Reclaiming process

In the Reclaimator, a high pressure extmder, fiber-free mbber is heated to 175—205°C with oils and other ingredients. High pressure and shear between the mbber mixture and the extmder barrel walls effectively devulcanize the mixture in one to three minutes. In the Lancaster-Banbury method, high temperature, pressure, and shear are appHed to the mbber in a batch process that is otherwise similar to the Reclaimator process. In another high pressure process, scrap mbber is devulcanized at 5.5—6.9 MPa (54—68 atm) for ca five minutes. The product is milled, baled, or pelletized as in other processes. 

Until the 1960s, reclaimed mbber was an important raw material in molded and extmded mbber products, eg, tires, mbber mats, and hard mbber battery cases. With the advent of vinyl, other plastics, and less expensive oil-extended synthetic polymers, reclaimed mbber sales stabilized and decreased. In 1973, the oil embargo and rising energy costs increased costs of the energy-intensive mbber reclaiming process to the point where they matched virgin polymer costs. Increased radial tire production required crack resistance that could not be provided by reclaimed mbber compounds (46). 

Allowable when the pan, dry digestion, mechanical reclaimed processes are integrated with a wet digestion reclaimed rubber process. 

Wastewater is from both tire and reclaiming processes. 

Waste Clarifier This clarifier will treat the overhead liquor from the hydroseparator to concentrate any solids and to reclaim process liquor for reuse in the process. The overflow from this clarifier will be retnrned to the process and the underflow will be filtered to prodnce a filter cake for disposal. The filtrate from the filter press will be returned to the process. 

A principal plastic reclaiming process used was developed in the Netherlands by a resin manufacturing firm. In this process, after removal of labels and base cups by machine, the bottles (clear or green) are color sorted and granulated. The PET flake is then washed to remove glue. Closure material is separated by flotation from Hie PET. The remaining PET is dried and sifted for fines and then is ready for reuse. 

Figure 6.18 Schematic of the polyvinyl alcohol reclaim process by inorganic membrane ultrafiltration [adapted from Gaston County, 1976J...

OTHER COMMENTS liberated from petroleum refining operations liberated from solutions in glass and metal etching, from the manufacture of dry cell batteries, and from vulcanizing and reclaiming processes for rubber. 

Up to the time of World War 11, scrap tires contained only natural rubber. Reclaiming processes were well established, and a reasonable proportion (20%) of reclaim was accepted in compounding of new tires. (Frequently, the percentage was much more in other rubber products.) In 1941 the consumption of reclaim was 32% of the consumption of new rubber. 

The significant reclaim processes in use in 1974 were the digester process, heater process, and mechanical processes [3], But there were at that time numerous variations and combinations of these. All have similar finishing steps. The reclaim is usually further compounded, refined on tight mills, and strained to remove foreign solids. 

A few examples of reclaim process of scrap rubber are briefly described. However important they may be for either the quality of the process or for the amount of rubber reused, they should not be considered as a limitation in the possibilities. 

As already said in the Preface, a question arose as to the appropriateness of having a chapter in this book devoted to the cure of rubbers and to their properties concerned with the recovery of scrap rubber obtained from old tires. However, the amount of old tire rubber is so large that it could be considered as a raw material, and reclaiming will become a necessity when crude oil and natural rubber experience shortages. This problem is so vast that only a book in itself could describe all the possibilities of reusing. Nevertheless, a large number of opportunities has been identified, and the reclaiming processes based on the cure of these scrap rubbers have been considered. 

Worn-out tires and scraps and trimmings of other vulcanized products constitute the raw material for reclaimed rubber. Therefore a good reclaiming process must not only turn the rubber soft and plastic but also must remove reinforcing cords and fabrics that may be present. There are a number of commercial processes [43] for rubber regeneration (1) alkali digestion process, (2) neutral or zinc chloride digestion process, (3) heater or pan process, and (4) reclaimator process. 

The reclaimator process is more attractive than the above processes. The reclaimator is essentially a high-pressure extruder that devulcanizes fiber-free rubber continuously. Ground scrap is mechanically treated in hammer mills to remove the textile material, mixed with reclaiming oils and other materials, and then fed into the reclaimator. High pressure and shear between the rubber mixture and the extruder barrel walls effectively reclaim the rubber mixture. Devulcanization occurs at 175-205°C in a few minutes and turns the rubber into reclaim that issues from the machine continuously. The whole regeneration, which is a dry process, may be completed in about 30 min. 

A mechanical or reclaimator process (LaGrone, 1986 Szilard, 1973 Klingensmith, 1991 Leyden 1991) has been used for the continuous reclaiming of whole tire scrap. Fine mbber crumb (typically 30 mesh) mixed with various reclaiming oils is subjected to high temperature with intense mechanical working in a modified extmder for reclaiming the mbber scrap. 

Many different reclaiming processes [8, 13, 15-17, 19-22] have been applied through the years in an attempt to solve the problem of rubber recycling. Generally, ground rubber scrap is, in most cases, the feedstock for the devulcanization step. Warner [13] and recently Adhikari et al. [23] and Isayev [24] presented reviews of the existing literature that is relevant to various methods of devulcanization. 

A mechanical or reclaimator process [25, 32-34] has been used for the continuous reclaiming of whole tire scrap. Fine rubber crumb (typically 30... 

Chemical reclaiming process is a possible method for devulcanizing the vulcanized network through the use of chemical agents that attack the C-S or S-S bonds. However, this process of devulcanization is very slow and creates further problems with the removal of the solvents, and additional waste is generated in the form of sludges. Also, some processes require elaborate chemical process techniques, therefore handling and safety become a concern. 

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