Awareness of environmental issues has led to increasing interest from composite researchers in using “greener” materials to replace synthetic fiber reinforcements and petrochemical polymer matrices. Natural fiber bio-based thermoplastic composites could be an appropriate choice with advantages including reducing environmental impacts, using renewable resources and being recyclable. The choice of polymer matrix will significantly affect the cost, manufacturing process, mechanical properties and durability of the composite system. The criteria for appropriate monomers are based on the processing temperature and viscosity, polymer mechanical properties, recyclability, etc. This review considers the selection of thermoplastic monomers suitable for in situ polymerization during resin, now monomer, infusion under flexible tooling (RIFT, now MIFT), with a primary focus on marine composite applications. Given the systems currently available, methyl methacrylate (MMA) may be the most suitable monomer, especially for marine composites. MMA has low process temperatures, a long open window for infusion, and low moisture absorption. However, end-of-life recovery may be limited to matrix depolymerization. Bio-based MMA is likely to become commercially available in a few years. Polylactide (PLA) is an alternative infusible monomer, but the relatively high processing temperature may require expensive consumable materials and could compromise natural fiber properties.

Smart materials and structures are capable of active or passive changes in terms of shapes (geometries), properties, and mechanical or electromagnetic responses, in reaction to an external stimulus, such as light, temperature, stress, moisture, and electric or magnetic fields

Short-fibre-reinforced polymer-matrix composites have attracted considerable interest owing to their processing versatility, cost efficiency, and adaptability to complex geometries; however, their relatively limited mechanical performance restricts their practical applications. In this study, a viscoelastic prestressing (VP) pretreatment was applied to short nylon fibres prior to moulding short-fibre-reinforced polymer-matrix composites (SFPMCs) and short-fibre-reinforced CFRP (SFR-CFRP) samples, with the aim of improving their impact performance. A comprehensive experimental framework was established to evaluate both the initial impact response and post-impact residual behaviour. Drop weight impact results revealed that TEST SFPMCs with VP-treated fibres consistently showed a higher stiffness under impact load than their CONTROL counterparts, as evidenced by increased peak contact force, reduced deformation, and shortened interaction time. The VP treatment also effectively suppressed damage evolution, leading to smaller damage areas and reduced damage depths by at least 35% and 25% over the impact energy range of 3–22 J. Especially under 22 J impact, TEST SFPMCs retained structural integrity, whereas CONTROL samples exhibited catastrophic failure (perforation). Reduced impact damage severity by VP treatment was further supported by the improved residual modulus in compression-after-impact (CAI) testing. Furthermore, by incorporating VP-treated short fibres between the layers of SFR-CFRP laminates, an additional 17% increase in Charpy impact strength was found compared to CONTROL SFR-CFRP. Overall, this study demonstrates that VP technique offers a promising approach for enhancing the impact performance of short-fibre composites with complex structural geometries.