| In recent years,flexible fabric sensors have attracted great attention because of their comfort and wearability.The fabric sensor can be used to observe and record human activities and physiological signals,including heart rate,joint movement,physical condition,sleep quality and so on.Conductive fiber,as the core component of fabric sensor,was studied in detail in this paper.In order to fabricate elastic conductive fiber in mass and low cost,a one-step wet-spinning device,including the forming,drawing,drying and collecting of the fibers,was designed.The elastically conductive fibers with pure polyurethane core and carbon black/polyurethane sheath with different process parameters were prepared by the experimental device.The conductive mechanism was studied by observing the inner structure of the fibers,and the influence of process parameters on the mechanical and electrical properties of the conductive fibers was investigated by means of electrical tests of the fibers.Fiber strain sensors and piezoresistive flexible fabric sensors were fabricated by different weaving methods.The specific research contents of this paper are as follows.(1)A one-step wet-spinning device for the preparation of core-sheath conductive fiber was designed.Compared with the traditional spinning device,we designed a part of the device for drying and winding collection of the fibers based on the originally simple forming and stretching operation in this paper.Coaxial nozzle was used as spinneret forming part to prepare conductive fibers with different components and layers in the core and sheath.In the design of the spinning device,two injection pumps were used to complete the solution propulsion,and different injection rates of the injection pumps were changed to prepare fibers with different components and contents in the core and sheath.The primary fibers were dried for different periods by a number of ceramic heating rings placed side by side,and the fibers were cross-reciprocated collected by means of a winding device containing reciprocating screw mechanism.The wet-spinning device for the preparation of core-sheath structure fibers was obtained by assembling the subassemblies of each part in the experiment.(2)Completed the preparation of spinning liquid in wet-spinning process.Through the established spinning device and the infusion pump that sets the uniform injection rate,the single-factor model was adopted to adjust the content of carbon black in the sheath of the fiber and the draw ratio between the spinneret and the first drafting roller downstream of the spinneret(DR1)to obtain conductive fibers with different parameters by controlling the variables.(3)The internal structure of the fibers was observed by CCD camera and scanning electron microscope(SEM),and the conductive mechanism of the conductive fiber was studied.The linear density values of the fiber under different parameters were obtained by weighing method with electronic balance.The electrical resistance of the fiber with different parameters per unit length was measured by using a multimeter based on the four-probe method.The mechanical properties of fibers were tested by electric universal tensile testing machine,and the effect of different process parameters on the mechanical properties of fiber was studied.In the process of fibers being stretched,the fracture strength and fracture strain of the fibers with different parameters were obtained by combining the linear density of the fibers.In the mechanical tensile experiment,a digital bridge was used to record the change of electrical resistance of the conductive fibers during the tensile process,and the influence of different technological parameters on the electrical properties of the fiber was studied.The results showed that the cores of the conductive fibers prepared under different parameters were irregular shape or slightly dispersed appearance,and the outer edge of the fibers was serrated.Unidirectional tensile test showed that the carbon black content and the drafting ratio had a great influence on the mechanical and electrical properties of the fibers.With the increase of the content of carbon black,electrical resistance of the fiber per unit length decreased gradually.However,with the same content of carbon black,the electrical resistance value of the fiber per unit length increased with the increase of the draw ratio.The percolation threshold of the fiber was within the range of15 wt%-16 wt%.When the content of carbon black was between 14 wt%-15 wt%,the fiber resistance is greatly affected by the content.When the content of carbon black is between 16 wt%-21 wt%,electrical resistance of the fiber decreased slowly with the increase of the content;when the content of carbon black was between 21wt%-30wt%,electrical resistance of the fiber basically had no obvious change.With the increase of the content of carbon black,the fracture strength and strain of the fiber would decrease gradually.The increase of draw ratio also led to the increase of fiber fracture strength.In the cyclic stretching experiment,the fibers that had been pre-stretched showed different resistance variation rules under different cyclic strains.During the 1000 cycles of cyclic stretching,the fibers showed better resistance repeatability,wider monitoring range,smaller strain response(0.23%)and faster response time.(4)Conductive fiber was used as a fiber strain sensor to study the conductive mechanism of the sensor,and the detection experiment was carried out by fixing the sensor at the human joint.The result showed that the sensor has high sensitivity and fast resistance response.The conductive fabric gloves were prepared by inserting the fiber strain sensor into the gloves by the method of embedded weave.The application tests of conductive fabric gloves on different occasions were carried out.The data proved that the conductive fabric gloves had good strain discrimination,and could be used in medical and industrial production activities.(5)Fabric sensors with different weaving structures were prepared according to different weaving methods.Based on weaving method,fabric sensors with woven plain and twill structures were prepared.Due to their compact fabric structure,the sensors showed lower sensitivity and better change rule in cyclic compression test.Based on the embedding method,fabric sensors with layered and over-pressed structure were prepared.In different performance tests,the sensor showed great sensitivity and good repeatability.The experimental data showed that the pressure sensors could be used in the fields of carpet and mattress. |
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