Kemira is dedicated to pioneering renewable alternatives to conventional plastic-based coatings and films prevalent in today’s paper and board packaging. Through our partnership with Danimer Scientific, we’ve harnessed the potential of renewable PHA (polyhydroxyalkanoate) in aqueous dispersion barrier coatings for paper and board packaging. Here are the 5 key benefits that make PHA coatings an ideal option for the packaging value chain seeking more sustainable solutions.
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One of the greatest benefits of PHA is its ability to biodegrade in any environment without leaving a harmful footprint. Unlike many conventional fossil-based plastics – or even novel bioplastics – commonly used in paper and board packaging to create needed barrier properties, PHA is certified to be, e.g., marine biodegradable and home compostable. Its biodegradability profile is comparable to that of cellulose, starch, and other natural polymers, making it an ideal choice for enhancing the functionality of renewable fiber-based packaging materials.
Promoting a circular economy is essential for sustainable packaging practices. Paper and board are inherently recyclable packaging materials, and thus the primary end-of-life option for them should be recycling, as it enables the recovery and reuse of the fiber raw material. PHA-coated paper and board can be integrated into existing recycling streams, facilitating the efficient recycling of coated packaging materials. In the repulping process, where paper is broken down into a pulp slurry for recycled paper production, PHA coating does not hinder separation of the paper fibers, resulting in high fiber yield and efficient recovery, maximizing the lifecycle of fiber-based packaging materials.
PHA is derived from renewable resources such as vegetable oils, using advanced biotechnology. Being fully biobased, it provides a more sustainable alternative to traditional petroleum-based coatings like PE (polyethylene). PHA is also approved for use in food contact applications, making it a suitable alternative to harmful compounds such as PFAS (per- and polyfluoroalkyl substances) in barrier applications.
In food packaging, protecting products from external elements is crucial for maintaining freshness and extending shelf life. Especially with greasy products and liquids, it’s equally important to prevent deterioration from inside the packaging. PHA coatings exhibit excellent barrier properties against oil and grease, water and moisture. During development, different PHA formulations have been extensively tested, to optimize the performance and ensure applicability to different types of substrates.
Versatility is key in packaging applications. PHA can be applied to various substrates, including paper and board as well as flexible films, facilitating a variety of packaging formats. Additionally, PHA coatings provide good converting properties, such as cold welding and heat sealability, ensuring performance in different packaging applications such as cupstock or flexible packaging.
For paper, recycling has higher priority over composting in the Sustainability Pyramid and the Circular Economy. This is because it guarantees that paper’s valuable fibers will be reclaimed for reuse. However, even though paper fibers can be recycled many times (up to 25 times, depending on the type of fiber and end-use), fiber degradation is a concern, as fibers tend to become shorter and weaker after multiple rounds of recycling. Because of this, fibers are sorted before processing. Screened-out fiber or waste can be incinerated at end of life for energy recovery, e.g., combustion for steam and electrical energy production, with carbon neutral emissions.
Composting offers no reuse of valuable fibers and no recovery of energy. It is "cold incineration" without utilizing or recovering the entrapped energy; it can also lead to the production of methane. Furthermore, there is no way for foreign substances to be screened out efficiently. Thus, materials such as metal, plastic, process chemicals, functional chemicals, and microplastics can be released into the environment if the compost is used as fertilizer or soil improver. Composting is only a viable alternative to recycling in cases when it is difficult to recycle, such as an item heavily contaminated with food. Composting should be viewed as an opportunity to divert food waste from landfills.
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Plastic film—like polyester, polypropylene, polyethylene, or others—when laminated to paper, creates many recycling issues for paper mills. The use of laminates is increasing, and mills are having a hard time processing the increased amount of film. Film decreases the capacity of a paper mill’s pulper because it takes more time for the paper to repulp due to the plastic film protecting the fibers from water. The strong plastic film will either be sorted out using a specific drum-shaped pulper and bypass systems, or beaten down into smaller flakes, which increases the energy needed to separate the fibers from the filmic flakes.
In any case, the higher the amount of plastic films in the recycling mix, the higher the amount of waste, the higher the cost for separation, and the higher the cost for disposal. A laminated paper-plastic film is also difficult to recycle as a plastic, as the paper fibers cause contamination and are difficult to extract from the film.
Water-dispersed emulsion polymer coatings—sometimes referred to as polymeric coatings—are often used as barrier/functional coatings on paper to replace plastic film and give paper specific functionality, such as grease resistance, water repellency, moisture vapor, aroma or oxygen barrier, and heat sealing. The polymer material forms a continuous thin film that can not function as a main structural component of the final article, as it does not have structural integrity on its own; nor does it add to the structural integrity of the final product.
These water-based barrier coatings behave similarly to traditional binders used in pigment-coated papers for decades. In repulping, the water-based barrier coating particles will either stick to the fibers or fillers, or follow these appropriate fiber/filler recycle streams:
The biological (aerobic or anaerobic) and/or physiochemical treatment transforms these particles into sludge. The sludge is either incinerated or sent to a landfill. Some mills pump the sludge back into the middle layers of their board.
Barrier coatings for heat seal at very low temperatures can be tacky and create agglomerates of tacky substances known as "stickies" in the web forming and drying stages when recycled. Controlling the formation of stickies can be managed by choosing the right barrier, using sticky control measures such as masking additives, and limiting the amount of barrier coated papers added to the recycled paper mix (or by separating it with deinking cells).
Many polymer barriers are hydrophobic and attract inks in the recycling process, resulting in dirt spots. Therefore, if deinking is not part of the recycling process, it is preferable to reuse barrier-coated papers for the production of grades where color consistency is not important.
When using the standard paper waste stream, functional water-based barrier coatings have the following advantages over paper-plastic film structures like PE, PP, and PET:
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