Highly-efficient Fabrication Of PAN Micro/Nanofiber And Study On Its Properties

PAN micro/nanofiber has very excellent adsorption,mechanical and electrical properties,and is widely used in super capacitors,micro devices due to its small diameter,uniform size distribution.How to prepare the excellent performance of PAN micro/nanofiber is the key of preparing carbon micro/nanofiber,so the PAN micro/nanofiber has been one of the hotspot research,and preparing PAN micro/nanofiber efficiently has become the main bottleneck of scale production of carbon fibers.To enhance the properties of PAN micro/nanofiber we considered it in two aspect,one is changing the micro/nanofiber itself,the other is adding nano materials.Carbon nanotube and graphene owing to its excellent mechanical,adsorption and electrical properties,had become one of hotspot researchs,especially after the discovery of graphene.Because of the stability and surface inertia of carbon nanotube and graphene,the application of carbon materials is very limited.The method of doping the carbon nanotubes and graphene into micro / nanofibers has been get more and more attention of researchers.Polyacrylonitrile(PAN)precursor micro/nanofibers are prepared by traditional electrospinning device and the centrifugal spinning device respectively.Then the nanofiber bundles are drew in hot air with a constant force into 1 and 3 times of the original lengths.Subsequently,the crystalline structure,orientation,morphology,diameter of PAN micro/nanofibers before and after drawing treatment were characterized by the methods including WAXD and SEM.The results show that:(1)the efficiency of centrifugal-electrospinning is far higher than electrospinning as much as 120 times(the fluid flow rate of centrifugal-electrospinning: 2m L/min,the fluid flow rate of electrospinning: 1m L/h).(2)Despite a low of crystallinity from centrifugal spinning or electrospinning(the crystallinity of precursor centrifugal spinning PAN nanofiber is 25%,while the crystallinity of precursor electrospinning PAN nanofiber is 10.1%),the PAN precursor micro/nanofibers prepared by centrifugal spinning have certain orientation(60.5%).while the PAN precursor micro/nanofibers prepared by electrospinning have almost no orientation.(3)Hot-air-drawing with a constant force(1.00N)contributes to a higher crystallinity(centrifugal spinning: 45.8%,electrospinning: 36.2%)and orientation(centrifugal spinning: 72.5%,electrospinning:59.8%)of PAN micro/nanofibers.Moreover,the increasing drawing temperature and force resulted in the decrease of the diameter of PAN nanofiber bundles(the diameter of PAN micro/nanofibers prepared by centrifugal spinning decreased from 675 nm to 510 nm,while the diameter of PAN micro/nanofibers prepared by electrospinning decreased from 460 nm to 355nm).The carbon nanotubes and graphene were treated by potassium sulfate,carboxyl and hydroxyl groups were successfully introduced on its surface,meanwhile,with the methods of ultrasound and centrifugation,both the acidified graphene and the acidified carbon nanotubes are effectively combined by pi-pi and van der Waals forces,graphene/carbon nanotube hybrid materials are successfully prepared.The graphene and carbon nanotube hybrid materials are doped into carbon micro/nanofibers by centrifugal-electrospinning,no matter graphene,carbon nanotube or hybridized materials can be distributed uniformly in carbon micro/nanofibers in a doping ratio that is higher than the carbon micro/nanofibers prepared by electrospinning.Through mechanical properties test,the addition of the acidified carbon nanotubes improved the mechanical properties of micro/nanofibers,and under the synergy of the acidified graphene,the mechanical properties of the micro/nanofibers is further improved,the addition of the hybrid materials can significantly improve the mechanical properties of the micro/nanofibers.