Effects of the presence of water on ultrasonic devulcanization of polydimethylsiloxane

The effects of the presence of water on ultrasonic devulcanization of 30 phr silica-filled polydimethylsiloxane (PMDS) were investigated at increasing feed rates and different die gap sizes. The results showed that the initial die entrance pressure without ultrasound for wet rubber was higher than in the case without water and then it decreased monotonously with applying ultrasound. The die pressure for wet rubber decreased significantly even at low ultrasonic amplitude, while that for dry rubber changed little at low amplitude. The power consumption at an amplitude of 10 μm, where devulcanization was most effectively achieved, was lower for wet rubber even though the pressure was lower. The crosslink density and gel fraction after the devulcanization of wet rubber were lower than those of dry rubber, indicating that the presence of water facilitates the devulcanization process under the same devulcanization conditions. The good mechanical properties of recycled silica-filled PDMS were obtained at higher feed rates and at lower ultrasound amplitudes, which are directly related to the economics of a recycling process.