Study of Thermal Degradation of Several Polymers by Torsional Braid Analysis

Abstract

The thermal degradation of several polymers in air was studied by TBA (Torsional Braid Analysis) and IR spectroscopy. The samples are poly(vinyl chloride) (PVC), poly(acrylonitrile)(PAN), po1y(styrene) (PSt) and poly(methyl methacrylate) (PMMA), TBA measurement was carried out in the range of 200-350C and in the freguency range of 0.15-0.30 Hz. IR spectra of these polymers, degraded in air for 20 minutes, were also measured.
Relative shear moduli were plotted against the reaction time, and their initial slopes were fitted to the Arrhenius equation as function of temperature. From this analysis, the apparent activation energies were obtained as 24.7 kcal mol (170-250C) and 24.2kcal mol (250-340C)for PVC, 18.6 kcal mol(220-280 c)and 16.9kcal mol(280-340)for PAN, and 22.5 kcal mo1(initial stage)and 24.4 kca1 mol(1ater stage)for PSt. The IR, DTA and TGA measurements suggest that these changes of mechanical properties were associated with some chemical reactiens as follows. ln PVC, formation of C-C double bond by dehydrochlorination, crosslinking and oxidation are presumed in PAN, intramolecular cyclization by the reaction of nitrile groups and oxidation and in PSt, crosslinking by oxidation. lt was found that superposition procedure of the reaction time-temperature curves is possible for relative shear moduli of these polymers. ln the case of PMMA, change of mechanical properties assoiated with depolymerization was not observed.