The reversible glue, developed by experts from Newcastle University’s School of Engineering, is a water-based emulsion – similar to a paint – that bonds materials together, but can be separated on-demand by acidic or alkaline water.
Two years ago, the team introduced the first version of a glue which uses inexpensive polymers containing electrical charges to both keep the emulsion stable and to stick to different surfaces. When a surface coated with a positively charged emulsion is joined to a surface coated with a negatively charged one, the two components stick together. However, if the bond is immersed in water that is either acidic or alkaline, the adhesive bond fails. This opens up possibilities for recycling, because it allows the separation on demand of components that have reached the end of their useful life. This technology required two formulations: one for each surface to be coated. It also had a tendency to drip on vertical surfaces.
In this latest version, the team added clays to the formulations. While clays are commonly used as thickening agents to inhibit dripping, their addition also had the remarkable effect of enabling debonding without the need for two separate formulations. This “one-pot” reversible glue is a game changer because of how it simplifies the recycling workflow.
Offering sustainable solutions
First author of the paper, Dr Adriana Sierra-Romero, Research Associate at the School of Engineering, said: “Reversible adhesives are starting to attract attention in industry. They’re not yet mainstream, but we expect adoption to grow as companies look for more sustainable solutions.”
The glue is based on current industrial manufacturing processes – those for making a paint – and is developed from cheap materials so it can be scaled up easily. Because it is water-based it does not have the volatile organic solvents used in many commercial glues, but unlike other water-based adhesives, exposure to humid environments does not cause bond failure. The team has shown that its shelf life at room temperature is at least a year, so it is also inherently stable. It is as strong as other water-based adhesives (so called white-glues), but crucially it works on a wider variety of surfaces.
