Preparation Of Cellulose Acetate Based Flexible Strain Sensor And Its Performance

With the continuous improvement of living standards,people’s demand for physical health monitoring is getting higher and higher.Various types of sensors have been widely studied,while traditional metal or semiconductor-based strain sensors are expensive,rigid and brittle,and have a small strain range,making it difficult to meet the needs of sports and physiological health detection.How to obtain a large strain range and high sensitivity at the same time by using conductive materials and ingenious conductive network structure design is one of the key technologies urgently needed to be solved in the development of flexible strain sensors.In this paper,we used cellulose acetate(CA)as raw material.Firstly,the oriented CA nanofiber membrane was prepared by designing a multi-edge electrospinning drum receiving device.The effects of spinning process parameters on the morphology and degree of orientation of CA nanofiber membranes(hereinafter referred to as orientation degree)were explored;then the effects of alkali treatment concentration and time on the molecular structure of CA nanofibers were investigated;finally,cellulose nanofiber membranes were pre-oxidized and carbonized,and the obtained carbon nanofiber membranes were encapsulated in polyurethane(TPU)to prepare the CA-based flexible strain sensor.The strain sensing performance under stretching and torsion behaviors was investigated,and its practical applications in detection of human physiology and motor behaviors were explored.The experimental results showed that the spinning solution flow rate and the rotating speed of the receiving drum significantly affect the orientation degree of the nanofibers.The optimal spinning parameters were as follows:the concentration of spinning solution was 20 wt.%,the flow rate of spinning solution was 0.7 mL/h,the rotational speed of receiving drum was 900 rpm,and the spinning voltage was 13 kV.The CA nanofibers prepared under the above conditions showed a diameter of 794.53±146.40 nm and an orientation degree of 92.86±2.13%.The irreversibly shrink of fiber membrane would occur when alkali treatment concentration was too high.The long alkali treatment time would make the nanofiber membranes loose and easy to deform,and the orientation would decrease.The optimal alkali treatment parameters were the concentration of alkali solution of 0.1 M and the treatment time of 24h.The CA-based flexible strain sensor showed a gauge factor(GF)value of 14.27 in the strain range of 0-70%,and had a linearity of 0.946.The GF value was 6175.70 in the 70-80%strain range with a linearity of 0.772.The resistance changes of the sensor exhibited a response characteristic that was related to the strain amplitude and independent of the strain frequency,and the response time was less than 200 ms with more than 1000 stable tensile cycle.Attaching the above flexible strain sensor to the skin surface can accurately detect the bending of the human wrist and neck,neck torsion and other large-scale strains,as well as changes in the human pulse and heartbeat before and after exercise,voice of different syllables from larynx and other small strains,the signals were stable and repeatable.The sensor was fixed on the wrist position for table tennis player swing motion detection,which can accurately distinguish the posture of the forehand and backhand swing.We could detect and correct the regularity of table tennis beginners’ movements through the change characteristics of peak shape and peak value.The sensor was attached to the first dorsal interosseous muscle of the right hand to detect muscle movement,which could accurately distinguish the up-down and left-right movements of the thumb.It could identify different gestures and could be used for the diagnosis and detection,adjuvant treatment and prognosis evaluation of muscle and joint diseases such as flexor tendonitis.