Identification of pyrolysis reaction model of polypropylene

This paper attempted to identify a pyrolysis reaction model of polypropylene (PP) and to elucidate its macroscopic decomposition mechanism correspondingly. Among various reaction models, we chose a reaction model that allowed the best fit to experimental reduced-time- plots (RTPs). Surprisingly, the pyrolysis reaction model of PP varies with reaction temperature within a temperature range between 683 and 738 K. At lower temperatures (683-693 K), the "contracting-cylinder" model accounts for the pyrolysis reaction of PP. Bubble nucleation may be a major reaction mechanism of PP pyrolysis at higher temperatures (728-738 K). High generation rates of volatiles lead to the accumulation of volatiles in the melt until reaching a critical concentration where bubble nucleation sets forth, thus mimicking "Avrami-Erofeev" model. Hence, the classical expression of the reaction model, f (alpha) = (1 - alpha)", assumed by most previous studies is inappropriate for pyrolysis reaction of PP. At lower temperatures, chemical reactions may limit the pyrolysis reaction of PP, whereas at higher temperatures the rate of bubble nucleation closely related to heat, mass, and momentum transfer along with thermodynamic properties of melt may limit its pyrolysis reaction.