Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be molded, extruded or pressed into solid objects of various shapes. This adaptability, plus a wide range of other properties, such as being lightweight, durable, flexible, and inexpensive to produce, has led to their widespread use. Plastics typically are made through human industrial systems. Most modern plastics are derived from fossil fuel-based chemicals like natural gas or petroleum; however, recent industrial methods use variants made from renewable materials, such as corn or cotton derivatives.[1]
Between 1950 and 2017, 9.2-billion metric tons of plastic are estimated to have been made; more than half of this has been produced since 2004. In 2020, 400-million tons of plastic were produced.[2] If global trends on plastic demand continue, it is estimated that annual global plastic production will reach over 1.1-billion tons by 2050.
The success and dominance of plastics starting in the early 20th century has caused widespread environmental problems,[3] due to their slow decomposition rate in natural ecosystems. Most plastic produced has not been reused, or is incapable of reuse, either being captured in landfills or persisting in the environment as plastic pollution and microplastics. Plastic pollution can be found in all the world's major water bodies, for example, creating garbage patches in all of the world's oceans and contaminating terrestrial ecosystems. Of all the plastic discarded so far, some 14% has been incinerated and less than 10% has been recycled.[2]
In developed economies, about a third of plastic is used in packaging and roughly the same in buildings in applications such as piping, plumbing or vinyl siding.[4] Other uses include automobiles (up to 20% plastic[4]), furniture, and toys.[4] In the developing world, the applications of plastic may differ; 42% of India's consumption is used in packaging.[4] In the medical field, polymer implants and other medical devices are derived at least partially from plastic. Worldwide, about 50kg of plastic is produced annually per person, with production doubling every ten years.
The word plastic derives from the Greek πλαστικός (plastikos), meaning "capable of being shaped or molded;" in turn, it is from πλαστός (plastos) meaning "molded."[8] As a noun, the word most commonly refers to the solid products of petrochemical-derived manufacturing.[9]
The noun plasticity refers specifically here to the deformability of the materials used in the manufacture of plastics. Plasticity allows molding, extrusion or compression into a variety of shapes: films, fibers, plates, tubes, bottles and boxes, among many others. Plasticity also has a technical definition in materials science outside the scope of this article; it refers to the non-reversible change in form of solid substances.
Most plastics contain organic polymers.[10] The vast majority of these polymers are formed from chains of carbon atoms, with or without the attachment of oxygen, nitrogen or sulfur atoms. These chains comprise many repeating units formed from monomers. Each polymer chain consists of several thousand repeating units. The backbone is the part of the chain that is on the main path, linking together a large number of repeat units. To customize the properties of a plastic, different molecular groups called side chains hang from this backbone; they are usually hung from the monomers before the monomers themselves are linked together to form the polymer chain. The structure of these side chains influences the properties of the polymer.
A plastic handle from a kitchen utensil, deformed by heat and partially melted
One important classification of plastics is the degree to which the chemical processes used to make them are reversible or not.
Thermoplastics do not undergo chemical change in their composition when heated and thus can be molded repeatedly. Examples include polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC).[13]
Thermosets, or thermosetting polymers, can melt and take shape only once: after they have solidified, they stay solid.[14] If reheated, thermosets decompose rather than melt. In the thermosetting process, an irreversible chemical reaction occurs. The vulcanization of rubber is an example of this process. Before heating in the presence of sulfur, natural rubber (polyisoprene) is a sticky, slightly runny material; after vulcanization, the product is dry and rigid.
Thermosets consist of closely cross-linked polymers. Cross-links are shown as red dots in the figure.
Elastomers consist of wide-meshed cross-linked polymers. The wide mesh allows the material to stretch under tensile load.
Thermoplastics consist of non-crosslinked polymers, often with a semi-crystalline structure (shown in red). They have a glass transition temperature and are fusible.
Commodity, Engineering and High-performance plastics
Commodity plastics
Chemical structures and uses of some common plastics
Around 70% of global production is concentrated in six major polymer types, the so-called commodity plastics. Unlike most other plastics these can often be identified by their resin identification code (RIC):
Polyurethanes (PUR) and PP&A fibers[15] are often also included as major commodity classes, although they usually lack RICs, as they are chemically quite diverse groups. These materials are inexpensive, versatile and easy to work with, making them the preferred choice for the mass production everyday objects. Their biggest single application is in packaging, with some 146-million tonnes being used this way in 2015, equivalent to 36% of global production. Due to their dominance; many of the properties and problems commonly associated with plastics, such as pollution stemming from their poor biodegradability, are ultimately attributable to commodity plastics.
A huge number of plastics exist beyond the commodity plastics, with many having exceptional properties.
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Global plastic production by polymer type (2015)[16]
Engineering plastics are more robust and are used to make products such as vehicle parts, building and construction materials, and some machine parts. In some cases they are polymer blends formed by mixing different plastics together (ABS, HIPS etc.). Engineering plastics can replace metals in vehicles, lowering their weight and improving fuel efficiency by 6–8%. Roughly 50% of the volume of modern cars is made of plastic, but this only accounts for 12–17% of the vehicle weight.[18]
Polycarbonate + acrylonitrile butadiene styrene (PC + ABS): a blend of PC and ABS that creates a stronger plastic used in car interior and exterior parts, and in mobile phone bodies
Polyethylene + acrylonitrile butadiene styrene (PE + ABS): a slippery blend of PE and ABS used in low-duty dry bearings
Polymethyl methacrylate (PMMA) (acrylic): contact lenses (of the original "hard" variety), glazing (best known in this form by its various trade names around the world; e.g. Perspex, Plexiglas, and Oroglas), fluorescent-light diffusers, and rear light covers for vehicles. It also forms the basis of artistic and commercial acrylic paints, when suspended in water with the use of other agents.
Silicones (polysiloxanes): heat-resistant resins used mainly as sealants but also used for high-temperature cooking utensils and as a base resin for industrial paints
Urea-formaldehyde (UF): one of the aminoplasts used as a multi-colorable alternative to phenolics: used as a wood adhesive (for plywood, chipboard, hardboard) and electrical switch housings
High-performance plastics
High-performance plastics are usually expensive, with their use limited to specialized applications which make use of their superior properties.
Aramids: best known for their use in making body armor, this class of heat-resistant and strong synthetic fibers are also used in aerospace and military applications, includes Kevlar and Nomex, and Twaron.
Polyetheretherketone (PEEK): strong, chemical- and heat-resistant thermoplastic; its biocompatibility allows for use in medical implant applications and aerospace moldings. It is one of the most expensive commercial polymers.
Polyetherimide (PEI) (Ultem): a high-temperature, chemically stable polymer that does not crystallize
Polyimide: a high-temperature plastic used in materials such as Kapton tape
Polysulfone: high-temperature melt-processable resin used in membranes, filtration media, water heater dip tubes and other high-temperature applications
Polytetrafluoroethylene (PTFE), or Teflon: heat-resistant, low-friction coatings used in non-stick surfaces for frying pans, plumber's tape and water slides
Polyamide-imide (PAI): High-performance engineering plastic extensively used in high performance gears, switches, transmission and other automotive components, and aerospace parts.[19]
Amorphous plastics and crystalline plastics
Many plastics are completely amorphous (without a highly ordered molecular structure),[20] including thermosets, polystyrene, and methyl methacrylate (PMMA). Crystalline plastics exhibit a pattern of more regularly spaced atoms, such as high-density polyethylene (HDPE), polybutylene terephthalate (PBT), and polyether ether ketone (PEEK). However, some plastics are partially amorphous and partially crystalline in molecular structure, giving them both a melting point and one or more glass transitions (the temperature above which the extent of localized molecular flexibility is substantially increased). These so-called semi-crystalline plastics include polyethylene, polypropylene, polyvinyl chloride, polyamides (nylons), polyesters and some polyurethanes.
Intrinsically Conducting Polymers (ICP) are organic polymers that conduct electricity. While a conductivity of up to 80 kS/cm in stretch-oriented polyacetylene,[21] has been achieved, it does not approach that of most metals. For example, copper has a conductivity of several hundred kS/cm.[22]
Biodegradable plastics are plastics that degrade (break down) upon exposure to sunlight or ultra-violet radiation; water or dampness; bacteria; enzymes; or wind abrasion. Attack by insects, such as waxworms and mealworms, can also be considered as forms of biodegradation. Aerobic degradation requires that the plastic be exposed at the surface, whereas anaerobic degradation would be effective in landfill or composting systems. Some companies produce biodegradable additives to enhance biodegradation. Although starch powder can be added as a filler to allow some plastics to degrade more easily, such treatment does not lead to complete breakdown. Some researchers have genetically engineered bacteria to synthesize completely biodegradable plastics, such as polyhydroxy butyrate (PHB); however, these were still relatively costly as of 2021.[23]
While most plastics are produced from petrochemicals, bioplastics are made substantially from renewable plant materials like cellulose and starch.[24] Due both to the finite limits of fossil fuel reserves and to rising levels of greenhouse gases caused primarily by the burning of those fuels, the development of bioplastics is a growing field.[25][26] Global production capacity for bio-based plastics is estimated at 327,000 tonnes per year. In contrast, global production of polyethylene (PE) and polypropylene (PP), the world's leading petrochemical-derived polyolefins, was estimated at over 150 million tonnes in 2015.[27]
Plastic industry
The plastic industry includes the global production, compounding, conversion and sale of plastic products. Although the Middle East and Russia produce most of the required petrochemical raw materials, the production of plastic is concentrated in the global East and West. The plastic industry comprises a huge number of companies and can be divided into several sectors:
Production
Between 1950 and 2017, 9.2-billion tonnes of plastic are estimated to have been made, with more than half this having been produced since 2004. Since the birth of the plastic industry in the 1950s, global production has increased enormously, reaching 400 million tonnes a year in 2021; this is up from 381-million metric tonnes in 2015 (excluding additives).[2][16] From the 1950s, rapid growth occurred in the use of plastics for packaging, in building and construction, and in other sectors.[2] If global trends on plastic demand continue, it is estimated that by 2050 annual global plastic production will exceed 1.1-billion tonnes annually.[2]
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Plastics are produced in chemical plants by the polymerization of their starting materials (monomers); which are almost always petrochemical in nature. Such facilities are normally large and are visually similar to oil refineries, with sprawling pipework running throughout. The large size of these plants allows them to exploit economies of scale. Despite this, plastic production is not particularly monopolized, with about 100 companies accounting for 90% of global production.[28] This includes a mixture of private and state-owned enterprises. Roughly half of all production takes place in East Asia, with China being the largest single producer. Major international producers include:
Historically, Europe and North America have dominated global plastics production. However, since 2010 Asia has emerged as a significant producer, with China accounting for 31% of total plastic resin production in 2020.[29] Regional differences in the volume of plastics production are driven by user demand, the price of fossil fuel feedstocks, and investments made in the petrochemical industry. For example, since 2010 over US$200billion has been invested in the United States in new plastic and chemical plants, stimulated by the low cost of raw materials. In the European Union (EU), too, heavy investments have been made in the plastics industry, which employs over 1.6-million people with a turnover of more than 360 billion euros per year. In China in 2016 there were over 15,000 plastic manufacturing companies, generating more than US$366billion in revenue.[2]
Plastic is not sold as a pure unadulterated substance, but is instead mixed with various chemicals and other materials, which are collectively known as additives. These are added during the compounding stage and include substances such as stabilizers, plasticizers and dyes, which are intended to improve the lifespan, workability or appearance of the final item. In some cases, this can involve mixing different types of plastic together to form a polymer blend, such as high impact polystyrene. Large companies may do their own compounding prior to production, but some producers have it done by a third party. Companies that specialize in this work are known as Compounders.
The compounding of thermosetting plastic is relatively straightforward; as it remains liquid until it is cured into its final form. For thermosoftening materials, which are used to make the majority of products, it is necessary to melt the plastic in order to mix-in the additives. This involves heating it to anywhere between 150–320°C (300–610°F). Molten plastic is viscous and exhibits laminar flow, leading to poor mixing. Compounding is therefore done using extrusion equipment, which is able to supply the necessary heat and mixing to give a properly dispersed product.
The concentrations of most additives are usually quite low, however high levels can be added to create Masterbatch products. The additives in these are concentrated but still properly dispersed in the host resin. Masterbatch granules can be mixed with cheaper bulk polymer and will release their additives during processing to give a homogeneous final product. This can be cheaper than working with a fully compounded material and is particularly common for the introduction of color.
Converting
Short video on injection molding (9 min 37 s)
Blow molding a plastic drinks bottle
Companies that produce finished goods are known as converters (sometimes processors). The vast majority of plastics produced worldwide are thermosoftening and must be heated until molten in order to be molded. Various sorts of extrusion equipment exist which can then form the plastic into almost any shape.
Film blowing - Plastic films (carrier bags, sheeting)
Blow molding - Small thin-walled hollow objects in large quantities (drinks bottles, toys)
For thermosetting materials the process is slightly different, as the plastics are liquid to begin with and but must be cured to give solid products, but much of the equipment is broadly similar.
The most commonly produced plastic consumer products include packaging made from LDPE (e.g. bags, containers, food packaging film), containers made from HDPE (e.g. milk bottles, shampoo bottles, ice cream tubs), and PET (e.g. bottles for water and other drinks). Together these products account for around 36% of plastics use in the world. Most of them (e.g. disposable cups, plates, cutlery, takeaway containers, carrier bags) are used for only a short period, many for less than a day. The use of plastics in building and construction, textiles, transportation and electrical equipment also accounts for a substantial share of the plastics market. Plastic items used for such purposes generally have longer life spans. They may be in use for periods ranging from around five years (e.g. textiles and electrical equipment) to more than 20 years (e.g. construction materials, industrial machinery).[2]
Plastic consumption differs among countries and communities, with some form of plastic having made its way into most people's lives. North America (i.e. the North American Free Trade Agreement or NAFTA region) accounts for 21% of global plastic consumption, closely followed by China (20%) and Western Europe (18%). In North America and Europe, there is high per capita plastic consumption (94kg and 85kg/capita/year, respectively). In China, there is lower per capita consumption (58kg/capita/year), but high consumption nationally because of its large population.[2]
The largest application for plastics is as packaging materials, but they are used in a wide range of other sectors, including: construction (pipes, gutters, door and windows), textiles (stretchable fabrics, fleece), consumer goods (toys, tableware, toothbrushes), transportation (headlights, bumpers, body panels, wing mirrors), electronics (phones, computers, televisions) and as machine parts.[16] In optics, plastics are used to manufacture aspheric lenses.[31]
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Additives
Additives are chemicals blended into plastics to change their performance or appearance, making it possible to alter the properties of plastics to better suit their intended applications.[32][33] Additives are therefore one of the reasons why plastic is used so widely.[34] Plastics are composed of chains of polymers. Many different chemicals are used as plastic additives. A randomly chosen plastic product generally contains around 20 additives. The identities and concentrations of additives are generally not listed on products.[2]
In the EU, over 400 additives are used in high volumes.[35][2] In a global market analysis, 5,500 additives were found.[36] At a minimum, all plastic contains some polymer stabilizers which permit them to be melt-processed (molded) without suffering polymer degradation. Other additives are optional and can be added as required, with loadings varying significantly between applications. The amount of additives contained in plastics varies depending on the additives' function. For example, additives in polyvinyl chloride (PVC) can constitute up to 80% of the total volume.[2] Pure unadulterated plastic (barefoot resin) is never sold, even by the primary producers.
Leaching
Additives may be weakly bound to the polymers or react in the polymer matrix. Although additives are blended into plastic they remain chemically distinct from it, and can gradually leach back out during normal use, when in landfills, or following improper disposal in the environment.[37] Additives may also degrade to form other toxic molecules. Plastic fragmentation into microplastics and nanoplastics can allow chemical additives to move in the environment far from the point of use. Once released, some additives and derivatives may persist in the environment and bioaccumulate in organisms. They can have adverse effects on human health and biota. A recent review by the United States Environmental Protection Agency (US EPA) revealed that out of 3,377 chemicals potentially associated with plastic packaging and 906 likely associated with it, 68 were ranked by ECHA as "highest for human health hazards" and 68 as "highest for environmental hazards".[2]
As additives change the properties of plastics they have to be considered during recycling. Presently, almost all recycling is performed by simply remelting and reforming used plastic into new items. Additives present risks in recycled products, as they are difficult to remove. When plastic products are recycled, it is highly likely that the additives will be integrated into the new products. Waste plastic, even if it is all of the same polymer type, will contain varying types and amounts of additives. Mixing these together can give a material with inconsistent properties, which can be unappealing to industry. For example, mixing different colored plastics with different plastic colorants together can produce a discolored or brown material and for this reason plastic is usually sorted by both polymer type and color before recycling.[2]
Absence of transparency and reporting across the value chain often results in lack of knowledge concerning the chemical profile of the final products. For example, products containing brominated flame retardants have been incorporated into new plastic products. Flame retardants are a group of chemicals used in electronic and electrical equipment, textiles, furniture and construction materials which should not be present in food packaging or child care products. A recent study found brominated dioxins as unintentional contaminants in toys made from recycled plastic electronic waste that contained brominated flame retardants. Brominated dioxins have been found to exhibit toxicity similar to that of chlorinated dioxins. They can have negative developmental effects and negative effects on the nervous system and interfere with mechanisms of the endocrine system.[2]
Health effects
Many of the controversies associated with plastics actually relate to their additives, as some compounds can be persistent, bioaccumulating and potentially harmful.[38][39][32] The now banned flame retardants OctaBDE and PentaBDE are an example of this, while the health effects of phthalates are an ongoing area of public concern. Additives can also be problematic if waste is burned, especially when burning is uncontrolled or takes place in low- technology incinerators, as is common in many developing countries. Incomplete combustion can cause emissions of hazardous substances such as acid gases and ash which can contain persistent organic pollutants (POPs) such as dioxins.[2]
A number of additives identified as hazardous to humans and/or the environment are regulated internationally. The Stockholm Convention on Persistent Organic Pollutants (POPs) is a global treaty to protect human health and the environment from chemicals that remain intact in the environment for long periods, become widely distributed geographically, accumulate in the fatty tissue of humans and wildlife, and have harmful impacts on human health or on the environment.[2]
Other additives proven to be harmful such as cadmium, chromium, lead and mercury (regulated under the Minamata Convention on Mercury), which have previously been used in plastic production, are banned in many jurisdictions. However they are still routinely found in some plastic packaging including food packaging. The use of the additive bisphenol A (BPA) in plastic baby bottles is banned in many parts of the world, but is not restricted in some low-income countries.[2]
In 2023, plasticosis, a new disease caused solely by plastics, was discovered in seabirds. The birds identified as having the disease have scarred digestive tracts from ingesting plastic waste.[40] "When birds ingest small pieces of plastic, they found, it inflames the digestive tract. Over time, the persistent inflammation causes tissues to become scarred and disfigured, affecting digestion, growth and survival."[41]
80–90% of world production is used in PVC, much of the rest is used in cellulose acetate. For most products loadings are between 10 and 35%, high loadings are used for plastisols
Traditionally derivatives of lead, cadmium & tin. Safer modern alternatives include barium/zinc mixtures and calcium stearate, along with various synergists
Very common. All examples form a coating between the plastic and machine parts during production. Reduces pressure and power usage in the extruder. Reduces imperfections.
Pure plastics have low toxicity due to their insolubility in water, and because they have a large molecular weight, they are biochemically inert. Plastic products contain a variety of additives, however, some of which can be toxic.[43] For example, plasticizers like adipates and phthalates are often added to brittle plastics like PVC to make them pliable enough for use in food packaging, toys, and many other items. Traces of these compounds can leach out of the product. Owing to concerns over the effects of such leachates, the EU has restricted the use of DEHP (di-2-ethylhexyl phthalate) and other phthalates in some applications, and the US has limited the use of DEHP, DPB, BBP, DINP, DIDP, and DnOP in children's toys and child-care articles through the Consumer Product Safety Improvement Act. Some compounds leaching from polystyrene food containers have been proposed to interfere with hormone functions and are suspected human carcinogens (cancer-causing substances).[44] Other chemicals of potential concern include alkylphenols.[39]
While a finished plastic may be non-toxic, the monomers used in the manufacture of its parent polymers may be toxic. In some cases, small amounts of those chemicals can remain trapped in the product unless suitable processing is employed. For example, the World Health Organization's International Agency for Research on Cancer (IARC) has recognized vinyl chloride, the precursor to PVC, as a human carcinogen.[44]
Some plastic products degrade to chemicals with estrogenic activity.[45] The primary building block of polycarbonates, bisphenol A (BPA), is an estrogen-like endocrine disruptor that may leach into food.[44] Research in Environmental Health Perspectives finds that BPA leached from the lining of tin cans, dental sealants and polycarbonate bottles can increase the body weight of lab animals' offspring.[46] A more recent animal study suggests that even low-level exposure to BPA results in insulin resistance, which can lead to inflammation and heart disease.[47] As of January 2010, the Los Angeles Times reported that the US Food and Drug Administration (FDA) is spending $30million to investigate indications of BPA's link to cancer.[48]Bis(2-ethylhexyl) adipate, present in plastic wrap based on PVC, is also of concern, as are the volatile organic compounds present in new car smell. The EU has a permanent ban on the use of phthalates in toys. In 2009, the US government banned certain types of phthalates commonly used in plastic.[49]
Because the chemical structure of most plastics renders them durable, they are resistant to many natural degradation processes. Much of this material may persist for centuries or longer, given the demonstrated persistence of structurally similar natural materials such as amber.
There are differing estimates of how much plastic waste has been produced in the last century. By one estimate, one billion tons of plastic waste have been discarded since the 1950s.[50] Others estimate a cumulative human production of 8.3-billion tons of plastic, of which 6.3-billion tons is waste, with only 9% getting recycled.[51]
It is estimated that this waste is made up of 81% polymer resin, 13% polymer fibers and 32% additives. In 2018 more than 343 million tons of plastic waste were generated, 90% of which was composed of post-consumer plastic waste (industrial, agricultural, commercial and municipal plastic waste). The rest was pre-consumer waste from resin production and manufacturing of plastic products (e.g. materials rejected due to unsuitable color, hardness, or processing characteristics).[2]
The Ocean Conservancy reported that China, Indonesia, Philippines, Thailand, and Vietnam dump more plastic into the sea than all other countries combined.[52] The rivers Yangtze, Indus, Yellow, Hai, Nile, Ganges, Pearl, Amur, Niger, and Mekong "transport 88% to 95% of the global [plastics] load into the sea."[53][54][verify quote punctuation]
The presence of plastics, particularly microplastics, within the food chain is increasing. In the 1960s microplastics were observed in the guts of seabirds, and since then have been found in increasing concentrations.[55] The long-term effects of plastics in the food chain are poorly understood. In 2009 it was estimated that 10% of modern waste was plastic,[56] although estimates vary according to region.[55] Meanwhile, 50% to 80% of debris in marine areas is plastic.[55] Plastic is often used in agriculture. There is more plastic in the soil than in the oceans. The presence of plastic in the environment hurts ecosystems and human health.[57]
Research on the environmental impacts has typically focused on the disposal phase. However, the production of plastics is also responsible for substantial environmental, health and socioeconomic impacts.[58]
Prior to the Montreal Protocol, CFCs had been commonly used in the manufacture of the plastic polystyrene, the production of which had contributed to depletion of the ozone layer.
Efforts to minimize environmental impact of plastics may include lowering of plastics production and use, waste- and recycling-policies, and the proactive development and deployment of alternatives to plastics such as for sustainable packaging.
Microplastics in sediments from four rivers in Germany. Note the diverse shapes indicated by white arrowheads. (The white bars represent 1 mm for scale.)Photodegraded Plastic Straw. A light touch breaks larger straw into microplastics.
They cause pollution by entering naturalecosystems from a variety of sources, including cosmetics, clothing, construction, renovation, food packaging, and industrial processes.[59][64] The term microplastics is used to differentiate from larger, non-microscopic plastic waste. Two classifications of microplastics are currently recognized. Primary microplastics include any plastic fragments or particles that are already 5.0mm in size or less before entering the environment.[64] These include microfibers from clothing, microbeads, plastic glitter[65] and plastic pellets (also known as nurdles).[66][67][68] Secondary microplastics arise from the degradation (breakdown) of larger plastic products through natural weathering processes after entering the environment.[64] Such sources of secondary microplastics include water and soda bottles, fishing nets, plastic bags, microwave containers, tea bags and tire wear.[69][68][70][71]
Both types are recognized to persist in the environment at high levels, particularly in aquatic and marine ecosystems, where they cause water pollution.[72] 35% of all ocean microplastics come from textiles/clothing, primarily due to the erosion of polyester, acrylic, or nylon-based clothing, often during the washing process.[73] Microplastics also accumulate in the air and terrestrial ecosystems. Airborne microplastics have been detected in the atmosphere, as well as indoors and outdoors. Because plastics degrade slowly (often over hundreds to thousands of years),[74][75] microplastics have a high probability of ingestion, incorporation into, and accumulation in the bodies and tissues of many organisms.[59] The toxic chemicals that come from both the ocean and runoff can also biomagnify up the food chain.[76][77] In terrestrial ecosystems, microplastics have been demonstrated to reduce the viability of soil ecosystems.[78][79] As of 2023, the cycle and movement of microplastics in the environment was not fully known.[64] Microplastics in surface sample ocean surveys might have been underestimated as deep layer ocean sediment surveys in China found that plastics was present in deposition layers far older than the invention of plastics.
Microplastics are likely to degrade into smaller nanoplastics through chemical weathering processes, mechanical breakdown, and even through the digestive processes of animals. Nanoplastics, or NPs, are a subset of microplastics and they are smaller than 1 µm (1 micrometer or 1000 nm). Nanoplastics cannot be seen by the human eye.[63]
Plastics degrade by a variety of processes, the most significant of which is usually photo-oxidation. Their chemical structure determines their fate. Polymers' marine degradation takes much longer as a result of the saline environment and cooling effect of the sea, contributing to the persistence of plastic debris in certain environments.[55] Recent studies have shown, however, that plastics in the ocean decompose faster than had been previously thought, due to exposure to the sun, rain, and other environmental conditions, resulting in the release of toxic chemicals such as bisphenol A. However, due to the increased volume of plastics in the ocean, decomposition has slowed down.[80] The Marine Conservancy has predicted the decomposition rates of several plastic products: It is estimated that a foam plastic cup will take 50 years, a plastic beverage holder will take 400 years, a disposable diaper will take 450 years, and fishing line will take 600 years to degrade.[81]
Microbial species capable of degrading plastics are known to science, some of which are potentially useful for disposal of certain classes of plastic waste.
In 1975, a team of Japanese scientists studying ponds containing waste water from a nylon factory discovered a strain of Flavobacterium that digests certain byproducts of nylon 6 manufacture, such as the linear dimer of 6-aminohexanoate.[82] Nylon 4 (polybutyrolactam) can be degraded by the ND-10 and ND-11 strands of Pseudomonas sp. found in sludge, resulting in GABA (γ-aminobutyric acid) as a byproduct.[83]
Several species of soil fungi can consume polyurethane,[84] including two species of the Ecuadorian fungus Pestalotiopsis. They can consume polyurethane both aerobically and anaerobically (such as at the bottom of landfills).[85]
Phenol-formaldehyde, commonly known as Bakelite, is degraded by the white rot fungus P. chrysosporium.[91]
Acinetobacter has been found to partially degrade low-molecular-weight polyethylene oligomers.[83] When used in combination, Pseudomonas fluorescens and Sphingomonas can degrade over 40% of the weight of plastic bags in less than three months.[92] The thermophilic bacterium Brevibacillus borstelensis (strain 707) was isolated from a soil sample and found capable of using low-density polyethylene as a sole carbon source when incubated at 50°C. Pre-exposure of the plastic to ultraviolet radiation broke chemical bonds and aided biodegradation; the longer the period of UV exposure, the greater the promotion of the degradation.[93]
Hazardous molds have been found aboard space stations that degrade rubber into a digestible form.[94]
Several species of yeasts, bacteria, algae and lichens have been found growing on synthetic polymer artifacts in museums and at archaeological sites.[95]
In the plastic-polluted waters of the Sargasso Sea, bacteria have been found that consume various types of plastic; however, it is unknown to what extent these bacteria effectively clean up poisons rather than simply release them into the marine microbial ecosystem.
Plastic-eating microbes also have been found in landfills.[96]
Nocardia can degrade PET with an esterase enzyme.[97]
The fungus Geotrichum candidum, found in Belize, has been found to consume the polycarbonate plastic found in CDs.[98][99]
Futuro houses are made of fiberglass-reinforced polyesters, polyester-polyurethane, and PMMA. One such house was found to be harmfully degraded by Cyanobacteria and Archaea.[100][101]
Plastic recycling is the processing of plastic waste into other products.[102][103][104] Recycling can reduce dependence on landfill, conserve resources and protect the environment from plastic pollution and greenhouse gas emissions.[105][106] Recycling rates lag behind those of other recoverable materials, such as aluminium, glass and paper. From the start of plastic production through to 2015, the world produced around 6.3 billion tonnes of plastic waste, only 9% of which has been recycled and only ~1% has been recycled more than once.[107] Of the remaining waste, 12% was incinerated and 79% was either sent to landfills or lost to the environment as pollution.[107]
Almost all plastic is non-biodegradable and without recycling, spreads across the environment[108][109] where it causes plastic pollution. For example, as of 2015, approximately 8 million tonnes of waste plastic enters the oceans annually, damaging oceanic ecosystems and forming ocean garbage patches.[110]
Almost all recycling is mechanical and involves the melting and reforming of plastic into other items. This can cause polymer degradation at the molecular level, and requires that waste be sorted by colour and polymer type before processing, which is often complicated and expensive. Errors can lead to material with inconsistent properties, rendering it unappealing to industry.[111] Though filtration in mechanical recycling reduces microplastic release, even the most efficient filtration systems cannot prevent the release of microplastics into wastewater.[112][113]
In feedstock recycling, waste plastic is converted into its starting chemicals, which can then become fresh plastic. This involves higher energy and capital costs. Alternatively, plastic can be burned in place of fossil fuels in energy recovery facilities, or biochemically converted into other useful chemicals for industry.[114] In some countries, burning is the dominant form of plastic waste disposal, particularly where landfill diversion policies are in place.
It has been advocated since the early 1970s,[115] but due to economic and technical challenges, did not impact the management of plastic waste to any significant extent until the late 1980s. The plastics industry has been criticised for lobbying for expansion of recycling programmes, even while research showed that most plastic could not be economically recycled.[116][117][118][119] This has resulted in occasions where plastic waste dropped into recycling bins has not been recycled, and been treated as general waste.[120]
Pyrolysis
By heating to above 500°C in the absence of oxygen (pyrolysis), plastics can be broken down into simpler hydrocarbons. These can be reused as starting materials for new plastics.[121] They can also be used as fuels.[122]
According to the OECD, plastic contributed greenhouse gases in the equivalent of 1.8 billion tons of carbon dioxide (CO2) to the atmosphere in 2019, 3.4% of global emissions.[123] They say that by 2060, plastic could emit 4.3 billion tons of greenhouse gas emissions a year.
The effect of plastics on global warming is mixed. Plastics are generally made from fossil gas or petroleum, thus the production of plastics creates further fugitive emissions of methane when the fossil gas or petroleum is produced. Also, much of the energy used in plastic production is not sustainable energy, for example high temperature from burning fossil gas. However, plastics can also limit methane emissions, for example packaging to reduce food waste.[124]
A study from 2024 found that compared to glass and aluminum, plastic may actually have less of a negative effect on the environment and therefore might be the best option for must food packaging and other common uses.[125] The study found that, "replacing plastics with alternatives is worse for greenhouse gas emissions in most cases." and that the study involving European researchers found, "15 of the 16 applications a plastic product incurs fewer greenhouse gas emissions than their alternatives."[125]
Production of plastics
Production of plastics from crude oil requires 7.9 to 13.7 kWh/lb (taking into account the average efficiency of US utility stations of 35%). Producing silicon and semiconductors for modern electronic equipment is even more energy consuming: 29.2 to 29.8 kWh/lb for silicon, and about 381 kWh/lb for semiconductors.[126] This is much higher than the energy needed to produce many other materials. For example, to produce iron (from iron ore) requires 2.5-3.2 kWh/lb of energy; glass (from sand, etc.) 2.3–4.4 kWh/lb; steel (from iron) 2.5–6.4 kWh/lb; and paper (from timber) 3.2–6.4 kWh/lb.[127]
Incineration of plastics
Quickly burning plastics at very high temperatures breaks down many toxic components, such as dioxins and furans. This approach is widely used in municipal solid waste incineration. Municipal solid waste incinerators also normally treat the flue gas to decrease pollutants further, which is needed because uncontrolled incineration of plastic produces carcinogenicpolychlorinated dibenzo-p-dioxins.[128] Open-air burning of plastic occurs at lower temperatures and normally releases such toxic fumes.
In the European Union, municipal waste incineration is regulated by the Industrial Emissions Directive,[129] which stipulates a minimum temperature of 850°C for at least two seconds.[130]
Facilitation of natural degradation
The bacterium Blaptica dubia is claimed to help degradation of commercial polysterene. This biodegradation seems to occur in some plastic degrading bacteria inhabiting the gut of cockroaches. The biodegradation products have been found in their feces too.[131]
The development of plastics has evolved from the use of naturally plastic materials (e.g., gums and shellac) to the use of the chemical modification of those materials (e.g., natural rubber, cellulose, collagen, and milk proteins), and finally to completely synthetic plastics (e.g., bakelite, epoxy, and PVC). Early plastics were bio-derived materials such as egg and blood proteins, which are organic polymers. In around 1600 BC, Mesoamericans used natural rubber for balls, bands, and figurines.[4] Treated cattle horns were used as windows for lanterns in the Middle Ages. Materials that mimicked the properties of horns were developed by treating milk proteins with lye. In the nineteenth century, as chemistry developed during the Industrial Revolution, many materials were reported. The development of plastics accelerated with Charles Goodyear's 1839 discovery of vulcanization to harden natural rubber.
Plaque commemorating Parkes at the Birmingham Science Museum
Parkesine, invented by Alexander Parkes in 1855 and patented the following year,[132] is considered the first man-made plastic. It was manufactured from cellulose (the major component of plant cell walls) treated with nitric acid as a solvent. The output of the process (commonly known as cellulose nitrate or pyroxilin) could be dissolved in alcohol and hardened into a transparent and elastic material that could be molded when heated.[133] By incorporating pigments into the product, it could be made to resemble ivory. Parkesine was unveiled at the 1862 International Exhibition in London and garnered for Parkes the bronze medal.[134]
In 1893, French chemist Auguste Trillat discovered the means to insolubilize casein (milk proteins) by immersion in formaldehyde, producing material marketed as galalith.[135] In 1897, mass-printing press owner Wilhelm Krische of Hanover, Germany, was commissioned to develop an alternative to blackboards.[135] The resultant horn-like plastic made from casein was developed in cooperation with the Austrian chemist (Friedrich) Adolph Spitteler (1846–1940). Although unsuitable for the intended purpose, other uses would be discovered.[135]
After World War I, improvements in chemistry led to an explosion of new forms of plastics, with mass production beginning in the 1940s and 1950s.[56] Among the earliest examples in the wave of new polymers were polystyrene (first produced by BASF in the 1930s)[4] and polyvinyl chloride (first created in 1872 but commercially produced in the late 1920s).[4] In 1923, Durite Plastics, Inc., was the first manufacturer of phenol-furfural resins.[136] In 1933, polyethylene was discovered by Imperial Chemical Industries (ICI) researchers Reginald Gibson and Eric Fawcett.[4]
The discovery of polyethylene terephthalate (PETE) is credited to employees of the Calico Printers' Association in the UK in 1941; it was licensed to DuPont for the US and ICI otherwise, and as one of the few plastics appropriate as a replacement for glass in many circumstances, resulting in widespread use for bottles in Europe.[4] In 1954 polypropylene was discovered by Giulio Natta and began to be manufactured in 1957.[4] Also in 1954 expanded polystyrene (used for building insulation, packaging, and cups) was invented by Dow Chemical.[4]
Work is currently underway to develop a global treaty on plastic pollution. On March 2, 2022, UN Member States voted at the resumed fifth UN Environment Assembly (UNEA-5.2) to establish an Intergovernmental Negotiating Committee (INC) with the mandate of advancing a legally-binding international agreement on plastics.[137] The resolution is entitled "End plastic pollution: Towards an international legally binding instrument." The mandate specifies that the INC must begin its work by the end of 2022 with the goal of "completing a draft global legally binding agreement by the end of 2024."[138]
Plastics engineering– Engineering field studying polymer materialsPages displaying short descriptions of redirect targets
Plasticulture– Use of plastic materials in agriculture
Plastisphere– Plastic debris suspended in water and organisms which live in it
Refill (scheme)– British environmental campaignPages displaying short descriptions of redirect targets
Roll-to-roll processing– countinous printing method that prints directly onto a roll of fabric or other materialsPages displaying wikidata descriptions as a fallback
Self-healing plastic– Substances that can repair themselvesPages displaying short descriptions of redirect targets
Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradation occurs under a specific set of circumstances.
Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a poor barrier to air and water vapor and has a relatively low melting point. Polystyrene is one of the most widely used plastics, with the scale of its production being several million tonnes per year. Polystyrene is naturally transparent, but can be colored with colorants. Uses include protective packaging, containers, lids, bottles, trays, tumblers, disposable cutlery, in the making of models, and as an alternative material for phonograph records.
Polymer degradation is the reduction in the physical properties of a polymer, such as strength, caused by changes in its chemical composition. Polymers and particularly plastics are subject to degradation at all stages of their product life cycle, including during their initial processing, use, disposal into the environment and recycling. The rate of this degradation varies significantly; biodegradation can take decades, whereas some industrial processes can completely decompose a polymer in hours.
Plastic recycling is the processing of plastic waste into other products. Recycling can reduce dependence on landfill, conserve resources and protect the environment from plastic pollution and greenhouse gas emissions. Recycling rates lag behind those of other recoverable materials, such as aluminium, glass and paper. From the start of plastic production through to 2015, the world produced around 6.3 billion tonnes of plastic waste, only 9% of which has been recycled and only ~1% has been recycled more than once. Of the remaining waste, 12% was incinerated and 79% was either sent to landfills or lost to the environment as pollution.
Bioplastics are plastic materials produced from renewable biomass sources. Historically, bioplastics made from natural materials like shellac or cellulose had been the first plastics. Since the end of the 19th century they have been increasingly superseded by fossil-fuel plastics derived from petroleum or natural gas. Today, in the context of bioeconomy and circular economy, bioplastics are gaining interest again. 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.
Polyethylene or polythene film biodegrades naturally, albeit over a long period of time. Methods are available to make it more degradable under certain conditions of sunlight, moisture, oxygen, and composting and enhancement of biodegradation by reducing the hydrophobic polymer and increasing hydrophilic properties.
Biodegradable plastics are plastics that can be decomposed by the action of living organisms, usually microbes, into water, carbon dioxide, and biomass. Biodegradable plastics are commonly produced with renewable raw materials, micro-organisms, petrochemicals, or combinations of all three.
A plastic bottle is a bottle constructed from high-density or low density plastic. Plastic bottles are typically used to store liquids such as water, soft drinks, motor oil, cooking oil, medicine, shampoo or milk. They range in sizes, from very small bottles to large carboys. Consumer blow molded containers often have integral handles or are shaped to facilitate grasping.
Polymer stabilizers are chemical additives which may be added to polymeric materials to inhibit or retard their degradation. Mainly they protect plastic and rubber products against heat, oxidation, and UV light. The biggest quantity of stabilizers is used for polyvinyl chloride (PVC), as the production and processing of this type of plastic would not be possible without stabilizing chemicals. Common polymer degradation processes include oxidation, UV-damage, thermal degradation, ozonolysis, combinations thereof such as photo-oxidation, as well as reactions with catalyst residues, dyes, or impurities. All of these degrade the polymer at a chemical level, via chain scission, uncontrolled recombination and cross-linking, which adversely affects many key properties such as strength, malleability, appearance and colour.
In polymer chemistry photo-oxidation is the degradation of a polymer surface due to the combined action of light and oxygen. It is the most significant factor in the weathering of plastics. Photo-oxidation causes the polymer chains to break, resulting in the material becoming increasingly brittle. This leads to mechanical failure and, at an advanced stage, the formation of microplastics. In textiles the process is called phototendering.
Oxo-degradation refers to the breakdown mechanism caused by heat, light or oxygen on plastics that contain additives that accelerate the process of breaking them into smaller fragments called microplastics. These plastics contrast biodegradable or compostable plastics, which decompose at the molecular or polymer level. Oxo-degradable plastics are currently banned in the EU, but are still permitted in other jurisdictions such as the UK.
Biodegradable bags are bags that are capable of being decomposed by bacteria or other living organisms.
Microplastics are fragments of any type of plastic less than 5 mm (0.20 in) in length, according to the U.S. National Oceanic and Atmospheric Administration (NOAA) and the European Chemicals Agency. US EPA researchers define microplastics, or MPs, as plastic particles ranging in size from 5 millimeters (mm), which is about the size of a pencil eraser, to 1 nanometer (nm). For comparison, a strand of human hair is about 80,000 nanometers wide.
Recycling can be carried out on various raw materials. Recycling is an important part of creating more sustainable economies, reducing the cost and environmental impact of raw materials. Not all materials are easily recycled, and processing recyclable into the correct waste stream requires considerable energy. Some particular manufactured goods are not easily separated, unless specially process therefore have unique product-based recycling processes.
Plastic pollution is the accumulation of plastic objects and particles in the Earth's environment that adversely affects humans, wildlife and their habitat. Plastics that act as pollutants are categorized by size into micro-, meso-, or macro debris. Plastics are inexpensive and durable, making them very adaptable for different uses; as a result, manufacturers choose to use plastic over other materials. However, the chemical structure of most plastics renders them resistant to many natural processes of degradation and as a result they are slow to degrade. Together, these two factors allow large volumes of plastic to enter the environment as mismanaged waste which persists in the ecosystem and travels throughout food webs.
Biodegradable additives are additives that enhance the biodegradation of polymers by allowing microorganisms to utilize the carbon within the polymer chain as a source of energy. Biodegradable additives attract microorganisms to the polymer through quorum sensing after biofilm creation on the plastic product. Additives are generally in masterbatch formation that use carrier resins such as polyethylene (PE), polypropylene (PP), polystyrene (PS) or polyethylene terephthalate (PET).
The plastisphere is a human-made ecosystem consisting of organisms able to live on plastic waste. Plastic marine debris, most notably microplastics, accumulates in aquatic environments and serves as a habitat for various types of microorganisms, including bacteria and fungi. As of 2022, an estimated 51 trillion microplastics are floating in the surface water of the world's oceans. A single 5mm piece of plastic can host 1,000s of different microbial species. Some marine bacteria can break down plastic polymers and use the carbon as a source of energy.
The economics of plastics processing is determined by the type of process. Plastics can be processed with the following methods: machining, compression molding, transfer molding, injection molding, extrusion, rotational molding, blow molding, thermoforming, casting, forging, and foam molding. Processing methods are selected based on equipment cost, production rate, tooling cost, and build volume. High equipment and tooling cost methods are typically used for large production volumes whereas low - medium equipment cost and tooling cost methods are used for low production volumes. Compression molding, transfer molding, injection molding, forging, and foam molding have high equipment and tooling cost. Lower cost processes are machining, extruding, rotational molding, blow molding, thermoforming, and casting. A summary of each process and its cost is displayed in figure 1.
Polymateria Ltd is a British technology company developing biodegradable plastic alternatives. In 2020, the privately owned company was the first to achieve certified biodegradation of the most commonly-littered forms of plastic packaging in real-world conditions, in less than a year without creating microplastics.
Plastic degradation in marine bacteria describes when certain pelagic bacteria break down polymers and use them as a primary source of carbon for energy. Polymers such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) are incredibly useful for their durability and relatively low cost of production, however it is their persistence and difficulty to be properly disposed of that is leading to pollution of the environment and disruption of natural processes. It is estimated that each year there are 9-14 million metric tons of plastic that are entering the ocean due to inefficient solutions for their disposal. The biochemical pathways that allow for certain microbes to break down these polymers into less harmful byproducts has been a topic of study to develop a suitable anti-pollutant.
↑ Brandl H, Püchner P (1992). "Biodegradation Biodegradation of Plastic Bottles Made from 'Biopol' in an Aquatic Ecosystem Under In Situ Conditions". Biodegradation. 2 (4): 237–43. doi:10.1007/BF00114555. S2CID37486324.
↑ Pfaendner, Rudolf (September 2006). "How will additives shape the future of plastics?". Polymer Degradation and Stability. 91 (9): 2249–2256. doi:10.1016/j.polymdegradstab.2005.10.017.
↑ "Impact modifiers: how to make your compound tougher". Plastics, Additives and Compounding. 6 (3): 46–49. May 2004. doi:10.1016/S1464-391X(04)00203-X.
↑ Franzen H (November 30, 2017). "Almost all plastic in the ocean comes from just 10 rivers". Deutsche Welle. Retrieved December 18, 2018. It turns out that about 90 percent of all the plastic that reaches the world's oceans gets flushed through just 10 rivers: The Yangtze, the Indus, Yellow River, Hai River, the Nile, the Ganges, Pearl River, Amur River, the Niger, and the Mekong (in that order).
↑ Klein S, Dimzon IK, Eubeler J, Knepper TP (2018). "Analysis, Occurrence, and Degradation of Microplastics in the Aqueous Environment". In Wagner M, Lambert S (eds.). Freshwater Microplastics. The Handbook of Environmental Chemistry. Vol.58. Cham.: Springer. pp.51–67. doi:10.1007/978-3-319-61615-5_3. ISBN978-3319616148. See Section 3, "Environmental Degradation of Synthetic Polymers".
↑ Nex, Sally (2021). How to garden the low carbon way: the steps you can take to help combat climate change (First Americaned.). New York. ISBN978-0744029284. OCLC1241100709.{{cite book}}: CS1 maint: location missing publisher (link)
↑ Ward PG, Goff M, Donner M, Kaminsky W, O'Connor KE (April 2006). "A two step chemo-biotechnological conversion of polystyrene to a biodegradable thermoplastic". Environmental Science & Technology. 40 (7): 2433–7. Bibcode:2006EnST...40.2433W. doi:10.1021/es0517668. PMID16649270.
↑ Cappitelli F, Principi P, Sorlini C (August 2006). "Biodeterioration of modern materials in contemporary collections: can biotechnology help?". Trends in Biotechnology. 24 (8): 350–4. doi:10.1016/j.tibtech.2006.06.001. PMID16782219.
↑ Lazarevic, David; Aoustin, Emmanuelle; Buclet, Nicolas; Brandt, Nils (December 2010). "Plastic waste management in the context of a European recycling society: Comparing results and uncertainties in a life cycle perspective". Resources, Conservation and Recycling. 55 (2): 246–259. doi:10.1016/j.resconrec.2010.09.014.
↑ Andrady, Anthony L. (February 1994). "Assessment of Environmental Biodegradation of Synthetic Polymers". Journal of Macromolecular Science, Part C: Polymer Reviews. 34 (1): 25–76. doi:10.1080/15321799408009632.
↑ Ahmed, Temoor; Shahid, Muhammad; Azeem, Farrukh; Rasul, Ijaz; Shah, Asad Ali; Noman, Muhammad; Hameed, Amir; Manzoor, Natasha; Manzoor, Irfan; Muhammad, Sher (March 2018). "Biodegradation of plastics: current scenario and future prospects for environmental safety". Environmental Science and Pollution Research. 25 (8): 7287–7298. Bibcode:2018ESPR...25.7287A. doi:10.1007/s11356-018-1234-9. PMID29332271. S2CID3962436.
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