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

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 pre-exponential 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.