Waterproof Coating Transforms Paper into an Excellent Plastic Substitute

For the first time, scientists have discovered a method to imbue sustainable paper materials with the beneficial properties of plastic. This could be done in a simple, effective, and efficient manner. A coating known as Choetsu not only waterproofs paper but also retains its flexibility and degrades safely.

Choetsu crane. A classic origami crane made from paper and coated with Choetsu (left) and uncoated (right). When submerged in water, the coated paper crane keeps its shape while the uncoated one quickly saturates with water and starts to disintegrate. ©2022 Hiroi et al.

Plastic materials are harmful to the surrounding, causing plastic pollution that washes up on beaches, spoiling rivers and killing innumerable animals.

Professor Zenji Hiroi from the Institute for Solid State Physics at the University of Tokyo and his team have come up with ways that materials science can help, and their recent breakthrough aims to substitute plastic with a sustainable paper alternative.

The main problem with plastic materials as I see it is their inability to degrade quickly and safely. There are materials that can degrade safely, such as paper, but obviously paper cannot fulfill the vast range of uses plastic can.

Zenji Hiroi, Professor, Institute for Solid State Physics, University of Tokyo

Hiroi added, “However, we’ve found a way to give paper some of the nice properties of plastic, but with none of the detriments. We call it Choetsu, a low-cost biodegradable coating that adds waterproofing and strength to simple paper.”

Choetsu is a combination of materials that, when smeared on paper, produces a strong and waterproof film when subjected to air and moisture. The coating includes safe and affordable chemicals, primarily methyltrimethoxysilane, a few isopropyl alcohols, and a small amount of tetraisopropyl titanate.

Paper structures, for instance, food containers, are sprayed with or dipped into this liquid mixture and are then dried at room temperature. As soon as it is dried, a thin layer of silica consisting of methyl—a type of alcohol—develops on the cellulose making up the paper, thereby offering strong and waterproof properties.

Moreover, reactions that occur during the coating procedure tend to automatically create a layer of titanium dioxide nanoparticles. These develop into a speck of dirt and a bacterial-repellent property called photocatalytic activity, safeguarding the coated item for a prolonged period.

All of the chemicals that have been involved in the coating collapse over time into water, carbon, and sand-like silicon.

The technical challenge is complete, and some applications could be realized soon, such as items for consuming, packaging or storing food. We now hope to use this approach on other kinds of materials as well.

Zenji Hiroi, Professor, Institute for Solid State Physics, University of Tokyo

Hiroi added, “The liquid composition can be tuned for other materials, and we can create a dirt- and mold-resistant coating that could form onto glass, ceramics, and even other plastics to extend their usefulness. Alongside researcher Yoko Iwamiya, who has been working in this field for some time now, and the rest of my team, I hope we can do something truly beneficial for the world.”

Journal Reference:

Iwamiya, Y., et al. (2022) Photocatalytic Silica–Resin Coating for Environmental Protection of Paper as a Plastic Substitute. Industrial & Engineering Chemistry Research. doi.org/10.1021/acs.iecr.2c00784.

Source: https://www.u-tokyo.ac.jp/en/

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