Master curve approach to polymer crystallization kinetics

Abstract

Nonisothermal crystallization kinetic data obtained from differential scanning calorimetry (DSC) for a poly(ethylene terephthalate) are corrected for the effects of temperature lag between the DSC sample and furnace using the method of Eder and Janeschitz‐Kriegl which is based on experimental data alone without resort to any kinetic model. A method is presented for shifting the corrected nonisothermal crystallization kinetic data with respect to an arbitrarily chosen reference temperature to obtain a master curve. The method is based on experimental data alone without reference to any specific form of kinetic model. When the isothermal crystallization kinetic data for the same material are shifted with respect to the same reference temperature, a master curve is also obtained which overlaps to a large extent the corresponding master curve from nonisothermal data. It follows that nonisothermal DSC measurements provide the same crystallization kinetic information as isothermal DSC Measurements, only over a wider range of temperatures. The shift factors obtained from experimental data alone are compared in turn with the corresponding values calculated from the Avrami equation, the Hoffman‐Lauritzen expression, and the Nakamura equation as a means of evaluating these models individually. It is concluded that the Avrami equation is very good at describing isothermal crystallization kinetics, the Hoffman‐Lauritzen extrapolation of the limited isothermal data to a wide range of temperatures is quite good, and the Nakamura equation yields reliable crystallization kinetic information over a narrower range of temperatures than nonisothermal data alone without using any specific model.

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

“…Otherwise, (dθ/dt) t = 0 will be zero and θ t + Δt will always be zero, as clearly demonstrated by Galera et al [8]. They showed that θ t = 0 equal to 10 -3 was a good value to be used instead of 10 -14 suggested by Chan [10]. Therefore in the present study it was tested 10 -3 , 10 -4 and 10 -14 as the initial crystallinity in the Nakamura's model.…”

“…About 3.0 mg of the material, sealed in an aluminum pan, was heated to 200°C and held at this temperature for 5 minutes before cooling at different rates (50, 40, 30, 20, 10 and 5 °C/min) to 30°C under nitrogen atmosphere. According the procedure recommended by Isayev et al [10][11][12] the experiments were carried out with the same sample for all the six cooling rates in order to obtain good repeatability for the heat transfer conditions between DSC furnace and the aluminum pan.…”

Cristalização não isotérmica de poliamida 66: Determinação dos parâmetros da Equação de Nakamura via Método da Curva Mestre

“…Os dados de K(T) versus T podem então ser ajustados a uma equação do tipo Hoffman & Lauritzen [8,14] representada pela equação 10:…”

“…Entretanto, como já mencionado, estes experimentos isotérmicos só são possíveis em temperaturas mais elevadas, em condições bem distantes das observadas nas cristalizações em condições de processamento, sendo necessária grande extrapolação. Assim, para diminuir a extensão desta extrapolação, Isayev et al [8] propuseram o método da Curva Mestre ("Master Curve Approach") para determinar a constante cinética de cristalização não-isotérmica, K(T). Este método emprega experimentos de cristalização não-isotérmica obtidos por Calorimetria Exploratória Diferencial, DSC, a diferentes taxas de resfriamento, permitindo a obtenção dos parâmetros cinéticos em temperaturas mais baixas que os experimentos isotérmicos.…”

P80 SRM low torque flex-seal development − thermal and chemical modeling of molding process

“…Classical polynomial or purely phenomenological models such as Isayev model [3] widely used for reticulation modeling fail to address correctly the main phenomena of sulphur vulcanization, i.e., induction time, acceleration of cross-linking, and reversion. The reason is that such models do not rely on any chemical consideration.…”