Recycling Tires
One of the oldest recycling efforts involve used tires. Since almost the first tires, recycling has been a problem. Even though they are bascially a biodegradable biopolymer, they are very difficult to discard without degrading the environment. They simply do not disappear readlly and burning can be an environmental disaster. Lots of efforts, projects and money have been applied without many good solutions. The work goes on. (RDC 1/19/2011)
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“Almost 3 million tons of scrap tires are annually generated in North America. Among the rubber recycling approaches, size reduction is a feasible approach for the most beneficial reuse of these materials. Currently, there are limited applications for the size reduced rubber particles, and development of new products is essential to expanding useful applications. One restricting factor on reusing rubber particles is the hydrophobic nature that limits the use to only non-aqueous media.”
“Polymers are generally classified as thermoplastics and thermosets. Thermoplastic polymers can generally be melted and recycled using heating and remolding processes. Thermoset polymers are crosslinked and, once they are set, the simple approach of melting and reforming into a new shape does not apply to them. Recycling of thermoset polymers is thus a challenging technical problem. Vulcanized rubber materials are thermoset polymers, and scrap tires represent the largest stream of waste rubber materials. Over 250 million tires (about one tire per person) are annually generated in North America and, for the most part, these are inefficiently used or disposed of in landfills.”
“More attention has been focused on reusing scrap tires in the past few years, but the current applications are generally limited to "low value" applications. Understanding the present markets for scrap tires is a key to continuation and expansion of the recycling efforts toward higher value added uses of these materials. Currently, there are typically three major markets for scrap tires: tire derived fuel (TDF); civil engineering applications; and crumb rubber applications. In addition, small percentages of scrap tires used are often exported or used in agricultural applications.”
“Incineration of scrap tires to generate energy is a well-known technology and is the largest market for scrap tires in North America. TDF as a source of energy is probably as efficient, and possibly less expensive, than fossil fuels. As late as 1990, the only recycling approach for scrap tires was the use of TDF. More environmentally friendly applications have been developed since then, such that now only about 50 percent of the total recycled scrap tires are in TDF applications.”
“TDF is a sufficient way for reducing the number of stockpiled scrap tires. However, a valuable source of raw materials is lost using this approach. Possible reuse of scrap tires in new products provides considerably more energy than simply burning.”
“Civil engineering is a fast growing and the second largest market for scrap tires. In the typical civil engineering application, shredded tire is used where there is an economic benefit as compared to the price of soil or other fill materials. The two major factors contributing to the dynamic growth of this market are the existence of a considerable amount of tire shreds from stockpile abatement projects and availability of significant guidelines and information for shredded tire in civil engineering applications. Civil engineering applications are not considered high value added uses of scrap tires, because in most applications the rubber particles are used as a replacement for generally inexpensive materials like soil.”
“Size reduction seems to be a promising recycling approach for beneficial uses of scrap tires in high performance products. Size reduction generally refers to grinding the vulcanized rubber into shredded particles in the typical size range of 25 mm to 150 mm. Further size reduction of the shredded materials into smaller particles (less than 2000 microns) is defined as pulverization. According to ASTM D 5603-96, the recycled rubber particles are classified as coarse and fine particles. Rubber particles in the size range of 2000 microns to 425 microns are coarse particles and the particles smaller than 425 microns are classified as fine particles.”
“Today, there are four major applications of crumb rubber usage: rubber modified asphalt (RMA), molded products, tire/automotive industry and sport surfacing. These applications could be considered as higher value added use of recycled rubber materials, compared to the civil engineering and TDF applications discussed above.”
“The crumb rubber applications have a limited market compared to the other applications. An important factor impacting this market is the imbalance in supply and demand of crumb rubber materials. To increase demand, there is a need for more focus on developing more products for new applications.”
“Direct addition of rubber particles into the matrix of another polymer that is incompatible with rubber particles generally results in poor mechanical properties of the produced materials. Poor interfacial adhesion between surfaces of the rubber particles with matrix is typically the main reason for these failures. Surface modification of the rubber particles, or addition of a compatiblizer, may enhance the mechanical properties of the resulting composite materials. The molded product of the binder and rubber particles might have limited application due to the particular shape of the mold used. A broader range of applications could be obtained without using a mold if the binder is also in the particulate form. The potential application of such composite materials is in polymeric surface coatings such as waterborne polymeric coatings or dry powder coatings. Waterborne polymeric emulsions are the most suitable choice of binders in particulate form. However, recycled rubber particles have a very poor dispersibility in aqueous media due to their hydrophobic nature. Addition of a hydrophilic character to hydrophobic rubber particles would allow their utilization in such media.”
(Shahidi, Hamid and Fouad, US Patent 7,816,446; 10/19/2010)
Materials
Pyrolysis of Tires
Recycling
Recycling Elastomers /Rubber
Recent US Patents
12/14/2010
7,850,855
Methods of utilizing recycled rubber
Pomerleau and Gibbs of Engineered Drilling Solutions, California, used recycled rubber including recycled rubber from tires to absorb hydrocarbons. The method is particularly applicable to absorbing waste or contaminating hydrocarbons from solid surfaces or particles where hydrocarbons may have been spilt or otherwise have contaminated the surfaces. The methods may also be used for removing spilt hydrocarbons from a liquid such as crude oil spills at sea. (RDC 6/2/2011)
11/30/2011
7,842,106
Process for using polymeric waste materials to produce fuel
Gonchar et al of Recarbon, Pennsylvania, uses biodiesel and other high boiling esters containing short alkyl groups to produce liquid fuels from tires. The tires are refluxed in biodiesel to 345 C. Steel wires and other solids were filtered out. "Biodiesel" is a mixture of methyl, ethyl, or n-propyl esters of carboxylic acids or combinations thereof formed as a result of transesterification of fats with methanol, ethanol, or n-propanol. (RDC 4/18/2011)
11/2/2010
7,825,213
Method of making a metal terephthalate polymer
Steinmeyer et al of Chem Engineering Energy, Missouri, formed a metal-terephthalate polymer from polyester ethylene terephthalate by reacting polyester ethylene terephthalate with a metal compound in a non-aqueous melt environment at an elevated temperature. The elevated temperature will be greater than 270 C., and preferably rises to a temperature of about 520 C. The method is preferably carried out at a low pressure. The method may be used in the recycling of passenger vehicle tire shreds to produce a carbon black rich powder that is enriched in the metal-terephthalate polymer (RDC 3/2/2011)
7,823,812
Recycling method of used tyres and installation for the actuation of the same method
Fazzinit of Tires S.p.A., Italy recycles tires by grinding, separating the rubber from metals and textiles, pulvering the rubber, mixing with a polyurethane resin and molding. (RDC 2/21/2011)
8/3/2010
7,767,187
Method and apparatus for separating carbon product from used tire with microwave
Hong has developed a microwave process for decomposing used tires into carbon products including oil and carbon black and iron cores.
Recent Journal Articles
Synthesis of carbon nanostructures from residual solids waste tires
(1960–1967)Journal of Applied Polymer Science 123 #4 (2012)
Fernández, et al, Mexico, synthesized carbon nanostructures obtained from the decomposition of residual solid from waste tires (RSWT) in quartz tubes under reduced pressure (1.33 Pa) at 900°C for 15 min. The synthesis led to the formation of two phases, a fragmented solid black powder composed of multi-walled carbon nanotubes (MWCNTs), onion-type fullerenes, and spheres, and a very bright metallic dark film. The MWCNTs had an average diameter of approximately 25 nm and a length greater than 100 nm while the diameter of the onion-type fullerenes was found to be 8 nm. The nanospheres showed different diameters ranging from 500 nm to 1.5 μm, and some had a metallic core surrounded by layers of carbon. (RDC 11/2/2011)
Compatibilizer in waste tire powder and low-density polyethylene blends and the blends modified asphalt
(485–492)Journal of Applied Polymer Science 123 #1 (2012)
Ouyang et al of the Shanghai Institute of Technology. China, showed that with the increasing ratio of waste tire powder (WTP) to low-density polyethylene (LDPE), the hardness and tensile strength of the WTP/LDPE blends decreased while the elongation at break increased. Five kinds of compatibilizers, such as maleic anhydride-grafted polyethylene (PE-g-MA), maleic anhydride-grafted ethylene-octene copolymer (POE-g-MA), maleic anhydride-grafted linear LDPE, maleic anhydride-grafted ethylene vinyl-acetate copolymer, and maleic anhydride-grafted styrene-ethylene-butylene-styrene, were incorporated to prepare WTP/LDPE blends, respectively. PE-g-MA and POE-g-MA reinforced the tensile stress and toughness of the blends. The toughness value of POE-g-MA incorporating blends was the highest, reached to 2032.3 MJ/m3, while that of the control was only 1402.9 MJ/m3. Therefore, POE-g-MA was selected as asphalt modifier. The toughness value reached to the highest level when the content of POE-g-MA was about 8%. Besides that the softening point of the modified asphalt would be higher than 60°C, whereas the content of WTP/LDPE blend was more than 5%, and the blends were mixed by stirring under the shearing speed of 3000 rpm for 20 min. Especially, when the blend content was 8.5%, the softening point arrived at 82°C, contributing to asphalt strength and elastic properties in a wide range of temperature. (RDC 10/12/2011)
SOME OBSERVATIONS FROM STUDIES OF RF PLASMA PYROLYSIS OF WASTE TIRES
(1541 – 1552) Chemical Engineering Communications 197 #12 (2010)
Tangand Huang from Guangdong University of Technology, Guangzhou, China using a 1600 to 2000 W radio frequency plasma reactor produced a hydrogen, carbon monoxide and methane gas and a pyrolytic char from waste tires.