Novel Ultrasonic Technology for Devulcanization of Waste Rubbers

Abstract

A novel patented process and several reactors have been developed for devulcanization of waste rubbers. The technology is based on the use of the high power ultrasonics. The ultrasonic waves of certain levels in the presence of pressure and heat rapidly break up the three-dimensional network in crosslinked rubbers. The devulcanized rubber can be reprocessed, shaped and revulcanized in much the same way as a virgin rubber. The first laboratory reactor has been scaled up to pilot-plant level by the National Feedscrew and Machining, Inc. Various devulcanization experiments were carried out with model styrene-butadiene rubber (SBR) and with ground rubber tire (GRT). Curing behavior, Theological properties, and structural characteristics of rubbers devulcanized at various processing conditions were studied, as well as mechanical properties of revulcanized rubber samples. A possible mechanism of the devulcanization is discussed. The performed measurements indicate that the rubbers are partially devulcanized, and the devulcanization process is accompanied by certain degradation of the macromolecular chains. In spite of these observations, the processing conditions are identified at which the retention of the mechanical properties is found to be good. A further work is in progress to find the optimal conditions of devulcanization and to improve the selectivity of the process towards breaking up the chemical network only.

Blends of ground tire rubber devulcanized by microwaves/HDPE - Part A: influence of devulcanization process

“…In general, it can be observed that the optimum cure time and scorch time, represented by t 90 and ts 1 respectively, were lower for samples with the highest exposure times to microwaves in one step as well as in multistep treatments. This behavior is characteristic of reclaimed rubber and it was observed by some other authors [14][15][16][17] , which probably happens due to the presence of residual curatives from the first vulcanization. The devulcanization process increases the freedom degree of the polymeric chains, accelerating the reaction with the increasing of the exposure time of the GTR to microwaves, possibly due to the great amount of effective shocks during the process.…”

Review of the Reclaiming of Rubber Waste and Recent Work on the Recycling of Ethylene–propylene–diene Rubber Waste

“…They include thermal process, heater or pan process, and digester process, [8][9][10][11][12][13][14][15] [30][31][32][33][34][35][36][37][38][39] thermomechanical. 40 thermochemical, [41][42][43][44][45][46][47][48] ultrasonic devulcanization, [49][50][51][52][53][54][55] and many other less efficient methods. 56,57 Numerous techniques for recycling rubber waste have also been developed.…”

“…They are autoclave, 82 microwaves heater, [83][84][85] , ultrasonic reactor, [49][50][51][52][53][54][55]80 twin screw extruder, 86,87 and internal batch mixer. 6,58,59 The analytical methods for testing and characterizing devulcanized rubber waste are: solvent swelling, 88 thermogravimetry analysis (TGA), 64,74,76,78 solid-State H neutron mass spectroscopy (NMR), 93,95-100 differential scanning calorimeter (DSC), 101 atomic absorption spectroscopy, 93,101 inductively coupled plasma atomic emission spectroscopy (ICP-AES), 93,101 inductively coupled plasma optical emission spectroscopy (ICP-OES), 93,101 and elemental analysis which involves the determination of the mass fraction of carbon, hydrogen, nitrogen, 93,101 and heteroatoms (X) (CNHX).…”

“…Water is then separated from the crumb, dried and then the physical properties such as bulk density, particle size and particle size distribution measured. [30][31][32][33][34][35][36][37][38][39] thermomechanical, 40 thermochemical, [41][42][43][44][45][46][47][48] ultrasonic, [49][50][51][52][53][54][55] and some less effective methods, 56,57 and microbial devulcanization.…”

“…The process does not require solvent or plasticizer and the resulting material can be revulcanized. 49 The early work of Isayev et al 50 on the development of ultrasonic technology for devulcanization of waste rubbers showed that the ultrasonic waves of certain levels in the presence of pressure and heat rapidly break up the three dimensional network in crosslink rubbers. The devulcanized rubber was reprocessed, shaped and revulcanized in much the same way as a virgin rubber.…”