Biodegradable plastic facts for kids

Disposable plastic cups made from biodegradable plastic

Biodegradable plastics are special kinds of plastics that can be broken down by tiny living things, like microbes (germs). When they break down, they turn into water, carbon dioxide, and natural materials. These plastics are often made from things that grow, like plants, or from tiny organisms, or even from oil, or a mix of these.

It's important to know that "bioplastic" and "biodegradable plastic" are not the same thing. A bioplastic is made from natural sources, but it might not always break down easily. And some biodegradable plastics are made completely from oil. Many companies want to show they are "Green," so they are looking into using bioplastics. But some people are not sure if bioplastics will really solve all our plastic problems.

How Biodegradable Plastics Started

Scientists first noticed a natural plastic called PHA in bacteria way back in 1888. Later, in 1926, a French scientist named Maurice Lemoigne figured out what it was after getting it from a type of bacteria.

It wasn't until the 1960s that people started thinking about making these plastics on a large scale. But it was hard to make enough, and it cost too much.

Then, in 1973, when oil prices went up, companies started investing more in making plastics from natural sources. A company called Imperial Chemical Industries (ICI) in the UK successfully made a type of PHA. But production slowed down because the plastic wasn't perfect, and oil prices went back down.

In 1983, ICI created a company called Marlborough Biopolymers to make the first widely used biodegradable plastic, called Biopol. It was still too expensive to really change the market. In 1996, another company, Monsanto, found a way to make one of the parts of Biopol in plants, which could make it cheaper.

When oil prices went up again in the early 2000s, plastic makers finally started looking seriously at these natural plastic options. Since then, many new types of biodegradable plastics have been created from plants, seaweed, and even plant waste.

What Are Biodegradable Plastics Used For?

Biodegradable plastics are often used for things we throw away after one use. This includes packaging, plates, forks, spoons, and food containers.

These plastics could replace many regular plastics, but there are some challenges:

• Many biodegradable plastics need special industrial composting places to break down properly. If they end up in regular trash (like landfills) or in nature (like rivers or oceans), they might not break down. This can even make plastic pollution worse.
• Some plastics labeled "biodegradable" only break into tiny pieces called microplastics. These tiny pieces might not break down completely, which isn't much better than regular plastic.
• A study in 2009 found that using biodegradable plastics only made financial sense when there were rules limiting regular plastics. For example, in Italy, biodegradable plastic bags have been required since 2011.

Kinds of Biodegradable Plastics

Developing biodegradable containers

Plastics Made from Natural Sources

Developing an edible casein film overwrap at USDA

These plastics, also called bioplastics, are made from natural things like plants, animals, or tiny living organisms.

Polyhydroxyalkanoates (PHAs)

PHAs are a type of biodegradable plastic made naturally by different tiny organisms (like a bacteria called Cupriavidus necator). Scientists can make these organisms produce more PHA by giving them lots of carbon (like sugar) but not enough of other nutrients. The PHA is then collected from the organisms.

PHAs come in two main types:

• scl-PHA are made from short chains of carbon atoms (3 to 5). Many bacteria, including Cupriavidus necator, make these.
• mcl-PHA are made from medium chains of carbon atoms (6 to 14). For example, a bacteria called Pseudomonas putida can make these.

Polylactic Acid (PLA)

Polylactic acid (PLA) is a type of plastic made from things that can be regrown, like fermented plant starch. This starch often comes from corn, cassava, sugarcane, or sugar beet pulp. In 2010, PLA was the second most used bioplastic in the world.

PLA can be composted, but it doesn't break down easily outside of special composting places. (See the section on #Home compostable plastics.)

Starch Blends

Starch blends are plastics made by mixing starch with other substances that make them more flexible. Starch on its own can be brittle. While all starches can break down, not all the things mixed with them can. So, how well a starch blend breaks down depends on what it's mixed with.

Some biodegradable starch blends include starch mixed with polylactic acid, polycaprolactone, or polybutylene-adipate-co-terephthalate. Other blends, like starch mixed with polyolefin, do not break down.

Cellulose-based Plastics

Cellulose bioplastics are mostly made from cellulose esters, like cellulose acetate. Cellulose can become plastic-like when changed a lot. Cellulose acetate is an example, but it's expensive, so it's not often used for packaging.

Lignin-based Polymer Composites

Lignin-based plastics are made from lignin, a natural material found in plants. Lignin is a byproduct when we make paper or ethanol from plants. There's a lot of it available, with millions of tons created each year by paper factories.

Lignin is good because it's light, and it's better for the environment. When lignin breaks down, it doesn't release carbon dioxide (CO₂), unlike some other plastics. Lignin is also strong, flexible, and can even help stop germs from growing. Because it's so common and has good properties, lignin is becoming a promising environmentally friendly plastic material.

Plastics Made from Oil

Most common plastics made from oil, like PET, polyethylene (PE), polypropylene (PP), and polystyrene (PS), do not break down naturally. However, some plastics made from oil can be biodegradable.

Polyglycolic Acid (PGA)

Polyglycolic acid is a plastic often used in medicine, for example, in stitches that dissolve. It can break down into a harmless substance called glycolic acid. This process can happen faster with the help of certain enzymes. In the body, glycolic acid can be turned into water and carbon dioxide.

Polybutylene Succinate (PBS)

Polybutylene succinate is a plastic that feels similar to propylene. It's used in packaging for food and makeup. In farming, PBS is used as a plastic film that covers soil and can break down. Different types of microbes can break down PBS.

Polycaprolactone (PCL)

Polycaprolactone (PCL) is used in medical implants because it can break down in the body. Certain bacteria and fungi can break down PCL. Some types of bacteria can even break it down without oxygen.

Poly(vinyl Alcohol) (PVA, PVOH)

Poly(vinyl alcohol) is one of the few plastics that can dissolve in water and also break down naturally. Because it dissolves in water (which is cheap and safe), PVA is used in many things like food packaging, fabric coatings, paper coatings, and health products.

Polybutylene Adipate Terephthalate (PBAT)

Polybutylene adipate terephthalate (PBAT) is a type of plastic that can break down naturally.

Home Compostable Plastics

Some plastics are designed to break down in a home compost pile, not just in big industrial composting places. There isn't a single international rule for these yet, but countries like Australia and France have their own rules. These rules help make sure that plastics labeled "home compostable" really do break down at home.

Some examples of plastics that meet these home composting standards include certain types of BioPBS, BWC, Ecopond, and Torise resins, often used for thin films.

What Makes Plastics Break Down?

Whether a plastic item breaks down depends on many things, not just the plastic itself. It also depends on the environment where it ends up. How fast plastic breaks down in a certain place depends on things like temperature and if the right tiny organisms are there.

Inside the Plastic

• Chemical makeup: Some chemicals in plastics break down more easily than others.
• Physical features: The shape, how much surface area is exposed, and the thickness of the plastic can also affect how fast it breaks down.

Outside the Plastic

• Non-living factors: Things like temperature, how much water or salt is in the air, sunlight, and water can all affect breakdown.
• Living factors: The presence of the right kinds of tiny organisms (microbes) is very important.

How Biodegradable Plastics Affect the Environment

Good Things for the Environment

Broken Down by Microbes: The main goal of biodegradable plastics is to replace regular plastics that stay in landfills for a very long time and harm nature. The fact that tiny organisms can break down these plastics is a huge environmental benefit. This process happens in three steps: first, microbes stick to the plastic; then, they release enzymes that break the plastic's bonds; finally, the plastic turns into water and carbon dioxide. Even though CO₂ is released, biodegradable plastics generally have a smaller impact than regular plastics that pile up and cause pollution.

Less Trash in Cities: In 2010, the US had 31 million tons of plastic waste, which was a big part of all city trash. Only a small amount of this plastic was recycled. Regular plastics often get mixed with food scraps, wet paper, and liquids, making them hard to recycle and leading to more trash in landfills.

Composting is a great way to deal with mixed organic waste (food scraps, yard trimmings, and wet paper). Biodegradable plastics can replace the non-degradable plastics in this waste. This means that composting can become a much bigger tool to keep large amounts of trash out of landfills. Compostable plastics offer the good qualities of plastics (lightweight, strong, cheap) but can also fully break down in a composting facility. Instead of worrying about recycling small amounts of mixed plastics, supporters say that certified biodegradable plastics can be easily mixed with other organic waste. This allows a much larger part of our trash to be composted.

This shift can make commercial composting for all mixed organic waste more practical and affordable. More cities can send less waste to landfills, helping to reduce plastic pollution.

So, using biodegradable plastics is seen as a way to fully recover large amounts of city waste that couldn't be dealt with in other ways besides landfills or burning.

Worries for the Environment

Oxo-biodegradation: Some people worry that certain "biodegradable" plastic bags might release metals or take a very long time to break down. They also worry that these plastics might just break into tiny pieces that don't disappear. However, the Oxo-biodegradable Plastics Association says their plastics don't contain harmful metals, only safe metal salts. They also say that their plastics can break down significantly in soil over time.

Effect on Food Supply: There's also a big discussion about how much energy, fossil fuels, and water are used to make biodegradable bioplastics from natural materials. Some worry if this process negatively impacts the human food supply. For example, making 1 kilogram (about 2.2 pounds) of polylactic acid (PLA), a common compostable plastic, needs 2.65 kilograms (about 5.8 pounds) of corn. Since a lot of plastic is made each year, replacing all regular plastic with corn-based PLA would use up a huge amount of corn that could be food. This is a concern, especially as global warming affects farm productivity.

Methane Release: Another concern is that methane, a greenhouse gas, might be released when any biodegradable material, including truly biodegradable plastics, breaks down in a landfill without oxygen. In the US, many landfills capture this methane gas to use for energy. Some even burn it off to reduce methane going into the air. Burning non-biodegradable plastics also releases carbon dioxide. If non-biodegradable plastics made from natural materials end up in landfills without oxygen, they can last for hundreds of years.

Breaking Down in the Ocean: Biodegradable plastics that haven't fully broken down sometimes end up in the oceans. People might assume they will break down quickly there. However, the ocean is not the best place for biodegradation because the process works best in warm places with lots of microbes and oxygen. Any plastic pieces that don't break down can harm marine animals.

Energy Needed to Make Them

Scientists have studied how much energy it takes to make biodegradable plastics compared to regular plastics made from fossil fuels. For example, making 1 kilogram (about 2.2 pounds) of PHA (a type of biodegradable plastic) can take about 50.4 to 59 MJ of fossil fuel energy. PLA (another biodegradable plastic) was estimated to take 54-56.7 MJ/kg. However, new ways of making PLA have reduced its fossil fuel energy use by using wind power and other natural sources. Now, it can take as little as 27.2 MJ/kg, and they expect it to drop even lower. In comparison, regular plastics like polypropylene and high-density polyethylene need much more energy (85.9 and 73.7 MJ/kg, respectively).

One study found that making PHA required more total fossil fuel energy than polyethylene. The decision to use biodegradable plastics will depend on what society values most: energy, environment, or cost.

It's important to remember that these new technologies are still developing. The energy needed to make PHA, for example, could be reduced by changing how it's made or by using food waste as a starting material. Using other crops like sugar cane instead of corn could also lower energy needs. For example, making PHAs in Brazil uses less energy because they use a byproduct of sugar cane processing for power.

Many biodegradable plastics made from renewable sources (like starch, PHA, PLA) also compete with food production because they often use corn. If the US wanted to make all its current plastic output using biodegradable plastics, it would need a lot of land for growing corn.

Rules and Standards

To make sure products labeled "biodegradable" are truly what they say, certain rules and standards have been set up.

United States

ASTM International sets up ways to test biodegradable plastics. They test how plastics break down with and without oxygen, and even in marine (ocean) environments.

• For conditions without oxygen:

* ASTM D5511-18 and ASTM D5526-18 say that at least 70% of the plastic should break down within 30 days (or the test time) to be called biodegradable in these conditions.

• For conditions with oxygen:

* ASTM D6400 and ASTM D6868 describe how to test and label plastics that are meant to be composted with oxygen in city or industrial facilities. Plastics are considered biodegradable if 90% of the material turns into CO₂ within 180 days (about 6 months).

European Union Standards

• For conditions without oxygen:

* EN 13432:2000 is a standard for packaging that can be recovered through composting and biodegradation. Like the US standards, it requires 90% of the plastic to turn into CO₂ within 6 months.

• For conditions with oxygen:

* EN 14046:2004 evaluates how well packaging materials break down and fall apart under controlled composting conditions.

• Future European Standards: In 2021, experts advised the European Commission to create new rules for how plastics break down in nature (like in soil, rivers, and oceans). They want to check how well plastics actually break down, assess environmental risks, and create clear labels for people to know how to dispose of biodegradable plastics correctly.

British Standards

In October 2020, British Standards released new rules for biodegradable plastic. To meet these rules, biodegradable plastic must break down into a wax that has no microplastics or nanoplastics within two years. This breakdown can be started by sunlight, air, and water. One company, Polymateria, said they made plastic film that broke down in 226 days and plastic cups that broke down in 336 days.

How Genetic Engineering Helps

With growing worries about plastic waste, scientists are using genetic engineering and synthetic biology to make biodegradable plastic production better. This means changing the natural genetic code or other biological systems of organisms.

Back in 1995, a paper talked about using synthetic biology to make more PHAs (a type of biodegradable plastic) in Arabidopsis plants. In 1999, another study looked at how oil seed rape plants could be genetically changed to make PHBVs. Even though they didn't get a lot of plastic, it showed early efforts in using genetic engineering for this purpose.

Scientists are still working on this. A 2014 paper described how genetic engineering helped increase the amount of biodegradable plastic made by cyanobacteria (a type of algae). They changed the cyanobacteria to produce more of certain proteins, which led to more PHBs.

Currently, a student group at the University of Virginia (Virginia iGEM 2019) is genetically engineering Escherichia coli bacteria to turn styrene (a building block of polystyrene plastic) into P3HBs (a type of PHA). This project aims to show that waste polystyrene can be used to make biodegradable plastic, helping with both polystyrene waste and the high cost of making PHAs.

Biodegradable Conducting Plastics in Medicine

Biodegradable Conducting Polymers (CPs) are special plastic materials designed to be used inside the human body. They can conduct electricity, like regular conductors, but they can also break down naturally. These materials are very useful in medicine, especially for things like tissue engineering and regenerative medicine.

In tissue engineering, these plastics can help damaged organs repair themselves by giving them signals. In regenerative medicine, they help new cells grow and improve the body's healing process. Biodegradable CPs can also be used in medical imaging and implants.

Scientists started designing these CPs by mixing biodegradable plastics like polylactides and polycaprolactone with conductive materials. Now, they are engineering CPs that are even better for medical use. These new CPs have conductive parts built into their structure. They can also be designed so that their parts break down when exposed to things like acid, heat, or enzymes. There are three main types of biodegradable CPs based on their chemical makeup:

• Partially biodegradable mixtures of conductive and biodegradable plastics.
• Conductive parts made of biodegradable CPs.
• Modified parts and links that can break down in biodegradable CPs.

See also

• Biodegradation
• Biodegradable bags
• Cellophane
• Microplastics
• Photodegradation
• Plastic bag