Preparation of Thermally-Resistant Nanohybrids Based on Novolac and Epoxy Resins and Epoxidized Carbon Nanotubes

Hypothesis: Thermally stable nanocomposites were prepared by incorporation of carbon nanotubes (CNT) into the epoxy resin matrix cured by novolac resin. CNT modified with epoxy functional groups is capable of reaction with hydroxyl groups of novolac resin. Therefore, a new and robust method was planned for development of covalent bonding between the filler and matrix. On the other hand, due to slow reaction of epoxy and hydroxyl groups in the absence of catalyst, triphenylphosphine was used as the catalyst to accelerate the curing process.

CNT was modified with nitric acid to obtain oxidized CNT (CNTCOOH). After grafting of butane diol at the surface of CNTCOOH, hydroxyl-containing CNT (CNTOH) was prepared. Afterward, epoxy functional groups were applied at the surface of CNTOH through its modification with (3-glycidyloxypropyl) triethoxysilane in order to prepare epoxy-containing CNT (CNTG). Finally, CNTG and epoxy resin were placed in the hybrid network through the curing process with novolac resin. Finding: The results of FTIR-spectroscopy and X-ray photoelectron spectroscopy showed that modification of CNT was effectively carried out. X-ray diffraction analysis confirmed uniform distribution of CNTG in the matrix of cured epoxy resin. As thermogravimetric analysis exhibited, char yield of the cured epoxy resin (26.6%) was considerably increased to 32.8% and 38.2% through incorporation of 2 and 4 wt% of CNTG into the network, respectively. According to the scanning electron microscopy and transmission electron microscopy images, CNT showed tubular and entangled structure with smooth and uniform surface which even retained its structure after modification reaction. Finally, this approach can be successfully used for production of thermally-resistant thermoset hybrids for thermal protection applications