Recycling of monomers and fillers from high-temperature-vulcanized silicone rubber using tetramethylammonium hydroxide

The effects of reaction conditions on a novel monomer recycling method for high-temperature-vulcanized silicone rubber are described. A mixture of a methanol solution of (CH3)4NOH, diethylamine and hexane was adopted to partially depolymerize and dissolve the high-temperature-vulcanized silicone rubber under reflux. Hexane was useful to completely separate the fillers from the suspension of depolymerized products. After the removal of fillers followed by treatment of the filtrate with KOH and distillation under reduced pressure, cyclosiloxane monomers were obtained in high yields (∼78%). (CH3)4NOH adsorbed and chemically bound to the fillers was found to be pyrolyzed to (CH3)3N and CH3OH. The separated fillers were thermally treated to be reused without further purifications. The yields of recovered fillers were as high as over 95%.