Cyclic water absorption behavior of glass-vinylester and glass-epoxy composites

The cyclic water absorption behavior of vinylester (VE) and epoxy matrices and their composites with mat glass fiber is studied. The water absorption increases with the cycle. Degradation of the matrix occurs during fast drying and this leads to a very different behavior of the materials in both cycles. Epoxy-based materials absorb more water than VE-based ones due to their different hydrophilicity. The diffusion coefficient increases with temperature and it is higher in the second cycle than in the first one. The diffusion coefficients of VE composites are similar to that of the matrix, but the epoxy composites absorb water at a higher rate than the matrix. The mechanical properties decrease with immersion but the change in strength is higher than the modulus loss. The fiber-matrix interface presents good adhesion at low temperature but it decreases as temperature increases and there are more voids with the worst interface for the last cycle.