Morphology and barrier properties of nanobiocomposites of poly(3-hydroxybutyrate) and layered silicates

Polyhydroxybutyrate (PHB) is generally considered to be a very uneasy biopolymer to handle because of significant instability during melt processing and some excessive brittleness. This work studied the morphological, thermal, and barrier properties of novel melt-mixed nanobiocomposites of PHB, poly(epsilon-caprolactones) (PCL), and layered phyllosilicates based on commercial organomodified kaolinite and montmorillonite clay additives. The addition of PCL component to the blend was seen to reduce oxygen permeability but it was also found to lead to a finer dispersion of the clay. The addition of highly intergallery swollen organomodified montmorillonite clays to the PHB blend led to a highly dispersed morphology of the filler, but this simultaneously increased to a significant extend the melt instability of the biopolymer. Nevertheless, the organomodified kaolinite clay, despite the fact that it was found to both lead to less dispersed and irregular morphology, particularly for higher clay loadings, it led to enhanced barrier properties to oxygen, D-limonene, and water. D-limonene and specially water molecules were, however, found to sorb in both hydrophobic and hydrophilic sites of the filler, respectively, hence diminishing the positive barrier effect of an enlarged tortuosity factor in the permeability. Mass transport properties were found to depend on the type of penetrant and modeling of the permeability data to most commonly applied formalisms was not found to be satisfactory because of factors such as morphological alterations, heterogeneity in the clay dispersion, and penetrant solubility in the filler. (C) 2008 Wiley Periodicals, Inc.