Understanding hygrothermal degradation of crosslinked epoxy polymers with ReaxFF

Computational scientists at the North Dakota State University have published a paper where they described how they used a reactive molecular dynamics to study the physical and chemical degradation in polymeric epoxy network contaminated with moisture. They have shown a way to simulate cross-linked polymeric networks with the presence of moisture using ReaxFF which is boosting the efficiency of the calculations. Their paper “Reactive Molecular Dynamics Study of Hygrothermal Degradation of Crosslinked Epoxy Polymers” is published in the journal ACS Applied Polymer Materials. The team working on this project was led by Prof. Bakhtiyor Rasulev and Prof. Wenjie Xia and included Anas Karuth, Amirhadi Alesadi and Prof. Aniruddh Vashisth. 

Crosslinked epoxy polymers are often exposed to high humidity environments in various application. The water absorption of the epoxy thermoset would typically lead to the deterioration of its physical and mechanical properties. Besides physical degradation, it can undergo irreversible chemical degradation. In a recent study, reactive molecular dynamics are used to study the physical and chemical degradation in moisture contaminated epoxy network. The MD simulations show that in addition to the plasticization effect from the moisture ingress, the epoxy network shows recovery in mechanical properties and density due to the multi-site interaction of the water molecule with the electronegative sites within the network. Moreover, long-term exposure to humidity or direct exposure due to cracking can induce irreversible changes in the epoxy–amine network. The protonation of the water molecule and nucleophilic attack on the C–O bond of the ether linkages in the epoxy–amine networks are successfully simulated by applying reactive MD simulations. Remarkably, the simulations show that the selectivity of water molecules for the hydrolysis reaction in the epoxy network depends on the spatial arrangement and the steric hindrance of the network. 

A. Karuth, A. Alesadi, A. Vashisth, W. Xia, and B. Rasulev, Reactive Molecular Dynamics Study of Hygrothermal Degradation of Crosslinked Epoxy Polymers, ACS Applied Polymer Materials 4, 4411 (2022)