In today's world, imagining life without plastic is nearly impossible. From packaging to everyday items, plastics permeate our lives in myriad ways. However, the concern surrounding single-use plastics (SUP) has risen dramatically as their environmental impact becomes increasingly evident. As we grapple with pollution and the depletion of natural resources, it's crucial that we shift our focus towards sustainable alternatives.

One promising solution that deserves attention is barrier coating. This technology offers the potential to replace traditional SUP while maintaining the functionality and safety required in various applications.

Coatings are an indispensable component of modern packaging, serving multiple essential purposes, such as extending shelf life and enhancing visual appeal. They play a crucial role in transforming packaging into a versatile tool that safeguards, conserves, and mitigates environmental impact. From food and beverage containers to pharmaceutical packaging, cosmetics, and industrial products, coatings are omnipresent in various types of packaging.

What are barrier coatings? They are thin layers applied to packaging materials like paper, cardboard, metal, and flexible films to create a protective shield against environmental factors.

According to Oliver Waddington from Siegwerk's CE Coatings Unit, “Barrier coatings enhance fibre-based materials by resisting external aggression such as water, moisture, grease or oxygen, and maintain the internal condition of a packed product. In the case of plastic-based packaging, particularly flexible packaging, barrier coatings enable us to reduce plastic layers, reduce plastics and microplastics. It allows simplifying packaging to get better recycling, and a second life.”

Multiple chemistries can be used to achieve barrier properties on different substrates. Barrier coatings include materials like polyethene (PE), polyvinylidene chloride (PVDC), and ethylene vinyl alcohol (EVOH). While these materials have traditionally been favoured for their effectiveness, the search for more sustainable solutions has brought water-based and bio-based coatings to the forefront.

One key function of barrier coatings is to protect the packaged contents from external elements that could compromise their integrity. For example, in food packaging, barrier coatings can prevent moisture from seeping into the package and causing spoilage. Similarly, in pharmaceutical packaging, barrier coatings can safeguard the potency and stability of medications by minimising oxygen transmission.

Environmental impact of disposable cups and sustainable alternatives

In recent years, the surge in coffee consumption and takeout food has led to a significant increase in the use of disposable cups. While convenient, these cups pose a considerable threat to our environment, contributing to pollution and landfill waste. In response, many companies have started using eco-friendly options to reduce their carbon footprint. One such alternative is water-based barrier-coated paper cups, which are a more sustainable option than traditional plastic cups.

Water-based barrier-coated paper cups are made of paperboard, which is coated with a thin layer of a water-based coating material. This coating material is made of natural minerals and polymers, and it creates a barrier between the paperboard and the liquid, making it resistant to moisture and liquid. The coating material used in these cups is free from harmful chemicals such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), making it safe for human consumption.

The ten coating manufacturers WhatPackaging? interviewed discussed how water-based barrier-coated paper cups have a lower environmental impact than traditional plastic cups. They are made from renewable resources and are biodegradable, which means that they can be composted and will not contribute to landfill waste.

How safe are coated paper cups?

Yes, coatings can offer barrier properties without harmful side effects, especially with the FDA certification, says Prashant Atre, managing director at Artience.

Acrylic, olefin-based, and bio-based are all possible for different applications. Acrylic is UV-based, and olefin is PE. Atre informs, “Currently, we are working on bio-based. In Japan, we have multiple bio-based products, especially in printing ink. Artience’s focus is bio-based products.”

Upal Roy, managing director of India and Middle East group for the Flint Group, is in line with Atre's opinion. He says, “Flint Group’s coatings, including our barrier coatings, are safe to use and do not have harmful side effects.” The Flint Group manufactures energy-curable, water-based and solvent-based coatings. For water-based, these coatings are based on acrylic and olefin chemistries; for solvent-based, we offer both nitrocellulose (NC) and polyurethane (PU) chemistries, and energy-curable coatings are based on cross-linking acrylates.

Hubergroup has been focusing on offering solutions for the market for some time now. Andre Garber, head of business development for water-based systems and UV coatings, has developed many barrier coatings in recent years. “For example, oxygen barrier coatings and grease or water barriers, to name the most recent developments.”

Garber adds that his company is in the final stages of developing a coating that provides a barrier against water vapour. “Additionally, Hubergroup is not exclusively focused on fibre-based materials. For example, it has an oxygen barrier coating for use on polymer films, enabling the production of recyclable mono-materials.”

Shailesh Nema, vice-president of sales Asia and managing director of India at Michelman, informs that his company has been working with many substrate suppliers to enhance its new innovations with our coatings and provide barrier properties that are workable on their existing machines—including converting equipment and packaging lines.

Nema adds, “We have been working on multifunctional coatings for papers in collaboration with multiple paper mills. These coatings can provide multiple barrier properties—such as moisture, water, oil, and grease—and heat sealing properties—all in a single coating.”

Michelman also supplies paper cup coatings for the Asian market, which comply with the recyclability regulations of the US, Europe, and parts of Asia.  “We are looking forward to introducing this product in India as well. However, the regulation is still unclear. In certain states of India, PE-coated paper cups are banned, but in certain states, they are not. There is still uncertainty regarding when these regulations will become more explicit.”

Challenges and considerations

Despite the promising advantages, implementing barrier coating technologies involves challenges. One major hurdle is the cost of developing and applying these coatings. While prices are falling as technology advances, initial investments can deter small businesses.

The coating is mostly compatible with gravure, flexo, and different coating applications like air knife coater, and curtain coater. “A 5- to 6-gsm dry deposition is required since the coating is applied on the back side of the board. At times, a double coat can improve the barrier property where the first coat is applied as a primer with a top coat,” says Farid Sorathiya, technical director - technical & commercial graphic division at Astra Chemtech.

Atre, whose company Artience manufactures products using different methods, says coatings are compatible with all printing methods. “However, UV is compatible with each of the printing processes, but solvent-based chemistry will not work for offset.”

While flexo or gravure printing offers lower deposit capacity and typically requires low viscosity with high dry content, offline coating machines can reach a higher deposit with higher viscosity as long as the drying capacity is sufficient. “Depending on the targeted performance, paper-based substrate, and end-of-life product management, the application method must be chosen carefully,” says Waddington of Siegwerk.

The initial cost difference between normal lamination and chemical coating is significant. “When comparing normal lamination on paper using materials like polyvinyl chloride (PVC), biaxially-oriented polypropylene (BOPP), or polyethylene terephthalate (PET), the cost typically falls between 28-38 paise per 100 square inches. On the other hand, barrier-coated papers range from 35-40 paise per 100 square inches,” says Anuj Agarwal of Texochem. “In cases where PE extrusion-coated papers are used, barrier-coated papers tend to be about 30-35%  more expensive on average.”

Other costs associated with normal laminations include process costs and wastage. “The cost difference can be ignored if one wants to be a responsible participant and maintain the ecological balance,” says Sorathiya.

Agarwal agrees. He says, “The long-term environmental benefits, including recyclability and reduced plastic use, make barrier coatings a more sustainable choice, aligning with the increasing demand for eco-friendly packaging solutions.”

Additionally, regulatory standards must be met, especially in the food industry, where safety is paramount. Continual research and development are essential to ensure that barrier coatings are effective, safe, and compliant with health regulations. “The water-based barrier coating provides sustainability. It is a safe and eco-friendly technology. Although it may not be as robust as lamination, ongoing research aims to address this limitation,” asserts Sorathiya.

Ban on SUP is one of the best opportunities to produce such paper on which barrier coating may be cost-effective. Some coaters and converters in India do not find Indian paper suitable for oil and grease resistance (OGR) coating. However, this is one opportunity.

In conclusion: Transitioning to barrier coatings as an alternative to single-use plastics is not just a possibility; it’s a necessity as we face increasing environmental challenges. The industry must invest in innovative solutions and collaborate with researchers and policymakers to streamline the process of adoption.