Biodegradable, compostable or recyclable: the problem with plastics

Clare Taylor of Clare Taylor Consulting discusses navigating the terminology of breaking down plastics substrates sustainably.

The terms biodegradable and compostable are often used interchangeably, but they are different in meaning: things can be biodegradable but not compostable. There are also subcategories that need to be understood.

To add to that, there is confusion about the term ‘bioplastics’: sometimes it’s used for fossil-based plastics that are biodegradable, and sometimes for plastics made with plant-based feedstock. And then there is often an assumption that bio-based plastics (made from plant-based feedstock) will be biodegradable, whereas many are formulated for durability and are not. 

Paper is generally biodegradable, and compostable, but with caveats – by the time it reaches the end user, dyes and surface treatments such as certain inks, adhesives and coatings may have changed this. 

And if you want the paper product to be suitable for composting, you need to think about what you might be adding to a potential food-growing medium. How plastic is printed or treated can also change its suitability for composting.

Why the terminology matters

Distinctions are important, as using the wrong kind of substrate can create more problems than you are trying to avoid. 

It’s also a good idea to find out what the relevant (whether municipal, commercial or industrial) waste management options are where your printed materials will be used, as even compostable plastic may not end up being composted. 

Where I live, I see many items labelled to say they should be home-composted or disposed of in local council food or garden waste bins. However, the food waste here is not composted, but goes to an anaerobic digestion (AD) plant, and any plastics within the waste will be automatically removed and sent to incineration. 

It doesn’t matter that they may be labelled as compostable, the technology is not there for sorting it from other plastics that would add microplastics to the digestate created, generally used for food-growing. Even if they could be sorted, compostable plastics need a composting stage prior to anaerobic digestion, and AD systems are not usually set up for this as they are designed for food waste. 

There are concerns about biodegradable and compostable plastics contaminating the recycling stream

The same types of issue apply to garden waste, although that is processed differently where I am, using in-vessel composting. This situation is not unique. For plastics suitable for home-composting, there is again a consideration of how many end customers receiving it will have gardens – in Europe as a whole, for example, nearly half the population live in flats, with the percentage varying country by country: in Spain it’s nearly two-thirds.

There are concerns about biodegradable and compostable plastics contaminating the recycling stream: consumers may just see a symbol and misinterpret it as being a recycling instruction, or not even read what’s printed on it but simply put it into the plastics recycling.

The situation may change as consumers become more aware and as new technology develops and becomes widely available: various organisations are already carrying out trials of non-mechanical, or chemical recycling, in which the plastics are broken down to their basic chemicals for use as a feedstock for new plastics. As a complement to existing mechanical systems, this can overcome many of the limitations in separating mixed plastics and of handling and processing flexible plastics.

Bearing all this in mind, definitions for the various types of plastic are as follows:

Biodegradable 

To take a dictionary definition, something is biodegradable if it is “capable of being decomposed by bacteria or other living organisms”. There is no timescale for this, and that is highly relevant when considering the end of life for your printed materials: something may take many years to biodegrade, depending on what and where it is. The term biodegradable is therefore best avoided.

You may also come across the term oxo-degradable plastic; this is plastic with an additive that makes it break down into micro-fragments, and it is either already banned or due to be banned in many places.

Compostable 

Compostable items are biodegradable within specific conditions, so is a more specific term than biodegradable, but still quite broad as home composting conditions are different from industrial composting, and materials suitable for industrial composting may not break down in a home compost heap for many years, if at all. If you are buying compostable plastic substrates, asking for certifications helps ensure you are getting what you expect. 

To manufacture compostable packaging, EN Standard 13432:2000 – requirements for packaging recoverable through composting and biodegradation, was developed to help add some clarity to a very confusing issue. There are certifications associated with this standard.

What are they for?

One of the reasons many favour compostable plastics is because of media images of plastics in the rivers and seas; however, under water, without oxygen and often in low temperatures, they may not biodegrade – there is still research being carried out on this.

Another is a belief that composting is generally ‘good for the environment’ as it leaves no waste. Again, this is not necessarily the case – a lot of resources and energy go into making substrates or items; making them compostable means they become a single-use item by default. Reuse or recycling, where that is feasible, maximises use of these resources. Even if the plastic is bio-based, growing the crops to make it may be displacing food crops.

Making products compostable means they become a single-use item by default. Reuse or recycling, where that is feasible, maximises use of these resources

Composting is considered part of nature’s cycle and allows soil improvement, but although fossil-based plastics do break down, they do not contain the nutrients that your food or garden waste does. In situations where plastic can be recycled, that is the better option. 

However, there are times when compostable materials are the right choice, particularly for food labelling and packaging – tea bags spring to mind, or labels stuck on bananas – or in a closed-loop situation where waste packaging is recovered where it is sold and used, such as food at festivals: the EU, the UK and others have published guidance.

The simplest way to find information relevant to your location is through the Ellen MacArthur Foundation on the Plastics Pact Network page here. You can find the global network, with introductory videos and links to regional pacts, information and resources. 

Questions to ask when considering materials

• Why is a biodegradable or compostable material required? Would recyclable be better?
• Will your processing change the above qualities?
• Check with your substrate provider so you know exactly what you are getting – ask for more detail about anything called bioplastic or biodegradable, and certifications for compostable materials if such certifications are available in your location.
• What is it going to be used for?
• What will happen to it afterwards?
• What are the waste collection and treatment systems for the location?
• Can you make sure it is clearly labelled to prevent contamination of the recycling stream?