Bioplastic
Bioplastics are plastic materials produced from renewable biomass sources, such as vegetable fats and oils, corn starch, straw, woodchips, sawdust, recycled food waste, etc. Some bioplastics are obtained by processing directly from natural biopolymers including polysaccharides (e.g., starch, cellulose, chitosan, and alginate) and proteins (e.g., soy protein, gluten, and gelatin), while others are chemically synthesised from sugar derivatives (e.g., lactic acid) and lipids (oils and fats) from either plants or animals, or biologically generated by fermentation of sugars or lipids. In contrast, common plastics, such as fossil-fuel plastics (also called petro-based polymers) are derived from petroleum or natural gas.
One advantage of bioplastics is their independence from fossil fuel as a raw material, which is a finite and globally unevenly distributed resource linked to petroleum politics and environmental impacts. Life cycle analysis studies show that some bioplastics can be made with a lower carbon footprint than their fossil counterparts, for example when biomass is used as raw material and also for energy production. However, other bioplastics' processes are less efficient and result in a higher carbon footprint than fossil plastics.
The distinction between non-fossil-based (bio)plastic and fossil-based plastic is of limited relevance since materials such as petroleum are themselves merely fossilized biomass. As such, whether any kind of plastic is degradable or non-degradable (durable) depends on its molecular structure, not on whether or not the biomass constituting the raw material is fossilized. Both durable bioplastics, such as Bio-PET or biopolyethylene (bio-based analogues of fossil-based polyethylene terephthalate and polyethylene), and degradable bioplastics, such as polylactic acid, polybutylene succinate, or polyhydroxyalkanoates, exist. Bioplastics must be recycled similar to fossil-based plastics to avoid plastic pollution; "drop-in" bioplastics (such as biopolyethylene) fit into existing recycling streams. On the other hand, recycling biodegradable bioplastics in the current recycling streams poses additional challenges, as it may raise the cost of sorting and decrease the yield and the quality of the recyclate. However, biodegradation is not the only acceptable end-of-life disposal pathway for biodegradable bioplastics, and mechanical and chemical recycling are often the preferred choice from the environmental point of view.
Biodegradability may offer an end-of-life pathway in certain applications, such as agricultural mulch, but the concept of biodegradation is not as straightforward as many believe. Susceptibility to biodegradation is highly dependent on the chemical backbone structure of the polymer, and different bioplastics have different structures, thus it cannot be assumed that bioplastic in the environment will readily disintegrate. Conversely, biodegradable plastics can also be synthesized from fossil fuels.
As of 2018, bioplastics represented approximately 2% of the global plastics output (>380 million tons).
IUPAC definition
The International Union of Pure and Applied Chemistry define biobased polymer as:
Biobased polymer derived from the biomass or issued from monomers derived from the biomass and which, at some stage in its processing into finished products, can be shaped by flow.
Proposed applications
Few commercial applications exist for bioplastics. Cost and performance remain problematic. Typical is the example of Italy, where biodegradable plastic bags are compulsory for shoppers since 2011 with the introduction of a specific law.
Bioplastics are used for disposable items, such as packaging, crockery, cutlery, pots, bowls, and straws.
Biopolymers are available as coatings for paper rather than the more common petrochemical coatings.
Bioplastics called drop-in bioplastics are chemically identical to their fossil-fuel counterparts but made from renewable resources. Examples include bio-PE, bio-PET, bio-propylene, bio-PP,
Types
Polysaccharide-based bioplastics
Thermoplastic starch represents the most widely used bioplastic, constituting about 50 percent of the bioplastics market.
Starch-based bioplastics are often blended with biodegradable polyesters to produce starch/polylactic acid,
Starch is cheap, abundant, and renewable.
Starch-based films (mostly used for packaging purposes) are made mainly from starch blended with thermoplastic polyesters to form biodegradable and compostable products. These films are seen specifically in consumer goods packaging of magazine wrappings and bubble films. In food packaging, these films are seen as bakery or fruit and vegetable bags. Composting bags with this films are used in selective collecting of organic waste.
Starch-based nanocomposites have been widely studied, showing improved mechanical properties, thermal stability, moisture resistance, and gas barrier properties.
Cellulose bioplastics are mainly the cellulose esters (including cellulose acetate and nitrocellulose) and their derivatives, including celluloid.
Cellulose can become thermoplastic when extensively modified. An example of this is cellulose acetate, which is expensive and therefore rarely used for packaging. However, cellulosic fibers added to starches can improve mechanical properties, permeability to gas, and water resistance due to being less hydrophilic than starch.
A group at Shanghai University was able to construct a novel green plastic based on cellulose through a method called hot pressing.
Protein-based plastics
Bioplastics can be made from proteins from different sources. For example, wheat gluten and casein show promising properties as a raw material for different biodegradable polymers.
Additionally, soy protein is being considered as another source of bioplastic. Soy proteins have been used in plastic production for over one hundred years. For example, body panels of an original Ford automobile were made of soy-based plastic.
There are difficulties with using soy protein-based plastics due to their water sensitivity and relatively high cost. Therefore, producing blends of soy protein with some already-available biodegradable polyesters improves the water sensitivity and cost.
Some aliphatic polyesters
The aliphatic biopolyesters are mainly polyhydroxyalkanoates (PHAs) like the poly-3-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and polyhydroxyhexanoate (PHH).
Polylactic acid (PLA) is a transparent plastic produced from maize
The biopolymer poly-3-hydroxybutyrate (PHB) is a polyester produced by certain bacteria processing glucose, corn starch
Polyhydroxyalkanoates
Polyhydroxyalkanoates (PHA) are linear polyesters produced in nature by bacterial fermentation of sugar or lipids. They are produced by the bacteria to store carbon and energy. In industrial production, the polyester is extracted and purified from the bacteria by optimizing the conditions for the fermentation of sugar. More than 150 different monomers can be combined within this family to give materials with extremely different properties. PHA is more ductile and less elastic than other plastics, and it is also biodegradable. These plastics are being widely used in the medical industry.
Polyamide 11
PA 11 is a biopolymer derived from natural oil. It is also known under the tradename Rilsan B, commercialized by Arkema. PA 11 belongs to the technical polymers family and is not biodegradable. Its properties are similar to those of PA 12, although emissions of greenhouse gases and consumption of nonrenewable resources are reduced during its production. Its thermal resistance is also superior to that of PA 12. It is used in high-performance applications like automotive fuel lines, pneumatic airbrake tubing, electrical cable antitermite sheathing, flexible oil and gas pipes, control fluid umbilicals, sports shoes, electronic device components, and catheters.
A similar plastic is Polyamide 410 (PA 410), derived 70% from castor oil, under the trade name EcoPaXX, commercialized by DSM.
Bio-derived polyethylene
The basic building block (monomer) of polyethylene is ethylene. Ethylene is chemically similar to, and can be derived from ethanol, which can be produced by fermentation of agricultural feedstocks such as sugar cane or corn. Bio-derived polyethylene is chemically and physically identical to traditional polyethylene – it does not biodegrade but can be recycled. The Brazilian chemicals group Braskem claims that using its method of producing polyethylene from sugar cane ethanol captures (removes from the environment) 2.15 tonnes of CO2 per tonne of Green Polyethylene produced.
Genetically modified feedstocks
With GM corn being a common feedstock, it is unsurprising that some bioplastics are made from this.
Under the bioplastics manufacturing technologies there is the "plant factory" model, which uses genetically modified crops or genetically modified bacteria to optimise efficiency.
Polyhydroxyurethanes
The condensation of polyamines and cyclic carbonates produces polyhydroxyurethanes.
Lipid derived polymers
A number bioplastic classes have been synthesized from plant and animal derived fats and oils.
Environmental impact
Materials such as starch, cellulose, wood, sugar and biomass are used as a substitute for fossil fuel resources to produce bioplastics; this makes the production of bioplastics a more sustainable activity compared to conventional plastic production.
Although bioplastics save more nonrenewable energy than conventional plastics and emit less greenhouse gasses compared to conventional plastics, bioplastics also have negative environmental impacts such as eutrophication and acidification.
Other environmental impacts of bioplastics include exerting lower human and terrestrial ecotoxicity and carcinogenic potentials compared to conventional plastics.
Although bioplastics are extremely advantageous because they reduce non-renewable consumption and GHG emissions, they also negatively affect the environment through land and water consumption, using pesticide and fertilizer, eutrophication and acidification; hence one's preference for either bioplastics or conventional plastics depends on what one considers the most important environmental impact.
Another issue with bioplastics, is that some bioplastics are made from the edible parts of crops. This makes the bioplastics compete with food production because the crops that produce bioplastics can also be used to feed people.
Biodegradation of Bioplastics
Biodegradation of any plastic is a process that happens at solid/liquid interface whereby the enzymes in the liquid phase depolymerize the solid phase.
Industry and markets
While plastics based on organic materials were manufactured by chemical companies throughout the 20th century, the first company solely focused on bioplastics—Marlborough Biopolymers—was founded in 1983. However, Marlborough and other ventures that followed failed to find commercial success, with the first such company to secure long-term financial success being the Italian company Novamont, founded in 1989.
Bioplastics remain less than one percent of all plastics manufactured worldwide.
COPA (Committee of Agricultural Organisation in the European Union) and COGEGA (General Committee for the Agricultural Cooperation in the European Union) have made an assessment of the potential of bioplastics in different sectors of the European economy:
History and development of bioplastics
*This is not a comprehensive list. These inventions show the versatility of bioplastics and important breakthroughs. New applications and bioplastics inventions continue to occur.
Testing procedures
Industrial compostability – EN 13432, ASTM D6400
The EN 13432 industrial standard must be met in order to claim that a plastic product is compostable in the European marketplace. In summary, it requires multiple tests and sets pass/fail criteria, including disintegration (physical and visual break down) of the finished item within 12 weeks, biodegradation (conversion of organic carbon into CO2) of polymeric ingredients within 180 days, plant toxicity and heavy metals. The ASTM 6400 standard is the regulatory framework for the United States and has similar requirements.
Many starch-based plastics, PLA-based plastics and certain aliphatic-aromatic co-polyester compounds, such as succinates and adipates, have obtained these certificates. Additive-based bioplastics sold as photodegradable or Oxo Biodegradable do not comply with these standards in their current form.
Compostability – ASTM D6002
The ASTM D 6002 method for determining the compostability of a plastic defined the word compostable as follows:
that which is capable of undergoing biological decomposition in a compost site such that the material is not visually distinguishable and breaks down into carbon dioxide, water, inorganic compounds and biomass at a rate consistent with known compostable materials.
This definition drew much criticism because, contrary to the way the word is traditionally defined, it completely divorces the process of "composting" from the necessity of it leading to humus/compost as the end product. The only criterion this standard does describe is that a compostable plastic must look to be going away as fast as something else one has already established to be compostable under the traditional definition.
In January 2011, the ASTM withdrew standard ASTM D 6002, which had provided plastic manufacturers with the legal credibility to label a plastic as compostable. Its description is as follows:
This guide covered suggested criteria, procedures, and a general approach to establish the compostability of environmentally degradable plastics.
The ASTM has yet to replace this standard.
Biobased – ASTM D6866
The ASTM D6866 method has been developed to certify the biologically derived content of bioplastics. Cosmic rays colliding with the atmosphere mean that some of the carbon is the radioactive isotope carbon-14. CO2 from the atmosphere is used by plants in photosynthesis, so new plant material will contain both carbon-14 and carbon-12. Under the right conditions, and over geological timescales, the remains of living organisms can be transformed into fossil fuels. After ~100,000 years all the carbon-14 present in the original organic material will have undergone radioactive decay leaving only carbon-12. A product made from biomass will have a relatively high level of carbon-14, while a product made from petrochemicals will have no carbon-14. The percentage of renewable carbon in a material (solid or liquid) can be measured with an accelerator mass spectrometer.
There is an important difference between biodegradability and biobased content. A bioplastic such as high-density polyethylene (HDPE)