Pyrolysis and combustion of polymer mixtures: Exploring additivity of the heat release rate

The microscale combustion calorimetry study of polymer mixture pyrolysis is presented. Binary mixtures of HDPE with a number of massively produced polymers (LDPE, PET, PS, PP PC, PVC, PMMA), binary PC-PS and PMMA-PVC mixtures, and the ternary mixture composed of HDPE, PC, and PS are considered. The extent of interaction between the mixture components in pyrolysis is assessed by comparing the shapes of the measured temperature dependencies of the heat release rate in volatile oxidation with those for the curves obtained by the mass-weighted summation of the individual contributions of the pure polymers constituting the mixture. The strongest interaction is observed in HDPE-PET, HDPE-PS, HDPE-PS-PC, and in PMMA-PVC mixtures. A destabilizing interaction occurs in mixtures containing polyethylene and polystyrene, while the presence of polyvinylchloride has a stabilizing effect. In the binary mixtures, no clear correlation of the dependence of the conversion-averaged apparent activation energy (obtained by the iso-conversional method of Friedman) on the component proportion has been observed. In HDPE-PET mixture, in which the temperatures of peak pyrolysis rates are separated, the dependence of the apparent activation energy on conversion is interpreted in terms of the dependencies derived for pyrolysis of the individual components. Except for PMMA-PVC mixtures, in all binary mixtures considered in this work the heat of volatile combustion and the char yield were found to be additive quantities and varied almost linearly with the variation of the component mass fractions. Dissimilar to that, the PMMA-PVC mixtures produced a higher amount of charring residue and a lower heat of combustion of volatiles compared to the component-based predictions assuming additivity. (C) 2019 Elsevier Ltd. All rights reserved.