Mechanical performance and recyclability of hybrid flax/carbon fiber composites by Vacuum Assisted Resin Infusion using traditional and fully recyclable epoxy resins

The aim of the present work is to study the mechanical performance and recyclability of hybrid flax/carbon fiber-reinforced composites produced by Vacuum Assisted Resin Infusion (VARI). To carry out the study, two distinct epoxy systems were investigated: a conventional epoxy (E) and a fully recyclable epoxy system (BE, Polar Bear + R*101) modified with a reactive diluent (R*Diluent) to enhance processability. The study examined both flax fiber-reinforced laminates (F) and hybrid configurations, considering two stacking sequences: FCF (flax outer layers) and CFC (carbon outer layers). Mechanical behavior was assessed through flexural testing and low-velocity impact (LVI), and the resulting properties were implemented within a comparative materials database. The impact response was only marginally influenced by the adoption of the bio-based recyclable resin, leading to a slight improvement in the impact resistance of flax-dominated laminates (peak force increased by 2.5–4.7% up to 5 J), while a moderate reduction was observed for carbon-rich hybrids, attributed to differences in fiber–matrix interactions. Flexural performance of the fully recyclable epoxy system was highest when flax layers occupied the core of the hybrid laminate (CFC configuration). Moreover, a chemical recycling strategy previously demonstrated on laboratoryscale specimens was successfully extended to an industrially relevant composite component. The process enabled the recovery of flax and carbon fiber fabrics together with the recyclable matrix, achieving efficiencies close to 100%.