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On the effects of very low levels of long chain branching on rheological behavior in polyethylene
Author(s) -
Bersted B. H.
Publication year - 1985
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1985.070300916
Subject(s) - branching (polymer chemistry) , rheology , polyethylene , peroxide , materials science , activation energy , thermodynamics , polymer chemistry , chemistry , composite material , organic chemistry , physics
A comparison is made of the effects of very low levels of long chain branching (less than 0.1 branch per 1000 CH 2 ) on the rheological behavior of polyethylene for samples, in which the branching has been introduced by means of peroxide decomposition or thermal‐mechanical degradation. Both the activation energy and viscosity at low rates are shown to increase considerably more rapidly with branching level for samples containing branching formed from peroxide decomposition than for samples containing branching formed as a result of thermal or mechanical degradation. A model, which is based on parameters obtained for highly branched low density polyethylene and experimental molecular structure measurements, is shown to adequately account for the flow curves of samples containing branching introduced by thermal or mechanical degradation. Poor agreement of the model with experimental flow curves for peroxide branched samples is obtained, presumably because of the inability of the low density polyethylene parameters to adequately describe the flow properties of these samples, which are thought to contain tetrafunctional branch points. The good agreement between theoretical models, predicting relationships between activation energy and branching level, and experimental data is taken as lending further credence to the idea that the large variations seen in the rheological behavior with branching concentration at low branching levels are due to changes in the relative proportion of discrete branched and linear species with branching level. In accord with experimental results, a maximum in low rate viscosity with branching level is predicted. The maximum is predicted at approximately 0.25 branches/1000 CH 2 .