Heat sensitive materials change color when hot

New polymer could prevent burns, food poisoning, traffic accidents

Imagine a fire door that changes color when hot, football jerseys that can tell when a player is overheating, road signs that change color indicating icy road conditions, and food packaging stamps that disappear when products have been kept at room temperature for too long. At the University of Rhode Island, chemists Brett Lucht and Bill Euler and chemical engineer Otto Gregory are working to make these products a reality.
The scientists are developing heat sensitive materials (polymers) that change color at various temperatures. Thus far they have been successful in creating a polymer that changes from red to yellow at 180°Fahrenheit (the temperature at which a person would suffer a burn) and at other warm temperatures.

Work on this project began when Gregory was approached by a company interested in coating cookware with a material that would change color when hot. A polymer was created, but it decomposed upon repeated exposure to high oven temperatures.

Since then, the trio has been successful in placing this polymer in plastics from which it cannot be extracted. This discovery is important to the food storage industry because it is the only FDA approved pigment that changes color.

“This polymer has an important safety application,” said Lucht. “It has the potential to prevent people from burning themselves and eating spoiled foods.” He calls this “smart packaging” because the packages would tell consumers the temperature of the product. For example, coffee lids could change color at extreme temperatures or milk cartons could have a mark that disappears if the carton reaches room temperature.

Funding for this project is provided by KM Scientific, the URI Foundation, and the URI Transportation Center, which envisions public safety applications for the polymers. The polymers can be added to a variety of products, including plastics, paints, inks, and rubbers. For instance, Gregory recalls when Ford Explorers were experiencing tire blow-outs due to heat caused by improper inflation.

“Using these polymers, we can help to prevent accidents such as these from occurring,” he said.

The polymers can also be placed in vinyl seating to warn of hot seats, on the wheels or brakes of trains to show when they are beginning to wear out, on radiator caps and engine hoses to warn of extremely high temperatures, and on road signs to warn drivers of potentially hazardous conditions. “The potential uses for these polymers are endless. These products could forewarn people that they are in potentially dangerous situations,” Gregory said.

Lucht and Euler are now concentrating on creating color changes for low temperatures and working on creating polymers that make more than one color change, ideally red for hot and blue for cold. Other vivid colors are also being studied. Gregory is focusing his research on uniformly dispersing polymers throughout different materials.