Glass package transparency is key to ensuring proper sortation in a MRF, according to a recent study from glass recycling and packaging stakeholders. | Pornpawit/Shutterstock
A major recycled glass processor teamed up with a cosmetics giant to identify how cosmetics packaging is sorted in MRFs and which attributes are impeding greater recycling. Their findings offer suggestions for material design.
Strategic Materials and Estée Lauder partnered on the four-year study, carried out from 2020 to 2024, with the aim of providing greater nuance to the question of what makes a glass package more recyclable.
“While most North America public information and instructions for recycling have suggested that glass, if amber, green or clear, could be recyclable, this tends to be more complex in the luxury cosmetics industry,” the companies wrote. In cosmetics, they added, “multiple decorations, colors and formats are used to achieve a unique packaging aesthetic, that at times, inadvertently inhibits recyclability.”
The study focused solely on residential curbside recycling of cosmetics packaging made from soda lime glass, the type used in all beverage containers recyclable in curbside programs. It looked at more than 250 samples of glass packages, ranging from white to black and with various design finish features like matte, gloss, metallic and pearlescent. Such packaging types are common in the cosmetic packages used by Estée Lauder brands, which include Aveda, Clinique, Tom Ford, the namesake Estée Lauder and many more.
The project put a handful of pieces of broken glass about an inch in size from each package through an optical sorting system at a Strategic facility and recorded the results. It also featured tests in a lab setting.
The study found glass opacity is a major design feature affecting recyclability. In tests on glass with less than 1% light transmission — very opaque — about two-thirds of the samples were sorted as ceramic, stone or porcelain contaminants, and only one-third correctly identified as glass. At 2% light transmission, 82% of the samples were identified as glass. At 3% and above, 100% of samples were properly sorted as glass.
With that in mind, the study advised that packaging be designed with light transmission of 5% or higher to ensure maximum likelihood of proper sorting.
Virtually all of the design best practices go back to ensuring that level of transparency in the glass material. Glass of all colors and thicknesses is technically not problematic in the recycling process, but it can create challenges when those attributes prevent proper optical identification by making the glass too opaque.
For example: “Amber glass containers with a thick bottom or walls make it difficult for light to penetrate during the color sorting process,” the study found. “As a result, the optical sorting machines mistake the thick amber glass for non-glass material and reject the material from the recycling process.”
The study advised designers to limit use of metallized coatings that, although they may not impede sortability, are a chemical contaminant that the glass processor will have to deal with. End market specifications only allow limited amounts of such contaminants, so the processor has to blend glass with those coatings with non-coated glass.
Besides prioritizing package opacity in design, Strategic and Estée Lauder advised packaging designers to conduct sortability tests, similar to those in their joint study, when using features like textured glass and various types of coatings. They also advised designers to gauge light transmission using proper equipment, and ideally to do those tests at a recycling facility.