Kinetics of thermal degradation and fire retardant efficiency of polyesters

Abstract

AbstractSeven polyesters having different amounts of halogen were studied for kientics of degradation and fire retardant efficiency. Out of them, the polyesters number 1, 2, 3, and 4 had the molar ratios of chlorendic acid to isophthalic acid of 0.25, 0.67, 1.5, and 4.0 respectively. The polyesters number 5, 6, and 7 were based on dimethyl‐di‐(p‐oxyacetoxymethylphenyl)‐methane, dimethyl‐di‐(3,5‐dichloro‐4‐oxyacetoxymethylphenyl) methane and dimethyl‐di‐(3,5‐dibromo‐4‐oxyacetoxymethylphenyl)‐methane respectively. These studies were done with the help of thermogravimetric analysis (TGA), differential thermal analysis (DTA), infra‐red spectroscopy and glow rod apparatus. The thermal stability of these polyesters decreased in the following order: 5 > 6 > 7 > 1 > 2 > 3 > 4, taking the threshold temperature as a measure of the thermal stability. The 50% weight loss temperature determined from TGA curves supported this to some extent. These studies further revealed that these polyesters degrade in two stages. The first stage of degradation ranged from 250–450°C. The second stage of degradation is in the range of 450–600°C. In the first stage, the range of temperature for degradation is constricted by increasing the halogen content. Bromination is more effective than chlorination. The activation energy for degradation of these polyesters showed the same trend as the thermal stability. But the flame resistance is somewhat in the reverse order of thermal stability. These studies also confirm a cyclic mechanism for flame retardancy.