How a new epoxy could boot BPA from cans

A chemical of concern that first grabbed headlines in 2008 could finally be on its way out of metal food packaging.

The substance, bisphenol A, was once prevalent as a monomer used to make epoxy linings for food and beverage cans. Scientists and nongovernmental organizations raised the alarm that BPA’s ability to act as an artificial estrogen in the body could harm reproductive and developmental health. In response, many brands and retailers vowed to replace it.

Yet replacing BPA in food and beverage cans proved difficult because epoxy does its job unusually well. It prevents corrosion across all manner of foods and beverages, on both steel and aluminum, and regardless of processing method.

Food brands, coatings companies, and can manufacturers spent several years working to develop and deploy replacement linings for steel cans. Eventually they settled mainly on acrylic and polyester formulas. By early 2018, 90% of food-can production used the alternative materials, according to the Can Manufacturers Institute.

The beverage industry, which uses aluminum rather than steel, has not made equivalent progress removing BPA. But that could soon change, thanks to intense chemical sleuthing and material development work by scientists at the coatings company Valspar, which is now part of Sherwin-Williams.

Rather than look in the toolbox of epoxy alternatives for food and beverage cans, Valspar sought to develop a new epoxy without using monomers that affect the endocrine system. And it sought scientists who had raised the alarm about BPA’s potential to harm human health to weigh in on its lead candidate.

Now, after a decade of effort, Sherwin-Williams is commercializing a new can-lining epoxy, built from the ground up with a new monomer. The company says it is safe and performs just like those made with BPA.

The epoxy is already being used in beverage cans in California, where food and beverage cans with BPA-containing liners require a health warning under Proposition 65. As the company continues to scale up the new polymer, called valPure V70, it aims to expand its use in other states and into food cans as well.

In 2008, Valspar, like other coatings companies, was diligently searching for a replacement for BPA-based epoxies, recalls Tom Mallen, now director of global regulatory and strategic services at Sherwin-Williams. Valspar evaluated formulations made from materials already approved for food contact by US regulators. But none were epoxies, and none worked as well as the BPA-based epoxies that brands wanted to move away from.

So the company decided to devote time and resources to designing a new material. “We started blazing this new trail in chemistry to make epoxy without BPA,” Mallen says. “It was not a trivial challenge.”

Jeff Niederst, now Sherwin-Williams’s global marketing director for beverage coatings, led the charge. He understood that there were good reasons why, back in the 1950s, the packaging industry chose an epoxy resin rather than acrylics or polyesters. He felt those alternatives were still lacking compared with epoxy.

“My belief is we’d be offering up technology that has already proven to be less robust. This is not the type of industry that likes to see a reduction in performance or higher risk,” Niederst says. “But we saw, and still see, a lot of our competitors are trying to get new light through those old windows.”

Niederst made the case to his bosses that his team could achieve high performance without using BPA. The trick was to find a substance that would be a one-for-one swap for BPA but without the endocrine activity. The team looked at various members of the bisphenol family of monomers. They built a computer model to predict how each would fit into hormone receptors and if it would function in an epoxy.

First they dialed the number and length of side chains all the way up. That resulted in molecules that did not react with cells or receptors but were too clunky to perform in a polymer. But it turned out that a bisphenol with four short side chains was biologically inert while reactive enough to make a polymer and a coating.

The next challenge was to get enough of the monomer, tetramethyl bisphenol F (TMBPF), to scale up the new polymer. They called all the usual chemical companies, without success. Eventually they found a company in India that was making the molecule in a commercial process. Niederst and his colleagues visited the firm, Deepak Chemicals, which quickly got on board. It has since scaled up production of TMBPF and continues to be a supplier to Sherwin-Williams.

Deepak got an early assignment to provide TMBPF for assays to measure endocrine activity. Valspar provided unrestricted research funds and substances extracted from cans coated with the new epoxy for outside researchers to test. The outside scientists, in turn, suggested tests that went beyond those required by regulatory agencies.

Ana M. Soto, a professor of immunology at Tufts University School of Medicine, studies sex steroids, endocrine disruption, and fetal origins of adult disease. She and her collaborators tested TMBPF using in vitro and in vivo assays. The team also tested migration products of the polymeric coating by using a bioassay of estrogen-sensitive human breast cancer cells (Environ. Sci. Technol. 2017, DOI: 10.1021/acs.est.6b04704).

Soto’s research showed that the Valspar epoxy differed from BPA-based epoxies in two important ways. One is that the TMBPF monomer did not show estrogen activity in assays or in rat studies. The other is that tests of the epoxy polymer showed that migration of the monomer, such as into food, was below the detection limit of 0.2 ppb. In the paper, Soto’s team concluded that there is “compelling evidence” of an absence of endocrine activity and negligible human exposure.

Soto’s team performed the follow-through necessary to confirm that a chemical does not activate endocrine receptors, Soto tells C&EN. “A simple assay can tell you if something is an estrogen or partial estrogen agonist. But to prove that it is not, you have to do more work.”

Sherwin-Williams calls the method it used to select its materials “safety by design.” Soto says she is pleased with the company’s approach to developing the epoxy. “Starting with a monomer that is not estrogenic and is in a polymer that doesn’t break down into estrogenic compounds—but is very similar to the regular epoxy—I think that is very clever,” she says. “I also like the idea they are going beyond what is normally done for testing.”

With research results in hand, Valspar connected with advocacy groups. One of those groups was Safer Chemicals, Healthy Families. “We’ve had a lot of interest in BPA over the years,” says Mike Schade, director of the organization’s Mind the Store campaign. “We coauthored a bunch of reports and publicly campaigned for leading grocery chains and food firms to eliminate or reduce BPA in canned foods.”

Other coatings manufacturers did not reach out to his organization the way Valspar did, Schade says. Valspar “developed a pretty exhaustive approach to develop the material and evaluate its safety.”

Sherwin-Williams is now applying for approval under the European Union’s chemical regulations and continues to test V70 for developmental end points in animals, which requires examining multiple generations.

It will take some time to find out how far V70 will go in the food-and-beverage-packaging world, cautions Tom Van Kuren, a packaging coatings consultant at Vantek Surface Solutions. Valspar’s approach lowers the risk to customers that want to avoid introducing a new chemical with unknown human health risks, he says, but it can still take years of formula and cost optimization to gain market share.

“Can manufacturers want the same speed of application, cure rate, output, and performance in the packaging,” Van Kuren says. “Those challenges are not simple.”

Sherwin-Williams’s Mallen says beverage-can manufacturers want to continue to use an epoxy because it’s what their manufacturing lines were designed to use. To date, he says, V70 has been applied to 15 billion beverage cans in California.

Coca-Cola’s website tells consumers that it uses BPA-based coatings in its beverage cans and that US Food and Drug Administration reviews show the coatings are safe. However, a federal indictment in a trade-secret theft case last month revealed that Coca-Cola has been working hard to find replacements for the coatings. The beverage company had a confidential R&D pact with six materials firms that collectively spent an estimated $106 million on the effort by the summer of 2017.

The canned-food industry, meanwhile, is confident in the solutions it has in hand, emphasizes Sherrie Rosenblatt, vice president for communications at the Can Manufacturers Institute. But she also says a material’s effectiveness on multiple food types is an important performance requirement. For now, different linings are needed for different types of foods, such as peaches, peas, and tomatoes. In contrast, Sherwin-Williams says its epoxy is as versatile as older, BPA-based epoxies.

Even if the Sherwin-Williams epoxy doesn’t take the packaging world by storm, advocates and health scientists would like to see the company’s approach to finding and selecting biologically benign materials catch on. The recent finding that some paper takeout containers are coated with per- and polyfluoroalkyl substances (PFAS) shows that prioritizing human health when choosing food-contact materials is still not routine, they say.

PFAS are in some ways “becoming the new BPA,” Schade says. As they seek reform in how chemicals used in food packaging are regulated, Safer Chemicals, Healthy Families and others will keep up the public pressure on food manufacturers and retailers, he says. “In many respects, we have transformed the food-packaging industry away from BPA,” Schade says. “It is a success story.”