Manufacturing nanofibrous bundles and the roller drafting effects on the bundle properties

This research reports a new product form made of nanofibers and the method used to produce it. Nanofibers are electrospun into a web form on a moving collector and the web is continuously transformed into a bundle by passage through a condenser. Since the web is made of loops of nanofibers and peeled off from the collector surface, the condensed bundle deforms very easily and is too weak for further processing. Thus, the bundle is drafted through a roller drafting system to improve the fiber array in the bundle length direction in various levels of draft temperature, since the temperature may affect the bundle drafting process and thus the bundle properties. Using a newly designed system, we tried to produce nanofibrous bundle of polyvinylidiene difluoride. The nanofiber arrangement and the tensile properties of the bundle were measured before and after the roller drafting process under various conditions. Results showed that the technology suggested in this paper had the feasibility to manufacture a new product form composed of nanofibers, which implied the possible improvement of the productivity and product quality. Thickness reduction of the bundle occurring during the roller drafting straightened the nanofiber loops in the bundle and rearranged the nanofibers along the bundle axis. The drafting process was affected by the process temperature. Uni-axial tensile tests demonstrated that the bundle strength reached 4.8 cN/tex, and the strain at breakage was 0.087, when the draft ratio was 4.0 and the temperature 110 °C, whereas the raw nanofiber bundle in process had a strength of 0.014 cN/tex and the strain at breakage of 0.65. The thickness of the constituent nanofibers was not significantly affected by drafting.