Mechanical and thermal properties of spent coffee bean filler/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) biocomposites: Effect of recycling

Green composites were fabricated using poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as the matrix and spent coffee bean powder (SCBP) as a filler by simple solution casting method. The effect of varying concentrations (5-25 wt.%) of SCBP on the thermal and mechanical properties was studied. The SCBP filler had better thermal properties than the matrix and the composites. There was slight increase in the glass transition temperature of the composites with higher concentration of the filler when compared to the PHBV matrix. The weight remaining at endset temperatures of the composites was found to be higher than for the matrix indicating enhanced thermal stability. The contact angle of the composites increased with increasing filler content changing from 75.8 degrees to 97 degrees. The tensile strength and modulus of the composite films reduced with increasing filler concentration but a reverse trend was observed in case of the % elongation at break. However, the tensile properties were comparable with other synthetic polymers such as LDPE, HDPE etc. Furthermore, the recycling of films did not significantly affect the mechanical and thermal properties. Hence, with comparable thermal and tensile properties, these biocomposite films can be considered for replacing the conventional synthetic non-biodegradable polymers such as polyethylene and polypropylene for packaging applications. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.