Fibers & Textiles
Fibers & Textiles Monofilament melt spinning of biopolymer-blends By: Pavan Kumar Manvi, Jonas Hunkemöller and, Thomas Gries Institut für Textiltechnik ITA, RWTH University Aachen, Germany Several efforts have been made to produce biobased multifilament yarn for textile applications. While these have generated considerable interest, monofilament applications of biopolymers have not yet been sufficiently researched to allow their use in textile applications. In the present research, a monofilament spinning process is developed for biopolymer blends with the aim of producing biobased monofilaments for use in agrotextile applications. Arboblend 3327 V is a renewable resource-based product manufactured by Tecnaro (Ilsfeld, Germany). The potential of this polymer blend for multifilament melt spinning was studied within the scope of the projects “Tailor-made melt the speed of Duo 1 between 20 m/min and 100 m/min was experimented with, but to no avail. Other efforts were made to decrease the throughput to make the filament thinner and more flexible. This decreased the frequency of filament breaks, but failed to eliminate them completely. During the experiments, a brittle fracture (break) of the filament was observed, which, it was thought, could be due to intensive cooling and the brittle nature of polylactic acid (a component in Arboblend 3327 V) at room temperature. The water cooling of the molten filament was therefore removed and replaced by a single godet. As the cooling rate of the filament was expected to be slower with air cooling, brittle fracture of the filament would be less likely to occur. Hopper Extruder Spinning head Water bath Filament DUO 1 DUO 2 Heated drawing chamber Fig. 1: Set-up of monofilament spinning machine with water bath Winder spinnable biopolymer compound for textured filament yarn, elastic combination yarn and other fibrous materials (BioKombiGarn)”, a two year project running from 2015 – 2017 and “Starch-based textiles: Cost-effective textiles made from biopolymers (Star-Tex)”, which ran from 2015 – 2018. The blend was shown to offer good spinnability. It was therefore chosen to use Arboblend 3327 V to develop a monofilament melt spinning process. For the development of a melt spinning process, a melt spinning set-up with single screw extruder, a spinning head, a water bath, two duo godets, one heating chamber and a winder was used, as shown in Fig. 1. The initial parameters shown in Tab. 1 were chosen on the basis of previous experiments with multifilament melt spinning of Arboblend 3327 V. Observations and results: Experiments were started with the machine set-up shown in Fig. 1 and the process parameters listed in Tab. 1. During the experiments, intensive filament breakage was observed at the first galette duo (Duo 1). To stop the filament break at Duo 1, varying Tab. 1: Initial process parameters for monofilament melt spinning of Arboblend 3327 V Parameter Unit Value Extruder temperature zone 1 °C 180 Extruder temperature zone 2 °C 200 Extruder temperature zone 2 °C 220 Spinning pump temperature °C 220 Spinning head temperature °C 220 Through put of spinning pump g/min 5.9 Speed of drawing godet set 1 (Duo1) m/min 50 Speed of drawing godet set 2 (Duo2) m/min 100 Temperature of heating chamber °C 180 Speed of winder m/min 201 Aimed fineness dtex 70.4 A schematic view of the machine set-up with a mono take-up godet is shown in Fig. 2. 20 bioplastics MAGAZINE [05/19] Vol. 14
Fibers & Textiles Hopper Extruder Spinning head Filament Fig. 2: Set-up of monofilament spinning machine mono godet Winder Take-up godet DUO 1 DUO 2 Heated drawing chamber It was observed that after replacing the water bath with the godet, the filament could be passed through the first godet duo successfully. This led to the conclusion that monofilaments containing brittle polymers should preferably be cooled by air to prevent an increase in brittleness. Subsequent experiments were conducted using the setup shown in Fig. 2. Further challenges were observed when passing the filament through a heated drawing chamber. As soon as the filament passed through the heated chamber and the second godet duo, filament break occurred. After several trials, this problem remained, meaning it could not be considered an artefact of the experiment. Further improvement in the set-up and the process parameters became necessary. One hypothesis to explain the phenomenon was that a sudden increase in the filament temperature resulted in too little tension on the filament. This in turn caused slugging, leading to breakage of the filament in contact with the bottom of heating chamber. By decreasing the temperature of the heated drawing chamber it was thought that the problem could be solved. This was tested by lowering the temperature by 10 °C steps. As the temperature of the heated drawing chamber dropped, the number of filament breaks also decreased. The temperature was therefore lowered to 100°C, at which point a significant improvement in the process stability was observed. Another approach to solving the problem was to increase the draw ratio, which would increase the tension on the filament and thus avoid or reduce the slugging of the filament. To test this, the draw ratio between Duo 1 and Duo 2 was increased by decreasing the speed of Duo 1 and increasing the speed of Duo 2. This approach again improved the process stability. The optimization of the process parameters led to a stable process. However, some sudden breaks were still observed in the heated drawing chamber during a continuous run of the filament. It was concluded that a movement of the filament on Duo1 and Duo 2 caused sudden contact of the monofilament with the wall of the heated chamber, leading to filament break. To avoid this, two filament guides were placed at the entrance and at the exit of the heated drawing chamber to ensure a continuous pass of the monofilament through the heated drawing chamber without contact with the hot surface. The changes in the process and the machine set-up outlined above enabled a stable monofilament melt spinning process with Arboblend 3327 V polymer. The process parameters for a stable monofilament melt spinning process with Arboblend 3327 V polymer are shown in Tab. 2. A successful monofilament melt spinning process with biobased Arboblend 3327 V polymer could be established and a melt spun monofilament is shown in Fig. 3. The melt spun Arboblend 3327 V monofilament was also tested for its mechanical and shrinkage properties. These properties are shown in Tab. 3. Tab. 2: Process parameters for a stable monofilament melt spinning process with Arboblend 3327 V polymer Parameter Unit Value Extruder temperature Zone 1 °C 180 Extruder temperature Zone 2 °C 190 Extruder temperature Zone 2 °C 200 Spinning pump temperature °C 200 Spinning head temperature °C 200 Through put of spinning pump g/min 8.8 Speed of mono godet m/min 27 Speed of Duo 1 m/min 30 Speed of Duo 2 m/min 150 Temperature of heating chamber °C 100 Speed of Winder m/min 153 Fig. 3: Arboblend 3327 V monofilament bobbin Tab. 3: Properties of Arboblend 3327 V monofilament Property Unit Arboblend 3327 V monofilament Monofilament fineness dtex 141 Tensile strength cN/tex 28,28 Breaking elongation % 26,51 Hot air shrinkage % 27,49 www.ita.rwth-aachen.de bioplastics MAGAZINE [05/19] Vol. 14 21
