Thermal Degradation of High Density Polyethylene

Abstract

Thermal degradation experiment of high density polyethylene was carried out by using a continuous flow reactor in the temperature range of 400° to 445°C under atmospheric pressure to investigate the rate of thermal degradation and properties of decomposition products at the steady state. The products of thermal degradation were separated into two parts, the one, volatile gaseous product at 25°C and the other, less–volatile oily product. The gaseous product was analyzed by gas chromatography and was found to be consisted of H2 and C1~C6 hydrocarbons, having the average molecular weight of 35 to 37. The composition of gaseous products did not change appreciably with the degradation temperature. The oily product was found to be consisted of a wide spectrum of hydrocarbon fragment, saturated and unsaturated, varying in carbon numbers from 3 to 30 (see Fig. 6, 7). The average molecular weight of the oily product varied from 180 to 232 with degradation temperature (see Fig. 9). Other physical properties of oily products are shown in Table 3. The average yield of product oil was 94.5% of the total products in the temperature range investigated. The reactor content was the degraded polymer and its molecular weight was decreased to about 1200. Some physical properties of the reactor contents are shown in Table 3. The correlation between the rate of decomposition of the polyethylene and the rate of formation of double bonds, was also investigated. Both rates are plotted in Fig. 4 as a function of the degradation temperature. Carbon–carbon double bonds were found in gaseous products, oily product and reactor contents, but as shown in Fig. 5, the increase in double bonds of the reactor content was negligible. The activation energies of thermal degradation of the polyethylene, calculated on the basis of the above two rates, were 47.5 kcal/mol and 49.4 kcal/mol, respectively. © 1973, The Chemical Society of Japan. All rights reserved.