Production and Evaluation of Biodegradable Composites Based on Polyhydroxybutyrate and Polylactic Acid Reinforced with Short and Long Pulp Fibers

In this study, two biodegradable polymers, polylactic acid (PLA) and polyhydroxybutyrate (PHB), were mixed with short and long fiber pulps using a torque rheometer. PLA/PHB-fiber composites consisting of up to 40 wt% paper pulp were produced through a unique procedure and evaluated using various techniques including thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD) and dynamic mechanical analysis (DMA). Changes in the matrix polymers and pulp fibers were analyzed using gel permeation chromatography (GPC) and Fiber Lab microscopy. The results showed that the composites reinforced with pulps showed significantly increased tensile stiffness and impact strength; the addition of a coupling agent did not improve the mechanical performance of PHB biocomposites. The degradation of PLA and PHB observed during the heating process is thought to be caused by the release of acidic organic compounds, such as crotonic and lactic acids, which chemically enhance the existing interface between the pulps and the matrix polymers. The storage modulus and loss modulus of the composites decreased as the pulp fiber content increased, and the damping capability (increase in dimensional stability) decreased with increasing pulp fiber content.