ULTRASOUND DEVULCANIZATION OF SBR - MOLECULAR MOBILITY OF GEL AND SOL

In an effort to support the recycling of rubbery polymers and composit es, H-1 NMR relaxation and pulsed-gradient spin echo diffusion measure ments have been performed on virgin and unfilled vulcanized strene-but adiene rubber (SBR), and networks after various extents of devulcaniza tion using an ultrasound technique. The NMR methods recognize unentang led light molecules (e.g. sol), but do not distinguish between unattac hed entangled large molecules and chemical network segments. Devulcani zation generates additional soi with a wide mass distribution, thus in creasing both sol and gel mobility, but decreasing sol mean diffusivit y. The latter effect is accounted for by the increasing mean sol molec ular mass but also by the increasing glass transition temperature, whi ch is related to main-chain stiffening seen in our earlier C-13 NMR ex periments. In addition to improving the molecular-level understanding of devulcanization, this study provides guidance for the optimization of the devulcanization parameters.