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Biodegradable(可降解的) food packaging is designed to detect to what degree the food has gone bad by changing its color. Best-before labels are often poor predictors of when food becomes dangerous to eat, which can lead to waste and food poisoning, says Benedetto Marelli at the Massachusetts Institute of Technology. So he and his colleagues tried to create the package that can react to changes in food.

They made four films(膜) similar to plastic package, each consisting of two layers. One layer was made from a protein extracted from silkworm silk, while the other was made of one of four so-called covalent organic frameworks (COFs). These materials contain carbon and hydrogen, as well as atoms like oxygen or nitrogen, all arranged in a network that allows air and water to go through easily.

After checking the films were non-toxic and strong, the researchers tried to compost(堆肥处理) them. For the best performing film, 50 percent of it degraded after being placed in soil for 30 days, which is comparable to existing biodegradable plastics.

The material also changed colour when immersed in water with different pH values, due to the COF layer’s interaction with the liquid. Because the pH of food increases as it spoils, the researchers tried to use a piece of the film as a colour-changing label attached to a packet of raw chicken. The label started off orange but turned yellow and got 17 percent lighter after 20 hours at 30℃, indicating that the meat had begun to spoil. The researchers also loaded the COF layer with a chemical. After 15 days, so ya beans packaged in the film and left in high heat and humidity went bad, but only a third as much as beans wrapped in traditional plastic.

“For a successful market entry, the material will need to be affordable and easy to produce. The standard for competing with plastic production is very high.” says Marelli.