Wall slip peculiarities in PVC processing

Autori: J.M. Maia, J.A. Covas
Presentato al: Southern Europe Conference on Rheology
Anno: 1999
Volume: 1
Issue: Unico
Casa Editrice: SIR-Cuen Napoli
Lingua: English


Abstract
The anomalous rheological behaviour of PVC ‘melts’ is dictated by the presence of additives, by the complex polymer particle hierarchy and by the range of practical operating conditions (which do not, in general, induce the complete melting of the ordered material). In practice, this behaviour produces strong non-Newtonian characteristics, such as time dependence, non-linear temperature dependence and an small die-swell, amongst others.
Most of the above phenomena are induced by the supermolecular nature of PVC melts present in the practical processing range. In fact, the flow of a PVC compound is a suspension of molecular flow containing solid additives, primary particles and eventual remains of original PVC grains; these will affect both the flow conditions at the wall and in the bulk. Most of these phenomena are well-known by processors, but there is only limited quantitative information and, also, little is known on the effects of specific additives.
This work aims at improving upon the current understanding of wall-slip during the flow of PVC compounds, namely by trying to identify the physical mechanisms that are relevant to its occurrence.


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