Bioplastic
Bioplastics are plastic materials produced from renewable biomass sources. In the context of bioeconomy and the circular economy, bioplastics remain topical. Conventional petro-based polymers are increasingly blended with bioplastics to manufacture "bio-attributed" or "mass-balanced" plastic products—so the difference between bio- and other plastics might be difficult to define.
Bioplastics can be produced by:
- processing directly from natural biopolymers including polysaccharides and proteins,
- chemical synthesis from sugar derivatives and lipids from either plants or animals,
- fermentation of sugars or lipids,
- biotechnological production in microorganisms or genetically modified plants.
Whether any kind of plastic is degradable or non-degradable 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, 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 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. In 2022, the commercially most important types of bioplastics were PLA and products based on starch.
IUPAC definition
The International Union of Pure and Applied Chemistry define biobased polymer as:Types
Polysaccharide-based bioplastics
Starch-based plastics
starch represents the most widely used bioplastic, constituting about 50 percent of the bioplastics market. 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. Plasticizers 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 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. The properties of starch bioplastic is largely influenced by amylose/amylopectin ratio. Generally, high-amylose starch results in superior mechanical properties. 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 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 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. Further, starch-based films can be used as a paper.
Starch-based nanocomposites have been widely studied, showing improved mechanical properties, thermal stability, moisture resistance, and gas barrier properties.
Cellulose-based plastics
bioplastics are mainly the cellulose esters 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.
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 like the poly-3-hydroxybutyrate, polyhydroxyvalerate and polyhydroxyhexanoate.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 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.Poly-3-hydroxybutyrate
The biopolymer poly-3-hydroxybutyrate is a polyester produced by certain bacteria processing glucose, corn starch or wastewater. Its characteristics are similar to those of the petroplastic polypropylene. 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
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
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, 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, low moisture absorption and excellent resistance to various chemical substances.