14 th AUTEX World Textile Conference May 26 th to 28 th 2014, Bursa, Turkey DEVELOPMENT OF AN EXPERIMENTAL AUTOMATIC WET- SPINNING MACHINE P.WEISSER 1, A. HEKMATI 1, G. BARBIER 1, J-Y. DREAN 1 1 ENSISA-Laboratoire de physique et Mécanique Textiles EA 4365 UHA, 11 Rue Alfred Werner, F-68093 MULHOUSE cedex France pauline.weisser@uha.fr Key Words: wet-spinning, Programmable Logic Controller 1. Introduction The growing needs of textile industries, concerning innovative and high performances materials, explain the significant increase of man-made fibers production over the last ten years, which represents at least 68% of the total fiber production [1]. Depending on the type of the raw material, three main processes can be distinguished to obtain synthetic fibers: melt-spinning, dry-spinning and wet-spinning. In each case, a polymer melt or solution is extruded through a spinneret having one or several holes with specific size and shape which will define the fibers cross-section geometry. Next, the material is solidified during a phase transformation and then drawn to achieve a sufficient level of mechanical properties. The obtained filaments are finally wound on a spool. This work focuses on wet-spun fibers which are formed by extruding a viscous polymer solution through a spinneret, directly immersed in a coagulation bath. The solidification is brought about by a countercurrent diffusion between the solvent contained in the forming filament and the non-solvent from the coagulation bath [2]. The aim of this work is to develop an automatic experimental device for the wet-spinning of monofilaments having a large diameter (above 1 mm). Such products could be used as binder yarns for three dimensional woven fabrics [3-4] or as matrices to encapsulate an active substance for medical applications [5]. To be able to study the influence of the experimental conditions on the characteristics of the final product, for a wide range of polymer solutions, the machine must also present a high degree of adaptability. 2. Materials and methods 2.1. Wet-spinning process The wet-spinning process is classified in the solution spinning category. Hence, spinning polymer is firstly dissolved in the appropriate solvent and then, wet-spun fibers are formed by the extrusion of the obtained solution, through the spinneret, in the adequate coagulation bath (Figure 1). The spinneret can be directly immersed (immersed method) or there may be a small gap between the spinneret and the surface of the coagulation bath (airgap method). Three methods of solidification can be distinguished which are named liquidcrystalline, gel formation and phase separation method. The coagulation firstly occurs on the
surface of the filament, creating a skin/core structure which will slow down the diffusion process described by Fick s second law. Hence, controlling the coagulation kinetic is a key factor for ensuring a homogeneous final product with optimal properties. The other steps that are essential for the wet-spinning process (Figure 1) are: injection, drawing system to achieve mechanical properties, washing bath to remove the remaining solvent and finally drying system possibly coupled to a second drawing step [6]. Figure 1 : Wet-spinning process 2.2. Development of the experimental device [7] Like every automated system, the wet-spinning machine will consist of two basic parts: an operative part which enables the different steps needed for the transformation of the raw material into monofilaments and a controlling part which ensures the coordination of those steps. To fulfil the requirements imposed by the wet-spinning process and ensure the quality of the monofilaments, the production process is controlled with a Programmable Logic Controller (PLC, Modicon M340, Schneider Electric) [8]. 2.2.1. Development of the operative part Each operative part of the developed wet-spinning machine comprises: - handlers, ensuring the wet-spinning process ; - actuators, enabling the motion of the previous tools ; - sensors, informing about the state of the production. The choice of equipment has been made taking into account the characteristics of the polymer solution, of the coagulation and washing baths but also the expected properties of the final product. Firstly, the injection system has been selected according to the high viscosity of polymer solution that can be experienced. Hence, to optimize the adaptability of the experimental device, a gear pump with magnetic drive is used. To ensure a high degree of chemical
resistance, the coagulation bath is designed in polypropylene and built with a triangular shape to reduce the volume of solvent needed. The third step refers to the drawing system which consists of two drafting rolls. Each axis is moved by a brushless servo motor through a planetary speed reducer, associated to a Lexium 32 servo motion drive (Schneider Electric) connected by a CanOpen network, and controlled with the PLC. Hence, kinetic of coagulation can be therefore controlled by adapting the injection flow and the drawing ratio applied in the coagulation bath, defined with regard to the rotational speed of the first cylinder of the drawing system. After the washing step, a drying system is available to increase homogeneity and properties of the obtained filaments. It consists of two infrared lamps, allowing a heating power of 600W or 1200W. Temperature and residence time in the drying chamber are adjustable parameters. Finally, a winding system allows a regular distribution of the filament around the spool by combination of rotary and linear motions. Like the drawing system, it consists of two Brushless DC electric motors completed by two planetary speed reducers. Figure 2 : Picture of the wet-spinning machine developed 2.2.2. Development of the control part The control part consists of three different dialogues to send orders to the operative part and receive informations back : - the dialogue with the machine, to control the actuators by means of pre-actuators like contactors, variable speed drives, ; - the dialogue between the user and the machine to issue instructions and being informed about the progress of the production process ; - the dialogue with others potential machines, to coordinate their control parts. In the developed device, control of the spinning process is provided by a programmable logic controller (PLC). The application program has been developed under Unity Pro especially by means of motion function blocks (MFB) which allow the motion in speed or position of the different Brushless motors. Data is transmitted from PLC to variable speed drives via a CanOpen link.
Figure 3 : Control structure of the wet-spinning machine developed Although is the wet-spinning process fully automated, a dialog between the operator and the machine is possible due to a communication interface (XBT-GT 5330, Schneider Electric), connected to the PLC by an Ethernet Network. It allows sending instructions and receiving informations about the production conditions. 3. Validation of the experimental device The validation of the experimental device, has been conducted with spinning tests on a sodium alginate solution. Alginic acid sodium is a natural polysaccharide polymer, extracted from brown seaweeds. Chemically, alginate is composed of α-l-guluronic acid and β-dmannuronic acid. Alginate filaments are spun by extruding an aqueous solution of sodium alginate into an aqueous calcium chloride bath. By varying the spinning conditions it is possible to produce fibers with different proportions of sodium and calcium and then, different properties. The polymer solution was prepared by dissolving 1.6 g of sodium alginate in 100 ml distilled water and stirring was performed for 24 hours to homogenize the solution. The obtained polymer solution was extruded in the coagulation bath which was a 20 g.l -1 calcium chloride solution. The experimental spinning conditions are provided in the table below. Table I : Experimental data of wet-spinning process Alginate sodium concentration (wt%) 1.6 Calcium chloride concentration (wt%) 20 Spinneret internal diameter (mm) 1.1 Alginate solution feeding rate (ml/min) 0.4 Drawing ratio (%) 20 Solution temperature ( C) 20
4. Results and discussion After wet-spinning, alginate filaments have been physically and mechanically characterized. SEM microscope has been used for morphological studies and tensile test has been carried out for mechanical investigations. 4.1. SEM study The monofilament samples were coated with gold and morphologically analyzed by SEM (Hitachi S-2360N). The SEM pictures (Figure 5) show an almost smooth surface of the monofilament, with a semi-circular cross section. Having such characteristics for a wet-spun monofilament is important and quite difficult to obtain. 4.2. Mechanical study Figure 4 : SEM pictures of wet-spun alginate monofilaments Mechanical properties of alginate monofilaments were studied by simple tensile test. Samples of 18 cm long were conditioned in textile testing standard conditions (20 ± 2 C temperature and 65 ± 2% relative humidity) for 48 hours, before being tested. The initial length and elongation rate were respectively 15 cm and 10 mm.min -1. All tests were carried out by using a 10 N load-cell. For a batch of ten samples, a quite similar mechanical behavior is observed, with the two characteristic zones : elastic and plastic (Figure 6). Such a result reflects a good repeatability of the wet-spinning process and then a good reliability of the experimental device developed. From the statistical analysis, it has been found that the average tenacity of alginate monofilaments is 8,27 cn/tex, for an average count about 15,4 tex. We can conclude that wetspun monofilaments are able to withstand stresses induced by the weaving process.
5. Conclusion Figure 5 : Load - Elongation curves of wet-spun alginate monofilaments The wet-spinning machine developed in this study meets the user s needs for producing continuous polymeric monofilaments. By implementing a programmable logic controller, spinning parameters can be changed during a production, as a result of the synchronization of the different axes. Such a feature allows easy and flexible operations to study the spinnability of a wide range of polymer solution. Moreover, results of the SEM and mechanical studies show a good repeatability in the production process and satisfying properties to use the obtained monofilaments in textile applications. As a pilot project, this robust experimental device provides two important possibilities: studying the influence of the spinning parameters on the properties of the final monofilaments and simulating an industrial fiber production. 6. References [1]. CIRFS: European Man-made Fibres Association [Online]. Avalaible on <http://www.cirfs.org/keystatistics/worldmanmadefibresproduction.aspx>. [2]. PAUL D. R.: Diffusion during the coagulation step of wet-spinning. Journal of Applied Polymer Science, 1968b, Vol. 12, p. 383-402. [3]. BEHERA B. K., MISHRA R.: 3-dimensional weaving. Indian Journal of Fibre and Textile Research, 2008, Vol. 33, p. 274-287. [4]. YIP J., NG S.-P.: Study of three-dimensional spacer fabrics : physical and mechanical properties. Journal of Materials Processing Technology, 2008, Vol. 206, Issue 1-3, p. 359-364. [5]. CORBMAN B. P.: Textiles : Fiber to Fabric, 6 th Edition. McGraw-Hill International Editions, Singapore, 1983. [6]. GRISKEY R. G.: Polymer Process Engineering. Chapman & Hall. New York : ITP, 1995, 478p. [7]. WEISSER P. : Etude de monofilaments à hautes performances thermiques : développement d outils de filage et caractérisation. Thèse Mécanique. Mulhouse : UHA, 2013, 246p. [8]. SCHNEIDER ELECTRIC : Plate-forme d automatisme Modicon M340 [online]. Available on < http://www.e-catalogue.schneiderelectric.fr/navdoc/catalog/a5/big/big.htm?type=module&module=43400>