Science Buddies: "Ask an Expert"

Hello everyone,

For my science project, I'd like to test the biodegradability/compostability of a bioplastic that I would create myself. However, when I look this up, there are all sorts of complicated standards (ATSM D6400, ATSM D5988, etc.) I was wondering if there was any biodegrability or compostability test that I could do at home or in my school lab?

Thanks so much,
hello1910

Hi,
I'm sorry it took us so long to get back to you! I've searched and searched, but I couldn't come up with a simpler standard that could be tested in a school lab, or at home, but it doesn't mean that you can't go through with this project. Industrial compost standards are based on 3 characteristics: biodegration, disintegration, and ecotoxicity. You can test all three of these at home. For biodegredation, attempt to compost your plastic and measure how long it takes to degrade. It might be good to do this test in a container that you place outside, so every day you know where to look to find the plastic. Once it has degraded (don't bury use too much soil, or the effects measured during the ecotoxicity test won't show), take the compost that you have created and plant some small plants in them (bean plants should do, but if you know of a plant that are affected easily by toxins, use it). Make sure you have a control group too so you can compare the effects of your plastic on the plants to their normal growth (so you are able to tell if it has any effects). Lastly, for a disintegration test, pin a piece of your plastic outside on a fence and measure how long it takes for it to tear apart and distribute itself onto the soil. For a standard of comparison, you may want to test a normal plastic bag in these ways also too see if yours is more compostable. If you could obtain other commercially biodegradable plastics and test them in these ways, you would be able to tell where your plastic falls.

I hope this helps!
-Meg

Hi Meg,

First of all, I must say that it is extrodinarily generous of you to volunteer your time to help others with their science project questions. As a busy junior (I clicked on your profile page), this is no easy feat. You've inspired me to answer other people's questions.

Secondly, thanks for your excellent answer. It was very helpful.

Sincerely,
hello1910

I'm glad I could help!

Hi Meg,

Do you have any suggestions for testing the tensile strength and mechanical resistance of bioplastics at home?
Thanks,
hello1910

Sorry it took me soooo long to respond! I didn't see this until now! If you still need help, I think you could measure tensile strength by taking a piece of your plastic and clamping it securely on one end. Then if you could either purchase or borrow a spring scale that measures newtons from a physics teacher and secure it to the other end of the plastic. Then, slowly pull on the plastic until it rips across the center. The amount of newtons of force you had to use to rip it is a measure of its tensile strength. To test mechanical resistance, you could take sandpaper and calculate its coefficient of friction, attach it to objects of different weights, and lightly rub the sandpaper over the plastic, and the one that breaks it will be used to find the force that the plastic can withstand, or mechanical resistance. The formula for the force of friction is f =un where u is the coefficient of friction and n is the normal force (the weight of the object the paper was attached to in newtons). Hopefully this works!

I'm so sorry that this is so late! If you have any other questions, I promise I'll respond faster!

Sorry,
Meg

Thanks so much Meg! I'm sorry that I noticed your reply so late- you've been tremendously helpful!