Thermal degradation under wet conditions is considered as an important aging mechanism in polyamide 6,6 (PA 6,6). The effect of water on thermal degradation of amorphous PA 6,6 is investigated at relatively low temperatures, varying from 1000 to 2000 K, using reactive force field molecular dynamics (MD) and collective variable-driven hyperdynamics simulations. The simulation of the related long-term chemical reactions is made possible thanks to the self-learning accelerated MD concept of hyperdynamics in combination with the corresponding accurate reproduction of the correct dynamics, consistent with unbiased MD simulations. The kinetics of cleavage reactions of the amide bonds in the backbone of the polymer chains, responsible for the thermal degradation of the polymer, is studied, and the influence of water content on the activation energy and pre-exponential factor of the cleavage reactions is explored. The results show that activation energy and pre-exponential factor are in agreement with experimental data. The proposed simulation framework not only estimates kinetic properties of thermal degradation that are consistent with experimental observations but also provides a predictive tool for studying long-term thermal degradation of PA 6,6.

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We perform reactive molecular dynamics simulations to investigate the mechanism of chemical aging of polyamide polymers by means of hydrolysis in an acidic solution at high temperature. The molecular dynamics approach is based on the ReaxFF reactive force field. The role of temperature and pH of the acidic solution on the degradation rate of polyamide polymers is studied at the nanometer scale. The simulation results show that higher temperatures and acidic condition eventuate in the breaking of more bonds within the backbone of polymer chains.@en