Research On Flexible Heating Element And Sensing Element Based On Carbonized Cotton Fabric

With the development of material science and electronic technology,flexible wearable electronics have attracted extensive attention and greatly improve the quality of people's life.As important parts of flexible wearable devices,flexible heating elements and flexible pressure sensors are highly desirable in applications such as cold protection,health care,signal monitoring,and electronic skin.Due to the good flexibility,light weight,low cost,abundant raw materials,and excellent electrical conductivity,carbonized fabrics are expected to play a role in the field of flexible wearable electronics.To develop carbonized cotton fabric based flexible electric heating elements and piezoresistive sensors with a simple process,low cost,and excellent performance.Carbonized cotton fabrics and carbonized cotton/thermoplastic polyurethane(TPU)composites were fabricated through carbonization treatment and dip-and-dry method.The surface morphology,Raman spectra,Fourier transform infrared spectra,X-ray photoelectron spectra,electrical conductivity,and mechanical performance were tested.Then,combining with the heat transfer theory,the influence of carbonization temperature,fabric structure,and TPU content on the electric heating performance of carbonized cotton fabrics and composites was discussed.The relationship among the voltage,temperature,and power density of carbonized fabrics was also analyzed.The heating stability and electrical resistance stability were tested and evaluated.Besides,a flexible heater was fabricated using the composites.Finally,carbonized cotton/TPU composites were used as the sensitive materials to fabricate the flexible piezoresistive sensors.The pressure sensing performance of the flexible piezoresistive sensors with different fabric structures and TPU content was analyzed.Furthermore,the flexible piezoresistive sensor with the optimal performance was selected for practical application testing.Based on the analysis,the conclusions are as follows:the fabrics remained the original structures,and the cotton fibers could be transformed into graphite-like carbonized fibers after carbonization treatment.Through dipping and drying,the carbonized fibers were coated with TPU uniformly.The composites exhibited good flexibility and mechanical properties.Carbonation temperature,fabric structure,and TPU content all affect the electric heating performance of carbonized cotton fabrics and carbonized cotton/TPU composites.The carbonized plain weave cotton fabric carbonized at 1000°C showed excellent electrical conductivity(10.17?/sq),and its surface temperature could reach 60.6°C at an applied voltage of 5 V.With the increase of TPU content,the surface temperature of the composites decreased slightly,but it could still meet the demand of flexible electric heating elements.Meanwhile,carbonized cotton/TPU composites showed excellent heating stability and resistance stability.The flexible heater made of the composite exhibited satisfactory electric heating temperature rise performance and heating uniformity,which can be combined with clothing.For carbonized cotton/TPU flexible piezoresistive sensors with different fabric structures and different TPU content,the sensor with interlock stitch and a TPU content of 4 wt%possessed the optimal performance.The sensor exhibited high sensitivity(98.77 k Pa^-1),wide working range(0-16 k Pa),and excellent stability(>4000 cycles).The wrist pulse,finger pressing,and finger bending motions could be monitored in real-time,which demonstrated the good application prospect of the flexible sensors in human health and movement monitoring.