Morphology and property changes in PLA/PHBV blends as function of blend composition

PLA/PHBV blends were prepared by melt mixing. The morphology and physical properties of the blends and neat polymers were investigated. Scanning electron microscopy (SEM) studies provided evidence of interfacial cavities and weak interfacial interaction between the two polymers, and no obvious co-continuous morphology was observed in any of the investigated blends. Positron annihilation lifetime spectroscopy (PALS) indicated the presence of open-volume cavities with sub-nanometre diameters; far smaller than observed from the SEM images. The mean size and relative concentration of these cavities increased with increasing PHBV content. A weak negative deviation in the mean size for low PHBV content possibly indicates some degree of partial miscibility. The glass transition temperature of PLA in the blends decreased with increasing PHBV content, and offers support to some PHBV being miscible with the PLA. The degree of crystallinity in the blends show interesting behaviour that may be explained in terms of the complex morphology observed for these blends. The thermal conductivity of the samples varied with composition, but increased with increasing PHBV content, which was probably related to the increasing crystallinity. Both the tensile strength and Young's modulus decreased with increasing PHBV content for the sequence of blends, and both parameters exhibited maximum values for 10 wt.% PHBV. For samples between 50/50 and 10/90 PLA/PHBV the tensile strength and Young's modulus were comparable to or lower than those for both the neat polymers.