Effect of Surface-Limited Reactions on the Properties of Kevlar® Fibers

Aromatic diamides have been investigated as models for aramid fibers to select reagents and conditions suitable for surface-controlled heterogeneous reactions on Kevlar filaments. Reactions have been done on Kevlar fibers to introduce functional groups designed to interact with matrix resins and improve adhesion in fiber reinforced composites. The effects of reaction environments and conditions on the mechanical properties and surface topography of modified fibers have been investigated. For Kevlar fibers modified by nitration and subsequent reduction of nitro groups to amino groups, significant concentrations of functional groups have been introduced on the surface with minor strength losses and with improvements in the interfacial shear strength measured with an epoxy resin using the microbond technique. Surface-controlled chlorosulfonation reactions (in solutions of chlorosulfonic acid and by exposure to chlorosulfonic acid vapor) have also been investigated for Kevlar fibers to introduce chlorosulfonyl groups on fiber surfaces and to study conversion of — SO2Cl to sulfonic acid (hydrolysis) and sulfonamide (reaction with amines). For Kevlar modified by chlorosulfonation, followed by reaction of — SO2Cl with some amines [e.g., ethyl enediamine (EDA) and triethylenetetramine (TETA)], the improvement in interfacial shear strength of chlorosulfonated / aminated fiber with epoxy resin ( evaluated by the microbond method) was significant.