Let's say you buy a bag of coffee. The bag itself is thin and flexible, making it easy for shops to transport and store multiple bags before they get to your kitchen. With several layers of material holding it together, protecting the beans and blocking out moisture and oxygen, the bag keeps that delicious coffee fresh until it's ready for your morning cup.
Then there's that leafy green symbol on the package: the mark of a compostable product. That symbol means you can safely compost the packaging and it won't stick around for hundreds of years, polluting the earth and putting ecosystems at risk.
To earn compostability certification, all those protective layers need to degrade under specific conditions — including the adhesives that hold the materials together.
But compostable adhesives are difficult to formulate without the right polymers. BASF has water-based solutions that make matters easier for formulators — but first, here's a bit of background on compostability certifications for flexible packaging.
What is a compostable adhesive?
Like your bag of coffee, any flexible package is made of several layers, each one with a distinct purpose.
"In flexible packaging, the construction is a set of layers that determine the functional properties of the package," says Augusto Cucala, Market Segment Manager for Adhesives at BASF. "The adhesive holds the whole structure together. In order to make the whole package compostable, the adhesive must also be compostable."
Manufacturers gauge compostability with the help of legal standards in their part of the globe, including ASTM D6400 in the United States and EN-13432 and ISO 17088 in Europe. Third-party organizations — notably the Biodegradable Products Institute (BPI) in North America — test and verify products against those standards to ensure they are worthy of compostability certification.
In North America, if it's not certified by BPI, it's not compostable. To meet legal standards, a flexible packaging adhesive must live up to stringent scientific criteria.
"It is very difficult to formulate compostable adhesives," Cucala explains. "Put simply, you need an adhesive that, under specific temperature conditions, will be eaten by microorganisms and disappear."
The adhesive has a maximum of 90 days to decompose. In that time, at least 90 percent of the adhesive must convert into water vapor and carbon dioxide at a temperature between 50 and 60 degrees Centigrade.
The mechanism of conversion depends on microorganisms, Cucala says. "The adhesive basically feeds anaerobic microbes, and they will convert the material in to CO2 and water."
The remaining, unconverted 10 percent cannot have any negative effects on composting — that's another important aspect of the certification criteria.
"The compost generated by the packaging must allow plants to grow, so it cannot contain heavy metals or toxic content," says Cucala.
Meeting compostability certification standards
The first step in formulating a compostable adhesive for flexible packaging is finding products that help surmount all those common challenges.
Cucala says BASF's Epotal® ECO 3702 and Epotal® CF 430 are designed to make the process not only possible, but more user-friendly for formulators as well.
"Epotal is considered the first water-based compostable adhesive," he explains. "The 3702 is the base polymer. We developed the 430 to have a coater-ready material that is ready to be applied in the laminator's equipment."
Because these adhesives are water-based, it also helps formulators keep their VOC emissions to a minimum and brings safety to a maximum. Additionally, the Epotal products have a very good stability throughout the application process.
"Because it's so user friendly to work with, any laminator in the industry could eventually use the Epotal ECO 3702 or Epotal CF 430 for their compostable flexible packaging needs," Cucala says.
With a water-based solution helping them meet compostability standards, flexible packaging manufacturers can continue to improve the sustainability of their products.