Ultrafast Thermal Conduction of Phase Change Fiber Enabled by Sheath Confinement‐Induced Ordered Orientation of Hydroxylated BNNs

Abstract Phase change fibers (PCFs) are increasingly popular in thermal storage and release applications, such as temperature management. However, a simple but effective integration of thermal conductive materials into PCFs to deliver ultrafast thermal conduction remains a big challenge. Herein, a facile one‐pot coaxial wet spinning strategy based on sheath‐confinement‐induced orientation arrangement of hydroxylated boron nitride nanosheets (BNNs‐OH) is proposed to fabricate the high‐performance PCFs. For the core‐sheath PCFs, the cellulose nanofiber (CNF)‐reinforced paraffin (CNF/PW) emulsions serve as the phase change core, while the dissolved cellulose and well‐dispersed BNNs‐OH act as the sheath precursor. By increasing the extrusion speed of the liquid core, the contraction of the fiber sheath is gradually finalized to induce the alignment of BNNs‐OH based on the confinement effect. Consequently, the highly oriented BNNs‐OH nanosheets in fiber sheath ( f = 0.8) endow PCFs with high phase transition enthalpy (125.1 J g −1 ), excellent thermal conductivity (10.15 W m −1 K −1 ), rapid heat transfer rate (1.6 cm s −1 ); moreover, the as‐prepared PCFs show good tensile strength (11.21 MPa) and leakage‐proof (0.13%). The as‐prepared PCFs are combined with thermochromic dyes for functional fabrics or applied as thermal management for a phone, demonstrating excellent thermal conduction and heat dissipation.