Is grey the new black? How your garbage bag colour affects recycling

Does the colour of a garbage bag matter in the context of recycling? It turns out that it does! This is why the supermarket chains belonging to the Schwarz Group (Lidl and Kaufland) have committed to removing black plastic from their own-brand packaging, in a step towards a closed-loop economy. So why has black pigment started to be censored, what role does dye play in the production of recycling bags, and how could this affect the future of the industry? We spoke to Katarzyna Wi?cek, Technology Leader at Cedo, to find out.

The supermarket shelves are stocked with garbage bags of different sizes and colours – black, yellow, blue, or purple – scented or unscented. This wide range of colours certainly gives the consumer a choice, but does the use of a specific dye also have other implications?

"At Cedo, we produce around 80,000 tons of garbage bags per year, made from processed post-consumer waste. The colour and width of the produced rolls are dictated by the expectations of a given market, and these differ from one to another. For example, the employees of a global chain of restaurants recognise the bags' intended use by their colours, which significantly helps to facilitate waste segregation."

Katarzyna added: "In the UK, garbage bags are divided into white for domestic use, with black used for storing waste outside. Meanwhile, the French market mainly uses black materials, and products in other pigments belong to the premium category. Transparent bags are used in public places to make their contents visible and meet safety requirements. In Poland, Italy, and Spain, coloured bags, often scented, are very popular."

"It's also worth remembering that operating in the German, French, or Belgian markets is not only about meeting requirements regarding colouring, but above else it's about meeting specific quality requirements – including ecological standards – regulated by European directives."

Black pigment and recycling

Although the quality requirements for the composition of garbage bags differ in individual markets, they share a common denominator: the circular economy. On the one hand, the raw material used for production must be obtained through recycling, but on the other hand, the used garbage bag should be disposed of and reused. But what happens when that bag is black?

Katarzyna explained: "Black is never the base colour of a garbage bag. To achieve the material's opacity, black dye is added to it, which is usually of carbon origin and contains soot. The problem arises when such used film ends up in waste sorting facilities, where machines wash, dry, and separate polyethylene from polypropylene – black pigment absorbs infrared light used during sorting, making it impossible to recognise the material."

Although the bag is a full-value polyethylene material from which raw material can be easily recovered, it is automatically rejected by the sorting facility as being unsuitable for recycling. This means tons of plastic going unused, which is a huge loss in terms of sustainable business.

Katarzyna said: "Some manufacturers, instead of adding soot, add dyes of a different origin to their products, but this results in a higher cost. At Cedo, we are strongly focused on producing products from polyethylene obtained from recycling. Therefore, we take a different approach by offering bags that are not black, but grey. We need to educate consumers that this change is better for our environment."

Is grey the new black?

Removing black pigment from plastic products made from recycled materials will reduce waste and promote sustainable practices. However, lasting change requires time and consistency. So what does the future hold?

"Eliminating black pigment from garbage bags is more of an evolution than a revolution. Cedo's mission is for production to be based on recycled materials. We are constantly working with our suppliers to ensure that the recycled material is of a high quality and free of contaminants. We will strive to ensure that the polyethylene contained in our products comes from recycling and is 100% post-consumer, as well as free of colouring agents. This is the direction in which the European Union is heading, but raising consumer awareness is also important."

"We already see a change in attitude towards this issue, especially in the Benelux countries. These markets rely on clean, high-density polyethylene, which allows for the production of very thin bags with a thickness of 6 microns. However, Belgium is moving towards change and is willing to increase the thickness of the film to 14, 16 microns in exchange for using recycled material instead of pure polyethylene from oil fields."

Katarzyna concluded: "We are all responsible for the planet, and the industry is increasingly seeing the need for change, moving towards a closed-loop system."