Wood/PHAs biocomposites with mechanical properties comparable to conventional plastics: Model-based prediction and experimental validation

The development of cost-effective, biodegradable engineering materials as drop-in replacements for traditional plastics is crucial for mitigating global plastic pollution. Recent research has focused on biocomposites combining biodegradable bioplastics such as polyhydroxyalkanoates (PHAs) with waste-derived fibres to enhance circularity, reduce costs and improve biodegradation. However, current PHA-based biocomposites lack the performance needed to replace conventional plastics, limiting market adoption. This study presents innovative wood fibre biocomposites based on PHAs like poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) blends, achieving properties equivalent to polypropylene and polyethene. The optimal biocomposites achieved a tensile strain at break of 12.1–29.5 %, tensile stress of 20–23 MPa, and tensile modulus of 1814–2329 MPa, depending on P34HB content. Thermal analysis and predictive modelling indicate strong interactions between PHBV, P34HB and wood fibres, with mechanical behaviour varying based on P34HB content. The addition of P34HB enhances ductility and flexibility, increasing tensile strain but reducing modulus and strength, while wood fibres improve modulus but reduce strength and strain. Microcrystalline and blend morphology analyses via scanning near-field optical microscopy highlight sensitivity to P34HB content and blending conditions. Optimised screw profiles with reduced shear zones minimise PHA thermal degradation, enhancing mechanical properties. The predictive models developed accurately forecast tensile properties, providing a framework for designing wood/PHAs biocomposites as sustainable alternatives to conventional plastics.