Greener polyurethanes start with plant-based raw materials.

Mar 10, 2011

Helou, M, J-F Carpentier and SM Guillaume.  2010.  Poly(carbonate-urethane): an isocyanate-free procedure from a,x-di(cyclic carbonate) telechelic poly(trimethylene carbonate)s. Green Chemistry http://dx.doi.org/10.1039/c0gc00686f.

Synopsis by Evan Beach

Polyurethane plastic can be manufactured without dangerous raw materials called isocyanates with a new approach that uses bio-based starting materials and avoids toxic metal catalysts.

A shift to a bio-based raw material can reduce several chemical hazards associated with making one of the most popular plastics – polyurethanes – in production today, researchers report in the journal Green Chemistry. The new process means polyurethane plastic may be less hazardous to make and easier to break down in the environment.

Polyurethanes are a family of commodity plastics very commonly encountered in everyday life. They are widely used in industrial, automotive, engineering and medical applications and are found in a large range of products, including paints, foams, adhesives and coatings.

The new process for making polyurethanes focuses on one class called polycarbonate urethanes. These are found commercially in coatings and medical devices.

Almost all polyurethanes are prepared from chemicals called isocyanates. Most isocyanates are acutely toxic and pose a health risk to workers during manfacturing and to people who live in the communities surrounding the facilities.
 
The manufacturing of polyurethanes usually relies on toxic metal catalysts that can be released from the products into the environment. Research has shown that environmental exposures to these chemicals can lead to disruption of hormonal processes in animals.
 
To avoid the isocyanates and toxic catalysts, the researchers use a method that creates bonds between carbon and nitrogen atoms. Isocyanate chemistry creates carbon-oxygen links. By changing this strategy, the scientists can incorporate a variety of bio-based raw materials into the final plastic. One of their key starting materials is glycerol, a by-product of biofuels made from plant oils.
 
The report shows that the process leads to longer polymer chains. Longer chains offer better performance in commercial applications. The new type of polycarbonate urethanes are also biodegradable.
 
One potential catch in the new method is that one of the chemicals used in the process, called DCC, is itself very commonly produced from isocyanates. DCC acts as a promoter, making one of the chemical reactions easier to accomplish. However, it is very likely that other promoters could be used in its place. Replacement of DCC would be an obvious improvement for a process that aims to be isocyanate-free.

 

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