Polyurethane—used in everything from insulation to floor coatings—is made with toxic isocyanates. But maybe not for long.
If you've ever skipped across a hardwood floor, taken shelter in a building insulated with spray foam, or been treated in a hospital, chances are good you've come into contact with polyurethane. The large class of plastics has many uses, especially in coatings and foams, and it can be soft and flexible or hard and rigid.
Unfortunately, polyurethane is currently made with toxic chemicals called isocyanates. It was the release of methyl isocyanate gas that was largely responsible for the thousands of deaths and tens of thousands of injuries in Bhopal, India, in 1984. Smaller doses have been implicated in the disruption of hormone processes in animals. The toxin has been enough of a threat that scientists have been looking for ways to make polyurethane without it—and in the latest issue of the Green Chemistry Journal, researchers from France's Université de Rennes have published the results of promising trials into exactly that.
"Trying to make polyurethanes
without isocyanates has been a huge challenge for a long time; there have been very few examples that have come close," Beach said.
I spoke to Justin R. Breiner, the head of business development for foam insulation installer Ecologic Energy Solutions in Westport, Connecticut, to learn more about the problem. "From an environmental and hazard standpoint, isocyanate can be a real concern, particularly for installers and anyone who is going to come in contact with it," he said. Breiner added that he is aware of installers who have suffered skin, eye, and respiratory problems after coming into contact with isocyanates, which are used throughout the spray foam industry. "Our installers all use fresh air systems, which means they wear masks that have fresh air supplied directly from the outside," Breiner said.
Breiner claims that once polyurethane is cured, the isocyanates no longer pose a threat. "There is no offgassing of isocyanates once a plastic is formed, because it becomes a different chemistry," he explained.
Still, that hasn't stopped Marion Helou, Jean-François Carpentier, and Sophie M. Guillaume of the Université de Rennes from developing a relatively simple way to synthesize polyurethane without isocyanate or another toxic metal catalyst.
In an article for Environmental Health News, Evan Beach, an associate research scientist and lab manager at Yale's Center for Green Chemistry and Green Engineering, explains that the French researchers use a method that creates bonds between carbon and nitrogen atoms. In contrast, the usual way of making polyurethane, with isocyanates, creates bonds between carbon and oxygen. "By changing this strategy, the scientists are able to incorporate a variety of bio-based starting materials into the final plastic. One of their key starting materials is derived from glycerol, a byproduct of biofuel manufacturing," Beach explained.
Beach adds that the French process seems to produce high-performance polyurethane, and that it is also biodegradable. He points out that one possible drawback could be that one of the chemicals used in the reaction, DCC, is often made from isocyanates as well, though he adds that this could be replaced.
"Trying to make polyurethanes without isocyanates has been a huge challenge for a long time; there have been very few examples that have come close," Beach said.
Of course, the French results describe only lab tests, so it would be quite a while before isocyanate-free polyurethanes would go into commercial production. According to Beach, the next step would be to do mechanical testing, "to see if you can make foams and other plastics people are used to out of it."
Beach says that if the process is scalable, it could be a boon to the spray foam industry and other related businesses. "Currently, when someone calls a polyurethane product green they are focused on one part of it, like they are getting part of it from soy or something, but they are still using isocyanate," Beach said.
For his part, Breiner added, "Creating a polyurethane that could be made from something other than isocyanate would have a lot of ramifications."
As one potential example, less-toxic foams could be used more extensively for insulation, bringing added comfort and energy efficiency. It's easy to see how temporary and DIY structures like the ZipFlat concept out of Irvine, California, would benefit. The ZipFlat is a low-cost, temporary structure designed for use in disaster relief, food storage, and other applications. The walls are designed to be filled with spray insulation—and if the process were less toxic, the insulation would be safer and easier for people to install, without the need for sophisticated safety equipment.
It's true that finding a less-toxic way to make plastics won't eliminate all the environmental drawbacks. But plastics are all around us, and finding better ways to make them could be a step toward a greener world.
Image: Bree Bailey/flickr
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