(572f) Melting, Crystallization, and Morphological Modifications of Biodegradable Polyesters in Dense Carbon Dioxide

The melting temperature depression, crystallization, and morphological modifications have been investigated for a biodegradable polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) in the presence of CO₂. Experiments have been carried out in a special variable-volume view cell that permits investigations using thin polymer films. Melting temperature depressions were determined at pressures up to 35 MPa by monitoring the changes in the transmitted light intensities [1]. Morphological modifications that develop were then explored at pressures up to 24MPa. These evaluations were carried out by investigations of the changes in the thin films that were melt-crystallized in the view cell using a polarized optical microscope. These films display banded spherulitic morphologies. These banded spherulites are found to display radially oriented pores in the bands which themselves consist of the radially oriented lamellae. The formation of these oriented pores is interpreted as being the result of the exclusion of CO₂from the crystal growth front to the amorphous region in between the bundles of the lamellar stacks.

[1] S. Takahashi, J.C. Hassler, E. Kiran, Melting behavior of biodegradable polyesters in carbon dioxide at high pressures, Journal of Supercritical Fluids 72 (2012) 278-287.