Effect of pressure on poly-L-Lactic Acid morphology

When exposed to pressures below and above its glass transition temperature (T_g) over time, both the amorphous and crystalline regions of Poly-L-Lactic Acid (PLA) can be oriented. The most pronounced effect was the existence of an intense birefringence which lacked any sign of crystalline structure as observed by polarized light microscopy as well as the existence of a non-birefringent area in some of the same samples. Differential Scanning Calorimetry (DSC) analysis of the birefringent areas revealed decreased enthalpy of relaxation (ΔH_ER) and specific heat capacity (ΔC_P) values as well as the existence of at least two T_g’s when samples were treated at 63 °C and above, indicating increased orientation of the amorphous region. These same samples additionally displayed increased crystallinity which was depicted by an increased enthalpy of crystallization (ΔH). Additionally, X-Ray Diffraction (XRD) revealed a shift from an amorphous to a crystalline structure. Regions that did not display intense birefringence revealed minimal changes in T_g, ΔH_ER, and ΔC_P.