Effect of modified montmorillonite on biodegradable PHB nanocomposites

Abstract

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 °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.