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Linear low density polyethylenes and their blends: Part 3. Extensional flow of LLDPE's
Author(s) -
Schlund B.,
Utracki L. A.
Publication year - 1987
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760270511
Subject(s) - linear low density polyethylene , materials science , composite material , strain hardening exponent , rheometer , extensional definition , low density polyethylene , polyethylene , rheology , hardening (computing) , viscoelasticity , paleontology , layer (electronics) , biology , tectonics
The uniaxial extensional flow at 150°C of 11 linear low density polyethylenes (LLDPE) and one low density polyethylene was measured in a Rheometrics Extensional Rheometer. The presence of silicone oil did not affect the results. However, large effects of the molding time were observed. For specimens molded for 14 min, strain hardening was not observed for any gas‐phase polymerized LLDPE. As the molding time was increased to 40 min, the strain hardening was quite apparent, the elongational viscosity nearly doubled, the equilibrium plateau vanished, and the maximum strain at break Increased by about 20 percent. Explanation for the molding time effects can be found in the concept of low entanglement density in the virgin gas‐phase resins. The entanglement increases with time at temperatures above the melting point. The specimens molded for longer time show strain hardening.