Journal
EUROPEAN POLYMER JOURNAL
Volume 44, Issue 8, Pages 2652-2658Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.eurpolymj.2008.05.028
Keywords
LDPE; degradation; light scattering; viscometry; GPC; rheology
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The influence of the repeated extrusion on the molecular parameters of low density polyethylene (LDPE) Bralen NA 7-25 was studied. Virgin polyethylene was submitted up to 20 extrusion cycles and the processed samples were fractioned using precipitation fractionation. Non-fractionated samples and the individual polymer fractions were characterized by their weight average molar masses M-w (static light scattering), number average molar masses M-n (osmometry) and limiting viscosity numbers fill (viscometry). Rheological properties in terms of shear viscosity curve, zero shear viscosity and flow activation energy were also determined by using high pressure capillary rheometer. The course of the changes in molecular parameters of LDPE is influenced both by the initial polymer structure and by the changes induced by the mechano-chemical degradation. The suggested degradation mechanisms during multiple extrusion of Bralen are chain scission predominating in the early stage of processing followed by recombination of macromolecules resulting in crosslinking and formation of microgel. which is clearly notable for the samples extruded 3-20 times. (c) 2008 Elsevier Ltd. All rights reserved.
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