PEER-REVIEWED ARTICLE bioresources.com Oktaee et al. (2017). “Willow fibers in composites,” BioResources 12(2), 4270-4282. 4270 Characterization of Willow Bast Fibers (Salix spp.) from Short-Rotation Plantation as Potential Reinforcement for Polymer Composites Javane Oktaee, a, * Thea Lautenschläger, b Markus Günther, b Christoph Neinhuis, b André Wagenführ, a Mirko Lindner, c and Anja Winkler d Short-rotation coppices have potential to be the future source of raw materials for many applications in the wood and paper industries. It is important to establish methods and products to handle their waste biomass. In this paper, the properties of bast fibers extracted from the bark of willow trees (Salix spp.) were evaluated for potential future use in the production of natural fiber-polymer composites. The anatomy of the fibers was investigated through optical and electron microscopy. The thermogravimetric analysis of these fibers showed that the major mass loss occurs at 257 °C. The density of the fibers was measured with a gas pycnometer (1.19 ± 0.2 g/cm 3 ). The chemical analysis showed that willow bark fibers have a composition similar to willow wood. As an indicator of mechanical properties, single willow bast fibers were characterized by tensile tests. The results revealed values for tensile strength (307.6 ± 130.1 MPa) and Young’s modulus (16.9 ± 8.4 GPa) that are comparable to some commonly used natural fibers. The overall results showed that willow bast fibers have the required mechanical properties as well as thermal stability for application in reinforcement of polymers. Keywords: Willow; Bark; Bast fibers; Natural Fibers; Short-rotation coppices Contact information: a: Institute of Natural Materials Technology, Dresden University of Technology, P. O. Box 01307, Dresden, Germany; b: Institute for Botany , Dresden University of Technology, Zellescher Weg 20b, 01217 Dresden, Germany; c: Institute of Natural Materials Technology, Dresden University of Technology P. O. Box 01069, Dresden, Germany; d: Institute of Lightweight Engineering and Polymer Technology, Dresden University of Technology, P. O. 01307 Dresden, Germany; * Corresponding author: javane.oktaee@tu-dresden.de INTRODUCTION During recent decades, natural fibers have gained a significant share in composite markets. Several favorable properties, such as good mechanical properties, low density, biodegradability, renewability, low cost, etc., make them quite competitive with synthetic or man-made fibers in many applications (Nishino 2004; Pickering et al. 2016). Natural fibers can be extracted from different parts of a plant, such as the seed, bast, leaf, or wood (Nishino 2004; Mohanty et al. 2005; Zimniewska and Wladyka-Przybylak 2016). In Europe, non-wood, natural fiber polymer composites are most commonly used in automotive industries (Carus et al. 2014). These same fibers can be used in the form of short or long fibers and as textile material in polymeric matrices. Currently, most natural fibers are harvested from forests or agricultural feedstocks (Mohanty et al. 2005), whereas short-rotation coppices (SRCs) can also serve as a promising source. SRCs are defined as plantations of fast-growing species in high density,