Effect of Particle Size on Ultrasonic Devulcanization of Tire Rubber in Twin-Screw Extruder

Abstract

Ultrasonic devulcanization of tire rubber particles of 10 and 30 meshes by means of a new ultrasonic twin-screw extruder was investigated. The ultrasonic amplitude and devulcanization temperature were varied at a fixed frequency of 40 kHz. The die pressure and ultrasonic power consumption during devulcanization were recorded. The degree of devulcanization was investigated by measuring the cross-link density, gel fraction, and revulcanization behavior. Rubber of 30 mesh exhibited a lower die pressure and higher degree of devulcanization than that of rubber of 10 mesh. Because of the higher level of devulcanization and lower viscosity of devulcanized rubbers at higher amplitudes, the temperature of devulcanized rubbers at the die was reduced with an increase of the ultrasonic amplitude. Generally, the torque at the start of curing and maximum torque on the curing curve measured during revulcanization is higher for rubber of 10 mesh and rubbers devulcanized at a lower temperature. Rheological properties of devulcanized and revulcanized rubbers and mechanical properties of revulcanizates were measured. The complex viscosity of devulcanized and revulcanized rubbers of both meshes as a function of frequency exhibited a power-law behavior, with the power-law index being 0.06 for devulcanized rubbers and 0.02 for revulcanized rubbers. The consistency index of devulcanized and revulcanized rubbers was higher for rubber of 10 mesh; however, both rubbers showed a higher consistency index at a lower temperature. Cole–Cole plots, cross-link density, and gel fraction of devulcanized and revulcanized rubbers, revulcanization behavior, and modulus of revulcanizates separated in two distinct groups based on the level of devulcanization and effect on molecular structure of devulcanized rubber. Revulcanizates with a greater degree of devulcanization exhibited a higher elongation at break, whereas those with a lower degree of devulcanization exhibited higher strength and modulus. Revulcanizates of rubber of 30 mesh exhibited a consistently higher elongation at break. The normalized gel fraction versus normalized cross-link density was described by a unique function independent of the processing conditions and rubber particle size.

Comparative Properties of Styrene-Butadiene Rubbers (SBR) Containing Pyrolytic Carbon Black, Conventional Carbon Black, and Organoclay

“…It has been recognized, however, that the latter applications require -at least -partial devulcanization [2]. Promising approaches of industrial scale for devulcanization/reclaiming are related with ultrasonic [5] and microwave techniques [6][7]. Pyrolysis of waste tires is considered nowadays as an economic option [1,8].…”

Properties of polyetherimide/graphite composites prepared using ultrasonic twin‐screw extrusion

“…25 In this study, three different graphites, namely, natural graphite (UG), modified graphite (MG), and expanded graphite (EG), were incorporated into PEI to manufacture PEI/graphite composites by means of recently developed ultrasonic twin-screw extruder. 26 The rheological, mechanical, and electrical properties of the composites are investigated along with their morphology. The effect of ultrasound on dispersion and exfoliation of various graphites in PEI matrix was elucidated.…”

Effect of ultrasonic extrusion of star styrene‐butadiene rubber on properties of carbon black‐ and silica‐filled compounds and vulcanizates

“…Ultrasonic extrusion of polymers has been extensively studied by Isayev and his coworkers. It can be used for devulcanization of rubbers, [5][6][7] decrosslinking of crosslinked thermoplastics, 8 compatibilization of polymer blends, 9,10 and improvement of filler dispersion in polymer composites. [11][12][13][14] The properties of ultrasonically treated polymers are determined by their molecular structures.…”