Modeling film casting of polymers with crystallization along the draw line
Giuseppe Titomanlio, Gaetano Lamberti
University of Salerno
Italy

Keywords: Film Casting, Crystallization, modelling

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In the film casting process a polymer melt is extruded through a slit die, stretched in air and cooled on a chill roll. During the path in air, while the melt cools, a reduction of both thickness and width takes place.
In this work film casting experiments were carried out with an iPP supplied by Montell and on-line measurements of width, velocity, temperature and crystallinity distribution along draw direction were performed. Operating conditions were selected so as to have a relevant cooling and eventually crystallization along the draw line (during the path in air).
The film casting process was modeled adopting standard hypotheses and either a viscous Cross or a viscoelastic non linear Maxwell rheological description based on entanglement dynamics. Temperature distribution, considered constant in each cross section, was modeled accounting also of the generation due to polymer crystallization. Solidification was described as a sharp increase of both relaxation time and viscosity by effect of the growing crystallinity; also the effect of the flow on crystallization kinetics was taken in account.
Main features of the whole set of experimental data were reproduced by the viscous model; surprisingly, a worse comparison was obtained adopting the viscoelastic model. The hypotheses adopted are reconsidered on the basis of this result