MSE 02 Biodegradable Plastics Synthesis
- Jinwook Chang
- Oct 8, 2022
- 6 min read
Updated: Oct 3
Learn how to make biodegradable plastics from everyday materials like starch and glycerin, exploring their chemistry, properties, and potential as eco-friendly alternatives to conventional plastics.
Introduction
Plastics are some of the most common textiles used in everyday life as a result of their versatility, durability, and low cost. They have become an indispensable part of modern-day life, used in virtually every industry, from packaging and construction to consumer electronics. Its prominent characteristics include a high tensile strength-to-weight ratio, resistance to moisture, as well as its ability to be shaped into molds. This makes bioplastics ideal for a wide range of applications.
However, the most commonly used types of plastic, which include polyethene terephtalate (PET), High-density polyethene (HDPE), and Polyvinyl Chloride (PVC), aren't biodegradable, meaning that when disposed of, conventional plastics do not break down naturally and can easily accumulate in landfills and oceans and eventually break down to become microplastics. Biodegradable plastics offer an alternative to the use of conventional, environmentally harmful plastics.
Unlike conventional plastics, biodegradable plastics can break down within a matter of weeks in the natural environment, with the help of microorganisms, such as bacteria and fungi. The development and use of biodegradable plastics align with the SDG goals of promoting sustainable cities and communities, as well as responsible consumption and production.
Aim
This experiment aims to investigate the synthesis of biodegradable plastics made from everyday goods and to evaluate their potential as an alternative to conventional petroleum-based plastics.
Context
With the estimated number of plastics created each year at around 400 million tonnes, this figure is expected to rise significantly by 2040, indicating that plastic pollution already poses significant harm to ecosystems, including our own. Around 9% of plastics are either recycled or reused, which means that over 360 million tonnes of plastic is discarded in landfills, oceans, or the environment every year. Additionally, traditional plastics can take hundreds of years to decompose, which contributes to environmental pollution, as well as the accumulation of microplastics. In comparison, bioplastics, which are made from sustainable resources, only take a couple of months to degrade back into natural waste products.
Theory
Biodegradable plastics are often composed of renewable raw materials, such as starch, polylactic acids, or polyhydroxyalkanoates, which are chosen because of their ability to be consumed by microorganisms and broken down into environmentally friendly substances such as water, carbon dioxide, and biomass. A combination of microbial activities and enzymes targets and breaks down the bonds found within the plastic’s polymer chains, turning it into smaller fragments that are to be consumed and converted into metabolic products by microorganisms.
Materials
Cornstarch (or any starch powder) - 1 tablespoon
Glycerin - 1 teaspoon (available at pharmacies or online)
White vinegar - 1 teaspoon
Water - 4 tablespoons
Heat-resistant non-stick pan or small saucepan
Stirring spoon or spatula
Measuring spoons
Aluminum foil or a silicone mat (for drying)
Optional: Food coloring, glitter, or natural dyes (for customization)
Procedure
Step 1: Preparing the Mixture
Measure Ingredients:
In the saucepan, mix 1 tablespoon of cornstarch with 4 tablespoons of water. Stir until the starch dissolves completely.
Add 1 teaspoon of vinegar and 1 teaspoon of glycerin to the starch-water mixture.
Optional Customization:
If desired, add a few drops of food coloring or natural dye to customize the plastic’s color.
Stir well to ensure even distribution.
Step 2: Heating the Mixture
Apply Heat:
Place the saucepan on low to medium heat. Continuously stir the mixture to prevent clumping or sticking.
As the mixture heats, it will begin to thicken and turn translucent.
Monitor Consistency:
Continue stirring until the mixture becomes gel-like and starts pulling away from the sides of the pan. This usually takes 3–5 minutes.
The plastic is ready when it has a dough-like consistency.
Step 3: Shaping the Plastic
Transfer to Drying Surface:
Remove the saucepan from the heat and let it cool slightly for 1–2 minutes.
Spread the mixture evenly onto aluminum foil or a silicone mat to the desired thickness. Use a spatula for smooth application.
Shaping (Optional):
While the mixture is warm, shape it into molds or press objects into it for patterns (e.g., cookie cutters for designs).
Step 4: Drying and Hardening
Air Drying:
Allow the plastic to air dry for 24–48 hours, depending on the thickness.
Avoid disturbing the plastic during this period to prevent cracks or warping.
Optional Faster Drying:
Use a hair dryer or place it in a warm, dry area to speed up the process.
Observations
The dried plastic will feel flexible and slightly elastic, resembling traditional plastic.
Thinner layers will dry faster and be more transparent, while thicker pieces may be sturdier but take longer to dry.
When dried, the bioplastic exhibited flexibility similar to conventional plastics
such as polyethene – the type of plastic commonly found in plastic bags. After being cooled, the bioplastic remained translucent and exhibited properties
similar to those of non-biodegradable plastics, being able to withstand tension
and being highly durable.
Further Testing & Applications
Testing
Strength and Flexibility: Test how strong and flexible the plastic is by bending or cutting it.
Biodegradability: Place a sample in soil or water to observe how it degrades over time compared to traditional plastics.
Application
Use the biodegradable plastic for lightweight packaging, small containers, or as an eco-friendly craft material.
Explore modifications by adjusting the ratios of glycerin (for flexibility) or starch (for firmness) to achieve different properties.
Qualities of Bioplastic
The bioplastic synthesized in this experiment is made from starch, which is a renewable and widely available resource, making it a sustainable alternative to
conventional petroleum-based plastics.
By altering the ratio of glycerin to starch, it is possible to customize the
bioplastics properties and change their flexibility and strength, enabling this
bioplastic to be used for various applications.
Biodegradability is one of the driving factors that makes bioplastics an appealing alternative to petroleum-based plastics, as they can decompose much faster
than other plastics in the natural environment, thus decreasing its adverse
effects on the environment.
By switching over to bioplastics and using renewable materials instead, we can
reduce our reliance on fossil fuels, which can minimize greenhouse gas emissions
associated with the production of plastics.
Economic and Environmental Factors
The cost to produce one kilogram of bioplastics ranges from 2.5-15$, depending
on the quality of the material. This is substantially higher than the average cost of
conventional plastics, which sit at a low price of 1-5$ per kilogram. This increase in cost is likely due to the higher cost of raw materials that are required
to synthesize bioplastics, as well as the lack of maturity of the production
process, which leads to limited large-scale production of bioplastics, keeping
costs high.
By switching over to bioplastics, we can also reduce spending on the cleanup
processes for plastic pollution. Currently, it is estimated that 15 billion USD is
spent annually on the removal of plastic waste. Switching to bioplastics will
reduce plastic pollution cleanup costs and lower overall carbon footprint
because of more sustainable production methods and the biodegradability of
bioplastics.
Furthermore, bioplastics do not contribute to the production of persistent
microplastics, as they do not degrade into permanent secondary microplastics when broken down, as most natural environments are home to microbes
that are able to metabolize these polymers.
Chemical Properties and Structure
Bioplastics are mainly comprised of three elements that are commonly found in all plastics, which are: hydrogen, oxygen, and carbon. Starch-made bioplastics, such as the one made in this experiment, are made from polysaccharides, which are long-chain glucose molecules. Two other notable types of bioplastics include polylactic acid (PLA) bioplastics and polyhydroxyalkanoates (PHAs), with the former being made up of repeating ester bonds, and the latter being comprised of hydroxyalkanoate units being chemically joined with ester bonds. In general, bioplastics are biodegradable, meaning that they can be decomposed naturally in the environment by microorganisms. Additionally, bioplastics are less heat-resistant than conventional plastics and have weaker mechanical properties, such as tensile strength, which can affect durability.
Conclusion
In conclusion, this experiment demonstrated the synthesis of bioplastics using starch as a base and showed the feasibility of using bioplastics as a replacement for conventional petroleum-based plastics. Bioplastics offer a creative solution to the ever-worsening problem of plastic pollution, and with the continuation of manufacturing development and innovation, bioplastics may be able to outcompete the use of conventional plastics by helping us step up our action against plastic pollution and minimize the significant risks it poses to the environment.
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