The thermal degradation of some epoxy resins

Abstract

AbstractThe thermal degradation of epoxy resins was studied in a static system over the temperature range 300–450°C. The reaction proceeds without an induction period, the initial rate being maximum. The rate W increases with temperature according to the law W = Ae–E/RT. The effective activation energy was 35 kcal./mole. The reaction products consist of gases, a resinous liquid, and a solid residue. The liquid has practically the same spectral characteristics in the infrared as the initial epoxy compound. In the infrared spectrum of the residue the bands characteristic of the epoxy group are absent. Water and formaldehyde were found among the liquid products. Methane and carbon monoxide were found in large amounts by means of a chromatographic method. In the thermal degradation of the unhardened epoxy resin the low molecular fraction volatilizes, and the high molecular fraction degrades liberating the radical which isomerizes and decomposes to CO and ĊH3. The methyl radical abstracts a hydrogen atom from the polymer and is converted to methane. The ROĊH2 radical formed on liberation of the epoxy group yields formaldehyde. Among the gaseous products formed in the thermal degradation of the epoxy resin hardened by polyethylene polyamine (PEPA) were found H2, CO, CH4, C2H6, C2H4, C3H6, and C3H8. Ethane, ethylene, propylene, and propane are possibly produced by decomposition of the PEPA radical. The thermooxidative degradation of epoxy resins was investigated in a static system. The reaction was shown to be of the degenerate branching chain type. The dependence of the induction period on the oxygen pressure and on the temperature was determined.