Recycle waste rubber

Recycling waste rubber is a very important problem, in theory as well as economically and practically. For many years, in addition to industrial applications, theoretical studies have been carried out and sometimes developed, which would require a book exclusive to this work to describe adequately. Thus, in Chapter 8, we will focus on presenting a description of the trends in recycling up to 1974, followed by a few applications done afterward. Thus, it will be possible to visualize somewhat the scale and complexities involved. 

This section will review the different technologies that are currently available for the devulcanisation of waste rubber from waste tyres, or from products in the general rubber goods (GRG) sector. Devulcanisation, although important, is only one way of recycling waste rubber and the extensive range of other technologies that have been developed for this purpose are covered in later sections of this book e.g., crumb manufacture and the use of crumb in the production of a variety of different products are reviewed in Chapters 6 and 7. 

S. Bandyopadhyay, S.L. Agrawal, P. Sajith, N. Mandal, S. Dasgupta, R. Mukhopadhyay, A.S. Deuri, and S.C. Ameta, Research on the application of recycled waste RFL (Resorcinol-Formaldehyde-Latex) dip solid in Styrene Butadiene Rubber based compounds. Progress in Rubber, Plastics and Recycling Technology, 23(1), 21, 2007. 

Tires, Rubber—Recycling. 2. Recycling (Waste, etc.)—United States. 3. Waste products as fuel—United States. I. United States. Office of Solid Waste. II. Clark, Charlotte. 

The process is being used on a commercial scale on Hokkaido, Japan, but appears to be uneconomical in the United States. (Mixtures of scrap tires with waste plastics have also been pyrolyzed.247) It appears to be cheaper in the United States to burn the tires for energy at lime kilns, paper mills, and such.248 The sulfur in the tires must be trapped by the lime or by other means. The combustion conditions must be such that the usual thick black smoke of burning rubber is not present. Recycling the rubber in the tires to more items of rubber would be preferable to just burning them as fuel. The real key to fewer tires to recycle is to devise better land use systems that require fewer automobiles (see Chap. 15). 

While many studies have been carried out aimed at the feedstock recycling of rubber wastes by pyrolysis and hydrogenation processes (see Chapters 5 and 7), little information is found on the catalytic cracking and reforming of rubber alone. Larsen35 has disclosed that waste rubber, such as used tyres, can be degraded in the presence of molten salt catalysts with properties as Lewis acids, such as zinc chloride, tin chloride and antimony iodide. The decomposition proceeds at temperatures between 380 and 500 °C to yield gases, oil and a residue, in proportions similar to those obtained by simple thermal decomposition. 

Another application of the injection system consists of recycling old and waste rubber. The reactive mixing of crumb rubber with a melted polymer represents an innovative way of recycling these waste rubbers [6]. Some thermoplastic elastomer may contain up to 60% recycled rubber derived from used vehicle tires, and thus through the reactive injection system the rubber scrap is revulcanized [7]. 

There are various ways to recycle waste tire rubber. The first approach consists of reducing the tire rubber into scrap rubber. Sometimes, before retreading old tires with new rubber, the part of the tire that needs extracting is converted into scrap. 

Waste ground rubber tire powder was devulcanized and mixed with 30 per hundred rubber (phr) natural rubber to give satisfactory vulcanizate properties. An intermeshing counter-rotating twin-screw extruder with constant root and flight diameters of the screw was designed and installed for waste rubber recycling [31]. 

Reactive mixing of crumb rubber with polypropylene by melting represents an innovative way of recycling old and waste rubber. A machine technology can easily be applied through injection molding. Results are examined for quasi-static and dynamic tests applied to the final materials. Moreover, the properties of this elastomer alloy remains constant after several recycling processes [59]. 

Recycling waste tire rubber is such large a problem that it could be covered only by a book entirely devoted to the subject. Eollowing the scope of the present book concerned with the cure of rubbers, only general considerations have been made by giving attention to applications employing, to some extent, the cure process. 

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