Recoverable compliance behavior of high‐density polyethylenes

Abstract

SynopsisEight samples of high-density polyethylene with weight-average molecular weights ranging from 5.5 X lo4 to 17.3 X lo4 have been studied. In addition to GPC molecular weight characterization, the recoverable compliance, the shear viscosity, and the extrudate swell were determined a t temperatures between 138 and 200°C. The range of the maximum creep stresses ranged from 60 to 1840 dynes/cm2. The creep recovery response was in the linear or near-linear range. The results are interpreted in the light of the anomalous results of Mendelson and Finger.

Deriving comprehensive structural information on long-chain branched polyethylenes from analysis of thermo-rheological complexity

“…In the last years, the analysis of the complex modulus, viscosity, and compliance as a function of time or shear rate/frequency dependencies as well as the analysis of relaxation spectra have added knowledge to the behavior of LCB-PE [34,[37][38][39][40][41][42][43][44][45][46][47][48][49]. Other quantities used for the rheological analysis of LCB-PE include the recoverable compliance [43,47,[50][51][52][53][54] and the strain-hardening in elongation induced by long-chain branches [16,[55][56][57][58][59]. However, except for the η0-Mw-relation, the abovementioned indicators are influenced additionally by the molar mass distribution in a non-trivial way and so far it has not been possible to clearly distinguish between effects of branching and molar mass distribution in rheology as both have rather similar behavior.…”

Linear Viscoelastic Characterization of Polymer Melts with Long Relaxation Times

“…Another proof that this condition is fulfilled is the overlapping of data from shear oscillations and creep, as will be shown in Figure . Plazek and Raghupathi used for their “complete” creep tests with melts of HDPE a shear stress of 15 N/m 2 at 138 °C and concluded that under this condition their HDPE samples respresented linear viscoelastic behavior for times shorter than 1000 s and, furthermore, that “...the departure of the higher molecular weight samples from linear behavior is deferred to longer times...” …”

“…Rheological studies of melts of linear polyethylene (HDPE) are rare in the literature , despite the practical importance of this material in polymer engineering and as a reference melt for theoretical studies. Already in 1969 Lee pointed out that at a temperature of 220 °C in a start-up test (step function shear rate) different HDPE samples did not show a constant equilibrium shear stress but instead the shear stress, after some tendency to level-off, started to steadily increase again.…”

Gapwise density distributions in injection‐molded poly(methylmethacrylate)

“…A qualitative explanation for that difference comes from the difference in the relaxation times for orientation and density. The latter is part of the so-called (Y relaxation, which always has shorter relaxation times, since it is a precursor of the entropy elastic orientational relaxation (21)(22)(23). This means that when one talks about a vitrifying layer during molding, one has to distinguish between the freezing-in of orientation and the freezing-in of the excessive compression.…”