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.