Chloe Zhang
Plastics are typically poor conductors of heat due to their lack of free electrons. However, advancements in filler technologies and polymer chemistry have led to the development of thermally conductive plastics, which have become increasingly important in managing heat build-up in electronics, appliances, lighting, automotive systems, and industrial products. These plastics are created by adding fillers such as graphite, carbon black, or carbon fibres to polymers like propylene (PP) or polyphenylene sulphide (PPS), resulting in thermal conductivity values ranging from 1 to 100 W/mK. The use of these plastics can provide cost savings of up to 30% compared to metal alternatives, making them a viable option for thermal management applications. This paragraph introduces the topic of thermal conductivity in plastics, highlighting the recent advancements, applications, and benefits of using plastics with improved thermal conductivity.
Characteristics and Values of Plastics with the Best Thermal Conductivity
| Characteristics | Values |
|---|---|
| Examples of plastics with good thermal conductivity | Polycarbonate with added fillers, PI, PEEK (polyether ether ketone), PolyOne Corp., Cool Polymers, LNP Engineering Plastics, RTP Co., Ticona Corp., GE Plastics, DuPont, A. Schulman |
| Common applications | Housings for LED lighting, battery casings, electronic equipment, automotive parts, and industrial products |
| Thermal conductivity of unfilled plastics | 0.2 W/mK |
| Thermal conductivity range of thermally conductive plastic compounds | 1-10 W/mK |
| Thermal conductivity measurement instruments | C-Therm Trident Thermal Conductivity Instrument, Modified Transient Plane Source (MTPS), Transient Plane Source (TPS), Transient Line Source (TLS) |
| ASTM standard for measuring thermal transmission properties | ASTM C177 |
| ISO standard for determining steady-state thermal resistance | ISO 8302 |
| Heat transfer measurement method | Guarded hot plate apparatus |
| Commonly used thermally conductive additives | Graphite carbon fibers, aluminum nitride, boron nitride |
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What You'll Learn
- Amorphous plastics have higher thermal conductivity in solid state than melt state
- Semi-crystalline thermoplastics have better conductivity
- Low-conductivity plastics are used in construction and refrigeration
- Polycarbonate with added fillers is used for LED lighting
- PI and PEEK polymers are used in high-performance applications
Amorphous plastics have higher thermal conductivity in solid state than melt state
Plastics are widely used across industries due to their lightweight nature, corrosion resistance, and ease of fabrication. However, their thermal conductivity coefficients play a crucial role in determining their suitability for specific applications, especially in thermal insulation, electronics, and high-temperature environments.
Thermal conductivity is the measure of a material's ability to conduct heat. For plastics, this value is typically low compared to metals, making them excellent thermal insulators. The thermal conductivity of most common plastics ranges between 0.1 to 0.5 W/m·K, although specialty-engineered polymers can achieve higher values.
Amorphous plastics, such as polystyrene, have lower thermal conductivity than their crystalline counterparts. This is because the atoms in amorphous plastics are held together in a loose structure, resulting in lower thermal conductivity. At temperatures below the glass transition temperature (Tg), the amorphous polymer chains cannot rotate or move in space, resulting in a rigid and brittle state. As the temperature rises above Tg, the chains become more flexible and can move, leading to increased thermal conductivity.
Despite this, amorphous plastics have higher thermal conductivity in the solid state than in the melt state. This is due to an increase in density upon solidification. However, in the melt state, the thermal conductivity of these polymers reduces to that of amorphous polymers. The thermal conductivity of plastics can be enhanced by incorporating thermally conductive fillers such as graphite, boron nitride, or metal oxides. For example, high-density polyethylene (HDPE) filled with aluminum particles can achieve values exceeding 1 W/m·K.
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Semi-crystalline thermoplastics have better conductivity
Thermal conductivity is a key indicator of a material's ability to transfer heat. Unlike metals, plastics are generally poor conductors of heat. However, some plastics have higher thermal conductivity than others, and this is important for specific applications. For example, plastics with higher thermal conductivity are used in LED lighting or battery casings, where heat dissipation is required.
Semi-crystalline thermoplastics have ordered crystalline regions, which allow for better heat transfer. In semi-crystalline polymers, the thermal conductivity increases as the crystallinity increases. This is in contrast to amorphous polymers, where the polymer chains are unstructured, leading to lower thermal conductivity. The higher thermal conductivity of semi-crystalline polymers is due to their structure, which allows for more efficient heat transfer.
The thermal conductivity of plastics can be altered by adding fillers. For instance, inorganic fillers increase the thermal conductivity of polymers, while gaseous fillers have the opposite effect. This is why polymeric foams, like expanded polystyrene (EPS) and polyurethane foam, are used for insulation in the construction and refrigeration industries.
The temperature also affects the thermal conductivity of plastics. In semi-crystalline polymers, thermal conductivity tends to decrease with increasing temperature. However, this relationship is complex and non-linear, and it depends on the specific type of polymer. For example, in a study on polyethylene, the thermal conductivity declined linearly with increasing temperature up to 100 °C, but above the melting point, all samples showed similar thermal conductivity.
In summary, semi-crystalline thermoplastics have better thermal conductivity due to their ordered crystalline regions, and this can be further enhanced by adding certain fillers. However, the thermal conductivity of plastics is also influenced by temperature, and this effect varies depending on the specific plastic and its properties.
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Low-conductivity plastics are used in construction and refrigeration
Low-conductivity plastics are commonly used in construction and refrigeration due to their ability to act as thermal insulators by minimising heat transfer. Expanded polystyrene (EPS) and polyurethane foam are two examples of low-conductivity plastics that are staples in these industries. Their structure is designed to trap air, which reduces the amount of heat that can pass through. This makes them ideal for applications where maintaining temperature differentials is important, such as in refrigeration and wall insulation in construction.
In the construction industry, there is a growing interest in utilising plastic waste to create low-thermal-conductivity concrete. This type of concrete has the potential to be more environmentally friendly and renewable while also improving the insulation properties of buildings. Studies have shown that incorporating plastic fibres from waste high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), and polyethylene terephthalate (PET) can result in concrete with lower thermal conductivity than plain concrete. The lowest thermal conductivity was recorded for concrete samples containing 30% LDPE fibres by volume, followed by HDPE, PP, and PET.
The use of plastic waste in concrete production not only reduces waste but also enhances the concrete's properties. By increasing the porosity of the concrete, the plastic fibres create more air voids, further reducing heat transfer. Additionally, the lightweight nature of plastics contributes to their effectiveness in insulation applications.
While low-conductivity plastics are essential for thermal insulation, there are also applications where heat dissipation is required. In such cases, specialty thermally conductive plastics are used. For instance, polycarbonate with added fillers is commonly employed in LED lighting housings and battery casings. Furthermore, polymers like PI and PEEK (polyether ether ketone) offer a balance of insulation and heat resistance, making them suitable for high-performance applications.
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Polycarbonate with added fillers is used for LED lighting
Polycarbonate is a popular choice for LED lighting due to its versatility, durability, and excellent light transmission properties. It is a tough and impact-resistant plastic that can be formed into various shapes, making it ideal for lenses, optics, covers, and light diffusers in LED applications.
Polycarbonate with added fillers is specifically favoured for LED lighting due to its enhanced thermal conductivity. This modification addresses the heat generated by lighting applications, ensuring the material can withstand the proximity to the light source. The added fillers also improve the material's ignition resistance or flame retardancy, making it safer for high-powered LED light sources.
Polycarbonate diffusers are designed to scatter light evenly, reducing "hot spots" of focused light that can detract from the visual appeal of LED fixtures. These diffusers can be engineered in different grades to balance light transmission and diffusion, depending on the specific application. For example, TUFFAK® Lumen XT is a polycarbonate sheet with LED light-diffusing additives that effectively minimises hot spots while maintaining high light transmission.
Polycarbonate's ability to be tailored through the compounding process further enhances its suitability for LED lighting. Manufacturers can adjust the material's properties to meet specific requirements, such as achieving light transmission greater than 90% for transparent polycarbonate resins or adding light diffusion additives to achieve uniform light distribution while hiding the bright LED light source.
Overall, polycarbonate with added fillers is a preferred choice for LED lighting due to its thermal conductivity, toughness, light diffusion capabilities, and customisability. These properties make it a versatile and reliable material for a wide range of LED lighting applications.
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PI and PEEK polymers are used in high-performance applications
PI and PEEK polymers are high-performance materials with exceptional properties that other general plastics cannot match. They are widely used in various demanding industries, including aerospace, automotive, electronics, and electromechanical. These polymers offer a unique combination of mechanical, chemical, electrical, and thermal properties, making them ideal for high-performance applications.
One of the key advantages of PI and PEEK polymers is their high-temperature resistance. PEEK, for example, can withstand temperatures up to 260°C and even up to 300°C without significant mechanical property degradation. This makes it suitable for high-temperature applications such as in aerospace and automotive industries. PEEK's thermal stability also contributes to its resistance to thermal degradation, ensuring its durability in demanding environments.
Another advantage of these polymers is their exceptional tensile strength and toughness. PEEK, in particular, exhibits superior tensile strength compared to other high-heat polymers, making it ideal for structural applications. Its toughness further enhances its durability and impact resistance. The high strength and toughness of these polymers contribute to their overall performance and reliability in demanding applications.
PI and PEEK polymers also offer good wear resistance and chemical resistance. They are resistant to corrosion and attack by various substances, including organic and aqueous environments. This makes them suitable for use in harsh chemical applications and ensures their longevity in extreme conditions. The polymers' ability to resist wear and maintain their structural integrity contributes to their high performance in demanding industries.
In addition to their mechanical and chemical properties, PI and PEEK polymers also have excellent electrical properties. PEEK, for example, has excellent electrical insulation properties, making it suitable for electrical cable insulation. Its stability ensures that it can maintain its electrical properties over a wide range of temperatures and frequencies. This versatility makes PEEK particularly useful in applications where electrical performance is critical, such as in electronics and semiconductor industries.
Overall, the unique combination of properties exhibited by PI and PEEK polymers makes them ideal for high-performance applications. Their high-temperature resistance, exceptional tensile strength, good wear resistance, chemical resistance, and excellent electrical properties contribute to their versatility and reliability in demanding industries. The ability of these polymers to maintain their structural integrity and performance in extreme conditions sets them apart from other general plastics.
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Frequently asked questions
There are a few plastics with high thermal conductivity, including PolyOne, DuPont, and A. Schulman, who have development programs in this area. Cool Polymers is a firm that offers products with 100 to 500 times the conductivity of a base polymer.
Thermal conductivity is the rate at which heat is transferred through a material.
Plastics are typically good insulators, but advancements in technology have led to the development of thermally conductive plastics. These plastics can be used in applications where heat dissipation is required, such as LED lighting or battery casings.
The thermal conductivity of plastics can be measured using instruments such as the C-Therm Trident Thermal Conductivity Instrument, which provides a fast and easy way to determine the thermal conductivity of plastics and polymers.
Thermally conductive plastics can be used in electronics, appliances, lighting, automotive, and industrial products. They can also be used in HVAC heat exchangers and high-speed differential connectors, where they can withstand high temperatures during soldering and operation.
