Degradable coatings for food packaging block made of compostable grease and oil paper
EMBARGOED FOR RELEASE: Thursday, August 26, 2021, 5 a.m. EST
Note to Editors: Please note that this research will be presented at a meeting of the American Chemical Society.
Newswise – ATLANTA, August 26, 2021 – Paper cups, cartons and food packaging may appear to be biodegradable, but many contain a plastic coating that cannot be composted. While durable, plastic-free paper products are available, they often allow grease and oil to pass through, weakening the paper and creating a mess. Today, scientists report that they have developed a degradable polymer coating that can block this infiltration and could lead to new biodegradable paper-based materials.
The researchers will present their findings at the American Chemical Society (ACS) fall meeting. ACS Fall 2021 is a hybrid meeting that will be held virtually and in person from August 22-26, and on-demand content will be available from August 30 to September. 30. The meeting includes over 7,000 presentations on a wide range of scientific topics.
“Consumers are pushing for more sustainable products,” says Matthew Carter, Ph.D., principal investigator of the project. “But making a fully degradable paper product for single-use applications – like the sandwich wrappers, bowls, and trays you get in a cafeteria – is a big challenge,” adds Carter, who presents the work at the time. meeting.
Current oil and grease resistant coatings for disposable paper products often include fluorocarbons or polyolefins, but these polymers are persistent in the environment and cannot be composted. “One of the things that makes conventional polymers useful is their durability,” says fellow senior researcher Andrew Hejl, Ph.D., who works with Carter at Dow. This toughness, which comes from the stable carbon-to-carbon bonds that form during polymerization, is desirable, for example, in a household latex paint that must last for years but problematic in a paper bowl intended for composting.
One way to make polymers less durable is to insert degradable bonds to disrupt their carbon-carbon backbones, Carter explains. To do this, the researchers turned to a radical polymerization technique that had been around for years but had not been widely adopted. Noting a recent resurgence of interest in universities in using this technique with cyclic ketene and vinyl acetal monomers, the Dow team began to explore how to translate this chemistry in an industrial environment. In academia, the reaction was typically carried out in organic solvents, but Dow wanted to switch to water as a “greener” substitute. This was difficult because cyclic ketene acetal monomers are unstable in water, but the researchers solved this problem by adjusting the reaction conditions, including pH, temperature, and monomer concentration.
Their reaction mixed 2-methylene-1,3-dioxepane cyclic ketene acetal and vinyl acetate to form a polymer with ester linkages in the backbone. The team then coated the paper with a water-based emulsion of this polymer – a synthetic “latex” unrelated to natural latex rubber, and therefore unlikely to trigger an allergic reaction – and left it. to dry. They recently reported that the coating was an effective barrier against oil and grease and that its ester bonds could break down in water, quite slowly at neutral pH but faster at higher pH under laboratory conditions. Today, researchers are starting to assess the degradability of the coating under relevant industrial conditions. So far, they have shown that microorganisms used in industrial composters can help biodegrade the polymer in simulated wastewater. “The concept is to have a long polymer that breaks down into smaller pieces that will eventually be broken down by the microbes into CO2“, says Hejl.
Other researchers and companies have developed biodegradable restoration products with coatings based on natural materials such as whey or chitosan. “These are great options, but they have limits in terms of getting the performance you want at an appropriate price,” Hejl said. And some coatings have to be applied as a very dilute solution, so a lot of water has to be evaporated to dry them, he adds. “So there are a lot of potential materials, and I don’t think anything has ticked all the boxes yet. But researchers at Dow believe their coating may well fill the bill.
“More broadly, if you look at the concept of disrupting a stable carbon-carbon backbone with degradable bonds, it really opens up a lot of opportunities beyond just paper coatings,” Carter said. “Other applications include personal care or home care formulations, such as shampoo and wax. Many of these materials currently contain synthetic carbon-carbon bond polymers. This approach could therefore be a powerful way to introduce degradability into new classes of materials in the future. “
Researchers acknowledge the support and funding of Dow.
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Note to Editors: Please note that this research was presented at a meeting of the American Chemical Society.
Degradable backbone vinyl acetate emulsion polymers: coatings for single-use paper products
Research in our laboratories has largely focused on the development of sustainable paper coatings for the catering industry. Paper trays, bowls, and wrappers are often coated with synthetic polymers to improve oil and grease resistance, but these films are generally non-degradable and environmentally friendly. Here we report an approach to water-based and degradable latex polymers based on the emulsion polymerization of vinyl acetate (VA) with cyclic ketene acetal 2-methylene-1,3-dioxepane (MDO). . These latex-based polymer particles and films are degradable by hydrolysis due to the presence of MDO-based backbone ester groups. Controlling the conditions during processing is essential: a slightly basic pH and low temperature favor ring-opening copolymerization of MDO, but when the pH is too acidic or the temperature too high, MDO is lost by hydrolysis. When coated onto commercial paper, VA-MDO films exhibit excellent resistance to oils and greases compared to non-degradable, only VA compositions. This new class of polymer latex is therefore well suited to the design of new generation biodegradable and compostable single-use restoration products, as well as other applications where erosion or degradation of films and coatings is required.