Durability under natural outdoor weathering of sustainable composites developed with bio-based unsaturated polyester and epoxy resins reinforced with glass, basalt, and carbon fibres

This paper presents, for the first time, an experimental study about the natural weathering durability of composite materials with bio-based resins - epoxy and unsaturated polyester (UPR) - and synthetic fibres - glass, basalt, and carbon - produced by vacuum infusion. The glass and basalt fibre reinforcements were used with two different compositions of bio-UPRs, developed in-house, while renewably sourced epoxy resin was used with carbon fibres. To compare the performance of the bio-resin based composite materials, reference composites, produced with oil-based resins and similar fibre reinforcements, were also assessed. These materials were naturally aged for up to two years in Lisbon city centre. The effects were evaluated through mechanical (tensile, compressive, in-plane shear, interlaminar shear) and thermomechanical tests, which were complemented by visual observation, scanning electron microscopy, and nano-computed tomography. Overall, the short-term unaged properties and natural weathering durability performance of the bio-composites were comparable to their respective oil-based counterparts. The epoxy-carbon composites were the least affected, irrespective of the type of resin, retaining around 90 % of unaged properties. The highest degradation in mechanical properties occurred in the UPR-glass composites (up to 35 %), followed by the UPR-basalt composite (up to 25 %). Although the durability of bio-based UPR-glass and UPR-basalt composites was comparable to their conventional composites, the UPR-basalt bio-composite showed higher property retention than the UPR-glass bio-composite. Matrix embrittlement was noticed in all materials, mostly in the bio-composites, as well as glass transition temperature increase (up to 10 %).