Quiescent polymer crystallization: Modelling and measurements

Abstract

The problem of predicting nonisothermal crystallization kinetics based on isothermal data is considered, with reference to the difficulties involved, both experimental and theoretical. The kinetic model used is the differential form of the Nakamura equation which is an extension of the Avrami equation so as to apply to nonisothermal crystallization. Nonisothermal induction times are obtained from isothermal induction times according to the concept of induction time index. The theory of Hoffman Lauritzen is used to extrapolate the limited isothermal crystallization rate data. Good agreement between DSC (differential scanning calorimetry) nonisothermal crystallinity results and model predictions is obtained for our own data on poly(ethylene terephthalate) (PET) and some literature data on nylon‐6, if the temperature lag between the sample and the DSC furnace is taken into account. The advantages of the present approach in process modeling are pointed out. Quenching experiments have also been performed in which PET slabs are allowed to cool and crystallize from the melt under quiescent conditions. The resulting crystallinity distributions in the thickness direction are measured and predicted by using kinetic parameter values obtained from isothermal DSC measurements alone.

Effect of nucleating agents on crystallization kinetics of PET

“…The crystallization rates at different temperatures were expressed in the form of reciprocal of crystallization half-time t 1/2 . Using Hoffman-Lauritzen relationship between the radial growth rate of crystal and crystallization temperature based on crystallization regime theory [25], and following Chan and Isayev [26] (1/t 1/2 ) and (1/t 1/2 ) 0 were used to Figure 4. The determination of the equilibrium melting temperature substitute for the growth rate G and a pre-exponential factor G 0 , respectively.…”

Quiescent crystallization kinetics: Embedded artificial neural model

“…The melted samples were then cooled at various constant cooling rates of 0.5, 2.5, 5 ,10, 20, 50, 75°C/min. Before the samples were tested, a standard indium calibration was run by heating at a rate of 20°C/min in order to correct all the results of temperature lag between the sample and the DSC furnace 10 at high cooling rate runs, as discussed in Appendix A.…”

Non-Isothermal Crystallization Kinetics of Poly(ethylene terephthalate) from the Point of View of Isokinetic Models

“…It is observed that 0(Tin) is only dependent on n, i.e., independent of heating and cooling rates q, as it is expected following the theory presented in the previous sections. Moreover, every experimental, nonisothermal crystallization curve 0(T) shows only one inflexion point independent of the cooling or heating rate q, 9 facilitating the application of the theory based on apparent m-order reaction functions of the type given by eq 1. The highest precision in determining the A vrami index n graphically is achieved for small slopes 80(T)/8Tlr=T,n• i.e., a low Tin for melt crystallization and a high Tin for cold-crystallization.…”

“…Small slopes are technically accomplished by performing DSC-measurements with relatively high cooling or heating rates q. 9 Then-values, which have been evaluated graphically with the inflexion-point method, are equal for cold-and melt-crystallization (n 2.4). 6 • 9 The isokinetic approach of Nakamura et al 4 is experimentally clearly supported by the results displayed in Tables I and II, since a approximately symmetrical distribution of k(Tin) is obtained for cold-resp.…”