Polymer optical fibers for textile applications e Bicomponent melt spinning from cyclic olefin polymer and structural characteristics revealed by wide angle X-ray diffraction Felix A. Reifler a, b, * , Rudolf Hufenus a , Marek Krehel c , Eugen Zgraggen d , Ren  e M. Rossi c , Lukas J. Scherer c a Laboratory for Advanced Fibers, Empa, Swiss Federal Laboratories for Materials Science and Technology, Lerchenfeldstrasse 5, 9014 St. Gallen, Switzerland b Center for X-Ray Analytics, Empa, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600 Dübendorf, Switzerland c Laboratory for Protection and Physiology, Empa, Swiss Federal Laboratories for Materials Science and Technology, Lerchenfeldstrasse 5, 9014 St. Gallen, Switzerland d Laboratory for Reliability Science and Technology, Empa, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600 Dübendorf, Switzerland article info Article history: Received 6 June 2014 Received in revised form 26 August 2014 Accepted 28 August 2014 Available online 16 September 2014 Keywords: Polymer optical fibers Melt-spinning Wide angle X-ray diffraction abstract To obtain thin and flexible polymer optical fibers (POFs) for textile applications, bicomponent melt-spun fibers with a cyclo-olefin polymer (COP) in the core and a tetrafluoroethyleneehexafluoropropylene evinylidene fluoride terpolymer (THV) in the sheath have been co-extruded on the pilot scale. With higher draw ratio, the orientation within the amorphous COP core increases and the preferred interchain distances gradually change in response to the drawing parameters, as could be revealed by wide angle X- ray diffraction (WAXD). The bicomponent arrangement can promote the formation of a regular core surface because irregularities at the interface between the core and the sheath component can even out thanks to thermal shielding by the sheath component. Light propagation loss (9 dB/m at 652 nm for the most transparent fibers) and tensile properties of the fibers turned out to be adequate to enable their use in industrially produced luminous textiles. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Since the digitalization of the data communication in the 1990s, there is an ever growing need on flexible and cheap solutions of optical fibers. Optical fibers made of polymers are not only more flexible, but also cheaper than glass optical fibers. Compared to glass optical fibers, the light attenuation of polymer optical fibers (POFs) is higher, which limits their use to short-range applications. But with the advent of digital technologies, POFs came into focus for short range data transmission in, e.g., cars and home networks [1,2]. Production and use of textiles are very demanding for the fibers in terms of flexibility and toughness. Flexible POFs made the incorporation of optical fibers into textiles possible [1]. The main use of these POF fabrics is design or illumination applications [3e7]. Other research activities focus on the use of POF fabrics as wearable and flexible sensing devices, for instance for body and health monitoring, or for monitoring the environment [1,8e20]. The optical fibers used for textile applications are usually real- ized without an additional protective jacket and are multi-mode fibers with a coreecladding geometry. Its commercial availability, the low material cost and its adequate thermal stability made poly(methyl methacrylate) (PMMA) the most frequently used material for these applications [1,21], usually in combination with a fluorinated polymer as a cladding material [2]. Polymer materials like polycarbonate, polystyrene, and silicone elastomers were also used as light guides in optical fibers [2,22]. The use of rather un- common polymers like polyether sulfones, polysulfones or poly- ether imines is still in the research phase [23]. PMMA, however, has also some drawbacks. Although it is a hydrophobic polymer, PMMA can absorb up to 2% of water [24], which also influences its attenuation characteristics [2]. Its rather high brittleness compared to other polymers used in the fabrication * Corresponding author. Laboratory for Advanced Fibers, Empa, Swiss Federal Laboratories for Materials Science and Technology, Lerchenfeldstrasse 5, 9014 St. Gallen, Switzerland. Tel.: þ41 58 765 78 66. E-mail addresses: felix.reifler@empa.ch (F.A. Reifler), rudolf.hufenus@empa.ch (R. Hufenus), mkrehel@wp.pl (M. Krehel), eugen.zgraggen@empa.ch (E. Zgraggen), rene.rossi@empa.ch (R.M. Rossi), lukas.scherer@empa.ch (L.J. Scherer). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2014.08.071 0032-3861/© 2014 Elsevier Ltd. All rights reserved. Polymer 55 (2014) 5695e5707