Polymer Film Changes Color to Signal Different Packaging Conditions

A polymer developed by researchers at Rice University and the Massachusetts Institute of Technology will change color inside of a package, indicating that the conditions inside have changed and the food is spoiled.

The scientists made a metamaterial, comprising several layers, out of the polymers that, when exposed to certain ions in the environment, change color depending on whether the ions penetrate the water-loving layers, reports FoodProductionDaily.com. Thefood packaging nanoscale layers are composed of hydrophobic (water-repelling) polystyrene and hydrophilic (water-loving) poly(2-vinyl pyridine) (P2VP). Together, this material is called a photonic gel, which is a co-polymer.

This gel is what changes color, depending on the amount of water that is absorbed by the hydrophyllic layers. While the polystyrene molecules clump together to keep the water molecules out, the P2VP forms its own layers between the polystryrene, making what the researchers call “nano-pancakes.”

When the researchers exposed these materials to various solutions, they found that they turned different colors, depending on how much solvent was absorbed by the P2VP layers. On the other hand, when they exposed the materials to a chlorine/oxide/iron solution, it was not readily absorbed, and thus the material stayed in its natural color, transparent.

The clear film turned blue when it was exposed to thiocyanate, to green when exposed to iodine, to yellow when exposed to nitrate, to orange when exposed to bromine, and to red when exposed to chlorine. A summary of the research appeared in the American Chemical Society journal, ACS Nano.

The film is easy to make and fairly inexpensive, which means that industrial demand could be met, says Ned Thomas, dean of Rice’s George R. Brown School of Engineering. “If it’s inside a sealed package and the environment in that package changes because of contamination or aging or exposure to temperature, an inspector would see that the sensor change from blue to red and know immediately the food is spoiled,” he says.

The next step for the development could be to license it or use it to start up a company, Thomas says. Alternatively, the material could be used for security and multiband optical elements in laser-driven systems.

Source: “Scientists create ultra-thin material that could be used as food sensor,” FoodProductionDaily.com, 10/23/12
Image by Dino Quinzani.