Studies On Structure Design And Performances Of Conductive Composite Fibers And Textiles Based On Transition Metal Carbide

Two-dimensional（2D）transition metal carbide（MXene）not only has high electrical conductivity,but also has a large number of surface active groups,making it attractive for fabricating novel conductive fibers and textiles.This work aims at addressing the difficult problems in the construction and functionalization of Ti₃C₂T_xMXene-based high-performance conductive fibers and textiles,such as the difficulty in retaining the inherent air permeability of the textile when depositing conductive substances on the textile substrate,the poor spinnability of pure MXene spinning dope,and the difficulty in balancing high tensile strength and/or high toughness of MXene-based composite fibers while maximizing the retention of their high conductivity.By regulating the assembly method of nanomaterials and compounding with polymers,the fiber and textile composites are endowed with excellent electrical,mechanical and thermal properties.We have designed highly breathable MXene-based hydrophobic electromagnetic interference（EMI）shielding textiles,highly strong MXene-based conductive composite fibers,high-tough MXene-based hollow and solid core-shell conductive fibers,and ultrastrong,supertough,and highly conductive MXene-based coaxial fibers.The research contents and innovative results are given as follows:（1）To address the conflict between air permeability and conductivity in Ti₃C₂T_xMXene-based textiles,a conductive textile with high porosity,high permeability and multifunctionality is prepared by spraying 2D Ti₃C₂T_xMXene nanosheets and one-dimensional（1D）silver nanowires（Ag NWs）alternately on a silk fabric substrate with a vacuum-assisted layer-by-layer assembly technique.The 1D Ag NWs form a highly conductive vein skeleton while the 2D MXene nanosheets act as the lamina.Biomimetic leaf-like nanostructures are built on silk fibers,forming a perfect conductive structure.The conductive active materials are successful introduced while retaining the porosity of the substrate.Meanwhile,the Ti-F bonds on MXene convert to a large number of C-F bonds during long-term aging,making the hydrophilic conductive textile hydrophobic with a high water contact angle of>140°.The sheet resistance of the MXene/Ag NW conductive textile is as low as 0.8±0.2??sq^-1.The textile presents outstanding EMI shielding effectiveness（SE）of 54d B in the X-band at a small thickness（120μm）.Furthermore,the water adsorption/desorption effect of MXene also endows the textile with humidity monitoring performances.（2）To address the problem of low tensile strength of highly conductive Ti₃C₂T_xMXene-based composite fibers,highly strong and conductive MXene/calcium alginate composite fibers are prepared by a one-step wet spinning technique using 10 wt%sodium alginate（SA）polymer assisted and calcium ion cross-linking.The coagulation mechanisms of neat MXene fibers and MXene/alginate fibers by acetic acid and calcium chloride coagulation baths are investigated in depth,and the enhanced mechanism of ionic crosslinking is demonstrated.Due to the synergistic effect of hydrogen bonds and ionic bonds,as well as the highly oriented structure,the MXene/calcium alginate composite fiber with 90 wt%of MXene has a tensile strength of 275.9MPa and a conductivity of 1985 S cm^-1,achieving the goal of significantly increasing the tensile strength of MXene-based composite fiber while essentially maintaining the conductivity of MXene.After the composite fibers are densely packed into textiles,the EMI SE in the X-band at a thickness of225μm reaches 95 d B.The highly strong and highly conductive MXene/calcium alginate composite fibers also have excellent humidity response properties and electro-thermal energy conversion properties.（3）To address the problems of poor spinnability of Ti₃C₂T_xMXene and the difficulty of combining high toughness and high conductivity of MXene-based composite fibers,graphene oxide（GO）is selected to improve the rheological and liquid crystal properties of MXene spinning dopes to form the conductive component GM,while regenerated cellulose（RC）is used as the toughness component.Hollow core-shell RC@GM fibers and solid core-shell GM@RC fibers are prepared by coaxial wet spinning method to regulate the distribution of conductive and tough layers.When RC is used as the shell,the RC@GM₉₀fiber shows a high toughness of 14.1 MJ?m^-3and a tensile strength of 134.7 MPa.Especially,the RC@MXene fiber with neat MXene as the core layer is also prepared,and its toughness and conductivity are 6.7 MJ m^-3and3.68×10⁴S m^-1,respectively.The tough and conducitve RC@MXene fibers can be woven into textiles,exhibiting excellent EMI shielding efficiency of over 90 d B in the X-band and outstanding solar-thermal energy conversion properties.When GM is used as the shell,the core-shell fibers are highly conductive.The conductivity of the GM₇₀@RC fibers reaches 1.68×10⁴S m^-1,which can increase to 9.90×10⁴S m^-1by further chemical reduction and show excellent electro-thermal energy conversion performance.（4）To address the conflict among high tensile strength,high toughness and high conductivity of Ti₃C₂T_xMXene-based composite fibers,supertough and ultrastrong MXene core-aramid nanofiber（ANF）shell fibers with exceptional environmental stability are prepared using the coaxial wet spinning methodology by adjusting the stretching ratio,shell thickness and MXene concentration.The outer ANF shell not only enables the high orientation and stacking of MXene core due to the spatial confinement effect,but also provides effective reinforcement and protection effects to optimize the comprehensive performances.As a result,the fabricated core-shell fiber integrates a record-high toughness of 48.1 MJ m^-3,a high strength of 502.9MPa,a high conductivity of 3.0×10⁵S m^-1,and an excellent EMI shielding efficiency.Moreover,the fibers show high chemical stability and exceptional resistance to cryogenic and high temperatures,and tensile and bending fatigue.The resistences to extreme environment and oxidation endow the fibers with satisfactory EMI shielding stability.