Dielectric relaxations in polyhydroxyalkanoates/organoclay nanocomposites

Two types of bacterial semi-crystalline copolyesters, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB) are studied neat or with 8 wt% of Cloisite® C30B (C30B) organoclays. Wide Angle X-ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC) reveal that the nanoclays are partially intercalated, exfoliated and agglomerated. With selected sample preparation, the crystalline phase is unaffected by the C30B presence. Broadband Dielectric Spectroscopy (BDS) measurements showed no influence of the nanoclays on the secondary local relaxations modes of both polymers and on the segmental relaxation of P3HB4HB. Nevertheless, a strong modification of the α relaxation of PHBV has been observed after incorporation of C30B. A strong decrease of the fragility index and of the glass transition temperature revealed an increase of the molecular mobility in the amorphous fraction influenced by the nanoclays.