Biopolymers and biodegradable plastics
Faced with the environmental challenges posed by traditional plastics, global attention has turned toward “green” alternatives. In this context, terms like biopolymers, bioplastics, and biodegradable plastics are widely used, but they often come with considerable confusion.
The main ambiguity lies here: Is plant-based plastic (made from sources like cornstarch) necessarily biodegradable? Is every biopolymer fully “biodegradable”? The answers to these questions are not always straightforward, and understanding their technical differences is essential for industries, researchers, and informed consumers.
What is a biopolymer and what does bioplastic mean
To understand this field, we must first familiarize ourselves with two basic and very important terms. Biopolymers and bioplastics are often used interchangeably, but they have different definitions. “Bioplastic” is a broader, umbrella term of which “biopolymers” are a subset.
What is a biopolymer
Biopolymers are polymers produced directly by living organisms (such as plants, bacteria, or algae). These materials are present in the cellular structure of those organisms. In other words, they are part of the natural carbon cycle, and their origin is entirely biological.
Classic examples: cellulose (found in wood and cotton), starch (energy storage in plants), chitin (in the exoskeleton of arthropods), and proteins.
Microbial examples: polyhydroxyalkanoates (PHA), which are produced by certain types of bacteria as an energy reserve
What is Bioplastic
Bioplastic is a broader, more commercial term that refers to a category of plastics that have at least one of these two characteristics:
Be bio-based: meaning all or part of their raw materials are derived from renewable resources (such as corn, sugarcane, potatoes).
Be biodegradable: meaning they can be broken down by microorganisms.
The key point is that a “bioplastic” does not necessarily have both of these properties at the same time. This is precisely where the confusion begins, and we will address it in the next section.
Classification of Bioplastics (Based on Source and Degradability)
To fully understand bioplastics, we must classify them based on two completely independent and separate criteria
the source they are made from, and 2) their degradability or ultimate fate
These two criteria are not directly related, and it is the misunderstanding of this intersection that is the root of the confusion. This classification creates four main groups of plastic materials.
Group 1: Bio-based and Biodegradable
This group is what consumers often expect from a “green plastic.” The materials in this group are both made from renewable sources (plant-based or microbial) and are broken down by microorganisms under suitable conditions.
Key examples:
Polylactic acid (PLA): (made from corn starch, industrially compostable).
Polyhydroxyalkanoate (PHA): (produced by bacteria, biodegradable in a natural environment).
Starch-based blends.
Group 2: Bio-based but non-biodegradable
This group includes plastics that are made from plant-based sources, but their final chemical structure is exactly the same as traditional petroleum-based plastics. These materials are not biodegradable at all and should be recycled like regular plastic. These materials are also called “Drop-in.”
Key examples:
Bio-PET (Bio-Polyethylene Terephthalate)
Bio-PE (Bio-Polyethylene) (both are often produced from sugarcane ethanol)
Group 3: Petroleum-based but biodegradable
This category is often surprising. These plastics are made entirely from fossil sources (oil), but their molecular chemical structure is such (often including weak ester bonds) that it can be broken down and degraded by microbes.
Key examples:
PBAT (polybutylene adipate terephthalate)
PCL (polycaprolactone)
Group 4: Petroleum-based and non-biodegradable
This group includes all traditional and common plastics (like standard PE, PP, PET) that are made from petroleum and will remain in the environment for hundreds of years
The Most Important Question: The Difference Between Bio-based and Biodegradable Plastic
These two terms cause more confusion than any other phrase in this field. Understanding the difference between bio-based and biodegradable plastic is the key to properly evaluating new plastic materials. These two concepts answer two completely separate questions: “What is it made of?” versus “What will its fate be?”
What is bio-based plastic?
Biobased plastic refers to the source or feedstock of the plastic. A plastic is considered “biobased” when all or part of its carbon content is derived from renewable biological sources (such as corn starch, sugarcane, potato, or cellulose), rather than from fossil sources (petroleum).
Standards like ASTM D6866 measure the Biobased Carbon Content.
The critical point is that a plastic being “biobased” provides no information about how it will degrade or its end-of-life fate.
What is biodegradable plastic?
Biodegradable plastic refers to the end-of-life fate of that plastic. This term relates to the chemical structure of the material. A plastic is “biodegradable” when it can be consumed by microorganisms (such as bacteria or fungi) and broken down into simple natural substances like water, carbon dioxide (CO2), and biomass.
This capability is not dependent on the source of the material (petroleum-based or plant-based), but rather on the presence of breakable chemical bonds (such as ester bonds) in the polymer structure that can be acted upon by microbial enzymes
Common Types of Biopolymers and Bioplastics
Now that we are familiar with the key categories and definitions (bio-based, biodegradable, and compostable), it is time to examine the most common materials available on the market. Each of these types of biopolymers and bioplastics has its own specific properties, applications, and limitations. In this section, we will introduce the four main groups that are most widely used in the industry today.
Polylactic Acid (PLA)
Polylactic acid (PLA) is undoubtedly the most well-known and widely used bioplastic in the world. It is an aliphatic polyester produced from renewable sources like corn starch or sugarcane. Its production process involves fermenting plant sugar into lactic acid and then polymerizing it.
The main characteristic of PLA is its rigidity and transparency, but it is also brittle. PLA is bio-based (Group 1) and breaks down under industrial composting conditions (according to the EN 13432 standard), but it does not break down easily in the natural environment (such as soil or the ocean). Its main applications include plant-based disposable containers (cups, food containers) and 3D printing filament
Polyhydroxyalkanoate (PHA)
Polyhydroxyalkanoates (PHAs) are a family of biopolymers produced by certain types of bacteria. In response to specific environmental conditions (such as a nutrient deficiency), these bacteria store excess carbon in the form of PHA granules inside their cells (similar to how animals store fat).
The unique feature of PHA is its true biodegradability. Unlike PLA, many grades of PHA can degrade not only in industrial compost but also in natural environments such as soil, freshwater, and even seawater. This characteristic makes PHA a very attractive option for applications that are likely to be released into nature. Its main challenge is its much higher price and smaller-scale production compared to PLA.
Starch-Based Biopolymers
Starch is, in itself, an abundant, inexpensive, and fully renewable biopolymer. However, pure starch (starch thermoplastic or TPS) absorbs moisture heavily and has poor, brittle mechanical properties. For this reason, it is rarely used on its own.
In commercial applications, starch is usually blended with other polymers (whether biodegradable, like PLA or PBAT). This both reduces the final product's cost and improves its physical properties (like flexibility). Compostable shopping bags are often an example of these blends.
Petroleum-based Biodegradable Plastics (PBAT and PCL)
As we saw in Group 3 of the categorization, these materials are made entirely from fossil (petroleum) sources, but due to their specific chemical structure, they are biodegradable (and compostable)
The Future of Bioplastics and Their Role in the Circular Economy
Current challenges with bioplastics, particularly competition with food sources (such as corn for PLA), have driven research toward new and more sustainable feedstocks. The future of the industry depends on developing materials that utilize waste or non-edible sources.
The main focus is on using lignocellulosic biomass—such as agricultural waste, wood, or sugarcane bagasse—as feedstock. Additionally, the use of algae as a fast-growing source that does not compete with agricultural lands has gained serious attention.
In this scenario, polymers like PHA play a key role, as their production process (microbial fermentation) can be fed by diverse waste streams, including industrial effluents or food waste. This approach transforms plastics from a linear product (production, consumption, disposal) into part of a Circular Economy, where waste from one sector becomes the raw material for another
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