Waterproof, plasticizing paper coating – it breaks down

Researchers have developed a coating for paper that makes it behave like plastic – yet breaks down.

The coating is a cheap and safe mixture of chemicals, which together make the paper sturdy, waterproof and bacteria-repellent. While they initially plan to see how the coating works in food packaging, the researchers believe their coating could eventually be applied to other materials as well.

“The biggest problem with plastic materials as I see it is their inability to break down quickly and safely,” said Professor Zenji Hiroi, a researcher at the Institute for Solid State Physics at the University of Tokyo, Japan, and co-author from a paper describing the coating, published in Research into industrial and technical chemistry

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An artistic rendering of a layer of silica up close, with titanium dioxide nanoparticles in blue harmful bacteria landing on the surface. Credit: ©2022 Hiroi et al.

“There are materials that can be safely broken down, such as paper, but it is clear that paper cannot meet the wide range of uses that plastic can.

“However, we have found a way to give paper the beautiful properties of plastic, but without the disadvantages. We call it Choetsu, a cheap biodegradable coating that simply makes paper water-repellent and more robust.”

Choetsu is a mouth-watering blend of methyltrimethoxysilane (a silicon-carbon compound used as a drying agent), isopropanol (an alcohol commonly used in hand sanitizers), and tetraisopropyl titanate (a carbon-titanium compound that acts as a surface coating in paints and plastics).

When a paper structure is dipped (or sprayed) in the mixture and then dried at room temperature, it forms a thin layer of silica and organic (carbonaceous) molecules. This strengthens the paper and makes it waterproof.

Read more: Land pathogens use microplastics to reach the ocean

It also has a thin layer of titanium dioxide nanoparticles, which help repel dirt and bacteria. (Titanium dioxide is also used in some toothpastes and cosmetics.)

According to the researchers, all these chemicals break down in the environment over time.

“The technical challenge has been completed and some applications may soon be realized, such as items for consuming, packaging or preserving food,” Hiroi says.

“We now hope to apply this approach to other types of materials as well. The liquid composition can be matched to other materials and we can create a dirt and mold resistant coating that can form on glass, ceramics and even other plastics to increase their usability.”

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