Mechanical and Morphological Properties of PHB/Oil-Free Coffee Dregs (OFCD) Composites

Poly(3-hydroxybutyrate) (PHB) and coffee dregs (CDs) are both biodegradable materials. The latter are household wastes with no commercial value that are discarded in landfills mixed with other organic wastes. PHB has properties equivalent to polypropylene (PP), but its prohibitive cost restricts its field of application. The incorporation of this residue in a PHB matrix is a way to obtain materials with a high cost/benefit ratio. The aim of this work was to investigate the effect of adding oil-free coffee dregs (OFCDs) on the mechanical and morphological properties of PHB. Soxhlet extraction using ethanol as a solvent was used to obtain OFCDs. The PHB/OFCD composites were prepared in a twin-screw extruder. Standardized methods were used to evaluate the tensile and flexural properties. The test specimens were obtained by compression molding. Scanning electron microscopy (SEM) was applied to evaluate the morphology of the composites obtained. The data obtained showed that the incorporation of 15 wt.% of OFCD caused no significant differences in the tensile modulus, tensile strength and flexural modulus. The flexural strength decreased with the incorporation of OFCD in the PHB. However, the material obtained was interesting, since it was more attractive in terms of cost and environmental impact. SEM micrographs showed good dispersion of OFCD in PHB when the OFCD content was 5 wt.%. However, when higher levels of residues were incorporated in the PHB, the formation of agglomerates became evident. Poor interfacial adhesion between the filler and matrix was indicated by the cracks and voids revealed in the micrographs. The results obtained indicated that PHB/OFCD composites prepared with 15 wt.% of OFCD particles have potential to be used in the production of PHB materials that require high stiffness, adequate strength, and lower cost, such as sheets and thermoformed products for food, medical, personal care and laboratory applications