Pressure dependence of equilibrium melting temperature of poly (lactic acid)

The behavior of the equilibrium melting temperature (View the MathML source) of poly(l-lactic acid) with pressure estimated using the Gibbs-Thomson method is presented. Differential scanning calorimetry and a High pressure differential thermal analyzer have been used to determine the melting temperatures of samples isothermally crystallized at atmospheric pressure and at pressures ranging from atmospheric to 300 MPa respectively. Lamellar thickness of the crystals was determined from small angle X-ray scattering. The View the MathML source was found to follow the second order polynomial View the MathML source = 206 + 0.309P – 3.86 × 10−4P2. The enthalpy and entropy of fusion of the perfect crystal up to 300 MPa determined through the Clapeyron equation remained more or less similar up to 200 MPa but increased significantly at 300 MPa. The View the MathML source and ΔS0 at atmospheric pressure were calculated to be 94.5 Jg-1 and 0.197 JK−1g−1, respectively while the fold surface energy was calculated to be 64 × 10−3 Jm−2