A mesoscale approach to model polyethylene degradation under a local temperature gradient

A major focus in recycling plastics has been towards chemically synthesizing monomers for low ceiling temperature polymers instead of controlled depolymerization of abundantly used polyethylene. Controlled depolymerization can be achieved by introducing microwave absorbing nanosheets in the bulk of the polymer. Under microwave irradiation, local temperature gradients are introduced in the vicinity of the nanosheets. In this work, we develop a framework for modeling the thermal random scission of polyethylene under the action of such local temperature gradients. We use the energy conserving dissipative particle dynamics (eDPD) approach along with the modified segmental repulsive potential (mSRP) and model bond breaking via a stochastic approach that simulates first order degradation reaction kinetics. We first simulate melts with various degrees of polymerization at various constant temperatures and measure the static and dynamic properties of the polymer chains. Then, we subject the equilibrated melt to depolymerization under constant temperature and track evolution of dispersity and average molecular weights in the system. The time evolution of these properties follows previously known analytical trends. Under the action of a temperature gradient, faster depolymerization near the high temperature region results in formation of shorter polymer fragments with higher diffusivity compared to the longer chains in the low temperature region.