Petroleum-based polymer fire-resistant fabric is not considered as eco-friendly, and has other problems like heavy weight and irritating tickling. On the other hand, even though Ca–alginate fiber is a natural fire-resistant polysaccharide derivative, its low tensile strength prevents the fiber from being a potential fire-resistant material. To enhance its mechanical performance, cellulose nanocrystal (CNC) functioned as reinforced nanofiller, assisted by a small amount of propanol to improve CNC dispersion in solution. CNC-doped alginate fiber (pC–Alg) was fabricated by the microfluidic spinning technique, and the effects of CNC content and the drawing ratio on the fibrous mechanical performance were investigated. Comparative studies indicated that a combination of 0.50 wt.% CNC, 6.00 v.% propanol, and 1.6 draft ratio helped pC–Alg fiber to achieve outstanding breaking strength of around 2.00 cN/dtex. It was shown that the use of propanol solvent and the incorporation of CNC can effectively eliminate CNC aggregation and reach a three-fold better tensile performance than the control. Limiting oxygen index test also showed that the resultant hybrid pC–Alg fiber still displayed good flame retardancy, making it an ideal candidate for fire-protection clothing.

With rapid development in the smart wearable field, new-style flexible energy storage devices are necessary to satisfy the demands of flexible smart clothing. Thereinto, fiber supercapacitors present promising application prospects. This work puts forward a facile and reliable strategy to fabricate coaxial fiber electrodes via binary wet spinning, and further assembles them into parallel or twisted nano-MnO2 fiber supercapacitors. In the obtained fiber electrode, a carboxymethylcellulose layer onto nano-MnO2 not only allows the requisite ion exchange between the electrochemical active materials and gel electrolyte, but also plays the role of separator to protect the two fiber electrodes effectively from contacting a short circuit, greatly ensuring the electrochemical stability of the nano-MnO2 fiber supercapacitors. The parallel nano-MnO2 fiber supercapacitor reaches a maximum CL of 19.7 μF/cm, EL of 0.0027 μWh/cm and PL of 1.49 μW/cm; the twisted MnO2 fiber supercapacitor achieves maximum CL, EL and PL of 49 μF/cm, 0.0053 μWh/cm and 1.0 μW/cm, respectively. Besides, the outstanding softness and tensile properties of the obtained nano-MnO2 fiber supercapacitors also guarantee stable electrochemical performance under bending, knotting or other large-distortion situations, which is beneficial to develop a new generation of metal oxide fiber supercapacitors for smart wearable clothing.