Rethinking plastics

KAUST Distinguished Professors Yves Gnanou and Nikolaos Hadjichristidis and their fellow researchers developed the first metal-free process for making aliphatic degradable polycarbonates using CO₂. The metal-free aliphatic polycarbonate is transparent and highly flexible. Photo by Asharaf AdulRahman.

​-By Sonia Turosienski, KAUST News

From plastic wrap to car tires, we demand a lot from our plastics—elasticity, strength, flexibility and recyclability. The ability to manipulate these qualities has made plastics into a diverse and almost ubiquitous material. The omnipresence of plastics, however, has grave implications for the environment and especially for the world's oceans. The United Nations Environment Programme predicts that by 2050, there will be as much plastic in the ocean as there are fish.

'White pollution' worldwide

Recently, there has been a change in the public's awareness of and concern for plastic pollution, also called "white pollution." In addition, many countries are releasing copious amounts of CO₂ into the atmosphere, contributing to global warming. While reducing plastic consumption and encouraging reuse is crucial, Yves Gnanou, KAUST distinguished professor of chemical science and acting vice president for Academic Affairs, working with Nikolaos Hadjichristidis, KAUST distinguished professor of chemical science, developed the first metal-free process for making aliphatic degradable polycarbonates using CO₂.

KAUST Distinguished Professors Yves Gnanou and Nikolaos Hadjichristidis' research groups are working to develop polymeric materials that are more sustainable at the point of production. Photo by Asharaf AdulRahman.

The first successful synthesis of a polycarbonate using CO₂ was done in 1969 by a group of Japanese chemists at the University of Tokyo. For the past five decades, researchers have worked on refining the catalytic process of coupling the greenhouse gas with epoxides using transition metals to make polymeric materials, but their effort yielded only limited commercial success.

The KAUST researchers work in the lab on their green chemistry process that does away with the use of toxic metals to produce aliphatic degradable polycarbonates using CO₂. Photo by Asharaf AdulRahman.

China has recently been leading the charge in producing polycarbonates made from CO₂ on a commercial scale. So far, polycarbonates made from CO₂ have been used in China for several applications, including food packaging, plastic shopping bags and protective film for agricultural applications. Industrial investment in polycarbonate production using CO₂ is part of a coordinated effort to reduce emissions. Novomer, a U.S. company specializing in the production of polycarbonates using CO₂, was acquired by Saudi Aramco in 2016. The Novomer process, like factories in China, continues to use metal-based catalysts.

Doing away with metal

Gnanou and his team developed an alternative green chemistry process that does away with toxic metals in favor of two non-metallic reactants—an ammonium compound that helps the coupling reaction between CO₂ and epoxides and a boron-based compound that activates the latter monomer.

The polycarbonate developed by KAUST researchers (pictured above) was made using CO₂ in a metal-free process. Photo courtesy of Prof. Yves Gnanou; taken at the University of Maastricht.

"Metal-based catalysts are problematic because they can be toxic and color the material. If you are making polycarbonates for food applications, this is particularly concerning. The metal needs to be removed meaning that the production process is more energy and resource intensive. Further, any metal left in the polycarbonate could also cause some degradation in the material," Gnanou explained.

Recently, the Intergovernmental Panel on Climate Change released a special report outlining that global warming must be kept to 1.5 degrees Celsius to avoid drastic changes to our ecosystem. The report added that "[g]lobal net human-caused emissions of carbon dioxide would need to fall by about 45 percent from 2010 levels by 2030, reaching 'net zero' around 2050."

KAUST Distinguished Professors Yves Gnanou (right) is shown here in the lab on campus working with a researcher. Photo by Asharaf AdulRahman.

"We are in the right place to use CO₂ to make polymers. We need to harness CO₂ as a commodity and utilize waste product that is harming our environment. The question is why isn't the rest of the world following China's example and taking action," Gnanou said.

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