Fingerprinting the processing behavior of polyethylenes from transient extensional flow and peel experiments in the melt state

The flow curves of linear (linear-low and high density) and branched polyethylenes are known to differ significantly. At increasing shear rates, the linear polymers exhibit a surface melt fracture or sharkskin region that is followed by an unstable oscillating or stick-slip flow regime when a consta...

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Bibliographic Details
Published in:Rheologica acta 2004-12, Vol.44 (1), p.1-15
Main Authors: SENTMANAT, Martin, MULIAWAN, Edward B, HATZIKIRIAKOS, Savvas G
Format: Article
Language:English
Subjects:
Applied sciences
Exact sciences and technology
Experiments
Extrusion moulding
Fingerprinting
Flow-density-speed relationships
Machinery and processing
Melt fracture
Moulding
Orange peel
Peel strength
Plastics
Polyethylene
Polyethylenes
Polymer industry, paints, wood
Shear
Slip flow
Technology of polymers
Tensile stress
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Summary:The flow curves of linear (linear-low and high density) and branched polyethylenes are known to differ significantly. At increasing shear rates, the linear polymers exhibit a surface melt fracture or sharkskin region that is followed by an unstable oscillating or stick-slip flow regime when a constant piston speed capillary rheometer is used. At even higher shear rates, gross melt fracture appears. Unlike their linear counterparts, branched polyethylenes rarely exhibit sharkskin melt fracture and although gross melt fracture appears at high shear rates there is no discontinuity in their flow curve. The various flow regimes of these two types of polyethylenes are examined by performing experiments in the melt state using a unique extensional rheometer (the SER by Xpansion Instruments) that is capable of performing accurate extensional flow and peel experiments at very high rates not previously realized. The peel strength curves of these linear and branched polyethylenes exhibit all of the distinct flow regimes exhibited in their respective flow curves, thereby providing a fingerprint of their melt flow behavior. Moreover, these extensional flow and peel results in the melt state provide insight into the origins and mechanisms by which these melt flow phenomena may occur with regard to rapid tensile stress growth, melt rupture, and adhesive failure at the polymer wall interface.
ISSN:0035-4511
1435-1528
DOI:10.1007/s00397-004-0398-z