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Abstract
This study presents a method for the determination of the dynamic pressure-dependent solidification of polycarbonate (PC) during flow using high pressure capillary rheometer (HPC) measurements. In addition, the pressure-dependent solidification was determined by isothermal pressure-volume-temperature (pvT) measurements under static conditions without shear. Independent of the compression velocity, a linear increase of the solidification pressure with temperature could be determined. Furthermore, the results indicate that the relaxation time at a constant temperature and compression rate can increase to such an extent that the material can no longer follow within the time scale specified by the compression rate. Consequently, the flow through the capillary stops at a specific pressure, with higher compression rates resulting in lower solidification pressures. Consequently, in regard to HPC measurements, it could be shown that the evaluation of the pressure via a pressure hole can lead to measurement errors in the limit range. Since the filling process in injection molding usually takes place under such transient conditions, the results are likely to be relevant for modelling the flow processes of thin-walled and microstructures with high aspect ratios.
Highlights
In the course of digitization and electrification, there is an increasing demand for components whose property profile can be adapted over a wide range to the respective application, while at the same time being manufactured economically in large quantities [1]
The solidification behavior of polymer melts at the glass transition as a function of temperature and time has already been investigated in terms of free volume using positron annihilation lifetime spectroscopy [10,15] and conventional pvT-measurements [8]
The Itlinear extrapolation to the of point with x-axis is marked by a cross, as shown in Figure should be noted that thepoint linear intersection with the x-axis does not mark the exact beginning of the solidification, since the difference extrapolation to the point of intersection with the x-axis does not mark the exact beginning of the from the pressure seems to from increase approx
Summary
In the course of digitization and electrification, there is an increasing demand for components whose property profile can be adapted over a wide range to the respective application, while at the same time being manufactured economically in large quantities [1]. Previous investigations on the pressure dependence of the glass transition are limited to specifying the time scale under consideration by a constant cooling rate in isobaric pressure-volume-temperature (pvT). The solidification behavior of polymer melts at the glass transition as a function of temperature and time has already been investigated in terms of free volume using positron annihilation lifetime spectroscopy [10,15] and conventional pvT-measurements [8]. The steady-state conditions which have always been the basis of previous investigations on the dependencies of glass transition do not reflect the real process either in micro injection molding or in CIS, since the material is not influenced statically but dynamically by pressure and temperature gradients. These measurements were carried out in overlapping temperature ranges to check the calculation of a master curve for implementation in existing simulation models
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