Mechanical Performance Enhancement in Natural Fibre-Reinforced Thermoplastic Composites Through Surface Treatment and Matrix Functionalisation

This study aims to investigate the behaviour of thermoplastic composites reinforced with natural fibres. Composite materials were developed using reactive methyl methacrylate (MMA) resin, commercially known as Elium^® (Arkema, Colombes, France), with the incorporation of cellulose nanocrystals (CNCs), dispersed in the matrix at different concentrations. Natural fibres, such as flax, were chemically treated by immersion in an aqueous solution based on NaHCO₃, during different periods of exposure. After this treatment, flax fibres were washed with distilled water and dried. The degree of fibre surface tension was measured in terms of the contact angle. Then, cellulose nanocrystals were incorporated and mixed in the thermoplastic resin, and the samples were developed via the incorporation of intercalated layers of treated flax fibres. The composites were produced using compression moulding. After that, the samples were evaluated, regarding their mechanical performance and morphology. The research results show that flax fibres treated with 9 wt. % NaHCO₃ for 48 h had improved flexural strength as a result of removing impurities and exposing hydroxyl groups that react with Na⁺ ions present in NaHCO₃, which enhances its mechanical properties. The incorporation of 1% CNCs into thermoplastic resin significantly enhanced the fibre/matrix interface, resulting in a remarkable 38% increase in flexural strength. These findings demonstrate the effectiveness of using treated natural fibres and CNCs to improve composites' performance.