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Thermosets vs Thermoplastics: How They Differ

The plastics industry offers a vast array of material options, each with their own unique qualities. These materials are categorized in many different ways, one of the most common being thermosets vs thermoplastics

Polymershapes stocks a wide selection of high-quality thermoplastic and thermoset materials for a number of industries across North America. Our experts will look at the demands of your application to determine if a thermoset or thermoplastic is best for you. 

What Are Thermosets?

Thermosets are plastic materials that remain solid once they cure, developing very strong chemical bonds during the curing process. Thermosetting polymers develop linked chemical bonds that lead to permanent physical and chemical properties.  These results provide a material that will not soften or melt, and will instead remain stable throughout its lifetime. Once cast, these polymers cannot be changed, reshaped, or altered. 

Thermosets are common in long-term applications that require regular exposure to harsh or fluctuating conditions. While thermoplastics soften or melt as they heat up, thermosets remain solid. Polyimide, for example, remains stable in high temperatures over 500 °F (260 °C). Some thermosets can even perform in conditions up to 700 °F (370 °C). Instead of melting, thermosets will burn or char. 

Long-term engineering/mechanical applications commonly use thermosets for their reliability and stability. Their strength gives them an extremely long service life despite the application’s high demands. 

Thermoset Material Properties

Materials classified as thermosets share several key qualities. Their consistent and durable performance properties make them a common replacement for metals. The materials’ molecular structure does not break down, providing reliable and predictable results in the most demanding applications. 

Properties of thermoset plastics include: 

  • Extreme temperature tolerances 
  • Excellent mechanical properties 
  • Hard, tough, and rigid 
  • Does not melt 
  • Once set, cannot reshape or recast 
  • Once set, cannot be modified with additives 

Examples of Thermoset Products

What Are Thermoplastics?

Many consumer products are made from thermoplastics. Unlike thermosets, thermoplastics have a melting point. Because they melt, they can be easily modified and infused with additives to provide enhanced qualities. Some thermoplastic materials can even be reshaped and rerouted into new products as they go out of service. 

Thermoplastics’ replaceability makes them very popular in consumer-based industries. Common applications include mass-produced products such as glazing, containers, packaging, tanks, pipes, and many more. 

Thermoplastic Material Properties

Thermoplastic materials feature high strength and durability, along with more manufacturing options. Due to their chemical makeup, these materials can be made through an array of manufacturing processes. Certain thermoplastic materials can also be melted down and recast as they reach the end of their service life. 

Properties of thermoplastics include: 

  • Melts once it operates above maximum service temperature 
  • May soften before it melts 
  • Can often be recycled/recast 
  • Can often be reshaped 
  • Limited temperature tolerances 

Examples of Thermoplastic Products

*PVC and Polystyrene are technically recyclable, but their outgassing properties make it extremely hazardous to do so. 

Difference Between Thermoplastics and Thermosets 

The primary difference between thermoplastics and thermosetting plastics is shown by their relationship with heat.  

Thermosets are developed with a specific heat index in mind and can withstand an extremely wide temperature range up to that index. However, once they set, their cross-linked chemical structure prevents them from being remolded or recast. The cross-linked bonds are irreversible, so they don’t break down when heated. Instead of melting, a thermoset material will burn or char once exposed to a temperature above its tolerance levels. 

Thermoplastics are more recyclable plastics that generally do not have the same temperature capabilities as thermosets. While thermosets do not melt, thermoplastics will soften as they approach temperatures above their tolerance levels. Unlike the thermosets’ cross-linked molecular structure, thermoplastics’ covalent bonds will break down when heated. Some thermoplastic materials can be melted down and recast repeatedly while retaining key properties. 

In short, thermosets remain stable when heated, and will burn instead of melt. They are so strong they can only be cast once. Their performance remains stable as conditions change. Thermoplastics soften when heated and have a melting point. Some thermoplastics can be recast or reshaped. Their performance fluctuates as they are pushed to their limits. 

Are Thermosets Stronger than Thermoplastics?

Generally speaking, thermosets are stronger than thermoplastics. Thermosets offer more reliable structural integrity and thermal stability, especially under extreme conditions.  

Many high-stress applications need a material that provides consistent performance as conditions change. While there are thermoplastics with good performance capabilities, thermosets are generally better at meeting extreme needs. Virtually all types of thermosets are stronger, offering consistent performance regardless of operating conditions. They do not soften, or melt; they simply burn when thermal conditions go above their capabilities.