Bioplastic

Plastics derived from renewable biomass sources
plastics made from renewable biomass

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). With continued research on bioplastics, investment in bioplastic companies and rising scrutiny on fossil based plastics, bioplastics are becoming more dominant in some markets, while the output of fossil plastics also steadily increases.

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. Beyond structural materials, electroactive bioplastics are being developed that promise to carry electric current. 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, and biobased nylons. Drop in bioplastics are easy to implement technically, as existing infrastructure can be used. A dedicated bio based pathway allows to produce products that cannot be obtained through traditional chemical reactions and can create products which have unique and superior properties, compared to fossil based alternatives. Simple starch bioplastic film can be made at home by gelatinizing starch and solution casting. Pure starch is able to absorb humidity, and is thus a suitable material for the production of drug capsules by the pharmaceutical sector. However, pure starch based bioplastic is brittle. Plasticizer such as glycerol, glycol, and sorbitol can also be added so that the starch can also be processed thermo plastically. The characteristics of the resulting bioplastic (also called "thermoplastic starch") can be tailored to specific needs by adjusting the amounts of these additives. Conventional polymer processing techniques can be used to process starch into bioplastic, such as extrusion, injection molding, compression molding and solution casting. However, high amylose starch has less processability because of its higher gelatinization temperature and higher melt viscosity. Starch based bioplastics are often blended with biodegradable polyesters to produce starch/polylactic acid, starch/polycaprolactone or starch/Ecoflex (polybutylene adipate co terephthalate produced by BASF) blends. These blends are used for industrial applications and are also compostable. Other producers, such as Roquette, have developed other starch/polyolefin blends. These blends are not biodegradable, but have a lower carbon footprint than petroleum based plastics used for the same applications. 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.

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.

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 or dextrose. Superficially, it is similar to conventional petrochemical based mass plastics like PS. It is derived from plants, and it biodegrades under industrial composting conditions. Unfortunately, it exhibits inferior impact strength, thermal robustness, and barrier properties (blocking air transport across the membrane) compared to non biodegradable plastics. PLA and PLA blends generally come in the form of granulates. PLA is used on a limited scale for the production of films, fibers, plastic containers, cups, and bottles. PLA is also the most common type of plastic filament used for home fused deposition modeling in 3D printers.

The biopolymer poly 3 hydroxybutyrate (PHB) is a polyester produced by certain bacteria processing glucose, corn starch or wastewater. Its characteristics are similar to those of the petroplastic polypropylene (PP). PHB production is increasing. The South American sugar industry, for example, has decided to expand PHB production to an industrial scale. PHB is distinguished primarily by its physical characteristics. It can be processed into a transparent film with a melting point higher than 130 degrees Celsius, and is biodegradable without residue.

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.

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. PA 410 is a high performance polyamide that combines the benefits of a high melting point (approx. 250 °C), low moisture absorption and excellent resistance to various chemical substances.

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 per tonne of Green Polyethylene produced.

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.

The condensation of polyamines and cyclic carbonates produces polyhydroxyurethanes. Unlike traditional cross linked polyurethanes, cross linked polyhydroxyurethanes are in principle amenable to recycling and reprocessing through dynamic transcarbamoylation reactions.

A number bioplastic classes have been synthesized from plant and animal derived fats and oils. Polyurethanes, polyesters, epoxy resins and a number of other types of polymers have been developed with comparable properties to crude oil based materials. The recent development of olefin metathesis has opened a wide variety of feedstocks to economical conversion into biomonomers and polymers. With the growing production of traditional vegetable oils as well as low cost microalgae derived oils, there is huge potential for growth in this area.

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. The environmental impact of bioplastics is often debated, as there are many different metrics for "greenness" (e. g., water use, energy use, deforestation, biodegradation, etc.). Hence bioplastic environmental impacts are categorized into nonrenewable energy use, climate change, eutrophication and acidification. Bioplastic production significantly reduces greenhouse gas emissions and decreases non renewable energy consumption. 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. Bioplastics also increase acidification. Minor environmental impacts of bioplastics include toxicity through using pesticides on the crops used to make bioplastics. 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. These bioplastics are called "1st generation feedstock bioplastics". 2nd generation feedstock bioplastics use non food crops (cellulosic feedstock) or waste materials from 1st generation feedstock (e. g. waste vegetable oil). Third generation feedstock bioplastics use algae as the feedstock.

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 ) 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.

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.

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) can be 100% biobased (i. e. contain 100% renewable carbon), yet be non biodegradable. These bioplastics such as HDPE nonetheless play an important role in greenhouse gas abatement, particularly when they are combusted for energy production. The biobased component of these bioplastics is considered carbon neutral since their origin is from biomass.

The ASTM D5511 12 and ASTM D5526 12 are testing methods that comply with international standards such as the ISO DIS 15985 for the biodegradability of plastic.