Effect of modified montmorillonite on biodegradable PHB nanocomposites

Polymer nanocomposites, based on a bacterial biodegradable thermoplastic polyester. poly(hydroxybutyrate) (PHB), and two commercial montmorillonites (MT), Na-M (MT) and 30B-M (organically modified MT), were prepared by melt-mixing technique at 165 degrees C. Both clays minerals were characterized by morphology, crystallochemical parameters, and thermal stability. Lower specific surface area (determined by adsorption methods) values were found for 30B-M. The apparent particle size from light scattering measurements, scanning electron microscopy observations, and crystallite size (determined from XRD patterns) of 30B-M indicated a higher degree of particles exfoliation than of Na-M. The nanocomposites PHBNa and PHB30B were characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), X-ray diffraction (XRD), transmission electron microscopy (TEM), mechanical properties, and burning behaviour. Intercalation/exfoliation observed by TEM and XRD was more pronounced for PHB30B than PHBNa, indicating the better compatibility of 30B-M with the PHB matrix. An increase in crystallization temperature and a decrease in spherullites size were observed for PHB30B. The intercalation/exfoliation observed by TEM and structure XRD increased the moduli of the nanocomposites. The burning behaviour of PHB30B was influenced by the aggregation of the clay mineral particles. (C) 2009 Elsevier B.V. All rights reserved.