Treatment of Kevlar(r) Polyaramid Fibers with Imidazolium-based Ionic Liquids

C.V. Moraes, V.D. da Silva, H.S. Schrekker, S.C. Amico
Federal University of Rio Grande do Sul,
Brazil

Keywords: polyaramid fibers, imidazolium salts, epoxy resins, interfacial compatibilization, ionic liquids

Summary:

Polyaramid fibers (Kevlar) can be used to strengthen materials due to their high tensile strength-to-weight ratio and high thermal stability. These properties of Kevlar fibers can be attributed to the intermolecular hydrogen bonds between the carbonyl groups and the NH- centers of the adjacent chains. Also, additional strength of great influence is derived from aromatic stacking interactions. Nevertheless, poor adhesion/interaction between Kevlar and matrix can be a disadvantage when these fibers are used for the preparation of reinforced composite materials, and as it is known, the mechanical properties of such composites drastically depend on the extent of the fiber-matrix interfacial adhesion. The surface of the fiber can be considered quite inert due to the polyaramids high crystalline nature, resulting in its poor adhesion with the matrix. Therefore, in this work, dicationic imidazolium-based ionic liquids are used to treat Kevlar with the aim of improving Kevlar and epoxy resin adhesion/interaction. The resulting fiber was characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Contact angle measurements were made in an optical tensiometer to investigate the wettability of epoxy on the untreated and treated fibers. SEM images showed differences between the surface of commercial and treated Kevlar®. TGA thermograms presented 16% of mass loss at 300˚C range, compatible with the degradation of the ionic liquid used. FTIR spectra of treated fiber showed new peaks that indicate presence of imidazolium ring and carbon nitrogen double bond. In addition, there was a decrease of the peak that is characteristic of nitrogen hydrogen bond on amide, suggesting new hydrogen bonds between Kevlar and the ionic liquid.