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Flow Activation Energy (flow + activation_energy)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

Influence of Short-Chain Branching of Polyethylenes on the Temperature Dependence of Rheological Properties in Shear

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 22 2007
Florian J. Stadler
Abstract This contribution describes the influence of short-chain branching on the temperature dependence of rheological properties of polyethylene (PE) melts in shear. The materials investigated are linear and short-chain branched, metallocene-catalyzed PEs of narrow molecular mass distribution. The linear viscoelastic properties are determined by dynamic-mechanical analysis. Short-chain branching (SCB) leads to an increase of the flow activation energy. The activation energy was found to increase linearly with rising weight comonomer content. [source]

Rheological characterization of HDPE/sisal fiber composites

POLYMER ENGINEERING & SCIENCE, Issue 10 2007
Smita Mohanty
The present paper summarizes an experimental study on the molten viscoelastic behavior of HDPE/sisal composites under steady and dynamic mode. Variations of the melt viscosity and die swell of the composites with an increase in shear rate, fiber loading, and coupling agent concentration have been investigated using capillary rheometer. The shear rate , at the wall was calculated using Rabinowitsch correction applied to the apparent shear rate values. It was observed that the melt viscosity of the composites increased with the addition of fibers and maleic anhydride-grafted PE (MAPE). Die swell of HDPE also decreased with the addition of sisal fibers and MAPE. Further, the dynamic viscoelastic behavior of the composites was measured employing parallel plate rheometer. Time,temperature superposition was applied to generate various viscoelastic master curves. Temperature sweeps were also carried out to study the flow activation energy determined from Arrhenius equation. The fiber,matrix morphology of the extrudates was also examined using scanning electron microscopy. POLYM. ENG. SCI., 47:1634,1642, 2007. © 2007 Society of Plastics Engineers [source]

Chemorheological analysis of an epoxy-novolac molding compound

POLYMER ENGINEERING & SCIENCE, Issue 2 2000
T. H. Hsieh
The chemorheological behavior of an epoxy-novolac molding compound was studied by a combination of differential scanning calorimetry and dynamic rheological measurements. Based on a modified version of Kamal and Sourour's kinetic expression, a procedure aiming at the phenomenological description of cure kinetics was developed. In combination with our kinetic study, an empirical Arrhenius-type expression was adopted for the description of the dependence of complex viscosity on temperature, frequency, and conversion by allowing the pre-exponential factor and the flow activation energy to be frequency- and conversion-dependent. At low conversions (, < ,0.05), the system behaves approximately as a thermoplastic material; at higher conversions, the rheological behavior of the system was dominated by the extent of cure reaction. [source]

Ultrasonic improvement of rheological and processing behaviour of LLDPE during extrusion

POLYMER INTERNATIONAL, Issue 1 2003
Shaoyun Guo
Abstract The effects of ultrasonic oscillations on die pressure, productivity of extrusion, melt viscosity and melt fracture of linear low density polyethylene (LLDPE) as well as their mechanism of action were studied in a special ultrasonic oscillation extrusion system developed in our Laboratory. The experimental results showed that, in the presence of ultrasonic oscillations, the melt fracture or surface distortion of LLDPE extrudate is inhibited or disappears. The surface appearance of the LLDPE extrudate was greatly improved. The productivity of LLDPE extrudate was increased in the presence of ultrasonic oscillations. The die pressure, melt viscosity and flow activation energy of LLDPE decreased with the rise in ultrasonic intensity. The shear sensitivity of LLDPE melt viscosity decreased due to the increase of its power law index in the presence of ultrasonic oscillations. Inducing ultrasonic oscillations into LLDPE melt greatly improved its processability. A possible mechanism for the improved processibility is proposed. © 2003 Society of Chemical Industry [source]