Melt compounding of poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/nanofibrillated cellulose nanocomposites

Using natural cellulosic fibers as fillers for biodegradable polymers can result in fully biodegradable composites. In this study, biodegradable nanocomposites were prepared using nanofibrillated cellulose (NFC) as the reinforcement and poly (3-hydroxybutyrate-co-3-hydroxyvalerate, PHBV) as the polymer matrix. PHBV powder was dispersed in water, mixed with an aqueous suspension of NFC fiber, and freeze-dried. The resulting PHBV/15 wt% NFC was then used as a master batch in a subsequent melt compounding process to produce nanocomposites of various formulations. Its properties such as its mechanical properties, crystallization behavior, solubility of carbon dioxide (CO2), foaming behavior, and thermal stability and degradation of PHBV due to NFC were evaluated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the dispersion of NFC fibers. Adding NFC increased the tensile modulus of the PHBV/NFC nanocomposites nearly twofold. Differential scanning calorimetry (DSC) analysis showed that the NFC served as a nucleating agent, promoting the early onset of crystallization. However, high NFC content also led to greater thermal degradation of the PHBV matrix. Dynamic mechanical analysis (DMA) showed an increase of the storage modulus in the glassy state with increasing NFC content, but a more significant increase in modulus was detected above the glass transition temperature. The solubility of CO2 in the PHBV/NFC nanocomposites decreased and the desorption diffusivity increased as more NFC was added. Finally, the foaming behavior of PHBV/NFC nanocomposites was studied and the addition of NFC was found to inhibit foaming.