Interfacial improvements in biocomposites based on poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) bioplastics reinforced and grafted with alpha-cellulose fibers

In this study, alpha-cellulose fibers reinforced green biocomposites based on polyhydroxybutyrate (PHB) and the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were prepared and characterized. The alpha-cellulose fibers were isolated from at-risk intermountain lodgepole pine wood by successive removal of extractives, lignin and hemicellulose. Grafting of PHB or PHBV onto cellulose was conducted using reactive extrusion with dicumyl peroxide free radical initiation at high temperature. It is postulated that the grafted copolymers at the interfaces of cellulose and the polymer matrix performed as an interfacial coupling agent. Grafting tended to interact with both the hydrophilic fibers and the hydrophobic PHB or PHBV matrix. The biocomposites were characterized by scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA) and indicated good interfacial bonding and compatibility between the two phases. The mechanical properties of the biocomposites were improved by grafting due to improved stress transfer between the two interphases of the fiber/polymer matrix as compared to the blend control composite. The crystallinity of PHB, PHBV and cellulose in the biocomposite were reduced as determined by Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC) analyses. This in situ reactive extrusion process offers an effective approach to improve the properties of biocomposite materials from sustainable resources.