Comparative Study of Kinetics of the Thermal Decomposition of Polypropylene Using Different Methods

Abstract

AbstractThe thermal degradation kinetics of powder isotactic polypropylene was investigated in a thermobalance system, at non‐isothermal heating conditions with heating rate of 5, 10, 15, and 20°C min−1 in the temperature range of 30–600°C under nitrogen atmosphere. The apparent activation energy (Ea) was determined using Ozawa–Flynn–Wall, Tang Wanjun, and Coats–Redfern (modified) methods. The apparent activation energies range from 61.3 to 110.9 kJ mol−1. Increasing the heating rate shifted the Tmax to a higher level. The lower activation energy observed indicates the breakage of the bonds at weak links. Moreover, the values of activation energy are significantly controlled by the heating rate, level of conversion, and calculation technique. A comparison among the different techniques has been made on the basis of the apparent activation energy from the TG data. The activation energies determined by all the three methods are in good agreement with each other. Furthermore, the pyrolysis of model polypropylene was carried out over the temperature range 350–415°C in a salt bath using Pyrex reaction vessel. The gaseous fraction produced was collected in gas sampling bag and monitored gas chromatographically. The major hydrocarbons detected were methane, propylene, propane, 2‐methylpentane, 2,4 dimethylpentane, and 2,4 dimethylheptane.