Surface rubber crumb

Presently DOE is funding Air Products Chemical Company for the development of a fluorine surface treatment of tire rubber (crumb rubber) to modify its adhesion properties. This modified rubber could be used in making polymers such as polyurethane and epoxies. The tire rubber might also be used in certain plastics such as polystyrene and PVC, and in rubber products (68). 

Most surfaces of this kind now are laid on a sub-base of hard core, tarmac, or concrete in which has been installed adequate drainage for surface water over this is spread a shock-absorbing layer of porous rubber crumb, made from shredded tyres bonded together as flexible planar material of thickness 5 to 25 mm and supplied in the form of continuous rolls. The rubber layer may be laid loose or pegged, and sometimes is bonded to the sub-base with a moisture-curing polyurethane adhesive. 

As can be seen from Table 5, the blends made with the surface devulcanized reclaimed rubber crumb did not have cure characteristics that differed substantially from the blend made without including any of the reclaimed rubber (the series labeled None ). In fact, the blends made with the surface devulcanized reclaimed rubber crumb had cure characteristics that... 

In sports such as athletics, traditional materials have been almost completely replaced by synthetic materials. Sports surfaces in modern indoor stadiums are usually made from a porous structure of rubber crumb and a binder such as polyurethane. Other polymeric materials used include flexible PVC or rubber sheet, polyolefins, polypropylene (PP) grasses, and foam laminates. 

This technology (Benko and Beers, 2002a,b,c) utilizes a solvent to treat (devulcanize) the surface of rubber crumb particles of sizes within about 20-325 meshes. It is a variation of earlier disclosed technology (Hunt et al., 1999). The process is carried out at a temperature range between 150°C and 300 C at a pressure of at least 3.4 MPa in the presence of solvent selected from the group consisting alcohols and ketones. Among various solvents, the 2-butanol exhibited the best ability to devulcanize sulfur-cured SBR rubber. Duration of the process is above 20 min. 

Natural rubber tends to cling to rotors, and most synthetic rubbers are torn into chunks. The addition of carbon black and oil to an internal mixer has been studied by flow visualization techniques for a wide range of elastomers. The tearing of elastomers into crumbs disrupts the mixing of carbon black, which proceeds more surely with natural rubber. The rate of oil absorption depends on available surface area of the elastomer and proceeds more rapidly with torn rubber crumbs and slowly with natural rubber. 

Experts investigating a failure do not always agree. Experts for one side in a dispute over failed polyurethane bound rubber crumb playground surfaces were convinced it was due to the installer using too low a ratio of binder. Consideration of the resin supplier s advice seemed to bear this out. However, the other side s experts could not reconcile this with the installer having laid many other successful installations using nominally the same ratio. Closer... 

Because it is primarily a surface phenomenon, bacterial devulcanisation often requires finely ground rubber powder (e.g., 200 mesh) to be most effective, as a high surface area to volume ratio is needed, and the reaction is usually carried out in a temperature-controlled bioreactor. Potential disadvantages of the process, therefore, can include the relatively high cost of the small-particle-size rubber crumb, the relatively high capital outlay, and the fact that the rubber crumb has to go through a post-treatment wash and drying process. 

It is important to stipulate therefore that this section covers a different type of recycled product than Chapter 7, which reviews the work that has been carried out to produce and characterise products from blends of rubber crumb with virgin rubber, thermoplastics and other materials (e.g., asphalt). In Chapter 7, the rubber crumb that is used is either unmodified, or has been through a surface activation process, but it has not been devulcanised. 

Another example of applying characterisation tests in this way concerns a group in Brazil [2], who started with scraps generated during the extrusion of SBR and EPDM profiles, and ground them under ambient conditions. The rubber crumb materials that were obtained had irregular-shaped particles with a high surface area and... 

Increasing the activity of the surface of rubber crumb can yield big... 

There are a number of general techniques that can be used to enhance the surface activity of rubber crumb, including ... 

Figure 6.11 Surface polymerisation to enable high inclusion rates of rubber crumb into retread compounds for truck and large earthmover tyres. Reproduced with permission from the Waste and Resources Action Programme, Banbury, UK, p.7. WRAP (see note with Figure 6.7)...

Workers at the Chinese university of Yangzhou [35] have used microwaves to modify the surface of waste rubber crumb by devulcanising it and then blending it with NR in various proportions. These mixtures were then vulcanised and the mechanical properties, compression set, swelling behaviour and crosslink density investigated. The results obtained were compared with those of blends that had been prepared using crumb that had not been treated with microwaves. 

A considerable amount of work has been carried out to establish if it is possible to produce good-quality rubber/thermoplastic blends by incorporating waste rubber crumb, whether surface-activated or not, into thermoplastics matrices. This work has often been carried out using commodity semi-crystalline thermoplastics, such as low-density polyethylene (LDPE), high-density polyethylene (HOPE) and polypropylene (PP), with the aim to produce final products that are either modified (e.g., improvements in impact strength) or have properties that are usually associated with thermoplastic rubbers. 

The investigations and studies presented in this section are concerned with the blending of waste rubber powder or crumb, which has not been through any devulcanisation processes of the type described in Chapter 4, into rubber compounds to produce new products. The rubber crumb in question may or may not have been surface-activated by one of the processes described in Chapter 6, Section 6.6. The properties of the resulting blends will depend upon whether this activation has taken place or not, as well as upon some of the variables already listed at the start of Section 7.2, namely the origin and type of rubber crumb, the proportion of rubber crumb in the blend, and... 

An example of waste rubber powder being used to produce a new road surface on a public road was reported in 2012 [58]. In that article it was reported that Breedon Aggregates, a UK-based company, had resurfaced a short stretch of a dual carriageway in the UK using asphalt that contained recycled ground rubber. The rubber crumb used had been obtained from a Danish company... 

Rubber crumb can be used very successfully in the manufacture of sports surfaces such as running tracks in sports stadiums and artificial turf for a variety of uses. Commercial examples of such products include a track marketed by Conica, a division of BASF, as Conipur SW, which is a sandwich system comprising an elasticated layer of recycled rubber granules and a PU binder that is applied in situ to an asphalt substrate with built-in finishers [76]. 

Although the technical argument can now be regarded as essentially won for recycling options that involve either devulcanisation or the use of ruhher crumb, the principal factor that has often restricted commercial exploitation of both is the cost of the replacement product relative to the existing product. As has been demonstrated with rubber crumb, the use of it in, say, a road surface, often results in a product with better properties, but the cost has to be justified. With the devulcanisation of rubber for return into new rubber products, often the best that can be aimed for technically is equivalence with the existing virgin product, and the additional cost of the devulcanisation process can be a problem. 

Plant 000012 produces 3.9 x 10" kkg/year (8.7 x lO lb/year) of emulsion crumb rubber, primarily neoprene. The contact wastewater flow rate is approximately 8.45 m /day (2.25 X 10 gpd) and includes all air pollution control equipment, sanitary waste, maintenance and equipment cleanup, and direct contact wastewater. The treatment process consists of activated sludge, secondary clarification, sludge thickening, and aerobic sludge digestion. Noncontact wastewater, with a flow rate of approximately 1.31 x 10 m /day (3.46 x 10 gpd), is used on a once-through basis and is remrned directly to the river source. Contact wastewater is also returned to the surface stream after treatment. 

There are 13 solution crumb rubber plants in the United States. Twelve of these plants discharge treated wastewater to surface streams the other plant discharges its treated wastewater into a neighboring oil refinery s noncontact cooling water system. 

Table 16 Toxic Pollutant Removal Efficiency at Emulsion Crumb Rubber Plant 000012, Verification Data (Treatment Technology Activated Sludge, Discharge Point Surface Stream)...

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