May 8, 2024

Jessica A. Dennehy

10th Grade

Williamsville East High School

In a constantly changing world, where certainty (not to be confused with stability) appears forever out of reach, the adhesive and sealant industry has evolved beyond its traditional boundaries. After sufficiently covering the bases of traditional heavy-duty adhesives and sealants that deal with even the toughest leaks, the industry has shifted its trajectory to prioritizing flexibility over rigidness. A team of expert engineers at England’s Newcastle University has invented a glue engineered to be reversible, making an adhesive as adaptable as the world around it. A water-based emulsion, this modern adhesive uses electrically charged polymers to both maintain stability and adhere to multiple, different surfaces. The emulsion will charge one surface positively and the other negatively, and when the two interact, the resulting reaction will force them to stick together. This electrostatic interaction will immediately fail and become non-sticky when immersed in a solution that is either strongly acidic or strongly alkaline. While seemingly counterintuitive at first glance, this transformative property opens doors to a realm of possibilities previously deemed unattainable or irrelevant.

This innovative sealant is manufactured using the same industrial process as paint. The copolymers that make up the sealant are composed of commercially accessible and affordable materials, like styrene and butyl acrylate. Due to its water-based formulation, many unstable solvents used in other commercial glues are not present. Furthermore, its polymer composition ensures resistance to degradation from humid environments. The Newcastle engineers have determined that their invention is not only inherently stable but that its shelf life at room temperature is at least a year. The dual-charged sides of the adhesive consist of copolymers containing styrene and butyl acrylate but differ in that one side will be a polycation (positively charged) while the other side will be a polyanion (negatively charged). For the polyanion portion, materials such as lauryl sulfate and polymerized acrylic acid were used, while chitosan contributes to the formation of the opposite polycation part. These electrostatic interactions are the reason why the reaction that stimulates adhesions and “stickiness” fails when bathed in highly basic or acidic solutions. The detachment of the two portions occurs only when the polyelectrolytes present exhibit distinctly different charged states.

The invention of the pH-sensitive electrostatic glue is seen as a middle ground between structural adhesives and pressure-sensitive adhesives. Structural adhesives, typically of a dual composition, adhere to surfaces due to chemical bonds formed during a reaction, resulting in a permanent seal. Pressure-sensitive adhesives, in contrast, can be manually removed like ripping off a bandage. The way this new adhesive combines the characteristics of both categories is like this: a chemical reaction based on opposing electrostatic charges promotes stickiness through structural bonding, yet these bonds can easily be neutralized and dissolved, over and over again. The Newcastle team has also repeatedly emphasized a particular property of their adhesive: the high capability of this glue to stick to water-repellent surfaces like polypropylene and polyethylene, an achievement not boasted by many other water-based adhesives.

Dr. Adriana Sierra-Romero, Research Associate at the School of Engineering and a team member of this project, comments on the fact that many labels of plastic recyclables are tossed into landfills because their adhesives are irritating to remove. In collaboration with Biffa, a waste management company, the team has determined that “a propylene label stuck to a PET bottle can be removed by the wash water in their recycling plant”. The team confidently believes that this glue heralds a better way to recycle, and further benefit the environment, the engineering team has already proposed the integration of a material from soybean oil into the base polymers that make up the adhesive. Dr. Sierra-Romero adds, “There will be many other industries where our glue can be used, and we look forward to working with other companies”. Other industries include but are not limited to the other forms of packaging and the recycling of automotive parts and electrical components.

The introduction of electrostatic reversible glue represents a pivotal moment in the adhesive and sealant industry, reflecting the field’s shift in values and priorities. With its reversibility, environmental sustainability, and versatility in adhering to diverse surfaces, the Newcastle glue opens up new possibilities that traditional static superglues sealed up. This technological invention embodies the human capability to adapt, change, and improve. With the continued funding of this project from the Engineering and Physical Sciences Research Council (EPSRC), ongoing research promises to unveil new applications and adaptations of this groundbreaking sealant, not only reshaping the idea of how we seal and stick objects together but also how we approach and navigate the modern issues of an ever-changing world.