Evaluation of the sample temperature increase during the quiescent and shear-induced isothermal crystallization of polyethylene

The isothermal crystallization of low-density polyethylene is analysed by differential scanning calorimetry and parallel plate rheometry. The temperature increase during the isothermal crystallization, resulting from the polymer sample's thermal resistance and the release of the heat of crystallization, is evaluated for the results obtained with both devices. The implication of this evaluation on the comparative overall crystallization kinetics is also analysed. Two different procedures for evaluating the degree of conversion to the solid phase from rheometry data are discussed. The sample temperature during isothermal DSC and rheometer experiments, these last performed over samples with different thicknesses, is evaluated and the relative crystallization kinetics compared by analysing the dependence of the reciprocal of the half of crystallization time on the estimated sample temperature at this instant. The results obtained indicate that, after performing the temperature corrections, and from an overall kinetics point of view, both procedures yield similar results. (C) 2003 Elsevier Ltd. All rights reserved.The authors acknowledge comments and criticisms made to this work by Prof J.J.C. Cruz Pinto and Dr Luzia Filipe, from Borialis, Portugal, for supplying the material used in this work. This work was carried out under financial support of the European Community fund FEDER, through the project POCTI/33061/CTM/2000 approved by the Portuguese Foundation of Science and Technology (FCT), that is also acknowledged by the grant BPD/5517/2001 assigned to WD. Zhang.