Dollar bills gradually get dirtier, eventually falling onto sidewalks and streets, then getting shredder-ready. In a journal Industrial & Engineering Chemistry Research, scientists from Brown University and Spectra Systems Corporation reported that a new method of laundering paper money can save billions and reduce the impact on the environment when it comes to disposing banknotes. Andrei Smuk, Nabil M. Lawrenceandy discuss how the problem of replacing currency with newer ones is becoming more serious. Central banks will replace banknotes that have become too rusty with newer bills if they find them to be of sufficient value. Treasuries around the world print approximately 150 trillion new bills each year at a cost close to $10 million. Additionally, they dispose of about 150,000 tonnes of dirty and old banknotes. Banknotes’ lifespan is reduced by human sebum. This oily and waxy substance found on the skin of humans, reduces banknote longevity. Accumulated sebum can also cause acne in adolescence or early adulthood. Sebum can build up over the banknotes’ lifetime, depending on their denomination. It reacts with oxygen and eventually turns yellowish. Lawandy and his colleagues tried to wash out the excess sebum from banknotes to prolong their life expectancy. The banknotes get yellowish because of the reaction between human sebum and oxygen. SCCO uses “supercritical” CO2 to clean paper money. This gas acts as both a gas, and a liquid. It is widely used in many cleaning methods. Researchers found that SCCO2 was able to remove oxidized motor oil and sebum from banknotes. It also destroyed common bacteria colonies. This allows for the preservation of their security features, such as holograms, inks and other markings. The journal abstract states that the researchers measured note soiling distributions using a banknote sorting device running at 10 notes per second. This supported the assertion that SCCO2-cleaned notes will result in substantially fewer notes being classified unfit for use due to soiling or shredded.
