Study On The Continuous Preparation And Sensing Properties Of Conductive TPU Composite Fiber Yarns

A new generation of wearable electronics put forward more requirements on materials,such as stretchability,directly attached on human skin surface,light,miniaturization and so on.Carbon nanotubes-based conductive yarns with good flexibility and special linear structure can be woven into different shapes and have been widely used for flexible strain sensor,gas sensor,supercapacitor,etc.However,simultaneously endowing yarns with good conductivity,stretchability and large-scale production may still have difficulties.In this paper,the directional arrangement of electrospun thermoplastic polyurethane(TPU)fibers were decorated with multi-walled carbon nanotubes(MWNTs)and single-walled carbon nanotubes(SWNTs),to obtain the high conductive SWNTs/MWNTs/TPU fiber yarns.Then,we systematically studied the relationship between structure and properties of the composite fiber yarns,and explored the response behavior to organic vapors.Furthermore,the SWNTs/MWNTs/TPU fiber yarns were impregnated with polydimethylsiloxane(PDMS)solution to fabricate stretchable and conductive SWNTs/MWNTs/TPU/PDMS fiber yarns with core-shell structure.Then we studied systematically on the sensitive behavior of tensile strain and applied it to the monitoring of human several joints movement,further to explore its potential applications in field of wearable strain sensors.The main research results are demonstrated as follows:(1)By pulling the electrospun and water-bath collected directional arrangement TPU fibers successively into MWNTs dispersion and SWNTs dispersion for ultrasonic adsorption process,we fabricated the SWNTs/MWNTs/TPU fiber yarns.Continuous ultrasonic adsorbing MWNTs and SWNTs enhanced thermal stability,mechanical strength and conductivity(up to 13 S/cm).Moreover,with the physical effect of ultrasonication,MWNTs and SWNTs got into the fibers and formed three-dimensional network.Through a series of structure characterization and adhesion test,we found that there might be interface interaction between MWNTs,SWNTs and TPU fibers.Then,we explored its potential in the application of flexible organic vapor sensors.Respectively studying the composite fiber yarn on the sensitivity of three kinds of organic vapors,we found it had different degree of response and stability on different organic vapors,while it showed the best response and good cycle stability on ethylacetate.(2)The composite fiber yarn was immersed in dilute PDMS solution to fabricate the stretchable SWNTs/MWNTs/TPU/PDMS fiber yarns.Through the cross section structure observation of the yarn,we found that the composite fiber yarn formed the core-shell structure.The interior PDMS encapsulated and fixed the fiber network,while the outside PDMS formed a uniform shell by cladding it with a certain thickness.PDMS encapsulation didn’t significantly influence the conductivity of the composite fiber yarn,so we further studied its strain sensing behavior.Study found that,the composite fiber yarns exhibited good strain sensor performance.The workable strain range could achieve as large as 100% and it could keep good recoverability and cyclic stability even under large strain(50%)for 2000 cycles.Finally,we combined them with the fabrics to fabricate wearable strain sensors and to monitor several human joint movements,such as the neck,the wrist,the knee and so on.