Researchers from the University of Tokyo developed a biodegradable and low-cost coating to make paper waterproof.

Called Choetsu, the coating consists of a combination of materials that, when applied to paper, spontaneously generate a strong and waterproof film when it makes contact with moisture in the air. The coating consists of safe and low-cost chemicals, mostly methyltrimethoxysilane, some isopropyl alcohol, and a small amount of tetraisopropyl titanate. Paper structures, for example food containers, are sprayed with or dipped into this liquid mixture and are dried at room temperature. Once dry, a thin layer of silica containing methyl, a type of alcohol, forms on the cellulose making up the paper, providing the strong and waterproof properties.

In addition, reactions that take place during the coating procedure also create a layer of titanium dioxide nanoparticles, which have a dirt- and bacterial-repellent property. This is known as photocatalytic activity, which protects the coated item for an extended period of time. All of the chemicals in the coating break down over time into harmless things such as carbon, water and sand-like silicon.

The aim of the research is to decrease our dependence on fossil fuel-based plastics.