This is the problem Droguet’s team set out to solve using commercially available wood pulp-derived cellulose. First, they had to figure out how to get the crystals to align properly. They will automatically form a structure, but which structure depends on the ionic composition of the water in which they are present. To change that ingredient, “you just add salt,” says Vignolini. Salt changes the way the molecules attract each other, and determines their shape and then the color of sparkle they produce. Adding just five milligrams changes the color of an entire kilogram of cellulose, causing the crystals to refract shorter wavelengths, like green and blue. With less salt, they refract longer wavelengths, like red.
The team has also figured out how to carefully control the manufacturing process so that they can now make metal sheets meters long using a roll-to-roll machine, a common industrial device. The machine coils the filaments of the polymer base, or “web”, while the dispenser sprays out an even amount of the nanocrystal solution. The mixture should be thin enough to settle easily on the roll, but viscous enough to create a deep and even color.
At this point, the mix is transparent, so the team can’t tell if they’ve successfully produced a good shipment until they run the web through a hot air dryer. After the water evaporates, only a film of nanocrystals remains. The color suddenly emerges and deepens. “At the end of the day, it’s really quick,” says Droguet, who created the green, blue, red and yellow sparkles. The film can then be peeled off the web and ground into craft tinsel or mixed into paint. The process requires less energy than making plastic glitter and the final product retains its sparkle even when it is mixed in soapy water, ethanol and oil, which means it can be used in makeup and even in food. “I think we’ve now proven that the principles work on a large scale,” said Droguet.
But they have not tried industrial quantity production yet. Using equipment at Cambridge, Droguet now takes about two months to create one kilogram of glitter. To increase production, he will need funding and access to commercial locations with larger reeling machines. So far, it has been difficult to get companies involved; Vignolini said manufacturers were excited but hesitant because the material was so different from the material they are currently using. “It’s brand new, and companies want to make sure it works,” she said.
Vignolini and Droguet also wanted to run experiments to understand how the material breaks down over its life cycle and how that decomposition might affect the environment. They teamed up with Dannielle Green, an ecologist at Anglia Ruskin University in the United Kingdom, who has been studying other cellulose-based sparkles to see how they affect algae growth. .
