Mechanical, rheological and thermal properties of montmorillonite-modified polyhydroxybutyrate composites

Abstract

Polyhydroxybutyrate (PHB), a bio-derived and biodegradable polyester, has the potential to be a substitute for traditional polymers. PHB was modified with montmorillonite (MMT), a nanoclay, with the aim of improving its mechanical properties. The clay dispersion, mechanical, rheological and thermal properties of untreated and acid-treated MMT-modified PHB nanocomposites were investigated. Nanocomposite specimens at three different clay loading were prepared using extruder and injection moulding machine. Energy dispersive X-ray mapping revealed that nanocomposites with clay content of 3 phr exhibited better dispersion compared to nanocomposites with higher clay content. The mechanical properties of the MMT-modified PHB, such as the tensile and flexural modulus, were enhanced when compared to neat PHB. From rheology, PHB and PHB nanocomposites modified with untreated MMT exhibited Newtonian fluid behaviour in the tested frequency range. However, for nanocomposites modified with acid-treated MMT, shear thinning behaviour was observed at higher clay content. The nanocomposites also exhibited higher complex viscosity compared to PHB. From transmission electron microscopy analysis, exfoliation of the MMT was observed for the treated MMT nanocomposites at all clay loading. MMT-modified PHB has lower melting temperature when compared to neat PHB. Furthermore, it was found that the addition of MMT influenced the crystallisation behaviour of PHB. The presence of acid-treated MMT also reduced the degree of crystallinity with increasing clay content.