Types Of Biodegradable Plastics
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The rise of bioplastics is noticeable, but what do we know about biodegradable plastics?
Also, what are the different types of biodegradable plastic?
The types of biodegradable plastics are:
- Bioplastics – produced partly or entirely with biologically sourced polymers. They can be derived from plants or in combination with synthetic polymers. Not all are biodegradable
- Bioplastics – derived from synthetic polymers.
- Oxo-degradable plastics – conventional plastics with additives to break down faster
- Photo-biodegradable – reacts to ultra-violet light, and it requires initial oxo-degradation
- Hydro-biodegradable plastics – made from plant sources (like starch) and the degradation is initiated by hydrolysis
The topic of bioplastics is very tricky, so let’s take a further look at the types of biodegradable plastics, and are there any better than regular plastics.
We will go through:
- What are the types of biodegradable plastics?
- Are biodegradable plastics really biodegradable?
- How do you make plastic biodegradable?
- FAQ: Common MYTHS about bioplastics
- Conclusion
1. What are the types of biodegradable plastics?
Often, a lot of people believe that terms like “bioplastic,” “oxo-degradative plastics,” “biodegradable,” and “compostable” indicate the same thing.
But there’s a vast difference between these terms, and they are not synonymous. Most importantly –
Not all bioplastics are biodegradable.
Let’s take a close look at EACH term, and see the differences between these materials.
Regular plastic:
Traditional plastic is made with chemical fillers that can be harmful to the environment when released when the plastic is melted down.
The average bag is used for ~20 minutes after that it is thrown away. A plastic bag takes 1000+ years to break down into microplastics.
Source: Unfantastic plastic: Review of the act plastic shopping bag ban
Regular plastics hold carbon. When the plastic is disposed of and begins to decompose or when it is melted, that carbon is released into the atmosphere.
Methane and other forms of pollutants could also be released from traditional plastic when they are burned, or thrown in a landfill.
Standard plastic bags are usually made from petroleum, while biodegradable bags are made from plant or organic material, which can decompose much faster.
Worldwide, we use approximately 2 million plastic bags every minute.
Source: Earth Policy Institute: Plastic Bags Fact Sheet
Regular plastics, in particular, will take hundreds, if not thousands of years to break down.
There are 7 different types of non-biodegradable regular plastic:
- Polyethylene Terephthalate (PETE or PET)
- High-Density Polyethylene (HDPE)
- Polyvinyl Chloride (PVC)
- Low-Density Polyethylene (LDPE)
- Polypropylene (PP)
- Polystyrene or Styrofoam (PS)
- Miscellaneous plastics (mixed materials)
Bioplastics:
Plastic is considered bioplastic if it is produced partly or entirely with biologically sourced polymers.
Plus, it will be considered biodegradable if it can degrade into water, carbon dioxide, and biomass in a given time frame (dependent on different standards).
Note that bioplastic isn’t a synonym for biodegradable. Not all bioplastics are biodegradable.
Bioplastic, moldable plastic material made up of chemical compounds that are derived from microbes such as bacteria or by genetically modified plants.
Source: Britannica: Bioplastic
Some biobased plastics are made from renewable resources instead of fossil fuels, but not all of them.
Examples of renewable carbon resources include corn, potatoes, rice, soy, sugarcane, wheat, and vegetable oil.
Usually, most biobased plastic is just partially biobased.
“Biodegradable” means when something is capable of being decomposed by bacteria or other living organisms.
Biodegradable plastic is a plastic that degrades because of the action of naturally occurring microorganisms such as bacteria, fungi, and algae.
Source: Study of the biodegradability of biodegradable plastic
This type of bioplastics are divided into 3 groups according to their origin:
- Bio-based plastic (derived from plants) that IS biodegradable
- Chemically synthesized plastic that IS biodegradable
- Bio-based plastic that is NOT biodegradable
Source: Degradation of oxo-biodegradable plastic
Most biodegradable plastics are a combination of organic materials, such as starch and cellulose, and chemical additives that degrade into carbon dioxide, methane, biomass, water, and mineral salts.
Biodegradable plastics should not release carbon, because usually, no carbon is involved in the manufacturing process.
Read more about biodegradable plastics here.
Oxo-degradable plastics:
Commonly perceived to be biodegradable.
However, they are simply conventional plastics with additives that quicken the breakdown through exposure to sunlight and oxygen.
Source: Oxo-biodegradable plastic association
The additives just promote fragmentation of the materials, meaning that the plastic doesn’t fully degrade – it simply breaks down into tiny fragments that remain in the environment.
Afterward, they persist as huge quantities of microplastics rather than a biological material.
Source: Focus on “biobased”, “biodegradable”, “compostable” plastics
The point of oxo-degradable plastics is to speed up the natural fragmentation processes, into smaller and smaller plastic particles.
However, there is no guarantee that oxo-degradable plastics would receive the necessary treatment of light and heat to start the fragmentation process.
There are two types currently on the market – plant-based hydro-biodegradable plastic and petroleum-based oxo-biodegradable plastic.
All in all, “oxo-degradability” might sound appealing, yet, the term is misleading as such plastics cannot be verified because of the absence of a standard specification.
Photo-biodegradable plastics:
This plastic reacts to ultra-violet light, and it requires initial oxo-degradation.
This means that that type of bioplastic will not degrade in a different environment.
Some other biodegradable forms of plastics are made from sugar, banana peel, avocado, waste frying oil.
These plastics are currently under research.
Hydro-biodegradable plastics:
Hydro-plastics are degrading faster than oxo-degradable plastics, and usually, they can be composted in an industrial composter.
Hydro-biodegradable plastic is made from plant sources (like starch) and the degradation is initiated by hydrolysis.
This type of plastic is temperature resistant, and the only bioplastic that can decompose, both in soil and water.
Compostable plastic:
The main difference between compostable and biodegradable is that compostable products need different and specific settings to break down.
Composting involves accelerating the decomposition of materials through the action of microorganisms – under aerobic conditions.
Compostable plastic degrades in carbon dioxide, water, inorganic compounds, and biomass. It doesn’t leave toxic chemicals.
Since compostable plastic is biodegradable in a composting environment, to be labeled compostable, it must meet precise standards.
Source: Focus on “biobased”, “biodegradable”, “compostable” plastics
Usually, compostable resins are made from potato starch, soybean protein, cellulose, as well as petroleum, and petroleum by-products.
Note that compostable plastics won’t break down on their own, in a landfill, as litter, or in marine environments. They need to be composted at commercial composting facilities.
European Standards for compostable plastics:
- it must break down under industrial composting conditions in less than 12 weeks.
Australian standards for compostable plastic:
- disintegrate after 12 weeks and completely biodegrade after six months. That means that 90 percent or more of the plastic material will have been converted to CO2. The remaining share is converted into water and biomass – i.e., valuable compost.
US standards for compostable plastic:
- No more than 10 percent of the original dry weight of a product must remain after 84 days in a controlled composting test.
- 90 percent of the organic carbon in the test materials must be converted to carbon dioxide within 180 days.
All in all, if disposed of correctly, compostable plastic can be re-integrated into the soil within a few weeks/months.
2. Are biodegradable plastics really biodegradable?
Almost anything can be biodegradable, given enough time.
Furthermore, biodegradation will be successful only if they are under the right conditions.
Biodegradable plastic is made of molecules that can break down naturally, but frequently, there is no particular timescale specified for this degradation. Under the wrong conditions, it can take many years.
For instance, if the biodegradable plastics end up in a landfill, or in the ocean, then the chances are that they will persist on our planet for hundreds of years.
Usually, it is required that biodegradable plastics take three to six months to decompose fully.
But how long a biodegradable item takes to break down will depend on various factors, such as temperature and the amount of moisture.
Biodegradable plastic study
An interesting study (2019) reported that biodegradable plastic bags were still whole after 3 years spent – both inside the sea or buried underground.
Source: Environmental deterioration of biodegradable, oxo-degradable, compostable, and conventional plastic carrier bags (in the sea, soil & open-air) over a 3-year period
Feel free to check a quick video that summaries the study here:
3. How do you make plastic biodegradable?
Most biodegradable plastics are made from traditional petrochemicals but are designed to break down faster.
They include additives that make them degrade rapidly in the presence of light, oxygen, moisture, and heat.
The biodegradable plastics decay faster also because of the naturally occurring microorganisms such as bacteria, fungi, and algae.
That is why biodegradable plastics often have a shorter lifespan in the environment – they can be decomposed into water, carbon dioxide, or methane, and biomass by living organisms, such as microbes.
4. FAQ: Common MYTHS about bioplastics
Biobased plastics are always biodegradable, while fossil-based plastics are never biodegradable?
Biobased plastics are not always biodegradable, and some fossil-based bioplastics are biodegradable.
The truth is that a material can biodegrade, and it does not always depend on its origin (renewable or fossil).
It depends on its chemical structure and if it can be eaten by bacteria, fungi, and algae in a set environment and timeframe.
Are biodegradable plastics always compostable?
First, remember that “biodegradable” and “compostable” are different terms, and they don’t mean the same thing.
Second, some biodegradable plastics aren’t biodegradable NOR compostable.
Are compostable plastics suitable for all industrial composting operations?
It is tricky.
Some standards for compostability require complete biodegradation within 180 days under composting conditions.
Many industrial composters finish their active composting process between 60 and 90 days, or even less.
This may not allow enough time for some products to biodegrade in those timeframes completely.
It depends on its chemical structure and if it can be eaten by bacteria, fungi, and algae in a set environment and timeframe.
Are all compostable plastics suitable for home composting?
No. Some compostable products need industrial composting facilities because they operate at higher temperatures than those found in backyard composters.
Many details conclude if a compostable plastic product will break down in your backyard:
- the type of composting system that you have and the conditions that it is capable of performing (heat, moisture)
- the compostable plastic composition
Can biodegradable plastics break down in landfill?
No. Most landfills will limit or even stop biodegradation because of the lack of oxygen and moisture.
Biodegradable vs. compostable: which one is better?
There might be a situation in which it is indispensable and unavoidable to use some compostable or biodegradable plastics.
If you wonder how to decide which one is the best, composting might be better, as is also a faster process.
However, remember that it requires special conditions.
Home compostable alternatives might be the best option, especially if you have a home composter. Just make sure to get a certified “home compostable” product.
Can you put compostable plastics in your home compost?
Not ALL compostable plastics can biodegrade in your home compost.
They need particular circumstances, such as heat, which is the main factor in the ability of compostable plastic to biodegrade.
Usually, it needs to be taken to an industrial composting facility where it can under the right heat conditions, and biodegradation can begin.
Look for labels, such as “home compostable”, if you want to be sure to get something that can biodegrade in your compost pile.
Sum up
All in all, biodegradable and compostable plastics require stricter standards and a specific environment in which they can decompose into biomass.
The truth is that the diversity of biodegradable materials on the market and their different characteristics make it extremely difficult to figure out what is the proper way to dispose of them.
Additionally, we can’t make generic decisions assuming that all biodegradable products are ‘good.’
In general, it is tricky because each municipality may have different requirements, or they may not have the proper conditions at all.
So, it is best to look into your local recycling, compost, or solid waste operators, so you can make the right choice when it comes to the end-of-life of biodegradable/compostable products.
The BEST thing you can do is to choose reusable, long-lasting, and durable items.
