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Green, yellow and pink granules of polypropylene. Image Credit: Shutterstock.com/Anastasiia Burlutskaia

All About Thermoplastic as Manufacturing Material

Learn more about this material and its different types and characteristics.

Xomety X
By Team Xometry
November 23, 2022
 6 min read
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Thermoplastic materials are made from polymer chains with repeating monomers. They can be augmented with fillers and stabilizers to further improve their properties. Thermoplastics are among the most widely used manufacturing materials due to their low cost, ease of use, and wide range of properties across the various available grades. 

Their wide variety means that specific thermoplastics are well-suited for certain tasks or requirements. For example, one application may demand tough, yet optically transparent  polycarbonate while others match better with polypropylene for its toughness, UV resistance, and chemical resistance. This article will explain what thermoplastics are, what they’re made of, and the mechanical properties of some of the more common grades. 

What is Thermoplastic?

The term thermoplastic represents a category of plastics that can be softened by heating and hardened by cooling. Unlike thermosetting polymers, thermoplastics can be molded and reshaped multiple times. The ability to form thermoplastics using heat can be appealing for many applications, including construction, consumer goods, and medical devices. Thermoplastics are made up of long chains of molecules called polymers. The three most common thermoplastics are polyethylene, polypropylene, and PVC. Each type of thermoplastic has unique properties that make it suitable for specific uses. Figure 1 below shows the type of thermoplastic pellets you may see when the material is in a raw and unformed state:

Slide 1 of 1
thermoplastic pellets in blue, green, and yellow
thermoplastic pellets in blue, green, and yellow
thermoplastic pellets in blue, green, and yellow

Blue, green, and yellow thermoplastic pellets.

Image Credit: Shutterstock.com/Mr_Mrs_Marcha

What Are the Components of Thermoplastic?

Each thermoplastic is made from a base polymer which is often accompanied by pigments, fillers, and stabilizers. The base polymer gives the material its overall mechanical, thermal, and corrosion-resistant properties. Any colors will come from pigments, though transparent and white thermoplastics often contain no pigments. Fillers are used to augment mechanical or thermal properties — for example, glass fiber will improve thermal resistance whereas carbon fiber will improve strength. Stabilizers are added to improve UV resistance, flame resistance, or other functional properties.  

What Are the Different Types of Thermoplastic?

There are many different types of thermoplastics. In general, they can be categorized as either commodity or engineering plastics. Commodity plastics are used for a wide range of applications and are the most widely produced plastics due, in part, to their low cost. Engineering plastics are specifically designed for more advanced applications. Table 1 below lists some common materials in each category:

Table 1: Common Types of Thermoplastics
ThermoplasticsDefinitionCharacteristics

Commodity

Thermoplastics

Polypropylene (PP)

Definition

Semi-crystalline structure made from polypropylene monomers

Characteristics

Tough, rigid, and corrosion-resistant

Commodity

Thermoplastics

Low-Density Polyethylene (LDPE)

Definition

Low crystallinity made from ethylene monomers

Characteristics

Tough, flexible, and corrosion resistant

Commodity

Thermoplastics

Polyvinyl Chloride (PVC)

Definition

Amorphous structure made from vinyl chloride monomers

Characteristics

Impact, water, and chemical resistance. Can be both rigid and flexible.

Commodity

Thermoplastics

High-Density Polyethylene (HDPE)

Definition

Linear molecular chain of ethylene monomers with increased crystallinity

Characteristics

Tough, rigid, good thermal and chemical resistance

Engineering

Thermoplastics

Polyetheretherketone (PEEK)

Definition

Semi-crystalline with an aromatic polymer backbone

Characteristics

Excellent chemical, thermal, and abrasion resistance. Excellent mechanical properties

Engineering

Thermoplastics

Polycarbonate (PC)

Definition

Amorphous structure made from repeating carbonate groups

Characteristics

Very tough, yet as optically clear as glass

Engineering

Thermoplastics

Polyacetal Copolymer (POM-H / Delrin®)

Definition

Highly crystalline structure made from carbon bonded to two organic functional groups.

Characteristics

Excellent mechanical and thermal properties. 

Engineering

Thermoplastics

Polyamide PA (Nylon)

Definition

Semi-crystalline made from monomers of diamine and an amino acid

Characteristics

Low friction, good UV resistance, good impact and fatigue resistance

What Are the Properties of Thermoplastic?

Some key mechanical properties for popular thermoplastics are listed in Table 2 below:

Table 2: Thermoplastic Properties
PPLDPEHDPEPVCPCPOM-HPEEKPA 6

Density (g/cm3)

PP

0.9

LDPE

0.921

HDPE

0.96

PVC

1.40

PC

1.20

POM-H

1.42 

PEEK

1.34

PA 6

1.14

Hardness (Shore D)

PP

72

LDPE

54

HDPE

70

PVC

89

PC

79

POM-H

-

PEEK

85.6

PA 6

77.3

Ultimate Tensile Strength (MPa)

PP

23.4

LDPE

11.7

HDPE

31.7

PVC

57.6

PC

74

POM-H

76

PEEK

98

PA 6

70.2

Elongation @ Break (%)

PP

300

LDPE

400

HDPE

400

PVC

5

PC

50

POM-H

45

PEEK

24.2

PA 6

66.1

Tensile Modulus (GPa)

PP

1.05

LDPE

0.393

HDPE

1.38

PVC

3.21

PC

2.4

POM-H

2.9

PEEK

-

PA 6

-

Flexural Strength (GPa)

PP

33.1

LDPE

-

HDPE

-

PVC

-

PC

-

POM-H

76

PEEK

156

PA 6

84.9

Flexural Modulus (GPa)

PP

1.24

LDPE

0.2

HDPE

1.2

PVC

2.74

PC

2.175

POM-H

2.8

PEEK

4.41

PA 6

2.34

Table Credit: https://www.bing.com/

Where is Thermoplastic Made?

Thermoplastics can be produced using a range of techniques depending on the specific type. The main techniques for thermoplastic synthesis are listed below:

  1. Transesterification: Used for copolyester elastomers.
  2. Dynamic vulcanization: Used for thermoplastic vulcanizates.
  3. Direct copolymerization: Used for TPEs (Thermoplastic elastomers).
  4. Esterification & polycondensation: Used for polyamides.
  5. Catalytic copolymerization of olefins: Used for RTPO (reactor thermoplastic polyolefin) plastics.

What Are the Applications for Thermoplastic?

Thermoplastics are used for a wide range of applications due to their ease of manufacture, low cost, and advantageous properties. Listed below is a small sample of the many possible applications of thermoplastics.

  1. Food containers
  2. Shopping bags
  3. Clothing
  4. Rope
  5. Consumer goods
  6. Car bumpers
  7. Pumps
  8. Gears

How Strong is Thermoplastic?

Because there are so many types, thermoplastics come in all manner of strength ratings. The specific type, plus the effects of any fillers, will determine the actual strength. Usually, this property is defined by the ultimate tensile strength. Engineering thermoplastics generally have higher strength than others. PEEK, one of the strongest thermoplastics, for example, has an ultimate tensile strength of 98 MPa.

What Are the Advantages of Thermoplastic?

Thermoplastics are popular manufacturing materials. Some of the reasons for this are listed below:

  1. Ease of Processing: Thermoplastics can be produced with a wide range of technologies like: injection molding, vacuum forming, blow molding, CNC machining, etc.
  2. Low Cost: Thermoplastics — especially commodity thermoplastics like polypropylene — cost very little per kilogram. The resulting products are thus very affordable, particularly when coupled with high-volume production technologies like injection molding. 
  3. Wide range of properties: Thermoplastics have a wide range of mechanical, thermal, and electrical properties. Specific properties depend on the type of thermoplastic, processing technique, and the types of fillers and additives used.
  4. High strength-to-weight ratio: Thermoplastics are lightweight. As such, components can be designed to take advantage of this while keeping the loads within acceptable limits. Plastic gears are great examples.

What Are the Disadvantages of Thermoplastic?

Despite their many advantages and widespread adoption, thermoplastics still have some disadvantages, some of which are listed below:

  1. Unimpressive thermal resistance: Thermoplastics have much lower maximum operating temperatures than metals, so they generally cannot be used in high-temperature applications. 
  2. Susceptible to creep: When exposed to long-term loading conditions, thermoplastics tend to creep over time. Loads must be selected to keep creep within acceptable limits.
  3. Chemical leaching: Some thermoplastics can leach chemicals over time. This can happen due to pigments, additives, fillers, or the base plastic itself. 
  4. Weakness to ultraviolet: Most thermoplastics will be damaged by exposure to UV radiation. This causes the plastics to become brittle and lose color over time. 

What is the Maximum Operating Temperature of Thermoplastic?

Every thermoplastic has its own maximum continuous operating temperature. This property can be further impacted by additives meant to improve thermal stability. The maximum operating temperature of a thermoplastic usually refers to the temperature at which the mechanical properties of the plastic begin to degrade. Table 3 below indicates the maximum operating temperatures of some common thermoplastics:

Table 3: Maximum Operating Temperatures of Some Common Thermoplastic
Type of ThermoplasticMax Service Temperature in Air (°C)
Type of Thermoplastic

PP

Max Service Temperature in Air (°C)

82.2

Type of Thermoplastic

LDPE

Max Service Temperature in Air (°C)

71.1

Type of Thermoplastic

HDPE

Max Service Temperature in Air (°C)

71.1

Type of Thermoplastic

PVC

Max Service Temperature in Air (°C)

60

Type of Thermoplastic

PC

Max Service Temperature in Air (°C)

120

Type of Thermoplastic

POM-H

Max Service Temperature in Air (°C)

76.9 - 96.9

Type of Thermoplastic

PEEK

Max Service Temperature in Air (°C)

263

Type of Thermoplastic

PA 6

Max Service Temperature in Air (°C)

122

Is Thermoplastic Safe to Use?

Yes, thermoplastic is safe to use for many different applications. However, if it is to be used in the presence of food or as part of a medical device, it is important to consult with suppliers to choose a safe grade of the material. 

Summary

This article presented thermoplastic, explained whatit is, and discussed the characteristics and types of this material. To learn more about thermoplastic, 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.

  1. Delrin® is a trademark of DuPont de Nemours, Inc.

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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.