Kinetics of crystallization of biodegradable PHA copolymers: a combined X-ray scattering and micro-indentation study

Abstract

Wide Angle X-ray scattering (WAXS) and indentation hardness have been used to study the development of crystallinity at room temperature of biodegradable poly(hydroxybutyrate) (PHB) and its copolymer with hydroxyvalerate (PHB/HV) containing 12% of valerate. Measurements were carried out immediately after quenching the samples from the molten state (200 ºC) in ice water and over two weeks of storage at room temperature. WAXS showed that the crystallization of the PHB-based polymers initiated within the first minutes of storage at room temperature, the copolymer displaying a higher rate of crystallization than the homopolymer. For all samples, the degree of crystallinity, α, nearly reached a plateau value within the first hour of crystallization. Concurrently to the development of crystallinity, microhardness values, H, clearly rose as crystallization occurred. Monitoring the crystallization for over two weeks showed that after the rapid increase of α and H, there was a slow monotonic growth of these properties. A correlation between nanostructure and microhardness is found at all stages of the crystallization process.