When exposed to pressures below and above their glass transition temperature (Tg) and melting temperatures (Tm) over time, both the amorphous and crystalline regions of Poly-L-Lactic Acid (PLA) and Polycaprolactone (PCL) can be oriented. This effect was observed with the existence of an intense birefringence which lacked any sign of traditional crystalline structure as observed by polarized light microscopy. Differential Scanning Calorimetry (DSC) analysis of the materials revealed the existence of increased orientation of the materials in addition to increased crystallinity. Consequently, X-Ray Diffraction (XRD) revealed a morphological change which appeared to be more crystalline in structure. Additionally, PCL was explored for use in hot melt encapsulation of three different types of molecules. Specifically, volatile oil and menthol in addition to a therapeutic lithium carbonate salt. Results indicated that PCL was quite capable of releasing volatile oil and menthol in a controlled and time dependent manner with no observable burst release effects noted. However, initial loading and storage temperature was observed to have a direct impact on total release as increased loading and temperatures were observed to increase total release. Finally, PCL was proven quit effective in controlled release of therapeutic lithium in a simulated gastric environment. Lithium much like the volatiles was observed to release in a very controlled and time dependent manner. With total release being observed to rely on initial loading once again.
Baker, Christopher Michael,
"Effects of Pressure on the Morphology of Semi-Crystalline Polymers"
Artificial Organs, Biomaterials, and Cell Technology Theses and Dissertations.
Brown Digital Repository. Brown University Library.