Study On Structural Regulation And Mechanical Sensing Properties Of Highly Elastic Conductive PU Nanofibers

Flexible strain sensors have many advantages,such as flexibility,foldability,light weight and high integration,which has broad development prospects in the fields of health monitoring,wearable electronic devices,and electronic skin.The core components of flexible strain sensor are composed of conductive sensitive film and flexible substrate.Flexible strain sensors have two important performance parameters,namely wide strain sensing range and high strain sensitivity.Under large strain,the wide strain range requires the flexible sensor to maintain a stable conductive network,while the high sensitivity requires the flexible sensor's conductive path to undergo large changes under small strain.They are contradictory to each other.In order to solve this contradiction,this paper introduces carbon nanotubes(CNT)and carbon black(CB)into polyurethane(PU)nanofibrous membrane.CNT has one-dimensional elongated tubular morphology,which can retain a large amount of contact sites and ensure the stability of the conductive network;the CB particles are in point-to-point contact,under small strain,the conductive path composed of CB can be destroyed sharply.In summary,this paper uses prepolymerization method to synthesize polyurethane(PU),and the CNT was added in the prepolymerization process,the CB was added in the process of chain extension,the conductive nanofibrous membrane was followed prepared by electrospinning technology.The mechanical properties of conductive PU nanofibrous membrane can be improved by adjusting the microstructure of PU,the synergistic effect of CNT and CB enables PU conductive nanofibrous membrane to simultaneously obtain a wide strain range and high sensitivity.Firstly,this paper uses polypropylene glycol 2000(PPG 2000),4,4 diphenylmethane diisocyanate(MDI-50)as raw materials,and anhydrous ethylene diamine(EDA)as chain extender to synthesize polyurethane by prepolymerization method.Under the premise that the quality of PPG 2000 is unchanged,change the amount of MDI-50 and EDA to prepare six kinds of PU spinning solutions with hard segment contents of 20%,25%,30%,35%,40%,and 45%,subsequently,six kinds of PU nanofibrous membranes with different hard segment contents were prepared by electrospinning technology.Test and analyze the micromorphology,chemical structure,thermal properties,crystallization and mechanical properties of six kinds of nanofibrous membranes.The results showed that the paper successfully synthesized polyurethane.The increase of PPG 2000 and EDA content can make the arrangement of hard chain segment more orderly and regularly.When the content of hard segments is 30%,the diameter of the PU nanofiber is 160.2nm,which possess the best microphase separation structure and the lowest glass transition temperature(-51.47?),the soft phase region forms a more regular crystalline region,has the highest diffraction peak intensity,the breaking strength of the PU nanofibrous membrane is 4.16 MPa,the elongation at break is290.6%,and the elastic recovery rate is the highest(98.3%).Secondly,the CNT is uniformly dispersed in PPG 2000 by ultrasonic dispersion method,and the PPG 2000 mixed with CNT is used for prepolymerization to synthesize carbon nanotubes / polyurethane(CNT / PU)to restrict the CNT to the PU soft phase region;CB is evenly mixed with chain extender EDA,as the chain extension reaction occurs,CB is restricted to the polyurethane hard phase region to prepare carbon black / polyurethane(CB /PU).Subsequently,two conductive nanofibrous membranes of CNT / PU and CB / PU were prepared by electrospinning technology.Test and analyze the micro-morphology,chemical structure,thermal properties,crystallization,mechanical properties,electrical properties and strain sensing properties of the two conductive nanofibrous mebranes.The results indicates that the diameter of CNT / PU nanofiber is 226.1nm,and the diameter of CB / PU nanofiber is171.6nm.Conductive fillers were added in the different stages of polyurethane synthesis,which makes CNT and CB selectively dispersed in the soft and hard phase regions of polyurethane.In addition,the introduction of carbon nanotube and carbon black increased/decreased the microphase separation of polyurethane;the existence of CNT hinderd the movement of soft segment macromolecule,which increases the glass transition temperature of CNT/PU nanofiber to-46.23?;there is preferential interaction between CB and the hard phase region of polyurethane,which promotes crystallization of hard chain segment,the breaking strength of polyurethane nanofibrous membrane was increased(6.66MPa),the elongation at break of polyurethane nanofibous membrane was not affected(270.5%).After the introduction of conductive filler,the polyurethane nanofibrous membrane completed the transformation from insulator to conductor.The introduction of CNT increased the sensing range of the conductive nanofibrous membrane(200%).The introduction of CB greatly improved the sensitivity of the conductive nanofibrous membrane(182.9).Finally,CNT was added in the prepolymerization process of polyurethane,CB was added in the process of chain extension,and the CNT / CB / PU conductive nanofibrous membrane was prepared by electrospinning.The electrical performance and strain sensing properties of the CNT / CB / PU conductive nanofibrous membrane were studied.The results showed that the synergistic effect of CNT and CB can greatly reduce the resistivity of polyurethane nanofibrous membrane.CNT / CB / PU conductive nanofibrous membrane has a wide strain sensing range(200%)and high strain sensitivity(256.51);CNT / CB / PU conductive nanofibrous membrane has excellent sensing repeatability under different strains and different frequencies,which can withstand a cyclic load of about 2000 times,possess excellent cyclic stability,CNT / CB / PU conductive nanofibrous membrane can monitor human body movements of different amplitudes.