Non-isothermal crystallization of polymers

Traditional studies of crystallization kinetics are often limited to ideali zed conditions, in which the parameters of state (temperature, pressure, et c.) are constant. In real situations, however, the external conditions chan ge continuously, which makes the kinetics of crystallization dependent on i nstantaneous conditions, as well as on rate of change. This article provides an overview of the current state-of-the-art of non-is othermal crystallization of polymers during the cooling from the melt. The majority of the proposed theoretical formulations that predict non-isotherm al crystallization kinetics, concern bulk crystallization and are based on modifications of the Avrami equation. The Ziabicki, Nakamura and Ozawa mode ls are examined here in same detail together with treatments from other aut hors. The basic hypotheses of the various models, as well as their relative drawbacks, are underlined. Alternative empirical approaches to calculate t he main parameters of non-isothermal crystallization and to compare the cry stallization rate of different polymeric systems are also discussed. This article reviews the data concerning non-isothermal crystallization pro cesses for different classes of polymers. Major attention is directed towar ds the dynamic crystallization of polyolefins, a class of materials of larg e industrial interest. Other results for polyoxyolefins, polyesters, polyam ides and polyketones are also examined. (C) 1999 Elsevier Science Ltd. All rights reserved.