Scientists create fire-safe ‘green’ plastic

A synthetic polymer that doesn't burn has been created by scientists from the University of Massachusetts (UMass) Amherst.

The new polymer doesn't need the flame-retardant chemicals that are added to many plastics before they can be used in bus seats, airplanes, textiles and countless household items. Some of these additives have been showing up in dust in homes and offices, fish, fat cells and breast milk, raising concern that they pose a risk to human health and the environment.

When something burns, it decomposes thermally; some of it becomes a gas "” that's what burns as flame "” and what doesn't burn becomes what polymer scientists refer to as "char' "” the solid that is left behind.

The goal when creating flame-resistant plastics is to have a very high char yield; more char means less fire and fewer volatile chemicals being released. Most common plastics burn readily (polypropylene has a char yield of zero), so fire-retardant additives are mixed in "” these are often halogenated molecules that contain reactive chemicals such as chlorine, bromine or phosphorous.

These additives have been particularly effective at reducing the flammability of plastics, but have come under increased scrutiny for being potentially damaging to human health and the environment.

The polymer that the UMass Amherst team synthesised has a naturally high char yield (70%) and doesn't contain any halogens. It uses bishydroxydeoxybenzoin or BHDB as a building block, which releases water vapour when it breaks down in a fire, rather than hazardous gasses.

The flame-resistant synthetic polymer is clear, flexible, durable and much cheaper to make than the high-temperature and heat-resistant plastics in current use, which tend to be brittle and dark in colour.

"The great thing about BHDB is that it's really a two-birds-with-one-stone approach for a new polymer," said UMass Amherst scientist Bryan Coughlin.

"It is extremely fire-safe, and does not contain halogenated additives, which are known to be environmentally hazardous."

The next step, according to the researchers, is to make a couple of tons of BHDB "”enough to make aircraft parts and do more tests. Eventually it may end up in combat gear for soldiers, in circuit boards, bus seats and numerous household products.