Surface Energetics of Nylon 66 Fibers

Abstract

Surface energy of nylon 66 fibers is of considerable importance in the conversion of these fibers into consumer products such as tirecord, carpets, and various composite materials in combination with other polymers. Adhesion of nylon 66 fibers to rubber or the coupling agent in tirecord, or to the fluoropolymer used as a soil resist finish in carpets, depends on the surface energy of these fibers. If produced undrawn, nylon 66 fibers can be drawn later, up to 8×, to attain desirable fiber properties. Since hydrogen bonds rearrange during drawing it would be of interest to see if these changes also result in changes in surface energy. An attempt has been made to understand this aspect in this article. We have determined the dispersion and the acid–base (donor–acceptor) components of the surface energy of nylon 66 fibers by wettability measurements in appropriate probe liquids using the Wilhelmy principle, as well as by inverse gas chromatography (IGC), where interactions between the fiber surface and the probe molecules are studied in a chromatography column in which fibers form the stationary phase. By suitable data treatment these chromatograms could be converted to adsorption isotherms. The probe molecules were reasonably well matched to give comparable values by the two methods. Adsorption of site-specific fluorescent dyes showed increases in acid and basic surface groups by microfluorometry on drawn fibers. The density of the surface groups depended on the drawing environment, especially the one involving liquid water. The apparent discrepancy between microfluorometry results and the surface energy by wettability measurements resolved itself when the surface energy components were calculated by assuming that the entire work of adhesion results from hydrogen bonding interactions only, in solids with functional groups capable of forming strong hydrogen bonds, such as nylons, as suggested by Gutowski.