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The phenomenon of "extrudate fracture",
an obstacle in the industrial manufacturing of polymer fibers by extrusion
could not be explained until now. The root of this instability has just
been unearthed by a team at the Statistical Physics Laboratory (Laboratoire
de Physique Statistique, CNRS, Ecole Normale Supérieure and the
Universités de Paris 6 and 7), under the supervision of Daniel
Bonn, in partnership with the Lorentz Institute of the University of Leiden
in the Netherlands.
The arrival of polymer fibers revolutionized
the textile industry during the 1950's: photos of the day showed well-dressed
woman grabbing up "nylons" made by Dupont de Nemours. Since
that time and still today, the most popular manufacturing process used
for nylon is extrusion, and this is true for Kevlar, acrylic fiber and
polyamide as well. However, this industrial process has a serious shortcoming:
when these polymer fibers are manufactured, production speed is limited
by the appearance of a series of instabilities that lead to unwanted undulations
of the surface (see photo below). At even greater speeds, these undulations
become so pronounced that the fibers fracture, thus, the origin of the
expression, "extrudate fracture".
Researchers explain this phenomenon by the presence of "elastic turbulence"
in the die due to the visco-elastic nature of polymers. The flow causes
the polymer chains to stretch, leading to elastic stress. This elastic
stress can destabilize the flow, creating a sort of "elastic turbulence",
at the root of the instabilities observed at the outlet end of the spinneret
or the extrusion tube.
Now that this phenomenon has been explained, it is hoped that a process
can be found that will make it possible to increase extrusion speeds without
the appearance of this instability. This development is of interest to
major textile manufacturers since the textile industry produces 118 million
tons of plastic every year.
The results of this research can be found in
two publications, the first theoretical and the second experimental:
- Bernard Meulenbroek, Cornelis Storm,
Volfango Bertola, Christian Wagner, Daniel Bonn, Wim van Saarloos, "Origin
of melt fracture in polymer extrusion: a weakly nonlinear subcritical
instability of visco-elastic Poiseuille flow", Phys.Rev.Lett.,
90, 024502 (2003)
- Volfango Bertola, Bernard Meulenbroek, Christian Wagner, Cornelis Storm,
Wim van Saarloos, Daniel Bonn, "Melt fracture in polymer extrusion",
Phys.Rev.Lett., 90, 114502 (2003)
Researcher contact:
Daniel Bonn
Laboratoire de Physique Statistique
Tel: + 33 1 44 32 38 02
E-mail: bonn@pop.lps.ens.fr
http://www.lps.ens.fr/recherche/films-aux-interfaces/interests.html
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