Free Radical Motion in the Supramolecular Structure of Nylon 6,6 and Elastane, Studied by Quantitative Spin Probing

Abstract

An electron paramagnetic resonance investigation of the nano-environment within Nylon 6,6 and Elastane fibers, using the TEMPOL (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy) nitroxide radical as a spin probe is reported as a function of radical loading, temperature, and relative humidity. Within Elastane, only rapidly rotating radicals are observed and assigned to radicals absorbed in the bulk amorphous regions. Within Nylon, slowly moving radicals are found which are thought to be adsorbed on the surface of crystallites. From simulation of the spectra, the rotational correlation times are extracted, and the activation energy and preexponential factor for the motion are obtained from the temperature dependence. For both fibers, the activation energy was much lower than in liquids and showed small but pronounced variation with the fiber water content. The local polarity experienced by the probe was extracted from the spectra via the hyperfine constant and indicated a nonaqueous polar environment more or less independent of water content. These effects are rationalized in terms of the chain relaxations in the fibers. At high radical loadings (>10 -2 mol kg -1 ) in Nylon, strong spin exchange effects were seen and assigned to the onset of radical aggregation in the fiber; however, in Elastane, there was no evidence of spin exchange up to a loading of 5 × 10 -2 mol kg -1 .

New insights into dye chemistry and physics

“…When the spin probe method was applied to nylon and elastane fibres , similar models could be used to explain the results, although of course the fractions of each species were quite different. In nylon the crystallite‐adsorbed radicals dominated, while in elastane it was the freely mobile radicals in the amorphous regions that were dominant.…”