Natural plastics, or bioplastics, are gaining attention as alternatives to petroleum-based materials. Derived from renewable sources like plants and microorganisms, their development is driven by a desire for more sustainable options that lessen the reliance on fossil fuels. This article explores what these materials are, their sources, environmental aspects, and current uses.
Defining Natural Plastics and Key Types
Natural plastics are polymers derived from renewable biomass sources such as vegetable fats and oils, corn starch, or woodchips. A distinction in this category is between “bio-based” and “biodegradable.” Bio-based means the material comes from a natural source, while biodegradable means it can be broken down by microorganisms. Not all bio-based plastics are biodegradable.
One of the most common types of natural plastic is Polylactic Acid (PLA). PLA is derived from the sugars in crops like corn or sugarcane and is known for its rigid, transparent properties, similar to conventional plastics. Another significant category is Polyhydroxyalkanoates (PHAs), which are produced by microorganisms. PHAs are notable because they can biodegrade in a wider range of environments, including soil and marine settings.
Starch-based plastics are another prevalent type, created from sources like corn, potato, or tapioca starch. These plastics are often blended with other materials to improve their properties and are used in applications like loose-fill packaging. Cellulose-based plastics, derived from wood pulp or cotton linters, represent one of the earliest forms of natural plastics. They can be processed to create materials with a variety of textures and flexibilities.
Sources and Production Processes
The production of natural plastics involves several distinct pathways. The raw materials, or feedstocks, for natural plastics are diverse and increasingly focus on non-food sources to avoid competition with food supplies. These include agricultural waste, algae, and energy crops. This approach helps create value from materials that might otherwise be discarded.
For materials like starch and cellulose, the polymers are extracted directly from the plant biomass. The plant matter is harvested, and the desired polymer is separated and purified through physical and chemical processing. It is then treated and modified to be formed into pellets, which can be melted and molded into final products. This method is straightforward as the basic polymer structure already exists in nature.
A more complex method involves fermentation, which is used to create monomers for plastics like PLA. In this process, microorganisms are fed sugars from crops like corn, which they convert into lactic acid. This lactic acid is then purified and undergoes a chemical process called polymerization, where individual molecules are linked together to form the long polymer chains of PLA.
A third method uses microorganisms as tiny factories. To produce PHAs, specific types of bacteria are cultivated in large tanks and fed a nutrient-rich diet, often based on vegetable oils or sugars. Under controlled conditions, these bacteria naturally produce and store PHA polymers inside their cells as an energy reserve. The PHA is then harvested by breaking open the cells and extracting the polymer.
Environmental Aspects and Biodegradation
The environmental profile of natural plastics is complex, depending on how they are made, used, and disposed of. A benefit is their renewable origin, which can reduce dependence on fossil fuels. The production of some bio-based plastics can also result in a lower carbon footprint than their petroleum-based counterparts, though this varies with agricultural practices and manufacturing energy.
The term “biodegradable” requires specific conditions. Many natural plastics, like PLA, are compostable, meaning they break down into natural elements only in the high-temperature, microbe-rich environment of an industrial composting facility. They will not readily decompose in a backyard compost bin, a landfill, or the ocean, a distinction that is important for end-of-life management.
Production issues include land and water use for feedstock crops. The cultivation of crops like corn and sugarcane for plastics can compete with land for food production and require significant water resources. To address this, research is focused on using non-food feedstocks like agricultural waste or algae, which do not divert resources from the food chain.
Disposal is also a challenge, as some natural plastics can contaminate conventional plastic recycling streams if not sorted correctly. If bioplastics end up in landfills, which lack the oxygen for biodegradation, they can release methane, a potent greenhouse gas. For types like PLA, recycling is a potential option, but dedicated facilities are not widely available.
Current Applications of Natural Plastics
Natural plastics are used across a growing number of sectors, often in applications where their unique properties are advantageous. A visible use is in single-use food packaging and serviceware. Items like disposable cups, cutlery, food containers, and bags are made from PLA or starch-based plastics, as their compostability offers an alternative to landfilling.
In the agricultural sector, these materials are used as mulch films and planting pots. Biodegradable mulch films can be tilled directly into the soil after the growing season, saving farmers the labor of removal and disposal. Seedlings can be planted in biodegradable pots, which break down in the soil and reduce transplant shock to the plant’s roots.
Consumer goods are another area where natural plastics are used. Some electronics manufacturers use bio-based plastics for device casings, and they can be found in textiles and 3D printing filaments. The medical field utilizes these materials for applications like dissolvable sutures and certain implants, where the ability to safely break down within the body is a benefit.