Silanols cured by borates as lubricants in extrusion of LLDPE. Impact of elasticity of the lubricant on sliding friction |
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Authors: | Oleg Kulikov Klaus Hornung Manfred Wagner |
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Institution: | 1.Universit?t der Bundeswehr München,Neubiberg,Germany;2.Fachgebiet Polymertechnik/Polymerphysik,TU Berlin,Berlin,Germany |
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Abstract: | Addition of a viscoelastic material based on silanols cured by boron oxide was used to delay sharkskin and stick–slip instabilities
in extrusion of linear low-density polyethylene (LLDPE). Delay of flow instabilities to rates of extrusion 25–35 times higher
than without additive and about 40% less extrusion pressure at the same throughput are achieved by the use of this material
as an additive (∼0.1%) to LLDPE or as a coating of the extrusion die. Mechanical properties of the lubricant were changed
by small variations of composition to investigate the impact of elasticity on lubrication and sharkskin delay. Both lubrication
and sharkskin delay were considerably improved when more elastic lubricants were used while the chemical composition of the
lubricants was nearly the same. Filling the lubricants with powders of metal oxides or especially particulates having plate-like
particles (kaolin, mica, BN) helped to delay the flow instabilities further to even higher throughputs. Together with experimental
results, we present a tentative explanation for the importance of elasticity of polymer processing aids in the delay of sharkskin
and the stabilization of slip.
This paper was presented at Annual European Rheology Conference (AERC) held in Hersonisos, Crete, Greece, April 27–29, 2006. |
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Keywords: | Sharkskin Stick-slip Melt fracture Polymer processing additives Elasticity Shear cracks |
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