Thermal behaviour and miscibility of poly(3-hydroxybutyrate)/poly(vinyl alcohol) blends

Abstract

Thermal behaviour and miscibility of poly(3-hydroxybutyrate) (P(3HB)/poly(vinyl alcohol) (PVA) blend films prepared by casting have been analysed by d.s.c., n.m.r. and density measurements. Blends containing glycerine were also analysed by d.s.c. Melting temperature ( T m) of the P(3HB) crystalline phases decreased as PVA content increased, whereas T m of the PVA phase remained almost unchanged. The crystallinity of P(3HB) in the blends also decreased with increase of PVA content. These results indicated that the thermal behaviour of the P(3HB) phase was influenced by the existence of PVA. Glycerine had no effect on the thermal properties of the blend, except for depression of T m of the PVA phase. Miscibility in the amorphous phase of the blend has been analysed by density measurement. If P(3HB) is completely immiscible with PVA, the crystallinity of PVA can be estimated from the crystallinity of P(3HB) and the density of the sample. However, the crystallinities of the PVA phase estimated for some blend samples were greater than unity. This behaviour can be accounted for when these blends are partially miscible in the amorphous phase. In order to investigate the miscibility in detail, we have determined the 1H spin-lattice relaxation times in the laboratory frame ( T 1) and in the rotating frame ( T 1 ϱ ). Both T 1 and T 1 ϱ values for the P(3HB) and PVA phases tend to approach those of blend partners with increase of PVA content. That is to say, the increase of PVA content in a blend enhances the miscibility.