Abstract
Accelerated-sulfur-vulcanized 13C-labeled EPDM with and without carbon black and extender oil was analyzed using 13C solid-state NMR to determine the chemical structure of the network. High-resolution solid-state 13C NMR reveals that sulfur cross-linking takes place at the allylic positions of the ENB independent of the presence of carbon black and oil. From the integrated intensities of the 13C signals, the conversion of ENB into a cross-link can be quantitatively determined during the vulcanization process. The ENB conversion for gumstock EPDM is ∼10% after 10 min of vulcanization at 150 °C, which is a typical optimum vulcanization time in commercial applications. In the presence of carbon black the ENB conversion is marginally faster and reaches ∼12% in 10 min, while a maximum conversion of ∼20% was obtained. The efficiency of the ENB conversion was ∼20% less at 150 °C and ∼30% less at 180 °C in the compound with carbon black and oil compared to the compound without carbon black and oil. The substituti...
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