Keywords: nanofibers, carbon fiber, fiber reinforcement composite, fiber embedding, 3D printing, fiber placement
Summary:For industrial applications, polymeric nanofibers need to be fabricated on a per-pound basis. Currently, centrifugal spinning is the most popular and fastest method for producing polymer nanofibers in such quantities using a high-speed rotary spinneret. However, polymer solutions spun centrifugally are normally formed circumferentially around static posts that require additional post-processing for continuous collection and fiber alignment. Herein, we implemented a novel automated centrifugal trackspinning system for the high volume production and collection of highly aligned polymer nanofiber arrays with the ability to post-draw micro- and nanofiber to a smaller diameter reduction for enhanced mechanical and physical properties such as increased thermal conductivity and crystallite orientation. Polyacrylonitrile (PAN) nanofibers were prepared by selectively varying parameters that can affect intrinsic solution properties and operational conditions. The resultant PAN nanofibers were characterized by SEM, FTIR, and tensile tests. The correlation between fiber morphology and processing conditions was established. Results demonstrated that the fiber morphology could be easily manipulated by controlling the centrifugal spinning and trackspinning parameters. Also, the correlation of higher aspect ratio, crystallinity, and crystallite alignment with fiber diameter reduction can attribute to increases in stiffness, strength, and toughness, combined with fewer defects and enhanced chain slip associated with small diameter and high specific surface area. While, electrospinning has to date been the most successful and versatile method of producing nanofibers with random and aligned configurations, scale-up and commercial production of large quantities of nanofibers from commodity polymers are quite challenging. Even though laboratory-scale electrospinning has gone through numerous stages of improvement, the major drawback of the process is its relatively low productivity and dependence on high voltage, which runs the potential risk of inflammation of volatile solvents when scaling up. Also, with increasing thickness of the mat, the alignment of fibers is lost due to the presence of residual charge present on the fibers, which hinders further deposition. It is an even more significant challenge to make nanofibers from high-performance polymers such as ultra-high molecular weight polyethylene used (UHMWPE), which has minimal solubility in common organic and polar solvents. The centrifugal trackspinning process is a facile approach for fabricating, collecting, and post-drawing high aligned mechanically enhanced polymer nanofibers from a wide variety of synthetic polymers (ex. PAN, PCL, PEEK, polyimide, PVDF, etc...), biopolymers (ex. PLA, silk fibroin, zein, soy, peanut, etc...), polymeric carbohydrates (cellulose, lignin, etc...), and melts. These nanofibers can be used in many fields for a wide range of applications such as automotive, aviation, construction, batteries, filtrations, sensors, and others. Low-cost, high-performance fiber-reinforced composites are of the high interest for military and aerospace composite applications, which include carbon fibers and such organic fibers as aramids and UHMWPE. Protection systems ranging from wound dressings, body armor, and helmets to spall liners in ground vehicles are also promising opportunities in components made from nanofibers, which can reduce weight and cost.