Transform of nano-fibers to bundle by surface friction and features of the nano-fibrous bundle

Electrospun nano-fibers are characterized by relatively large surface area per unit mass, offering numerous applications. They are produced in forms of web, which, however, restricts the usage of the nano-fibers due to high deformability and thus difficulties in further processing the web. To take advantage of the shape characteristics and to widen the application field of nano-fibers, this research introduces a novel process to transform the web made of nanofibers to a bundle based on the friction bundling principle, while investigating the characteristics of the structural and mechanical properties of the output bundle. We also tested if the new process was feasible for industrial implementation. According to the results from the trials in this study, the web-to-bundle transform process suggested here was practicable to produce the nanofibrous bundle. The cross-sectional structure of the output bundle was multi-layered due to the web rolling on the friction drum. Tensile tests turned out that the nano-fibrous bundle possessed some mixed properties; one with strain hardening, another with strain softening, that is, the initial modulus was high, and then arrived at a yielding point. After the yielding point, the modulus decreased continuously or with some sudden steep-up in between and then steadily decreased until the fracture occurred. The mean strength of the bundle produced under the experimental conditions of this research was in the level of about 229 MPa and the mean breaking strain reached up to 1.8 under the test speed of 2.5 cm/min with the gauge length of 2.5 cm.