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Tire recycling

Two projects suggest alternatives for reusing rubber

Samples of concrete containing particles obtained from discarded, shredded tires

Eduardo Cesar Samples of concrete containing particles obtained from discarded, shredded tiresEduardo Cesar

Of every 100 tires changed in Brazil, about 55 are kept by their owners to use as a spare or for some other reason, according to the data of the Brazilian Tire Industry Association (ANIP). The other 45 end up at collection stations because they are no longer usable. Of these, 67% are used as alternative fuel in cement industry furnaces, generating power to manufacture clinker, the principal raw material in cement. The remaining 33% are recycled and end up in products such as flooring for sports courts, synthetic grass, automotive carpeting and shoe soles.  Two research projects, one at the Federal University of the ABC (UFABC) and the other at the University of São Paulo (USP), developed new alternatives for reuse of discarded tires, one that would encapsulate automotive engines in order to reduce noise, and the other that would produce more flexible concrete.

Kelly Cristina de Lira Lixandrão, a PhD student in nanosciences and advanced materials at UFABC, worked with Mercedes-Benz do Brasil to develop a polypropylene-rubber powder compound. The rubber powder is obtained from shredded tires and the compound is used to encapsulate automotive engines. “Our objective is to simultaneously reduce the number of tires improperly disposed of and curb noise and air pollution, since tires are sometimes burned in the open and release toxic substances,” explains her advisor, physicist Fabio Furlan Ferreira, of the Center for Natural and Human Sciences (CCNH) at UFABC.

Thermoplastic polypropylene resin (in the form of powder or pellets) and rubber powder are melted in a heated cylinder and then passed through a matrix to arrive at a final form,” explains Ferreira. The physicist reports that plates of the compound were produced that contained 20% and 30% tire powder in a polypropylene matrix. “Since it was easier to process, the 20% material was used to manufacture a prototype that was fitted into a commercial Mercedes truck for external noise testing on a standard test track,” he says. “The results were satisfactory. The noise of the engine encapsulated with our product was similar to that obtained using the normal material.”

The advantage, according to Ferreira, is that the material developed by Lixandrão is approximately 53% lighter and 20% cheaper than the material currently used, because it is partly made of recycled polypropylene (a hard plastic material used in products such as crates, chairs and toys). Additionally, the prototype was produced as a single piece that can be easily installed on a vehicle, without requiring use of metallic belts, which also helps reduce costs.

Fernando Casa, an analyst in the Mercedes-Benz materials engineering department, says that the goal of the decision to form a partnership with UFABC was to ensure that the company keeps up-to-date and takes advantage of any innovations that might arise from graduate research done at the university. “We can take advantage of the ideas of students and researchers and also suggest research topics of interest to us,” he explains. According to Casa, Lixandrão and Ferreira’s solution for the tires appears to be feasible, although it is still in development.

New solutions for an environmental problem involves converting tires into powder (above) and using them in concrete or to encapsulate engines

Miguel Boyayan | Eduardo Cesar New solutions for an environmental problem involves converting tires into powder (above) and using them in concrete or to encapsulate enginesMiguel Boyayan | Eduardo Cesar

Rubber particles
In another project, this one from the Materials Engineering Department at the School of Engineering on USP’s Lorena campus, chemist Clodoaldo Saron developed an alternative way to reuse tires, as an ingredient in new types of cement. “We developed a kind of concrete that contains about 15% tire rubber particles mixed with sand,” he explains.  Saron explains that rubber is organic and not very compatible chemically with sand and cement, which are inorganic materials. The solution was to add compatibilizers, composed of anhydride and epoxide chemical functional groups that are highly reactive and able to form stable bonds. “The results obtained show that both compatibilizers were efficient for this purpose.” That process is followed by the same procedures employed to prepare conventional concrete, adding cement and water in predetermined quantities.

According to the researcher, the new concrete could be used in construction in various ways, such as for sidewalks. “It can absorb impact better when walked upon, resulting in improved comfort and a reduced risk of injury,” he says. “Its greater deformation capacity means it could also be used for sidewalks that are lined with trees, where it would reduce the incidence of cracks in pavement caused by tree roots.” Concrete made with rubber can also be used for buildings in environments subject to strong vibrations, as long as the structures are developed to absorb them, preventing physical damage to those buildings. Saron cautions that the tests were carried out only in the laboratory; three more years of development are thought to be necessary. The research, which has already resulted in one patent application, is now being worked on by two additional team members: Professor Sebastião Ribeiro and PhD candidate Diego David Pinzón Moreno.

Waste that is difficult to get rid of
In 2015, 71.9 million tires were sold in Brazil and 45.7 million were discarded. Used tires are hard to dispose of because they are not biodegradable and take up a lot of space. If they are discarded just anywhere, they can pollute rivers and creeks or become the home of disease-carrying mosquitoes. If burned in the open, they release toxic substances. That is why a 2009 resolution by the National Environment Council ordered that, for every new tire sold on the replacement market, manufacturers or importers must properly dispose of one tire that is “unserviceable,” which is the term applied to useless tires. According to the ANIP president Alberto Mayer, manufacturers are complying with this rule. “There are 1,008 collection stations, some operated under agreements with cities and others set up as temporary collection points at resellers,” he says. In 2015 alone, 451,700 metric tons of tires were collected, the equivalent of 90 million passenger car tires.

In the United States, about 60% of discarded tires are used to generate electricity at cement companies, paper manufacturers, or for power generation. The remainder are recycled, according to ANIP data. “In Germany, a country that greatly values recycling, the product attracts collectors to resellers,” says Mayer. According to Fabio Furlan Ferreira, of UFABC, Japan is the most advanced country in terms of recycling unserviceable tires. “There, they reuse up to 91% of the total volume and the three principal markets for recycled tires are energy generation, construction, and export for reuse and retreading.”

Study of the mechanical recycling of PET and tire waste using FTIR spectroscopy (nº 2007/07676-9); Grant Mechanism Regular research project; Principal investigator Clodoaldo Saron (EEL/USP); Investment R$145,493.09.