Abstract:

Objective Although cellulose fiber has advantages in high moisture absorption, good wearing comfort and low cost, its applications are limited due to its singular function and poor mechanical properties. The introduction of functional materials to give cellulose good electrical conductivity is significant to expand its applications. This research worked to disperse carboxyl-modified carbon nanotubes (CNT) evenly in the cellulose spinning dope so as to achieve high strength and good electrical conductivity of the modified cellulose fibers.
Method In the experiment, carboxyl-modified CNT was dispersed well in sodium hydroxide/urea solution, which can dissolve cellulose at a low temperature (-10 ℃). The composite fibers with different CNT contents (mass fractions of 5%, 10%, 15%, and 20%) were prepared by a laboratory wet spinning device. Meanwhile, the microstructure, mechanical properties and electrical properties of the composite fibers were characterized by scanning electron microscope, X-ray diffractometer,infrared spectrometer,mechanical property tests, and multimeter.
Results When the composite fibers were prepared by wet spinning, CNT maintained directional alignment because of the powerful shearing effect, which effectively improved the performance of the fiber. The surface of the cellulose fiber was smooth, while CNT was uniformly distributed along the radial direction of the composite fiber. It can be seen from the cross-sectional structure that the obtained fibers were dense when a large amount of CNT was encapsulated in the cellulose matrix to form a composite structure(Fig.4). In addition, the XRD and FT-IR spectra (Fig.5, Fig.6) indicated that hydrogen bonding interactions formed linkage between the CNT and cellulose molecular chains. The oriented structure of CNT and the hydrogen bonding interaction with the cellulose molecular chains benefited the composite fiber's mechanical properties. The stress-strain curves of the composite fibers with cellulose/CNT (C/CNT) show that the addition of CNT significantly improved the strength and stiffness of the composite fibers(Fig.7). The breaking strength was 165 MPa when the mass fraction of CNT was 20%, representing an improvement compared to the pure cellulose fiber. In addition, the composite fiber demonstrated electrical resistance of 100,3 kΩ when the mass fraction of CNT was 10%, 20%. Based on cellulose's moisture-absorbing and swelling properties, the composite fiber was further applied to the field of humidity sensing. The composite fiber exhibits excellent humidity sensitivity at room temperature, both air blowing and water immersion of the fiber resulted in detectable resistance changes (Fig.8). The electrothermal performance test revealed that the C/CNT composite fiber with a 20% CNT mass fraction exhibited excellent electrical heating performance. The temperature of the specimen rose to 62.3 ℃ within 15 s when the voltage was increased to 30 V (Fig.9).
Conclusion A homogeneous and stable spinning solution was prepared by virtue of the fact that carbon nanotubes can be well dissolved in sodium hydroxide/urea. The C/CNT composite fibers were prepared by wet spinning. Compared with the original cellulose fiber, the good dispersion and the enhanced interface provided the composite fiber with superior mechanical properties. Combined with the scalability of the wet spinning process and the versatility of flexible conductive fibers, the related work reported in this paper provides a reference for the development and design of lightweight and flexible sensing fabrics in wearable electronics.

Key words: cellulose, carbon nanotube, wet spinning, functional fiber, composite fiber, humidity sensing, smart textile