Researchers from the University of California, Irvine (UCI) and the Shanghai Institute of Organic Chemistry (SIOC) have found a new way to break down the strong bonds of polyethylene, the most commonly used synthetic plastic, and convert it into useful liquid fuels and waxes. The new technique is less toxic and less energy-intensive than current approaches to breaking down the polymers' chemical bonds.
“Synthetic plastics are a fundamental part of modern life, but our use of them in large volume has created serious environmental problems,” said UCI chemist Zhibin Guan. “Our goal through this research was to address the issue of plastic pollution as well as achieving a beneficial outcome of creating a new source of liquid fuel.”
Scientists have been seeking better ways to recycle plastic bags, bottles and other plastic trash generated by humans. Polyethylene is chemically inert, which makes it difficult to degrade. Current methods include using caustic chemicals known as radicals or heating the material to more than 700 degrees Fahrenheit to break down the chemical bonds of the polymers.
Guan and Zheng Huang, his collaborator at SIOC, together with their research team, sought out a more efficient process that could use milder conditions. They focused on the use of alkanes – specific types of hydrocarbon molecules – to scramble and separate polymer molecules into other useful compounds.
As it happens, some widely available and low-value substances can do the trick. The chemists found that short alkanes, such as petroleum ethers, could be used to degrade plastics through a process known as cross-alkane metathesis. The substances needed for the new technique are byproducts from oil refinement, so they are readily available.
The plastics completely convert into liquid fuels and waxes, the proportions of which can be controlled by changing the catalyst structure and reaction time. No pre-treatment is required, even for postconsumer polyethylene bottles, bags and films.
The research team recently published their results in Science Advances.
Guan said that the U.S.-China joint team is still working on making the process more efficient and cost-effective. Remaining challenges include increasing the catalyst activity and lifetime, decreasing the cost, and developing catalytic processes to degrade other plastics, as well.
Researchers at IBM and from a UK-based partnership have also made recent discoveries related to plastic waste processing.
IBM scientists found a way to turn polycarbonate wastes such as old CDs into a new material with superior mechanical properties than the original. Polycarbonates are another common plastic, used in electronics, eyeglass lenses, kitchen utensils and more. Over time, polycarbonates decompose and leach BPA, causing concern among consumers. IBM’s new material, however, is strong enough that it prevents BPA leaching, to the extent that it is safe for water purification and medical equipment.
Meanwhile, consultancy Nextek and recycling manufacturer AShortWalk have developed a new resin called NextCupCycle that deals with the pesky problem of paper coffee cups. Hot beverage cups are notoriously difficult to recycle due to their mixed material composition, but the researchers found that they can “play to the strengths” of the materials in their combined form to create new high-strength composites.