Capillary flow of low‐density polyethylene

Abstract

The capillary flow of a commercial low-density polyethylene (LDPE) melt was studied both experimentally and numerically. The excess pressure drop due to entry (Bagley correction), the compressibility, the effect of pressure on viscosity, and the possible slip effects on the capillary data analysis have been examined. Using a series of capillary dies having different diameters, D, and length-to-diameter L/D ratios, a full rheological characterization has been carried out, and the experimental data have been fitted both with a viscous model (Carreau-Yasuda) and a viscoelastic one (the Kaye-Bernstein, Kearsley, Zapas/Papanastasiou, Scriven, Macosko, or K-BKZ/PSM model). Particular emphasis has been given on the pressure-dependence of viscosity, with a pressure-dependent coefficient b p . For the viscous model, the viscosity is a function of both temperature and pressure. For the viscoelastic K-BKZ model, the time-temperature shifting concept has been used for the non-isothermal calculations, while the time-pressure shifting concept has been used to shift the relaxation moduli for the pressure-dependence effect. It was found that only the viscoelastic simulations were capable of reproducing the experimental data well, while any viscous modeling always underestimates the pressures, especially at the higher apparent shear rates and L/D ratios. POLYM. ENG. SCI., 52:649-662, 2012. ª

Capillary Extrusion and Swell of a HDPE Melt Exhibiting Slip

“…When B s l ≈1, we have macroscopically obvious slip. For the present data, we get 0.442 < B s l < 1, showing a strong slip effect in the range of simulations, again unlike the LDPE melt, which shows no slip 39. It should be noted that the other HDPE‐42 used in our recent paper29 has similar slip behavior but a higher slip exponent b = 5.73.…”

“…This is defined as When B p =0, we have no pressure dependence of the viscosity. For the present data, we get 5.3 × 10 −4 < B p < 1.6 × 10 −3 , showing a weak dependence of viscosity on pressure in the range of simulations, unlike the LDPE melt 39. More details are given in Table IV.…”

50 Years of the K-BKZ Constitutive Relation for Polymers

“…These functions are independent of the strain-memory function (hence separability of the functions or factorized K-KBZ model), and only and can be determined from dynamic data of the viscoelastic moduli. As an example we give in Figure 4 and Table 1 the fitting of experimental and data for an LDPE melt [45] and an HDPE melt [46], where it is shown that a spectrum of 8 relaxation times, ranging from 10 −4 s to 10 +3 s, is able to capture well the data at all frequencies. It should be noted that the fitting is not very difficult and can be done even with an MS Excel software, provided that one uses a reasonable number of relaxation times (8 for polymer melts or 3 for polymer solutions) with initial guesses for the relaxation times submultiples or multiples of 10 and appropriate initial guesses for the relaxation moduli [30,47].…”

Comparisons of the rheological behaviors of polypropylene and polymethyl methacrylate in a capillary die

“…By comparing the experimental data with the results from finite element analysis software, MoldFlow Part Advisor, they found that the analysis software was not suitable for predicting the filling flow in a 0.5‐mm diameter channel. Ansari et al . studied the capillary flow of a commercial low‐density polyethylene (LDPE) melt both experimentally and numerically.…”