There are so many different types of plastic, it can be hard to wrap your head around. Here’s a guide to all the different categories and types, to give you a complete understanding of plastic!
While this may seem like a boring topic, the variance in plastics and the way they are manufactured is actually quite fascinating. Because of recent news around micro plastics, you may be wondering what are micro plastics? Or, you may be wondering what makes some plastics recyclable, and some not.
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptability, plus a wide range of other properties, such as being lightweight, durable, flexible, and inexpensive to produce, has led to its widespread use. Plastics typically are made through human industrial systems. Most modern plastics are derived from fossil fuel-based chemicals like natural gas or petroleum; however, recent industrial methods use variants made from renewable materials, such as corn or cotton derivatives.
9.2 billion tonnes of plastic are estimated to have been made between 1950 and 2017. More than half this plastic has been produced since 2004. In 2020 400 million tonnes of plastic were produced. If global trends on plastic demand continue, it is estimated that by 2050 annual global plastic production will reach over 1,100 million tonnes. Safe to say, they are a huge part of our lives, and all of the equipment we use, having both a positive impact on our quality of lives, but maybe also a long term negative impact on our health.
The Environmental Impact of Plastics
The success and dominance of plastics starting in the early 20th century has caused widespread environmental problems, due to their slow decomposition rate in natural ecosystems. Toward the end of the 20th century, the plastics industry promoted recycling in order to ease environmental concerns while continuing to produce virgin plastic and to push the responsibility of plastic pollution onto the consumer. The main companies producing plastics doubted the economic viability of recycling at the time, and the economic viability has never improved. Plastic collection and recycling is largely ineffective because of failures of contemporary complexity required in cleaning and sorting post-consumer plastics for effective reuse. Most plastic produced has not been reused, either being captured in landfills or persisting in the environment as plastic pollution. Plastic pollution can be found in all the world’s major water bodies, for example, creating garbage patches in all of the world’s oceans and contaminating terrestrial ecosystems. Of all the plastic discarded so far, some 14% has been incinerated and less than 10% has been recycled.
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 (up to 20% plastic), furniture, and toys. In the developing world, the applications of plastic may differ; 42% of India’s consumption is used in packaging. In the medical field, polymer implants and other medical devices are derived at least partially from plastic. Worldwide, about 50 kg of plastic is produced annually per person, with production doubling every ten years.
Recyclable Versus non-Recyclable Plastic
While it may seem that there is no rhyme or reason to the recycle sign placement on certain plastics and not others, there is in fact a logical explanation, and it may help you to better understand the significance of what you throw in the recycling versus garbage. The difference in the recyclability of plastic types can be down to how they are made; thermoset plastics contain polymers that form irreversible chemical bonds and cannot be recycled, whereas thermoplastics can be re-melted and re-molded.
Recycling any material, where possible, is fundamental to the environment, however recycling plastic has specific benefits. Plastic can take hundreds of years to biodegrade, between 500-1000 years for some types, meaning it takes up landfill space and pollutes the environment for longer. Also, recycling plastic can conserve limited natural resources and energy; as plastic is made from oil, the more plastic that is recycled and the less that is made from raw materials, the more oil is conserved.
Before being recycled, plastics are sorted according to their resin type, either manually or using mechanised automated processes, or even by colour. Following sorting, there are two main ways to recycle plastic; mechanical recycling, where plastic is washed, ground and melted, or chemical recycling, whereby plastic is broken down into monomers to form new polymers to be reused.
1. Recyclable Plastics
A) PET
The most widely recycled plastic in the world is PET. Nonetheless, despite being a relatively easy plastic to recycle, some countries are still struggling to reach decent recycling rates. India, Europe and South Korea all have rates higher than 50% but countries like the US and China are yet to scale up those numbers. Alternatively, PET bottles can be recycled into… PET bottles! In fact, they are made of one of the few polymers that can be recycled into the same form – a new beverage bottle – again and again. During the process the PET is generally blended in a ratio of virgin to recycled, to give strength to the material for use in a new product.
B) HDPE
HDPE is accepted at most recycling centers in the world, as it is one of the easiest plastic polymers to recycle. Recycling companies will usually collect HDPE products and send them to large facilities to be processed. In the US, the recycling rate for HDPE bottles is around 30%.
Just like PET, HDPE can be transparent or pigmented (colored). The primary markets of postconsumer recycled natural HDPE include non-food application bottles, such as for detergent, motor oil, household cleaners, etc. and film packaging. On the other hand, pigmented HDPE post-consumer recycled resin’s markets include pipe, lawn products, and non-food application bottles. Oftentimes, HDPE is also downcycled (a recycling practice that involves materials’ reuse for lower-value products) into plastic lumber, tables, roadside curbs, benches and other durable plastic products.
C) PP
The last plastic-type that can be recycled is PP also called polypropylene. While PP is easily among the most popular plastic packaging materials in the world, only around 1-3% is recycled in the US, which means most PP is headed for the landfill. Here it degrades slowly and takes around 20-30 years to completely decompose.
Again you may ask: “if it’s recyclable, why do we throw so much of it away?” And the answer, again, is that unfortunately, it doesn’t always make sense financially to reuse this material. Polypropylene recycling is difficult and expensive and, in many cases, it’s hard to get rid of the smell of the product this plastic contained in its first life. In addition, recycled PP usually ends up being black or grey, making it unsuitable for packaging use. For this reason, rPP is usually included in plastic lumbers, park benches, auto parts, speed bumps, and it’s used for other industrial applications.
2. Non-Recyclable Plastics
A) LDPE
Low-density polyethylene, also known as plastic-type #4, is used to make the infamous plastic bags like those provided by grocery stores and other retailers. Technically, LDPE can be recycled. However, as previously mentioned, just because something can be recycled doesn’t mean it will be recycled. Plastic bags, for example, tend to tangle in recycling machinery risking endangering the entire recycling process.
In addition, LDPE is a very cheap and low-quality plastic making its recycling not really financially worthwhile. As a consequence, many municipalities won’t accept #4 plastic in curbside recycling bins. Despite these difficulties, when recycled, LDPE can be transformed into bin liners and packaging films.
B) PVC
Unfortunately, plastic number 3, the so-called polyvinyl chloride is not recyclable in normal collections.Polyvinyl chloride is the world’s third-most widely produced synthetic polymer of plastic. About 40 million tons of PVC are produced each year. PVC comes in two basic forms: rigid and flexible. The rigid form of PVC is used in construction for pipe and in profile applications such as doors and windows.
C) PS (POLYSTYRENE) and 7-OTHER
Polystyrene is a versatile plastic most easily recognized as the white foam blocks in packaging or packing peanuts. It is also commonly used in takeaway food packaging. Polystyrene is identified as Plastic No 6 and features a 6 in the arrows. programs usually don’t allow polystyrene because it’s challenging to manage. It’s hard to separate polystyrene at the facility, as it can contaminate other recycling materials. Costs are also high as it needs to be transported to another facility for recycling.
The 3 Main Types of Plastics
1. Commodity Plastics
Around 70% of global production is concentrated in six major polymer types, the so called commodity plastics. Unlike most other plastics these can often be identified by their resin identification code (RIC). These materials are inexpensive, versatile and easy to work with, making them the preferred choice for the mass production everyday objects. Their biggest single application is in packaging, with some 146 million tonnes being used this way in 2015, equivalent to 36% of global production. Due to their dominance; many of the properties and problems commonly associated with plastics, such as pollution stemming from their poor biodegradability, are ultimately attributable to commodity plastics.
There are 6 main types of commodity plastics, which I will outline below:
1. Polyethylene Terephthalate
Polyethylene terephthalate, is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, and thermoforming for manufacturing, and in combination with glass fibre for engineering resins. PET was first synthesized in North America in the mid-1940s by DuPont chemists searching for new synthetic fibers. DuPont later branded its PET fiber as “Dacron.” Today, more than half of the world’s synthetic fiber is made from PET, which is called “polyester” when used for fiber or fabric applications. When used for containers and other purposes, it is called PET or PET resin.
2. High Density Polyethylene
This plastic 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, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes and plastic lumber. HDPE is commonly recycled, and has the number “2” as its resin identification code. HDPE is known for its high strength-to-density ratio. HDPE is resistant to many different solvents, so it cannot be glued. Pipe joints must be made by welding. As one of the most versatile plastic materials around, HDPE plastic is used in a wide variety of applications, including plastic bottles, milk jugs, shampoo bottles, bleach bottles, cutting boards, and piping.
3. Polyvinyl Chloride
Polyvinyl chloride is the world’s third-most widely produced synthetic polymer of plastic. About 40 million tons of PVC are produced each year. PVC comes in two basic forms: rigid and flexible. The rigid form of PVC is used in construction for pipe and in profile applications such as doors and windows. It is a white, brittle solid material available in powder form or granules. Due to its versatile properties, such as lightweight, durable, low cost and easy processability, PVC is now replacing traditional building materials like wood, metal, concrete, rubber, ceramics, etc. in several applications.
4. Low Density Polyethylene
Low-density polyethylene is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries using a high pressure process via free radical polymerization. Its manufacture employs the same method today. It is soft, flexible, lightweight plastic material. LDPE is noted for its low temperature flexibility, toughness, and corrosion resistance. It is not suited for applications where stiffness, high temperature resistance and structural strength are required.
5. Polypropylene
Polypropylene 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 and is partially crystalline and non-polar.
Polypropylene was first polymerized in 1951 by a pair of Phillips petroleum scientists named Paul Hogan and Robert Banks and later by Italian and German scientists Natta and Rehn. It became prominent extremely fast, as commercial production began barely three years after Italian chemist, Professor Giulio Natta, first polymerized it. Natta perfected and synthesized the first polypropylene resin in Spain in 1954, and the ability of polypropylene to crystallize created a lot of excitement. By 1957, its popularity had exploded and widespread commercial production began across Europe. Today it is one of the most commonly produced plastics in the world.
6. Polystyrene
Polystyrene is a synthetic aromatic hydrocarbon polymer made from the monomer known as 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 widely employed in the food-service industry as rigid trays and containers, disposable eating utensils, and foamed cups, plates, and bowls. You probably most know this plastic as styrofoam, which has become known as extremely hazardous for the health of living beings and the planet.
2. Engineering Plastics
These plastics are more robust and are used to make products such as vehicle parts, building and construction materials, and some machine parts. In some cases they are polymer blends formed by mixing different plastics together (ABS, HIPS etc). Engineering plastics can replace metals in vehicles, reducing their weight, with a 10% reduction 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. There are many different types of engineering plastics, which I will outline below!
1. Acrylonitrile butadiene styrene
These plastics are commonly seen in electronic equipment cases (e.g. computer monitors, printers, keyboards) and drainage pipes. ABS is an opaque thermoplastic and amorphous polymer. “Thermoplastic” (as opposed to “thermoset”) refers to the way the material responds to heat. Thermoplastics become liquid (i.e. have a “glass transition”) at a certain temperature (221 degrees Fahrenheit in the case of ABS plastic). They can be heated to their melting point, cooled, and re-heated again without significant degradation. Instead of burning, thermoplastics like ABS liquefy, which allows them to be easily injection molded and then subsequently recycled.
2. High impact polystyrene
The high impact polystyrene plastics are found often in refrigerator liners, food packaging and vending cups. HIPS, or HIS is a cost effective, versatile thermoformer that is known for being lightweight and easy to print on. High Impact Polystyrene is known for its stiffness, although it is considered a low strength material. You’ll find it in consumer products such as appliances, toys, televisions, as well as in the automotive industry for car components such as gas tanks. Even food service industry products like hot and cold drinking cups can be made of HIPS material.
3. Polycarbonate
Polycarbonates are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily worked, molded, and thermoformed. Polycarbonate is generally used for compact discs, eyeglasses, riot shields, security windows, traffic lights, and lenses. As a naturally transparent amorphous thermoplastic, polycarbonate’s usefulness is in its ability to internally transmit light almost as effectively as glass and to withstand impacts far greater than many other commonly used plastics. Furthermore, the pliability of the material allows it to be created at room temperature without cracking or breaking and to be reformed even without the application of heat.
4. Polycarbonate + acrylonitrile butadiene styrene
This plastic is a blend of PC and ABS that creates a stronger plastic used in car interior and exterior parts, and in mobile phones. With excellent impact resistance, heat resistance, and outstanding aesthetics. These resin blends provide an excellent design solution when both appearance and durability are important. The combination of the two plastics results in better balanced heat resistance and impact resistance. PC-ABS is often used when ABS properties are insufficient and PC is not cost effective.
5. Acrylic
Acrylic plastic is often used in contact lenses (of the original “hard” variety), glazing (best known in this form by its various trade names around the world; e.g. Perspex, Plexiglas, and Oroglas), fluorescent-light diffusers, and rear light covers for vehicles. It also forms the basis of artistic and commercial acrylic paints, when suspended in water with the use of other agents. It is a transparent thermoplastic. This plastic is often used in sheet form as a lightweight or shatter-resistant alternative to glass. It can also be used as a casting resin, in inks and coatings, and for many other purposes. Although not a type of familiar silica-based glass, the substance, like many thermoplastics, is often technically classified as a type of glass, in that it is a non-crystalline vitreous substance—hence its occasional historic designation as acrylic glass. It was developed in 1928 in several different laboratories by many chemists, such as William Chalmers, Otto Röhm, and Walter Bauer, and first brought to market in 1933 by German Röhm & Haas AG under the name plexiglass.
6. Silicones
Silicones are heat-resistant resins used mainly as sealants but also used for high-temperature cooking utensils and as a base resin for industrial paints. They are polymers made up of siloxane. They are typically colorless oils or rubber-like substances. F. S. Kipping coined the word silicone in 1901 to describe the formula of polydiphenylsiloxane. Kipping was well aware that polydiphenylsiloxane is polymeric whereas benzophenone is monomeric and noted the contrasting properties of the two. The discovery of the structural differences between Kipping’s molecules and the ketones means that silicone is no longer the correct term (though it remains in common usage) and that the term siloxane is preferred according to the nomenclature of modern chemistry. Although, it does still seem to be pretty common practice to refer to them as silicones.
7. Urea-formaldehyde
This type of plastic is one of the aminoplasts used as a multi-colorable alternative to phenolics: used as a wood adhesive (for plywood, chipboard, hardboard) and electrical switch housings. So named for its common synthesis pathway and overall structure, it is a nontransparent thermosetting resin or polymer. It is produced from urea and formaldehyde. These resins are used in adhesives, plywood, particle board, medium-density fibreboard (MDF), and molded objects. UF and related amino resins are a class of thermosetting resins of which urea-formaldehyde resins make up 80% produced worldwide.
3. High-performance Plastics
High-performance plastics usually expensive, with their use limited to specialised applications which make use of their superior properties. High performance plastics typically have a permanent operating temperature of more than 302°F. It is this material class that brings the superior properties of polymers – such as sliding friction characteristics, weight saving and chemical resistance – to bear, especially at high permanent operating temperatures. Using special reinforcing materials such as glass fiber, glass beads or carbon fiber, heat distortion resistance and rigidity can be increased even further. Additives such as PTFE, and graphite considerably improve the sliding and friction characteristics, and the addition of metal fibers and carbon black provide improved electrical conductivity. These plastics are typically strong, have high heat temperature resistance, and can bear a lot of weight.
1. Aramids
Best known for their use in making body armor, this class of heat-resistant and strong synthetic fibers are also used in aerospace and military applications, includes Kevlar and Nomex, and Twaron. The chain molecules in the fibers are highly oriented along the fiber axis. As a result, a higher proportion of the chemical bond contributes more to fiber strength than in many other synthetic fibers. Aramids have a very high melting point. Aromatic polyamides were first introduced in commercial applications in the early 1960s, with a meta-aramid fiber produced by DuPont as HT-1 and then under the trade name Nomex. This fiber, which handles similarly to normal textile apparel fibers, is characterized by its excellent resistance to heat, as it neither melts nor ignites in normal levels of oxygen.
2. Polyetheretherketone
This is a strong, chemical- and heat-resistant thermoplastic, which has a biocompatibility that allows for use in medical implant applications and aerospace moldings. It is one of the most expensive commercial polymers.PEEK is a semicrystalline thermoplastic with excellent mechanical and chemical resistance properties that are retained to high temperatures. The processing conditions used to mould PEEK can influence the crystallinity and hence the mechanical properties. This plastic, therefore, is used to fabricate items for demanding applications, including bearings, piston parts, pumps, high-performance liquid chromatography, columns, compressor plate valves, and electrical cable insulation.
3. Polyetherimide
This high performance plastic is a high-temperature, chemically stable polymer that does not crystallize. It is an amorphous, amber-to-transparent thermoplastic with characteristics similar to the related plastic PEEK. Relative to PEEK, PEI is cheaper, but is lower in impact strength and usable temperature. It is prone to stress cracking in chlorinated solvents. Polyetherimide is able to resist high temperatures with stable electrical properties over a wide range of frequencies. This high strength material offers excellent chemical resistance and ductile properties suitable for various applications, even those including steam exposure
4. Polyimide
This plastic is of the high-temperature variety, used in materials such as Kapton tape. It is a polymer containing imide groups belonging to the class of high performance plastics. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, e.g. high temperature fuel cells, displays, and various military roles. They are used to replace the conventional use of glass, metals and even steel in many industrial applications.
5. Polysulfone
Polysulfones are a family of high performance thermoplastics. These polymers are known for their toughness and stability at high temperatures. Technically used polysulfones contain an aryl-SO2-aryl subunit. Due to the high cost of raw materials and processing, polysulfones are used in specialty applications and often are a superior replacement for polycarbonates. high-temperature melt-processable resin used in membranes, filtration media, water heater dip tubes and other high-temperature applications
6. Polytetrafluoroethylene
You may be familiar with this plastic by the name of Teflon: heat-resistant, low-friction coatings used in non-stick surfaces for frying pans, plumber’s tape and water slides. It is now proven that Teflon has a toxic effect as a coating on frying pans, seeping into the food cooked on it. Where used as a lubricant, PTFE reduces friction, wear, and energy consumption of machinery. It is commonly used as a graft material in surgical interventions. It is also frequently employed as a coating on catheters; this interferes with the ability of bacteria and other infectious agents to adhere to catheters and cause hospital-acquired infections.
7. Polyamide-imide (PAI)
This High-performance engineering plastic is extensively used in high performance gears, switches, transmission and other automotive components, and aerospace parts. These amorphous polymers have exceptional mechanical, thermal and chemical resistant properties. Polyamide-imides are used extensively as wire coatings in making magnet wire. A prominent distributor of polyamide-imides is Solvay Specialty Polymers, which uses the trademark Torlon.
Plastics may seem like they are all similar, but there is a lot of variance within the field that constitutes what properties they have, and what they can be used for. Historically, Europe and North America have dominated global plastics production. However, since 2010 Asia has emerged as a significant producer, with China accounting for 28% of total plastic resin production and 64% of synthetic fibre production in 2016 (UNEP 2018; Geyer 2020). Regional differences in the volume of plastics production are driven by user demand, the price of fossil fuel feedstocks, and investments made in the petrochemical industry. It has been proven in many ways that plastics have detrimental environmental impacts, on wildlife and humans. Plastic bags in particular have gotten a lot of bad press, and therefore most places are attempting to eliminate the use. Plastics are a large part of almost everything we use, however, and it would take a lot more work to actually replace them over time.
