What are Biodegradable Plastics? Let us Break them Down for you…

Technically all organic (carbon-containing) materials can be biodegraded (broken down by microbes), it’s a matter of time. And the typical answer to ‘how much time?’ is ‘it depends.’ Without light, moisture and oxygen (i.e. similar to conditions in a landfill), very little degrades. Even newspapers have been known to be readable after decades in a dry landfill.

Traditional plastics made from petroleum products have not been around long enough to prove how many years they will take to degrade. When scientists apply the same tests to plastic bags as they do to other organic items to see how long it takes them to degrade (for the techies in the crowd, these are called respirometry tests), the bags don’t break down at all. Educated guesses based on this type of research put time to biodegrade for traditional plastics at 100 to 1,000 years.

Enter bioplastics — plastics made from plant-based sources, like corn or sugar cane. These plastics break down more easily and quickly than traditional plastics. They are considered more environmentally friendly than petroleum-based plastics because they are made from renewable resources (plants).

One of the most common bioplastics is polylactide acid (PLA). PLA is a transparent plastic made from corn. Not only does it have similar properties to conventional plastics like polyethylene and polypropylene, but it can be processed into products easily with the same equipment. PLA is growing in popularity with companies trying to adopt green practices. It is appearing in food trays, take-out containers and single-use dishes and many other packages.

The term ‘biodegradable’ has been applied liberally by some manufacturers. On its own, the word has no practical meaning since a product can be technically biodegradable even though it takes more than a century to break down. (It makes about as much sense as calling a product recyclable when no one actually recycles it.) The producers of true biodegradable plastics teamed up with the U.S. Composting Council to develop a standard for biodegradable plastics. The Biodegradable Products Institute certifies plastics as able to break down in large-scale-composting conditions. Look for this logo before buying biodegradable plastics:

Compostable label

The Compostable label does not certify that the product or package will break down in a home composting system. Generally, compostable plastics require sustained moisture, oxygen and temperature levels to ensure the composting happens within a reasonable time. Most home composters don’t achieve those conditions. Some people have tried putting biodegradable bags in a home compost bin. The bottom line: patience is required. The bags do break down, but they take longer than most other items, since they weren’t designed to do this.

What does this all mean at the consumer level? First, biodegradable plastics really don’t break down in landfills. We’re sorry to burst the bubble of hope for everyone that wanted to save the planet by putting their garbage in biodegradable bags, or by using biodegradable plastic dishes and throwing them away. Unless these items get composted in a large-scale facility, they won’t readily break down.

Second, biodegradable plastics cannot be mixed with other plastics going to recycling. Although PLA plastic carries a #7 plastics label (the "miscellaneous" category), its presence contaminates the regular recycling stream because the plastics are made from completely different things. Biodegradable plastics belong in the composting stream, not the recycling stream.

So, the bottom line? If your community has a commercial composting facility, feel free to use those compostable dishes, or biodegradable lawn and garden bags. Make sure they don’t get sent to landfill. And don’t mix bioplastics with your plastics recycling.

Caveat emptor! (buyer beware).


[Source: August 2008 WasteWatch ]