The Decomposition of Starch-based Bioplastics

By Shelby Hack
Junior Category (Grades 7-8)
Experiment | Energy and Natural Resources, Environment

In this project, I made three types of bioplastics and monitored their rates of decomposition in four different environments. I compared the bioplastics to conventional plastic and to each other. My purpose was to determine if I could make I bioplastic that would biodegrade in various environments.

Conventional plastics are flawed in multiple ways concerning the environment, such as their fossil fuel intake, and their rates of decomposition. Fossil Fuels are a non-renewable resource because it takes millions of years in the right conditions for fossil fuels to form. Fossil fuels also cause conventional plastics to never break down. They only break up into microplastics that pollute our oceans and eventually our food and water. Currently, 90% of North American drinking water is polluted with plastic micro fibres. You can see why I want a better solution.

All plastics are made up of polymers which are large molecules made up of repeating chains of smaller molecules called monomers. Conventional plastics have a petroleum-based polymer, bioplastics have a plant-based polymer. My bioplastics use potato starch, corn starch and tapioca starch for their polymers. I placed a sample of each type of bioplastic along with a sample of LDPE (conventional plastic) in each environment. My environments were: Cold seawater, to mimic the ocean, soil, to mimic a home compost, an outside ground surface, to mimic litter, and a control environment in my house. Before I placed each sample, I weighed it and measured the surface area.

My hypothesis was Starch-based bioplastics will begin to decompose more quickly that conventional plastics under a variety of environmental conditions. Different types of starch-based bioplastics will decompose at equal rates. Starch-based bioplastics will biodegrade more slowly in cold seawater than on an outside ground surface, but will degrade most quickly when buried in soil. Conventional plastics will not show signs of degradation in the same timeframe. Neither conventional plastics nor starch-based bioplastics will biodegrade in open air.

After one week my hypothesis was not supported by the data. In the soil environment, the tapioca bioplastic had biodegraded beyond the naked eye, the corn bioplastic had broken onto large pieces, and the potato seemed almost strengthened. Similar results followed in outside ground and seawater. Curiously, the open air (control) samples had all grown slightly. My guess is due to absorbing humidity. The mass and surface of the bioplastics grew in the first week, but then decreased in the second week. That show that they did in fact biodegrade. The conventional plastics showed no signs of biodegradation. All of the bioplastics absorbed moisture, which would be a flaw if they were put into commercial use.

My bioplastics were not perfect by any stretch, but I think they showed that if a twelve-year-old kid can make biodegrading bioplastics in their kitchen; companies can surely find a way to use bioplastics. I had some measurement issues that made some of the data unusable. I learned so much and would gladly do my project again. I made mistakes but I think that my project was still innovative, experimental, and a lot of fun. I did this on my own with some support from my mom in procedure but the ideas and writing are my own.

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