At a glance
Companies: Corning and PPG Industries
Challenge: Creating attractive, permanently antimicrobial surfaces
Response: Latex paint incorporating copper ions in a glass-ceramic matrix
Status: Awaiting Environmental Protection Agency approval
COVID-19 infection and hospitalization rates in the US shot back up in early November, closing bars, preschools, and other public amenities across the country. Public health officials are reemphasizing the cornerstone roles that handwashing, masks, and social distancing have in combating the pandemic.
At the same time, the home-care industry has been hard at work bringing new and existing cleaning products to the fight. The US Environmental Protection Agency’s List N, which contains all the products the agency permits to claim the ability to kill SARS-CoV-2 on surfaces, has grown from 200 entries in March to 508 in mid-November.
The EPA recently emphasized the need to supplement those efforts with surfaces and surface treatments that provide long-lasting activity against viruses and other microbes. In October, the agency issued guidance on how companies can prove a product’s efficacy against SARS-CoV-2 before making such claims, a move EPA administrator Andrew Wheeler says in a news release would provide “an expedited path for our nation’s manufacturers and innovators to get cutting-edge, long-lasting disinfecting products into the marketplace as safely and quickly as possible.”
Elemental copper provides permanent antimicrobial activity, but large surfaces clad in copper are expensive and not the right look for most places. To bring the disinfecting power of copper to a broader range of walls, handrails, and other surfaces around the home and workplace, Corning developed a copper-containing biphasic glass-ceramic material it calls Guardiant and worked with PPG Industries to incorporate it into a line of latex paints called Copper Armor.
“The overall idea here was to create a material that maintains the antimicrobial potency of copper while getting rid of its metallic character and metallic look so that it could be incorporated into a wide variety of materials and surfaces,” says Joydeep Lahiri, vice president of Corning’s specialty surfaces division. Though the pure Guardiant material is a pale blue-green powder, PPG was able to flex its formulation experience to make the paint in all the normal shades and sheens.
Cu+1 is the active antimicrobial form of the element. The challenge that Corning’s technology solved, Lahiri says, was keeping the copper in that oxidation state while also letting it get to the microbes. In April 2019, the firms published a paper in Nature Communications on their innovation, which they describe as an “alkali copper aluminoborophosphosilicate glass ceramic material that acts as a sustainable delivery system for Cu+1 ions” (DOI: 10.1038/s41467-019-09946-9).
As the publication date testifies, the firms were working together on the technology before the pandemic hit. But the novel coronavirus accelerated the formulation and commercialization work, says Eric Stevenson, director of product management for architectural coatings at PPG. “The COVID pandemic has heightened everyone’s awareness of viruses and bacteria and how quickly they spread,” he says.
The R&D team found literature describing the use of glass to keep copper in the +1 state, Lahiri explains. But in the team’s tests, paint incorporating a copper-glass phase wasn’t effective against pathogens, probably because the copper couldn’t escape the glass to do any microbe killing. Replacing some of the aluminum oxide in the glass with boron, phosphorus, and potassium oxides created a second phase in the material that is more water labile. Paint made with the biphasic ceramic-glass copper material reduced counts of SARS-CoV-2 as well as Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella aerogenes, and Escherichia coli on the surface by more than 99.9%, matching an efficacy previously achieved by metallic copper using EPA test standards.
In fact, Lahiri says, the firms went beyond the industry standard tests, which analyze the kill rate under warm, wet conditions. The paint also got a kill rate of 99.9% while dry at room temperature, much more like what it would see in a real-world setting.
Though it may seem like the water-labile phase would wash away during cleaning before long, Stevenson says PPG’s wear-simulation tests suggest that the antimicrobial action will stand up to more than 5 years of scrubbing and still meet that 99.9% kill standard. The firms are awaiting EPA approval and expect the paint to hit the market in the next few months.
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