Green composites from plasticized poly(3-hydroxybutyrate-co-3-hydroxyvalerate) bioplastic and cellulosic fiber: Effect of compatibilizer and grafting percentage on interfacial adhesion and biocomposite performance.

High-performance green composites were prepared from poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and cellulose fibers. PHBV is a bacterial polyester that is biodegradable and biocompatible but relatively expensive. This research aims to incorporate a high content of low-cost renewable fillers, up to 25 wt%, while enhancing the processability and performance by plasticization and compatibilization. Tributyl citrate (TBC) was used as a plasticizer to improve the flow properties and ease filler dispersion. The fiber-matrix adhesion was enhanced by adding a compatibilizer, namely maleic anhydride-grafted-PHBV (MA-g-PHBV) synthesized by reactive extrusion. Additionally, the impact of different grafting percentages of the MA-g-PHBV on the biocomposite performances was investigated. While the addition of the plasticizer increased the melt flow but decreased the mechanical properties such as stiffness, the incorporation of the fillers compensated for the decrease. This reinforcing effect became more prominent with the addition of the compatibilizers thanks to enhanced interfacial interaction. With 25 wt% filler, the tensile strength, modulus, and elongation-at-break were higher by a maximum of 44 %, 23 %, and 18 % after compatibilizer addition, compared to the uncompatibilized counterpart. MA-g-PHBV with the highest grafting percentage was found to be the most effective. This research presents viable strategies for producing highly-filled PHBV biocomposites for injection molding applications.