(395d) Polymeric Nanofiber Braid Manufacturing and Characterization

Using our previously reported Spinneret based tunable Engineering Parameters (STEP) technique, we demonstrate aligned deposition of  high aspect ratio uniform diameter Polystyrene (PS) fibers (diameter: sub 50nm to 800nm, length: mm-cm). PS fibers made from STEP technique were deposited in well aligned configuration with parallelism ≤ 2.5 degrees which makes it possible to prepare unidirectional PS fiber bands composed of thousands of individual fibers.  PS fiber bands having 600nm diameter uniform fibers of 22 mm in length were made from 10% wt PS(M_w=2000K) dissolved in xylene. PS fiber braids were made by twisting two parallel PS fiber bands using home-designed braiding device and the braiding angle was controlled by number of twists added to the braids. For 3 , 6, 9 and 12 twists braids, the braiding angles were measured to be 6°, 15°, 21° and 32 ° respectively.  The break load of PS fiber braids increases as braiding angle becomes larger and peaks ( around 700mN)at 21°. Further increase of braiding angle leads to decrease of break load.  Compared to non braided PS fiber bands, PS fiber braids demonstrate higher ultimate elongation, higher yield strength and lower modulus. The ultimate elongation increases from 15% to 36% as braiding angle increases from 0° to 15°while even larger braiding angle do not contribute to elongation.  SEM images of braids fracture reveals that sheath-core structure forms during the elongation of densely packed fiber braids, which causes fibers at inner portion of braids to fuse together. To further enhance mechanical properties of PS fiber braids, 2%wt multi wall carbon nanotubes(MWNTs) were embedded into polystyrene fiber, which causes the fiber diameter to increase from 600nm to 1000nm. The break load for non fiber bands and 9 twists braids of PS-CNT fibers are 431 mN and 1000mN respectively, both of which are much larger than corresponding pure PS fiber bands and braids. Besides, 9twists braids of PS-CNT fiber demonstrates ultimate elongation up to 82% which is twice of 9 twists braids of pure PS fibers. Ongoing efforts are devoted towards detecting reinforcing effect of CNTs with different aspect ratio and understanding the influence on CNTs on polymer chain orientation in PS fibers.