Lignin is a natural broad-spectrum sun blocker due to its UV-absorbing functional groups, e.g., phenol units. UV absorbers can protect materials such as paints and plastic from sun damage.

Richard Venditti, North Carolina State University, Raleigh, USA, and colleagues have developed sustainable, biodegradable, and transparent cellulose-lignin films that absorb UV radiation. The team functionalized cellulose with azide groups and lignin with propargyl groups and used a copper-catalyzed click reaction to form covalent bonds between them. They added between 0.5 wt% and 2 wt% lignin to the cellulose. The team cast the solution of the bonded product onto glass plates to produce the cellulose-lignin films.

The films are transparent in the visible region of the spectrum, are flexible, and remain stable up to temperatures of 120 °C. They are prepared from renewable resources and have good UV protection properties. The material with 2 wt% lignin blocks 100 % of UV-B rays and over 90 % of UV-A rays.

• Cellulose-Lignin Biodegradable and Flexible UV Protection Film,
  Hasan Sadeghifar, Richard Venditti, Jesse Jur, Russell E. Gorga, Joel J. Pawlak,
  ACS Sustainable Chem. Eng. 2016.
  DOI: 10.1021/acssuschemeng.6b02003