Morphological, crystallinity and thermal stability characterization of poly(3-hydroxybutyrate-Co-3-hydroxyhexanoate)/zinc oxide nanoparticles bionanocomposites: Effect of filler content

Abstract

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx)/ZnO-NP nanoparticles bionanocomposites were elaborated by melt compounding in a twin-screw extruder at content ratio of 1.5, 3 and 6 wt.%. Morphology, crystallinity and thermal stability of the PHBHHx-based bionanocomposite samples were investigated by scanning electron microscopy (SEM), wide angle X-ray Diffraction (WAXD) and thermogravimetric analysis (TGA) aiming at evaluating the structure-properties relationships with respect to filler content and to neat PHBHHx. Morphological observations by SEM of the fractured surface of the bionanocomposite samples showed that ZnO-NP was randomly dispersed in PHBHHx matrix, with however a noticeable presence of filler aggregates at 6 wt.%. WAXD patterns displayed an increase in crystallinity of PHBHHx bionanocomposites with increasing ZnO-NP content, whereas TGA data indicated a decrease in thermal stability in comparison with the neat polymer. This result showed that the addition of ZnO-NP promoted the thermal degradation of PHBHHx through a random chain scission mechanism. Moreover, it was found that beyond 3 wt.% of filler content, no significant change was observed in the properties of PHBHHx/ZnO-NP bionanocomposites. The study highlighted the potential use of ZnO-NP at low content, as reinforcement in PHBHHx without necessarily carrying out any filler surface treatment nor solvent casting process.