Reducing the dependency from petroleum-based monomers and crosslinkers is an increasingly important goal for the plastics industry. This is being enabled by the growing diversity and availability of alternative biobased products derived from renewable resources, some of which are compatible with the production of more sustainable resins for high-performance applications. This paper presents the development of unsaturated polyesters (UPs) and their crosslinked resins (UPRs) based on 2,5-furandicarboxylic acid (FDCA) and other biobased building blocks. The original features of these UPs are derived from (i) the use of FDCA as an aromatic monomer replacing phthalic anhydride, (ii) the introduction of a FDCA–isosorbide (ISO) block into the polyester backbone with the presence of unsaturations provided by biobased fumaric acid, (iii) the use of ISO and 1,3-propanediol instead of ethylene glycol and 1,2 propylene glycol, and (iv) the reduction of styrene content using 2-hydroxyethyl methacrylate. The developed UPRs have a similar thermal and mechanical behavior to the petrochemical ones, presenting glass transition temperatures up to 102 °C, tensile modulus and strength up to 3.9 GPa and 63.3 MPa, respectively, and viscosity between 800 and 1250 cP, making these resins greener alternatives to fully petroleum-derived UPRs for high-performance applications.

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This paper presents an experimental study of the wet freeze–thaw (FT) durability of a fibre–polymer composite produced by vacuum infusion using an innovative bio-based unsaturated polyester resin (UPR) and basalt fibres. As the benchmark, an equivalent composite produced with a conventional (oil-based) UPR was also tested. The composites were preconditioned in water immersion for 30 days at 20 °C followed by exposure to wet FT for up to 300 cycles; each FT cycle consisted of 3 h in dry freezing condition (−20 °C) and 8 h in thawing condition (23 °C) submerged in water. The composites’ properties were assessed after preconditioning and after 100, 200, and 300 FT cycles, through mechanical (tensile, compressive, in-plane shear, interlaminar shear) and thermomechanical (dynamic mechanical analysis) tests. Gravimetric and scanning electron microscope analyses were also carried out. The results obtained show that the preconditioning stage, involving water immersion, caused most of the damage, with property reductions of 5% to 39% in the bio-composite, while in the oil-composite they ranged between 4% and 22%, being higher for matrix-dominated properties. On the other hand, FT alone had an insignificant effect on the degradation of material properties; after exposure to FT, property recovery was observed, specifically in matrix-dominated properties, such as interlaminar shear strength, which recovered by 12% in the bio-composite during exposure to FT. The overall performance of the bio-composite was inferior to the conventional one, especially during the preconditioning stage, and this was attributed to the hydrophilicity of some of the components of its bio-based resin.