Chemical Bonding of Tetraethylenepentamine to Nitric Acid-Oxidized Carbon Fibers: An XPS/ISS Investigation

Abstract

The surface reaction of tetraethylenepentamine (TEPA) with nitric acid-oxidized type II PAN-based carbon fibers has been investigated by using X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), and acid/base surface titrations. Initially, nitric acid treatments of varying intensity impart different quantities of oxygenated functional groups onto the fibers, and surface roughening due to formation of pits and crevasses occurs. Subsequent treatment with TEPA at 190 °C introduces significant amounts of surface-bound TEPA via reaction with carboxyl groups on the oxidized carbon fiber surfaces. Angle-resolved XPS (ARXPS) spectra are consistent with a TEPA surface concentration that varies as a function of depth (into crevasses and pits) and remains greatest primarily within the outermost 15 Å. The extent of the TEPA surface reaction is proportional (but not linearly) to the fibers' initial oxygen content. Nonlinearity may be due to several factors including (1) decomposition of a portion of the carbon fibers' carboxyl groups under the TEPA reaction conditions and (2) a nonuniform reaction with the commercial TEPA mixture, which contains several different pentamine molecular structures together with small amounts of tetra- and hexamine impurities. An accurate determination of the TEPA bonding configuration is difficult to achieve; however, the data suggest that at least 70% of the TEPA molecules form two (or more) bonds to the carbon fiber surfaces.