Particle removal mechanisms in synergistic aging of polymers and glass reinforced polymer composites under combined UV and water

Complex degradation processes occur during synergistic aging of polymers and Polymer Matrix Composites (PMCs) by UV radiation and water condensation at elevated temperatures. The damage is associated with the formation of surface micro-particles and their subsequent removal by slowly moving water. The particle removal significantly accelerates the overall degradation process of the materials [1]. In this research, hydrodynamic effects have been analyzed to explain removals of micro-particles from polymeric materials affected by synergistic aging by UV and water. Viscous shear stresses generated by slowly moving water were determined on polymer surfaces as a function of surface morphology, flow rates, and volumetric forces. Subsequently, a new micro-particle removal mechanism was suggested by comparing the adhesion forces calculated using the Johnson-Kendall-Roberts (JKR) model and the Hamaker approach with the drag forces created by slow water flows. In the experimental part, the particle removal mechanism has been verified on an inclined unidirectional glass/epoxy surface with randomly distributed epoxy particles subjected to a gravitational flow of water. It has been shown that the movement of polymer particles on polymer/composite surfaces depends very strongly on particle sizes, water velocity and surface morphology. The research presented in this study clearly explains why polymer and GRP degradation by UV in the presence of occasional slow water flows is much faster than just by the individual exposure to UV radiation reported in Ref. 1.