Chemometric solid-state C NMR analysis of morphology and dynamics in irradiated crosslinked polyolefin cable insulation

The relative concentrations and carbon spin-lattice relaxation constants (T_1,C) of the amorphous, intermediate, and crystalline phases of unaged crosslinked polyolefin cable insulation (ultimate elongation, e=310%), ⁶⁰Co γ-irradiated (e=22%), and irradiated+annealed (e=220%) samples were determined by chemometric analyses of directly polarized solid-state ¹³C NMR spectra. The T_1,C relaxation curves of the intermediate and amorphous components were found to be mono-exponential. The intermediate component contains 23±5% of the CH₂ segments in the unaged sample and has an T_1,C relaxation constant of 1.4±0.3 s. γ-Irradiation caused a slight decrease in the amount of intermediate component to 19±5% and an increase of the relaxation constant to 1.8±0.3 s. The subsequent annealing of the irradiated sample resulted in an additional increase of the relaxation constant to 2.1 s and a slight loss of crystallinity. The amorphous T_1,C relaxation constants were found to be identical in all three samples and have a value of 0.38±0.03 s. At ambient temperature, the crystalline phase was found to relax via chain diffusion from the intermediate component. The rate of helical jumps was twice as fast in the irradiated and irradiated+annealed samples compared with the unaged material.