Recycling of roofing membrane rubber by ultrasonic devulcanization

Abstract

The recycling of vulcanizates based on EPDM roofing membrane rubber using a new ultrasonic devulcanization reactor with a grooved barrel was carried out. This reactor provided continuous devulcanization at an output as high as 2.52 g/s. Die pressure and ultrasonic power consumption were measured as a function of processing conditions. The mechanical properties of virgin vulcanized and revulcanized roofing membranes were measured. Tensile strength of the revulcanized rubber was found to be similar to that of the virgin vulcanizate. Gel fraction, crosslink density, and dynamic properties of the virgin vulcanizate, the ultrasonically devulcanized rubber, and the revulcanized rubber were determined. Also, dynamic properties and the cure behavior of the virgin compound and of the devulcanized roofing membrane were investigated. All these properties were found to be dependent on processing conditions during devulcanization. The thermal stability of the virgin compound, virgin vulcanizate, and devulcanized and revulcanized rubbers were studied by means of TGA. It was found that the thermal stability of all the vulcanizates in air and nitrogen environments remained practically intact, while that of devulcanized rubber in air environment was a function of processing conditions.

Molecular mobility and structure of ultrasonically treated unfilled butadiene rubber

“…The imposition of ultrasound at amplitudes of 10 and 12.5 μm generated significant additional gel. Gel formation was previously reported for ultrasonically treated SBR21 and EPDM22 gums. It was also reported that a crosslinking reaction in BR took place at high temperatures 25, 26.…”

“…Many researchers have studied the degradation of polymers in solution,4–7 polymerization in solution,8–11 the modification of the polymer surface,12 the devulcanization of rubber,13–18 and recently copolymerization at the melt interfaces of polymer blends 19, 20. Structure and property changes under the action of ultrasound have also been studied in styrene–butadiene rubber (SBR)21 and ethylene–propylene–diene monomer (EPDM) gums 22…”

Continuous ultrasonic devulcanization of unfilled butadiene rubber

“…As reported earlier, 22 in the case of EPDM roofing membrane particles, their size was reduced after passing through the extruder in the absence of the action of ultrasound. However, this reduction of the particle size did not change the value of their gel fraction, and this indicated that simple mechanical shearing of the rubber in the extruder did not cause devulcanization.…”

A novel industrial technique for recycling ethylene-propylene-diene waste rubber

“…Isayev et al [34][35] investigated the devulcanization of various rubbers, including EPDM in a reactor consisting of a single screw extruder and an ultrasonic source on the die. The effect of processing parameters and ultrasonic conditions on devulcanization were reported.…”