Differences Between Degradable & Biodegradable Plastic Bags

Difference Between Degradable and Biodegradable Plastic Bags

We have all now become more aware of the damage that plastic can cause to our environment. We produce an incredible 348 million tonnes of plastic9 globally every year. And around 10 per cent of the plastic that we produce ends up in our oceans7. However, science and innovation now present us with the choice to replace standard plastic bags with either degradable or biodegradable variants. Hence, let's take a look a look at what the difference is between degradable and biodegradable plastic bags? And are they really better for the environment?

The Problem With Regular Plastic Bags

Plastic waste is a problem that we all have to deal with. Reducing the amount of plastic we use should be a high priority for us all. For decades we have been using traditional plastic bags. We’ve used them in our waste bins as bin liners. We’ve used them to throw away food waste and we use them to carry our shopping. We can find them almost anywhere.

Our reliance on plastic bags cannot go unnoticed. They have become a part of everyday modern life for a great deal of us.

However, much of the plastic problem comes because we have treated plastic bags as a one-use item. We would use them and throw them away, with little care or thought for our environment.

Did you know that single-use plastic bags have a useful lifespan of 12 minutes on average? I.e. the average time we actually use them to carry our groceries or shopping before they get discarded.

And we get through a lot of plastic bags. In the UK prior to the plastic bag charge, each of us used to get through 140 single-use plastic bags a year on average. Globally, it's said we consume more than one trillion plastic bags a year10. That’s about one million of them every minute.

The Plastic Bag Problem

And that would be all very well if we weren’t faced with the problem of how they decompose once disposed of3. In fact, the problem is more the way in which they don’t decompose. Made from polyethene, regular plastic bags come from non-renewable petroleum-based sources.

Standard plastic takes hundreds of years to decompose6. So from the ocean to landfill, the plastic we use will still be decomposing way beyond our lifetime. When it does break down, a plastic bag breaks down into tiny pieces which can affect the wider environmental ecosystem.

Once the plastic has broken down into small particles, called microplastics, they leach into our waterways or our Oceans. Once there marine animals can consume them. As such plastic can enter the food chain. And it is washing up on shorelines across the globe8.

The plastic problem we face is huge but can we make a difference by making the switch to biodegradable or degradable bags?

Plastic bag in the ocean with diver

Despite their degradable status plastic bags in the Ocean can still take an awfully long time to break down. We're far better to avoid the stuff entering our waterways and natural environment in the first place. Photo by Cristian Palmer on Unsplash

Degradable Plastic Bags

If something is degradable, it means that large molecules can break down into smaller fragments1. Degradable plastics are still commonly petroleum-based yet with chemical additives included helping speed up the rate of degradation. However, degradation remains a problem for the environment.

The word degrades means “to break down” and essentially, all plastic is degradable. It can either be broken up by hand or machinery in large recycling or processing plants. Or it can go through the natural process, which can take thousands of years. A plastic bag labelled as degradable won’t have an official time stamp that indicates how long it takes to break down. It will take as long as it needs to take.

This might leave you wondering whether degradable plastic is a feasible alternative to traditional plastic bags?

The reality is that experts say that degradable plastic bags are not as eco-friendly as we might have thought4. Simply because the natural environment rarely presents the conditions required for these plastic bags to break down optimally.

The way to look at this is that degradable bags do not return to the earth organic matter. Rather they still return plastic particles, just faster. This means that we still face difficulties in removing the resulting degradation from the environment. And that degradation remains plastic.

Biodegradable Plastic Bags

On the other hand, biodegradable plastic bags work differently to degradable bags. They are made using renewable materials such as plant starches, micro-organisms or petrochemicals. In fact often a blend of all three. As such, they usually contain less petroleum-based plastic which is good news.

Manufacturers adapt the composition of Biodegradable plastic bags to also break down at a faster rate. And into less harmful particles when exposed to natural elements due to their composition.

Mostly they design biodegradable bags to break down when exposed to microorganisms such as bacteria, fungi or algae. Where they do still contain petrochemical plastics the resulting degradation problem can remain. Albeit less so.

Certainly one benefit comes as more and more biodegradable bags get made from materials that are plant-based. This can include the likes of corn-starch or wheat starch. And results in an improvement over petrochemical-based plastic. Coming from a higher proportion of natural sources reduces their chances of ultimately becoming nasty plastic pollutants.

Conditions for Degradation

However, they also require specific conditions in order for most of these bags to actually break down2. Usually, the temperature has to reach 50 degrees and there needs to be the correct amount of UV light5. So, for plastic waste that finds its way into the ocean, the conditions may not be right.

Also, once in landfill they breakdown without oxygen. This can then lead to the production of methane which is more harmful to the environment than carbon dioxide. In this case, this renders them no better than traditional bags.

All the same, biodegradable polymer research marches on at a pace whilst science grapples to aid our plastic pollution problem. Researchers make advances all the time resulting in new innovations that do in fact improve the biodegradable qualities of new plastics. Many have not yet made the mainstream but may well do so.

As a general rule, when buying biodegradable bags look for a composition containing as high a proportion of plant-based materials as possible. Compostable is almost always the best choice. Compostable plastic bags will in-fact break down more naturally in landfill and water in more natural conditions where moisture and warmth are present.

Is One Better than the Other?

It is clear to see that there are differences between the two. A degradable bag will take longer to break down, in fact, it can still take hundreds of years. Even then, tiny pieces of plastic will still remain.

A biodegradable bag breaks down at a different rate. It relies on microorganisms to speed up the process and that sounds like a good thing, but is it?

Whether degradable or biodegradable these new plastic bag variants cannot be easily recycled. And there is inevitably still by-products left behind after their different speeds of degradation. People might think that biodegradable means that it will disappear. They might also believe that it is good for the environment. Unfortunately, neither are absolutely true.

Also, whereas they present advances and improvements neither help to deal with the problem of consumption. In fact, if there is a belief that biodegradable is better, then it could add to the problem.

So, in our quest to reduce plastic waste, we should really be moving away from plastic bags altogether. Of course, we can make use of plastic bags by reusing them, however, there are alternatives. With the likes of compostable bags and bags made from wholly natural materials, we do have a choice. We just need to think a little differently and make better decisions.

Thank you plastic bag

Ditch the plastic bags entirely. There's little doubt that is the best answer when considering the difference between degradable and biodegradable plastic bags. The environment will thank you for it so another plastic bag doesn't have to. Photo by Griffin Wooldridge on Unsplash

1R. Mohee, G.D. Unmar, A. Mudhoo, P. Khadoo, Biodegradability of biodegradable/degradable plastic materials under aerobic and anaerobic conditions, Waste Management, Volume 28, Issue 9, 2008, Pages 1624-1629, ISSN 0956-053X, https://doi.org/10.1016/j.wasman.2007.07.003
2F.-D. Kopinke, M. Remmler, K. Mackenzie, M. Möder, O. Wachsen, Thermal decomposition of biodegradable polyesters—II. Poly(lactic acid), Polymer Degradation and Stability, Volume 53, Issue 3, 1996, Pages 329-342, ISSN 0141-3910, https://doi.org/10.1016/0141- 3910(96)00102-4
3H Bockhorn, A Hornung, U Hornung, Mechanisms and kinetics of thermal decomposition of plastics from isothermal and dynamic measurements, Journal of Analytical and Applied Pyrolysis, Volume 50, Issue 2, 1999, Pages 77-101, ISSN 0165-2370, https://doi.org/10.1016/S0165-2370(99)00026-1
4Plastics of the Future? The Impact of Biodegradable Polymers on the Environment and on Society. Tobias P. Haider Dr. Carolin Völker Dr. Johanna Kramm Prof. Dr. Katharina Landfester Dr. Frederik R. Wurm. First published: 04 July 2018. https://doi.org/10.1002/anie.201805766
5Plastics of the Future? The Impact of Biodegradable Polymers on the Environment and on Society. T. P. Haider, C. Völker, J. Kramm, K. Landfester, F. R. Wurm, Angew. Chem. Int. Ed. 2019, 58, 50.
6Decomposition and analysis of refractory oceanic suspended materials. D. W. Eggimann and P. R. Betzer. Analytical Chemistry 1976 48 (6), 886-890. DOI: 10.1021/ac60370a005
7Plastic Waste Inputs from Land into the Ocean. Jenna R. Jambeck, Roland Geyer, Chris Wilcox, Theodore R. Siegler, Miriam Perryman, Anthony Andrady, Ramani Narayan, Kara Lavender Law. Science, vol. 347, no. 6223, 13 Feb. 2015, pp. 768–771, doi:10.1126/science.1260352
8Invasions by marine life on plastic debris. David K.A. Barnes. Naturevolume 416, pages 808–809 (2002). https://doi.org/10.1038/416808a
9Plastics - The Facts 2018. PlasticsEurope. Association of Plastics Manufacturers
10Plastic Bag Fact Sheet. Earth Policy Institute.
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