Capillary Flow of Polymers

To quantitatively describe the flow of polymer fluids through a small-diameter pipe, the following assumptions are necessary  

No-slip at the wall, i.e., the velocity of the polymer fluid at the wall of the pipe is zero. 

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Melt Fracture Instabilities in Capillary Flow of Polymer Melts. 

Ito, K., Tsutsui, M., Kasajima, M., and Ojama, T, Capillary flow of polymer melts under hydrostatic pressure, App/. Polym. Symp., 20, 109-122 (1973). 

Synthetic polymer fibers and manufactured natural polymer fibers typically are produced by melt, solution, dispersion, or gel spinning. In these processes, polymer fluids are extmded through dies to form one-dimensional fiber stmctures (Figure 8.11). The dies typically have small diameters so thin fibers can be obtained. As a result, in order to form fibers with desired structure and properties, it is critically important to understand the capillary flow of polymers, i.e., the flow behavior in a small-diameter pipe. 

Solution (Wet) Spinning. In the most widely used solution spinnerette system (60) the spinnerette consists of two concentric capillaries, the outer capillary having a diameter of approximately 400 ]Am and the central capillary having an outer diameter of approximately 200 ]lni and an inner diameter of 100 ]lni. Polymer solution is forced through the outer capillary while air or Hquid is forced through the inner one. The rate at which the core fluid is injected into the fibers relative to the flow of polymer solution governs the ultimate wall thickness of the fiber. Figure 19 shows a cross section of this type of spinnerette. 

So far in this chapter we have looked into the viscous phenomena associated with the flow of polymer melts in capillaries. We now turn to the phenomena that are related to melt elasticity, namely (a) swelling of polymer melt extrudates (b) large pressure drops at the capillary entrance, compared to those encountered in the flow of Newtonian fluids and (c) capillary flow instabilities accompanied by extmdate defects, commonly referred to as melt fracture. ... 

C. McLuckie and M. Rogers, Influence of Elastic Effects of Capillary Flow of Molten Polymers, J. Appl. Polym. Sci., 13, 1049 (1969). 

Flow of polymer melts through narrow tubes and capillaries... 

As discussed in more detail below, recent experiments convincingly showed that the flow oscillation in capillary extrusion of LPE is interfacial in nature due to a reversible coil-stretch transition at the melt/die wall boundary. Pressure oscillation phenomenon has also been reported in extrusion of other polymer melts. In particular, there are well-defined oscillations in controlled-rate capillary flow of PB that were found to arise from the same interfacial molecular instability [62]. 

So, if we measure the rate of flow of polymer solutions through capillaries we can get a measure of their viscosity. Two simple... 

We have already discussed one aspect of non-linear behavior in polymer melts, namely shear thinning. A second aspect manifests itself when we examine the flow of polymer melts through small diameter tubes or capillaries. This is the phenomenon of jet or die swelling, where a polymer forced into a narrow tube, diameter d0, swells when... 

Polymer viscosity is strongly shear dependent. If we use the bulk viscosity measured at different shear rates to describe the flow behavior in porous media, our first task is to calculate the shear rate which is equivalent to that in the bulk viscometer. To do that, we start with the capillary flow of a non-Newtonian fluid. 

Fig. 3.7. A setup scheme for studying capillary flow of liquids over the polymer coatings surface...

One can also mention the case of composites-based conducting polymers electrodeposited and characterized on anodes of platinum- or carbon black- filled polypropylene from a stirred electrolyte with dispersed copper phthalocyanine. The electrolytic solution contained, besides the solvent (water or acetonitrile), the monomer (pyrrole or thiophene) and a supporting electrolyte. Patterned thin films were obtained from phthalocyanine derivatives, as reported in the case of (2,3,9,10,16,17,23,24-oktakis((2-benzyloxy)ethoxy)phthalocyaninato) copper . Such films were prepared by means of capillary flow of chloroform solutions into micrometer-dimension hydrophobic/hydrophilic channels initially created by a combination of microcontact printing of octadecylmercaptan (Cig-SH) layers on gold electrodes. These latter gave birth to a hydrophobic channel bottom while oxidative electropolymerization of w-aminophenol (at pH 4) led to hydrophilic channel walls. 

Ouibrahim, A. Effect of capillary tube diameter in laminar flows of polymer solutions. 2nd Inter. Conf. on Drag. Reduction, Cambridge (1974) F4-43-56. 

E.E. Rosenbaum, S.G. Hatzikiriakos,Wall slip in the capillary flow of molten polymers subject to viscous heating,... 

Rosenbaum EE, Hatzikiriakos SG (1997) Wall slip in the capillary flow of molten polymers subject to viscous heating. AICKE J 43 598-608 Rubin II (1972) Injection molding-theory and practice. Wiley, New York Santhanam N, Chiang HH, Himasekhar K, Tuschak P, Wang KK (1991) Postmolding and load-induced deformation analysis of plastic parts in the injection molding process. Adv Polym Tech 11 77-89... 

The forced flow of polymer solutions or melts through capillaries or small orifices has as effect the appearance of shear forces, able to promote the scission of the main chain covalent bonds, causing the mechano-chemical degradation, which has as the first result the decrease of the polymer molecular weight. 

In general, both effects are not found to any extent in the flow of polymer melts through a capillary. 

Lyngaae-Jrrgensen. J. (1981) Domain stability during capillary flow of well dispersed two phases polymer blends. ACS. Org. Coat. Plast. Chem. 15. 174... 

Schott, H. (1964) Elastic effects and extrudate distortior s in capillary flow of molten polyethylene resins, J. Polym. Sci, 2, 3791-801. 

Wales, J.L.S. (1975) A collaborative study of capillary flow of a highly lubricated implasticized poly(vinyl chloride), J. Polym. Sci, S5mip. No. 50, 469-85. 

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