Plastic

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Household items made of various types of plastic Plastic household items.jpg
Household items made of various types of plastic

Plastic is material consisting of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and so can be molded into solid objects.

Organic compound Chemical compound that contains carbon (except for several compounds traditionally classified as inorganic compounds)

In chemistry, organic compounds are generally any chemical compounds that contain carbon. Due to carbon's ability to catenate, millions of organic compounds are known. The study of the properties, reactions, and syntheses of organic compounds comprises the discipline known as organic chemistry. For historical reasons, a few classes of carbon-containing compounds, along with a handful of other exceptions, are not classified as organic compounds and are considered inorganic. Other than those just named, little consensus exists among chemists on precisely which carbon-containing compounds are excluded, making any rigorous definition of an organic compound elusive.

Molding (process) adding a soft but not fully liquid material into a mold (like wet clay)

Molding or moulding is the process of manufacturing by shaping liquid or pliable raw material using a rigid frame called a mold or matrix. This itself may have been made using a pattern or model of the final object.

Contents

Plasticity is the general property of all materials which can deform irreversibly without breaking but, in the class of moldable polymers, this occurs to such a degree that their actual name derives from this specific ability.

Plasticity (physics) The deformation of a solid material undergoing non-reversible changes of shape in response to applied forces

In physics and materials science, plasticity is the ability of a solid material to undergo deformation, a non-reversible change of shape in response to applied forces. For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the material itself. In engineering, the transition from elastic behavior to plastic behavior is called yield.

Polymer Substance composed of macromolecules with repeating structural units

A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Due to their broad range of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass, relative to small molecule compounds, produces unique physical properties including toughness, viscoelasticity, and a tendency to form glasses and semicrystalline structures rather than crystals. The terms polymer and resin are often synonymous with plastic.

Plastics are typically organic polymers of high molecular mass and often contain other substances. They are usually synthetic, most commonly derived from petrochemicals, however, an array of variants are made from renewable materials such as polylactic acid from corn or cellulosics from cotton linters. [1]

The molecular mass (m) is the mass of a given molecule: it is measured in unified atomic mass units. Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The related quantity relative molecular mass, as defined by IUPAC, is the ratio of the mass of a molecule to the unified atomic mass unit and is unitless. The molecular mass and relative molecular mass are distinct from but related to the molar mass. The molar mass is defined as the mass of a given substance divided by the amount of a substance and is expressed in g/mol. The molar mass is usually the more appropriate figure when dealing with macroscopic (weigh-able) quantities of a substance.

Petrochemical chemical product derived from petroleum

Petrochemicals are chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn, palm fruit or sugar cane.

Due to their low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in a multitude of products of different scale, including paper clips and spacecraft. They have prevailed over traditional materials, such as wood, stone, horn and bone, leather, metal, glass, and ceramic, in some products previously left to natural materials.

Wood Fibrous material from trees or other plants

Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic material - a natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin that resists compression. Wood is sometimes defined as only the secondary xylem in the stems of trees, or it is defined more broadly to include the same type of tissue elsewhere such as in the roots of trees or shrubs. In a living tree it performs a support function, enabling woody plants to grow large or to stand up by themselves. It also conveys water and nutrients between the leaves, other growing tissues, and the roots. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, or wood chips or fiber.

Rock (geology) A naturally occurring solid aggregate of one or more minerals or mineraloids

A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition and the way in which it is formed. Rocks are usually grouped into three main groups: igneous rocks, metamorphic rocks and sedimentary rocks. Rocks form the Earth's outer solid layer, the crust.

Horn (anatomy) anatomical feature

A horn - a permanent pointed projection on the head of various animals - consists of a covering of keratin and other proteins surrounding a core of live bone. Horns are distinct from antlers, which are not permanent. In mammals, true horns are found mainly among the ruminant artiodactyls, in the families Antilocapridae (pronghorn) and Bovidae.

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. [2] Other uses include automobiles (up to 20% plastic [2] ), furniture, and toys. [2] In the developing world, the applications of plastic may differ—42% of India's consumption is used in packaging. [2]

Piping system of pipes used to transport fluids (gases, liquids or pourable or pumpable solids) from one location to another;high-performance (high-pressure, high-flow, high-temperature or hazardous-material) conveyance of fluids in specialized applications

Within industry, piping is a system of pipes used to convey fluids from one location to another. The engineering discipline of piping design studies the efficient transport of fluid.

Plumbing Systems for conveying fluids

Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water delivery are among the most common uses for plumbing, but it is not limited to these applications. The word derives from the Latin for lead, plumbum, as the first effective pipes used in the Roman era were lead pipes.

Vinyl siding plastic exterior siding for a house

Vinyl siding is plastic exterior siding for houses and small apartment buildings, used for decoration and weatherproofing, imitating wood clapboard, board and batten or shakes, and used instead of other materials such as aluminum or fiber cement siding. It is an engineered product, manufactured primarily from polyvinyl chloride (PVC) resin. In the UK and New Zealand a similar material is known as uPVC weatherboarding.

Plastics have many uses in the medical field as well, with the introduction of polymer implants and other medical devices derived at least partially from plastic. The field of plastic surgery is not named for use of plastic materials, but rather the meaning of the word plasticity, with regard to the reshaping of flesh.

Plastic surgery is a surgical specialty involving the restoration, reconstruction, or alteration of the human body. It can be divided into two main categories: reconstructive surgery and cosmetic surgery. Reconstructive surgery includes craniofacial surgery, hand surgery, microsurgery, and the treatment of burns. While reconstructive surgery aims to reconstruct a part of the body or improve its functioning, cosmetic surgery aims at improving the appearance of it. Both of these techniques are used throughout the world.

The world's first fully synthetic plastic was bakelite, invented in New York in 1907, by Leo Baekeland [3] who coined the term 'plastics'. [4] Many chemists have contributed to the materials science of plastics, including Nobel laureate Hermann Staudinger who has been called "the father of polymer chemistry" and Herman Mark, known as "the father of polymer physics". [5]

The success and dominance of plastics starting in the early 20th century led to environmental concerns regarding its slow decomposition rate after being discarded as trash due to its composition of large molecules. Toward the end of the century, one approach to this problem was met with wide efforts toward recycling.

Etymology

The word plastic derives from the Greek πλαστικός (plastikos) meaning "capable of being shaped or molded" and, in turn, from πλαστός (plastos) meaning "molded". [6] [7]

The plasticity, or malleability, of the material during manufacture allows it to be cast, pressed, or extruded into a variety of shapes, such as: films, fibers, plates, tubes, bottles, boxes, amongst many others.

The common noun plastic should not be confused with the technical adjective plastic. The adjective is applicable to any material which undergoes a plastic deformation, or permanent change of shape, when strained beyond a certain point. For example, aluminum which is stamped or forged exhibits plasticity in this sense, but is not plastic in the common sense. By contrast, some plastics will, in their finished forms, break before deforming and therefore are not plastic in the technical sense.

Structure

Most plastics contain organic polymers. [8] The vast majority of these polymers are formed from chains of carbon atoms, 'pure' or with the addition of: oxygen, nitrogen, or sulfur. The chains comprise many repeat units, formed from monomers. Each polymer chain will have 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 "hang" from this backbone. These pendant units are usually "hung" on the monomers, before the monomers themselves are linked together to form the polymer chain. It is the structure of these side chains that influences the properties of the polymer.

The molecular structure of the repeating unit can be fine tuned to influence specific properties of the polymer.

Properties and classifications

Plastics are usually classified by: the chemical structure of the polymer's backbone and side chains; some important groups in these classifications are: the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics.

Plastics can also be classified by: the chemical process used in their synthesis, such as: condensation, polyaddition, and cross-linking. [9]

Plastics can also be classified by: their various physical properties, such as: hardness, density, tensile strength, resistance to heat and glass transition temperature, and by their chemical properties, such as the organic chemistry of the polymer and its resistance and reaction to various chemical products and processes, such as: organic solvents, oxidation, and ionizing radiation. In particular, most plastics will melt upon heating to a few hundred degrees celsius. [10]

Other classifications are based on qualities that are relevant for manufacturing or product design. Examples of such qualities and classes are: thermoplastics and thermosets, conductive polymers, biodegradable plastics and engineering plastics and other plastics with particular structures, such as elastomers.

Thermoplastics and thermosetting polymers

The plastic handle of a spatula that has been deformed by heat. Melted plastic.jpg
The plastic handle of a spatula that has been deformed by heat.

One important classification of plastics is by the permanence or impermanence of their form, or whether they are: thermoplastics or thermosetting polymers. Thermoplastics are the plastics that, when heated, do not undergo chemical change in their composition and so can be molded again and again. Examples include: polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyvinyl chloride (PVC). [11] Common thermoplastics range from 20,000 to 500,000 amu, while thermosets are assumed to have infinite molecular weight.

Thermosets, or thermosetting polymers, can melt and take shape only once: after they have solidified, they stay solid. [12] In the thermosetting process, a chemical reaction occurs that is irreversible. The vulcanization of rubber is an example of a thermosetting process: before heating with sulfur, the polyisoprene is a tacky, slightly runny material; after vulcanization, the product is rigid and non-tacky.

Amorphous plastics and crystalline plastics

Many plastics are completely amorphous, [13] such as: all thermosets; polystyrene and its copolymers; and polymethyl methacrylate.

However, some plastics are partially crystalline and partially amorphous in molecular structure, giving them both a melting point, the temperature at which the attractive intermolecular forces are overcome, and also one or more glass transitions, the temperatures 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.

Conductive polymers

Intrinsically Conducting Polymers (ICP) are organic polymers that conduct electricity. While plastics can be made electrically conductive, with a conductivity of up to 80 kS/cm in stretch-oriented polyacetylene, [14] they are still no match for most metals like copper which have a conductivity of several hundred kS/cm. Nevertheless, this is a developing field.

Biodegradable plastics and bioplastics

Biodegradable plastics are plastics that degrade, or break down, upon exposure to: sunlight or ultra-violet radiation, water or dampness, bacteria, enzymes or wind abrasion. In some instances, rodent, pest, or insect attack can also be considered as forms of biodegradation or environmental degradation.

Some modes of degradation require that the plastic be exposed at the surface (aerobic), whereas other modes will only be effective if certain conditions exist in landfill or composting systems (anaerobic).

Some companies produce biodegradable additives, to enhance biodegradation. Plastic can have starch powder added as a filler to allow it to degrade more easily, but this still does not lead to the complete breaking down of the plastic.

Some researchers have genetically engineered bacteria to synthesize completely biodegradable plastics, such as Biopol; however, these are expensive at present. [15]

Bioplastics

While most plastics are produced from petrochemicals, bioplastics are made substantially from renewable plant materials such: as cellulose and starch. [16] Due both to the finite limits of the petrochemical reserves and to the threat of global warming, the development of bioplastics is a growing field.

However, bioplastic development begins from a very low base and, as yet, does not compare significantly with petrochemical production. Estimates of the global production capacity for bio-derived materials is put at 327,000 tonnes/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. [17]

Types

Common plastics

A chair with a polypropylene seat Cadeira Palmetal - Modelo I - Preta - Simples.jpg
A chair with a polypropylene seat
iPhone 5c, a smartphone with a polycarbonate unibody shell IPhone 5c blue back.jpg
iPhone 5c, a smartphone with a polycarbonate unibody shell

This category includes both commodity plastics, or standard plastics, and engineering plastics.

Specialist plastics

History

Plastic (LDPE) bowl, by GEECO, Made in England, c. 1950 Plastic (LDPE) bowl, by GEECO, Made in England, c1950.jpg
Plastic (LDPE) bowl, by GEECO, Made in England, c.1950

The development of plastics has evolved from the use of natural plastic materials (e.g., chewing gum, shellac) to the use of chemically modified, natural materials (e.g., natural rubber, nitrocellulose, collagen, galalite) and finally to completely synthetic molecules (e.g., bakelite, epoxy, polyvinyl chloride). 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. [2] 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 (casein) with lye.

In the nineteenth century, as industrial chemistry developed during the Industrial Revolution, many materials were reported. The development of plastics also accelerated with Charles Goodyear's discovery of vulcanization to thermoset materials derived from natural rubber.

Blue plaque commemorating Parkes on the Birmingham Science Museum. Alexander Parkes Blue Plaque.jpg
Blue plaque commemorating Parkes on the Birmingham Science Museum.

Parkesine (nitrocellulose) is considered the first man-made plastic. The plastic material was patented by Alexander Parkes, in Birmingham, England in 1856. [19] It was unveiled at the 1862 Great International Exhibition in London. [20] Parkesine won a bronze medal at the 1862 World's fair in London. Parkesine was made 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. [21] By incorporating pigments into the product, it could be made to resemble ivory.

In 1897, the Hanover, Germany mass printing press owner Wilhelm Krische was commissioned to develop an alternative to blackboards. [22] The resultant horn-like plastic made from the milk protein casein was developed in cooperation with the Austrian chemist (Friedrich) Adolph Spitteler (1846–1940). The final result was unsuitable for the original purpose. [23] In 1893, French chemist Auguste Trillat discovered the means to insolubilize casein by immersion in formaldehyde, producing material marketed as galalith. [22]

In the early 1900s, Bakelite, the first fully synthetic thermoset, was reported by Belgian chemist Leo Baekeland by using phenol and formaldehyde.

After World War I, improvements in chemical technology led to an explosion in new forms of plastics, with mass production beginning in the 1940s and 1950s (around World War II). [24] Among the earliest examples in the wave of new polymers were polystyrene (PS), first produced by BASF in the 1930s, [2] and polyvinyl chloride (PVC), first created in 1872 but commercially produced in the late 1920s. [2] In 1923, Durite Plastics Inc. was the first manufacturer of phenol-furfural resins. [25] In 1933, polyethylene was discovered by Imperial Chemical Industries (ICI) researchers Reginald Gibson and Eric Fawcett. [2]

In 1954, polypropylene was discovered by Giulio Natta and began to be manufactured in 1957. [2]

In 1954, expanded polystyrene (used for building insulation, packaging, and cups) was invented by Dow Chemical. [2] The discovery of Polyethylene terephthalate (PET) 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. [2]

Plastics industry

Plastics manufacturing is a major part of the chemical industry, and some of the world's largest chemical companies have been involved since the earliest days, such as the industry leaders BASF and Dow Chemical.

In 2014, sales of the top fifty companies amounted to US$ 961,300,000,000. [26] The firms came from some eighteen countries in total, with more than half of the companies on the list being headquartered in the US. Many of the top fifty plastics companies were concentrated in just three countries:

BASF was the world's largest chemical producer for the ninth year in a row. [26]

Trade associations which represent the industry in the US include the American Chemistry Council.

Industry standards

Many of the properties of plastics are determined by standards specified by ISO, such as:

Many of the properties of plastics are determined by the UL Standards, tests specified by Underwriters Laboratories (UL), such as:

Additives

Blended into most plastics are additional organic or inorganic compounds. The average content of additives is a few percent. Many of the controversies associated with plastics actually relate to the additives: [27] organotin compounds are particularly toxic. [28]

Typical additives include:

Stabilizers

Polymer stabilizers prolong the lifetime of the polymer by suppressing degradation that results from UV-light, oxidation, and other phenomena. Typical stabilizers thus absorb UV light or function as antioxidants.

Fillers

Many plastics[ citation needed ] contain fillers, to improve performance or reduce production costs. [29] Typically fillers are mineral in origin, e.g., chalk. Other fillers include: starch, cellulose, wood flour, ivory dust and zinc oxide.

Plasticizers

Plasticizers are, by mass, often the most abundant additives. [28] These oily but nonvolatile compounds are blended in to plastics to improve rheology, as many organic polymers are otherwise too rigid for particular applications.

Dioctyl phthalate is the most common plasticizer. Bis(2-ethylhexyl) phthalate.svg
Dioctyl phthalate is the most common plasticizer.

Colorants

Colorants are another common additive, though their weight contribution is small.

Toxicity

Pure plastics have low toxicity due to their insolubility in water and because they are biochemically inert, due to a large molecular weight. Plastic products contain a variety of additives, some of which can be toxic. [31] For example, plasticizers like adipates and phthalates are often added to brittle plastics like polyvinyl chloride 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 European Union has restricted the use of DEHP (di-2-ethylhexyl phthalate) and other phthalates in some applications, and the United States has limited the use of DEHP, DPB, BBP, DINP, DIDP, and DnOP in children's toys and child care articles with 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. [32] Other chemicals of potential concern include alkylphenols. [28]

Whereas the finished plastic may be non-toxic, the monomers used in the manufacture of the 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. [32]

Bisphenol A (BPA)

Some polymers may also decompose into the monomers or other toxic substances when heated. In 2011, it was reported that "almost all plastic products" sampled released chemicals with estrogenic activity, although the researchers identified plastics which did not leach chemicals with estrogenic activity. [33]

The primary building block of polycarbonates, bisphenol A (BPA), is an estrogen-like endocrine disruptor that may leach into food. [32] Research in Environmental Health Perspectives finds that BPA leached from the lining of tin cans, dental sealants and polycarbonate bottles can increase body weight of lab animals' offspring. [34] 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. [35]

As of January 2010, the LA Times newspaper reports that the United States FDA is spending $30 million to investigate indications of BPA being linked to cancer. [36]

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 European Union has a permanent ban on the use of phthalates in toys. In 2009, the United States government banned certain types of phthalates commonly used in plastic. [37]

Environmental effects

This infographic shows that there will (predicted) be more plastic in the oceans than fish by 2050. More Plastic in the Ocean than Fish Infographic.png
This infographic shows that there will (predicted) be more plastic in the oceans than fish by 2050.

Most plastics are durable and degrade very slowly, as their chemical structure renders them resistant to many natural processes of degradation. 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. [38] Others estimate a cumulative human production of 8.3 billion tons of plastic of which 6.3 billion tons is waste, with a recycling rate of only 9%. [39] Much of this material may persist for centuries or longer, given the demonstrated persistence of structurally similar natural materials such as amber.

The Ocean Conservancy reported that China, Indonesia, Philippines, Thailand, and Vietnam dump more plastic in the sea than all other countries combined. [40] The rivers Yangtze, Indus, Yellow River, Hai River, Nile, Ganges, Pearl River, Amur, Niger, and the Mekong "transport 88–95% of the global [plastics] load into the sea." [41] [42]

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. [43] The long-term effects of plastic in the food chain are poorly understood. In 2009, it was estimated that 10% of modern waste was plastic, [24] although estimates vary according to region. [43] Meanwhile, 50–80% of debris in marine areas is plastic. [43]

Prior to the Montreal Protocol, CFCs were commonly used in the manufacture of polystyrene, and as such the production of polystyrene contributed to the depletion of the ozone layer.

Climate change

In 2019, the Center for International Environmental Law published a new report on the impact of plastic on climate change. According to the report plastic will contribute Greenhouse gases in the equivalent of 850 million tons of Carbon dioxide (CO2) to the atmosphere in 2019. In current trend, annual emissions will grow to 1.34 billion tons by 2030. By 2050 plastic could emit 56 billion tons of Greenhouse gas emissions, as much as 14 percent of the earth's remaining carbon budget. [44]

The effect of plastics on global warming is mixed. Plastics are generally made from petroleum. If the plastic is incinerated, it increases carbon emissions; if it is placed in a landfill, it becomes a carbon sink [45] although biodegradable plastics have caused methane emissions. [46] Due to the lightness of plastic versus glass or metal, plastic may reduce energy consumption. For example, packaging beverages in PET plastic rather than glass or metal is estimated to save 52% in transportation energy. [2]

Production of plastics

Production of plastics from crude oil requires 62 to 108 MJ/Kg (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: 230 to 235 MJ/Kg of silicon, and about 3,000 MJ/Kg of semiconductors. [47] This is much higher than the energy needed to produce many other materials, e.g. iron (from iron ore) requires 20-25 MJ/Kg of energy, glass (from sand, etc.) 18–35 MJ/Kg, steel (from iron) 20–50 MJ/Kg, paper (from timber) 25–50 MJ/Kg. [48]

Incineration of plastics

Controlled high-temperature incineration, above 850 °C for two seconds[ citation needed ], performed with selective additional heating, breaks down toxic dioxins and furans from burning plastic, and is widely used in municipal solid waste incineration. Municipal solid waste incinerators also normally include flue gas treatments to reduce pollutants further. This is needed because uncontrolled incineration of plastic produces polychlorinated dibenzo-p-dioxins, a carcinogen (cancer causing chemical). The problem occurs because the heat content of the waste stream varies. [49] Open-air burning of plastic occurs at lower temperatures, and normally releases such toxic fumes.

Pyrolytic disposal

Plastics can be pyrolyzed into hydrocarbon fuels, since plastics include hydrogen and carbon. One kilogram of waste plastic produces roughly a liter of hydrocarbon. [50]

Decomposition of plastics

Plastics contribute to approximately 10% of discarded waste. Depending on their chemical composition, plastics and resins have varying properties related to contaminant absorption and adsorption. Polymer degradation takes much longer as a result of saline environments and the cooling effect of the sea. These factors contribute to the persistence of plastic debris in certain environments. [43] Recent studies have shown that plastics in the ocean decompose faster than was once thought, due to exposure to 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. [51] 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 nappy will take 450 years, and fishing line will take 600 years to degrade. [52]

In 2018, a survey by the Global Oceanic Environmental Survey (GOES) Foundation found that the ecosystem in seas and oceans may collapse in the next 25 years, potentially causing failure of terrestrial ecosystem and "very possibly the end of life on Earth as we know it [53] "; the main agents of this prediction were hypothesized to be plastic, ocean acidification, and ocean pollution. In order to prevent such a catastrophe, experts have proposed a total single use plastic ban, wood burning bans while planting "as many trees as possible," "pollution-free recycling of electronics, and by 2030 all industries to be zero toxic discharge." One British scientist advocates "special protection and perservation of peat bogs, wetlands, marshlands and mangrove swamps to ensure carbon dioxide is absorbed from the atmosphere. [53] "

Microbial species capable of degrading plastics are known to science, and some are potentially useful for the disposal of certain classes of plastic waste.

Recycling

Thermoplastics can be remelted and reused, and thermoset plastics can be ground up and used as filler, although the purity of the material tends to degrade with each reuse cycle. There are methods by which plastics can be broken down to a feedstock state.

The greatest challenge to the recycling of plastics is the difficulty of automating the sorting of plastic wastes, making it labor-intensive. Typically, workers sort the plastic by looking at the resin identification code, although common containers like soda bottles can be sorted from memory. Typically, the caps for PETE bottles are made from a different kind of plastic which is not recyclable, which presents additional problems for the sorting process. Other recyclable materials such as metals are easier to process mechanically. However, new processes of mechanical sorting are being developed to increase the capacity and efficiency of plastic recycling.

While containers are usually made from a single type and color of plastic, making them relatively easy to sort, a consumer product like a cellular phone may have many small parts consisting of over a dozen different types and colors of plastics. In such cases, the resources it would take to separate the plastics far exceed their value and the item is discarded. However, developments are taking place in the field of active disassembly, which may result in more product components being reused or recycled. Recycling certain types of plastics can be unprofitable as well. For example, polystyrene is rarely recycled because the process is usually not cost effective. These unrecycled wastes are typically disposed of in landfills, incinerated or used to produce electricity at waste-to-energy plants.

An early success in the recycling of plastics is Vinyloop, an industrial process to separate PVC from other materials through dissolution, filtration and separation of contaminants. A solvent is used in a closed loop to elute PVC from the waste. This makes it possible to recycle composite PVC waste, which is normally incinerated or put in a landfill. Vinyloop-based recycled PVC's primary energy demand is 46 percent lower than conventionally produced PVC. The global warming potential is 39 percent lower. This is why the use of recycled material leads to a significantly better ecological outcome. [76] This process was used after the Olympic Games in London 2012. Parts of temporary Buildings like the Water Polo Arena and the Royal Artillery Barracks were recycled. In this way, the PVC Policy could be fulfilled, which says that no PVC waste should be left after the games had ended. [77]

In 1988, to assist recycling of disposable items, the Plastic Bottle Institute of the U.S. Society of the Plastics Industry devised a now-familiar scheme to mark plastic bottles by plastic type. Under this scheme, a plastic container is marked with a triangle of three "chasing arrows", which encloses a number denoting the plastic type:

Symbol Resin Code 1 PETE.svg Symbol Resin Code 2 HDPE.svg Symbol Resin Code 3 V.svg Symbol Resin Code 4 LDPE.svg Symbol Resin Code 5 PP.svg Symbol Resin Code 6 PS.svg Symbol Resin Code 7 OTHER.svg

Plastics type marks: the resin identification code [78]
  1. Polyethylene terephthalate (PET or PETE)
  2. High-density polyethylene (HDPE)
  3. Polyvinyl chloride (PVC)
  4. Low-density polyethylene (LDPE)
  5. Polypropylene (PP)
  6. Polystyrene (PS)
  7. Other types of plastic (see list below)

Representative polymers

Molded plastic food replicas on display outside a restaurant in Japan Plastic food.jpg
Molded plastic food replicas on display outside a restaurant in Japan
Plastic piping and firestops being installed in Ontario. Certain plastic pipes can be used in some non-combustible buildings, provided they are firestopped properly and that the flame spread ratings comply with the local building code. Plastic pipe firestops nortown casitas.jpg
Plastic piping and firestops being installed in Ontario. Certain plastic pipes can be used in some non-combustible buildings, provided they are firestopped properly and that the flame spread ratings comply with the local building code.

Bakelite

The first plastic based on a synthetic polymer was made from phenol and formaldehyde, with the first viable and cheap synthesis methods invented in 1907, by Leo Hendrik Baekeland, a Belgian-born American living in New York state. Baekeland was looking for an insulating shellac to coat wires in electric motors and generators. He found that combining phenol (C6H5OH) and formaldehyde (HCOH) formed a sticky mass and later found that the material could be mixed with wood flour, asbestos, or slate dust to create strong and fire resistant "composite" materials. The new material tended to foam during synthesis, requiring that Baekeland build pressure vessels to force out the bubbles and provide a smooth, uniform product, as he announced in 1909, in a meeting of the American Chemical Society. [79] Bakelite was originally used for electrical and mechanical parts, coming into widespread use in consumer goods and jewelry in the 1920s. Bakelite was a purely synthetic material, not derived from living matter. It was also an early thermosetting plastic.

Polystyrene

Styrene polymerization Styrene polymerization.png
Styrene polymerization

Unplasticised polystyrene is a rigid, brittle, inexpensive plastic that has been used to make plastic model kits and similar knick-knacks. It also is the basis for some of the most popular "foamed" plastics, under the name styrene foam or Styrofoam . Like most other foam plastics, foamed polystyrene can be manufactured in an "open cell" form, in which the foam bubbles are interconnected, as in an absorbent sponge, and "closed cell", in which all the bubbles are distinct, like tiny balloons, as in gas-filled foam insulation and flotation devices. In the late 1950s, high impact styrene was introduced, which was not brittle. It finds much current use as the substance of toy figurines and novelties.

Polyvinyl chloride

Vinylchloride polymerization Vinylchloride polymerization.png
Vinylchloride polymerization

Polyvinyl chloride (PVC, commonly called "vinyl") [80] incorporates chlorine atoms. The C-Cl bonds in the backbone are hydrophobic and resist oxidation (and burning). PVC is stiff, strong, heat and weather resistant, properties that recommend its use in devices for plumbing, gutters, house siding, enclosures for computers and other electronics gear. PVC can also be softened with chemical processing, and in this form it is now used for shrink-wrap, food packaging, and rain gear.

All PVC polymers are degraded by heat and light. When this happens, hydrogen chloride is released into the atmosphere and oxidation of the compound occurs. [81] Because hydrogen chloride readily combines with water vapor in the air to form hydrochloric acid, [82] polyvinyl chloride is not recommended for long-term archival storage of silver, photographic film or paper (mylar is preferable). [83]

Nylon

The plastics industry was revolutionized in the 1930s with the announcement of polyamide (PA), far better known by its trade name nylon. Nylon was the first purely synthetic fiber, introduced by DuPont Corporation at the 1939 World's Fair in New York City.

In 1927, DuPont had begun a secret development project designated Fiber66, under the direction of Harvard chemist Wallace Carothers and chemistry department director Elmer Keiser Bolton. Carothers had been hired to perform pure research, and he worked to understand the new materials' molecular structure and physical properties. He took some of the first steps in the molecular design of the materials.

His work led to the discovery of synthetic nylon fiber, which was very strong but also very flexible. The first application was for bristles for toothbrushes. However, Du Pont's real target was silk, particularly silk stockings. Carothers and his team synthesized a number of different polyamides including polyamide 6.6 and 4.6, as well as polyesters. [84]

General condensation polymerization reaction for nylon Condensation polymerization diacid diamine.svg
General condensation polymerization reaction for nylon

It took DuPont twelve years and US$27 million to refine nylon, and to synthesize and develop the industrial processes for bulk manufacture. With such a major investment, it was no surprise that Du Pont spared little expense to promote nylon after its introduction, creating a public sensation, or "nylon mania".

Nylon mania came to an abrupt stop at the end of 1941 when the US entered World War II. The production capacity that had been built up to produce nylon stockings, or just nylons, for American women was taken over to manufacture vast numbers of parachutes for fliers and paratroopers. After the war ended, DuPont went back to selling nylon to the public, engaging in another promotional campaign in 1946 that resulted in an even bigger craze, triggering the so-called nylon riots.

Subsequently, polyamides 6, 10, 11, and 12 have been developed based on monomers which are ring compounds; e.g. caprolactam. Nylon 66 is a material manufactured by condensation polymerization.

Nylons still remain important plastics, and not just for use in fabrics. In its bulk form it is very wear resistant, particularly if oil-impregnated, and so is used to build gears, plain bearings, valve seats, seals and because of good heat-resistance, increasingly for under-the-hood applications in cars, and other mechanical parts.

Poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA), also known as acrylic or acrylic glass as well as by the trade names Plexiglas, Acrylite, Lucite, and Perspex among several others (see below), is a transparent thermoplastic often used in sheet form as a lightweight or shatter-resistant alternative to glass. The same material can be utilised as a casting resin, in inks and coatings, and has many other uses.

Rubber

Natural rubber is an elastomer (an elastic hydrocarbon polymer) that originally was derived from latex , a milky colloidal suspension found in specialised vessels in some plants. It is useful directly in this form (indeed, the first appearance of rubber in Europe was cloth waterproofed with unvulcanized latex from Brazil). However, in 1839, Charles Goodyear invented vulcanized rubber; a form of natural rubber heated with sulfur (and a few other chemicals), forming cross-links between polymer chains (vulcanization), improving elasticity and durability.

In 1851, Nelson Goodyear added fillers to natural rubber materials to form ebonite. [30]

Synthetic rubber

The first fully synthetic rubber was synthesized by Sergei Lebedev in 1910. In World War II, supply blockades of natural rubber from South East Asia caused a boom in development of synthetic rubber, notably styrene-butadiene rubber. In 1941, annual production of synthetic rubber in the U.S. was only 231 tonnes which increased to 840,000 tonnes in 1945. In the space race and nuclear arms race, Caltech researchers experimented with using synthetic rubbers for solid fuel for rockets. Ultimately, all large military rockets and missiles would use synthetic rubber based solid fuels, and they would also play a significant part in the civilian space effort.

See also

Related Research Articles

Polyvinyl chloride Synthetic plastic polymer

Polyvinyl chloride is the world's third-most widely produced synthetic plastic polymer, after polyethylene and polypropylene. About 40 million tonnes are produced per year.

Biodegradation Decomposition by living organisms

Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi.

Polyethylene polymer

Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most common plastic. As of 2017, over 100 million tonnes of polyethylene resins are produced annually, accounting for 34% of the total plastics market. Its primary use is in packaging (plastic bags, plastic films, geomembranes, containers including bottles, etc.). Many kinds of polyethylene are known, with most having the chemical formula (C2H4)n. PE is usually a mixture of similar polymers of ethylene with various values of n. Polyethylene is a thermoplastic; however, it can become a thermoset plastic when modified (such as cross-linked polyethylene).

Polystyrene Polymer

Polystyrene (PS) is a synthetic aromatic hydrocarbon polymer made from the monomer styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and rather brittle. It is an inexpensive resin per unit weight. It is a rather poor barrier to oxygen and water vapour and has a relatively low melting point. Polystyrene is one of the most widely used plastics, the scale of its production being several million tonnes per year. Polystyrene can be naturally transparent, but can be coloured with colourants. Uses include protective packaging, containers, lids, bottles, trays, tumblers, disposable cutlery and in the making of models.

Thermoplastic plastic that becomes soft when heated and hard when cooled

A thermoplastic, or thermosoftening plastic, is a plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.

Polymer degradation is a change in the properties—tensile strength, color, shape, etc.—of a polymer or polymer-based product under the influence of one or more environmental factors such as heat, light or chemicals such as acids, alkalis and some salts. These changes are usually undesirable, such as cracking and chemical disintegration of products or, more rarely, desirable, as in biodegradation, or deliberately lowering the molecular weight of a polymer for recycling. The changes in properties are often termed "aging".

Plastic wrap Thin plastic film typically used for sealing food

Plastic wrap, cling film, shrink wrap, Saran wrap, cling wrap or food wrap is a thin plastic film typically used for sealing food items in containers to keep them fresh over a longer period of time. Plastic wrap, typically sold on rolls in boxes with a cutting edge, clings to many smooth surfaces and can thus remain tight over the opening of a container without adhesive. Common plastic wrap is roughly 0.0005 inches thick. The trend has been to produce thinner plastic wrap, particularly for household use, so now the majority of brands on shelves around the world are 8, 9 or 10 μm thick.

Plastic recycling process of recovering scrap or waste plastic for reprocessing

Plastic recycling is the process of recovering scrap or waste plastic and reprocessing the material into useful products. Since the vast majority of plastic is non-biodegradable, recycling is a part of global efforts to reduce plastic in the waste stream, especially the approximately 8 million metric tonnes of waste plastic that enters the Earth's ocean every year.

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 plastic plastic that can be biodegraded

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.

Plastic bottle bottle constructed of plastic

A plastic bottle is a bottle constructed from high-density plastic. Plastic bottles are typically used to store liquids such as water, soft drinks, motor oil, cooking oil, medicine, shampoo, milk, and ink. The size ranges from very small sample bottles to large carboys. Consumer blow molded containers often have integral handles or are shaped to facilitate grasping.

Polymer engineering is generally an engineering field that designs, analyses, and modifies polymer materials. Polymer engineering covers aspects of the petrochemical industry, polymerization, structure and characterization of polymers, properties of polymers, compounding and processing of polymers and description of major polymers, structure property relations and applications.

OXO-biodegradation is biodegradation as defined by the European Committee for Standardization (CEN) in CEN/TR 1535–2006, as "degradation resulting from oxidative and cell-mediated phenomena, either simultaneously or successively". This degradation is sometimes termed "OXO-degradable", but this latter term describes only the first or oxidative phase of degradation and should not be used for material which degrades by the process of OXO-biodegradation as defined by CEN. The correct term is "OXO-biodegradable".

A polymeric foam is a foam, in liquid or solidified form, formed from polymers.

Biodegradable bag

Biodegradable bags are bags that are capable of being decomposed by bacteria or other living organisms.

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).

Plastic is the generic name for a family of synthetic materials derived from petrochemicals. It is often product of two or more components.

Conservation and restoration of plastic objects

Conservation and restoration of objects made from plastics is an activity dedicated to the conservation of objects of historical and personal value made from plastics. When applied to cultural heritage this activity is generally undertaken by a conservator-restorer. Within museum collections there are a variety of artworks and artifacts that are composed of plastic material whether they are synthetic or semi-synthetic; these were created for a range of uses from artistic, to technical, to domestic use. Plastics have become an integral component of life and many plastic objects have become staple icons or objects worth preserving for the future. Although relatively new material for museum collections, plastics having originated in the 19th century, they are deteriorating at an alarming rate, risking the loss not only of the objects themselves, but through their deterioration processes they place objects within their vicinity at risk too. Plastics are made of synthetic, semi-synthetic and organic material, all of which are susceptible to degradation, with their respective off-gassing being harmful to the objects nearby in museum collections.

Biodegradable athletic footwear is athletic footwear that uses biodegradable materials with the ability to compost at the end-of-life phase. Such materials include natural biodegradable polymers, synthetic biodegradable polymers, and biodegradable blends. The use of biodegradable materials is a long-term solution to landfill pollution that can significantly help protect the natural environment by replacing the synthetic, non-biodegradable polymers found in athletic footwear.

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