Effect of Coffee Grounds Content on Properties of PHBV Biocomposites Compared to Similar Composites with Other Fillers

Spent coffee grounds (SCG) have potential as a sustainable bio-filler in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) composites, offering an environmentally friendly approach to waste utilization. This study investigated the effect of SCG content on the mechanical, thermal, and morphological properties of PHBV biocomposites and compared them with those of composites containing wood flour and hemp fibers. The biocomposites were fabricated via extrusion and injection molding, followed by the characterization of their mechanical performance, thermal behavior, and microstructure. The results indicated that SCG increased the stiffness of PHBV but did not enhance its tensile strength due to the weak interfacial adhesion between the filler and matrix. Unlike other lignocellulosic fillers, SCG requires lower processing temperatures, which is advantageous for thermally sensitive applications. SEM analysis revealed well-dispersed SCG particles at low concentrations, but visible aggregation and interfacial voids at higher loadings. While SCG serves as an effective and cost-efficient filler for improving the stiffness of PHBV, it does not reinforce the material in the conventional sense.