetic parameters were obtained by Kissinger and Ozawa method, with the apparent activation energy Ea was 64.82kJ/mol and a two-parameter (m, n) autocatalytic model was found with the resin system.