The application of the multipass rheometer to time-dependent capillary flow measurements of a polyethylene melt

This communication presents experimental data on the time-dependent capilla ry flow measurements for a high-density polyethylene using a newly develope d multipass rheometer (MPR). The experimental data consist of precision pre ssure measurements on the MPR, which has well-defined fully constrained bou ndary conditions. A model developed previously by Molenaar and Koopmans [Mo lenaar, J. and R. J. Koopmans, J. Rheol. 38, 99-109 (1994)] and incorporati ng melt compressibility has been adapted to suit the MPR boundary condition s and is shown to give good agreement with the experimental data without ne cessitating the use of any arbitrary adjustable parameters. The results, in particular, show that the experimentally observed pressure relaxation on c essation of the piston movement can be almost entirely attributed to the co mpressibility of the melt alone and this conclusion is consistent with the findings reported by Hatzikiriakos and Dealy [Hatzikiriakos, S. G. and J. M . Dealy, Polym. Eng. Sci. 34, 493-499 (1994)] for related time-dependent ex trusion experimental observations using a conventional capillary rheometer. (C) 1999 The Society of Rheology. [S0148-6055 (99)00802-0].