Molecular and Kinetic Models for High-Rate Thermal Degradation of Polyethylene

JMD Lane and NW Moore, JOURNAL OF PHYSICAL CHEMISTRY A, 122, 3962-3970 (2018).

DOI: 10.1021/acs.jpca.7b11180

Thermal degradation of polyethylene is studied under the extremely high rate temperature ramps expected in laser-driven and X-ray ablation experiments from 1010 to 10(14) K/s in isochoric, condensed phases. The molecular evolution and macroscopic state variables are extracted as a function of density from reactive molecular dynamics simulations using the ReaxFF potential. The enthalpy, dissociation onset temperature, bond evolution, and observed cross-linking are shown to be rate dependent. These results are used to parametrize a kinetic rate model for the decomposition and coalescence of hydrocarbons as a function of temperature, temperature ramp rate, and density. The results are contrasted to first-order random-scission macrokinetic models often assumed for pyrolysis of linear polyethylene under ambient conditions.

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