Plastic

Plastics are a wide range of synthetic or semisynthetic materials composed primarily of polymers. Their defining characteristic, plasticity, allows them to be molded, extruded, or pressed into a diverse range of solid forms. This adaptability, combined with a wide range of other properties such as low weight, durability, flexibility, chemical resistance, low toxicity, and low-cost production, has led to their widespread use around the world. While most plastics are produced from natural gas and petroleum, a growing minority are produced from renewable resources like polylactic acid.
Between 1950 and 2017, 9.2 billion metric tons of plastic are estimated to have been made, with more than half of this amount being produced since 2004. In 2023 alone, preliminary figures indicate that over 400 million metric tons of plastic were produced worldwide. If global trends in plastic demand continue, it is projected that annual global plastic production will exceed 1.3 billion tons by 2060. The primary uses for plastic include packaging, which makes up about 40% of its usage, and building and construction, which makes up about 20% of its usage.
The success and dominance of plastics since the early 20th century have had major benefits for mankind, ranging from medical devices to light-weight construction materials. The sewage systems in many countries rely on the resiliency and adaptability of polyvinyl chloride. It is also true that plastics are the basis of widespread environmental concerns, due to their slow decomposition rate in natural ecosystems. Most plastic produced has not been reused. Some are unsuitable for reuse. Much ends up in landfills or as plastic pollution. Particular concern focuses on microplastics. Marine plastic pollution, for example, creates garbage patches. Of all the plastic discarded so far, some 14% has been incinerated and less than 10% has been recycled.
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. Other uses include automobiles, furniture, and toys. In the developing world, the applications of plastic may differ; 42% of India's consumption is used in packaging. Worldwide, about 50 kg of plastic is produced annually per person, with production doubling every ten years.
The world's first fully synthetic plastic was Bakelite, invented in New York in 1907 by Leo Baekeland, who coined the term "plastics". Dozens of different types of plastics are produced today, such as polyethylene, which is widely used in product packaging, and polyvinyl chloride, used in construction and pipes because of its strength and durability. 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".

Etymology

The word plastic derives from the Ancient Greek πλαστικός, meaning "capable of being shaped or molded," which itself comes from πλαστός, meaning "molded" or "formed." In modern usage, the word plastic most commonly refers to the solid synthetic products of petrochemical-derived manufacturing.
The word plasticity, as a noun, specifically refers to the deformability of the materials used in the manufacture of plastics. Plasticity allows molding, extrusion, or compression into a variety of shapes, including films, fibers, plates, tubes, bottles, and boxes, among many others. In materials science, plasticity also has a more technical definition, describing the nonreversible change in form of solid substances when subjected to external forces. However, this definition extends beyond the scope of this article.

Structure

Most plastics contain organic polymers. 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 attached to 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.

Classifications

Plastics are usually classified by their chemical structure of the polymer's backbone and side chains. Important groups classified in this way include the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can be classified by the chemical process used in their synthesis, such as condensation, polyaddition, and cross-linking. They can also be classified by their physical properties, including hardness, density, tensile strength, thermal resistance, and glass transition temperature. Plastics can additionally be classified by their resistance and reactions to various substances and processes, such as exposure to organic solvents, oxidation, and ionizing radiation. Other classifications of plastics are based on qualities relevant to manufacturing or product design for a particular purpose. Examples include thermoplastics, thermosets, conductive polymers, biodegradable plastics, engineering plastics and elastomers.

Thermoplastics and thermosetting polymers

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, polypropylene, polystyrene, and polyvinyl chloride.
Thermosetting polymers, also known as thermosets, can melt and take shape only once: after they have solidified, they stay solid and retain their shape permanently. If reheated, thermosets decompose rather than melt. Examples of thermosets include epoxy resin, polyimide, and Bakelite. The vulcanization of rubber is an example of this process. Before heating in the presence of sulfur, natural rubber is a sticky, slightly runny material, and after vulcanization, the product is dry and rigid.

Commodity, engineering, and high-performance plastics

Commodity plastics

Approximately 80% of global plastic production includes commodity plastics, a type of plastics primarily chosen for their low cost and ease of manufacturing. These plastics are mass-produced and ubiquitous in packaging, food containers, and single-use items. Most commodity plastics are identifiable by their Resin Identification Codes, a standardized numbering system developed by ASTM International.
Beyond the six most widely recognized listed above, there are more commodity plastics that are also mass-produced and commonly used, such as polyurethanes. PURs are a class of plastics also designated as commodity plastics due to their low cost, ease of manufacturing, and versatility. However, they lack RICs because they encompass many chemically diverse formulations such as foams and adhesives.
Packaging represents the largest application of commodity plastics, consuming 146 million metric tons in 2015 alone. Beyond packaging, however, these plastics are critical in various other fields such as agriculture, construction, consumer goods, and healthcare.
Although many traits such as durability and resistance to biodegradability are desirable in various applications, they have led to significant environmental issues. An estimated 8 to 12 million tons of plastic enter oceans annually, primarily from mismanaged packaging waste. Commodity plastics account for the majority of this pollution, as their recycling rates remain low. Microplastics derived from their degradation further threaten ecosystems and human health.
The roughly 20% of remaining plastics are engineering and high-performance plastics, valued for their strength, heat resistance, chemical resistance, and other exceptional qualities. These kinds of plastics are more expensive, less common, and often used in more specialized applications.

Polymer	Production	Percentage of all plastics	Polymer type	Thermal character
Low-density polyethylene			Polyolefin	Thermoplastic
High-density polyethylene			Polyolefin	Thermoplastic
polypropylene			Polyolefin	Thermoplastic
Polystyrene			Unsaturated polyolefin	Thermoplastic
Polyvinyl chloride			Halogenated	Thermoplastic
Polyethylene terephthalate			Condensation	Thermoplastic
Polyurethane			Condensation	Thermoset
PP&A Fibers			Condensation	Thermoplastic
All Others			Various	Varies
Additives			-	-
Total	'	'	-	-

Engineering plastics

s are more robust and are used to manufacture products such as vehicle parts, building and construction materials, and some machine parts. In some cases, they are polymer blends consisting mixtures of polymers. 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.

Acrylonitrile butadiene styrene : electronic equipment cases and drainage pipes
High-impact polystyrene : refrigerator liners, food packaging, and vending cups
Polycarbonate : compact discs, eyeglasses, riot shields, security windows, traffic lights, and lenses
Polycarbonate + acrylonitrile butadiene styrene : 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 : a slippery blend of PE and ABS used in low-duty dry bearings
Polymethyl methacrylate : contact lenses, glazing, 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 : 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 : one of the aminoplasts used as a multi-colorable alternative to phenolics: used as a wood adhesive and electrical switch housings