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Crystal Morphology Control by Melt Phase Separation in Biodegradable Polymer Blends

Published online by Cambridge University Press:  15 March 2011

Y. A. Akpalu ,
J. C. Meredith  and
E. J. Amis
E. J. Amis
Affiliation:
Polymers Division, National Institute of Standards & Technology, Gaithersburg, MD 20899, Email: eric.amis@nist.gov
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Abstract

The effect of lower critical solution temperature (LCST) phase separation on the crystallization of poly(ε-caprolactone) PCL in PCL/poly(D,L-lactide) (PDLA) blends is studied by simultaneous small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS). Phase separation is induced by controlled temperature jumps into the LCST (two-phase) region, which is above the melting temperature (60 °C) of PCL and the glass transition temperature (50 °C) of PDLA. We have followed the nanoscale structural changes (< 100 nm) during subsequent crystallization at 45 °C of critical (0.36 PCL) and off-critical (0.50 PCL) blend compositions in both one-phase and two-phase melts. The spherulite morphology (1-100 μm) is examined with optical microscopy. When crystallization follows LCST phase separation, the shape, size and distribution of the spherulites depends on the extent of melt phase separation. In our x-ray measurements, the WAXS crystallinity of PCL is less than 40 % for the temperature range of interest. We perform a correlation function and intensity model analysis of our SAXS data to obtain morphological variables that characterize the intraspherulitic morphology. These morphological variables are relatively constant during crystallization and are also independent of melt phase separation. On the other hand, the ultimate crystallinity and the crystallization rate depend on the extent of melt phase separation.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 662: Symposia LL/MM/NN/OO – Biomaterials for Drug Delivery & Tissue Engineering , 2000 , LL6.6
Copyright
Copyright © Materials Research Society 2001

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