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Plastic bag production. Image Credit: Shutterstock.com/Matveev Aleksandr

Plastic: Definition, Types, Properties, Applications, Advantages, and Disadvantages

Learn more about this material in full detail and how it can be used in manufacturing.

Xomety X
By Team Xometry
April 21, 2023
 18 min read
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Plastic is an incredibly versatile category of materials that are used in packaging, construction, medical equipment, and electronics. This synthetic or semi-synthetic material is derived from either petrochemicals or natural substances such as cellulose or starch and can be molded using various techniques. However, with the increasing production and disposal of plastic, there is a growing concern about its impact on the environment and human health. 

In this article, we will delve into the world of plastic, exploring its composition, characteristics, types, applications, and advantages, as well as its potential impact on our planet.

What Exactly Is Plastic?

Plastic is a synthetic or semi-synthetic material typically derived from petrochemicals or substances such as cellulose or starch. The basic components are chemically treated to form long chains of molecules called polymers. These polymers can then be molded into various shapes using techniques such as injection molding, extrusion, or blow molding. Some plastics are also known as resins.  

Plastic is a versatile material that has become ubiquitous in modern society due to its durability, low cost, and ease of manufacturing. There are many different types of plastics, each with unique properties and characteristics. Some of the most common types include: polyethylene, polypropylene, PVC, PET, polystyrene, and nylon. Plastics can be classified into two main groups based on their composition: thermoplastics and thermosets. Thermoplastics can be molded, melted, and remolded again, whereas thermosets cannot be reprocessed when heated. 

What Is the History of Plastic?

Plastic was first discovered in 1839 when Charles Goodyear stumbled upon a method called vulcanization, which made rubber more resilient and elastic. Charles Goodyear's invention was also one of the first polymer mixtures to be created. In 1855, Alexander Parkes discovered celluloid, otherwise known as Parkesine. This material is a combination of camphor/lime and cellulose nitrate. It was also the first thermoplastic that became flexible when heated and stiff when cooled. There have been several significant discoveries in the succeeding years, including: the isolation of PVC in 1835 by French physicist Victor Regnault; John Wesley Hyatt’s creation of the first synthetic polymer (or industrial plastic) in 1869; and the introduction of transparent food packaging in 1900 by Edward Brandenberger.

What Is Plastic Made Of?

Many polymers, both artificial and natural, are used to make plastics. Coal, natural gas, cellulose, starch, crude oil, and salt are a few of the most common constituents in the production of plastic. The polymerization and polycondensation processes, which both require specific catalysts, are the main methods for producing plastics. In a polymerization reaction, monomers such as propylene and ethylene are joined to form long polymer chains. Each polymer has a distinct size, structure, and set of properties that depend on the different basic monomers involved.

What Are the Characteristics of Plastic?

Plastics have a few unique properties that make them practical for a wide range of applications. Plastic materials are regarded as: 

  1. Usually lightweight with a high strength-to-weight ratio.
  2. Very versatile.
  3. Moldable into different shapes and sizes. 
  4. Thermally and electrically insulating. 
  5. Inexpensive. 
  6. Resistant to chemicals. 
  7. Very durable. 
  8. Non-biodegradable. 
  9. Usually clear and can be colored in different hues. 
  10. Different textures are possible. 

What Is the Color of Plastic?

Plastic, or resin, is nearly colorless or milky-white and can be colored by adding colorants or pigments. 

What Does a Plastic Look Like?

Plastic can come in many different colors and textures, depending on the type of plastic and how it has been treated or processed. Plastic is a synthetic polymer made from various organic materials that can be molded into almost any shape. Some types of plastic are clear and transparent, like that used in disposable water bottles, while others are opaque and available in a range of colors. Plastic can also have different surface textures, ranging from smooth and shiny to rough and matte. Some types of plastic have soft and flexible textures, while others are rigid. Figure 1 below is an example of plastic:

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example of plastic
example of plastic
example of plastic

Plastic resin.

Image Credit: Shutterstock.com/Meaw_stocker

What Are Different Types of Plastic?

There are a lot of different types of plastic available today, each with its own unique set of properties and uses. The most prominent categories are defined and discussed below:

1. Polyethylene Terephthalate (PET)

PET is one of the most produced synthetic plastic and is the most popular thermoplastic resin in the polyester family. It offers excellent chemical resistance to organic compounds and water and is easy to recycle. PET also has a high strength-to-weight ratio and is almost shatterproof. This material is found in many everyday items, including food and drink containers, and garment fibers. For more information, see our guide on Polyethylene Terephthalate (PET).

2. Acrylonitrile Butadiene Styrene (ABS)

ABS is a glossy, highly processable, flexible, strong, and impact-resistant material that is made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. ABS plastic sheeting is relatively cheap to manufacture and is frequently used in the automotive and refrigeration sectors, as well as in items like boxes, protective headgear, luggage, gauges, and children's toys. For more information, see our guide on Acrylonitrile Butadiene Styrene (ABS).

3. Polyvinyl Chloride (PVC)

PVC, the third most common synthetic plastic polymer, can be made flexible or rigid. It is well known for its versatility in mixing with other materials. For example, foamed PVC sheets are ideal for store displays, exhibits, and kiosks. Rigid PVC is extensively used in construction materials, windows, bottles, doors, non-food packaging, and other products. Thanks to the addition of plasticizers like phthalates, the more flexible and softer version of PVC works well in clothing, plumbing supplies, medical tubing, and other related products.

4. Polypropylene (PP)

Polypropylene is a thermoplastic polymer and also the second most produced synthetic plastic. PP is one of the most flexible thermoplastics, which contributes to its popularity. And despite this flexibility, it is stronger than PE. Polypropylene sheets are used to produce food containers, automobile components, medical devices, and laboratory equipment because they are affordable, strong, flexible, and heat- and acid-resistant. For more information, see our guide on Polypropylene (PP).

5. Polyethylene (PE)

The most common plastic on the planet, polyethylene, comes in multiple densities. This results in plastics with distinct physical properties, so they function for a wide gamut of purposes. The four standard densities of polyethylene are LDPE, MDPE, HDPE (low-, medium-, and high-density polyethylene, respectively), and UHMWPE (ultra-high-molecular-weight polyethylene). The first three denote the relative number of polymer chains per unit volume and each is valuable for different purposes. MDPE is, for example, frequently used in shrink film, gas pipes, screw closures, carrier bags, and other products. UHMWPE, on the other hand, is not significantly denser than HDPE. This polyethylene plastic is significantly more abrasion-resistant than HDPE because of the unusually long polymer chains. UHMWPE goes into bearings, artificial ice skating rinks, hydraulic seals, and biomaterial for spine, knee, and hip implants due to its high density and low friction properties. For more information, see our guide on Polyethylene (PE).

Low-Density Polyethylene (LDPE)

Low-Density Polyethylene (LDPE) is one of the four standard densities of polyethylene. Due to its ductility, polyethylene at this density is perfect for plastic bags, disposable packaging, transparent food containers, and shopping bags. For more information, see our guide on Low-Density Polyethylene (LDPE).

High-Density Polyethylene (HDPE)

High-Density Polyethylene (HDPE) is another type of PE that is more robust than both LDPE and MDPE. It is used in items like plastic bottles, water and sewer piping, boat hulls, snowboards, and folding chairs. For more information, see our guide on High-Density Polyethylene (HDPE).

6. Polystyrene (PS)

Polystyrene, better known as Styrofoam, comes in both solid and foamed forms. This plastic is used in egg cartons, disposable dinnerware, insulation, and drinking cups because of its low cost per unit weight and ease of production. While common, it is extremely combustible and releases toxic compounds when heated. For more information, see our guide on Polystyrene (PS).

7. Acrylic or Polymethyl Methacrylate (PMMA)

As a transparent thermoplastic material that is lightweight and break-resistant, acrylic is great for optical products and gadgets. Mirrors and plexiglass are typically made using sheets of acrylic. Among other things, PMMA is resilient against projectiles, resists UV rays and static electricity, and can accept bright dyes. There are countless applications for acrylic sheeting, which is seventeen times more impact-resistant than glass and polycarbonate sheeting put together. Moreover, it is easier to handle and create. For more information, see our guide on Acrylic or Polymethyl Methacrylate (PMMA).

8. Polycarbonate (PC)

Polycarbonate is a good engineering plastic that is strong, stable, and transparent. Its strength-to-weight ratio is 250 times better than steel’s and it has glass-like clarity. Transparent polycarbonate sheets are 30 times stronger than acrylic and are easy to work with, mold, and thermo- or cold-form. Polycarbonate plastic's intrinsic design flexibility enables incredibly strong and impact-resistant construction. Unlike acrylic or glass, PC plastic sheets can be cold-formed or cut right away without needing to be pre-formed and manufactured. Polycarbonate plastic is used to make a variety of products, including greenhouses, CDs, sunglasses, police riot gear, and more. For more information, see our guide on Polycarbonate (PC).

What Are the Properties of Plastic?

Plastics can have a wide range of physical and chemical properties, depending on their chemical structures and how they are processed. However, some general physical and chemical properties are common to most plastics. These properties are given below:

What Are the Physical Properties of Plastic?

The physical properties of plastic include:

  1. Density: Plastics come in many different densities, from as low as 0.9 g/cm³ for foamed plastics to as high as 1.5 g/cm³ for some engineering plastics.
  2. Melting Point: The melting points of plastics vary widely depending on the type of polymer. Some plastics have low melting points and can be easily molded while others have high melting points and require specialized processing techniques.
  3. Hardness: Plastics can range from soft and flexible to hard and rigid, depending on the specific polymer and its processing.
  4. Transparency: Some plastics are optically transparent while others are opaque and block light. Many transparent plastics can accept dye if you need them to be opaque.
  5. Permeability: Plastics can be permeable to gasses and liquids, which can be an advantage in some applications (such as food packaging) and a disadvantage in others (such as chemical storage).

What Are the Chemical Properties of Plastic?

Here are some common chemical properties of plastic:

  1. Resistance to Chemicals: Many types of plastic are resistant to industrial chemicals, acids, and other corrosive substances. This makes them useful in a variety of industrial applications.
  2. Stability: Some plastics are sensitive to heat, light, and radiation, which can cause them to degrade over time. UV stabilizers and antioxidants are often added to plastics to improve their stability.
  3. Flammability: Plastics can be highly flammable, and many of them release toxic gasses when burned. Flame retardants are often added to plastics to improve their fire resistance.
  4. Degradation: The rate at which plastics degrade depends on a variety of factors, including the type of plastic, the conditions to which they are exposed, and the specific environmental factors they encounter. Some plastics, such as polyethylene (PE) and polypropylene (PP), degrade very slowly so they will persist in the environment for hundreds of years. Other plastics, such as polylactic acid (PLA), are designed to be biodegradable and can break down much more quickly when exposed to moisture, heat, or microorganisms. Some plastics can undergo physical degradation, such as cracking or fragmentation, even if they do not break down chemically. This can be caused by sunlight, temperature changes, or mechanical stress, and can lead to the release of hazardous plastic particles called microplastics into the environment.
  5. Solubility: Each plastic has unique solubility characteristics. Plastics that are amorphous (not crystalline), like polystyrene and polycarbonate, are more soluble in typical organic solvents than crystalline ones. Certain highly crystalline polymers, including nylon and polyolefin, resist dissolution while others like polyvinyl acetate (PVA) are highly soluble in water.
  6. Reactivity: Plastics can be reactive in different ways, depending on their chemical composition. For example, polyethylene reacts with oxygen to form carbon dioxide and water while polypropylene is relatively unreactive and stable in most chemical environments.
  7. Biodegradability: Some plastics, such as polyethylene, are not biodegradable and can persist in the environment for hundreds of years. Others, such as polycaprolactone (PCL), are biodegradable and can be broken down by bacteria and fungi over time.
  8. Recyclability:  Plastics can be difficult to recycle since they each have different chemical compositions and properties. Some types of plastics are easier to recycle than others, and recycling methods vary depending on the type of plastic.

What Are the Applications of Plastic?

Plastic has many different applications. Some of the most common uses of plastic are listed below: 

1. Toys

Plastics are often used in the production of toys because they can be molded into various shapes and colors. Plastic toys are durable and lightweight, so they withstand wear and tear.

2. Electronics

Plastics are non-conductive, meaning they can protect electronic components and allow for easy assembly. This is why you find plastic in computer and phone cases and as the insulation on wires. 

3. Automotive

Plastics are used in various parts of automobiles, including dashboards, bumpers, engine parts, and interior panels. Since they’re both lightweight and durable, they reduce the vehicle’s weight and improve fuel efficiency.

4. Construction

In the construction sector, plastics are used in a growing array of applications. Plastics are economically appealing thanks to their outstanding strength-to-weight ratio, cost effectiveness, durability, low maintenance requirements, and corrosion resistance. Plastics are used in, among other things, pipes, insulation, roofing materials, and windows.

5. Textiles

Plastics can be turned into synthetic fibers and fabrics for textiles. Modern clothing and upholstery commonly include plastics. 

6. Packaging

Plastic is an ideal material to use for product packaging. Plastics are adaptable, hygienic, light, flexible, and durable. Packaging is thus responsible for the majority of the plastics used globally, coming in the form of vending packaging, baby products, protective packaging, containers, bottles, drums, trays, boxes, cups, and much more.

7. Medical Devices

Plastics are used extensively in the medical industry, including, but not limited to, disposable syringes, IV and blood bags, prosthetic limbs, implantable devices, dialysis machines, heart valves, tubing, and wound dressing. Medical-grade plastics are sterile and biocompatible and can be easily molded into complex shapes. Plus, they’re often less expensive than traditional medical materials.

What Are the Advantages of Plastics?

Plastics have become so widespread because of their numerous advantages, including:

  1. Versatility: Plastics can be molded into various shapes and sizes.
  2. Durability: Plastics are strong and can withstand wear and tear, making them long-lasting and, in some cases, suitable for reuse.
  3. Lightweight: Plastics are generally lightweight. This makes them great when weight is an important consideration, such as in the automotive and aerospace industries.
  4. Cost-effectiveness: Plastics are often less expensive than other materials such as metals, making them a more cost-effective option for many applications.
  5. Ease of Manufacture: Plastics are easy to manufacture in large quantities, so they’re perfect for the sort of mass production that cuts per-unit costs. 
  6. Low Energy Consumption: The production of some types of plastics requires less energy compared to the production of other materials. That, in turn, helps reduce the environmental impact of manufacturing.
  7. Safety: Plastics can be designed to be non-toxic and safe for use in the medical and food industries.

What Are the Disadvantages of Plastics?

While plastics offer some distinct advantages, they also have several disadvantages. Here are some of the most significant ones:

  1. Environmental Impact: Most plastics are not biodegradable and can persist for hundreds of years. All that discarded plastic builds up as pollution, which can harm wildlife and ecosystems.
  2. Health Hazards: Some plastics contain chemicals, such as bisphenol A (BPA) and phthalates, which can leach out of the plastic and into food, water, and the broader environment. 
  3. Difficulty With Recycling: Not all types of plastic are easily recyclable, which can make proper disposal challenging. Additionally, even recycling processes can have negative environmental impacts since they require significant energy and resources. 
  4. Petroleum-Based: Many types of plastic are petroleum-based materials, meaning they’re non-renewable by nature. This can contribute to resource depletion and dependency on fossil fuels.
  5. Litter and Waste: Because disposable plastic products are so common, and because they don’t biodegrade easily, they build up as waste in landfills, oceans, and other natural environments. This can lead to negative environmental impacts and health hazards for humans and wildlife.

How Is Plastic Harmful?

Plastic is harmful for several reasons. Firstly, most plastic is not biodegradable and can remain in the environment for hundreds of years, causing plastic pollution. 

Secondly, some plastic contains toxic chemicals such as bisphenol A (BPA) and phthalates that can leach out into the environment or contaminate food and water sources, posing health risks to humans and wildlife. Although research on the health effects of plastics is far from complete, current scientific findings do show that plastic causes diseases, disabilities, and early death at every stage of its life cycle. Beyond that, animals can become entangled in plastic debris or ingest it, leading to injury, suffocation, and death. Additionally, plastic pollution can alter habitats and food sources, leading to ecosystem disruptions. 

The production of plastic uses non-renewable resources such as petroleum, contributing to resource depletion and dependency on fossil fuels. And finally, the production, transportation, and disposal of plastic can contribute to greenhouse gas emissions and climate change, further adding to the harmful effects.

What Causes Plastic Waste?

Plastic waste is caused by improper disposal of used plastics. Faulty part designs can also result in plastic waste especially when the part cannot be used as planned.

Is Plastic Necessary?

The short answer here is that it depends. Sometimes there are no alternatives that are viable, economical, and accessible. In many cases, though, plastic can be replaced with more sustainable materials such as paper, glass, or metal. However, in some industries, such as medical devices, plastic’s unique properties are what make it useful. It is important to assess the need for plastic on a case-by-case basis and consider its environmental and health impacts before deciding whether it is truly necessary.

What Are Alternatives to Plastic?

Several alternatives to plastic are often viable depending on the item’s purpose. Here are some examples:

  1. Paper: Paper is a renewable, biodegradable, and recyclable material that can be used as an alternative to plastic in many applications such as in packaging, bags, and straws.
  2. Glass: Glass is a reusable and recyclable material that can be used as an alternative to plastic in bottles, jars, and containers.
  3. Metal: Metal is a durable and recyclable material that can be used in cans, containers, and utensils.
  4. Bioplastics: Bioplastics are made from renewable resources, such as corn starch, and are biodegradable or compostable. They can be used as alternatives to conventional plastics for such purposes as packaging and bags.
  5. Natural Fibers: Natural fibers, such as cotton and hemp, can be used as alternatives to plastic in textiles, bags, and packaging.
  6. Wood: Wood is a renewable and biodegradable material that can be used to make utensils and packaging.
  7. Bamboo: Bamboo is a specific type of wood that has gained popularity in recent years due to its sustainability and versatility. Bamboo is a quick-growing, renewable resource that may be harvested without doing any environmental harm. Some examples of how bamboo can be used as an alternative to plastic include: utensils, straws, packaging, textiles, and furniture. 

What Is the Difference Between Polymer and Plastic?

Plastics and polymers are closely related concepts, but they are not the same thing. A polymer is a large molecule made up of repeating subunits called monomers, while plastic is a material made from polymers that can be molded into various shapes.

In short, plastics are made up of polymers, but not all polymers can be turned into plastics. Polymers can be natural or synthetic and take on many different forms including proteins, DNA, and cellulose. When the right polymers are chemically treated and processed, they can be turned into plastic.

While polymers exist in many forms, plastic is a specific type of polymer that is designed to be easily molded and shaped. Plastic is often used in packaging, consumer goods, automotive parts, and construction materials because it is lightweight, durable, and versatile.

So, in summary, polymers are large molecules made up of repeating subunits called monomers, while plastic is a material made from polymers that can be molded into various shapes.

Summary

This article presented plastic, explained what it is, and discussed the various types of plastic and how they are used. To learn more about plastic, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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Xomety X
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.