Comparing flax fibre/biopolymer woven composites with carbon fibre-enhanced, partially green alternatives: Mechanical performance versus sustainability

Natural fibre/biopolymer matrix, known as green/fully sustainable, composites are emerging as alternatives to non-sustainable or partially sustainable composites, while ideally targeting similar material properties. This study first characterizes and compares thermo-mechanical performance of novel green composites made of Flax Fibre (FF) reinforced in thermosetting bioresin options, fabricated via two different manufacturing techniques. Namely, flax fibre-reinforced bioepoxy (Bioepoxy/35%FF) woven biocomposite was fabricated via vacuum infusion, while FF-reinforced (bio)Polyfurfuryl Alcohol (PFA) woven prepreg was consolidated through vacuum bagging (PFA/45%FF) as the second option. Additionally, for design comparisons, Carbon Fibre (CF)-PFA (PFA/60%CF), as well as hybrid FF-CF-based PFA (PFA/45%FF-15%CF) samples were fabricated to understand the performance difference between the green composite options versus the latter partially sustainable or hybrid design alternatives. Results demonstrated that, despite their required different manufacturing techniques, Bioepoxy/35%FF and PFA/60%FF provided very comparable density, tensile strength, and impact properties. Both biocomposites outperformed the CF-added designs under damping property (by 150%) at low frequency and specific energy absorption property (by 37%), thanks to the unique micro-architecture of flax fibre that enhances deformation energy dissipation through inter- and intra-cell walls friction and internal failure mechanisms. However, incorporating 15% of CF into PFA/FF (i.e. hybrid PFA/45%FF-15%CF) increased the tensile strength by 130% and the tensile modulus by 90%, while keeping a similar impact energy absorption as the fully flax-based biocomposite options. The fully CF-based PFA (as a least sustainable option among the tested samples) revealed the highest tensile properties, hardness, and thermal stability, clearly highlighting the necessity for formal trade-off analyses during design.