Preparation And Characterization Of Highly Oriented Polyvinylidene Fluoride Fiber Membrane

Polyvinylidene fluoride?PVDF?has better performance than traditional piezoelectric materials.It has the characteristics of softness,light weight,wide frequency response and impact resistance and has become the research hotspot of emerging flexible sensors.Electrostatic spinning is an ideal method for the preparation of flexible wearable equipment,which is simple in operation and low in cost,and is superior to the traditional preparation method.In this dissertation,the PVDF fiber membrane and the PVDF/CNT composite fiber membrane were prepared by electrospinning.The effects of different spinning parameters on the morphology and crystallization properties of fiber/composite fiber membranes,and the influence of carbon nanotubes on the morphology and properties of PVDF composite fiber membranes were explored,which lay the foundation for the development of smart textiles and wearable piezoelectric sensing devices.The main research work of this dissertation is shown as follows:1.Preparation and characterization of electrospun PVDF fiber membrane.PVDF nanofiber membranes with different spinning voltage,spinning speed and needle diameter were prepared.The morphology of the fiber membrane was characterized by scanning electron microscope?SEM?.The diameter of the fiber was measured and counted,and the diameter distribution map of the fiber was made.The influence of the change of three spinning parameters on the diameter distribution was analyzed.The influence of the change of spinning parameters on the crystallinity of fiber was investigated by differential scanning calorimeter?DSC?.2.The preparation and characterization of electrospun PVDF oriented nanofiber membrane.The PVDF oriented nanofiber membrane was prepared by roller receiver.The effect of drum rotation speed on the morphology,crystallinity and crystal structure of the fiber was investigated by changing the rotational speed of the drum.The morphology of the fiber membrane was characterized by scanning electron microscope?SEM?.The diameter of fiber was measured,and the diameter distribution map of fiber was made.The influence of rotation speed on fiber diameter distribution was analyzed.The crystallinity and phase content of fiber membrane were characterized by X ray diffractometer?XRD?.3.The preparation and characterization of electrospun PVDF/CNT oriented composite nanofiber membrane.The dispersion of carbon nanotubes and modified by concentrated sulfuric acid and concentrated nitric acid carbon nanotubes in polymer solution was explored.The influence of carbon nanotubes on the morphology of PVDF fiber and the effect of carbon nanotubes content on the crystalline structure of fiber membrane were explored.The surface morphology of PVDF/CNT composite fiber membrane was characterized by SEM.The crystallinity of the fiber membrane was characterized by XRD.The crystallinity and the content of the beta phase of the fiber membrane were analyzed and calculated.The piezoelectric strain constant of the PVDF/CNT fiber membrane was measured by a quasi-static d₃₃ tester.The experimental results show that,?1?With increasing of the voltage,the fiber diameter distribution tends to be concentrated,the crystallinity of fibers increased;with increasing of the spinning speed,droplet and adhesion phenomenon were appearedfor the fibers,and fibers diameter distribution becomes wider,the crystallinity decreasing;with decreasing of the needle diameter,fiber diameter distribution becomes more uniform,and the crystallinity is improved.?2?Using a roller receiving device for collecting fibers,with increasing of the roller speed,the degree of orientation of fibers enhances.When the rotation speed is 1500rpm,the orientation degree of the fiber is between 70 degrees-90degrees.The orientation fiber membrane has higher crystallinity and beta phase content.When the rotation speed is 1500rpm,the crystallinity of the fiber is 43.66%and the content of the beta phase is 81.78%.?3?The unmodified CNT in the polymer solution is not well dispersed and easy to agglomerate.The dispersion of carbon nanotubes has been greatly improved after mixed acid modification.The addition of carbon nanotubes also makes the fiber diameter smaller and the fiber diameter distribution more concentrated.The crystallinity and beta phase content of PVDF/CNT composite nanofiber membrane with different CNT content are different.When CNT content is 0.05wt%,the crystallinity and content of beta phase is the largest,which is 50.70%and 84.88%,respectively.At the same time,the piezoelectric constant of the fiber membrane reaches 32pC/N.