Dependence of solid particle erosion on the cross-link density in an epoxy resin modified by hygrothermally decomposed polyurethane

Solid particle erosion of epoxy resin (EP) modified by various amounts of hygrothermally decomposed polyester-urethane (HD-PUR) was studied at oblique (30, 45, and 60°) and normal impact (90°). The cross-linked structure of the modified EP was characterised by the mean molecular weight between cross-links (Mc). It was established that the initial brittle erosion of the densely cross-linked EPs (Mc≤200 g/mol) changed to a rubbery one by increasing HD-PUR modification due to which a less cross-linked network was formed (Mc>1000 g/mol). This change was reflected by the impact angle dependence: compositions of low Mc showed the minimum resistance at normal (90°), whereas those of high Mc at 30° impact angle. The resistance to solid particle erosion changed linearly with increasing fracture energy (Gc) of the resins. Gc, on the other hand, followed the prediction of the rubber elasticity theory and increased linearly with Mc1/2.