A team from the Texas A&M University campus in Qatar (TAMU-Qatar) and Caltech has developed a new way to make synthetic rubber; once this material is discarded, it can be easily degraded back to its chemical building blocks and reused in new tires and other products. The researchers will present their work today at the 252nd National Meeting & Exposition of the American Chemical Society (ACS) in Philadelphia.
According to the Rubber Manufacturers Association, nearly 270 million tires were discarded in the US in 2013—more than one tire per adult living in the country. Many of the non-degradable scrap tires get stockpiled in landfills. More than half go on to become tire-derived fuel—shredded scrap tires that get mixed with coal and other materials to help power cement kilns, pulp and paper mills and other plants. But environmentalists are concerned that the emissions from this practice could be adding harmful pollutants to the air.
Since 2012, the research team led by Hassan S. Bazzi, Ph.D. at TAMU-Qatar has been working on making tires with degradable materials. The researchers started with a basic molecule called cyclopentene. Cyclopentene and its precursor cyclopentadiene are low-value major components of the abundant waste from petrochemical refining, in particular its steam-cracking operation C5 fraction, which contains hydrocarbons with five carbon atoms.
With colleagues at the California Institute of Technology, they have been experimenting with catalysts to string cyclopentene molecules together to make polypentenamers, which are similar to natural rubber.
Currently, synthetic-rubber makers use butadiene as their base material, but its cost has recently gone up, opening the door to competition. So Tuba turned to cyclopentene as a potential alternative. Calculations showed that polymerizing cyclopentene and degrading it under relatively mild reaction conditions—and thus requiring minimal energy and expense—should be possible.
We did theoretical studies to predict the feasibility of the synthesis and recyclability of polypentenamer-based tire additives using equilibrium ring opening metathesis polymerization. Then we did experimental studies and found that the concept works very well.—Antisar Hlil, TAMU-Qatar
Using ruthenium, a transition-metal catalyst, the researchers polymerized cyclopentene at 0 ˚C and decomposed the resulting material at 40 to 50 degrees. For industry, these are low temperatures that do not require a lot of energy. Additionally, in the lab, they could recover 100% of their starting material from several polypentenamer-based tire additives they developed.
In progress are new studies that mix the synthetic rubber with other tire materials, which include metals and fillers. The researchers are also scaling up their lab experiments to see whether the tire industry could realistically use their processes.
If the fundamental studies are very promising—which at this point, we believe they are—then our industry partner will come in to continue this project and bring the material to market.—Robert Tuba, Ph.D, one of the lead researchers
The researchers acknowledge funding from the Qatar Foundation and the Qatar National Research Fund.