Time Dependency of Extrudate Swell of Molten Polyethylene
Extrudate swell is of interest to rheologists because it is one of the very few readily measured properties that provide information on the elastic response of a melt to shearing at high strain rates. For a capillary, which is the flow normally used for rheological characterization, there is only one swell ratio, B ≡ D/Do, and this is usually represented as a function of wall shear rate or wall shear stress for steady flow. In fact, the swell ratio is also time-dependent, so that the swelling of an element of extrudate depends on the time which has elapsed since that element left the die. This introduces an element of uncertainty into the meaning of reported values of swell measured in the laboratory, and White and Roman1 have pointed out that measured values depend strongly on the details of the technique used.
KeywordsShear Rate Wall Shear Stress High Density Polyethylene Annular Flow Wall Shear Rate
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- 1.J.L. White and J.F. Roman, “Extrudate swell…”, J. Appl. Polym. Sci., 20:1005 (1976); 21, 869 (1977).Google Scholar
- 3.Data sheet G-14, Monsanto Co., Akron, Ohio, December 1976.Google Scholar
- 5.M.J. Crochet and R. Keunings, “Die swell of a maxwell fluid-numerical prediction”, J. Non-Newt. Fl. Mech., in press.Google Scholar
- 6.N. Sheptak and C. Beyer, SPE Journ., 21 (2): 190 (1965).Google Scholar
- 7.D. Kalyon, V. Tan and M.R. Kamal, “The dynamics of parison development in blow molding”, SPE Tech. Papers, 25:991 (1979) (to appear in Polym. Eng. & Sci.)Google Scholar
- 8.A. Garcia-Rejon, J.M. Dealy and M.R. Kamal, “Rheological comparison of four blow molding resins”, Can. J. Chem. Eng., in press.Google Scholar