As atmospheric carbon dioxide levels continue to rise, CO2-based polymers would appear to offer an intriguing means to capture and reuse CO2 that, up to now, was at best considered waste and at worst, an environmental hazard.
CO2 recycling is rapidly becoming a hot topic for the future for many large companies in the chemicals and plastics sector. The production of value-added products, materials and fuel from CO2 feedstocks could help to close the carbon cycle, and it offers an example of sustainable future technologies aimed at saving natural resources and energy.
The burgeoning interest in CO2 has prompted the organization in October of an international conference entitled "CO2 as Feedstock for Chemistry and Polymers" that will cover "an incredibly wide range of uses for CO2, developing a vision for a sustainable carbon dioxide economy". The conference is being held in Essen, Germany at Haus der Technik.
What are CO2-based polymers, anyway?
In the late 1960s, researchers discovered that by copolymerizing carbon dioxide and epoxide, an alternating copolymer - an aliphatic polycarbonate - could be formed, thus establishing for the first time the potential of CO2 as a feedstock. Today, with major research efforts around the world directed at combining traditional feedstocks with CO2 to synthesize polymers and high value chemicals, this potential is slowly starting to be realized.
The technology uses a metal-based catalyst system to couple CO2 and epoxide molecules. The technology is easily adjusted. The properties of the polymer created depend on the type of epoxide and can vary from transparent to opaque and solid to viscous based on the molecular weight of the polymer chains. The most important polymers created by this process are polypropylene carbonate (PPC) and polyethylene carbonate (PEC).
PPC is 43% CO2 by mass, biodegradable, and shows high temperature stability and elasticity, as well as transparency and a memory effect. These properties promise to open up a wide range of applications for this material, including countless uses as packing film and foams, dispersions and softeners for brittle plastics. PEC materials can provide an improved oxygen barrier layer, making them suitable for use in the food and beverage industry.
Now everybody's doing it
Work in this field used to be the sole preserve of a few university labs. But over the past three years, the U.S. Department of Energy and the German Ministry for Research (BMBF) have each provided some €100 million for research into new uses for CO2. These investments are already starting to bear fruit.
Evonik, BASF and Bayer MaterialScience have all devoted considerable R&D efforts to the development of CO2 polymers. Siemens and BASF successfully demonstrated the first applications in household appliances - refrigerator compartments and vacuum cleaner covers - at the ACHEMA fair in Frankfurt in June 2012. The refrigerator components were made of PPC/PLA combinations; the vacuum cleaner covers were made from a compound of polyhdroxybutyrate (PHB) bioplastic and polypropylene carbonate containing 43% CO2 (by weight) supplied by BASF. The properties of the latter composite are such that it can replace ABS in a host of applications. The addition of PPC to the PHB and PLA considerably reduced the brittleness of these biopolymers, eliminating the need for certain additives and enabling easy processing using normal machinery. Siemens is further on the look out to examine whether they can replace other types of plastic with co2 based composite materials.
Bayer Material Science showcased its "Dream Production" polyurethane samples at ACHEMA, which were made from CO2 polyols and, if all goes according to plan, will start industrial production of foams for mattresses and insulation materials for refrigeration and construction purposes in 2015. U.S. players in the CO2-based polymers field are Novomer and Empower Materials, while SK Innovation in South Korea is a major Asian company in the field.
The English-language "Conference on Carbon Dioxide as Feedstock for Chemistry and Polymers" is scheduled to take place from Oct. 10-11, 2012.