Slip behavior of high-density polyethylene at small shear stresses in the presence of esterified polyethylene glycol

Abstract

Viscoelastic instabilities in polymer melts can be mitigated using polymer processing aids (PPAs) that impose slip between melts and substrates. In this study, the effect of a newly synthesized esterified polyethylene glycol (PEG) on the slip behavior of a high-molecular-weight high-density polyethylene at small shear stresses was investigated. Rheological measurements were employed to capture the dependence of slip velocities on shear stress and calculate extrapolation lengths and friction coefficients. Our findings showed that the incorporation of PEG-based PPA increased slip velocities while an increase at temperature suppressed slip. At 190 °C, there was a strong slip zone at shear stresses smaller than 9 kPa for all samples with and without PEG. In this zone, the extrapolation length showed ascending and descending behavior while its values were almost constant beyond this zone. The incorporation of PEG-based PPA at 190 °C doubled the extrapolation length from 300 to 600 μm and amplified its variation in the first zone. The study of the slip behavior at 210 °C revealed that the samples did not experience the first zone. They showed a second zone with extrapolation lengths well below 100 μm, signifying the presence of a weak slip regime. This study highlights the importance of PPAs in altering the slip mechanisms for high-molecular-weight polymer melts.