Thermoset vs. Thermoplastic: What’s the Difference?

Understanding the different types of plastics used in precision engineering is crucial for ensuring the quality and durability of a designed component.

Two common types of plastics (polymers) used in manufacturing precision components like plastic screws are thermosetting plastics and thermoplastics. Each has unique properties and applications, and knowing the difference between them can help you select the right material for specific engineering needs.

Our comprehensive guide will delve into the nuances of thermoset and thermoplastic materials, examining their characteristics, differences, similarities, advantages, disadvantages and practical applications.

Whether you're an engineer, product designer or simply curious about types of plastics, this article will provide you with the knowledge you want, straight from our engineers.

Contents:

• What Is a Thermoset Plastic?

• What Is a Thermoplastic?

• What Is the Difference Between Thermoplastic and Thermosetting Plastic?

• Similarities Between Thermoplastic and Thermosetting Polymers

• Advantages & Disadvantages of Thermosetting Polymers vs. Thermoplastic

• Advantages & Disadvantages of Thermoplastic vs. Thermosetting Polymers

What Is a Thermoset Plastic?

Thermoset plastics, also known as thermosetting polymers, are a type of plastic that irreversibly hardens when heated. They undergo a chemical change during a curing process, creating a three-dimensional network of incredibly strong permanent bonds. This makes them highly durable and resistant to heat and chemical degradation, but also means they cannot be remoulded once set.

Definition of Thermosetting

The definition of thermosetting is a polymer that solidifies or "sets" irreversibly when heated. The process involves a chemical reaction that forms a permanent cross-linked structure. This setting process is known as curing and can be triggered by heat, light, moisture, activators/catalysts or even radiation.

Properties of Thermosetting Plastics

Thermosetting plastics possess several distinctive properties that make them suitable for specific project applications:

• High Heat Resistance: Once cured, thermoset plastics can withstand high temperatures without melting, making them ideal for applications involving exposure to extreme heat.

• Structural Integrity: The cross-linked molecular structure provides excellent dimensional stability and resistance to deformation under stress.

• Chemical Resistance: Thermoset plastics are often resistant to a variety of chemicals, including solvents and acids, which can degrade other plastics.

• Electrical Insulation: Many thermoset plastics are good insulators, making them valuable in electrical and electronic applications.

Examples of Thermoset Plastics

There are several examples of thermoset plastics, each with specific properties suited to different uses. These examples typically feature a makeup which mixes with air or a curing agent to begin an exothermic chemical reaction that starts the curing process.

• Epoxy/Phenolic/Polyester Resins: Commonly used in adhesives, coatings and composite materials for their strong bonding and excellent mechanical properties.

• Silicone: Used in sealants, adhesives and medical applications, silicone is valued for its flexibility and stability at various temperatures.

Applications in Precision Engineering

In precision engineering, thermoset plastics are particularly valued for components that require high performance under challenging conditions. For instance, precision screws made from thermoset materials are used in environments where high heat resistance and structural integrity are critical. The stability and durability of thermoset screws ensure that they maintain their performance over long periods, even in harsh conditions.

What Is a Thermoplastic?

Thermoplastics are a category of plastics that become pliable or moldable when heated and solidified upon cooling. Unlike thermoset plastics, thermoplastics can be repeatedly melted and reshaped without undergoing a chemical change. This reversibility makes them highly versatile and widely used in various applications, including precision engineering components.

Definition of Thermoplastic

A thermoplastic, by definition, is a polymer that can be melted and reformed multiple times without altering its chemical properties. This characteristic is due to the linear or branched structure of the polymer chains, which do not form permanent cross-links when heated.

Properties of Thermoplastics

Thermoplastics exhibit several notable properties that contribute to their widespread use:

• Recyclability: The ability to be remelted and reshaped makes thermoplastics highly recyclable, reducing waste and environmental impact.

• Versatility: Thermoplastics can be moulded into a wide range of shapes and sizes, making them suitable for various manufacturing processes, including injection moulding, extrusion and 3D printing.

• Impact Resistance: Many thermoplastics have high impact resistance and flexibility, making them suitable for applications that require durability and resilience.

• Lightweight: Generally, thermoplastics are lighter than thermosetting plastics, which is advantageous in applications where weight reduction is important.

• Cost-Effective: The ease of processing and recyclability of thermoplastics often make them more cost-effective than thermosetting plastics.

Examples of Thermoplastics

There are numerous types of thermoplastics, each with unique properties tailored to specific engineering applications:

• Polyethylene (PE): Widely used in packaging, containers, and plastic bags due to its flexibility and chemical resistance.

• Polypropylene (PP): Known for its toughness and fatigue resistance, making it ideal for automotive parts, textiles and reusable containers.

• Polyvinyl Chloride (PVC): Commonly used in construction materials, piping and medical devices due to its durability and resistance to environmental degradation.

• Acrylonitrile Butadiene Styrene (ABS): Valued for its strength and impact resistance, ABS is frequently used in automotive components, toys and consumer electronics.

• Polystyrene (PS): Often used in disposable food containers, insulation and packaging materials due to its rigidity and ease of moulding.

Applications in Precision Engineering

In the field of precision engineering, thermoplastics are used for components that benefit from their unique properties. Precision screws made from thermoplastics, for example, are employed in applications where flexibility, lightweight and ease of manufacturing are essential. These screws are particularly useful in electronics, medical devices and consumer goods, where precision and reliability are crucial.

What Is the Difference Between Thermoplastic and Thermosetting Plastic?

Understanding the differences between thermoplastic and thermosetting plastics is essential for selecting the appropriate material for specific applications in precision engineering. While both are types of polymers, their chemical structures, processing methods and performance characteristics differ significantly.

The core difference between thermosetting vs thermoplastic polymers is that thermoplastic plastics can be melted and reshaped multiple times, while thermosetting plastics harden irreversibly after curing and cannot be remelted.

That said, there are many other differences once we look deeper.

Chemical Structure and Bonding

Thermoset:

• Structure: Thermosetting plastics consist of polymer chains forming a three-dimensional, permanent cross-linked network during curing.

• Bonding: Once the chemical bonds are formed during curing, they become permanent. This creates a rigid structure that cannot be remelted or reshaped, resulting in an irreversible setting.

Thermoplastic:

• Structure: Thermoplastics have linear or branched polymer chains with weak intermolecular forces. This structure allows the polymer chains to slide past each other when heated, making the material pliable.

• Bonding: The bonds between polymer chains are not permanent and can be reformed upon cooling. This reversibility enables thermoplastics to be melted and reshaped multiple times without significant chemical change.

Processing and Manufacturing

Thermoset:

• Processing: Thermosetting plastics require a curing process that involves heat, light or radiation to set the material permanently. This can be in the form of compression, friction, chemicals or external influences.

• Manufacturing: The curing process is more complex and typically requires precise control of temperature and time. Once cured, thermosetting plastics cannot be reprocessed, limiting their flexibility in manufacturing.

Thermoplastic:

• Processing: Thermoplastics can be processed using various methods such as injection moulding, extrusion and 3D printing. The ability to reheat and reshape them allows for efficient manufacturing and recycling.

• Manufacturing: The flexibility in processing makes thermoplastics suitable for producing complex shapes and detailed components, which is advantageous for iterative design and prototyping.

Performance Characteristics

Thermoset:

• Heat Resistance: Thermosetting plastics are more resistant to high temperatures and do not melt when exposed to heat, making them ideal for applications involving extreme heat.

• Structural Integrity: The cross-linked structure provides excellent dimensional stability and resistance to deformation under stress, which is crucial for high-stress applications.

Thermoplastic:

• Heat Resistance: Thermosplastics are much less resistant to high temperatures and can melt or deform when exposed to heat.

• Structural Integrity: Many thermoplastics exhibit high impact resistance and flexibility, making them suitable for applications that require durability and resilience.

Applications in Precision Engineering

Thermoset:

• Typical Uses: Thermoset plastics are used in high-performance applications such as aerospace components, electrical insulators and high-temperature environments.

• Advantages: The superior heat resistance, chemical stability and structural integrity of thermosetting plastics make them essential for applications where durability and performance under stress are critical.

Thermoplastic:

• Typical Uses: Precision screws, electronic components, medical devices and consumer goods benefit from the versatility and ease of processing thermoplastics offer.

• Advantages: The ability to produce complex, precise shapes and the recyclability of thermoplastics make them a popular choice in industries requiring detailed and environmentally sustainable components.

Similarities Between Thermoplastic and Thermosetting Polymers

While thermoplastic and thermosetting polymers have distinct differences, they also share several similarities that make them both integral to the field of precision engineering. Understanding these commonalities can help highlight their complementary roles in manufacturing and material science.

Polymer Nature

• Basic Composition: Both thermoplastics and thermosetting plastics are polymers, meaning they are composed of long chains of molecules called monomers. These monomers are chemically bonded to form larger, repeating structures that provide the base for various plastic materials.

• Versatility: Both types of polymers can be formulated with a wide range of properties to meet specific engineering needs. By modifying the chemical composition and processing conditions, manufacturers can tailor the performance characteristics of both thermoplastics and thermosets.

Applications in Precision Engineering

• Precision Components: Both thermoplastic and thermosetting polymers are used to manufacture precision components, such as screws, gears and housings. Their ability to be moulded into exact shapes makes them ideal for applications requiring high dimensional accuracy.

• Performance Under Stress: While they achieve it through different mechanisms, both types of polymers can be engineered to perform well under stress. Thermoplastics often provide impact resistance and flexibility, while thermosets offer structural integrity and heat resistance. This adaptability ensures that both materials can be used in demanding albeit different environments.

Customisability

• Additives and Fillers: Both thermoplastics and thermosetting plastics can be enhanced with additives and fillers to improve their properties. For instance, adding glass fibres can increase strength, while adding flame retardants can improve fire resistance. This customisation allows engineers to fine-tune materials for specific applications.

• Processing Techniques: Although the techniques differ, both thermoplastics and thermosetting plastics can be processed using advanced manufacturing methods techniques such as moulding, casting and extrusion, enabling the production of complex and precise parts.

Environmental Considerations

• Sustainability Efforts: There is a growing focus on making both thermoplastics and thermosetting plastics more sustainable. Innovations in recycling and the development of bio-based polymers are being explored for both types of plastics, aiming to reduce their environmental impact.

• Lifecycle Management: Both types of plastics can be part of a comprehensive lifecycle management strategy. This includes considerations for durability, longevity and end-of-life disposal or recycling. Proper management ensures that both thermoplastic and thermoset components can be used efficiently and responsibly.

Industrial Relevance

• Widespread Use: Both thermoplastic and thermosetting polymers are widely used across various industries, including automotive, aerospace, electronics and consumer goods. Their diverse properties and capabilities make them essential materials in modern manufacturing.

• Economic Impact: The production and application of both types of plastics have significant economic implications. They contribute to the development of new technologies and the improvement of existing products, driving innovation and economic growth.

Advantages & Disadvantages of Thermosetting Polymers vs. Thermoplastic

When choosing between thermosetting polymers and thermoplastics for a specific application, it is essential to weigh their respective advantages and disadvantages. This section focuses on the benefits and limitations of thermosetting polymers, helping you make informed decisions for your precision engineering needs.

Advantages of Thermosetting Polymers

• High Heat Resistance: Thermosetting polymers are remarkably resistant to high temperatures and even fire. Once cured, they do not melt or soften, maintaining their structural integrity even in extreme heat conditions. This makes them ideal for applications requiring high thermal stability, such as electrical insulators and heat shields. They do not burn with a flame, but instead char which can often prevent further damage.

• Excellent Structural Integrity: The cross-linked molecular structure of thermosetting polymers provides outstanding dimensional stability and rigidity. This ensures that components made from thermosets retain their shape and strength under mechanical stress and load, making them suitable for high-stress applications like aerospace components and heavy-duty industrial parts.

• Chemical Resistance: Thermosetting polymers are generally resistant to a wide range of chemicals, including solvents, acids and bases. This property makes them suitable for applications in harsh chemical environments, such as chemical processing equipment and protective coatings.

• Electrical Insulation: Many thermosetting polymers exhibit excellent electrical insulating properties, making them ideal for use in electronic and electrical applications. Components like circuit boards, connectors, and insulating materials benefit from the superior insulating capabilities of thermosets.

Disadvantages of Thermosetting Polymers

• Irreversibility: Once cured, thermosetting polymers cannot be remelted or reshaped. This lack of recyclability limits their reuse and reprocessing, which can be a disadvantage from an environmental and economic perspective.

• Complexity in Processing: The curing process for thermosetting polymers is often more complex and time-consuming than the processing of thermoplastics. Precise control of temperature, pressure and time is required, which can increase manufacturing costs and complexity.

• Brittle Nature: Thermosetting polymers, while strong and rigid, tend to be more brittle compared to thermoplastics. This brittleness can lead to cracking or breaking under impact or flexural stress, limiting their use in applications where flexibility and impact resistance are crucial.

Advantages & Disadvantages of Thermoplastic vs. Thermosetting Polymers

In this section, we will explore the advantages and disadvantages of thermoplastics. This perspective will help highlight why thermoplastics might be chosen over thermosetting polymers in certain applications, emphasising their unique properties and performance characteristics.

Advantages of Thermoplastic Polymers

• Reusability and Recyclability: Thermoplastics can be melted and reformed multiple times without significant degradation. This property allows for the recycling and reuse of materials, making thermoplastics a more environmentally sustainable choice compared to thermosetting polymers.

• Design Flexibility: Thermoplastics offer great flexibility in design and manufacturing. They can be easily moulded into complex shapes and intricate designs. This flexibility is particularly beneficial for producing precision components with detailed specifications.

• Impact Resistance: Many thermoplastics are known for their excellent impact resistance and toughness. This makes them suitable for applications that require materials to withstand shocks, drops, and other physical stresses, such as automotive bumpers, protective gear and electronic housings.

• Lightweight: Thermoplastics generally have a lower density compared to thermosetting polymers, making them lighter. This is advantageous in industries where weight reduction is critical, such as aerospace, automotive and consumer electronics.

• Ease of Processing: The processing of thermoplastics is relatively straightforward and cost-effective. Techniques like injection moulding and extrusion allow for high-speed production, reducing manufacturing time and costs. Additionally, thermoplastics do not require the complex curing process that thermosetting polymers do.

Disadvantages of Thermoplastic Polymers

• Lower Heat Resistance: Thermoplastics typically have lower heat resistance compared to thermosetting polymers. They can soften or deform under high temperatures, which limits their use in applications involving extreme heat or thermal cycling.

• Limited Structural Stability: While thermoplastics can be strong and durable, they generally do not offer the same level of structural stability and rigidity as thermosetting polymers. This can be a disadvantage in applications requiring precise dimensional stability and resistance to deformation under load.

• Chemical Sensitivity: Some thermoplastics can be vulnerable to chemical attack, particularly from solvents and other aggressive chemicals. This can limit their use in environments where they are exposed to harsh chemical conditions.

Wrapping Up Plastics: Thermosetting and Thermoplastics

In this in-depth engineering guide, we've explored the key differences and similarities between thermoset and thermoplastic polymers, providing a thorough understanding of their properties, applications and performance characteristics. Let's recap the most important points covered:

Key Takeaways:

• Differences Between Thermoplastics and Thermosetting Plastics: Thermoplastics can be repeatedly melted and reshaped, making them recyclable and versatile. In contrast, thermosetting plastics, once cured, cannot be remelted, offering superior heat resistance and structural integrity.

• Unique Properties: Thermoplastics are known for their flexibility, impact resistance, and ease of processing, while thermosetting plastics excel in high-heat environments and provide excellent chemical resistance and dimensional stability.

• Applications in Precision Engineering: Both materials are crucial in precision engineering. Thermoplastics are ideal for components requiring recyclability and design flexibility, whereas thermosetting plastics are preferred for high-performance applications demanding durability and stability under stress.

Definitions Reinforced:

• Define Thermoset Plastic: A polymer that irreversibly hardens when heated, forming a three-dimensional network.

• Define Thermoplastic: A polymer that becomes pliable when heated and solidifies upon cooling, allowing for repeated melting and reshaping.

Bonus Tips:

• Selecting Materials: When choosing between thermoplastics and thermosetting plastics, consider the application's temperature range, mechanical stress and environmental exposure.

• Prototyping: Use thermoplastics for rapid prototyping due to their ease of processing and recyclability, which allows for iterative design adjustments.

• Maintenance: Regularly inspect thermosetting plastic components for signs of brittleness or cracking, especially in high-stress environments.

By understanding the differences between thermoplastic and thermosetting polymers, you can make informed decisions that enhance the performance, durability and sustainability of your engineering projects.

Thanks for reading, and we hope this guide has provided valuable insights to aid in your material selection process.

FAQs

Q: What are 5 examples of thermoplastics?

A: While not an exhaustive list, here are 5 popular examples of thermoplastic materials by name.

• Polyethylene (PE): Widely used in packaging, containers and plastic bags due to its flexibility and chemical resistance.

• Polypropylene (PP): Known for its toughness and fatigue resistance, making it ideal for automotive parts, textiles and reusable containers.

• Polyvinyl Chloride (PVC): Commonly used in construction materials, piping and advertising banners due to its durability and resistance to environmental degradation.

• Acrylonitrile Butadiene Styrene (ABS): Valued for its strength and impact resistance, frequently used in automotive components, toys and consumer electronics.

• Polystyrene (PS): Often used in disposable food containers, insulation and packaging materials due to its rigidity, lightweightness and ease of moulding.

Q: Is PVC thermosetting or thermoplastic?

A: Polyvinyl Chloride (PVC) is a thermoplastic. It can be melted and reshaped multiple times, making it highly versatile for various applications, from piping to medical devices.

Q: Why are thermoplastics better for the environment than thermosetting plastics?

A: Thermoplastics are better for the environment because they can be recycled. They can be melted and reshaped multiple times without significant degradation, reducing waste and promoting material reuse. In contrast, thermosetting plastics cannot be remelted or reshaped once cured, making them more challenging to recycle.

Q: Do thermosets melt or burn?

A: Thermosetting plastics do not melt upon heating within their temperature range. Instead, they maintain their shape until they reach their capacity, at which point they will degrade or burn rather than melt. This property makes them suitable for high-temperature applications.

Q: How do I identify a thermoset?

A: You can identify a thermoset by its properties. Heat Resistance: Thermosets do not melt when heated; instead, they retain their shape until they degrade. Rigidity: Thermosets are typically more rigid and brittle compared to thermoplastics. Curing Process: Thermosets undergo an irreversible curing process involving heat, light or radiation, resulting in a hardened, three-dimensional network.