Using Completely Degradable, Synthetic Rubber Could Reduce Tire Waste (Video)

According to the Rubber Manufacturers Association, nearly 270 million tires were discarded in the U.S. in 2013 — more than one tire per adult living in the country. Thousands get stockpiled in landfills. And because tires are non-degradable, they could potentially stick around indefinitely. 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.

One possible solution to the nation’s scrap-tire glut would be to make new tires with degradable materials. Since 2012, the research team led by Hassan S. Bazzi, Ph.D., at the Texas A&M University campus in Qatar (TAMU-Qatar) has been working on this option. They 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.

Using ruthenium, a transition-metal catalyst, the researchers polymerized cyclopentene at 0 degrees Celsius 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 percent 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,” Tuba says.