Ultrasonic devulcanization of carbon black filled polyurethane rubber

Following our success with the recycling of unfilled polyurethane rubber (PUR), an attempt was made to devulcanize carbon black (CB)-filled PUR. Although CB was added in various proportions, only samples with lower filler loading could be treated. Devulcanization experiments were carried out at various feed rates, gap sizes, and amplitudes in a grooved barrel as well as a coaxial reactor with ultrasonic attachments and the optimum processing conditions were determined. Gel fraction, cross link density, and dynamic properties of the treated samples were determined. However, attempts to cure the 100% devulcanized samples obtained from the grooved barrel reactor failed possibly due to severe degradation of main chains and reduced polymer-filler interactions under ultrasound treatment. Hence the next plausible step was to prepare blends of the devulcanized and filled virgin vulcanizates. These blends were successfully cured and their mechanical properties were determined. It was found that blends containing 50% or higher amount of devulcanized rubber exhibited reasonable mechanical properties thereby proving that the application of ultrasound is a suitable method for the recycling of CB-filled PUR.