Effects of hygrothermal and salt mist ageing on the properties of epoxy resins and their composites

Epoxy resins have a wide range of outdoor applications wherein they are affected by ageing. In this study, the ageing of epoxy resins and their carbon fibre reinforced composites was artificially accelerated under hygrothermal and salt mist conditions. The moisture penetration along the depth, water absorption, appearance, hardness, the density of the epoxy resins, and the variation pattern of impact strength and tensile strength of the epoxy-based composites were investigated. The ageing mechanisms were explored using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Both the ageing modes had essentially similar influences on the properties of the resins and their composites and did not significantly affect the chemical structure, thermal decomposition properties, and microstructure of the epoxy resin, with physical adsorption of water primarily observed during the ageing process. Though the water penetration rate in salt mist ageing was slightly higher than that in hygrothermal ageing in the early ageing stage, it was essentially the same in the later stage. The absorbed water during the ageing process caused micro-cracks at the interface between the fibres and the resin weakening the interfacial strength and reducing the mechanical properties of the composites.