Self Healing Biodegradable Plastic

WHY?

Plastic pollution is one of the biggest problems the earth is facing today. I wanted to see if there was an alternative to fossil fuel and petroleum based plastics. There was and it's called biodegradable plastic.

Biodegradable plastic is made out of natural materials which will break down into natural byproducts. Natural byproducts include carbon dioxide, water and biomass. Biomass is made from the actions of microorganisms like fungi or bacteria. Biodegradable plastic is also made up of biodegradable polymers which are a long chain of repeating molecules. A molecule is made up of a bunch of atoms. One biodegradable polymer is polylactic acid (PLA) and it can be made from cornstarch. The PLA in the cornstarch plastic provides structural strength and it helps the biodegradable plastic break down into natural byproducts. Another is collagen from gelatin and it is a natural protein structure. These proteins are a biodegradable polymer because it can be broken down by microorganisms easily. This means that microorganisms like fungi and bacteria can easily digest these different types of biodegradable polymers.

I wanted to see if biodegradable plastics can heal (like reattaching after being damaged) with moisture, heat, pressure or all three together making it last longer. I thought before doing this experiment that using all three together would work best. I also thought the gelatin plastic will heal better because it was supposed to be more flexible.

The whole world can benefit from these eco-friendly options to help the environment.

HOW?

I made two types of biodegradable plastics:

1) Cornstarch biodegradable plastic (starch based)

combine 1 Tbsp cornstarch, 1 tsp vinegar, 1 tsp glycerin and 4 Tbsp water into a small pot on low to medium heat

stir mixture until it thickens into a gel

pour mixture onto parchment paper or petri dish, spread evenly

2) Gelatin biodegradable plastic (protein based)

combine 1 package of unflavoured gelatin, 1 tsp glycerin and 4 Tbsp water into a small pot on low heat

stir mixture until fully dissolved with no clumps

pour mixture onto parchment paper or petri dish, spread evenly

Let both plastics dry for 48 hours until it feels plastic like.

Testing how strong each of the biodegradable plastics were:

how many times I could bend it before it broke

how stretchy it was/how much force it took to break

Testing self healing properties on biodegradable plastics

1) Damage the plastic by cutting equal sized pieces of either kind of plastic

2) Test the healing ability with each:

moisture - lightly mist damaged edges or wet with warm water and press together

heat - warm edges with blow dryer and press together

pressure - press edges together using hands or clips and hold for 30 seconds to 1 minute

all three together, apply all (water, heat and pressure) as mentioned above

3) allow the repaired pieces to heal for 12 hours

Testing the strength of healed plastic:

1) Test by seeing how many times you can bend it before it breaks or test the stretch ability

2) Record results and compare the healed plastic to regular biodegradable plastic (non healed) and compare the different healing abilities.

For every result I tested it three times and chose the best result but they were overall almost the same when I tried three times.

WHAT?

Table 1

This table shows the strength of my biodegradable plastic before it got healed. I tested the non healed plastic on stretch ability and how many times I could bend it before it broke. You can see that the starch based plastic had very good stretch ability but did not do well on how many bends before it broke. The protein based (gelatin) plastic had absolutely amazing stretch ability because I could not tear it with my bare hands, very strong. It was also very flexible because I did over 100 bends and it did not break.

Table 2

This table shows how each biodegradable plastic healed with different healing conditions (moisture, heat, pressure or all together). The categories I rated the healed plastics on was: not at all, poorly, good and great. In the great category was protein based plastic healed with moisture and protein based plastic healed with pressure. In the good category was starch based plastic healed with moisture, protein based plastic healed with heat and starch based plastic healed with all three. In the poorly healed category was starch based plastic healed with heat and protein based plastic healed with all three. Lastly, starch based plastic healed pressure was in the not at all category.

Table 3 - Graph 1

In graph 1, it shows the how many times you can bend it before it breaks and it was just comparing the results of the different healing conditions. This table is the strength of the starch based biodegradable plastic after being healed. I tested it with stretch ability and how many times I could bend it before it broke. The stretch ability for starch based plastic healed with water and starch based plastic healed with heat was poor. The stretch ability for the starch based plastic healed with pressure was terrible. The stretch ability for the starch based plastic healed with all three was decent.

Table 4 - Graph 2

In graph 2, it shows the how many times you can bend it before it breaks and it compares the results of the protein based biodegradable plastics after it got healed with different healing conditions. This table shows the strength of the protein based plastic after being healed with different healing conditions. I tested it with stretch ability and how many times I could bend it before it broke. The stretch ability for the protein based plastic healed with all three was poor. The stretch ability for the protein based plastic healed with heat was decent. The protein based plastic healed with water had an amazing stretch ability because it did not break with all my force. The protein based plastic healed with pressure also had a great stretch ability because it was very stretchy but it broke after a long time.

SO WHAT?

In my project I tested two types of biodegradable plastic, gelatin (protein based) and cornstarch (starch based). What I thought was going to happen was wrong because it was not all three healing properties that worked the best. Moisture healed the best for the protein based plastic and pressure did very good for the protein based but did very poorly for the starch based one. I was right about the how the gelatin biodegradable plastic would heal better and be more flexible. I think the gelatin was overall better than the cornstarch one because it was more flexible, healed better and stronger when I tested its strength. I think the moisture did the best at healing the plastics because it kind of made the plastic sticky and it allowed the molecules to create bonds with each other more easily. Both plastics are still good because they are made from natural materials which is great for the environment and if used more will cause less pollution. They would be great alternatives for regular plastics.

With the findings of my project, the biggest thing I learned was that if biodegradable plastic gets damaged it can heal itself. It can be done with heat, moisture, pressure or all three but moisture and pressure worked the best to heal.

WHAT'S NEXT?

To continue my project and further my research I would firstly test the biodegradable plastic and the healed biodegradable plastic with more strength tests. Secondly, try to make bowls, cups or straws out of biodegradable plastic to see if it actually would work. I would also reach out to biodegradable companies to expand my knowledge on this topic - to see what all my biodegradable plastic can do.

I would do more tests and make an overall average for my results. Lastly, I would of tested how long it took to biodegrade completely in different conditions.

Firstly, I would like to thank my mom for always being there and for supporting my journey through this. I would also want to thank her because she bought all of supplies making my project possible. Secondly, I would like to thank my teacher Mr.Fines for overall guiding me on how to make a science project. Lastly, I want to thank the Prince Albert Science Fair Committee and especially Trista and Kami for making all of this possible.

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