Morphology of Plastic Deformation and Fracture of a Biodegradable Biopolymer

PHBV is an important sustainable product as it is produced from renewable resources, is completely biodegradable, and can be moulded as a petrochemical thermoplastic. The mechanical behaviour and biodegradability of this semicrystalline material strongly depends on its morphology. In this article we show how the amorphous matrix and the spherulites of PHBV behave under tension until they fail. We prepared an acid etching agent to reveal details in the spherulitic structure of compressed moulded sheets. Microtensile tests on the stage of a polarized light microscope showed that crazing and shear bands are the strain mechanisms operating within the amorphous matrix of PHBV. In the closely packed spherulites, crack propagation occurred along the circumferential planes of the spherulites, trans-spherulitically along radial or circumferential planes, or through the boundaries between spherulites.