Ethan Clarke
Plastic is a versatile material used across almost every industry due to its ease of manufacture, low cost, and range of properties. While it is not a good conductor of heat, certain plastics have higher levels of thermal conductivity than others. There are two main groups of thermoplastics: amorphous and semicrystalline plastics. Amorphous plastics do not have a precise melting point but gradually soften as the temperature rises, while semicrystalline plastics have a distinct melting point. Heat-resistant plastics, which can withstand temperatures above 150°C (302°F), are essential for advanced applications requiring heat, mechanical, and corrosive resistance. PTFE, or Teflon, is a notable example with a melting point of 327°C and excellent chemical and electrical insulation properties. ULTEM® (polyetherimide), another commercially available amorphous thermoplastic, is widely used in aerospace due to its high melting point and resistance to various fuels and coolants. Polyetheretherketone (PEEK) is another heat-resistant thermoplastic with excellent mechanical properties, even at temperatures above 250°C. These plastics offer unique advantages in various industries, including automotive, aerospace, and medicine, showcasing the importance of understanding their heat exchange capabilities.
| Characteristics | Values |
|---|---|
| Plastic's ability to conduct heat | Poor conductor of heat |
| Plastic's ability to insulate heat | Good insulator of heat |
| Plastic's ability to withstand heat | Depends on the type of plastic. Polypropylene (PP) loses strength at 82°C (180°F), Polyethylene (PE) at 130°C (266°F) and Polycarbonate (PC) at 140°C (284°F). Advanced heat-resistant plastics can withstand temperatures above 150°C (302°F) and short-term exposure to 250°C (482°F) or more. |
| Plastic's ability to withstand heat without deformation | Depends on the type of plastic. Amorphous plastics slowly soften as the temperature increases and do not have a sharp melting point. Semi-crystalline plastics have a sharp melting point. |
| Plastic's ability to withstand heat without degradation | Depends on the type of plastic. The maximum temperature at which plastic can be used without significant degradation over its design lifetime is called the Continuous Use Temperature (CUT). |
| Plastic's ability to withstand heat without changing form | Depends on the type of plastic. The temperature at which a plastic loses its stability form is called the Vicat softening temperature. |
| Plastic's ability to withstand heat without deflection | Depends on the type of plastic. The temperature at which plastic will deform under a predefined load is called the Heat Deflection Temperature (HDT). |
| Plastic's ability to change form when heated | Depends on the type of plastic. Thermoplastics become molten when heated and can be reshaped. Thermosets harden when exposed to heat and cannot be reshaped after curing. |
| Plastic's ability to conduct heat when compared to metals | Poor conductor of heat when compared to metals. |
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What You'll Learn
Plastic is not a good conductor of heat
Plastic is widely used across industries due to its ease of manufacture, low cost, and diverse range of properties. However, it is essential to understand that plastic is generally not a good conductor of heat. This characteristic of being a poor heat conductor makes plastic an excellent insulator, which is why it is commonly used in cookware, plastic dishes, and bowls that can be safely used in microwaves.
The reason behind plastic's poor heat conduction lies in its molecular structure. Plastics are made up of long molecular chains with tightly bound molecules. When heated, the bonds between these chains break, causing the material to melt. However, because the molecules are so closely bound together, it requires a significant amount of energy for them to move and vibrate, impeding the transfer of thermal energy. This closely packed molecular structure is also why plastics are good insulators, as heat carriers have difficulty traversing the tangled molecular chains, and heat becomes trapped within the material.
While plastic, in general, is not a good heat conductor, it is important to note that there are exceptions. Certain plastics, such as synthetic polymers, exhibit higher levels of thermal conductivity and can act as electrical conductors. Polyurethane and polystyrene, on the other hand, are common types of plastic with lower thermal conductivity, making them ideal for everyday household items. Additionally, advanced heat-resistant plastics, such as ULTEM®, can withstand temperatures above 150°C (302°F) and have exceptional mechanical properties comparable to metals.
The ability of plastics to resist heat degradation is determined by various factors, including their chemical composition and structure. For instance, plastics with high melting temperatures typically contain aromatic rings, which require the breaking of two chemical bonds before the structure breaks down. Additives, such as glass fiber, can also enhance the heat resistance of plastics, making them suitable for applications requiring both heat and mechanical strength.
In conclusion, while plastic is generally not a good conductor of heat, there are specific types of plastic with higher thermal conductivity. The unique molecular structure of plastics, combined with additives and processing techniques, allows for the development of heat-resistant plastics with advanced properties. These heat-resistant plastics have found applications in various industries, including automotive, aerospace, and electronics, showcasing the versatility and importance of understanding plastic's thermal properties.
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Heat-resistant plastics exist
While plastic is not a good conductor of heat, there are certainly plastics that are heat-resistant. In fact, there are advanced heat-resistant plastics that can withstand temperatures that regular plastics cannot. These plastics are used in applications where a combination of heat resistance, mechanical strength, and corrosive resistance is required.
Heat-resistant plastics can take the form of thermoplastics, thermosets, or photopolymers. Thermoplastics, when heated, become molten and can be reshaped, while thermosets harden when exposed to heat and cannot be reshaped after curing. High-performance thermoplastics can retain their structural capabilities above 150°C and for short periods above 250°C. They are also chemical-resistant, corrosion-resistant, and excellent electrical and thermal insulators.
Thermoplastics fall into two categories: amorphous and semi-crystalline. Amorphous plastics have a disordered molecular structure and gradually soften when exposed to increasing temperatures. They do not have a defined melting point. Semi-crystalline plastics, on the other hand, have a semi-ordered molecular structure, with ordered crystalline areas interspersed between unordered amorphous areas. They have a precise melting point and will soften at that temperature.
Some of the most popular heat-resistant plastics include PEI, PEEK, PTFE, PAI, and PPS. PTFE, commonly known as Teflon, is a soft, heat-resistant, low-friction plastic with exceptional chemical resistance. It has a very large operating temperature range and is used in non-stick cookware, as well as to protect pipes and coat heat exchangers. PEEK, or polyether ether ketone, is a high-performance engineering thermoplastic that is resistant to chemicals, wear, fatigue, creep, and heat. It is so durable that it can replace metal in many applications, regardless of temperature.
In summary, heat-resistant plastics do exist and are used in a variety of industries for their unique properties.
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Plastic is a good insulator
While plastics are generally not good conductors of heat, some plastics have higher levels of thermal conductivity than others. Synthetic polymers, for example, can act as electrical conductors. However, common plastics like polyurethane and polystyrene have low thermal conductivity. These plastics are widely used for household items because of their insulating properties.
There are two main types of heat-resistant plastics: thermoplastics and thermosets. Thermoplastics become molten when heated and solid when cooled, and can be re-melted after cooling. Thermosets, on the other hand, harden when exposed to heat and cannot be reshaped after curing.
Heat-resistant plastics have a continuous-use temperature of above 150°C (302°F) or a short-term exposure resistance of 250°C (482°F) or more. PTFE (Teflon) is a heat-resistant plastic with a melting point of 327°C, and an operating range of +260°C to -200°C. It is often used to coat non-stick pots and pans.
Another heat-resistant plastic is polyetheretherketone (PEEK), which has a melting point of 250°C (482°F) and retains its mechanical properties at temperatures up to 300°C for short periods. PEEK is commonly used in the medical industry for spinal implants and fixation devices.
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Plastic's heat resistance can be improved
While metals tend to be more heat-resistant than plastics, there are many instances where engineers would benefit from using heat-resistant plastics for their high-performance applications. Heat-resistant plastics can take the form of thermoplastics, thermosets, or photopolymers. The heat resistance of plastics can be improved using additives, such as glass fiber, which also increases overall stiffness and material strength.
Thermoplastics gain their heat resistance from their molecular structure. When rigid aromatic rings are added to the resin instead of aliphatic groups, the backbone of the molecular chain is restricted and fortified in such a way that two chemical links must be broken to break the chain. With this new structure, a thermoplastic’s chemical and heat resistance can be equal to or better than a thermoset. Thermosets are plastics that harden when exposed to heat and cannot be reshaped after curing.
Polyether ether ketone (PEEK) is a semi-crystalline, high-performance engineering thermoplastic that’s resistant to chemicals, wear, fatigue, creep, and heat. This material is so strong and adaptable to harsh environments that manufacturers use it as a replacement for metal in many applications, regardless of the temperature. PEEK can withstand temperatures as high as 310°C for short periods and has a melting point of over 371°C.
Poly(lactic acid) (PLA) has attracted attention as a substitute for petroleum-based plastics, but its low heat resistance limits its application range. The addition of nucleating agents can improve the crystallinity of PLA and then improve heat resistance. Different processing strategies can also be adopted to improve the heat resistance of PLA, such as annealing, biaxial-stretching, or in-mold annealing.
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Plastic's molecular structure affects heat resistance
Plastic is a polymer made up of long chains of molecules. When heated, the bonds between these chains are broken, causing the material to melt. The heat resistance of plastics is determined by their molecular structure.
Plastics with low melting temperatures are often made up of aliphatic rings, which have a single chemical bond. High-temperature plastics, on the other hand, are made up of rigid aromatic rings, which have two chemical bonds. This additional bond makes it harder to melt these materials, thereby increasing their heat resistance.
The heat resistance of plastics can also be improved by adding glass fibres to the material. These fibres increase the overall stiffness and strength of the plastic.
There are two main types of thermoplastics: amorphous and semicrystalline. Amorphous plastics do not have a distinct melting point; instead, they gradually soften as the temperature increases. In contrast, semicrystalline plastics have a sharp melting point and transition from solid to liquid at this temperature.
Some plastics, such as PTFE (commonly known as Teflon), have very high melting points and excellent heat-resistant properties. PTFE is used in non-stick cookware and to protect pipes and electrical components from high temperatures. Ultem, another type of heat-resistant plastic, is commonly used in the aerospace industry due to its high melting point and excellent mechanical properties.
In summary, the molecular structure of plastic plays a crucial role in determining its heat resistance. By modifying the chemical composition and adding additives, engineers can create plastics with varying levels of heat resistance for specific high-performance applications.
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Frequently asked questions
No, plastic is not a good conductor of heat. It is a successful insulator, which is why it is used in items like plastic cookware and dishes. However, there are certain plastics that have higher levels of thermal conductivity than others.
Polyurethane and polystyrene are two common types of plastic with lower levels of thermal conductivity. Synthetic polymers and a polymer known as polythiophene are examples of plastics with higher levels of thermal conductivity.
PTFE (also known as Teflon), ULTEM, PEEK, and ABS are all examples of heat-resistant plastics.
Heat-resistant plastics are used in applications where a combination of heat resistance, mechanical strength, and corrosive resistance are necessary. This includes piston components in the automotive industry, cable conduits in the aerospace industry, and subsea connectors in the semiconductor industry.
