Study on rheological behavior of polymer melt flowing through micro-channels considering the wall-slip effect

Abstract

Micro molding is attracting more attention nowadays and determination of the rheological behavior of the polymer melt within micro structured geometry is considered to be very important for the accurate simulation modeling of micro molding. The lack of commercial equipment is one of the main hurdles in the investigation of micro melt rheology. In this study, the melt viscosity measurement system for PS (polystyrene) melt flowing through a micro-channel was established using a micro-channel mold operated at a mold temperature as high as the melt temperature. From measured pressure drop and volumetric flow rate both the capillary flow model and the slit flow model were used for the calculation of viscosity utilizing Rabinowitsch and Walters corrections. It was found that the measured viscosity values in the test ranges are significantly lower (decreased by a factor of about 1.4–4.1) than those obtained from the traditional capillary rheometer at a melt temperature of 200 °C using both the capillary flow model and the slit flow model. As the micro-channel size decreases, the reduction in the viscosity value increases when compared with data obtained from the traditional capillary rheometer. The ratio of slip velocity relative to mean velocity was also found to increase with decreasing size of micro-channels. It seems that wall slip plays a dominant role when melt flows through micro-channels and would result in a greater percentage in apparent viscosity reduction when the size of the micro-channel decreases. In addition, the wall-slip effect becomes more significant as the melt temperature increases. In the present study we emphasize that the rheological behavior of the melt in the microscopic scale is different from that of the macroscopic scale and that current simulation packages are not suitable for micro molding simulation without considering this difference.

Characterization of thermo-rheological behavior of polymer melts during the micro injection moulding process

“…Generally, wall slip can reduce the shear stress needed to force a polymer melt thought the slit cavities and consequently can serve to reduce the viscosity. Experimental work by Chien et al [9] and simulation by Yao & Kim [24] both confirm that wall slip can significantly reduce the viscosity of polymer melts.…”

“…This was attributed to molecular structure. Chien et al [9] developed a series of micro-channels in a die that was embedded in a mold in order to study the rheological behavior of polymer melts under isothermal conditions using an injection molding machine. They found that the viscosity of polymer melts in the micro-channels is significantly lower than that measured when using a conventional capillary rheometer.…”

The Micro Injection Moulding Process for Polymeric Components Manufacturing

“…Recent investigations report a series of measurement of melt viscosity within small dimension geometries using high-fluidity amorphous ABS and PS resin [28,29], and high-low density PE, as well as high crystallinity POM resin [30]. From the measured pressure drop obtained from pressure transducers and melt volumetric flow rate, it is possible to calculate the viscosity values.…”

On the performance of a viscoelastic constitutive model for micro injection moulding simulations

“…The rheological data used in current packages are obtained from macroscopic experiments and they are not suitable for modelling microscale flows. In fact, when flowing in micro channels a polymer has a strong tendency to slip [3]. If a classic no-slip boundary condition is used in current packages, the consequences of wall slip cannot be predicted.…”