Chemists at the University of Reading, UK, working with Domino Printing Sciences, have developed a new polyurethane adhesive that allows for clean label removal. The adhesive could help produce better quality recycled plastics.

Adhesives used to attach labels to plastic bottles often leave a residue, limiting recycling options for the bottles. The new polymer adhesive breaks down when treated with alkali. While the labels remain attached to the bottles during normal use, they are easily removed along with the adhesive during recycling.

The polyurethane adhesive contains sulfonylethylcarbamate as a chain extender, which is said to act as a chemical switch when exposed to certain substances, including alkali. In tests, treating the polyurethane adhesive with a solution of tetrabutylammonium fluoride triggered the decomposition of the chain extender, causing it to lose two-thirds of its adhesion on a range of different surfaces.

The new polyurethane adhesive was tested to be strong enough on both glass and aluminum surfaces at different temperatures, making it suitable for a variety of uses, including food containers, transport packaging, and electronic appliances.

By making it easier to separate different materials during the recycling process, the quality of recycled materials can be significantly improved. This can reduce the amount of waste that ends up in landfill.