Novel Solvent-free Electrospinning Technoledge To Fabricate Functional Ultrathin Fibers And Applications

In this paper,the history and growth of electrospinning(e-spinning)technique and the morphologies and wide applications of as-spun ultrathin fibers are reviewed.At the same time,the e-spinning process is analyzed thoroughly.It is pointed out that solution e-spinning faces a tremendous trouble: over 80 wt% of organic solvents using.These solvents are explosive,toxic and harmful.The conversion of fibers is less than 20%.A large number of volatile solvent is hard to recycle and seriously endangers the health of operators and cause environmental pollution.Melt e-spinning is solvent-free,but the device is complex and high temperature limits the functionality of resultant fiber.In the two oridinary e-spinning processes,it is a physical change that the jets are forming solid fibers by solvent volatizing or temperature decreasing.We have proposed a chemical change of jet to form solid fibers under the influence of external conditions,overcoming the defects of solution or melt e-spinning.Newly modified e-spinning devices,recipes of e-spinning precursor solution and e-spinning processes were investigated,by which the ultrathin fibers were fabricated successfully.Through adjusting the recipe or adding functional materials into the precursor solutions,the functional micro/nano fibers could be obtained readily.The main contents of research and development are as follows.First,UV-assisted solvent-free e-spinning to fabricate ultrathin fibers and its application:Ordinarily UV curing materials consist of reactive oligomers,monomer diluents and photo-initiator.Because of fast curing,solvent-free volatilization,they are widely used in coatings,inks,adhesives and other fields.The UV curable material is used as the e-spinning precursor solution and the traditional solution e-spinning device improved,which the nozzle and collector is placed in a transparent box filled with inert gas,such as N2.During the e-spinning operation,the jet left from the nozzle is cured into solid fibers by UV irradiation and deposited on the collector.This device overcomes strong oxygen inhibition effect on curing of the jet having high specific surface area.In this process there is not any "solvent" volatilized and e-spinning jet solidified completely.Because the recipe of UV system could be adjusted conveniently,this solvent-free e-spinning ways gave the functional ultrathin fibers conveniently,such as color fibers by doping dyes,conductive fibers by adding polyaninline(PANi)particles,magnetic fibers by adding iron oxide particles.Second,thermal assisted solvent-free e-spinning to fabricate ultrathin fibers and its applicationThere are many kinds of industrial thermal curing systems,such as epoxy adhesive,polyurethane(PU)adhesive,and so on.Among them,the reaction rate of isocyanate with hydroxyl group is faster,and depends on the temperature.So,the solvent-free two-component PU system was employed for e-spinning.Based on the synthetic process of conventional PU and given solventless e-spinning process,the synthesis of PU precursor solution was improved where the low molecular weight polyol(Low-Mw,PTMG-500)was employed for preparing prepolymer,and other Low-Mw polyol(PEG-400)used as chain extender.During the chain extension,the e-spinning was conducted and assisted by thermal radiation(~50 °C),and ultrathin PU fibers fabricated with average diameter of 25-60 μm.Adjusting the recipe of e-spinning precursor solution,the 2,2-bis(hydroxymethyl)propionic acid(DMPA)was introduced to take the place of chain extender,PEG-400 partially,and the surface of as-spun fibers had hydrophilicity to some extent,which was helpful for oxidization polymerization of aniline in situ and deposition on the fibers’ surface to afford conductive PU/polyaniline(PU/PANi)composite fibers.This thermal assisted e-spinning is a solvent-free and ecofriendly process which leads to a novel approach to fabricate a variety of PU-based function or composite fibers having potential applications in protective and anti-corrosive coatings,antistatic fabrics,sensors,etcIn this paper,two kinds of solvent-free e-spinning approach for preparing ultrathin fibers are presented.These approaches have solved the problem of solvent volatilization in conventional solution e-spinning which results in the limitation of large-scale application.And their e-pinning setups are modified simply.These two solvent-free e-spinning means have the advantages of being environment-friendly,widely available in materials and easy to be doped with functional materials,and are potential applications in the field of 3D e-spinning(direct writing / 3D printing).