Preparation And Properties Of Micro-nanofibers Core-spun Yarn And Its Fabric Piezoelectric Sensor

With the increasing popularity of smart wearable concept,more and more smart wearable devices are coming into daily life.Piezoelectric sensing devices have a wide application prospect in human movement and health monitoring due to their unique electromechanical coupling effect.As the core component of smart devices,the performance and structure of the sensor determine the accuracy of real-time monitoring and the comfort of human body wearing.Common piezoelectric thin film sensors are rigid and prone to cracking,poor permeability,and poor fit with human motion,resulting in poor motion monitoring response.Based on the high pressure induced dipole moment and electrodepolarization of electrospinning technology,PVDF piezoelectric micro-nano fibers with good flexibility and rich polarβ-phase content can be prepared,but the poor processability of PVDF fiber film restricts its practical application development.To solve this problem,in this paper,a flexible piezoelectric sensing based core yarn was developed in combination with conjugated electrospinning technology,and the preparation process of electrospun core yarn was investigated to explore the influence of process parameters on the piezoelectric properties of PVDF micro-nano fibers on the piezoelectric properties of PVDF micro-nano fibers.Further,a series of piezoelectric sensing fabrics with different structures of tissues were made using the developed flexible piezoelectric core yarn,and the laws of structure and performance were investigated to explore the application of motion sensing piezoelectric sensing monitoring.The main research contents are as follows.（1）Based on single-needle electrospinning technology,a series of concentration ratios of PVDF spinning solution were characterized by single-needle spinning,and the best spinning solution concentration ratio of 10 wt.%was obtained;then,PVDF micro-nanofiber piezoelectric core yarns with different winding/twisting speed ratios were prepared by conjugated electrospinning;according to the morphological structure characterization of piezoelectric core yarns by SEM,it can be seen that each yarn is generally uniformly wrapped,and different The spinning parameters affect the distribution orientation of the micro-nanofibers;combined with FTIR,DSC and XRD to determine,analyze and characterize the effect of piezoelectricβ-phase of PVDF micro-nanofibers with different speed ratios of core yarn shell layer during processing,the optimal polarβ-phase content and crystallinity were 93.82%and51.45%,respectively,and the grain size could reach 3.7 nm when the winding/twisting speed ratio was 700/1000.The positive effects of high pressure polarization and traction stretching on PVDF piezoelectricβ-phase during the conjugated electrospinning process were further verified by the determination of the piezoelectric constant d₃₃.（2）Combined with the optimal electrospinning process,piezoelectric core yarns with different micro-nanofibers cladding layers were prepared with silver-plated nylon as the conductive core wire electrode to investigate the structural properties of piezoelectric yarns with different cladding thicknesses.The morphological structure of the longitudinal and transverse surfaces of the PVDF/silver-plated nylon cored yarns was characterized by SEM,which showed that the yarns had uniform morphology and good surface micro-nanofibers orientation.The results show that the 7-layer PVDF micro-nanofibers core yarn is the best choice for subsequent fabric integration because it integrates as many PVDF piezoelectric micro-nanofibers as possible and has high skin-core bonding,better motion fit and deformation recovery in subsequent processing.（3）Piezoelectric PVDF/silver-plated nylon micro-nanofibers core yarns were integrated into three fabrics with different tissue structures to design flexible two-dimensional textile-based piezoelectric sensors.Firstly,their structural properties were characterized by the analysis of their appearance morphology and mechanical property tests.The results show that the PVDF micro-nanofibers core yarn has good processability.The fabrics differ in flexibility,breathability,comfort and deformation recovery depending on the tissue structure,and the content of piezoelectric PVDF/silver-plated nylon core yarn is also different,and the design can be selected according to the requirements.Secondly,combined with different application scenarios,the piezoelectric sensing performance and motion monitoring performance of different fabrics are analyzed and characterized:in the mechanical tapping piezoelectric performance test,the three fabrics have good sensing sensitivity to different tapping frequencies,all can produce greater piezoelectric signal output with the increase of tapping frequency,and also have stable signal output after long time and multiple impacts.In the same 1Hz frequency of the impact of plain fabric can produce up to 3.06 V,182.27 n A piezoelectric output signal;through different pressure voltage output signal fitting,the sensitivity is 35.01 mV/N.Three fabrics on the finger,back of the hand and elbow bending movement in 45°and 90°bending degree of motion changes in good induction,piezoelectric signal with the increase in bending angle and The piezoelectric signal increases as the bending angle increases,and the sensor has a good monitoring effect with fast test response when used.In summary,the flexible piezoelectric PVDF/silver-plated nylon core yarn prepared in this paper has good sensing properties and textile processability.Its integrated fabric sensor can be more easily compatible with curved joint motion compared to thin-film type piezoelectric devices,and has good motion sensing and piezoelectric sensing monitoring performance,which has great potential for the preparation and application of human wearable motion monitoring devices.