Plastic recycling is the reprocessing of
plastic waste
Plastic pollution is the accumulation of plastic objects and particles (e.g. plastic bottles, bags and microbeads) in the Earth's environment that adversely affects humans, wildlife and their habitat. Plastics that act as pollutants are catego ...
into new products.
When performed correctly, this can reduce dependence on
landfill
A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the waste ...
, conserve resources and protect the environment from
plastic pollution
Plastic pollution is the accumulation of plastic objects and particles (e.g. plastic bottles, bags and microbeads) in the Earth's environment that adversely affects humans, wildlife and their habitat. Plastics that act as pollutants are catego ...
and
greenhouse gas emissions.
Although recycling rates are increasing, they lag behind those of other recoverable materials, such as
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
,
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
and
paper
Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distributed ...
. Since the beginning of plastic production in the 20th century, until 2015, the world has produced some 6.3 billion tonnes of plastic waste, only 9% of which has been recycled, and only ~1% has been recycled more than once.
Additionally, 12% was incinerated and the remaining 79% disposed of to landfill or to the environment including the sea.
Recycling is necessary because almost all plastic is non-
biodegradable and thus builds-up in the environment, where it can cause harm. For example, approximately 8 million tons of waste plastic enter the Earth's oceans every year, causing damage to the aquatic ecosystem and forming large
ocean garbage patches.
Presently, almost all recycling is performed by remelting and reforming used plastic into new items; so-called mechanical recycling. This can cause
polymer degradation
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 cycl ...
at a chemical level, and also requires that waste be sorted by both colour and
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
type before being reprocessed, which is complicated and expensive. Failures in this can lead to material with inconsistent properties, rendering it unappealing to industry.
In an alternative approach known as feedstock recycling, waste plastic is converted back into its starting chemicals, which can then be reprocessed back into fresh plastic. This offers the hope of greater recycling but suffers from higher energy and
capital costs
Capital costs are fixed, one-time expenses incurred on the purchase of land, buildings, construction, and equipment used in the production of goods or in the rendering of services. In other words, it is the total cost needed to bring a project to a ...
. Waste plastic can also be burnt in place of
fossil fuel
A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels m ...
s as part of
energy recovery
Energy recovery includes any technique or method of minimizing the input of energy to an overall system by the exchange of energy from one sub-system of the overall system with another. The energy can be in any form in either subsystem, but mos ...
. This is a controversial practice, but is nonetheless performed on a large scale. In some countries, it is the dominant form of plastic waste disposal, particularly where
landfill diversion
A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the waste ...
policies are in place.
Plastic recycling sits quite low in the
waste hierarchy
Waste hierarchy is a tool used in the evaluation of processes that protect the environment alongside resource and energy consumption from most favourable to least favourable actions. The hierarchy establishes preferred program priorities based ...
as a means of reducing plastic waste. It has been advocated since the early 1970s,
but due to severe economic and technical challenges, did not impact plastic waste to any significant extent until the late 1980s. The plastics industry has been criticised for lobbying for the expansion of recycling programs, even while industry research showed that most plastic could not be economically recycled and simultaneously increasing the amount of virgin plastic, or plastic that has not been recycled, being produced.
[National Public Radio, 12 September 202]
"How Big Oil Misled The Public Into Believing Plastic Would Be Recycled"
/ref>[PBS, Frontline, 31 March 2020]
"Plastics Industry Insiders Reveal the Truth About Recycling"
/ref>
History
Although plastics were known before the 20th century, large-scale production was not realised until WWII
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
. With metal supplies allocated towards military use and an increased demand for high-performance materials, these hitherto untested synthetic alternatives became appealing. Nylon
Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic.
Nylon is a silk-like thermoplastic, generally made from petro ...
replaced silk in parachutes, while Perspex
Poly(methyl methacrylate) (PMMA) belongs to a group of materials called engineering plastics. It is a transparent thermoplastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Plexiglas, Acrylite ...
was a light-weight alternative to glass in aeroplanes. After the war these processes were commercialised rapidly, with the plastic age beginning from around 1950, greatly aided by the post-war economic boom
In Western usage, the phrase post-war era (or postwar era) usually refers to the time since the end of World War II. More broadly, a post-war period (or postwar period) is the interval immediately following the end of a war. A post-war period c ...
.
Global environmental movements
The environmental movement (sometimes referred to as the ecology movement), also including conservation and green politics, is a diverse philosophical, social, and political movement for addressing environmental issues. Environmentalists advo ...
in the 1960s and 1970s led to the formation of environmental agencies in many jurisdictions, including the U.S. (EPA
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
, 1970), EU (DG ENV
Directorate-General for Environment (DG ENV) is a Directorate-General of the European Commission, responsible for the Environmental policy of the European Union. In 2010 "relevant limate changeactivities in DG Environment" were moved to the new ...
, 1973) Australia (EPA
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
, 1971) and Japan (JEA
Kim Hyo-jin (Hangul: 김효진; born September 18, 1981) better known by her stage name JeA is a South Korean singer and songwriter. She is best known as the leader of South Korean girl group Brown Eyed Girls. As a solo artist, she has contri ...
1971). In this atmosphere of environmental awareness, plastic waste came under scrutiny. The earliest major development to abate plastic pollution was arguably the 1973 and 1978 MARPOL agreement, whose Annex V completely banned the dumping of plastics into the ocean.
Plastic industry lobbying
As the threat of more regulation from the environmental movement grew, the plastics industry responded with lobbying to preserve their business interests. In the U.S., the Resource Recovery Act, passed in 1970, directed the nation towards recycling and energy recovery. By 1976, there had been more than a thousand attempts to pass legislation to ban or tax packaging, including plastics. The plastics industry responded by lobbying for plastic to be recycled. This involved a $50 million per year campaign through organisations such as Keep America Beautiful
Keep America Beautiful is a nonprofit organization founded in 1953. It is the largest community improvement organization in the United States, with more than 700 state and community-based affiliate organizations and more than 1,000 partner organiz ...
with the message that plastic could and would be recycled, as well as lobbying for the establishment of curbside recycling collections.
However, petrochemical industry leaders understood plastic could not be economically recycled using the technology of the time. For example, an April 1973 report written by industry scientists for industry executive states that, "There is no recovery from obsolete products" and that, "A degradation of resin properties and performance occurs during the initial fabrication, through aging, and in any reclamation process." The report concluded that sorting the plastic is "infeasible". The scientific community also knew this, with contemporary reports highlighting numerous technical barriers.
Globally, plastic waste was almost entirely disposed of via landfill
A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the waste ...
until the start of the 1980s when rates of incineration
Incineration is a waste treatment process that involves the combustion of substances contained in waste materials. Industrial plants for waste incineration are commonly referred to as waste-to-energy facilities. Incineration and other high ...
increased. Although better technology was known, these early incinerators often lacked advanced combustors or emission-control systems, leading to the release of dioxins and dioxin-like compounds
Dioxins and dioxin-like compounds (DLCs) are a group of chemical compounds that are persistent organic pollutants (POPs) in the environment. They are mostly by-products of burning or various industrial processes - or, in case of dioxin-like PCBs ...
. The replacement or upgrading of these facilities to cleaner ones with waste-to-energy
Waste-to-energy (WtE) or energy-from-waste (EfW) is the process of generating energy in the form of electricity and/or heat from the primary treatment of waste, or the processing of waste into a fuel source. WtE is a form of energy recovery. Mo ...
recovery has been gradual.
It was not until the late 1980s that plastic recycling began in earnest. In 1988 the U.S. Society of the Plastics Industry
Founded in 1937, the Society of the Plastics Industry, Inc. was a professional society representing individuals in the plastics industry. In 2010, the organization began doing business as SPI: The Plastics Industry Trade Association, before changi ...
created the Council for Solid Waste Solutions as a trade association
A trade association, also known as an industry trade group, business association, sector association or industry body, is an organization founded and funded by businesses that operate in a specific Industry (economics), industry. An industry tra ...
to sell the idea of plastic recycling to the public. The association lobbied American municipalities to launch or expand plastic waste collection programs and to lobby U.S. states to require the labelling of plastic containers and products with recycling symbols. This coincided with their introduction of resin identification code
The ASTM International Resin Identification Coding System, often abbreviated RIC, is a set of symbols appearing on plastic products that identify the plastic resin out of which the product is made. It was developed in 1988 by the Society of t ...
s in 1988, which provided a standard system for the identification of various polymer types at materials recovery facilities
A materials recovery facility, materials reclamation facility, materials recycling facility or Multi re-use facility (MRF, pronounced "murf") is a specialized plant that receives, separates and prepares recyclable materials for marketing to end-u ...
, where plastic sorting was still largely performed by hand.
Global recycling trade
Increasing globalisation during the 1990's allowed the export of plastic waste from advanced economies to developing and middle-income ones, where it could be sorted and recycled more inexpensively.
This formed part of a growing global waste trade
The global waste trade is the international trade of waste between countries for further treatment, disposal, or recycling. Toxic or hazardous wastes are often imported by developing countries from developed countries.
The World Bank Report ' ...
, which saw the annual trade in plastic waste increase rapidly from 1993 onwards.
Many governments count items as recycled if they have been exported for that purpose, however the practice has been accused of being environmental dumping
Environmental dumping is the practice of transfrontier shipment of waste (household waste, industrial/nuclear waste, etc.) from one country to another. The goal is to take the waste to a country that has less strict environmental laws, or enviro ...
, as environmental laws and their enforcement are generally weaker in less developed economies and the exported plastic waste can be mishandled, allowing it to enter the environment as plastic pollution
Plastic pollution is the accumulation of plastic objects and particles (e.g. plastic bottles, bags and microbeads) in the Earth's environment that adversely affects humans, wildlife and their habitat. Plastics that act as pollutants are catego ...
. By 2016 about 14 Mt of all plastic waste intended for recycling was exported, with China taking around half of it (7.35 million tonnes). However, much of this was low quality mixed plastic which was hard to sort and recycle and ended up accumulating in landfills and at recyclers, or being dumped. Recycled plastic has been used extensively in manufacturing in China, and imported plastic waste was predominantly processed in an informal sector that provided low-technology processing services. High-income countries such as Germany, Japan, the United Kingdom and the United States were the top plastic waste exporters.
In 2017, China began restricting waste plastics imports in Operation National Sword The Operation National Sword was a policy initiative launched in 2017 by the Government of China to monitor and more stringently review recyclable waste imports. Before the policy, China was importing the vast majority of recyclables from North Amer ...
. Europe and North America suffered from extreme waste stream backlogs, and waste plastic ended up being exported to other countries mostly in South East Asia like Vietnam and Malaysia, but also to places like Turkey and India with less stringent environmental regulations. Governments including those of Indonesia, Malaysia and Thailand reacted swiftly to curtail illegal plastic waste imports by reinforcing border controls. With increased control of imports, repatriation of illegal containers is occurring although this remains a long and challenging process. Consequently, plastic waste containers accumulated in ports in Southeast Asia.
With global trading in waste becoming more difficult, attention has returned to solutions at a local level. Extended producer responsibility
In the field of waste management, extended producer responsibility (EPR) is a strategy to add all of the environmental costs associated with a product throughout the product life cycle to the market price of that product. Extended producer res ...
schemes have been proposed which would tax plastic producers in order to subsidise recyclers.
In 2019, international trade in plastic waste became regulated under the Basel Convention
The Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal, usually known as the Basel Convention, is an international treaty that was designed to reduce the movements of hazardous waste between nations ...
. Under the Convention, any Party can decide to prohibit imports of hazardous plastic waste and, since 1 January 2021, of some mixed plastic wastes. Parties to the Convention are required to make arrangements to ensure environmentally sound management of their wastes either through alternative importers or by increasing their own capacity.
The COVID-19 pandemic
The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was first identif ...
temporarily shrunk global trade in plastic waste, due among other reasons to reduced activity at waste management facilities, interruptions of shipping routes, and low oil prices which have reduced the cost of virgin plastic and made recycling plastics less profitable.
Production and recycling rates
The total amount of plastic ever produced worldwide, until 2015, is estimated to be 8.3 billion tonnes. Approximately 6.3 billion tonnes of this has been discarded as waste, of which around 79% has accumulated in landfills or the natural environment, 12% was incinerated, and 9% has been recycled, although only ~1% of all plastic has ever been recycled more than once.
By 2015 global production had reached some 381 Mt per year, greater than the combined weight of everyone on Earth. The recycling rate in that year was 19.5%, while 25.5% was incinerated and the remaining 55% disposed of, largely to landfill. These rates lag far behind those of other recyclables, such as paper, metal and glass. Although the percentage of material being recycled or incinerated is increasing each year, the tonnage of waste left-over also continues to rise. This is because global plastic production is still increasing year-on-year. Left unchecked, production could reach ~800 Mt per year by 2040, although implementing all feasible interventions could reduce plastic pollution by 40% from 2016 rates.
A focus on global averages can disguise the fact that recycling rates also vary between types of plastic. Several types are in common use, each having distinct chemical and physical properties. This leads to differences in the ease with which they can be sorted and reprocessed; which effects the value and market size for recovered materials. PET
A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence ...
and HDPE
High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or "polythene" when used for HDPE pipes. With a high strength-to-density ratio, ...
have the highest recycling rates, whereas polystyrene
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 ...
and polyurethane
Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from ...
are often barely recycled at all.
One of the reasons for low levels of plastic recycling is weak demand from manufactures, who fear that recycled plastics will have poor or inconsistent mechanical properties. The percentage of plastic that can be fully recycled, rather than downcycled or go to waste, can be increased when manufacturers of packaged goods minimise mixing of packaging materials and eliminate contaminants. The Association of Plastics Recyclers has issued a "Design Guide for Recyclability".
The most commonly produced plastic consumer products include packaging made from LDPE
Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization. Its ...
(e.g. bags, containers, food packaging film), containers made from HDPE
High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or "polythene" when used for HDPE pipes. With a high strength-to-density ratio, ...
(e.g. milk bottles, shampoo bottles, ice cream tubs), and PET
A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence ...
(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 than, for example, plastic packaging. 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).
Regional data
Plastic consumption differs among countries and communities, with some form of plastic having made its way into most people’s lives. North American countries ( NAFTA) account 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 (94 kg and 85 kg/capita/year, respectively). In China there is lower per capita consumption (58 kg/capita/year), but high consumption nationally because of its large population.
In 2012, 25.2 Mt of post-consumer plastic waste was collected in the European Union. Of this, more than 60% (15.6 Mt) was recovered and 40% (9.6 Mt) was disposed of with municipal solid waste (MSW). Of the 15.6 Mt of recovered plastic waste, about 6.6 Mt was actually recycled, while the remainder was likely used as refuse-derived fuel (RDF) or incinerated in MSW incinerators with energy recovery (about 9 Mt). While Europe can be considered a leader in plastics recycling, only about 26% of plastic waste is recycled.
The recycling activities of the largest produces of plastic waste have the greatest effect on global averages. These are a mix of advanced economies and large developing nations, however, not all of these publish official statistics on their plastic recycling rates. Others may release partial data, usually limited to population centres. This makes it difficult to draw accurate comparisons, especially as the published recycling rates vary hugely between counties.
* Although not formally a country, legislation affecting recycling is often made at the EU level
Identification codes
Many plastic items bear symbols identifying the type of polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
from which they are made. These resin identification codes, often abbreviated RICs, are used internationally, and were originally developed in 1988 by the Society of the Plastics Industry (now the Plastics Industry Association) in the United States, but since 2008 have been administered by ASTM International
ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, ...
, a standards organisation.
RICs are not mandatory in all countries, but many producers voluntarily mark their products. More than half of U.S. states have enacted laws that require plastic products be identifiable. There are seven codes in all, six for the most common commodity plastics
Commodity plastics or commodity polymers are plastics produced in high volumes for applications where exceptional material properties are not needed (such as packaging, food containers, and household products). In contrast to engineering plastic ...
and one as a catch-all for everything else. The EU maintains a similar nine-code list which also includes ABS and polyamides
A polyamide is a polymer with repeating units linked by amide bonds.
Polyamides occur both naturally and artificially. Examples of naturally occurring polyamides are proteins, such as wool and silk. Artificially made polyamides can be made throug ...
.[Official Journal of the EC]
Commission Decision (97/129/EC)
establishing the ID system for packaging materials pursuant to European Parliament & Council Directive 94/62/EC RICs are clearly based on the recycling symbol
The universal recycling symbol ( or in Unicode) is internationally recognized for symbol for recycling activity. The symbol's creation originates on the first Earth Day in 1970, where the logo depicted is a Möbius strip. The public domain sta ...
and have drawn criticism for causing consumer confusion, as it implies the item will always be recyclable when this is not necessarily the case.
RICs are not particularly important for single-stream recycling
Single-stream (also known as “fully commingled” or "single-sort") recycling refers to a system in which all paper fibers, plastics, metals, and other containers are mixed in a collection truck, instead of being sorted by the depositor into sepa ...
, as these operations are increasingly automated. However, in some countries citizens are required to separate their plastic waste according to polymer type before refuse collection and for this RICs are very useful. For instance, in Japan PET bottles are collected separately for recycling.
Plastic waste composition
Plastic waste consists of various polymer types, its exact composition will vary, but the estimated global average is shown below. Polyolefins make up nearly 50% of all plastic waste and more than 90% of waste is made of thermosoftening
A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Most thermoplastics have a high molecular weight. The polymer chains associate ...
polymers, which can be remelted.
Collecting and sorting
Recycling begins with the collection and sorting of waste. Curbside collection operates in many counties, with the collections being sent to a materials recovery facility
A materials recovery facility, materials reclamation facility, materials recycling facility or Multi re-use facility (MRF, pronounced "murf") is a specialized plant that receives, separates and prepares recyclable materials for marketing to end-u ...
or MBT plant where the plastic is separated, cleaned and sorted for sale. Anything not deemed suitable for recycling will then be sent for landfill or incineration. These operations account for a large proportion of the financial and energy costs associated with recycling.
Sorting plastic is more complicated than any other recyclable material because it comes in a greater range of forms. For example, glass is separated into three streams (clear, green and amber), metals are usually either steel or aluminum and can be separated using magnets or eddy current separators An eddy current separator (ECS) is a machine that uses a powerful magnetic field to separate non-ferrous metals from an input waste or ore stream. The device makes use of eddy currents to effect the separation. Non-ferrous metals typically separated ...
, and paper is usually sorted into a single stream. By comparison, about six types of commodity polymer account for about 75% of plastics waste, with the remaining 25% consisting of a myriad of polymer types, including polyurethane
Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from ...
s and synthetic fibers which can have a range of chemical structures. Different polymers are generally incompatible with each other when recycled, but even items made from the same type of polymer may be incompatible depending on what additives they contain. Additives
Additive may refer to:
Mathematics
* Additive function, a function in number theory
* Additive map, a function that preserves the addition operation
* Additive set-functionn see Sigma additivity
* Additive category, a preadditive category with fi ...
are compounds blended into plastics to enhance performance and include stabilisers, fillers
In processed animal foods, a filler is an ingredient added to provide dietary fiber, bulk or some other non-nutritive purpose.
Products like corncobs, feathers, soy, cottonseed hulls, peanut hulls, citrus pulp, screening, weeds, straw, and cere ...
and, most significantly, dyes. Clear plastics hold the highest value as they may yet be dyed, while black or strongly coloured plastic is much less valuable, as their inclusion can give discoloured products. Thus, plastic normally needs to be sorted by both polymer type and colour to give a material suitable for recycling.
Various approaches and technologies have been developed to sort plastic, which can be combined in different ways. As different polymer types can be incompatible with one another, accurate sorting is essential, although in practice no approach is 100% efficient.
The accuracy of sorting therefore varies between recyclers, producing a market where products are often not well standardised
Standardization or standardisation is the process of implementing and developing technical standards based on the consensus of different parties that include firms, users, interest groups, standards organizations and governments. Standardization ...
. This inconsistency in quality can act as a barrier to recycling. Bioplastics
Bioplastics are plastic materials produced from renewable biomass sources, such as vegetable fats and oils, corn starch, straw, woodchips, sawdust, recycled food waste, etc. Some bioplastics are obtained by processing directly from natural ...
and biodegradable plastics
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, ...
currently account for only a small share of household waste but their increasing popularity may yet further complicate waste plastic sorting.
Manual separation
Sorting through waste by hand is the oldest and simplest method of separating plastic. In developing countries this may be done by waste picker
A waste picker is a person who salvages reusable or recyclable materials thrown away by others to sell or for personal consumption. There are millions of waste pickers worldwide, predominantly in developing countries, but increasingly in post-i ...
s, while in a recycling center workers pick items off a conveyor-belt. It requires low levels of technology and investment, but can have high relative operating costs due to the need for a large workforce. Although many plastic items have identification codes workers rarely have time to look for them, so there are problems of inefficiency and inconsistency in the sorting process. Regardless, even advanced facilities retain manual pickers to troubleshoot and correct sorting errors by equipment. Globally, the process focuses on those materials which are most valuable, such as clear PET bottle
Although PET is used in several applications, (principally textile fibres for apparel and upholstery, bottles and other rigid packaging, flexible packaging and electrical and electronic goods), as of 2022 only bottles are collected at a substa ...
s, with a significant amount of the waste continuing on to landfill. Working conditions can be unsanitary.
Density separation
Plastics can be separated by exploiting differences in their densities. In this approach the plastic is first ground into flakes of a similar size, washed and subjected to gravity separation
Gravity separation is an industrial method of separating two components, either a suspension, or dry granular mixture where separating the components with gravity is sufficiently practical: i.e. the components of the mixture have different specific ...
. This can be achieved using either an air classifier or hydrocyclone Hydrocyclones are a type of cyclonic separators that separate product phases mainly on basis of differences in gravity with aqueous solutions as the primary feed fluid.
As opposed to dry or dust cyclones, which separate solids from gasses, hydrocy ...
, or via wet float-sink method. These approaches only allow partial sorting, as some polymers have similar density ranges. Polypropylene
Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer propylene.
Polypropylene
belongs to the group of polyolefins a ...
(PP) and polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...
(PE) will remain together as will polyethylene terephthalate (PET), polystyrene (PS), and PVC. In addition, if the plastic contains a high percentage of fillers
In processed animal foods, a filler is an ingredient added to provide dietary fiber, bulk or some other non-nutritive purpose.
Products like corncobs, feathers, soy, cottonseed hulls, peanut hulls, citrus pulp, screening, weeds, straw, and cere ...
, this may affect its density. The lighter PP and PE fraction is known as mixed polyolefin (MPO) and can be sold as a low-value product, the heavier mixed plastics fraction is usually unrecyclable.
Electrostatic separation
In electrostatic separators, the triboelectric effect
The triboelectric effect (also known as triboelectric charging) is a type of contact electrification on which certain materials become electrically charged after they are separated from a different material with which they were in contact. Rubb ...
is used to charge plastic particles electrically; with different polymers being charged to different extents. They are then blown through an applied electric field, which deflects them depending on their charge, directing them into appropriate collectors. As with density separation, the particles need to be dry, have a close size distribution and be uniform in shape. Electrostatic separation can be complementary to density separation, allowing full separation of polymers, however, these will still be of mixed colours.
Sensor based separation
This approach can be highly automated and involves various types of sensors linked to a computer, which analyses items and directs them into appropriate chutes or belts. Near-infrared spectroscopy
Near-infrared spectroscopy (NIRS) is a spectroscopic method that uses the near-infrared region of the electromagnetic spectrum (from 780 nm to 2500 nm). Typical applications include medical and physiological diagnostics and research inc ...
can be used to distinguish between polymer types, although it can struggle with black or strongly coloured plastics, as well as composite materials like plastic-coated paper Plastic-coated paper is a coated or laminated composite material made of paper or paperboard with a plastic layer or treatment on a surface. This type of coated paper is most used in the food and drink packaging industry.
Function
The plastic is u ...
and multilayered packaging, which can give misleading readings. Optical sorting
Optical sorting (sometimes called digital sorting) is the automated process of sorting solid products using cameras and/or lasers.
Depending on the types of sensors used and the software-driven intelligence of the image processing system, optical ...
such as colour sorter
Colour sorters or color sorters (sometimes called optical sorters, digital sorters, or electronic colour sorters) are machines used on the production lines in bulk food processing and other industries. They separate items by their colours, detect ...
s or hyperspectral imaging
Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. The goal of hyperspectral imaging is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifyi ...
can then further organise the plastics by colour. Sensor based separation is more expensive to install but has the best recovery rates and produces more high-quality products.
Plastic scrap
Plastic waste can be broadly divided into two categories; industrial scrap (sometimes referred to as post industrial resin) and post-consumer waste
Post-consumer waste is a waste type produced by the end consumer of a material stream; that is, where the waste-producing use did not involve the production of another product.
The terms of pre-consumer and post-consumer recycled materials are ...
. Scrap is generated during the production of plastic items and is usually handled completely differently to post-consumer waste. It can include flashings, trimmings, sprues and rejects. As it is collected at the point of manufacture it will be clean, and of a known type and grade of material, and is usually of high quality and value. As scrap is mostly traded company-to-company rather than via municipal facilities, it is often not included in official statistics.
Mechanical recycling
The majority of plastic waste is made of thermosoftening
A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Most thermoplastics have a high molecular weight. The polymer chains associate ...
polymers, which can be re-melted and reformed into new items in a practice known as mechanical recycling. Globally, this is by far the most common form of recycling and in many countries it is effectively the only type practised. This predominance is due to it being the simplest and most economical form of recycling, in addition to it having a lower carbon footprint
A carbon footprint is the total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, place or product, expressed as carbon dioxide equivalent (CO2e). Greenhouse gases, including the carbon-containing gases carbo ...
than most other processes. However, several factors can lead to the quality of the polymer being reduced when it is recycled this way, which limits its applicability and effectiveness. Thus, the limits of mechanical recycling are in practise often the current limits of plastic recycling overall.
Plastics are reprocessed at anywhere between , depending on the polymer type, and this is sufficient to cause unwanted chemical reactions which result in polymer degradation
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 cycl ...
. This reduces the physical properties and overall quality of the plastic and can produce volatile, low-molecular weight
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
compounds, which may impart undesirable taste or odour, as well as causing thermal discolouration. Additives present within the plastic can accelerate this degradation. For instance, oxo-biodegradable
OXO-degradation is the degradation of polymers such as plastic by an oxidative process. Such degradation breaks down plastic into small pieces that are easier to biodegrade (but not necessarily enough to be called "biodegradable"). When biodegrad ...
additives, intended to improve the biodegradability
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 biodegradati ...
of plastic, also increase the degree of thermal degradation.
Similarly, flame retardants
The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source and ...
can have unwanted effects.
The quality of the product also depends strongly on how well the plastic was sorted. Many polymers are immiscible with one another when molten and will phase separate (like oil and water) during reprocessing. Products made from such blends contain many boundaries between the different polymer types and cohesion across these boundaries is weak, leading to poor mechanical properties. In more extreme cases the polymers may degrade one another, this is often the case with PVC, as it can generate hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
which strongly affects condensation polymers such as PET.
Many of these problems have technological solutions, though they bear a financial cost. Advanced polymer stabilisers and can be used to protect plastics from the rigours of thermal reprocessing. Volatile degradation products can be removed by a range of devolatilisation techniques. Flame retardants can be removed by chemical treatment, while damaging metallic additives can be rendered inert with deactivators
''Deactivators'' is a 1986 puzzle video game designed by David Bishop and Chris Palmer, developed by Tigress Marketing and System Software, and published by Ariolasoft's action game imprint Reaktor. The player controls bomb disposal robots known ...
. Finally, the properties of mixed plastics can be improved by using compatibilisers. These are compounds which improve miscibility
Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also appl ...
between polymer types to give a more homogeneous product, with better internal cohesion and improved mechanical properties. They act at the boundary between different polymers and are small-molecules possessing two different chemical regions, each of which is compatible with a certain polymer. This allows them to act like molecular-nails or screws, anchoring the areas of different polymer to one another. As a result, compatibilisers are normally limited to systems dominated by two particular types of plastic and are not a cost-effective option for unsorted mixtures of various polymer types. There is no one-size-fits-all compatibiliser for all plastic combinations. Even with these technologies, it is particularly challenging to recycle plastic so that it can meet food contact standards.
Closed-loop recycling
In closed-loop, or primary recycling, used plastic is endlessly recycled back into new items of the same quality and sort. For instance, turning drinks bottles back into drinks bottles. It can be considered an example of a circular economy. The continual mechanical recycling of plastic without reduction in quality is very challenging due to cumulative polymer degradation, and risk of contaminant build-up. In 2013 only 2% of plastic packaging was recycled in a closed loop. Although closed-loop recycling has been investigated for many polymers, to-date the only industrial successes have been with PET bottle recycling
Although PET is used in several applications, (principally textile fibres for apparel and upholstery, bottles and other rigid packaging, flexible packaging and electrical and electronic goods), as of 2022 only bottles are collected at a subst ...
. The reason for this is that polymer degradation in PET is often repairable. PET's polymer chains tend to cleave at their ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
groups and the alcohol and carboxyl groups left by this can be joined back together by the use of chemical agents called chain extenders. Pyromellitic dianhydride is one such compound.
Open-loop recycling
In open-loop recycling, also known as secondary recycling, or downcycling
Downcycling, or cascading, is the recycling of waste where the recycled material is of lower quality and functionality than the original material. Often, this is due to the accumulation of tramp elements in secondary metals, which may exclude the ...
, the quality of the plastic is reduced each time it is recycled, so that the material is not recycled indefinitely and eventually becomes waste. It is the most common type of plastic recycling. The recycling of PET bottles into fleece or other fibres is a common example, and accounts for the majority of PET recycling. Although this approach only delays material from heading to landfill or incineration, life-cycle assessment shows it to be of ecological benefit. Environmentally successful recycling displaces demand for fresh plastic production and if open-loop recycling achieves this then its benefits are indistinguishable from closed-loop recycling. If instead, it is used to produce new cheap and low-quality items which would not otherwise have been made, then it is not displacing current production and is of little or no benefit to the environment.
The reduction in polymer quality can be offset by mixing recycled plastic with virgin material when making a new product. Compatibilised plastics can be used as a replacement for virgin material, as it is possible to produce them with the right melt flow index
The Melt Flow Index (MFI) is a measure of the ease of flow of the melt of a thermoplastic polymer. It is defined as the mass of polymer, in grams, flowing in ten minutes through a capillary of a specific diameter and length by a pressure applied ...
needed for good processing. Low quality mixed plastics can also be recycled in an open-loop, although there is limited demand for such products, as in addition to poor mechanical properties, incompletely sorted waste often contains a wide range of dyes and colourants. When these are mixed during reprocessing the result is usually a dark-brown product which is unappealing for many applications. These blends find use as outdoor furniture or plastic lumber
Plastic lumber is a plastic form of lumber made of virgin or recycled plastic (PL or RPL, respectively.) It is mostly made of plastic and binders such as fiberglass or rebar; not to be confused with wood-plastic composite lumber. Widely employe ...
. As the material is weak, but of low cost it is produced in thick planks so as to be sturdy.
Thermosets
Although thermoset
In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening (" curing") a soft solid or viscous liquid prepolymer ( resin). Curing is induced by heat or suitable radiation ...
polymers do not melt, technologies have been developed for their mechanical recycling. This usually involves breaking the material down to a crumb, which can then be mixed with some sort of binding agent to form a new composite material. For instance, polyurethanes
Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from ...
can be recycled as reconstituted crumb foam. Tire recycling
Tire recycling, or rubber recycling, is the process of recycling waste tires that are no longer suitable for use on vehicles due to wear or irreparable damage. These tires are a challenging source of waste, due to the large volume produced, th ...
similarly produces crumb rubber
Crumb rubber is recycled rubber produced from automotive and truck scrap tires. During the recycling process, steel and tire cord (fluff) are removed, leaving tire rubber with a granular consistency. Continued processing with a granulator or c ...
, which can be used as aggregate. Various devulcanisation technologies have also been developed to allow the recycling of rubber wastes, though few of these are commercially important.
Feedstock recycling
In feedstock recycling, also called chemical recycling or tertiary recycling, polymers are reduced to their chemical building-blocks (monomers
In chemistry, a monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization.
Classification
M ...
), which can then be polymerised back into fresh plastics. In theory, this allows for near infinite recycling; as impurities, additives, dyes and chemical defects are completely removed with each cycle. In practice, chemical recycling is far less common than mechanical recycling. Implementation is limited because technologies do not yet exist to depolymerise all polymers reliably on an industrial scale and also because the equipment and operating costs are much higher. In 2018 Japan had one of the highest rates in the world at ~4%, compared to 23% mechanical recycling, in the same period Germany, another major recycler, reported a feedstock recycling rate of 0.2%. Depolymerising, purifying and re-polymerising the plastic can also be energy intensive, leading to the carbon footprint
A carbon footprint is the total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, place or product, expressed as carbon dioxide equivalent (CO2e). Greenhouse gases, including the carbon-containing gases carbo ...
of feedstock recycling normally being higher than that of mechanical recycling. PET, PU and PS are depolymerised commercially to varying extents, but the feedstock recycling of polyolefins, which make-up nearly half of all plastics, is much more limited.
Thermal depolymerisation
Certain polymers like PTFE, polystyrene
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 ...
, nylon 6, and polymethylmethacrylate
Poly(methyl methacrylate) (PMMA) belongs to a group of materials called engineering plastics. It is a transparent thermoplastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Plexiglas, Acrylite ...
(PMMA) undergo thermal depolymerisation when heated to sufficiently high temperatures. The reactions are sensitive to impurities and require clean and well sorted waste to produce a good product. Even then, not all depolymerisation reactions are completely efficient and some competitive pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
is often observed; the monomers, therefore, require purification before reuse. The feedstock recycling of polystyrene has been commercialised,[ but global capacity remains fairly limited.
]
Chemical depolymerisation
Condensation polymers bearing cleavable groups such as esters
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are ...
and amides
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...
can be completely depolymerised by hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
or solvolysis
In chemistry, solvolysis is a type of nucleophilic substitution (S1/S2) or elimination reaction, elimination where the nucleophile is a solvent molecule. Characteristic of S1 reactions, solvolysis of a chirality (chemistry), chiral reactant affor ...
. This can be a purely chemical process but may also be promoted by enzymes, like PETase
PETases are an esterase class of enzymes that catalyze the hydrolysis of polyethylene terephthalate (PET) plastic to monomeric mono-2-hydroxyethyl terephthalate (MHET). The idealized chemical reaction is (where n is the number of monomers in the ...
, which is able to breakdown PET. Such technologies have lower energy costs than thermal depolymerisation but are more limited in terms of the polymers they can be applied to. Thus far polyethylene terephthalate has been the most heavily studied polymer, with commercial scale feedstock recycling being performed by several companies.
Energy recovery
Energy recovery, also called energy recycling or quaternary recycling, involves burning waste plastic in place of fossil fuels for energy production. Its inclusion as a type of recycling can be controversial, but it is nonetheless included in the recycling rates reported by many countries, although it is not considered recycling by the EU. Care should be taken not to conflate
Conflation is the merging of two or more sets of information, texts, ideas, opinions, etc., into one, often in error. Conflation is often misunderstood. It originally meant to fuse or blend, but has since come to mean the same as equate, treati ...
it with incineration
Incineration is a waste treatment process that involves the combustion of substances contained in waste materials. Industrial plants for waste incineration are commonly referred to as waste-to-energy facilities. Incineration and other high ...
without energy recovery, which is historically more common, but which does not offset either future plastic production or fossil fuel use.
Energy recovery is often the default waste management method of last resort, a position previously held by landfill. In urban areas a lack of suitable sites for new landfills can drive this, but it is also a result of regulation, such as the EU's Landfill Directive
The Landfill Directive, more formally Council Directive 1999/31/EC of 26 April 1999 is a European Union directive that regulates waste management of landfills in the European Union. It was implemented by its Member States by 16 July 2001.
The D ...
or other landfill diversion
A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the waste ...
policies. Compared to the other recycling options its appeal is largely economic. If the correct technologies are used then the plastics do not need to be separated from one another, or from other forms of municipal solid waste
Municipal solid waste (MSW), commonly known as trash or garbage in the United States and rubbish in Britain, is a waste type consisting of everyday items that are discarded by the public. "Garbage" can also refer specifically to food waste, ...
(garbage), which greatly reduces costs. Compared to the sometimes variable market for recyclates, demand for electricity is universal and better understood, reducing the perceived financial risk of operations. As a means of waste management
Waste management or waste disposal includes the processes and actions required to manage waste from its inception to its final disposal.
This includes the collection, transport, treatment and disposal of waste, together with monitoring ...
, it is highly effective, reducing the volume of waste by about 90%, with the residues sent to landfill or used to make cinder block. Although its CO2 emissions are obviously high, comparing its overall ecological desirability to other recycling technologies is difficult. For instance, while recycling greatly reduces greenhouse gas emissions compared to incineration, it is an expensive way of achieving these reductions when compared to investing in renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
.
Plastic waste may be simply burnt as refuse-derived fuel
Refuse-derived fuel (RDF) is a fuel produced from various types of waste such as municipal solid waste (MSW), industrial waste or commercial waste.
The World Business Council for Sustainable Development provides a definition:
''"Selected waste ...
(RDF) in a waste-to-energy process, or it may be chemically converted to a synthetic fuel
Synthetic fuel or synfuel is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by refo ...
first. In either approach PVC must be excluded or compensated for by installing dichlorination technologies, as it generates large amounts of hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
(HCl) when burnt. This can corrode equipment and cause undesirable chlorination of the fuel products. The burning of plastics has long been associated with the release of harmful dioxins and dioxin-like compounds
Dioxins and dioxin-like compounds (DLCs) are a group of chemical compounds that are persistent organic pollutants (POPs) in the environment. They are mostly by-products of burning or various industrial processes - or, in case of dioxin-like PCBs ...
, however these hazards can be abated by the use of advanced combustors and emission control systems. Incineration with energy recovery remains the most common method, with more advanced waste-to-fuel technologies, such as pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
, being hindered by technical and cost hurdles.
Waste-to-fuel
Mixed plastic waste can be depolymerised to give a synthetic fuel. This has a higher heating value
The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it.
The ''calorific value'' is the total energy relea ...
than the starting plastic and can be burnt more efficiently, although it remains less efficient than fossil fuels. Various conversion technologies have been investigated, of which pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
is the most common.
Conversion can take place as part of incineration in an IGC cycle, but often the aim is to collect the fuel so that it may be sold. Pyrolysis of mixed plastics can give a fairly broad mix of chemical products (between about 1 and 15 carbon atoms) including gases and aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
liquids. Catalysts can give a better defined product with a higher value. The liquid products can be used as synthetic diesel
Diesel fuel , also called diesel oil, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a result of compression of the inlet air and ...
fuel, with some commercial production taking place in several countries.
Life-cycle analysis
Life cycle assessment or LCA (also known as life cycle analysis) is a methodology for assessing environmental impacts associated with all the stages of the life cycle of a commercial product, process, or service. For instance, in the case o ...
shows that plastic-to-fuel can displace the production of fossil fuels and result in lower net greenhouse gas emissions (~15% reduction).
Compared to the widespread use of incineration, plastic-to-fuel technologies have historically struggled to be economically viable because of the costs of collecting and sorting the plastic and the relatively low value of the fuel produced. Large plants are seen as being more economical than smaller ones but require more investment to build.
Other processes
Millions of tonnes of plastic waste are generated annually, and this has led to numerous solutions being developed, many of which operate at a considerable scale. A process has been developed in which many kinds of plastic
Some familiar household synthetic polymers include: Nylons in textiles and fabrics, Teflon in non-stick pans, Bakelite for electrical switches, polyvinyl chloride (PVC) in pipes, etc. The common PET bottles are made of a synthetic polymer, polye ...
can be used as a carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
source (in place of coke) in the recycling of scrap steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
, with roughly 200,000 tons of waste plastics being processed this way each year in Japan.
Construction and concrete applications
The use of recovered plastics in engineering materials is being researched and is gaining ground. Ground plastic may be used as a construction aggregate
Construction aggregate, or simply aggregate, is a broad category of coarse- to medium-grained particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates ...
or filler material in certain applications. While it is generally unsuitable in structural concrete, its inclusion in asphalt concrete
Asphalt concrete (commonly called asphalt, blacktop, or pavement in North America, and tarmac, bitumen macadam, or rolled asphalt in the United Kingdom and the Republic of Ireland) is a composite material commonly used to surface roads, parkin ...
, (forming rubberised asphalt), subbase
In topology, a subbase (or subbasis, prebase, prebasis) for a topological space X with topology T is a subcollection B of T that generates T, in the sense that T is the smallest topology containing B. A slightly different definition is used by so ...
and recycled insulation can be beneficial. An example of this is the construction of plastic roads. These are rarely made entirely of plastic but can incorporate significant amounts of plastic waste in their design. The practice is popular in India, which by 2021 had constructed some 700 km (435 miles) of highways. However, the practise has also come in for criticism, in-part over uncertainties over the leaching
Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). and may refer to:
* Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amou ...
of plastic additives into the environment. Research is ongoing to use plastics in various forms in cementitious materials such as concrete. Densifying plastic materials such as PET and plastic bags and then using them to partially replace aggregate and depolymerizing PET to use as a polymeric binder to enhance concrete are actively being studied.
See also
* Economics of plastics processing
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, the ...
* Glass recycling
Glass recycling is the processing of waste glass into usable products. Glass that is crushed or imploded and ready to be remelted is called cullet. There are two types of cullet: internal and external. Internal cullet is composed of defective p ...
* Microplastics
Microplastics are fragments of any type of plastic less than in length, according to the U.S. National Oceanic and Atmospheric Administration (NOAA) and the European Chemicals Agency. They cause pollution by entering natural ecosystems from a v ...
* Phase-out of lightweight plastic bags
A plastic bag ban is a law that restricts the use of lightweight plastic bags at retail establishments. In the early 21st century, there has been a global trend towards the phase-out of lightweight plastic bags. Single-use plastic shopping bags, ...
* Plastics 2020 Challenge
The Plastics 2020 Challenge is a campaign to reduce the quantity of plastic waste sent to landfill. In 2009, the plastics industry, PlasticsEurope, the Packaging and Films Association (PAFA) and the British Plastics Federation (BPF), launched ...
* Electronic waste
Electronic waste or e-waste describes discarded electrical or electronic devices. Used electronics which are destined for refurbishment, reuse, resale, salvage recycling through material recovery, or disposal are also considered e-waste. Inform ...
* Mobro 4000
Sources
References
External links
*
* ISF's Plastics Recovery Manual
{{Plastics
Recycling by material
Energy conservation