Abstract:

Objective Electrospun nanofiber membranes have shown the shortcomings of low strength and poor stability for certain applications. To compare the mechanical properties of membranes and yarns and to further discuss the feasibility of industrial production of membrane-rolling yarns, polyurethane (PU) nanofiber membranes were prepared by needle-free electrospinning and membrane-rolling yarns were made by twisting and heat setting.

Method The PU nanofibrous membranes were prepared by the needle-less electrostatic spinning. Membrane-rolling yarns were prepared by bundling nanofiber membranes through a self-made twisting instrument, which was held at one end and twisted at the other. The membrane-rolling yarns were heat-set. The mechanical properties, surface properties and internal porosity of PU nanofibrous membranes and yarns were characterized by the scanning electron microscope, tensile tester and high-speed automatic specific surface and porosity analyzer.

Results Spinning solution was formed by dissolving PU particles in the mixed solution of dimethylformamide and tetrahydrofuran (mass ratio 1∶1). The concentration of PU in spinning solution has great influence on the surface morphology of nanofibrous membranes. With the increase of PU mass fractions, the diameter of nanofibers became larger, and the membrane forming ability was enhanced. When the mass fraction of PU was between 13% and 15%, the morphology of nanofibrous membranes were found to be stable and the nanofibrous diameters were uniform. The surface of the membrane-rolling yarns was smooth, and because the fibers were arranged along the direction of force during twisting, the surface of membrane-rolling yarns representing a three-dimensional network structure composed of oriented fibers and non-oriented fibers. With the increase of PU mass fractions, the diameters of the oriented fibers became thicker and the proportion of oriented fibers was increased. From the performance point of view, PU membrane-rolling yarn showed higher mechanical properties compared with nanofibrous membrane, and its tensile strength were slightly lower than that of commercially PU filaments. When the mass fraction of PU is 15%, the elastic recovery rate of PU membrane-rolling yarn reached 98%, and when the mass fraction of PU was 14%, the elastic recovery rate of PU membrane-rolling yarn (stretching 100 cycles) reached 83%. Before and after heat setting, the temperature did not have a great influence on the structure and properties of PU nanofiber membrane yarn, so the strength of membrane yarn did not change significantly. It was found that the nanofibrous membrane and the membrane-rolling yarn were porous in both meso and micro scales. The surface area of membrane-rolling yarn was 1.636 2 m²/g, the pore volume is 2.965 m³/g, and the average pore size is 12.39 nm.

Conclusion This work confirms a new idea for the efficient production and use of nanofibrous yarns. The prepared PU membrane-rolling yarns have the characteristics of high strength and high elastic recovery. Moreover, the PU membrane-rolling yarn has the advantages of high porosity, specific surface area and activity due to the composition of the nanofibers. Therefore, for PU membrane-rolling yarns itself, it can be applied to sound-absorbing textiles, filter materials and so on, and the PU membrane-rolling yarns could potentially be loaded with functional particles and applied to various functional and smart textiles.

Key words: electrostatic spinning, polyurethane, nanofibrous membrane, membrane-rolling yarn, orientation