Synthesis and Characterisation of Cellulose Nanocrystal-Reinforced Polyhydroxybutyrate Biocomposites for Packaging Applications

Single-use petroleum-derived plastic packaging contributes significantly to the environmental pollution crisis in Nigeria, and bio-based alternatives incorporating locally available renewable resources remain underexplored in Nigerian academic literature. This study synthesises cellulose nanocrystals from sugarcane bagasse sourced from Sokoto State and incorporates them as reinforcing fillers into polyhydroxybutyrate biopolymer matrices for food packaging film applications. Cellulose nanocrystals were prepared by sulphuric acid hydrolysis and characterised by transmission electron microscopy, X-ray diffraction, and zeta potential measurements. Composite films were prepared by solvent casting at nanocrystal loadings of 0, 2, 4, 6, and 8 weight percent and characterised for tensile strength, elongation at break, Young's modulus, water vapour transmission rate, oxygen permeability, transparency, and thermal stability by TGA-DSC. Neat cellulose nanocrystals exhibited an average diameter of 8 nm and length of 230 nm with high crystallinity (78.4%). Addition of 4 wt% nanocrystals increased polyhydroxybutyrate tensile strength from 22.6 to 41.8 MPa, an 85.0% improvement, while maintaining adequate elongation for packaging applications. Oxygen permeability decreased by 47% at 4 wt% nanocrystal loading relative to unfilled matrix, attributed to the tortuous path effect from well-dispersed nanofiller. Water vapour transmission rate decreased by 38%. DSC analysis confirmed that the nanocrystals nucleated crystallisation, increasing thermal stability onset temperature by 12 degrees Celsius. The study demonstrates the potential for a fully bio-based, locally resourced packaging composite as a plastic alternative in the Nigerian market. Keywords: cellulose nanocrystals, polyhydroxybutyrate, biocomposite, food packaging, sugarcane bagasse