*2.3. Preparation of Composite Fibers*

Polymer green fibers were prepared using a lab-scale melt-spinning apparatus (Paigujingmijixie Co. Ltd., Beijing, China). The composite polymer was first fed into the spinning tube and heated to the spinning temperature (about 130 °C) for 3 h. After the removal of the bubbles and an appropriate viscosity being obtained, the molten hybrid polymer was extruded through a single-capillary spinneret 0.20 mm in diameter by controlling the spinning pressure of N<sup>2</sup> (roughly 0.5 MPa), and the unmelts were eliminated by a filter. Then, the extrudate flow was drawn into the filament uniaxially and collected on a spool with an appropriate rotating speed of 10 m/s.

Afterward, the green fibers were cured in ammonia at a heating rate of 0.1 K/min to 300 ◦C and pyrolyzed up to 1000 ◦C in flowing ammonia at a heating rate of 1 K/min. Then, the fibers were heated to 1600 ◦C under flowing N<sup>2</sup> at 2 K/min. Finally, white composite ceramic fibers were obtained after cooling to ambient temperature.
