The thermal degradation of some epoxy resins

Abstract

Studies on the thermal and oxidative polymer degradation have been presented in monographs by Grassie' and Jellinek.The general consensus in the majority of these studies is that thermal and oxidative degradation of polymers is a radical reaction. Unlike the case of degradation of polymer products, the thermal decomposition of condensation resins has received virtually no attention, despite the fact that these resins have been widely used up to the present time in industry.In the present work we have investigated the thermal and oxidative degradation of epoxy resins. The kinetics of the thermal degradation of epoxy resins was evaluated on the basis of the increase in pressure in the system which is caused by gas evolution. The gases that appear during the degradation process are collected in a preliminary evacuated trap, where they are frozen with liquid nitrogen.During the degradation of the original epoxy resins, which were obtained on a base of epichlorohydrin and diphenylolpropane and designated ED-6 and ED-15 (molecular weight 500 and 2000, respectively) we found that at relatively low temperatures (2W250°C.), a small quantity of gaseous products slowly evolves from the resin, and a transparent colorless liquid distills off. At higher temperatures both the rate of formation and the amount of these gaseous products sharply increases; the liquid which distills off is yellowish brown in color. The quantity of infusible and insoluble residue is reduced with increased ' temperature. Also, with increasing temperature, there is a gradual increase in the amount of liquid which distills over.In the case of the degradation of hardened resins, even at low temperatures (25OOC.) the liquid is colored a dark hue.Curves showing the increase in gaseous pressure at different temperatures for the original and hardened resins are given in Figures 1-3. We can see from Figure 1 that the degradation of the epoxy resins begins at 240-25OOC. For resins that have been hardened with maleic anhydride (Fig. 3), this process begins at higher temperatures.

Ternary nanocomposites based on epoxy, modified silica, and tetrabutyl titanate: Morphology, characteristics, and kinetics of the curing process

“…The alteration of the thermal parameters of the cured neat epoxy and nanocomposites in nitrogen or air was due to the fact that, in addition to the effects of high temperature, the existence of oxygen in air reacted with the epoxy chain through the oxidation reaction. This led to the breaking of the epoxy chain to form lower molecular weight substances (aldehydes, carbon dioxide, carbon monoxide, methane, propylene, and water) . According to Neman et al ., the oxidative decomposition of epoxy resins is an autocatalytic process and is superficially associated with the formation and the further degradation of peroxide compounds by a radical mechanism.…”

“…This led to the breaking of the epoxy chain to form lower molecular weight substances (aldehydes, carbon dioxide, carbon monoxide, methane, propylene, and water) . According to Neman et al ., the oxidative decomposition of epoxy resins is an autocatalytic process and is superficially associated with the formation and the further degradation of peroxide compounds by a radical mechanism. Xiaoxing et al .…”

Thermal decomposition, combustion and flame‐retardancy of epoxy resins—a review of the recent literature

“…It was found that epoxies cured with meta ‐substituted aromatic amines are more thermally stable than epoxies cured with para ‐substituted aromatic amines 4. Both homolytic and heterolytic chain scission of allylic CN (CO) bonds were suggested in the literature,13, 16, 18, 23 which leads essentially to the same result (Scheme ).…”

Blends of unsaturated polyester and phenolic resins for application as fire-resistant matrices in fibre-reinforced composites. Part 2: Effects of resin structure, compatibility and composition on fire performance

“…The pyrolysis behaviours of all phenolic resins in nitrogen ( Fig. 3(b DTA peak with a maximum at 301 o C. This mass loss could be due to breakdown of epoxy groups for which, in epoxy resins, a free-radical mechanism has been suggested [24]. The main decomposition reactions are represented by the second stage, which is multi-step in PH1, PH2 and PH3, as can be seen from the multiple DTG and DTA peaks, listed in Table 2(a).…”