The truth about compostable plastics

By Hannah Cooper, Final Straw Foundation Intern

Compostable plastics are everywhere, from plastic bags to cups and straws. It’s great that we are seeing alternatives to fossil fuel-based plastic but compostables may not be the saving grace that they seem. Do they really break down at all? What happens in the ‘real environment’? Do they need special facilities to break down properly?

Firstly, let’s explore what compostable plastics are and how they are made. Most compostable plastics are made from PLA or Polylactic acid, a bioplastic made from plant starch from species such as corn or sugar cane. The production of PLA is renewable and its production uses 65% less energy and creates 68% fewer greenhouse gases than conventional plastics. These are great stats and certainly, show that PLA production is greener than conventional plastic. However, it’s not the production that we are so worried about when it comes to compostable plastics – it’s the disposal.

We have many businesses who approach us excitedly to say that they have switched to compostable disposable items, hoping that this will contribute to the fight against pointless plastic waste and the rising problem of plastic in our oceans. Unfortunately, often we have to tell them that although they may have the best intentions, products that contain PLA are just as likely to be found on one of our beach cleans as any other disposable plastic item. Although marketed as compostable, PLA plastic is not home compostable and will only decompose in industrial composting facilities. PLA requires moisture and heat over 140F to begin the self-hydrolyzation process reducing the molecular weight of the polymer to lactic acid. Polylactic Acid does not and will not biodegrade without these environments – if you have a home compost pile and it does not reach 140F and lacks water PLA will do nothing*. This means that if you throw compostable plastic on your home compost pile, it will not break down – unless otherwise labeled as approved for home composting, do not put these items in your compost bin. Unfortunately, if PLA plastic ends up in landfill it could take up to 1000 years to decompose, which is the same rate as conventional fossil fuel-based plastic. This plastic also doesn’t biodegrade in the ocean or countryside as it will not experience the correct temperatures and moisture levels, so has the same potential to harm marine creatures as normal plastic, something that we are so passionate about preventing.

Another issue with these items is that although biodegradable and compostable plastics are technically recyclable, they are currently not recycled back into plastic material. Rather, they are treated as an impurity in the recycling of conventional plastics when collected together and can contaminate the recycling stream if they are mistakenly placed in your recycling.

So, if not PLA, what options do we have? We always promote the use of reusable items such as bottles, cutlery, plates, and cups wherever possible as we find this to be the most sure-fire way to prevent waste. However, if this is not possible for you there are some alternatives to PLA which are more environmentally friendly. The first is to replace plastic cutlery with wooden cutlery made from birch or bamboo. If left to biodegrade, both of these materials would decompose and the carbon from the wood would return to the soil, making them home compostable and biodegradable. Bamboo is also great as it grows quickly, doesn’t require chemical pesticides, and produces more oxygen than trees. There are also options for plastic and plastic-lined cups or packaging. Cardboard products lined with an aqueous lining rather than PLA can be home composted and biodegraded at the same rate as newspaper, so you won’t find these products floating in our oceans in 500 years’ time! They also, unlike PLA products, can be recycled if unsoiled. Seaweed-based products that biodegrade naturally are also becoming available so there are plenty of options out there to avoid the PLA!

We hope we can get as many people adopting reusable items and naturally biodegradable products as possible and feel like It’s important to share this not-so-well-known message about PLA, so if your favourite business is using PLA without realising the environmental impact let them know! Maybe you could recommend some useful alternatives that really make a difference.

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One Comment Add yours

  1. Diana Morgan says:

    Great article. Just wondered why you put temperatures in F not C?


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