A biodegradable glue derived from soya bean oil forms high-strength bonds that later dissolve, offering hope for more sustainable commercial products, packaging and sticky labels.
The new adhesive can hold most materials together just as well as standard epoxies, which are plastics based on fossil fuels and take thousands of years to biodegrade. Replacing current epoxies with the soya alternative could prevent tonnes of microplastics being added into the oceans and landfills every year and potentially even cut glue-related carbon emissions fivefold, says Jonathan Wilker at Purdue University in Indiana.
“All these products that are held together with adhesive – electronics and shoes and furniture and walls and cars and books, and these cardboard boxes in my office with shipping labels on them – most of them never get recycled, because you just can’t get that stuff off,” he says.
Wilker and his colleagues were inspired by previous research on the natural adhesives mussels use to bond to rocks. They discovered that they could add specific acids to soya bean oil to mimic the sticky chemical properties in the mussel adhesive.
The team tested its soya-based adhesive with metal, wood and synthetic surfaces, finding that it generally created bonds of equivalent strength compared with petroleum epoxies. The soya glue was even about 30 per cent stronger than superglue for holding together polished aluminium. While heating at 180°C provided the greatest strength, 5 minutes of heating with a commercial hairdryer made a strong enough bond for many industrial applications.
After one week underwater, the bonds still maintained up to 78 per cent of their original strength. By varying the temperature and duration of heating, the adhesive’s strength and biodegradation timing can be tailored for different applications – such as glue that lasts a week for labels or years for telephones, says Wilker.
Petroleum epoxy manufacture generates about 5.8 tonnes of carbon dioxide for each tonne of product. While the calculations are complex and inexact, it is possible that net CO2 emissions would be negative for the new glue, since soya plants absorb carbon dioxide, says Wilker. Current manufacturing price estimates suggest that the soya glue would cost about 30 per cent more to manufacture than standard epoxy does – meaning it could still be reasonably affordable.
Even so, the soya adhesive might not be sufficient for glueing together automotive and aerospace structures, says Wilker. “If you’re trying to make a plane or a car, you never want it to come apart.”