Sayata Ghose

Formation of bubbles during ultrasonic treatment of cured poly(dimethyl siloxane)

A static ultrasonic treatment device was used to investigate the effect of ultrasound on degradation of unfilled poly(dimethyl siloxane) (PDMS) vulcanizate in the absence of shearing effect. The effects of pressure, ultrasound intensity and thickness of the disks upon ultrasonic treatment were investigated. The power consumption was measured as a function of sample thickness, ultrasonic amplitude, and applied pressure. The dynamics of bubble (nucleation, growth and coalescence) was also studied with respect to applied pressure and amplitude. An increase in thickness of the sample was observed during ultrasonic treatment. The unique correlation between gel fraction and crosslink density obtained in the present static experiments was compared with those of continuous devulcanization studied earlier.

Continuous Process for Recycling of Polyurethane Foam

The investigation deals with the recycling of high resiliency polyurethane (PU) foam by the application of high-power ultrasound in a continuous ultrasonic reactor. The foam has been decrosslinked at various screw speeds and various amplitudes, then blended at different ratios with the virgin polyurethane rubber (PUR) and cured. The die pressure and the total power consumption have been recorded as a function of processing conditions. Rheological and mechanical properties, hardness as well as gel fraction and crosslink density of the decrosslinked foam and cured blends have been measured and compared in an attempt to find out the optimum condition for decrosslinking. Blends have also been prepared using different proportions of ground samples and virgin rubber, and a comparison of the properties between these blends and the blends of the decrosslinked foam has been carried out. The results show that compared to the ground samples, the blends of the decrosslinked samples are easier to mix and exhibit enhanced properties.

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, crosslink 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.

Ultrasonic devulcanization of unfilled polyurethane rubber using coaxial and grooved barrel reactors: A comparative study

Substantial research using the ultrasound technology for recycling thermosets has been carried out in our laboratory. After the success met with polyurethane rubber using the coaxial reactor, experiments were carried out using the newly developed grooved barrel reactor in an effort to improve the efficiency of devulcanization. The current paper compares processing characteristics like die pressure and ultrasonic power consumption as well as gel fraction, crosslink density, dynamic and mechanical properties. There seems to be a significant difference in mechanical properties between the samples obtained from the two reactors. It was found that the samples obtained from the grooved barrel reactor showed a somewhat greater degree of degradation and devulcanization when compared to the coaxial extruder.