Nonisothermal Crystallization Kinetics of an Ethylene-Vinyl-Acetate: I Calorimetry Versus Rheology

The knowledge of the thermo-mechanical response of polymers during crystallization is of seminal importance for process control and modeling. Among the other subtle findings, the crystallinity-rheological simplicity, resembling the thermo-rheological one, was frequently reported, based on the observation that the same amount of crystallinity induces the same rheological hardening to the polymer, regardless the crystallization conditions. The crystallization kinetics, which is a fundamental issue in polymer science, is investigated with differential scanning calorimetry (DSC) measurements. However, the poor agreement of calorimetric data with data coming from rheological investigation remains a debated issue. The crystallization kinetics of a commercial poly-ethylene-vinyl-acetate copolymer (EVA) is here investigated both with DSC and rheological measurements. EVA is a nice model system since its melting point is below 100[degrees]C, thus allowing avoiding all the experimental shortcomings related to thermal degradation. We show that DSC and rheological crystallization data satisfactorily agree for the investigated copolymer and thus we conclude that all the discrepancies found in the literature must be principally due to experimental artifacts. Moreover, the observed agreement between DSC and rheological data confirms that the rheological hardening is proportional to the volume of crystallites only and not to the modality in which the crystallization takes place.
INTRODUCTION The process technologies of semi-crystalline polymers require a deep understanding of crystallization kinetics that dominate the quality and the performances of the final products. Depending on the processing techniques [...]