| With excellent thermal, electrical and mechanical properties, carbon nanotubeshave attracted high waves of scientists researches on it. In these noteworthy, lowdensity, high aspect ratio, high mechanical properties showing great potentiality in apolymer matrix reinforced phase. Kevlar, a new type of aramid fiber compositematerial, was developed by DuPont in1960s. Scince the invention, its high strength,good thermal stability drew lots of people’s attention. By deprotonation method,Yang dispersed macro structure of Kevlar fibers into nanofibers without destructionin2010. Since then, as a new one-dimensional polymer material,Kevlar nanofiberswas added into the "polymer family". Based on these, making a comprehensiveutilization of the ultra-high modulus and high strength, We blend carbon nanotubesand Kevalr nanofibes to effectively highlight their high strength, high modulus andelectrical properties. Undoubtedly, the composite film will add new highlights incomposite material area.As raw material,multi-wall carbon nanotubes are dealed with purification andsurface modification treatment respectively. After a series steps of pre-acidificationprocess with sulfuric acid and hydrogen peroxide,the carboxyl group was graftedonto the surface of multi-walled carbon nanotubes. Subsequently, we affirm theeffective purification is a necessary method of enhancing the quality of multi-walledcarbon nanotubes. Under a confirmed of the carboxyl group’s effective access, weprecisely calculateded the surface carboxyl content quantitatively.The processedcarbon nanotubes can be uniformly dispersed into DMSO solution with the contentof1mg/ml.After stirring in potassium hydroxide solution for a week, Kevlar fiber wasdeprotonated in DMSO. By observation, we found the microscopic size of theKevlar fibers with length of1-10μm and diameter of10-20nm range. By filtration,we have prepared carbon nanotubes reinforced Kevlar nanofiber composite filmunder appropriate proportion. We found that the structural integrity of the compositefilm can be maintained around400°C. As effective grafting of carbon nanotubes, the electrical properties of Kevlarcomposite films will inevitably improved. Based on this, we detailed characterizedthe conductivity and permittivity of films under different volume fraction of carbonnanotubes. With10%volume fraction of carbon nanotubes, the conductivity of thecomposite film improved to2.1×10-3S/cm. Under a frequency of1000Hz, we got amaximum dielectric constant of53.2with dielectric loss of less than2. Meanwhile,we fitted the conductivity and dielectric thresholds in accordance with measuredcurve. The conductive and dielectric calculated threshold are2.5%, and the criticalexponent are1.21and0.025respectivitily.Kevlar fiber reinforced often act as a strengthening phases in various polymers,ceramics, and metal matrix polymer. This article will change Kevlar nanofibers asmatrix, then by adding carbon nanotubes as reinforcements to obtain excellentmechanical properties. After being tested and summarized, we set up relationshipbetween the mechanical properties of thin films and carbon nanotubes mass fraction.As its degree of dispersion, we found that the strength and modulus of the filmsshowing a downward trend after rise with the mass fraction of carbon nanotubes.Finally, with the improvement method of annealing and layer by layer, we getaccess to enhance the mechanical performance of the composite films. Themaximum strength of the film is383MPa with modulus of35.6GPa.The carbonnanotubes are effectively added to improve the mechanical properties of the film.We concluded and discovered the mechanical properties of polymer films preparedin this article are the best in all composite films. We also explored the interactionsbetween them is strong π-π-conjugated hydrogen bonds. This mutual interactionbetween the matrix and the enhancement and the excellent mechanical properties ofraw materials are the two highlighting factors for the excellent mechanicalproperties of the composite film. |
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