In spite of environmentalists’ efforts for years, scrap tires remain a huge problem. In 2013, the Rubber Manufacturers Association estimated that more than 270 million tires were thrown away annually in the US alone. That’s more than the entire adult population of the country. Thousands are simply dumped in landfills where they could stick around forever, as they are not biodegradable. Many more are used as a component for fuel that is used to power pulp and paper mills, cement kiln and other plants. The emissions from these fires spew toxic pollutant into the atmosphere every day.
A team of researchers from the Texas A&M University campus in Qatar (TAMU-Qatar) has been working on this problem by using a byproduct of the petrochemical industry and turning it into recyclable value-added chemicals for use in tires. One of the lead researchers, Robert Tuba, Ph.D., says he wants to make something that is good for both the environment and the community.
The research, which started in 2012, focusses on making new tires with degradable materials. Petrochemical refining’s steam-cracking operation C5 fraction, produce the components cyclopentadiene and cyclopentene. Both of these low-value major components contain hydrocarbons with five carbon atoms. Tuba has been working with colleagues at the California Institute of Technology, to make polypentenamers, which are similar to natural rubber. This is achieved by stringing cyclopentene molecules together.
Butadiene is currently being used as the base material in the manufacturing of synthetic rubber. A recent price increase in butadiene has created an opportunity for competition to enter the market. Tuba sees cyclopentene as a commercially viable alternative. Theoretically, it should be possible to polymerize cyclopentene and then degrade it under mild reaction conditions. This should be inexpensive, as the process requires minimal energy.
Antisar Hlil, also at TAMU-Qatar, explains that the theoretical studies were conducted by using equilibrium ring opening metathesis polymerization. This was followed by experimental studies that found that the concept is indeed viable. The feasibility of the synthesis and recyclability of polypentenamer based tire additives has thus been proven.
Cyclopentene was polymerized at 0 degrees Celsius and the resulting material was decomposed at 40 to 50 degrees. A transition metal catalyst, ruthenium, was used to achieve this. To achieve 40 to 50 degrees in industry requires very small input energy. The team also managed to recover 100% of their starting material in the lab. The same result was achieved in tests involving various polypentenamer based tire additives developed by the team.
New studies are underway where synthetic rubber is mixed with other tire materials, including metals and fillers. The lab experiments have also been scaled up to determine whether the tire industry could use the processes realistically or not. If the results continue to be as promising as they have been, an industry partner will join the team and bring the material to market.
The researchers presented their work at the 252nd National Meeting & Exposition of the ACS.