Pressure Drop Estimation for Polyamide 6 Flow through Spinnerets and Filters A. Gus ˇtin, 1 A. Zupanc ˇic ˇ, 1 E. Mitsoulis 2 1 Department of Chemical Engineering, Faculty of Chemistry and Chemical Technology, University of Ljubljana, As ˇkerc ˇeva 5, 1001, Ljubljana, Slovenia 2 School of Mining Engineering and Metallurgy, National Technical University of Athens, Zografou, 157 80, Athens, Greece Received 9 September 2004; accepted 10 June 2005 DOI 10.1002/app.23308 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The pressure drop resulting from polyamide 6 flow through industrial spinnerets and wire-mesh filters was examined as a possible parameter for improving spin- ning process constancy with experimental techniques and a numerical approach. The rheological characterization of the polymer melt was performed with a capillary rheometer and a controlled-stress rotational rheometer equipped with a high-temperature oven cell. Measurements in a nitrogen atmosphere were carried out at different temperatures and at various moisture contents to determine the effect of the postcondensation process on the rheological properties of the polymer melt. These experiments were used to collect all basic material information necessary to fit the data with the purely viscous Cross model and the viscoelastic Kaye, Bern- stein, Kearsley, Zappas (K-BKZ) model. A spinning pilot plant (consisting of an extruder, a gear pump, a pressure sensor, and a spin beam with several spin packs installed) was used to measure pressure drop values through indus- trial spinnerets and through two types of filters: (1) Dutch twilled weave filters and (2) sintered filters. Pilot plant tests on filters showed that in the examined range of melt throughputs, the pressure drop increased linearly with an increase in the melt flow rate for all the filters considered. The results with respect to the spinneret geometry led to the conclusion that the numerical simulations gave satisfactory predictions even for experimental data coming from com- plex systems such as spinning plants, as long as extensional properties were accounted for by the model. On the con- trary, pressure drop predictions obtained from the Cross model underestimated the pilot plant values by approxi- mately 20% because of the inability of the model to consider the extensional component of the flow. © 2006 Wiley Periodi- cals, Inc. J Appl Polym Sci 100: 1577–1587, 2006 Key words: extrusion; polyamides; polycondensation; vis- coelastic properties INTRODUCTION Polyamide 6 (PA6) is a very common polymer used in different fields ranging from textile and carpet pro- duction to special technical applications (tires, heat- resistant plastics, etc.). Textile spinning in particular is a very demanding process. Yarns are getting thinner from day to day, and the use of dyeing stuff sensitive to polymer inhomogeneities is the main reason for constant research for polymer improvement. The PA6 textile spinning process, presented in Fig- ure 1, can be summarized as follows. Polymer chips are fed to screw extruders and melted at temperatures of approximately 250 –260°C. In the storage vessels, the chips are strictly kept under a flow of nitrogen with a constant dew point to guarantee a constant moisture content and to avoid at the same time PA6 oxidation. The polymer melt is then conveyed to a heated manifold, which is composed of several pipes departing to the single spinning positions. One gear pump, placed just before the spin packs, extrudes the melt through the spin packs into open air, transform- ing one single melt stream into many thin filaments. Filaments are finally cooled in the open air and wound in bobbins. One of the important parameters that can be related to the constancy of the yarn quality is the pressure drop measured through the spin pack because it di- rectly depends on the filtration grade chosen for poly- mer purification. Figure 2(a,b) shows the three main elements composing a typical textile spin pack: a po- rous packed bed of steel particles, a filter, and a spin- neret. The aim of the porous packed bed and the filter is to stop extraneous particles present as impurities in the polymer melt and to break possible gels, 1 whereas the spinneret generates high shearing conditions on the Correspondence to: A. Zupanc ˇic ˇ (andreja.valant@fkkt.uni- lj.si). Contract grant sponsor: Slovenian Research Agency; Slo- venian Ministry of Economy; contract grant number: 3311- 03-831805. Contract grant sponsor: General Secretariat of Science and Technology of Greece; contract grant number: 047-g. Journal of Applied Polymer Science, Vol. 100, 1577–1587 (2006) © 2006 Wiley Periodicals, Inc.