Biodegradable Water Bottles

Categories: Recycling


The purpose of this experiment is to find the best biodegradable alternative material to make plastic water bottles.


Which out of three homemade biodegradable plastics can replaces plastic used to make water bottles without deteriorating?


Each second 1500 plastic water bottles are used in the U.S. and people throw away approximately 60 million each day according to the Container Recycling Institute (CRI). The University of Columbia revealed that only 12 percent of water bottles have been recycled the rest are in landfills, litter roads, parks, and waterways.

Water bottles make up most of the plastic pollution in the ocean. Normal plastic bottles take much more water to manufacture than what ends up in them. Recycling seems to be the solution to this problem; however, only half of what is sent to be recycled is recycled. Since water bottles take 1000 years to decompose there needs to be a biodegradable alternative that does not decompose before the water bottle is used.

The three homemade biodegradable plastics being tested are made of:

  • Milk and vinegar
  • Cornstarch, oil and water
  • Gelatin and water

When milk and an acid-like vinegar are mixed the casein from the milk separates and the lumps can be removed and dried to form the plastic.

This reaction is quicker if it is heated. Cornstarch mixed with water and cooking oil makes bioplastic when the cornstarch is heated and its polymers attach and form long chains. Gelatin and water create bioplastic because gelatin is made of broken-down collagens that have long chains that bind molecules together.

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When gelatin is heated the chains loosen so when water is added, hydrogen atoms bond with the water to form a Jell-O-like consistency that hardens when it dries. Since the gelatin chains are loosened in water they might disintegrate faster in water, the cornstarch also has long chains so it may have the same reaction, the milk and vinegar bioplastic is made of casein, which is insoluble in water so it may last longer than the others.


I hypothesize that the biodegradable plastic made with milk and vinegar will work best because it is made of casein which is insoluble in water.



Type 1.

  • 1 TBSP of corn starch
  • 1 ½ TBSP of water
  • 3-5 drops of cooking oil
  • Microwave
  • Two small bowls

Type 2.

  • 4 tsp of gelatin
  • ¼ cup hot water
  • Saucepan
  • Stove or hotplate
  • Parchment paper
  • One small bowl

Type 3.

  • 1 of p milk
  • 4 TBSP of vinegar
  • Strainer
  • Towel
  • Saucepan
  • One small bowl


  • Gloves
  • Goggles
  • Lab Coat


  1. For the first type of plastic, begin by adding one TBSP of corn starch, 1.5 TBSP of water, and 3-5 drops of cooking oil into a small microwavable bowl
  2. Mix until the liquid becomes milky looking
  3. Microwave liquid for 30 seconds. It should start to bubble and be slightly transparent
  4. Let cool for approximately five minutes then mold into a thin sheet
  5. Leave it in a room temperature area for 24 hours to become solid
  6. For the second type of plastic, combine 4 tsp of gelatin and ¼ cup of hot water in a saucepan
  7. Place saucepan on stove or hotplate and continue to stir until it heats to 95 degrees Celsius and begins to froth
  8. Pour substance onto parchment paper on a smooth surface
  9. Leave the plastic to harden for 48 hours
  10. For the third type of plastic, heat one cup of milk to a least 49 degrees Celsius on a stove
  11. Add four tablespoons of vinegar to milk while still hot
  12. Pour liquid through a strainer and let cool
  13. Put the remaining clump onto a towel to remove any excess moisture
  14. Mold it into a thin sheet and let dry on a flat surface for 24 hours
  15. After all plastics are dried add 5 inches of water to three separate bowls
  16. Place each plastic into an individual bowl
  17. Let sit in water for 48 hours
  18. Carefully take plastics out of bowls to observe if they disintegrated


Independent variable: Formula for the plastics

Dependent variable: The durability of the water of plastics

Controlled variable: Sanitation of Environment

Extraneous variable: Human Error


These qualitative results are the average durability of the plastic which was made and tested five times. The percentages are the observable amount of disintegration after 48 hours in water. With 0% being no change and 100% being complete disintegration.

Types Test 1 Test 2 Test 3 Test 4 Test 5

Bioplastic type 1 30% 25% 35% 30% 30%

Bioplastic type 2 15% 10% 20% 15% 15%

Bioplastic type 3 5% 0% 5% 5% 10%

The chart shows that the first type of bioplastic made of cornstarch, oil, and water had the highest disintegration average of 35%. The second type of bioplastic made of gelatin and water had and disintegration average of 15%. The third type of bioplastic made of milk and vinegar disintegrated the least with an average of 5%.


The bioplastic made from milk and vinegar degraded the least in water with an average of 5%. None of the tests on the milk and vinegar plastic showed drastic disintegration. The bioplastic made of gelatin and water had a disintegration average of 15%. It showed a small amount of disintegration in all of the tests which were observable through its loss in mass and because the water it was immersed in for 48 hours was slightly cloudy. The bioplastic made of cornstarch, oil, and water had the highest disintegration average of 35%. Most of the tests on the cornstarch and water plastic showed that it was deteriorating because it got visibly smaller and fell apart during two of the tests. Since the gelatin’s cornstarch chains are loosened in water they might disintegrate faster water they would naturally deteriorate fast in water. The milk and vinegar bioplastic is primarily made of casein, which is insoluble in water so it lasts longer. The bioplastics were tested by if they disintegrated in water because the goal of this experiment is to find a plastic to make biodegradable water bottles. Each test was immersed in room temperate water for 48 hours in a controlled environment. If this experiment could be done again, using a different disintegration measuring system such as testing the specific gravity before and after soaking the plastics in water would be extremely helpful and make the results more accurate. Although the results supported the hypothesis it was surprising how much the cornstarch, oil, and water bioplastic disintegrated in the water.


I accept my hypothesis because the bioplastic made of milk and plastic disintegrated the least during 48 hours in water.

Future Research

In the future, it would be beneficial to test the plastic in water for a longer period. To test the plastics’ real-life application, one could make bottles or cups out of them and observe the bioplastics duration. The bioplastic that disintegrated the least was made from milk and vinegar but during this experiment only a fraction of the materials that were used created the plastic, making it impractical for all water bottles to be made of this. It would be fascinating to see if other kinds of bioplastics don’t disintegrate after 48 hours in water at all.

Cite this page

Biodegradable Water Bottles. (2022, Jul 25). Retrieved from

Biodegradable Water Bottles
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