Upcycled adhesive is one of the toughest materials ever reported
By carefully tinkering with the chemical structure of a common household plastic, scientists have managed to upcycle it into a reusable adhesive with unique and hugely promising properties. A small patch of the substance can be used to hold around 300 lb (136 kg) in the air, with the researchers claiming it is one of the toughest materials known to science.
The strong new adhesive is the handiwork of scientists at the US Department of Energy’s Oak Ridge National Laboratory (ORNL), who used polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene, or SEBS, as their starting point. This rubbery polymer can be found in toothbrushes, handlebar grips and diapers, and the researchers were able to equip it with powerful new capabilities by making tweaks to its chemical structure.
This was achieved through a process known as dynamic crosslinking, which enables the bridging of typically incompatible materials. The scientists used the technique to couple silica nanoparticles and the polymer with the help of compounds called boronic esters, resulting in a novel crosslinked composite material they've called SiNP. The boronic esters are key to the reusability of the adhesive, as they enable the crosslinked bonds to be formed and broken repeatedly.
“A fundamental discovery was that the boronic esters on SEBS can rearrange bonds with hydroxyl groups – oxygen and hydrogen – on SiNP to adapt properties for demanding jobs," said lead author Md Anisur Rahman. "We also found the formation of similar reversible boronic ester bonds with a variety of surfaces that have the hydroxyl groups."
These crosslinked bonds actually shift inside the novel material, which enables it to adhere to surfaces strongly enough for a square centimeter of it to hold up roughly 300 lb. The researchers also conducted toughness tests in which they tried to detach materials through force, with the material's performance off the charts and surpassing all the commercially available adhesives they tested in the study. The combination of strength and ductility makes it one of the toughest materials ever reported, according to the scientists.
“Strong, tough adhesives are difficult to design because they need to incorporate hard and soft features that are not typically compatible,” said ORNL scientist and corresponding author Tomonori Saito. “The challenge has been to add the toughness you get in flexible materials without sacrificing strength. Our approach uses dynamic chemical bonds to develop a novel adhesive with remarkable properties not seen in current materials."
The adhesive also happens to be recyclable and maintains its performance at temperatures of up to 400 °F (204 °C), making it suitable for high-temperature applications. The scientists imagine it finding use in aerospace, automotive and construction, and are now working to both commercialize and improve the technology.
“There are benefits to industry and the environment to save resources and reduce waste," said Saito. "By design, this adhesive allows you to make repairs or correct costly mistakes and can be reprocessed for new uses in very challenging applications."
The research was published in the journal Science Advances.
Source: Oak Ridge National Laboratory