Keywords: polymer extrusion, compounding, process modelling, twin-screw extruders.

Co-rotating twin-screw extruders are widely used by polymer materials producers and compounders as a result of the number of interesting constructive and functional features. The modular construction of screws and barrels provides great flexibility and adaptability to the particular requirements of each polymer system. Both are built from elements of various available types, thus allowing a good control of dispersive and distributive mixing, residence times, feeding sequence, etc. Therefore, in industrial practice the performance of twin screw extruders is dictated by the proper choice of the operating conditions (screw speed and output, which are controlled independently, and barrel temperature profile) and the screw configuration.

The optimization of such a system is a complex task, which is usually accomplished by experimental trial-and-error procedures (thus, not really ensuring that a true optimum has indeed been obtained). Nevertheless, many studies have contributed to a better understanding of the physical, thermal and rheological phenomena occurring in these machines [1,2,3,4,5,6,7,8,9,10,11]. Some attempts have also been made to develop optimization methodologies, able to define the best screw configuration and, or operating conditions for a given application, which are based on couplings between process modelling and optimization algorithms [12]. Unfortunately, most of these efforts have been compromised by the fact that the available modelling programmes are either too basic to provide precise or complete predictions, or are only capable of covering part of the process (usually melt conveying) [1,3,9].

This paper reports progress on the development of a global modelling program for co-rotating twin-screw extruders accounting for the entire process, i.e., from hopper to die (this is usually denoted as plasticating extrusion). It is organized as follows: initially, the relevant physical phenomena are identified and their mathematical description is presented briefly. Computer implementation is then presented. Finally, cases studies are used to discuss the influence of process parameters on performance measures.

A computer program able to take into account the main phenomena from hopper to die and process parameters of co-rotating twin screw extrusion was developed. In general, the predictions are in accordance with theoretical and experimental evidence, although direct comparison with experiments should be carried out in the next stage of the work.

1

J.L. White, "Twin Screw Extrusion; Technology and Principles", Hanser, Munich, 1990.

2

J.L White, A.Y. Coran, A Moet, "Polymer Mixing; Technology and Engineering", Hanser, Munich, 2001.

3

B. Vergnes, G. Della Valle, L. Delamare, "A Global Computer Software for Polymer Flows in Corotating Twin Screw Extruders", Polymer Engineering and Science, 38, 1781-1792, 1998. doi:10.1002/pen.10348

4

H. Potente, U. Melisch, K. P. Palluch, "A Physico-Mathematical Model for Solids Conveying in Co-Rotating Twin Screw Extruders", International Polymer Processing, XI, 29-41, 1996.

5

A.C.-Y Wong, F. Zhu, T. Liu, "Qualitative Study on Intermeshing co-rotating twin screw extrusion using novel visual technologies", Plastics, Rubber and Composites Processing and Applications, 26, 271-277, 1997.

6

H. Potente, U. Melisch, "Theoretical and Experimental Investigations of the Melting of Pellets in Co-Rotating Twin Screw Extruders", International Polymer Processing, XI, 101-108, 1996.

7

S. Bawiskar, J.L. White, "Composite Model for Solid Conveying, Melting, Pressure and Fill Factor Profiles in Modular Co-Rotating Twin Screw Extruders", International Polymer Processing, 331-340, 1997.

8

C. C. Gogos, Zehev Tadmor, Myung Ho Kim, "Melting Phenomena and Mechanisms in Polymer Processing Equipment", Advances in Polymer Technology, 17, 285-305, 1998. doi:10.1002/(SICI)1098-2329(199824)17:4<285::AID-ADV1>3.0.CO;2-N

9

B. Vergnes, G. Souveton, M.L. Delacour, A. Ainser, "Experimental and Theoretical Study of Polymer Melting in a Co-rotating Twin Screw Extruder", International Polymer Processing, XVI, 351-362, 2001.

10

D.B. Todd, "Drag and Pressure Flow in Twin Screw Extruders", International Polymer Processing, VI, 143-147, 1991.

11

L. Zhu, K.A. Narh, X. Geng, "Modeling of Particle-Dispersed Melting Mechanism and its Application on Corotating Twin-Screw Extrusion", Journal of Polymer Science: Part B, 39, 2462-2468, 2001. doi:10.1002/polb.1218

12

A. Gaspar-Cunha, B. Vergnes, J.A. Covas, "Defining the Configuration of Co-Rotating Twin-Screw Extruders with Multi-Objective Evolutionary Algorithms", Polymer Engineering and Science, 45, 1159-1173, 2005. doi:10.1002/pen.20391

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