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:
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)
For more information, see also our Composting page on biodegradable plastics.
Truly Biodegradable Plastics Now Available
Imagine being able to toss styrofoam coffee cups into your back yard compost pile. Or being able
to design a community composting program without having to worry about how you're going to
deal with all those plastic bags that everyone uses for leaves and grass.
Biodegradable plastics first appeared in the early 90's and didn't live up to their hype. They were
made of a mixture of starch and polyolefin. Only the starch portion could biodegrade which left
the durable plastic residue (plastic dust) behind.
Despite this poor beginning, people haven't given up on the basic idea. Research and development
of truly biodegradable plastics has been vigorously pursued by a number of research institutes and
This time around, there are standards to adhere to, like those developed by the International Biodegradable Products Institute and the US Composting Council. These now contain stricter
definitions of biodegradability.
Many of the new biodegradable plastics are made only from plant products (rather than from
petroleum products like traditional plastics). They will break down into organic material during
composting the same way other plants do. Even the biodegradable plastics made from traditional
sources have been redesigned to break down completely.
These products are truly revolutionary. Here is a sample:
EarthShell manufactures sandwich wraps, and styrofoam like bowls,
plates and lidded containers from a starch and limestone based plastic. It has won a major
package design award and been endorsed by Friends of the Earth and others organizations. They
are now aligned with DuPont and have working relationships with Walmart and McDonalds.
NatureWorks PLA is a clear PET-like plant based plastic developed by CargillDow with a wide
range of applications.
Novamont's Mater Bi resin is another plant based material that can be processed to make many
BASF's EcoFlex is another
biodegradable film plastic based on a petrochemical polymer.
Plantic is a new plant based biodegradable plastic developed by Australian public researchers. It
appears to be faster to decompose and cheaper to produce than many of the others, but is still in
the corporate testing stage.
The single use, disposable approach which characterizes so much of modern, first-world living
always needs to be carefully examined but there are some products which justifiably have short
lives. Biodegradable plastic development has focussed on products such as: containers for
take out food, bags for compostables, supermarket packaging, plastic mulches used in food
production. Currently, the costs are two to four times greater than their conventional
counterparts, but changing regulations and corporate greening are leading the way in use.
(Source: WasteWatch, Sept. 2002, updated Jan. 2013)
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