How to Test Biodegradability of Plastic

Co-authored by Hannah Madden

Last Updated: April 30, 2020 References

Plastic is one of the leading materials that fill up landfills. It takes hundreds of years to decompose, which is why our Earth is covered in it. Biodegradable plastics that are made of cornstarch or plant pulp can degrade much faster than normal ones. Materials like this are usually tested in a laboratory setting with industrial composting tools. If you have a product that says “biodegradable” or “compostable” on it and you’d like to see if that’s true, make some compost and place your plastic in it, wait 12 weeks, and examine your test material to see if it has broken down at all.

Part 1

Part 1 of 3:

Gathering Compostable Scraps and Materials

1
Cut your test product into three 4 in (10 cm) squares. Find the plastic that you’d like to test for biodegradability and use sharp scissors to cut it into squares. Make sure they are all roughly the same size and mostly even on each side.^{[1]
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- Make sure the plastic you want to test says “biodegradable” or “compostable” on it. Otherwise, it probably won’t biodegrade at all.
- Plastics made of cornstarch or plant pulp are usually biodegradable. Traditional plastics are not.
2
Cut 3 to 4 pieces of yarn 2 times the height of your compost bin. Grab the compost bin that you are going to use for your experiment and measure out 1 piece of yarn for each of your test squares. Make sure the yarn pieces are about twice the height of the compost bin so that they can hang outside of it during your experiment.^{[2]
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- If you don’t have yarn, you can use twine instead.
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3
Tie each piece of yarn to each square of your test product. Cut a slit or a small hole in each of your test squares using scissors. Thread a piece of yarn through the slit and make a knot in 1 end on each test square. Make sure your knots are secure and that they won’t slip out during your experiment.^{[3]
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4
Drill 12 holes in the bottom of your compost bin. Flip your compost bin over and use a ¹⁄₂ inch (1.3 cm) drill bit to make 12 evenly spaced holes in the bottom of it. Make sure the holes don’t touch each other. If your bin is not big enough for 12 holes, just drill as many as you can.^{[4]
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- The holes provide air flow that is needed for the compost to decompose later on.
5
Collect half a bucket of brown scraps, like leaves or dry hedge clippings. Brown scraps are part of the compost that help to break down because they are rich in carbon. Newspaper, dry leaves, dry yard debris, untreated cardboard, and coffee filters are all great materials to use as brown scraps.^{[5]
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- Do not use magazines or glossy printed paper, as the chemicals can affect the outcome of your compost.
6
Collect half a bucket of green scraps, like fruits and vegetables. Green scraps are wet and rich with nitrogen, so they also aid in the degradation process. Dead plants, weeds, tea bags, coffee grounds, and algae are all good materials to use as green scraps.^{[6]
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Warning: Do not use anything that has been treated with pesticides or herbicides. These chemicals can interfere with the degrading process.^{[7]
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Part 2

Part 2 of 3:

Making Compost

1
Balance your compost bin on 2 pieces of wood. Put your compost bin in an area outside where it is protected from the elements, like under a patio or covered porch. Balance the bin on 2 pieces of wood so that it is elevated slightly off the ground. Leave the holes in the bottom uncovered so that air can flow through them.^{[8]
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Tip: Compost can get kind of smelly, so place your bin away from any windows.
2
Add a 3 in (7.6 cm) deep layer of brown scraps to your compost bin. Use the brown scraps that you have collected to pad the bottom of the compost bin. Make sure the scraps are large enough so that they don’t fall through the air holes in the bottom.^{[9]
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- You may have to shred some of your larger scrap pieces to make them fit in your bin.
3
Put a 3 in (7.6 cm) layer of green scraps on top of the brown scraps. Make sure the green scraps sit just on top of the brown scrap layer. Do not mix the layers together yet. Fill up your compost bin another 3 inches (7.6 cm).^{[10]
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4
Sprinkle a small layer of soil on top of your green scraps. You can either use store-bought soil or some from your backyard. Sprinkle a small amount of soil on top of the green scraps so that it covers them up.^{[11]
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- You can purchase soil from most garden supply stores.
5
Add alternating layers of scraps and soil until the compost bin is half full. Add another brown scrap layer, another green scrap layer, and another small layer of dirt. Alternate this pattern until the compost bin is about ½ way full.^{[12]
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- Depending on the size of your compost bin, you may need 2 to 3 more altering layers.
6
Lay your test squares in your bin with the yarn hanging over the side. Carefully place your test squares of plastic into your compost bin on top of the last layer you put down. Space out each square so that they aren’t touching. Make sure the yarn is hanging outside of the bin so that you can find the scraps later on.^{[13]
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- If your compost bin is too small to hold each square without them touching, take 1 square away.
7
Add alternate layers of scraps and soil until the compost bin is full. Pile more brown scraps, green scraps, and soil on top of your test squares until your compost bin cannot hold anymore. Make sure the yarn stays hanging on the side of the compost bin the entire time.^{[14]
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Part 3

Part 3 of 3:

Examining the Plastic

1
Mix the compost once a week using your hands. The ingredients in your compost must be mixed together in order to break down. Put on gloves to protect your hands and then reach into your compost bin. Mix the layers from the bottom up for about 5 minutes once a week. Break up any clumps that you see in your compost.^{[15]
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- Make sure you leave the yarn hanging outside of the compost bin.
- If you accidentally unbury your test squares, just bury them again in the middle of the compost.
2
Dig up your test squares after 12 weeks. The European standard for biodegradable material is 12 weeks, so if your plastic hasn’t broken down by then, it is not technically biodegradable. Carefully remove the top layers of compost and find the test squares hidden underneath. Take each one out of the compost so that you can look at them.^{[16]
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Tip: You can put your compost in your garden to enrich the soil.
3
Examine the test squares to see if they have decomposed at all. When plastic starts to break down, it gets holes in it, becomes cracked, changes colors, and reduces in size. After 12 weeks of sitting in compost, your plastic pieces should be close to broken down if not completely degraded. Any pieces left, if there are any, should be small.^{[17]
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- If the plastic looks the same as when you buried it, it has not broken down and it is probably not biodegradable.
- Plastics that are slightly broken down but not completely degraded are still biodegradable, but they are not up to the biodegradability standard.