Improving the Gas Barrier Property of SBR/Clay Nanocomposite through In Situ Sulfur Modification during Curing Process

Rubber/clay nanocomposites have been explored as alternative materials to replace expensive halogenated butyl rubber. In order to further improve their gas barrier properties, a simple and efficient method through sulfur modification was applied in this work. Excess sulfur was added into SBR/clay nanocompound to prepare sulfur modified nanocomposite via the formation of cyclic sulfide in addition to crosslinking. The vulcanization behavior, mechanical properties, dynamic mechanical property and gas barrier property of the nanocomposites were investigated. It was found that the sulfur modified SBR/clay nanocomposites showed much increased glass transition temperature and lower gas permeability.

Solid State Carbon-13 NMR Studies of Vulcanized Elastomers. II, Sulfur Vulcanization of Natural Rubber

In summary, the solid-state C-13 NMR technique has proven to be a significant method for the detection of crosslinks and other structural modifications in sulfur-vulcanized NR systems. The use of sulfur as a crosslinking agent by itself generates a considerable amount of main-chain structural modifications. Cyclic sulfide structures and cis-to-trans chain isomerization are detected in addition to polysulfidic crosslinks which are found attached to different carbons of the NR repeat unit. The phenomenon of reversion has also been detected in this study. The nature of the spectral broadening in the NMR spectra of the highly cured vulcanizates has two origins. The broadening arises from lack of molecular motion in the system and from an increase in chemical shift dispersion due to the new structures formed with crosslinking.

Solid State Carbon-13 NMR Studies of Vulcanized Elastomers. III, Accelerated Sulfur Vulcanization of Natural Rubber

In summary, the solid state C-13 NMR technique has proven to be a significant method for the detection of crosslinks and other structural modifications in accelerated sulfur-vulcanized NR systems. When the amount of accelerator is high in proportion to the amount of sulfur used, the network structure appears to be simpler with less crosslinking, less main chain structural modification, and fewer cyclic sulfide structures as observed in the C-13 NMR spectra. Polysulfidic crosslinks have been detected in addition to polysulfides terminated by accelerator residues. Cis-to-trans chain isomerization is also evident in these vulcanizates.