Reading, UK – Chemists at the University of Reading, in collaboration with Domino Printing Sciences, have developed a novel PU-based adhesive that would allow labels to be removed cleanly. This could give better-quality recycled plastic.
The adhesive used to stick labels onto plastic bottles often leaves a residue behind that limits the recycling options for the bottles. The new polymer adhesive breaks down when treated with alkali. While labels would stay affixed to the bottles during normal use, they could be readily removed in the recycling process, along with the adhesive.
The polyurethane in the adhesive contains sulfonyl ethyl urethane units as chain extenders, which they say act as a chemical switch when exposed to some substances, including alkali. In tests, treating the PU adhesive with a solution of tetra-butylammonium fluoride triggered the degradation of the chain extenders, causing it to lose two-thirds of its sticking power across a range of different surfaces.
By making it easier to separate different materials during recycling, they said, the quality of recycled materials could significantly improve. This could reduce the amount of waste that ends up in landfill.
The work has been published in the journal Macromolecules.
