Electrospinning of Ultrahigh-Molecular-Weight Polyethylene Nanofibers
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Electrospinning of Ultrahigh-Molecular-Weight Polyethylene Nanofibers Dmitry M. Rein1, Yachin Cohen1, Avner Ronen1, Eyal Zussman2, and Kim Shuster2 1 Department of Chemical Engineering, Technion, Technion City, Haifa, Israel 2 Department of Mechanical Engineering, Technion, Technion City, Haifa, Israel ABSTRACT The electrospinning method was employed to fabricate extremely fine nanofibers of ultra-high molecular weight polyethylene (UHMWPE) for the first time, using a mixture of solvents with different dielectric constant and conductivity. A novel experimental device for elevated temperature electrospinning of highly volatile and quickly crystallizing polymer solutions and melts was developed. It was experimentally determined the influence of concentration and electrical conductivity of UHMWPE solutions on the diameter of electrospun fibers. The possibility to produce the highly oriented nanofibers from ultra-high molecular weight polymers suggests new ways for fabrication of ultra-strong, porous, surface modified fibers and single-component nanocomposite yarn with improved properties. INTRODUCTION Electrospinning is a technique for continuous production of fibers with characteristic diameters ranging from few tens to thousands of nanometers. This method attracts much interest due to its versatility in spinning a wide variety of polymeric fibers and the potential applications of such as membranes, electronic devices and nanocomposites, drug delivery, sensors, protective clothing, etc. [1, 2]. To date, hundreds different polymers have been successfully electrospun [3]. However, there are many potentially very attractive polymers, such as polyolefins [4], which up to now could be electrospun with great difficulties and does not give the stable product. Polyolefins are not particularly amenable to electrospinning due to solubility and conductivity issues and high melt and solution viscosity. They demand manipulation under relatively high temperatures of spinning (> 120 °C) to avoid the phase separation in polymer solutions or melts, which impedes the jet formation and its subsequent elongation and causes the occurrence of jams in the die. Dielectric properties of polyolefins and its solvents necessitate the use of additives to enhance the conductivity of the spinning melts or solutions [4]. When electrically driven, the thinning of the fiber occurs mostly at the nozzle area [5], which requires the polymer solution temperature and concentration to be well-controlled at the initial stage of electrospinning process. As electrospinning involves rapid solvent evaporation, solvent volatility plays a major role in formation of nanostructures by influencing the phase separation process. It was found, that the average fiber diameter decreases with an increase in the solvent volatility [6]. EXPERIMENT In our experiments we used UHMWPE powder GUR 415 from Hoechst (Mw=6·106 kg·kmol-1). The most volatile well-known solvent for UHMWPE is a p-xylene (pX). It is an acceptable solvent for electrospinning UHMWPE regarding i
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