Chemists at the University of Reading in the UK, in collaboration with Domino Printing Sciences, have developed a new polyurethane adhesive that cleanly removes labels. This adhesive helps produce higher-quality recycled plastic. Adhesives used to attach labels to plastic bottles often leave residue, limiting recycling options. This new polymer adhesive breaks down when treated with an alkali. While labels may stick to the bottle during normal use, they are easily removed along with the adhesive during recycling. This polyurethane adhesive contains sulfonyl ethyl carbamate as a chain extender, which is said to act as a chemical switch when exposed to certain substances, including alkalis. In tests, treatment of this polyurethane adhesive with a tetrabutylammonium fluoride solution triggered the decomposition of the chain extender, causing it to lose two-thirds of its adhesion on a range of different surfaces. Tests showed that this new polyurethane adhesive maintains sufficient strength on glass and aluminum surfaces at various temperatures, making it suitable for a variety of applications, including food containers, transport packaging, and electronics. By making it easier to separate different materials during recycling, the quality of recycled materials can be significantly improved. This can reduce the amount of waste that ends up in landfills.
