Ground tyre rubber

Fuhrmann, I. Karger-Kocsis. Promising approach to functionalisation of ground tyre rubber-photochemically induced grafting Short Com- 54. munication. J. Plast. Rubber Compos. 1999,... 

Diediich K.M. and B.J. Bums. 2001. Possibility of ground tyre rubber recycling with trans-polyoctenamer. Elastomery. 5(4) 17-24. 

Sonnier R., E. Leroy, L. Clerc, A. Bergeret, and J.M. Lopez-Cuesta. 2006. Compatibilization of polyethylene ground tyre rubber blends by gamma irradiation. Polym Degradat. Stability. 91 2375-79. 

A team of workers in India [52] have described the use of tetramethyl thiuram disulfide (TMTD) in the presence of Spindle oil for the devulcanisation of ground tyre rubber at near ambient temperatures. Small-scale (-100 g batches) devulcanisation experiments were carried out on a two-roll mill and the products produced characterised using a variety of analytical techniques (e.g., dielectric analysis and TGA). The amounts of TMTD and Spindle oil were 2.75 and 10%, respectively. The DR was mixed with virgin, uncompounded NR and a cure system, with the DR content varying from 0 to 60%. Vulcanisates were produced, which were characterised by both physical (e.g., tensile strength and swelling) and analytical (e.g., SEM and DMA) tests. The tensile strengths that resulted were found to vary from 7.7 MPa (60% DR) to 14 MPa (0% DR). 

Devulcanised ground tyre rubber that resulted from a mechano-chemical process. 

Vulcanisates that resulted from blends of the devulcanised ground tyre rubber with virgin rubber. 

At the 4th Rubber Modified Asphalt Conference held in Akron, OH, USA in 2009, a wide-ranging paper was presented by Baumgartner [54] that addressed topics such as modified asphalt formulations, optimisation of the process temperature, and the ground tyre rubber loadings and particle size optimisation. The paper showed that rubber crumb produced from whole tyres contains around 30% reactive material for asphalt modification and that the asphalt source and chemistry directly influence the rubber loading and the final properties of the product. The processing time and temperature are also very important, as is the particle size of the crumb, which affects the efficiency of modification and the long-term performance. 

Likewise, Orr et al.29,30 have explored the possible use of tyre pyrolysis oil as a solvent for coal liquefaction. The potential of this alternative was demonstrated by the fact that coal-TPO mixtures were transformed with higher conversion than when coal was reacted directly with ground waste rubber tyres. It is proposed that the polyaromatic compounds present in the TPO favour coal dissolution during liquefaction. Treatment of coal-TPO mixtures (50/50%) at 430 °C under 68 atm of cold-hydrogen pressure in the presence of a Mo catalyst led to a high coal conversion in just 10 min of reaction. From electron probe microanalysis of the coal particles after the reaction, the authors conclude that TPO favours the catalyst dispersion and its contact with coal, which results in enhanced coal conversion. 

Figure 7.7 The third-generation artificial football pitch at Woodley Sports Football Club, near Stockport, UK, contains cryogenically ground car tyre rubber. Reproduced with permission from the WRAP Quality Protocol, Waste and Resources Action Programme, Banbury, UK. WRAP (see note with Figure 7.1)...

Rubber tyres are by far the most visible of rubber products. Identification is trivial and collection is well organized. Recycling and disposal, however, are less evident. A major route for tyres is their use as a supplemental fuel in cement kilns. Major compounds in tyres are styrene-butadiene rubber (SBR), synthetic and natural polyisoprene rubber, steel cord, carbon black, zinc oxide, sulphur and vulcanization-controlling chemicals. Tyres can be retreaded, which is economic for large sizes (truck tyres), or ground to crumb or powder (cryogenic grinding). Such materials have some limited market potential as an additive in asphalt, and in surfaces for tennis courts or athletics. 

Bandyopadhyay S., S. Dasgupta, N. Mandal et al. 2005. Use of recycled tyre material in natural rubber based tyre tread cap compound Part 1 (with ground crumb mbber). Progress in Rubber, Plastics and Recycling Technology. 21(4) 299-317. 

On economic grounds the cost of the termonomer has been a significant factor as have certain aspects of production costs so that, at the time of writing the EPDMs are significantly more expensive than natural rubber and SBR. Technical problems such as the lack of building tack have proved a deterrent to their use in tyre applications which involve extensive assembly operations whilst problems of compatibility and covulcanization in the case of a far from impossible stock mix-up have also been significant. 

If the starting material is a composite one, such as tyres, it has been found that ambient grinding processes tend not to remove as much fabric and metal from the final crumb product as cryogenic processes. For example, an ambient ground rubber has been found to have a fibre content of 0.5% and a steel content of 0.1%, whereas that produced by a cryogenic process had levels below the detection limit for these two components [10, 11]. 

The type of ground rubber (e.g., whole tyre, tyre tread or other type, e.g., ethylene-propylene-diene monomer, EPDM). 

WRAP have also funded a project that looked into the use of cryogenically ground 0.5-1.5 mm rubber particles from waste car tyres [79] to help create a new artificial football pitch at Woodley Sports Football Club in the UK (Figure 7.7). The rubber particles were used in the FieldTurf third-generation artificial sports pitch product, which is supplied worldwide by the American company... 

Thermal process Tyre pieces are steam-heated in a pan in the presence of air for around 2.5 h at up to 260 "C. The rubber product is then cooled, ground and consolidated on a two-roll rubber mill. 

---