Melting and crystallization temperatures, foaming, and fluid-induced crystallization of poly (ε-caprolactone) in compressed CO2 and N2

Melting and crystallization temperatures of poly(ε-caprolactone)(PCL) exposed to CO₂ and N₂ have been evaluated at pressures up to 125 bar using High Pressure Torsional Braid Analysis. It is shown that in contrast to CO₂, exposure to high pressure N₂ does not lead to a significant depression of T_m or T_c. Instead, these transition temperatures tend to increase in nitrogen, reflecting more of a hydrostatic pressure rather than a solvent effect. Another factor that may play a role is the fluid-induced crystallization which tends to increase the melting temperature. By conducting foaming at properly selected temperatures along the rigidity reduction paths which are scaled with respect to the melting temperatures in CO₂ or N₂, foams with low bulk foam densities of about 0.2 g/cm³ could be generated in CO₂ at 100 bar and in N₂ at 200 bar.