Sustainable manufacture of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-based biocomposites incorporating sorghum-derived microfibrillated cellulose

Microfibrillated cellulose (MFC) from forage sorghum shows strong potential as a biocomposite reinforcement owing to its high aspect ratio and polar surface chemistry. A major challenge, however, is achieving uniform dispersion in polymer matrices, as drying induces irreversible fibril aggregation (hornification) through strong interfibrillar hydrogen bonding. This study presents a scalable, cost-effective, and environmentally sustainable dispersion method (MFC-PEB) using conventional equipment (drying oven and twin-screw extruder) and compares it with dry powder blending (MFC-DPB) and water-assisted blending (MFC-WPB), with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as the reference polymer. The effects of alkaline treatment (2 % NaOH, 2 h) and twin-screw fibrillation on sorghum biomass were assessed. Thermogravimetric and infrared analyses confirmed a release in extractives, hemicellulose, and less stable lignin, while solid-state NMR showed a 7 % decrease in lignin. MorFi analyses and SEM confirm the fibrillation of treated sorghum fibres, with fibre aspect ratio increasing approximately twofold. Optical microscopy of composites containing 20 wt% MFC demonstrated that MFC-PEB achieved dispersion quality comparable to MFC-WPB. Differential scanning calorimetry and polarised optical microscopy revealed marked changes in crystallisation kinetics and spherulite morphology, highlighting the critical role of formulation and processing in defining polymer structural development. Finally, the mechanical tests revealed a 20 % improvement in tensile strength and a 22 % increase in tensile modulus for the MFC-PEB biocomposite compared with the untreated sorghum biocomposite and 37 % increase in tensile modulus compared with neat PHBV.