Freeze-thaw durability of vacuum infused glass fibre composites with unsaturated polyester and vinyl ester matrices

This paper presents an experimental study about the effects of freeze-thaw cycles (FTC) on the mechanical and thermomechanical properties of glass-fibre reinforced polymer composite laminates produced by vacuum infusion using two different polymer resins: unsaturated polyester (UP) and vinyl ester (VE). Following preconditioning in distilled water for 30 days at 20 degrees C, the composites were subjected to 100, 200 and 300 FTC, with temperature ranging from -20 degrees C to 23 degrees C. After the preconditioning and each ageing period, the mechanical properties of the composites were assessed through tension, compression, flexure, in-plane shear and interlaminar shear tests, as well as DMA, which were complemented by FTIR analysis and SEM observations. The results obtained indicate a slight-to-moderate reduction of glass transition temperature and mechanical properties, especially of flexural strength (up to 29 %) and compressive strength (up to 16 %). These reductions were partially reversible upon drying, highlighting relevant moisture-induced plasticization effects. On the other hand, no clear evidence of significant hydrolysis or fibre-matrix debonding was identified from respectively FTIR and SEM. Overall, the VE composite exhibited better overall performance than the UP composite. It was not possible to identify clear differences in the freeze-thaw durability performance of the vacuum infused composites tested in this study compared to pultruded composites reported in the literature.