Green Composite Based on a Polymer Mixture Containing Biopolymer and Waste Coffee Husks

This study presents the results of investigations into the properties of a composite made from the commercial biopolymer with varying concentrations of ground coffee husks (CH) at 10, 30, and 50 wt%. Thermal, thermomechanical, physical, and mechanical properties were determined for the composites. Results indicate that the inclusion of CH into the polymer matrix significantly enhances the thermomechanical properties of the obtained composites, particularly in terms of storage modulus at 30 °C. The addition of coffee filler did not alter the characteristic thermal curves. Still, it reduced the thermal resistance of the composites, lowering the degradation temperature by approximately 40 °C compared to the pure polymer. Furthermore, the incorporation of CH introduced an additional stage of mass loss on the thermogravimetric curves, associated with the thermal decomposition of CH. The physico-mechanical properties of the composite depend on the content of the filler. Increasing the coffee content increases the dynamics of water absorption by the composite. It also increases the composite's stiffness while reducing its tensile and flexural strength. The obtained results suggest that biopolymer-based composites filled with ground CH can be effectively used for manufacturing biodegradable products, with the moisture diffusion behavior indicating susceptibility to degradation that is modulated by the CH content.