Development of Poly(lactic acid)/Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Biocomposite Films: Influence of Cellulose Microfiber Source on Structural and Functional Properties

The incorporation of cellulosic-based fillers as reinforcements into biocomposites represents a promising strategy to enhance the performance of sustainable packaging materials. In this study, poly(lactic acid)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PLA/PHBV) films reinforced with 1 and 3 wt% of cellulose microfibers (CM) derived from yam, potato, and cassava hulls were developed through melt extrusion followed by compression molding. The physicochemical, mechanical, optical, microstructural, thermal, and molecular properties of the films were evaluated. Results showed that both the CM source and concentration significantly influenced the biocomposites performance. Cassava-derived CM at 3 wt% provided the best barrier properties, while increasing CM content, regardless of the source, generally reduced solubility, increased moisture content, enhanced stiffness, and decreased elongation at break, although excessive loading negatively affected structural homogeneity. CM incorporation also reduced film gloss and transparency, particularly in yam-based composites. Thermal analysis indicated a multi-step degradation process with only minor variations in thermal stability, and no major chemical modifications of the biocomposites were detected. Overall, cassava-derived CM produced the most balanced performance, highlighting the importance of filler source and loading in tailoring PLA/PHBV biocomposite functional properties.