what is biodegradable plastic?

What is Biodegradable Plastic anyway?

by Lisa Fletcher, Tofino

the letter 'T'

The other day, a friend of mine commented on the number of green doggie bags she'd noticed littered along the beach. Granted, no one likes the sight of or to step in dog poo, but somehow wrapping it up in a neat little package and leaving it on the beach doesn't make sense either. This got me thinking about these biodegradable plastic bags. Do they really breakdown completely, even in our chilly Pacific Ocean? We've definitely come a long way with the use of plastic bags, but this whole 'biodegradable' phenomenon has somehow managed to ease people's minds without a second thought.

First, a few terms: Degradable is given to a substance that can be broken down by natural processes into smaller parts, with no time frame for when it will break down. Everything is 'degradable' eventually, even if it takes 1000's of years.

Photodegradable is given to a substance that breaks down with exposure to ultraviolet light (uv). Biodegradable materials can be broken down completely by naturally occurring microorganisms (bacteria, fungi, and algae) and converted in raw materials of nature. Compostable refers to something being biodegradable within in a certain time frame, under typical composting conditions.

Until recently, plastics were commonly used. We now know that plastics, being made from oil, may not be the most sustainable solution. They are harmful to wildlife and can take 1000's of years to decompose. As a 'greener' solution, biodegradable plastics have been manufactured from a variety of materials, including starch-based polymers (potato, corn, wheat or tapioca starch), polyester (still made from oil products), water-soluble polymers, polymers that degrade with light or oxygen, or a blend of these.

Two very common types of biodegradable plastics are oxo-biodegradable and hydro-biodegradable. Oxo-biodegradable plastics are usually still made from an oil by-product but contain an additive, allowing them to break down in the presence of oxygen to be consumed by microorganisms. Hydro-biodegradable plastics are starch-based plastics (sometimes a blend with oil-based material) that degrade with moisture. Bags made of 100% cornstarch can break down very quickly in the right conditions. The more starch in the blend, the faster it will degrade. However, the controversy with starch products is similar to that of the bio-fuel debate; food crops for non-food use. Although hydro-biodegradable plastics tend to degrade faster, oxo-biodegradable plastics are used more often because they are less expensive and easier to manufacture.

Common misconceptions of these 'green' solutions are that they can be recycled, composted or sent to the landfill where they will completely breakdown. Unfortunately, this is not always the case. Biodegradable plastics vary in the rate that they degrade and in their effects on the environment, depending on what they are made from. Many products cannot be recycled because there are few facilities set up for it. If they are added to regular plastic recycling, they can 'contaminate' the process because they are made from different substances. Plastic bags labeled "compostable" have passed a standard test to break down within a specific time period. For plastics to be compostable they must:

  1. Break down into carbon dioxide (CO2), water and biomass.
  2. Decompose at the same rate as other compostable materials (like plants).
  3. Not emit any type of toxin into the environment.

Of course, each compost time varies depending on substances, amount of air it receives, and how often it is turned. As for sending things to the landfill, in all reality anything bio?degradable that ends up in a landfill probably does not get enough oxygen, sun, or dirt (or microorganisms) it needs to return to the earth naturally. Most gets buried and therefore stays relatively intact (this is why you can find newspapers from 20 years ago). Some landfills are now actually being designed to promote biodegradation through the injection of water, oxygen, and even microbes, which could potentially even be marketable for soil.

The topic of biodegradable plastics is pretty complicated. It seems the more heat, moisture, and air there is, the faster things will degrade. As for the little green bags, I'm not sure how they decompose in the frigid waters of the Pacific Ocean, but they do have 'Do Not Litter' written right on them. Ultimately it is up to consumers to find out the proper disposal methods of biodegradable plastics. It seems to me that by reducing our dependency on plastics, whether they are biodegradable or not, is part of the solution.

After finishing years of university, Lisa finally gets to save the world!

Tofino Time Magazine January 2009

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Tofino biologist Lisa Fletcher writes an introduction about 'biodegradable plastic' and where you see in most in Tofino - on the beach.

tofino time january 2009

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