New Insights into the Pyrolysis Behavior of Polycarbonates: A Study Based on DFT and ReaxFF-MD Simulation under Nonisothermal and Isothermal Conditions
Xin Wei, Jie Yu, Jiaxing Du, Lushi Sun
Abstract
In this work, a combined ReaxFF-MD simulation and density functional theory (DFT) study was performed to study the pyrolysis behavior of polycarbonates under nonisothermal and isothermal conditions. Nonisothermal simulations were implemented at temperatures from 300 to 2800 K at various heating rates of 10, 25, 50, and 100 K/ps. The nonisothermal simulation revealed that the pyrolysis processes can be categorized into three different stages: structure adjustment, decomposition, and condensation/deep decomposition. At the low heating rate, the longer residence time at high temperature ranges can decrease tar formation but increase char and gas yields. Comparatively, a higher heating rate delayed the onset decomposition temperature. For isothermal simulations, the influence of temperature was carried out between 1400 and 3400 K. Below 2200 K, the increase in temperature promoted the decomposition of char into gas and liquid. Further increasing temperature from 2200 to 3400 K led the heavier tar to crack into lighter one and more gas. The reaction path of various pyrolysis products and related energy demand were also conducted based on DFT simulations. From the results, the random chain scission was proposed for the pyrolysis of polycarbonates. CO2 and CO were mainly generated from carbonate groups. CH4 and H2 were mainly formed by abstracting H· from isopropylidene groups. This work helped to understand the nonisothermal and isothermal pyrolysis behavior of polycarbonates.