Cellulose is oxidized by the TEMPO oxidation reaction to introduce carboxyl groups in its crystal. Then, amines with long alkyl chains (C12 to C18: octadecyl, oleyl, dodecyl, and so on) are immobilized with the carboxyl groups by the amidation reaction. The modified cellulose can be microfibrilized and dried to films. When the ratio of amine per carboxyl groups is in the range of 20-90 %, the film exhibits the oil-repellency. The obtained oil-repellent film possesses sufficient optical transparency and mechanical strength for anti-fingerprint coatings and self-standing films.

This technology realizes oil-repellant films with biodegradable and eco-friendly materials.
Conventionally, oil-repellency is hardly attained without fluoride compounds, and therefore, films for oil-repellency and anti-fingerprint coating have used fluoride compounds, typically perfluorides. However, the perfluorides are expensive and non-biodegradable. The known-technology uses short-chain fluoride compounds to avoid the issues. In contrast, we develop oil-repellent films made of cellulose nanofiber hydrophobized with long alkyl chains, which can be cheap and biodegradable. Our materials possess sufficient mechanical strength and transparency, which allow anti-fingerprint applications as both of the self-standing and the coating layer on various substrates.

The preparation of TEMPO-oxidized cellulose nanofiber is known technology, and its modification using alkyl amines via amidation reactions is also achievable as an ordinary chemical reaction. The cellulose is originated from the pulp, and the amines are available as common chemicals on market. Therefore, the production of our film is easy and low cost. Since the material doesn’t contain the fluoride compounds, high biodegradability is anticipated.
Our film is high transparent and applicable to the optical devices such as mobile phone. Since the film is colorless, the film doesn’t disturb designs under the coat. The film is mechanically strong, and its oil-repellency is from the material itself. Therefore, the film is scratch resistance and can also be used as the self-standing film.