All About Plastic: Definition, Types and Applications

All About Plastic: Definition, Types and Applications

Plastic is a common material used here at Xometry. We make thousands of parts out of plastic using CNC machining, laser cutting, 3D printing, injection molding and more. In this article, we will go in-dept into the world of plastic, exploring its composition, characteristics, types, applications, and advantages.

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 material that has become ubiquitous in modern society due to its durability, low cost, and manufacturability. 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. 

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.

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.

The Primary Characteristics of Plastics

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.

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 those 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 a plastic custom part made using injection molding by Xometry:

Common Types of Plastics in Manufacturing

There are a lot of different types of plastic available today and Xometry offers a lot of them. The most prominent categories that we see and use here at Xometry 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.

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).

Interconnected ABS parts 3D printed by Xometry
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.

An example of PVC
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).

 

 
The molecular structure of Polyethylene
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.

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).

A polycarbonate material sample 3D printed part

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:

Physical Properties of Plastic

  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).

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.

Applications of Plastic: Key Industries That Use It

Plastic has many different applications and we see engineers from many industries quoting plastic parts with Xometry. Some of the most common uses of plastic we have seen 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. 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.

5. 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.

Advantages of Plastics in Manufactured Parts

  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. Easy to 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.

Disadvantages of Plastics

  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. 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. 
  3. 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.

Xometry provides a wide range of manufacturing capabilities including plastic 3D printing, laser cutting, and injection molding for all of your prototyping and production needs. Start your instant quote today.

Disclaimer

The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.