Kinetics of irreversible melting of polyethylene crystals revealed by temperature modulated DSC

Temperature modulated differential scanning calorimetry (TMDSC) has been applied to study the irreversible melting kinetics of polyethylene crystals on heating. The apparent heat capacity obtained by TMDSC showed strong dependences on the applied frequency (modulation period) and on the heating rate. Considering the details of the melting kinetics, the dependence has been explained by a frequency response function similar to Debye's type with a characteristic time representing the melting kinetics. From the analysis, it has been confirmed that the 'reversing' heat flow extrapolated to omega-->0 is correspondent to the 'total' heat flow, when re-crystallization and re-organization are not significant during the melting process. It is further suggested that the characteristic time is related to the superheating effect seen in the 'total' heat flow. It is pointed out that the distribution of the melting points may be estimated by the deconvolution of the melting kinetics from the 'total' heat flow. (C) 1998 Elsevier Science B.V. All rights reserved.