Study On In Situ Modification Of Aramid Fiber Ⅲ And Electromagnecit Properties Of The Prepared Composite Fibers

With the rapid development of electronics,communications and information technology,electronic instrument and equipment have been widely used in various fields in modern society.The development of composite materials with electromagnetic function is of great significance.Due to the outstanding mechanical properties,admirable resistance to high temperature and harsh environmental,aramid fiber Ⅲ is expected to possess excellent electromagnetic function after electromagnetic modified.In order to combine excellent properties of aramid fiber Ⅲ with electromagnetic function,in this paper,in situ liquid phase synthesis method can be used to prepare conductive polypyrrole（PPy）and magnetic particles（Fe₃O₄）coating layer on the surface of aramid fiber.Therefore,there is a facile method to prepare excellent electromagnetic function aramid Ⅲ composite fibers;namely,to control the thickness and particle size of coating layer on the surface of composite fibers by adjusting the process parameters of in situ synthsis.The conditions of in situ preparation of conductive aramid Ⅲ composite fibers are explored.Firstly,PPy coating on composite fibers are prepared with different dopants and FeCl₃ as oxidant.The effects of different dopants are investigated.According to SEM analysis,PPy coating on the surface of composite fibers can be realized by in situ polymerization without dopant,and the quality of the PPy film was poor.The results of SEM and FT-IR show that,composite fibers are prepared by in situ polymerization,with the acid（HCl,PhA,SA,OA）and salt（MAP,IC）as dopants.The dopants lead to the homogeneous micromorphology of the PPy coating layer on the composite fibers surface,in which OA/PPy-F₃ is optimal.The XRD results show that the crystallinity of OA/PPy-F₃ is the best among the composite fibers.Moreover,according to the electromagnetic properties analyses,compareing with the original aramid fiber Ⅲ,the conductivity of the composite fibers with the dopants can be increased to 14 orders of magnitude.The reflection loss OA/PPy-F₃is the best among all the composite fibers,and the value is up to-39.7 dB at the 3.5 mm thickness.Next,in the preferred choice of OA as dopant,the effects of different concentration of OA on the composites are investigated.According to SEM results,it is found that with the OA concentration increasing,the diameter of the prepared fibers product increases at first and then decreases.The morphology of OA-2 is the most homogeneous.According to the SEM and FT-IR results,the mechanism of PPy coating can be infered.Coordination compounds[Fe（C₂O₄）₃]^3-are formed by OA and FeCl₃ and leads to the orientation growth of the PPy coating layer,and the uniform PPy coating is formed at a suitable concentration of OA and FeCl₃.The electromagnetic properties show that,the conductivity of the composite decreases with the concentration of OA increasing,from 0.933 S/cm down to 0.0094 S/cm.When the thickness of composite material is 3.5 mm,OA-2 has the best reflection loss value.The third,in the preferred choice of the concent of OA,the effects of concentration of FeCl₃ are studied.SEM and XRD results show that,with the increase of concentration of FeCl₃,the diameter of the prepared product gradually increased,and the crystallinity gradually decreased.The PPy coating on the product OX-3（namely,OA-2）is the most homogeneous.The results of electromagnetic properties show that,the conductivity of the composite fibers increases with the concentration of FeCl₃ increasing,from 0.0138 S/cm up to 1.433 S/cm.In the case of thickness at 3.5 mm,OX-3 with moderate and dense PPy coating has the optimal reflection loss.The hydrothermal synthesis method of in situ preparation of ferrite magnetic particles coating on aramid fiber III is explored.FeCl2 and NaOH as precursors and SDBS as dispersant are used to in suit prepare Fe₃O₄ coating on m-F（aramid fiber III is modified by potassium permanganate）.And the effect of different reaction temperature was investigated.The SEM and FT-IR results show that,the chelating effect of hydroxyl groups with Fe2+ or Fe3+ ions leads to Fe₃O₄ coating on the surface of m-F fibers because of mechanical and chemical adsorption.According to XRD,the crystallinity of m-F decreased significantly after etching.The Fe₃O₄coating is further oxidized to Fe₂O₃ at higher temperatures.The crystallinity of the composite fibers continuously decreases as temperatures increasing.The results of the electromagnetic properties of the composite fiber show that,at the thickness is 3.5mm,Fe₃O₄/F₃-2 has the best absorbing performance at-2.25 dB at 4.32 GHz.In the range of 7-15 GHz,and Fe₃O₄/F₃-4 has the optimal absorbing performance,and the reflection loss is-3.37 dB at 14.32 GHz.