Research On The Yarn Processing Technology Of Carbon Nanotube Fibers And Its Application

Carbon nanotubes have been receiving great attention since they were discovered,and they are assembled into various structures such as fibers,films,and aerogels.Among them,carbon nanotubefiber(CNT)is an important one-dimensional macroscopic of carbon nanotubes.It not only has mechanical properties comparable to high-performance fibers such as carbon fiber,but also well maintains the rich heat,electricity,field emission and other functions,so it is the focus of nanomaterials research in the 21 st century.Especially in the past 10 years,research scholars from all over the world have vigorously researched and developed various materialforms of carbon nanotubes,also adjusted and controlled the material structure to enhance the performances in various ways.Currently,in many studies the CNT fiber's length is short and the diameter is only about 10 microns.Such small diameter,short legth and small amount of CNT fiber are not suitable for engineering use,which limits its processing applications in the textile field,such as smart textiles and wearable device.Therefore,it is very necessary to assemble or compound small diameter CNT fibers into large-size CNT yarn(diameter> 100 ?m),but the carbon nanotube fiber tensile stress hardly stronger than 1GPa due to the weak van der waals force if the fiber diameter is greater than 50 microns.This paper designs principle and constructs devices for pre-treatment and posttreatment for the purpose of assemble the CNT fiber into large-scale CNT yarns.Pretreatment includes drying,denseing and assembly process and twisthing post-treatment.Further,exploring the non-twisting means of carbon nanotube yarn assembly method,and application possibilities of carbon nanotube yarn in textiles.The main research contents and conclusions of the paper are as follows:(1)Based on the characteristics of the CNT fiber grown by chemical vapor deposition method(CVD),it is dried,densified and assembied before twisting.After drying,the fiber is separatedfrom the water bath and convenient to storage and use.While drying and collecting,the roller has a weak convergence effect on the fiber surface,which can prevent the surface adhesion of the dried fibesr.The drawing speed,drying temperature and the length of drying zone all affect the drying effect.The winding part sets the winding program according to the fiber diameter to ensure the stable winding without interlining between the fiber layers.(2)The denseing treatment makes the CNTs mechanical properties well transmitted and enhanced in the macro CNT yarns.The principle and device of denseing treatment are designed based on the mechanical force and frictional force.The device is equipped with three independently controllable roller groups,each group contains four rollers and is arranged according to the height interval which to expand the contact area between the fiber and the rollers.The operation of the roller generates traction and friction on the fiber,so that the internal structure of the fiber is densed and the carbon nanotube bundlesare stretched and highly oriented.The dense structure and high orientation can enhance the mechanical properties of carbon nanotube fiber.A single group of rollers has 1.03 times drawing effect on the fiber and three groups are 1.09 times.The density of carbon nanotube fibers is enhanced with the numbers of used rollers.(3)The assembly device is designed and constructed to combine multiple carbon nanotube fibers into a large fiber strand.In order to acoid the path difference between each fiber,the device provide 5 vertical shaft columns for placing the dried carbon nanotube fiber bobbin.Due to the poor mechanical properties of single carbon nanotube fibers,steel ball bearings are used at the bottom of the shaft to reduce the dragresistance and ensure the smooth rotating of the compact process.Components such as rollers,yarn guide hooks and different yarn guide paths are used to controlling the accumulation tension.The maximum gathering speed is 50 m / min.(4)Carbon nanotube fiber twisting principle and device are constructed based on flying wing spinning method,which abandon the ring and traveller and rubber rollers and the spinning path is bottom-up.The structural parameters of the flying wing include wing length,opening angle,weight,and coefficient of friction with the spindle.The opening angle of the flying wing ensures the unwinding angle of the carbon nanotube fiber when it is unwound sideways along the bobbin.The flying wing follows the passive rotation to apply a certain unwinding tension to the fiber.The flying wing's own weight and coefficient of friction make the spinning balloon stable,and the rollers,guide hooks,and yarn guide path control the spinning tension to ensure even twist.The winding speed slows down as the number of winding layers increases to ensure that the carbon nanotube yarn twists are consistent during the continuous twisting process.The active winding and collection is designed for to reduce twisting tension fluctuation and yarn damage,so the yarn twist is more uniform and the quality is more better.(5)Based on the developed twisting device,the small-diameter(45-55?m),medium-diameter(80-100?m)and large-diameter(180-200?m)carbon nanotube yarns were prepared.Further exploring the mechanism of twist on carbon nanotube yarn and the difference between different diameters.When the twist is increased,the twist angle and the radial centripetal force of the yarn is increased,so the carbon nanotubes inside the yarn are compressed and bundled tightlyand the yarn structure is tight.Therefore,the diameter gradually shrinks and the breaking strength increases first and then decreases and the tensile strain increases with the increase of twist.And twist can improve the performance uniformity of the carbon nanotube yarn.(6)Based on the material effects of carbon nanotube fibers and the mechanism of polymers,the yarn method and technology of non-twisting means are studied.This paper uses polymer composite to enhance the fiber interface to obtain carbon nanotube composite yarn.The compact device is used to merge multiple carbon nanotube fibers through a drawing die which is saturated with a polymer solution.The fibers compressed and contracted by the drawing dieand the polymer penetrates into the inside of the fiber,then the carbon nanotubes are rearranged and fused under the action of the polymer,so that the interface between the fibers is strengthened and assembled into large-diameter carbon nanotube yarns.The branched-chain polyethyleneimine(PEI)has relatively good interface enhancement effect on carbon nanotube yarns,and the single fiber has a high mechanical retention rate.The yarn structure and performance are stable under other conditions,such as heat treatment,friction,bending,hot pressing,etc.(7)The prepared continuous carbon nanotube yarn is blended with natural fibers in a core-spun structure to develop functional yarns to explore the application possibilities of textiles and smart farbics.Eight CNT fibers are combined into a strand and added about 2500-3000 twist per meter to design a spring structure,which is wrapped with different content of short wool fibers.The carbon nanotube spring structure and the combined interface with the wool fiber can improve the fatigue resistance of the yarn.The excellent electrical and thermal properties of carbon nanotubes make composite yarns useful for electrical heating,warmth and electromagnetic shielding fabrics,and wool / CNT composite yarns are resistant to washing.