No abstract

In this work, the structural, thermal, mechanical, and biocompatibility characteristics of biopolyester-based nanocomposites with phyllosilicate clays, namely those of poly(3-hydroxybutyrate) (PHB) with octadecylamine-modified montmorillonite (C 18 MMT), are reported. PHB/clay nanocomposites with various loadings were prepared by melt mixing. X-ray diffraction measurements and transmission electron microscopy images revealed the coexistence of intercalated and exfoliated states in the produced nanocomposites. Atomic force microscopy imaging also shed light to the morphological characteristics of the pure PHB and the prepared nanocomposites. The thermal stability of the nanohybrid materials was improved with the 5 wt % loading nanocomposite to show the best improvement. In addition, the nanohybrids have lower melting point compared to pure PHB and enhanced storage modulus (E 0 ). Finally, the biocompatibility of pristine PHB and the 5 wt % nanocomposite was assessed by studying the morphology and proliferation of osteoblast cells attached on their surfaces. The results after 3 and 7 days of cell culturing indicate the incorporation of nanoclays does not change the cell adhesion and spreading as compared to those on pure PHB.

Poly(3-hydroxybutyrate) (PHB) is a biopolymer that can be degraded by extracellular PHB depolymerase. This enzyme is secreted by various microorganisms, but bacterial PHB depolymerases are the most widely studied. The biodegradability rate depends on various factors. By controlling them, the biodegradability rate can change and be customized, and thus, the applications of the polymer can increase and become more diverse. In this work, the role of organomodified montmorillonite (OMMT) on PHB biodegradation was investigated. Using the melt-mixing method, nanocomposites of PHB and OMMT as the nanofiller were prepared. The enzyme was isolated from the fungus Penicillium pinophilum and the enzymatic degradation was studied for both pure polymer and its nanocomposites. It was found that, after 25 days of enzymatic degradation, the mass loss was very low, while the polymer's average molecular weight as measured by gel permeation chromatography was significantly reduced (more than 50%). Additional peaks corresponding to PHB oligomers (from pentamers to nonamers) appeared after biodegradation. This behavior was observed for pure PHB and the hybrid materials. Scanning electron microscopy imaging of the biodegraded surfaces and analysis of these images showed that the higher amount of nanoclay (10 wt %) resulted in larger biodegraded area of the specimens. The results presented here demonstrate that the presence of the nanoclays enhances the biodegradation rate of pure PHB polymer and provide quantitative data for the biodegradation of PHB/organoclay hybrid materials.