High‐pressure viscosity and density of polyethylene solutions in n‐pentane

Abstract

SYNOPSISViscosity and density of homogeneous one-phase solutions (1 wt %) of polyethylenes with narrow molecular weight distributions ( M , = 2150, 15,520, 108,000, and 420,000) in npentane were determined at 398,413, and 428 K over a pressure range from 20 to 60 MPa. Measurements were done with a special falling cylinder type viscometer that permits simultaneous determination of viscosity, density, and phase state of the solutions. It is shown that the viscosities of these solutions can be correlated with density ( p ) using the exponential relationships p = A exp {B/(1 -V,p)} or p = C1 exp (C,p), which are based on free-volume considerations. Analysis of the temperature dependence of viscosity at fixed pressures, and its pressure dependence a t fixed temperatures show that the flow-activation energies for these solutions are in the range 8-12 kJ/mol, and the apparent activation volumes are in the range 30-45 cm3/mol. Evaluation of the specific viscosity and analysis of the molecular weight dependence of intrinsic viscosity in accordance with Mark-Houwink type relationship p = KM" suggest a value of 0.5 for the exponent a, which is typical of poor or theta solvents.

High-Pressure Viscosity and Density of Polymer Solutions at the Critical Polymer Concentration in Near-Critical and Supercritical Fluids

“…It is observed that flow activation energies show a small increase with increasing pressure which has also been observed by others [54,55] showing that at higher pressure the viscosity becomes more temperature dependent for this system. …”

“…The activation volumes increase with temperature but observed to decrease with pressure. Activation volumes are higher when compared with values reported for 1 wt % solutions of different molecular weight PE samples in n-pentane [54] that are shown in Table 5.10., which may be due to the higher concentration of the polymer. Ln(viscosity), mPa.s…”

“…The activation energy shows a maximum at 34.5 MPa, which has been observed for some other systems at critical polymer concentrations [62]. Table 5.6 shows the activation energies reported for 1 wt % solutions of PE (with M w = 2150, 15,520, 108,000) in n-pentane earlier by Kiran and Gokmenoglu [54]. The present values are higher as shown in Table 5.6.…”

“…With the growing interest in using near-critical and supercritical fluids in polymer synthesis and modifications, there is a growing need for basic and applied data on both the thermodynamic and the transport properties of polymer solutions at high pressures for successful design and implementation of processes [53][54][55][56][57].…”

“…Information on high-pressure viscosity of polymer solutions is of special importance in a variety of applications such as high-pressure lubrication, enhanced oil recovery, and processing of polymers using near and supercritical fluids [52][53][54][55]. With the growing interest in using near-critical and supercritical fluids in polymer synthesis and modifications, there is a growing need for basic and applied data on both the thermodynamic and the transport properties of polymer solutions at high pressures for successful design and implementation of processes [53][54][55][56][57].…”