Thermal Degradation of Polypropylene

Thermal degradation of polypropylene under atmospheric pressure at 370 - 410 C was studied by using a continuous flow reactor, which was the same as that used for thermal degradation of high density polyethylene shown in the preceeding paper. Rate studies on polypropylene degradation were made at the steady states. Two rates, i. e., formation of double bonds and volatilization of degradation products, were measured and plotted in Fig.4 as a function of degradation temperature. The activation energies of polypropylene degradation, as calculated on the basis of these two rates, were 61 and 60 kcal/mol, respectively. Gas-liquid chromatography showed that volatile products at room temperatures consisted of H2 and C1 - C5 hydrocarbons, mainly of propylene and isobutene, having an average molecular weight of 41 - 44 (see Table 2). And less volatile oily products consisted of C5 - C28 hydrocarbons, identified by comparing their boiling points (retention values determined by chromatographing) with those of n-paraffins. As illustrated in Fig.7, peaks do not always appear at a multiple of three carbon numbers, e. g., at 6, 9, 11, 14 and so on. The boiling points of a series of branched paraffins and olefins which are the chain fractions of various sizes produced by the degradation of polypropylene, were estimated by Wiener's method, and are shown in Table 3. It was found that above mentioned peaks contained branched mono-olefins whose numbers of carbon were a multiple of three. The average molecular weight of oily products and reactor contents, determined ebullioscopically, are plotted in Fig.8, and numbers of double bonds per molecule are plotted in Fig.9. Oily products were found to consist mainly of mono-olefins, while reactor contents mainly of di-olefis. n