Week 3: “Non-biodegradable Biodegradable Plastic Bags”

The biodegradable plastics have come a long way and made themselves known to the general public. The companies have portrayed a really idealistic image with the biodegradable plastics: like naturally-made plastic bags that will naturally break down and disappear. If things really go like what people envisioned, biodegradable products would be the “hero” to solve the plastic issue on earth. But pay attention to the word “If” I used in that sentence, because the reality suggests that biodegradable plastics might not be as cool as we wish them to be.

What is Biodegradation?

First, let’s examine what biodegradation is. 

In nature, biodegrations means the process of the microorganism breaking down certain substances into water, CO2 and biomass. The water, CO2 and biomass can enter the natural cycles once again and get repurposed. When it comes to plastics, it means that they are made out of organic/natural materials, and will be broken down by microorganisms after disposal. 

What are biodegradable bags made of?

Mainstream biodegradable plastic bags are made of PLA (polylactic acid), aka, sugars in corn starch (sometimes cassava or sugarcane too). It is biodegradable — only under the right condition: right amount of oxygen, right temperature and right moisture level. And the right conditions cannot be easily achieved in a landfill nor in your garden. PLA is also restricted to the land: it doesn’t really degrade in the ocean environment. So the instances when they will biodegrade are very limited.

PHA (polyhydroxyalkanoate) is another type of material used to make biodegradable plastics. It takes up a small portion in the market but is expected to grow. It does a better job biodegrading in the ocean, but still, it has a very limited range where it degrades. It does its best to biodegrade in tropical areas, but places like the Mediterranean and the polar area will take extra long. 

How to determine biodegradability? 

There are many standards used in different parts of the world. 

Here is a list of common testings: 

  • ASTM Testing 
  • EN Testing 
  • ISO testing. 
  • OECD Testing 

Under each organization/company there is a series of different tests, and each test aims at different materials under different conditions. 

According to Situ Biosciences LLC, the “commonly requested biodegradation test for solids is ISO 16929, for liquids is OECD and ASTM D5864 for lubricants”.

The standard may vary from country to country, but ideally, we want the plastic items to be degraded in 6 months to 12 months. 

So How Is Our Market Doing?  

I selected few of the top choices popped up when I searched for biodegradable plastic bags and examined the materials that it’s made of. 

The first one is made out of “100% Virgin Low Density Polyethylene” (LDPE). 

  • LDPE is #4 plastic, usually used to make plastic wraps, squeezed bottles, grocery bags. 
  • Studies say that it does biodegrade, but at a very slow rate, also requires the right environment. 
  • In other words, it is mostly not biodegradable if you just put it in your trash bin.

The second one is made out of “Recycled HDPE” (High Density Polyethylene).

  • HDPE is #2 plastic generally recycled and repurposed. 
  • But it is NOT biodegradable.
  • Caution!
    • The website claimed their bags “break down faster than other bags”.
    • This can mean that the bag will be physically broken down into small particles that are not perceivable by human eyes; but chemically and biologically, plastic is still plastic. 

The third store did not specify what the bag is made of. 

  • Truly not a good sign for consumers to buy their products. 

The fourth one didn’t specify their ingredients either, but they have specified what they have passed ASTM D5511. 

  • ASTM D5511 claims that they are bio-degradable under landfill conditions.
  • They have also specified that their bags will “Biodegrade fully within 4 years”, which is longer than expected 6-12 months, but it is acceptable. 

Conclusion:

After researching Biodegradable bags, I just want to say that this industry still has space for huge developments and scientific advances in the future.

But now, the products that claim to be biodegradable are mostly just greenwashing hoaxes. Be cautious of the advertising and still carry your reusable bags around 🙂

Wenqian L.

References : 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3781136/

https://www.sciencedirect.com/science/article/pii/S187802961630161X#:~:text=Low%20Density%20Polyethylene%20(LDPE)%20is,detrimental%20effects%20on%20the%20environment.

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