PEER-REVIEWED ARTICLE bioresources.com Mashkour et al. (2011). “Unidirectional magnetic paper,” BioResources 6(4), 4731-4738. 4731 FABRICATING UNIDIRECTIONAL MAGNETIC PAPERS USING PERMANENT MAGNETS TO ALIGN MAGNETIC NANOPARTICLE COVERED NATURAL CELLULOSE FIBERS Mahdi Mashkour, a,b, * Mehdi Tajvidi, a Tsunehisa Kimura, b Fumiko Kimura, b and Ghanbar Ebrahimi a This paper reports a simple innovative method to align magnetic cellulose fibers by using a simple permanent magnet to fabricate unidirectional magnetic papers. Magnetic cellulose fibers were made by in situ synthesis of magnetite nanoparticles on alpha cellulose pulp extracted from American southern pine. Scanning electron microscope micrographs and energy dispersive X-ray spectroscopy maps indicated that magnetite nanoparticles completely covered the cellulose fibers. Suspensions of magnetic cellulose fibers were prepared at three levels of concentration (0.02, 0.04, and 0.08 g/L) and poured into the designed magnetic forming machine. Flow rate of suspension into the forming column was adjusted at 0, 0.3, 0.5, and 1 cm/s. The strength of the applied external magnetic field was the same in all cases and lower than 0.18 T. Orientation analysis indicated that the designed magnetic forming machine has a high performance to be used for aligning magnetic cellulose fibers and fabricating unidirectional magnetic cellulose papers. Observed anisotropic magnetic and mechanical properties confirmed the unidirectional structure. Keywords: Unidirectional magnetic paper; Magnetic alignment; Magnetic nanoparticle; Magnetic cellulose fiber; Permanent magnet Contact information: a: Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran, Karaj 31585-4314, Iran; b: Division of Forest and Biomaterials Science, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan; * Corresponding author: mahdimashkour@gmail.com INTRODUCTION Although magnetism and magnetic materials have been well known for many years, it is only recently that a number of new techniques to provide more sophisticated methods of material processing have been developed (Kimura and Kimura 2008). Different materials respond differently to externally applied magnetic fields depending on their nature and structures. Cellulose is well known as the most abundant biopolymer on Earth (Kim et al. 2008). It has been demonstrated that anisotropic natural cellulose fibers show negative diamagnetic behavior intrinsically when affected by external strong magnetic fields and can align perpendicular to the applied magnetic field direction. Because the diamagnetic property is a feeble magnetic behavior, the externally applied magnetic field must be strong enough, up to about 20 T, to provide sufficient torque to align the cellulose fibers perpendicular to the magnetic field direction efficiently (Revol et al. 1994; Kimura et al. 2005; Fujimura et al. 2010; Sundar et al. 2011). Producing such