Analysis of Crosslinked Natural Rubber by Spin-spin Relaxation Spectra

Abstract

The higher-order structure of natural rubbers which were crosslinked by peroxide or sulfur were analyzed by 1H pulsed NMR. The relaxation spectrum was obtained as a relationship of relaxation time and component by applying the Gaussian expansion to the spin-spin relaxation decay. The difference between the structures could be viewed clearly by the NMR measurements of samples that were swollen by deuterated toluene. The deficient component with active molecular mobility existed much more in peroxide-crosslinked NR than sulfur-crosslinked one. Therefore, it was estimated that the tensile strength of peroxide-crosslinked NR was lower than that of sulfur-crosslinked one. Improvement in the tensile properties due to filling of the carbon black was more pronounced in peroxide-crosslinked system than sulfur-crosslinked system. The filling of carbonblack resulted in a decrease of deficient component in the relaxation spectrum for peroxide-crosslinked NR. The shape of spectra of peroxide-crosslinked NR became similar to that of the sulfur-crosslinked NR with the filling of carbon black.