Balancing Sustainability and Performance: Bio-Based Epoxy Systems for Durable Flax Fiber-Reinforced Composites

Three bio-based epoxy systems-Polar Bear, Green Turtle, and Plankton-featuring bio-carbon contents of 28% to 70%, were combined with recyclable (Recyclamine R101) and non-recyclable hardeners to produce flax fiber-reinforced biocomposites. The Polar Bear system demonstrated superior mechanical and thermal properties, while Plankton with recyclable hardener exhibited incomplete curing and poor mechanical performance. Accelerated salt-fog aging up to 3 months revealed substantial degradation in flexural and interlaminar shear properties within 30 days for most composites, except Green Turtle with recyclable hardener, which maintained mechanical stability and exhibited marked interfacial strengthening even after prolonged exposure. Low-velocity impact tests up to 7.5 J showed no penetration and comparable energy absorption, with aging causing increased compliance and matrix plasticization. SEM analysis identified significant fiber/matrix debonding in Plankton composites, contrasting with preserved interfacial integrity in Green Turtle systems. Thermogravimetric analysis confirmed negligible changes in thermal degradation post-aging. These findings highlight the interplay between bio-carbon content, recyclability, and durability, underscoring the potential of Green Turtle and Polar Bear epoxy systems for sustainable polymer composites with balanced performance and durability.