Chemometric solid-state 13C NMR analysis of morphology and dynamics in irradiated crosslinked polyolefin cable insulation

The relative concentrations and carbon spin-lattice relaxation constants (T-1,T-C) of the amorphous, intermediate, and crystalline phases of unaged crosslinked polyolefin cable insulation (ultimate elongation, e = 310%), Co-60 gamma-irradiated (e = 22%), and irradiated + annealed (e = 220%) samples were determined by chemometric analyses of directly polarized solid-state C-13 NMR spectra. The T-1,T-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,T-C relaxation constant of 1.4 +/- 0.3 s. gamma-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,T-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. (C) 2002 Elsevier Science Ltd All rights reserved.