Photoacoustic FT-IR Analysis of Surface-Modified Kevlar 49® Fibers

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Abstract
Kevlar fiber-reinforced composites are limited in use by their comparatively low compressive properties relative to other high modulus fibers, generally attributed to low adhesion between Kevlar fibers and the matrix resin. Epichlorohydrin (ECH) was reacted with metalated Kevlar 49 fibers in an attempt to introduce epoxy groups on the surface of the Kevlar. This should increase the compressive properties and fracture toughness of Kevlar/epoxy composites without degradation of the tensile properties. Photoacoustic FT-IR spectroscopy (PAS) was utilized to characterize this reaction. Several new peaks appeared in the region 3100 to 2800 cm−1 which appear similar to the C-H stretch peaks that are present in ECH, but are shifted down several wavenumbers, presumably due to the conjugation and resonance which exists in Kevlar. Least-squares subtraction revealed a new peak at 3335 cm−1, attributed to a change in the N-H stretching modes. Also, a triplet appears at 1055, 1034, and 1017 cm−1, similar to triplets which have been seen in many aromatic esters and acrylates. Finally, several peaks in the region 3900 to 3500 cm−1 appear which are assumed to be due to hydrogen bonding. However, they cannot be fully resolved because of the loss of PA signal in this region. This spectroscopic evidence could indicate the presence of one of the following: an epoxy, an ester, or a carboxylic acid. It was determined that the reaction spectrum was due to ether formation.