A polymer is a large molecule made of repeating smaller units, similar to a chain of beads. While many plastics are traditionally made from petroleum, a non-renewable fossil fuel, bio-based polymers are derived from renewable biological sources. These materials come from biomass, which includes plants, animals, and microorganisms, representing a shift toward more sustainable manufacturing.
Sources of Bio-Based Polymers
A primary source for bio-based polymers is starch, a carbohydrate extracted from plants like corn, potatoes, and cassava. The starch from these plants serves as a foundational material for creating different types of bioplastics. Sugars derived from crops are another major feedstock. Sugarcane and sugar beets are cultivated for their high sugar content, which can be fermented and converted into polymer building blocks.
Cellulose, the most abundant organic polymer on Earth, provides another avenue for bio-based plastics. Wood pulp is a primary source, but cotton linters and agricultural waste, such as straw and bagasse, are also used. This structural component of plants can be chemically modified to create various materials.
Polymers can also be derived from oils and fats. Vegetable oils from soy or castor beans are composed of triglycerides that can be chemically altered to form polymers. Animal fats are another source, although they are used less frequently. These lipid-based materials can be used on their own or blended with other polymers to achieve specific properties.
Common Types and Their Production
One of the most widely recognized bio-based polymers is Polylactic Acid (PLA). It is produced from the fermentation of carbohydrate-rich sources. In this process, sugars are fermented by microorganisms to produce lactic acid. This lactic acid is then subjected to a chemical process that links the molecules together, forming the long polymer chains of PLA.
Another class of bio-based polymers is Polyhydroxyalkanoates (PHAs). Unlike PLA, PHAs are produced directly by microorganisms. Certain bacteria, when fed a carbon-rich diet from sources like sugar or lipids, naturally create PHA granules inside their cells as a form of energy storage. These granules are then harvested from the bacteria to be used as a plastic material.
Starch-based polymers represent a different production approach. This method often uses starch in a more direct way by blending it with plasticizers, which are additives that increase the material’s flexibility and processability. This process modifies the inherent properties of the starch, making it behave more like a conventional plastic without fundamentally altering its core chemical structure.
Applications in Modern Industry
The most extensive use of bio-based polymers is in the packaging sector. Materials like PLA are frequently used to make food containers, such as clear clamshells for salads and fruits. Compostable waste bags, disposable cutlery, and cups for cold beverages are also common applications.
Bio-based polymers are becoming increasingly prevalent in consumer goods. They are used to manufacture casings for electronics like mobile phones and have found a market in 3D printing as a primary filament material. Everyday items such as disposable razors and various household goods are also being produced from these materials.
Agriculture and horticulture have adopted bio-based polymers for practical uses. Biodegradable mulch films cover soil to suppress weeds and conserve water before breaking down. Plant pots made from these materials can be planted directly into the ground, where they decompose over time, reducing transplant shock and eliminating plastic waste.
These polymers have also made inroads into the textile and medical industries. Fibers made from PLA can be woven into fabrics for clothing and upholstery. In the medical field, these polymers are used for applications such as dissolvable stitches, systems for controlled drug delivery, and implants used in surgery.
Understanding Biodegradability and Lifecycle
The terms “bio-based” and “biodegradable” are not interchangeable. “Bio-based” signifies that a material is derived from renewable biological sources. In contrast, “biodegradable” describes a material’s end-of-life characteristic, meaning it can be broken down into natural elements by microorganisms under specific conditions. A material’s origin does not guarantee its ability to biodegrade.
This distinction creates four categories of plastics.
- Some materials are both bio-based and biodegradable, such as PLA and PHA.
- Others are bio-based but not biodegradable, like bio-polyethylene (bio-PE).
- Conversely, some petroleum-based plastics can be biodegradable, such as poly(butylene adipate-co-terephthalate) (PBAT).
- Finally, traditional plastics are both petroleum-based and not biodegradable, like conventional polyethylene terephthalate (PET).
The conditions required for biodegradation are specific. A material like PLA will not readily break down in a backyard compost pile, a landfill, or the ocean. It requires the high temperatures, humidity, and specific microorganisms found in an industrial composting facility to decompose effectively. Proper disposal is necessary to realize the environmental benefits of its biodegradability.
A bio-based material that is not biodegradable will persist in the environment just like a conventional plastic if not recycled. Similarly, a biodegradable plastic must be sent to the correct facility to ensure it breaks down as intended. The environmental impact is determined by both the material’s origin and its end-of-life management.