Non-isothermal crystallization of polyvinylalcohol-co-ethylene

Abstract

Non-isothermal crystallization of polyvinylalcohol-co-ethylene with different ethylene contents was studied. Several models were used to predict the crystallization behavior of these materials under non-isothermal conditions at a constant cooling rate. Kinetic parameters determined from isothermal date were employed. Experimental data were in accordance with model prediction at low cooling rate and relative degree of crystallization lower than 0.8, but it did not fit at high cooling rate.Kinetic parameters obtained by using a non-linear regression method, i.e, Kamal's model and Dietz's modification, were able to describe better the non-isothermal crystallization behavior of the studied materials. The full model, that takes into account the induction and growth of the crystal during cooling under non-isothermal conditions was used to obtain a continuous cooling transformation diagrams for polyvinylalcohol -co-ethylene.Finally, non-isothermal models, coupled with the proposed expressions for induction time and kinetic constant, were used to represent the development of crystallinity during the processing of the polymer.

Determination of non-isothermal crystallization rate constant of a rotational molding grade LLDPE

“…The nonlinear regression method can be used for obtaining the parameters of kinetic crystallization models, such as Nakamura's [1,2], Kamal and Chu's [3], Dietz [4] and Malkin's [5], directly from the nonisothermal crystallization data obtained by Differential Scanning Calorimeters. Results of this method are usually considered good.…”

“…Results of this method are usually considered good. However, literature mentions unsatisfactory results related to nonlinear regression, but this behavior is more likely associated to limitations of the crystallization model in describing the nonisothermal crystallization process of the polymer than by the nonlinear regression method itself [4,7]. One advantage of nonlinear regression is that its procedure for calculating the crystallization kinetic constant is faster than the master curve approach [8].…”

Determination of non-isothermal crystallization rate constant for pseudo-experimental calorimetric data

“…The nonlinear regression method is being used as an alternative way of obtaining the parameters for kinetic crystallization models, such as Nakamura's 10,11 , Kamal and Chu's 12 , and Dietz 13 and Malkin's 14 , directly from the non-isothermal crystallization data obtained by DSC. In most cases, the results obtained through this method are considered good.…”

“…In most cases, the results obtained through this method are considered good. The literature contains reports of unsatisfactory results related to nonlinear regression; however, these unsatisfactory results are more likely to be justified by the limitations of the model of crystallization kinetics in describing the non-isothermal crystallization of the polymer than by the nonlinear regression method itself 13,15 . One advantage of nonlinear regression is that it requires less work than the master curve approach.…”

“…One advantage of nonlinear regression is that it requires less work than the master curve approach. However, in order to perform nonlinear regression, which is usually based on the Leven-Marquardt 12,13 method, sophisticated software is indispensable. The master curve approach has the advantage that it can be applied through any electronic spreadsheet.…”