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Licensed Unlicensed Requires Authentication Published by De Gruyter 2016 (Print 1987)

A Collaborative Study of the Stability of Extrusion, Melt Spinning and Tubular Film Extrusion of some High-, Low- and Linear-Low Density Polyethylene Samples

  • James L. White and Hideki Yamane

Abstract

A comparative study by several industrial and academic laboratories of the shear and elongational rheological behavior and unstable processing behavior of a series of well characterized linear and branched polyethylene is reported. The processing operations investigated were flew through a die, melt spinning and tubular film extrusion. Broadening molecular weight distribution in the linear polyethylenes increased deviations from Newtonian flow, increased elastic memory and decreased filament stability in elongational flow. It also deteriorated melt spinning stability but broadened the range of stable operation in tubular film extrusion. Extrudate distortion occurred at the same critical die wall shear stress, but the characteristics of the unstable region were changed. Long chain branched polyethylenes exhibited generally enhanced elastic memory, greater stability and deformation rate hardening in uniaxial extension. Melt spinning and tubular film extrusion characteristics were stabilized relative to linear polyethylenes, but extrudate distortion first occurred at a lower shear stress. The unstable extrusion characteristics were quite different from the linear polyethylenes. The linear low density polyethylene investigated generally responded similarly to a linear polyethylene of about the same molecular weight distribution.

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