Maya Ellison
Heat-resistant plastics are materials that can exceed 300ºF in continuous operating temperature without compromising their mechanical properties. They are used in a variety of applications across industries, from aerospace to automotive, and are often used as an alternative to metal parts. Heat-resistant plastics fall into two broad categories: thermosets and thermoplastics. Thermosets harden when exposed to heat and cannot be reshaped after curing, while thermoplastics become molten when heated and can be re-melted after cooling. The structural integrity of thermoplastics is affected by factors such as the glass transition temperature (Tg) and melting point. Some common heat-resistant plastics include PEI, PEEK, PTFE, PAI, and PPS.
| Characteristics | Values |
|---|---|
| Melting Point | Semi-crystalline plastics have a precise melting point, whereas amorphous plastics gradually soften when heated. |
| Heat Deflection Temperature | The heat deflection temperature is a measure of how well a material maintains its stiffness under an applied load. |
| Glass Transition Temperature | The glass transition temperature (Tg) refers to the point at which a material transitions from a ductile to a brittle material. |
| Flame Resistance | A plastic’s resistance to burning is measured using UL 94 standards. Plastics with V-0, V-1, and V-2 ratings are accepted for use in consumer products. |
| Thermoplastics | PEI, PEEK, PTFE, PAI, and PPS are examples of thermoplastics that melt or soften when heated but re-solidify and regain their properties if not burned. |
| Thermosets | Thermosets break down chemically if heated past their maximum temperature and do not regain their properties once cooled. |
| Polyetherimide (PEI) | A high-performance amorphous thermoplastic with high tensile strength, chemical and temperature resistance, and dielectric strength. Commonly known by its trade name, Ultem®. |
| PEEK | A semi-crystalline, high-performance engineering thermoplastic that is resistant to chemicals, wear, fatigue, creep, and heat. It has high tensile and flexural strength and is used as a replacement for metal. |
| PTFE (Teflon) | A soft, heat-resistant, low-friction plastic with exceptional chemical resistance, high flexural strength, adequate weathering resistance, and good electrical insulating power. PTFE is chemically inert and insoluble in most solvents. |
| UHMW | A family of materials known for their great versatility and advantageous mechanical properties. Some UHMWs are specifically developed to withstand high temperatures. |
| Celazole® PBI | A thermoplastic with the highest heat and wear resistance, strength, and mechanical property retention of any engineered polymer. It has a continuous service capability of 750ºF in inert environments and 650ºF in air. |
| Vespel® | A heat-resistant plastic that can endure temperatures up to 550ºF and even up to 900ºF for limited periods without altering its properties. It is used in jet engines, cars, trucks, and industrial machinery. |
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What You'll Learn
Common heat-resistant plastics
Heat-resistant plastics are of two main types: thermosets and thermoplastics. Thermosets harden when exposed to heat and cannot be reshaped after curing. Thermoplastics, on the other hand, melt or soften when heated and re-solidify when cooled. They can also be re-melted after cooling.
Some common heat-resistant plastics are:
Polyetherimide (PEI)
Polyetherimide, commonly known by its trade name Ultem®, is a high-performance amorphous thermoplastic. It has high tensile strength, excellent chemical resistance, and temperature resistance. It also has high dielectric strength, which makes it a good electrical insulator. Ultem® is widely used in the chemical and healthcare industries, as well as for the production of electrical components. However, it is quite expensive.
Polyether Ether Ketone (PEEK)
Polyether Ether Ketone, abbreviated as PEEK, is a semi-crystalline, high-performance engineering thermoplastic. It is resistant to chemicals, wear, fatigue, creep, and heat. It has the highest tensile and flexural strength of any high-performance polymer. PEEK is widely used in the medical, automotive, and aerospace industries.
Polytetrafluoroethylene (PTFE)
Polytetrafluoroethylene, commonly known as Teflon, is a soft, heat-resistant, low-friction plastic with exceptional chemical resistance. It has high flexural strength, adequate weathering resistance, and good electrical insulating power in both hot and wet environments. PTFE is almost completely chemically inert and highly insoluble in most solvents, making it ideal for high-temperature applications. It is often used to coat non-stick pots and pans, protect pipes from corrosive materials, and provide insulation for electrical components.
Polyamide-imide (PAI)
Polyamide-imide, or PAI, is a semi-crystalline thermoplastic with excellent heat resistance and mechanical properties. It has a high melting point, typically above 275°C, and good dimensional stability. PAI is commonly used in applications where high temperatures and mechanical strength are required, such as in the automotive and aerospace industries.
Polyphenylene sulfide (PPS)
Polyphenylene sulfide, or PPS, is a semi-crystalline thermoplastic with a good balance of mechanical and thermal properties. It is inherently flame-resistant and has good chemical resistance, but poor dielectric strength. PPS is a cost-effective option for applications such as frying pan handles, centrifugal pump components, and rod guides.
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How heat resistance is classified
Heat-resistant plastics are those that can withstand temperatures above 150°C (302°F) in continuous operation or short-term exposure to temperatures of 250°C (482°F) or higher. These plastics are used in advanced applications requiring heat resistance, mechanical strength, and corrosion resistance.
There are several methods for classifying the heat resistance of plastics. Here are some of the most significant ways:
- Heat Deflection Temperature (HDT): This is the temperature at which plastic will deform under a predefined load. However, this measure does not account for potential long-term effects on the material when exposed to high temperatures for extended periods.
- Glass Transition Temperature (Tg): Tg refers to the temperature at which an amorphous plastic polymer changes from a hard, glassy state to a softened, rubbery-like state. As the temperature increases further, the plastic becomes a viscous fluid. It is important to note that for some plastics, this value can be well below zero degrees Celsius, making it less useful as a measure of heat resistance.
- Melting Point: The melting point is the temperature at which plastic transitions from an ordered molecular structure to a disordered one. Semi-crystalline plastics have a precise melting point, while amorphous plastics gradually soften when heated.
- Continuous Use Temperature (CUT): CUT defines the maximum temperature at which plastic can be used continuously without significant degradation.
- Flame Resistance: A plastic's resistance to burning is measured by its ability to resist ignition, whether it produces flammable plastic drops, and how it performs when exposed to high temperatures for extended periods.
These classification methods help determine the suitability of different plastics for various applications, ensuring that the chosen material can withstand the required temperatures without compromising its mechanical properties.
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Applications of heat-resistant plastics
Heat-resistant plastics have a wide variety of applications across many industries. They are used in the automotive industry, for example, for piston components and other lightweight parts. They are also used in the aerospace industry for cable conduits, aircraft exterior parts, and insulation for electrical components. In the medical industry, they are used for medical devices and in the semiconductor industry for subsea connectors.
One of the most popular heat-resistant plastics is PTFE, also known as Teflon. PTFE is a soft, heat-resistant, low-friction plastic with exceptional chemical resistance and good electrical insulating power in both hot and wet environments. PTFE is chemically inert and insoluble in most solvents, making it ideal for high-temperature applications. It is used to protect pipes from corrosive materials, coat heat exchangers, and provide insulation for electrical components. PTFE is also food-grade and commonly used to coat non-stick pots and pans due to its anti-adhesion properties.
Another popular heat-resistant plastic is PEEK, a semi-crystalline, high-performance engineering thermoplastic. PEEK is resistant to chemicals, wear, fatigue, creep, and heat. It is so durable that it is often used as a replacement for metal in applications where high temperatures are present. PEEK is also used in the medical industry, for active components in car transmissions, and aircraft exterior parts.
Other heat-resistant plastics include PEI (also known as Ultem® or polyetherimide), PPS, and PAI. These plastics are all thermoplastics, which means they will melt or soften when heated but will re-solidify and regain their properties unless they are heated past their maximum operating temperature. Polyetherimide (PEI) is a high-performance amorphous thermoplastic with high tensile strength, favourable chemical and temperature resistance, and dielectric strength, allowing it to act as an electrical insulator.
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The benefits of using heat-resistant plastics
Heat-resistant plastics are an excellent alternative to metals in many applications. They offer a range of benefits, including:
Lightweight
Plastics are lighter than metals, making them ideal for industries such as automotive and aerospace, where lightweight components improve overall efficiency.
Corrosion Resistance
Some heat-resistant plastics have better corrosion resistance than metals when exposed to a wide range of chemicals. This is particularly important in the chemical industry, where applications involve both high temperatures and corrosive environments.
Manufacturing Flexibility
Plastic components can be manufactured using high-volume production technologies like injection moulding. This flexibility allows for efficient, high-volume production.
High-Performance
Heat-resistant plastics can offer continuous service temperatures of up to 500°F (260°C). They are designed to perform in harsh conditions without compromising their mechanical properties. For example, PEEK, a type of heat-resistant plastic, can withstand temperatures as high as 310°C for short periods and has a melting point of over 371°C.
Electrical Insulation
Some heat-resistant plastics, such as PTFE, have good electrical insulation properties in both hot and wet environments. This makes them ideal for electrical components.
Wide Range of Applications
Heat-resistant plastics are used in a variety of industries, including automotive, aerospace, semiconductor, and medical device manufacturing. Their unique properties make them suitable for highly specialized applications.
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Thermosets vs thermoplastics
Heat-resistant plastics are classified into two broad categories: thermosets and thermoplastics. Both have distinct behaviours under heat.
Thermoplastics
Thermoplastics can be heated, cooled, and reshaped repeatedly without altering their chemical structure. They gain their heat resistance from their molecular structure. When rigid aromatic rings are added to the resin, the backbone of the molecular chain is restricted and fortified in a way that two chemical links must be broken to break the chain. This gives thermoplastics excellent heat and chemical resistance. Thermoplastics generally fall within two categories that define how they react when heated: amorphous and semi-crystalline. Amorphous plastics gradually soften when heated, while semi-crystalline plastics have a precise melting point at which they transition from a solid to a liquid state. Thermoplastics with high heat resistance include PEI, PEEK, PTFE, PAI, and PPS. PEI, for example, has a high tensile strength and favourable chemical and temperature resistance. PEEK, on the other hand, is a high-performance engineering thermoplastic that is resistant to chemicals, wear, fatigue, creep, and heat. PTFE, commonly known as Teflon, is a soft, heat-resistant plastic with exceptional chemical resistance, high flexural strength, adequate weathering resistance, and good electrical insulating power.
Thermosets
Thermosets, on the other hand, are plastics that harden when exposed to heat and cannot be reshaped after curing. They undergo a chemical reaction when heated, creating irreversible, three-dimensional networks of bonded molecules. This process makes thermosets stronger and more heat-resistant than thermoplastics. Thermosets will typically break down chemically if heated past their maximum operating temperature and will not regain their properties once cooled. Thermosets are excellent choices for parts that require excellent dimensional stability at elevated temperatures. Examples of thermosets include silicon, which is commonly used in electrical wire insulation due to its flexibility, tear strength, and chemical resistance.
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Frequently asked questions
Heat-resistant plastics are materials that can exceed 300ºF in continuous operating temperature without compromising their mechanical properties. They are used in various industries, such as aerospace, automotive, and chemical, as an alternative to metal parts.
Some examples of heat-resistant plastics include:
- PEI (polyetherimide) or Ultem®: a strong, chemical-resistant, and flame-resistant thermoplastic.
- PEEK (polyether ether ketone): a semi-crystalline, high-performance thermoplastic with excellent resistance to chemicals, wear, fatigue, creep, and heat.
- PTFE or Teflon®: a soft, heat-resistant plastic with low friction, exceptional chemical resistance, and high electrical resistance.
When choosing a heat-resistant plastic, factors such as the material's chemical resistance, friction and wear performance, tensile strength, and operating temperature range should be considered. Additionally, the glass transition temperature (Tg) and melting point of the plastic are important parameters to keep in mind.
