Research On Strain Sensing Fibers Based On TPU And Mechanism Of Electromechanical Performance

Nowadays,conductive polymer composites material(CPCs material)is a kind of popular sensing material for the transformation from stress to resistance signal.With the advantage of great flexibility,CPCs material is more suitable for the application including human wearable equipment,electronic skin and other applications rather than traditional metal strain sensors.Although great progress has been achieved in the research of strain sensors which based on CPCs,problems such as electromechanical response attenuation and low linearity of electrical signal still occur and they are under urgent need of further research to release from to limitations on the practical application value of CPCs.In this paper,in order to study the electromechanical response and its mechanism of CPCs,we prepared a series of homogeneous conductive composite fibers based on thermoplastic polyurethane elastomer(TPU),and studied their strain sensing properties and mechanism of electromechanical response.In addition,based on the research results of electromechanical response mechanism,we improved the conductive composite fiber which based on TPU and constructed a series of sheath core sensing fibers with supreme strain sensing performance.The specific research contents and conclusions are as follows:(1)We prepared two series of homogeneous conductive composite fibers based on TPU(including single conductive filler component and two conductive filler components,respectively)by wet spinning method.The influences of conductive filler,fiber diameter and other parameters on variable sensing performance were studied.We demonstrate the applications of conductive fibers as strain sensors for monitoring human joints motion.The advantages of strain sensor based on these fibers are as following: high sensitivity under small strain stimulation(gauge factor of 6.0 within3.0% strain),remain conductive under 280.5% deformation,and are stable for more than 2000 cycles.The comparison of two kinds of conductive fibers shows that the combination of different conductive fillers is beneficial to connect the internal conductive network,improving the conductivity and strain sensing performance as a result.However,the problem of electromechanical response attenuation occurs on both conductive composite fibers.(2)We use the model for polymer viscoelasticity to explain the electromechanical response attenuation of two kinds of conductive composite fibers,and establish a connection between electrical signals and mechanical properties.After the model optimization process,MaxwellWeichert model is mainly used to fit the electromechanical properties of the conductive composite fibers we prepared.It is found that the fundamental mechanism of resistance relaxation under quasistatic load and dynamic cyclic load are the same Both are derived from the conduction network relaxation caused by polymer viscoelasticity.To reduce the direct impact of polymer chain relaxation on the conductive network is the fundamental measure to improve the stability of electromechanical response.(3)In order to reduce the influence of viscoelasticity on the conductive network and improve the stability of electromechanical response,a kind of carbon black-hydrogenated styrene butadiene block copolymer/thermoplastic polyurethane elastomer(CB-SEBS/TPU)sheath core conductive composite fiber was prepared.With pure elastomer as the core layer and conductive layer as the skin layer,this kind conductive fibers were constructed by the method of wet spinning,surface modification and coating.Compared with homogeneous conductive composite fibers,sheath core fibers can provide better strain sensing performance.The linear sensing range of sheath core fiber(larger than 100.0% deformation)is much higher than that of homogeneous conductive composite fiber(0-3.0% deformation).The signal provided by sheath core fibers has no shoulder peak phenomenon during the cyclic loading.The attenuation time under quasi-static and dynamic loading are respectively 170.67% and 39.62% longer than that of homogeneous conductive composite fiber,offering excellent signal stability and practical value.