The Influence of Porous Media on the Flow of Polymer Melts in Capillaries†

Abstract

porous media placed in the entrance of capillaries were found to reduce the pressure drop across the capillaries (t>P,) by a factor of two or three for polystyrene. The reduction in t>P, was found to be a function of the distance of the porous media from the capillary entrance, the type of porous media, the length of the capillary, and the rheological properties of the polymer melt. No significant reduction in t>P, was observed for a polymer melt such as polyethyleneterephthalare (PET) which is nearly devoid of memory. The apparent shear rate for the onset of melt fracture was extended by a factor of three when polystyrene passed through the porous media before entering the capillary. No significant difference in die sweIJ values was observed with the use of porous media in the entrance of the capillaries. The mechanism which accounts for these phenomena is believed to be associated with the break up of the entanglement network in the porous medium which lemporarily changes the rheological properties of the polymer melt.

Extrusion Defects and Flow Instabilities of Molten Polymers

“…Therefore, when the temperature increases, the viscosity is lower and the critical stress is reached for a higher flow rate. As in the case of the oscillating defect, the presence of upstream filters stabilizes the flow and delays the onset of volume defects, but always at the expense of an increase in pressure (Done et al, 1983;Piau et al, 2000;Goutille and Guillet, 2002a). It seems that the disentanglement of the polymer chains when passing through the filters can explain this effect (Goutille and Guillet, 2002b).…”

“…As previously, some solutions, efficient at the laboratory scale, are not necessarily useful at the industrial level. For example, some authors (Done et al, 1983;Piau et al, 2000;Goutille and Guillet, 2002a) have proposed to install filters upstream of the die. It can be seen in Fig.…”

Effect of radial flow in the die entrance region on gross melt fracture of PDMS extrudate

“…However, Den Otter [17] underlined that the oscillations of the strand are of lower amplitude and higher frequency through the conical die as for the die with flat entrance. Another possibility studied by Done et al [19] and Piau et al [20] was to dispose of different kinds of porous media at the entrance of the die in order to diminish the elongational rates imposed on the flowing polymer in this contraction zone. Concerning Done et al [19] they studied the extrusion of a polystyrene (PS) and a polyethylene terephtalate (PET) through different axisymetric dies.…”

“…Another possibility studied by Done et al [19] and Piau et al [20] was to dispose of different kinds of porous media at the entrance of the die in order to diminish the elongational rates imposed on the flowing polymer in this contraction zone. Concerning Done et al [19] they studied the extrusion of a polystyrene (PS) and a polyethylene terephtalate (PET) through different axisymetric dies. They showed that the addition of porous media in the entry region was found to obviously increase the total pressure drop.…”

Numerical Analysis of Elongation Behavior of Melt Flow in Contraction Channels with Cylindrical Barriers

“…Actually, extrusion of polymer melts at high extrusion speed encounters various extrusion defects such as sharkskin, stick-slip and gross melt fracture, as clearly identified in the review by Petrie and Denn. 1) Considering the effect of filter or porous medium, it is interesting to note that the addition of filter or porous medium at the entrance of contraction can mitigate the gross melt fracture defect [2][3][4] , thus increases the possible speed for the process. However the mechanism of the phenomenon has been poorly understood yet, and further investigation is required.…”