Devulcanization Process Research Articles

THE USE OF THERMOGRAVIMETRY IN THE STUDY OF RUBBER DEVULCANIZATION

Thermogravimetry was employed to study the changes occurring in rubber vulcanizates during devulcanization carried out by microwave treatment, a new promising method of recycling rubber waste. The thermogravimetric parameters Ti, T5 and Tp and the compositions of devulcanizates in comparison with vulcanizates were determined. The results obtained allowed estimation of the degree of destruction of the polymer chains in response to microwave treatment and permitted establishment of the most advantageous conditions of devulcanization in order to obtain the best properties of rubber devulcanizates for reuse in rubber processing. The results demonstrated that thermogravimetry is a very useful method for investigation and control of the microwave devulcanization process.

せん断流動場反応制御技術によるゴムの連続再生 （第３報） ＥＰＤＭにおける脱硫反応過程の解析

We studied devulcanization process by measuring rubber state, viscosity, gel fraction, its effective network chain density and average molecular weight of sol. When passing through grinding zone, vulcanized rubber was ground by screw rotation and its size became small. Next, devulcanization proceeded in the devulcanizing zone and viscosity of rubber decreased. Gel fraction and its effective network chain, density decreased too. Finally, gel fraction of devulcanized rubber was 45% and its effective network chain density was one twentieth of virgin vulcanized rubber. On the other hand, average molecular weight of sol part did not change and its value was nearly equal to virgin raw rubber. Devulcanization process depended on shear stress by screw rotation. Gel fraction and its effective network chain density decreased by increasing screw rotation. Devulcanization rate depended on reaction temperature and became high by raising temperature.

Effect of Crosslink Type on the Ultrasound Devulcanization of SBR Vulcanizates

Abstract Sulfur-cured non-reinforced SBR with different amounts of poly-, di- and monosulfidic crosslinks is devulcanized by high power ultrasound irradiation in a continuous process under various processing conditions. Total crosslink density, the proportion of polysulfidic crosslinks, gel fraction, and glass transition temperature are measured. The effect of the initial fraction of polysulfidic bonds on the devulcanization process is discussed.

Ultrasonic devulcanization of rubber vulcanizates. II. Simulation and experiment

The simulation results based on the devulcanization model presented in Part I of this study are described for devulcanization of SBR vulcanizates. The vulcanizates are conveyed by a single-screw extruder to a thin gap between a stationary die and a vibrating horn. Gapwise velocity, temperature, and shear-rate distributions along the die length are calculated. Predictions of the model for changes of various structural characteristics including gel fraction, fraction of various broken bonds, rate of their breakup, and void formation along die length are given. Devulcanization energy consumption and energy dissipated by ultrasonic waves are calculated. Comparison of these energies indicates that the devulcanization energy represents only a small fraction of the dissipated energy. The predicted results for gel fraction, crosslink density, die characteristics, and “mixing cup” temperature are compared with the experimental data. These predicted results are found to be only in qualitative agreement with experimental observations. The theoretical and experimental results indicate that the rubber is partially devulcanized and the devulcanization process is accompanied by some degradation of the macromolecular chains. © 1996 John Wiley & Sons, Inc.

Ultrasonic devulcanization of rubber vulcanizates. I. Process model

Tire and rubber waste recycling is an important issue facing the rubber industry. In addressing this issue, the present article describes the first attempt to formulate a model and to simulate a novel continuous ultrasonic devulcanization process. The proposed model is based upon a mechanism of rubber network breakup caused by cavitation, which is created by high-intensity ultrasonic waves in the presence of pressure and heat. Dynamics of bubble behavior is described by the Notlingk-Neppiras equation with incorporation of an additional term based upon elastic strain-energy potential. Acoustic pressure arising in the ultrasonic field is related to void formation. Their concentration is calculated based upon nucleation and growth of gas bubbles in crosslinked elastomers under negative driving pressure. The breakup of a three-dimensional network in crosslinked rubbers is combined with flow modeling. The viscosity function required for this modeling is based upon a power-law model which includes temperature, shear rate, and gel fraction dependence.

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.

4459450 Method of reducing pollution in microwave devulcanization process: Keith A Tyler, Gene L Cerny assigned to The Goodyear Tire & Rubber Company

4459450 Method of reducing pollution in microwave devulcanization process: Keith A Tyler, Gene L Cerny assigned to The Goodyear Tire & Rubber Company