Abstract:

Objective Heating methods such as air conditioning are most popularly used for warmth keeping in cold environments, but such methods would raise temperature to the entire space, causing unnecessary energy waste and accelerating the greenhouse effect. Therefore, we hope to heat up a small space around the human body to make people feel comfortable in the cold space. In addition, when the two sides of the membrane show obvious differences in infiltration, that is when the membrane has an asymmetric structure, it can be unidirectional transport liquid, which helps to timely discharge the sweat generated when the human body is heated, and keep the human body dry and comfortable. With this purpose, in-situ polymerization and electrospinning methods were used to prepare PU/MXene-C fibrous membranes with asymmetric structure.

Method Using two dimensional transition metal nitrogen compounds (MXene), polydopamine (PDA) and polyurethane (PU) as raw materials, cotton fabric (Fc) as substrate, the PDA-adhesive MXene (MXene/PDA-C) as hydrophilic layer and PU fibrous membrane as hydrophobic layer were prepared by in-situ polymerization and electrospinning. The asymmetric structure of polyurethane/cotton fabric based polydopamine adhesion two-dimensional transition metal carbon nitrogen compound (PU/MXene/PDA-C) fiber film was obtained. The prepared PU/MXene/PDA-C was characterized by scanning electron microscopy, moisture management tester, contact angle tester and Fourier infrared spectrometer.

Results MXene was successfully adhered to cotton using PDA through in-situ polymerization, ultimately obtaining MXene/PDA-C. The content of Ti element on the surface of MXene/PDA-C was analyzed by EDS spectrum, which further proved the success of the preparation. After exploring the conditions of electrospinning PU fibers, PU fibrous membrane was electrospun on MXene/PDA-C with a mass fraction of 12.5% spinning solution, and the fiber diameter obtained by four different electrospinning nozzles was measured, and it was found that the diameter of the fiber increases with the increase of the inner diameter of the nozzles. After obtaining PU/MXene/PDA-C asymmetric structure fibrous membrane, the unidirectional liquid transport of PU/MXene/PDA-C was studied. Since the electrospinning time of the asymmetric structure fibrous membrane, and hence the thickness of the hydrophobic layer, would affect the unidirectional liquid transport of the fibrous membrane, the influence of different electrospinning time on the unidirectional liquid transport of PU/MXene/PDA-C was investigated. The strength of unidirectional liquid transport of PU/MXene/PDA-C was indicated by the size of hydrostatic pressure. The hydrostatic pressure of PU/MXene/PDA-C with electrospinning time of 5, 10 and 15 minutes was studied, and the optimal time of electrospinning was determined to be 15 min. With the optimal electrospinning time, the hydrostatic pressure of PU/MXene/PDA-C obtained with four different electrospinning nozzles was measured, and the nozzle type was determined to be 10G. The two conditions above were determined, and electrospinning was carried out with 10% and 12.5% PU electrospinning solution respectively. By comparing the difference of hydrostatic pressure, the optimum electrospinning solution was determined as 12.5% PU solution. PU/MXene/PDA-C obtained at electrospinning time of 15 min, nozzle type was 10G and 12.5% electrospinning solution mass fraction demonstrated excellent unidirectional liquid transport and water vapor transmission. Due to the addition of MXene with photothermal conversion ability to the asymmetric structure fibrous membrane, the temperature of it was about 30 ℃ higher than that of cotton fabric under the irradiation of simulated sunlight lamp, and the thermal images under the irradiation of infrared lamp also confirmed this result.

Conclusion In this research, the asymmetric structural fiber membrane with MXene/PDA-C as hydrophilic layer and PU as hydrophobic layer was prepared by the combination of in-situ polymerization and electrospinning methods. SEM and EDS characterization proved that MXene was successfully loaded on the surface of cotton fabric. The optimum conditions for preparing PU/MXene/PDA-C were obtained by hydrostatic test as electrospinning time 15 min, nozzle type is 10G and electrospinning solution mass fraction 12.5%. MMT test and water vapor transmittance test show that PU/MXene/PDA-C fibrous membrane has excellent unidirectional liquid transmittance. The outcome from this study would help expand the application of asymmetric structural membranes in personal moisture and heat management, leading broad development prospects in the field of smart wearable textiles.

Key words: electrospinning, fibrous membrane, asymmetric structure, thermal management, unidirectional liquid transport, functional cotton fabric, polyurethane