Polyhydroxyalkanoate Nanocomposites with Cellulose Nanocrystals as Biodegradable Coating and Packaging Materials

Nanocomposites of polyhydroxybutyrate (PHB) and poly-(hydroxybutyrate-co-hydroxyvalerate) (PHBV) with cellulose nanocrystals (CNCs) were prepared by dispersion of CNCs into (aqueous) poly(vinyl acetate) (PVAc) emulsion or poly(ethylene glycol) (PEG) solution, followed by melt mixing of dried PVAc/CNC and PEG/CNC master-batches with neat polyesters. Ternary nanocomposites PHB/PVAc/CNC, PHB/PEG/CNC, PHBV/PVAc/CNC, and PHBV/PEG/CNC were obtained with CNC contents of 2.4 and 4.8 wt %, designed for potential applications in the field of biodegradable packaging, as well as in the biomedical sector. Binary blends of PHB and PHBV with PVAc and PEG, obtained by melt mixing, were also analyzed to investigate the polymer miscibility and crystallization behavior. The results of microscopic, wide-angle X-ray scattering, Fourier-transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and mechanical analyses of nanocomposites indicated that the polymer blending procedure of PHB and PHBV enhanced the CNC dispersion into the polymer matrices and modified the phase morphology and properties. For both PHB and PHBV nanocomposites, the addition of PVAc resulted in higher tensile strength and elongation at break by increasing the CNC content.