A comparative theoretical and experimental investigation on thermal parameters and initial pyrolysis mechanism of methyl-phenyl-dimethoxy silane modified phenolic resin

Abstract

In this paper, classical molecular dynamics and reactive molecular dynamics are used to study the glass transition temperature, thermal conductivity, and initial reaction of pyrolysis of methyl-phenyl-dimethoxy-silane-modified phenolic resins. The simulation results showed that silanes increased the glass transition temperature and thermal conductivity of phenolic resins, resulting in an increase in glass transition temperature from 426.4 K to 449.8 K and thermal conductivity from 0.21 W/(m·k) to 0.226 W/(m·k). To verify the accuracy of the simulation calculations, we experimentally tested the glass transition temperature and thermal conductivity of silane-modified phenolic resins. The results showed that the glass transition temperatures of phenolic resin and silane-modified phenolic resin were 333.5 K and 353.5 K, respectively, while the thermal conductivities were 0.221 W/(m·k) and 0.235 W/(m·k), respectively. The error between the simulated and experimental thermal conductivity values was 5 %. At the same time, the glass transition temperature did not match the experimental value due to the difference in cooling rate between the simulation and experiment. Then, it was corrected using the WFL equation at a low cooling rate, resulting in an error of about 1.6 % between the glass transition temperature and the experimental value. In addition, the silane-doped phenolic resin produced a large amount of protective gas during the pyrolysis process, which carries away heat as it evaporates and forms a reaction barrier. Since a silicon-oxygen bond replaces the phenolic hydroxyl group, the production of hydroxyl groups during pyrolysis is reduced. At the same time, the silicon radicals produced by silane pyrolysis form silicon hydroxides with the hydroxyl groups. This dramatically reduces the likelihood of hydroxyl groups oxidizing other functional groups, slowing down the formation of CO and increasing the carbon residual rate.