Effects of high shear stress on the devulcanization of ground tire rubber in a twin‐screw extruder

Abstract

The devulcanization reactions of ground tire rubber (GTR) and thermoplastic elastomer (TPE) mixtures performed during the melt‐extrusion process through the induction of high shear stress by increases in the screw rotation speeds and reaction temperatures were investigated in this study. The results show that the high shear stress induced crosslink breakage and/or chain scission of GTR; this led to decreases in the gel contents and Mooney viscosities of the devulcanized GTR(DGTR)/TPE blend and decreases in the sizes of the unfused gel particles in the revulcanized blends of styrene–butadiene rubber [SBR/(DGTR/TPE)]. When the main composition of GTR was natural rubber, its allylic unit structures in the main chains were susceptible to degradation. Although the main composition of GTR was SBR, its main chains contained lower contents of double bonds and were more stable; this led to significant changes in the gel contents and Mooney viscosities of the devulcanized blend and in the mechanical properties of the revulcanized SBR/(DGTR/TPE) blend. The ethylene–propylene–diene monomer (EPDM4770) rubber had better compatibility with GTR than the ethylene/1‐octene copolymer and also had a higher molecular weight than that of EPDM3745. This led to a lower gel content and a higher Mooney viscosity in the devulcanized blend and higher mechanical properties in the revulcanized SBR/(DGTR/EPDM4770) blend. The alkylphenol polysulfide 420 and 450 accelerated the devulcanization reaction and prevented the crosslinking reaction; this led to significant increases in the mechanical properties of the revulcanized SBR/(DGTR/TPE) blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013

Reclaiming waste tire rubber by an irradiation technique

“…They used several strategies for reclaiming (devulcanization) tire rubbers. They were included mechanical shear by two roll mill and a chemical agent [10e12], mechanical shear by an internal mixer and a devulcanization aid [7,9,14,16] mechanical shear by a single or twin screw extruder [4,13] and miscellaneous techniques using supercritical carbon dioxide and a chemical agent [6]. However, the produced devulcanizates had low degree of devulcanization, resulting in poor mechanical and dynamical properties when they revulcanized.…”

Thermomechanical reclaiming of ground tire rubber via extrusion at low temperature: Efficiency and limits

“…Si et al investigated the effect of strong shear forces on the properties of reclaimed GTR and thermoplastic elastomer blends. Thermomechanical reclaiming process was carried out using a co‐rotating twin‐screw extruder, in which the temperature of the barrel was 180–270°C, and the screw rotation speed was 400–1200 rpm.…”

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

“…In mechanical processes, a shearing action is applied to the rubber which breaks down the rubber network. Shearing can be created on a two roll mill [10][11][12], in a batch mixer [4], or in a singleor twin-screw extruder [13][14][15][16][17]. Irradiation processes include microwave [18][19][20][21][22] and ultrasonic wave devulcanization [23,24].…”