| Mica/aramid paper-based composites was a kind of functional material which can be widely used in the fields of electric power,rail transit,new energy,national defense and so on.However,the poor interfacial bonding properties of paper-based composites and the poor anti-ultraviolet properties of aramid fibers had seriously limited the further improvement of their mechanics,dielectric properties and stability.Therefore,it has become the core of the research to improve the interfacial binding and ultraviolet resistance of mica/aramid paper-based composites.Due to the excellent ultraviolet shielding and surface activity,nano-TiO2 was often used to improve properties of composites.In this study,nano-TiO2 layer was introduced on the surface of aramid fiber(AF)by liquid phase deposition.The two-step activation method was used to graft polyethylenimine(PEI)with high charge density on the surface of mica(M).Then the aramid/mica paper-based composites were prepared by the traditional paper making technique.At the same time,the morphology,chemical structure,ultraviolet resistance and mechanical properties of the composites were studied by means of scanning electron microscope(SEM),fourier infrared spectroscopy(FT-IR),ultraviolet spectrophotometer and tensile testing machine.First,the effects of mica types,particle size and addition amount on the mechanical properties,insulation and UV resistance of aramid/mica paper-based composites were analyzed and evaluated.The results showed that the synthetic properties of the composites prepared by mica with uniform particle size were not good.The composites prepared by muscovite had the best performance.The insulation and UV resistance of the composites can be significantly improved by the introduction of muscovite,accompanied by serious loss of its mechanical strength.According to the comprehensive evaluation,it was the best preparation scheme to introduce 50 wt.%muscovite into the aramid/mica paper-based composites.Mica can be embedded in the three-dimensional network structure of aramid fiber.However,the poor surface activity of mica resulted in its poor interfacial binding with aramid fiber.After being irradiated by ultraviolet light for a long time,the fibrid which plays a bonding role in the composites will be seriously decomposed and damaged,while the chopped fiber and mica will not change significantly.Second,the two-step method was selected to activate the mica surface to improve its interface performance,in which dopamine(DA)was used as the adhesion substrate and PEI as the functional activator to obtain DA/PEI-mica((D/P)-M).The results showed that the interface binding and breakdown strength of(D/P)-M/A were 493.43 J/m2 and 11.91 kV/mm,respectively,which were 173.62%and 14.30%higher than those of the composites prepared by unmodified mica,prepared by electrostatic interaction between(D/P)-M and aramid fiber.Due to the hydrogen bond between(D/P)-M and aramid fiber,its interface binding strength and structure were improved.Finally,nano-TiO2 was grafted on the surface of aramid fibrid modifided by DA through liquid phase deposition method.4T-A,obtained by modified aramid fiber by nano-TiO2 for 4 h,can be used to prepare(D/P)-M/4T-A with the best performance.The breakdown strength and tensile strength of(D/P)-M/4T-A were 16.86 kV/mm and 19.54 Mpa,respectively,which were 41.92%and 165.13%higher than that of(D/P)-M/A.And its mechanical strength did not decrease significantly,under the irradiation of ultraviolet light for a long time.Nano-TiO2,helped to improve the ultraviolet resistance,can form a uniform coating on the surface of the fibrid and disperse in the coposites.At the same time,nano-TiO2 can maintain good mechanical strength by reducing structural defects in the composites. |
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