PHA reinforced natural Fibres composites: a review

Petroleum-based plastics drive high carbon emissions and persistent pollution, creating demand for renewable, biodegradable alternatives. Polyhydroxyalkanoates (PHAs), bacterial polyesters that combine biodegradability with biocompatibility, are promising candidates, but high cost, brittleness, and a narrow processing window limit their use. Natural fibres (NFs) from agricultural residues can lower cost and improve stiffness and thermal stability while preserving biodegradability. This review critically assesses PHA/NF bio-composites, examining how fibre type, content, surface treatment, and processing govern performance. Across studies, 20–40 wt.% NF raised modulus by up to 200% but reduced tensile strength, elongation, and impact strength because of weak hydrophilic–hydrophobic interfacial adhesion. Alkali, silane, maleic anhydride, and isocyanate treatments partially recovered these losses, and most composites biodegraded within 40–120 days in soil or compost. An optimal melt-processing window of 170–190 °C is identified. Circular-economy, life-cycle, and end-of-life aspects, current limitations, and routes to commercial, net-zero deployment are also discussed.