Self-sensing Properties Study Of PVDF Piezoelectric Fibers And Textiles

As a kind of new functional material,smart textiles have taken tremendous energy to the textile industry.Due to the unique mechanism of perception,feedback and response,the smart textiles are widely used in the field of protection,detection,etc.Smart textile materials are the base of advanced smart textiles,its own features determine the intelligent degree and perceptional direction of the textiles.To some extent,the weaving structure requires flexible textile materials.Owing to excellent piezoelectric effect,poly(vinylidene fluoride)has the ability to make electrical signal response to external load.The fibrous PVDF can easily combine with the ordinary fiber to make smart textiles,hence,PVDF is a sort of ideal smart textile materials.In this research,we fabricated the continuous PVDF fiber with the method of melt spinning.We studied the influence factors of fiber performance,such as melting temperature,diameter of nozzle and coiling speed during the melting process,and we found that in the condition of 230?,nozzle hole under 2 mm in diameter and coiling speed at around 8 m/min,the fiber obtains good quality and uniform diameter.Because the piezoelectric effect of PVDF is closely related to the content of ? phase,we studied the effects of different tensile process on the crystallization conditions of the PVDF fiber.Under a bigger stretching ratio,the average size of crystals becomes smaller,simultaneously,the degree of crystallinity and the content of ? phase are greater.The higher temperature is in favor of crystallinity increasing,however the excessive temperature can lead to sharp decrease of ? phase.Therefore,the best stretching temperature is 90 ?.The faster stretching rate is beneficial to the promotion of crystallinity and content of ? phase,however,the effect is not significant.After twining the double spiral electrodes on the surface of fiber,we disposed the fiber with process of heat polarization,in order to make the electric dipoles in the polymer to orient in the direction of the electric field.The study found that the piezoelectric effect is not significant under polarization electric field lower than 20 MV/m,the polarization effect approaches the saturation point under polarization electric field higher than 40 MV/m.The optimum polarization temperature is 90?,the lower temperature goes against the orientation of electric dipoles,however,the higher temperature results in the decrease of ? phase content.As you know,the polarization process need take a period of time to get to the electric dipoles frozen,but after 1 h,the increase of piezoelectric effect is not obvious,which indicates the electric dipoles have basically oriented along the electric field.Loading different stretching frequencies and maximum strains caused by the load on the axis direction,the PVDF fiber is always able to output signals to match the applied load,showing the great self-sensing properties.We fixed a single fiber on the cantilever beam to work at free vibration.The frequency of feedback signal is basically consistent with the natural frequency of the beam,which reflects the vibration of the cantilever beam.Combining PVDF fibers with ordinary textiles in transverse and longitudinal directions,the smart textiles can output signals to record the transient impact.The 3D histogram drawn after processing can roughly describe the shape of the weight and the impact position,which represents the self-sensing properties of the PVDF textiles.