Abstract:

Objective Existing hygroscopic and perspirant fabrics have poor moisture conductivity and insufficient wearing comfort. The essence of hygroscopic and perspirant wicking is to use the difference in the absorption of sweat between the inner and outer layers of the fabric to conduct human sweat to the outer side of the fabric and evaporate, so as to keep the surface of the skin dry. In order to meet people's demand for clothing comfort, fabrics with moisture absorption and sweat wicking function have good development prospects and high practical value. In this study, a single wet double-layer fiber membrane with polyvinylidene fluoride(PVDF) as hydrophobic layer and polyacrylonitrile(PAN) and silica as hydrophilic layer was prepared.

Method The hydrophobic PVDF layer and the hydrophilic PAN/SiO₂ layer with orientation structure were prepared by electrospinning technology according to the single guided wetting mechanism of the fiber membrane. The double-layer composite fiber membrane has pore size gradient structure and surface wettability gradient structure. The pore size gradient was constructed by adjusting the thickness of PVDF layer, and the relationship between the thickness and the single moisture index, moisture permeability and mechanical properties of the double-layer composite fiber membrane was analyzed.

Results The spinning time of PVDF layer was adjusted to 2.0,2.5,3.0 and 3.5 h respectively, and the corresponding fiber membrane thickness was 295.1, 305.8, 314.7 and 324.5 μm, respectively, which showed a positive correlation with the spinning time. With the increase of the spinning time of the PVDF layer, the pore size of the hydrophobic layer was decreased and the distribution range of the pore size were narrowed gradually, while the pore size of the hydrophilic layer became much smaller than that of the hydrophilic layer, thus constructing a gradient structure from the hydrophobic layer to the hydrophilic layer. PVDF layer spinning time of 3.0 h showed the best wetting effect, where water was able to penetrate the fiber membrane within 2 s, and the unidirectional transfer index reached 1 778.2%. With the increase of PVDF layer spinning time, the positive AOTC(accumulative one-way transport index) increased from 1 259.6% to 1 778.2%. Therefore, the increase in the thickness of the PVDF layer led to the improvement of the directional transport performance of the liquid. However, when the spinning time of PVDF layer increased from 3.0 h to 3.5 h, AOTC was decreased from 1 778.2% to 1 204.2%, further indicating that Janus membrane with appropriate thickness was more likely to achieve better unidirectional liquid conductivity. Further, the water pressure resistance of the fiber membrane was tested. The positive and negative water pressure resistance of the composite fiber membrane with different PVDF spinning time was significantly different. The positive water pressure resistance was always lower than that of the reverse water pressure, and the water pressure difference showed an increasing trend with the increase of the spinning time of the PVDF layer fiber membrane. The hydrophilic layer with orientation structure showed a core suction height of 10 cm in 10 min, which provides good reverse osmosis performance for the fiber membrane. In addition, when the spinning time of PVDF is 3.0 h, the fiber membrane also has good moisture permeability and air permeability, with the moisture permeability reaching 8.7 kg/(m²·d), and the air permeability is 196.5 mm/s.

Conclusion In this study, PVDF-PAN/SiO₂ double-layer composite micro-nano fiber membrane containing oriented hydrophilic layer was prepared by electrospinning technology, and the effects of PVDF layer thickness on the pore size, single wizard moisture index, moisture permeability and mechanical properties of the composite fiber membrane were investigated. The results show that when the spinning time of PVDF layer is 3.0 h, the fiber membrane has the best single wet performance, and the unidirectional transfer index can reach 1 778.2%. In addition, the fiber membrane has good moisture permeability (8.7 kg/(m²·d)) and excellent air permea-bility (196.5 mm/s). The composite membrane can absorb human sweat and quickly conduct it to the outer layer of the fiber membrane within 2 s, which is much better than the existing single guide wet fiber materials. The double-layer composite fiber membrane prepared in this paper has a broad application prospect in the fields of hygroscopic and perspiratory textiles and medical and health textiles.

Key words: functional material, electrospinning, micro-nano fiber, single guide wet, double-layer composite, fiber membrane, oriented structure