Waste tyre rubber

Radziszewski R, M. Kalabinska, and J. Pilat. 2001. Applications of waste tyre rubber granulate to modification of asphalts used in road building. Elastomery. 5(4) 8-16. 

San Miguel, G., Fowler, G. D., SoUars, C. J. (2003). A Study of the Characteristics of Activated Carbons Produced by Steam and Carbon Dioxide Activation of Waste Tyre Rubber. Carbon, 41(5), 1009-1016. 

Meysami and Tzoganakis [27,28] of Waterloo University in Canada have used an industrial-scale twin-screw extruder with supercritical CO2 to devulcanise waste tyre rubber, tyre tread rubber and EPDM... 

Shen and co-workers [29] used a twin-screw extrnder to devnlcanise waste tyre rubber and then blended the resnlting DR into high-density polyethylene (HDPE) to produce thermoplastic elastomers (TPE). They found that the high shear conditions during the extrusion process induced chain scission and oxidative degradation of the GTR. The reduction in crosslink density was apparent in a decrease in the gel content of the rubber/HDPE blends and an increase in the melt flow of the materials. 

A research group in Canada [34] have used supercritical CO2 in a twin-screw extruder to devulcanise waste rubber from the automotive sector. They have used the process on both waste tyre rubber and EPDM-based products, such as door seals, and claim to have achieved good results with both types of material. The process uses that fact that as the CO2 swells the rubber in the high shear environment within the twin-screw extruder, the sulfur-sulfur crosslink bonds break preferentially compared to the carbon-carbon main-chain bonds (Section 4.2). 

Roy and co-workers [57] at the Indian Institute of Technology have evaluated the performance and the chemical behaviour of a range of disulfide compounds when applied to waste tyre rubber. The DR that were obtained in each case were revulcanised to assess their cure characteristics, and then samples tested to determine their mechanical properties, morphology, dynamic properties and thermal stability. 

Because of the interest in the recycling of waste tyre rubber, the University of Akron team has carried out a large number of studies on the application of ultrasound to the devulcanisation of SBR. These studies have evaluated the effect that variables such as crosslink type [69], styrene content [70], and crosslink density and molecular mobility [71] have on the results that are obtained. 

At the conclusion of the project, the benefits of the DevulC02 process for devulcanising waste tyre rubber could be summarised as follows ... 

Using Waste Tyre Rubber in Retreads at High Inclusion Rates, Project TYR3-008, WRAP, Banbury, UK, 2007. 

Work carried out in China and Korea [6] has looked into the role that bitumen and compatibilisers can play in waste tyre rubber/waste PP blends. In addition to assessing the effect of the level of bitumen, the study also investigated the effect that various compatibilisers had on the properties of the final products. The team carried out this assessment using a universal testing machine, a scanning electron... 

Da Costa and Ramos [20] have prepared LLDPE and EPDM blends, with and without waste tyre rubber, in a single-screw extruder operating with a temperature profile from 180 to 210 C. They observed that when the EPDM in the blend is partially replaced by the waste tyre rubber, differences in the thermal behavionr of the material... 

Figure 7.1 Lightweight construction blocks for the construction industry manufactured using waste tyre rubber as a partial replacement for aggregate. Reproduced with permission from the WRAP Quality Protocol, Waste and Resources Action Programme (WRAP), Banbury, UK. WRAP...

El-Gammal and co-workers [49] investigated the density and compressive strength of concrete that contained waste tyre rubber at various levels. The waste rubber had been used to replace equivalent amounts of fine and coarse aggregate in the test mixes. The results showed that, although there was a significant reduction in the compressive strength of the rubber modified concrete, the products demonstrated a ductile, plastic mode of failure as opposed to the brittle failure common with standard concrete. 

Gypsum plaster can cause problems by cracking in the first hours after hardening due to a lack of elasticity, and workers in Spain have evaluated the use of waste tyre rubber to reduce the possibility of this occurring by reducing the elasticity modulus of the set plaster [62]. Their study analysed the mechanical behaviour of gypsum plaster that contained rubber particles of three different sizes (0-1,1-2 and... 

An area that has seen a lot of interest is in the use of waste rubber to produce sound insulation materials. Zhao and co-workers [68] have investigated the properties of waste tyre rubber/wood composites for sound insulation applications. They used a four-microphone method to measure and compare the sound transmission losses of three different composite panels the waste tyre/wood material, a commercial wooden floorboard, and a commercial wood-based particle board. The waste tyre rubber/wood product was manufactured in the laboratory with commercial urea-formaldehyde and a PU adhesive. The results obtained indicated that the sound insulation properties of the waste rubber/wood material were better than the other two products. Also, its insulation properties were significantly affected by the amount of rubber crumb and the amount of PU adhesive used, the performance improving as the quantity of both ingredients was increased. In the case of the PU adhesive, this was due to the formation of more complete rubber-adhesive interfaces within the material. 

Another type of depolymerisation process involves reducing the waste rubber from tyres back to its very basic chemical units of carbon monoxide and hydrogen. For example, a process for the conversion of waste tyre rubber into butadiene has been reported by GEM Fuels [21]. The process first converts the rubber into ethanol, which is oxidised to acetaldehyde, and then catalytically reacts with additional ethanol to generate butadiene. The butadiene can then be mixed with styrene in various proportions and copolymerised to produce virgin SBR, which has similar properties to the SBR used initially to produce the tyre. 

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