A team of engineers at Newcastle University has created a water-based adhesive that is capable of securely bonding materials and then separating them on demand using acidic or alkaline water.

This so-called reversible glue is expected to address challenges encountered in recycling and end-of-life disassembly, specifically where permanent adhesives prevent the separation of components.

The team built upon an earlier version of the adhesive that relied on electrically charged polymers to stabilize a water-based emulsion and encourage adhesion to different surfaces. In this first iteration, one surface was coated with a positively charged formulation and the other with a negatively charged one. When they were brought together, the opposite charges formed a bond. Yet, the team discovered that the joint would fail if immersed in either acidic or alkaline water. This approach required two separate formulations and was vulnerable to dripping when used on vertical surfaces.

As such, the researchers added clay particles into the latest iteration of the adhesive. While clays are typically used to increase viscosity and reduce dripping, in this case, the team explained that the clay enabled the adhesive to function without the need for two different coatings. Additionally, the bond could still be reversed by exposing the adhesive to acidic or alkaline water.

The team noted that the adhesive is created through processes similar to those used in paint manufacture and is derived from low-cost materials. Further, because it is a water-based product, it does not contain the volatile organic solvents commonly found in many commercial adhesives.

While the glue is intended for plastic substrates — such as polypropylene and polyethylene, which is commonly used in packaging — it can also reportedly bond to other materials.

The team suggests that glue could have possible applications in packaging, automotive component recycling and electronics, wherein controlled disassembly could assist in material recovery.

The adhesive is detailed in the article, One-pot polymer–clay composite reversible adhesive, which appears in the journal Soft Matter.