Nucleated solution flow models have been previously developed by Baldwin and coworkers to aid modular design of the foam extrusion process. A framework of previously developed design models is applied here to investigate the flow of nucleated polypropylene–CO2 solution system. Refinement to the design models is introduced through viscosity reduction factors and Redlich‐Kwong equation of state to describe nonideal gas. These models incorporate temperature and concentration dependency of viscosity, surface tension, and solubility. Simulated results of pressure profiles and volumetric flow rates using a power law rheological equation are compared with experimental values from a three pressure tapping slit die. The influence of temperature on the profiles and its effect on design models is discussed. Preliminary results show that temperature plays an important role in the categorization of process design models. POLYM. ENG. SCI., 46:751–762, 2006. © 2006 Society of Plastics Engineers

The parallel-disk viscometer is a widely used instrument for measuring the rheological properties of Newtonian and non-Newtonian fluids. The torque-rotational speed data from the viscometer are converted into viscosity and other rheological properties of the fluid under test. The classical no-slip boundary condition is usually assumed at the disk-fluid interface. This leads to a simple azimuthal flow in the disk gap with the azimuthal velocity linearly varying in the radial and normal directions of the disk surfaces. For some complex fluids, the no-slip boundary condition may not be valid. The present investigation considers the flow field when the fluid under test exhibits wall slip. The equation for slow steady azimuthal flow of Newtonian fluids in parallel-disk viscometer in the presence of wall slip is solved by the method of separation of variables. Both linear and nonlinear slip functions are considered. The solution takes the form of a Bessel series. It shows that, in general, as a result of wall slip the azimuthal velocity no longer linearly varies in the radial direction. However, under conditions pertinent to parallel-disk viscometry, it approximately remains linear in the normal direction. The implications of these observations on the processing of parallel-disk viscometry data are discussed. They indicate that the method of Yoshimura and Prud’homme (1988, “Wall Slip Corrections for Couette and Parallel-Disk Viscometers,” J. Rheol., 32(1), pp. 53–67) for the determination of the wall slip function remains valid but the simple and popular procedure for converting the measured torque into rim shear stress is likely to incur significant error as a result of the nonlinearity in the radial direction.

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The blown film process with polymer melts is modelled using nonisothermal viscoelastic rheological constitutive equations that are suitable for polyolefins. The model correlates the operating parameters such as mass flows, extruder temperature, tensile axial force and takeup force on processes such as bubble geometry and bubble temperature profile. Unlike Luo and Tanner [Poly. Eng. Sci., Vol. 25, 1985] who used the Maxwell constitutive equation, this study considers the viscoelastic Kelvin model that avoids any assumption regarding stress at the die exit. Like Luo and Tanner, the model uses shooting techniques