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

Publication date: 2 June 2017
Source:Polymer, Volume 118
Author(s): David Rohindra, Keiichi Kuboyama, Toshiaki Ougizawa
The behavior of the equilibrium melting temperature (Tmo) 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 (dTmodP)o was found to follow the second order polynomial Tmo = 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 ΔHf0 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.

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