Document Type : Original research

Author

• Ahmed Hamdi

New materials research laboratory, New Borg El Arab city, Alexandria, Egypt

Abstract

The effect of hydrostatic pressure on the viscosity of polymer melts plays a critical role in injection molding processes, particularly under high-pressure conditions typical of thin-walled and micro-scale components. Despite its importance, pressure-dependent viscosity data are often incomplete or unavailable in commercial simulation software, especially for semi-crystalline polymers such as polyolefins. In this study, the pressure dependence of viscosity for polypropylene (PP) and high-density polyethylene (HDPE) was investigated by analyzing rheological and volumetric parameters retrieved from the Moldflow material database. The coefficient describing the pressure effect on viscosity was evaluated using a thermodynamic approach based on polymer compressibility, thermal expansion, and the temperature dependence of zero-shear viscosity, and was compared with the corresponding parameter obtained from experimental rheological measurements embedded in the Cross–WLF viscosity model. A clear linear correlation was found between the estimated and experimentally derived pressure coefficients, with the former systematically exceeding the latter by a nearly constant proportionality factor. The proposed approach enables a simple determination of material parameters for injection molding simulations and contributes to improved prediction accuracy under high-pressure processing conditions

Keywords

• Polypropylene
• High density polyethylene
• pressure effect on viscosity
• compressibility

Main Subjects

• Plastics processing