Nanocomposites of poly(3-hydroxybutyrate)/organomodified montmorillonite: Effect of the nanofiller on the polymer's biodegradation

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.