Study Of Complexation On Surface Modification Of Kevlar Fiber

Kevlar fiber exhibits an excellent thermal stability, lightweight, lower dielectric, as well as superior tensile strength and modulus and chemical inertness. They are widely used as an excellent reinforcement material for the advanced polymer composites such as fiber-reinforced composites, rubber goods, ropes and cables, ballistic, gaskets, and so forth. However, the Kevlar fiber-reinorced composites show poor interfacial adhesion between the Kevlar fiber and matrix resin, due to the low surface energy and chemically inert surface of the fiber. Therefore, surface modification or functionalization of Kevlar fiber is considerably urgent and necessary to obtain high performance Kevlar fiber/epoxy composites from effective interfacial interaction. Various methods of fiber surface modification have been developed. In this paper we used a new method complexation to treat Kevlar fiber.Firstly, in this study we used calcium chloride(CaCl2) and lithium chloride(LiCl) to treat Kevlar fiber. We studied the effect of different solvent(water and ethanol) on Kevlar fiber surface modification. Through the result of scanning electron microscope, we found that the ethanol solution was better than water solution. So we chosed ethanol as the solvent.Secondly, we studied the mechanism between CaCl2(LiCl) and Kevlar. The surface elements of Kevlar fibers were determined by X-ray photoelectron spectroscopy(XPS). The possible changes of the chemical structure of Kevlar fibers were investigated by Fourier transform infrared spectrum(FTIR). The crystalline state of Kevlar fibers was determined by X-ray diffraction instrument(XRD). The surface morphology and roughness of Kevlar fibers were analyzed by Scanning electron microscope(SEM) and Atomic force microscopy(AFM). It was found that the complexation was happened between CaCl2(LiCl) and Kevlar-29 fiber. Complexation had great influence on the structure and properties of Kevlar-29 fibers. The aminogroups of Kevlar-29 fiber were freed and the contents of-C-N- increased. The changes can improve the surface roughness of Kevlar-29 fibers. This can increase the adhesive of Kevlar fiber/epoxy composites.Thirdly, from the interlaminar shear strength(ILSS) of Kevlar fiber/epoxy composites and mechanical properties values, it can be concluded that treatment with 5wt% CaCl2 for 5h is the optimum complexation condition. And the optimum complexation condition for LiCl was 6wt% and 3h. We also compared the effect of CaCl2 and LiCl on Kevlar fiber surface, the result was that CaCl2 ethanol solution was better than LiCl ethanol solution with the same treatment time and concentration.Forthly, we did a preliminary study on the adhersion between Kevlar fiber and natural rubber. After complexation treatment, the tear strength and stress at 300% of Kevlar fiber/natural rubber composites increased significantly with the increasing of LiCl treatment time. The interfacial adhesion between Kevlar fiber and natural rubber was increased due to the grooves and increased specific surface area.