Non-Isothermal Crystallisation Kinetics of Polypropylene at High Cooling Rates and Comparison to the Continuous Two-Domain pvT Model.

Jonathan Alms,Jian Wang,Tobias Hohlweck,Christian Hopmann

doi:10.3390/polym12071515

Jonathan Alms, Jian Wang + Show 2 more

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https://doi.org/10.3390/polym12071515

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Abstract

The modelling of the correlation between pressure, specific volume and temperature (pvT) of polymers is highly important for applications in the polymer processing of semi-crystalline thermoplastics, especially in injection moulding. In injection moulding, the polymer experiences a wide range of cooling rates, for example, 60 °C/min near the centre of the part and up to 3000 °C/min near the mould walls. The cooling rate has a high influence on the pvT behaviour, as was shown in the continuous two-domain pvT model (CTD). This work examined the Hoffman–Lauritzen nucleation and growth theory used in the modified Hammami model for extremely high cooling rates (up to 300,000 °C/min) by means of Flash differential scanning calorimeter (DSC) measurements. The results were compared to those of the empirical continuous two-domain pvT model. It is shown that the Hammami model is not suitable to predict the crystallisation kinetics of polypropylene at cooling rates above 600 °C/min, but that the continuous two-domain pvT model is well able to predict crystallisation temperatures at high cooling rates.

Highlights

The prediction of the correlation between pressure, specific volume and temperatureof polymers is highly important for applications in the polymer processing of semi-crystalline thermoplastics, especially in injection moulding
Of polymers is highly important for applications in the polymer processing of semi-crystalline thermoplastics, especially in injection moulding
In order to within Hoffman–Lauritzen theory (HL) is based on quiescent conditions present during cooling. It can be stated from the results enable a precise description of crystallization at all injection moulding-relevant cooling rates, a model in Figure 7 that the cooling of isotactic polypropylene (iPP) with 3000 °C/min and above can no longer be treated as quiescent for dynamic processes must be developed from thermodynamics at non-quiescent conditions

Summary

Introduction

The prediction of the correlation between pressure, specific volume and temperature (pvT)of polymers is highly important for applications in the polymer processing of semi-crystalline thermoplastics, especially in injection moulding. The Tait model is widely used for polymers because of its high fit accuracy and simple form [5,6,7,8,9]. Wang et al [10] improved the Tait model to even higher fitting accuracy due to the consideration of second-order polynomials. It removes the discontinuity at the transition temperature between the models for the molten and solid states (two domains). This leads to accurate data prediction during the injection moulding simulation, since a small change in temperature around the transition temperature causes significant changes in the specific volume. The discontinuity is solved by enforcing the model of Polymers 2020, 12, 1515; doi:10.3390/polym12071515 www.mdpi.com/journal/polymers

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