Miscibility, thermal behaviour, morphology and mechanical properties of binary blends of poly[(R)-3-hydroxybutyrate] with poly(gamma-benzyl-L-glutamate)

The miscibility, thermal behaviour, morphology and mechanical properties of poly[(R)-3-hydroxybutyrate] (PHB) with poly(gamma -benzyl-L-glutamate) (PB LG) are investigated by means of differential scanning calorimetry (DSC), s canning electron microscopy (SEM) and tensile tests. The DSC results show t hat PHB and PBLG are immiscible in the melt state. Such immiscibility also exists in the amorphous state due to a clear two-phase separated structure observed by SEM measurements. The blend samples with different thermal hist ory, namely as original and melt samples separately, display differences in thermal behaviour such as the DSC scan profile, the crystallinity and the melting temperature of PHB. The crystallization of PHB both from the molten state and the amorphous state is retarded on addition of the second compon ent. The SEM measurements reveal that a phase inversion occurs between the PHE/PBLG (60/40) and PHB/PBLG (40/60) blends. Except for the PHB/PBLG (40/6 0) blend, a microphase separated structure is observed for all blend compos itions. The mechanical properties vary considerably with blend composition. Compared with pure components, the PHB/PBLG (20/80) blend shows a certain improvement in mechanical properties. (C) 2001 Society of Chemical Industry .