Abstract:

Objective In order to meet the demand for warmth and comfort of warm clothing in cold environment, intelligent warm clothing was developed. Carbon nanotube (CNT) is a new type of conductive material with high thermal conductivity, high strength and high electrical conductivity, and its excellent performance makes it widely applicable to the preparation of flexible heat-generating electronic devices. In this research, two types of heating elements are made of CNT materials, including CNT conductive film heating element and CNT conductive fabric heating element. The heating module is the core of heating clothing, aiming to meet the needs of wearing and heating.
Method CNT were dispersed by grinding and then mixed with waterborne polyurethane (WPU) to obtain CNT conductive slurry. CNT conductive films were prepared from the CNT slurry by vacuum filtration. CNT conductive fibers were prepared by coating the CNT slurry on the surface of polyester fibers using sizing and weaving the CNT conductive fibers into fabrics. The film and fabric were prepared, respectively, as simple heating elements, and compared with conventional resistance wire heating elements and CVD-CNT films prepared by CVD method to analyze its heating performance and wearability such as washability, permeability, flexibility and perspective.
Results In the heating test (with the power of the four electric heating elements set to 31 W by adjusting the heating area and voltage), the heating rate of CNT conductive film was found to be the highest, up to 1.96 ℃/s (the resistance wire was the lowest, 0.53 ℃/s). The heating temperature of CNT conductive fabric was the highest, up to 121.54 ℃ (the lowest temperature of resistance wire was 56.87 ℃). It showed that the thermal image of the resistance wire during heating was a curve, while the images of the other three of thermal images were two-dimensional planes. The washability test showed, that the heating elements made of CNT conductive film, CVD-CNT film and CNT conductive fabric were washable. After two washing cycles, the mass of CVD-CNT film was reduced the most, by 7.1%, and the resistance was increased the most, by 3.8%, while the resistance wire heating elements were not washable. The air permeability test showed that CNT fabric has air permeability of 463 mm/s, and other heating elements had no air permeability. The flexibility test showed that the flexibility of CNT conductive film, CVD-CNT film and CNT fabric (the test direction is radial) was almost the same, which was above 300% higher than that of resistance wire and above 60% higher than that of CNT fabric (the test direction is weft). Finally, the moisture permeability of four electric heating elements was tested. The results showed that the moisture permeability of CNT conductive film was 2 980 g/(m²·24 h), that of CNT-CVD film was 2 880 g/(m²·24 h) and that of CNT conductive fabric was 3 970 g/(m²·24 h). Obviously, CNT conductive fabric has good moisture permeability. Because the effective working area of resistance wire heating elements was a curve, the moisture permeability could not be tested.
Conclusion The successfully prepared CNT conductive films and CNT conductive fabrics can be assembled into electric heating elements and tested for heating performance. The results indicate that CNT conductive films not only generate heat quickly, but also exhibit excellent flexibility. CNT fabric has a high heating temperature, good permeability and certain flexibility. Introducing CNT into the heating module not only solves the problem of missing heating elements in intelligent heating clothing, but also expands the market application of CNT, proving the feasibility of CNT as a heating element and providing strong reference for the design of subsequent CNT heating systems.

Key words: carbon nanotube, conductive film, conductive fabric, electric heating fabric, intelligent heating clothing