ON THE DESIGN OF COEXTRUSION DIES FOR POLYMERIC MULTILAYER PRODUCTS

An effective way to synergistically combine the properties of individual polymers is to manufacture multilayer products, whose performance is directly linked to the individual layers thickness, which should be kept as uniform as possible [1]. Multilayer polymer coextrusion is a manufacturing process in which two or more polymers are fed to a common extrusion die to form a multilayered product [1]. The usual manufacturing approach begins by coextruding two layers that are duplicated in a number Interfacial Surface Generator (ISG) module [1], each one duplicating the number of layers. Each layer duplication operation is achieved by dividing the layered inlet flow into two individual streams, and them deforming and overlapping them to achieve a duplicated layer structure [1]. Due to the complex rheology of the materials employed and the intricate geometry of the ISG, it is usually difficult to assure the desired uniformity of the layers thickness. This work comprises a computational study carried out with the support of multiphase flow solvers from the OpenFOAM computational library interFoam. The main objective of the study is to improve the knowledge related to ISG geometry design, aiming to propose a number of design guidelines for these devices. Each ISG comprises several geometric transformations, which can be made simultaneously or sequentially, producing effects on the velocity fields that impact the layers uniformity. The simultaneous combination of geometrical transformations, allows reducing both the ISG length and, in general, the total pressure drop. However, when specific effects are combined, the layers tend to became unevenly distributed. To better understand the system behaviour, several configurations for the ISG were studied, aiming at identifying the geometry details that tend to promote a non-uniform layer distribution. The results obtained showed that just a few combinations of some geometric transformations do not affect the uniformity of the final product layer thickness distribution. The detailed analysis of the results obtained allowed, as desired, the identification of some guidelines to better design ISGs.

Acknowledgements The authors would like to acknowledge the funding by FEDER funds through the COMPETE 2020 Programme and National Funds through FCT - Portuguese Foundation for Science and Technology under the projects UIDB/05256/2020/UIDP/05256/2020 and TSSiPRO - Technologies for Sustainable and Smart Innovative Products (NORTE-01-0145-FEDER-000015). The authors also acknowledge the support of the computational clusters Search-ON2 (NORTE-07-0162-FEDER-000086) and Minho Advanced Computing Center (MACC). M.M. Martins would like to thank also the support of the University Centre - Catholic of Santa Catarina (Brazil).

References

[1] J. Dooley, Viscoelastic flow effects in multilayer polymer coextrusion. Ph.D. Thesis, Technische Universiteit Eindhoven, Eindhoven, 2002.