A Light-Driven Process to Oxidize Plastic Surfaces for Industry Safely

Researchers at Osaka University have developed a light-driven process for oxidizing polypropylene (PP), a widely used plastic, without creating waste.

The process uses a reactive chlorine dioxide radical to make the plastic reactive. PP is normally an unreactive material; however, the researchers made a highly reactive radical by mixing sodium chlorite and hydrochloric acid. The radical was then photochemically activated using an LED lamp as the light source.

Surface oxygenation of side-chain methyl groups in polypropylene under photoirradiation with chlorine dioxide. Courtesy of Osaka University.

As a result of the process, while the bulk polymer remained intact, its surface showed a multitude of carboxylic acid groups that affected the chemical reactivity. For example, the colorless plastic could be stained with cationic dyes, such as rhodamine B or brilliant green. The originally water-repellent surface became more hydrophilic.

Spot staining after treatment with rhodamine as a red ink after site-selective photo-oxygenation. Spot emission under black-light irradiation. Courtesy of Osaka University.

Previous methods for oxidizing olefinic polymers such as PP were either poorly controlled or highly polluting, the researchers said. The new process could be the first clean and convenient solution to this problem, and could prove to be a valuable industrial tool in the customization of synthetic plastics.

Polypropylene films after water-soluble ink treatments without/with ClO₂photo-oxygenation. Courtesy of Osaka University.

The research was published in Chemical Communications (http://dx.doi.org/10.1039/c9cc01037h).