Bioplastic is the name given to any plastics made from renewable biomass sources, including corn, potatoes, wood, food waste, agricultural by-products and lobster shells. The name is also given to biodegradable plastics, which are plastics that can be broken down into natural substances such as water, carbon dioxide and compost. Most bioplastics are a combination. Bioplastics are generally considered to be less harmful to the environment and to contribute less to the human impact on climate than traditional plastics which are derived from petroleum or natural gas and do not break down into natural substances. A 2017 study included in Environmental Research Letters suggested plastic production was responsible for 1 to 3 percent of the United States annual greenhouse gas emissions and that the adoption of corn-based PLA in place of traditional plastics would reduce those emissions by 25 percent.
As of 2015, it was estimated 8.3 billion tonnes of plastic had been produced globally and 70 percent had become waste. They are the third-most commonly used petroleum derivative.
In the United States, under the Department of Agriculture rules, for a plastic product to be labelled "biobased" or a "bioplastic" it need only contain a minimum of 25 percent carbon from biological sources.
Bioplastics made from corn or sugarcane convert into polylactic acid, often referred to as PLA plastics and used in food packaging. To transform corn into plastic, kernels are immersed in sulfur dioxide and hot water where its components break down into starch, protein, and fiber. The kernels are ground and the corn oil is separated from the starch. The starch removed in this process is comprised of long chains of carbon molecules similar to the chains found in petroleum-based plastics. Citric acids are included in the starch chains to form a long-chain polymer. PLA can look and behave like polyethylene, polystyrene, or polypropylene. The similarity of PLA to polyethylene has seen adoption in food-packaging, such as soda bottles, and PLA is often referred to as "drop-in" plastics for its ability to be used as a direct replacement of polyethylene or mixed in any quantity with polyethylene.
Bioplastics made from polyhydroxyalkanoates, or PHA plastics, are engineered from microorganisms and are often used in medical devices, sch as sutures and cardiovascular patches. To manufacture PHA, microorganisms – sometimes genetically engineered – produce plastics from organic material. The process involves depriving the microbes of nutrients such as nitrogen, oxygen and phosphorus and give them high levels of carbon. This process can be done through purchasing sugars, although as of 2017 there were processes being tested which used wastewater, food waste, and solid human waste to create a more efficient system. The microbes produce PHA as carbon reserves stored in granules until they have the other nutrients necessary for their reproduction. The manufacturers of PHA harvest the microbe-made PHA which has a chemical structure similar to plastic while being biodegradable and not producing harm to living tissue. This lends to the bioplastics use in medical applications, although it is also used for single-use food packaging.
PLA and PHA are the main bioplastics and their means of production are relatively standardized. But there are other methods and plastics being tried and produced. These include using methane from waste treatment plants and landfills to feed plastic-producing bacteria and transform their by-product in PHA suitable for use in plastic caps, soap bottles, or biopolyester fibers. This PHA degrades back into methane in a soil or compost environment and can be naturally digested by marine microorganisms. Another method is to add carbon dioxide to sugars at room temperature to create a polycarbonate which will break down into carbon dioxide and sugar in soil environments.
Overall, the lifecyle of bioplastics, although involving some emissions intensive processes and including potentially harmful chemicals and by-products, has been shown to produce fewer emissions than traditional plastics and shows no net increase over the plastics lifecycle.
The production of bioplastics is considered to have less of an impact on the environment and save more nonrenewable energy and their sources than the production of traditional plastics. However, the production of bioplastics, especially those from agricultural biomass, can cause an increase in nitrate and phosphate in bodies of water. This increase can cause eutrophication, a process in which a body of water gains an excessive richness of nutrients. The use of agricultural biomass for a source of bioplastics can also be problematic when the increased use of fertilizers and pesticides in growing the crops and the use of chemical processing to turn the biomass into bioplastic are accounted for.
Bioplastics are often considered to be superior to traditional plastics in their ability to break down and return to the environment. Where traditional plastics can be recycled – and some degrade through a process where additives cause the larger plastic to break down into smaller and smaller plastic pieces – the plastic products still end up in landfills and contribute to pollution and the smaller and smaller pieces of plastic never "return to nature" (or breakdown into natural products such as carbon dioxide, water, methane, or compost). Bioplastics are expected to help with this by breaking down into natural substances – depending on the plastic; water, carbon dioxide, and compost – and in their breakdown reduce the strain on landfills and the harm done to wildlife and ecosystems.
Bioplastics degrade most efficiently in compost environments due to their high microbial environments. They will also degrade well in soil environments thanks to the diversity of microorganisms, although soil based degradation requires higher temperatures and more time than compost environments. Bioplastics also degrade more efficiently than traditional plastics. However, the product resulting from the degradation leads to the death of aquatic organisms and can lead to unhealthy water.