Trystan Casey
For a long time, it was commonly understood that metals conduct electricity and plastics do not. However, this notion has since been challenged by the discovery that plastics can, in fact, conduct electricity under certain circumstances. In 2000, chemist Alan MacDiarmid, along with his colleagues, was awarded the Nobel Prize in Chemistry for proving that plastics can be electrically conductive. This discovery has led to the development of conductive plastics, which are engineered materials filled with conductive additives, such as carbon fillers or metal salt technology, to achieve specific levels of electrical conductivity. These conductive plastics have found applications in various industries, including medical devices, food processing, military, and industrial sectors, where they play a crucial role in dissipating static build-up and transferring electrical charges.
| Characteristics | Values |
|---|---|
| Conductivity | Can be made conductive by adding substances like carbon black, graphite, arsenic pentafluoride, or iodine |
| Use cases | Anti-static additives, anti-electromagnetic screens, solar cells, switches, pressure-sensitive components, connectors, electromagnetic shields, resistors, light-emitting diodes, mobile phones, miniature television screens, and medical devices |
| Advantages over metals | Lighter, tougher, more design freedom |
| Disadvantages | Poor conductor of heat, can melt |
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What You'll Learn
- Under certain circumstances, plastics can conduct electricity
- Alan MacDiarmid, Hideki Shirakawa and Alan J. Heeger proved plastics can conduct electricity
- Conductive plastics are made with conductive additives
- Metal salt technology can be used to make plastics conductive
- Conductive plastics can be used in medical devices, food processing systems, military and industrial applications
Under certain circumstances, plastics can conduct electricity
Plastics are typically insulators of electricity, but under certain circumstances, they can become electrical conductors. In 2000, chemist Alan MacDiarmid, along with his colleagues, proved that plastics can conduct electricity, for which they were awarded the Nobel Prize in Chemistry.
The traditional method to make plastics conductive is by adding conductive fillers such as carbon black, graphite, and other conductive elements. These fillers increase the electrical conductivity of the plastic, making it capable of conducting electricity. The conductive properties of plastics can also be altered by adding certain chemicals. For instance, adding iodine to the polymer structure increases the conductivity of the plastic by attracting the electrons in the polymer. This causes the electric charge carriers in the polymer to become more agile and flow, similar to the behaviour of electrons in metals.
Conductive plastics have a wide range of applications, especially in product design. They can be used to dissipate static build-up in machines, transfer electrical charges, and play a conductive role in electro-mechanical mechanisms. Conductive plastics are commonly used in medical devices, food processing systems, military and defence equipment, and industrial applications. The use of conductive plastics in these applications offers design flexibility and allows designers to create products that meet specific requirements, such as tear strength, coefficient of friction (COF), and hardness.
Furthermore, different technologies are being developed to achieve conductivity in plastics. For example, Durethane® C conductive formulas use patented metal salt technology to achieve uniform conductivity without leaving streaks, which can be a problem with carbon black fillers.
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Alan MacDiarmid, Hideki Shirakawa and Alan J. Heeger proved plastics can conduct electricity
In the 1970s, Alan MacDiarmid, Alan J. Heeger, and Hideki Shirakawa proved that plastics can conduct electricity. MacDiarmid was a New Zealand-born chemist and professor at the University of Pennsylvania. Heeger was a natural scientist from the University of California in Santa Barbara. Shirakawa was a Japanese chemist and researcher at the Tokyo Institute of Technology.
Together, they discovered and developed conductive polymers, which are synthetic polymers such as plastics that can conduct electricity. This discovery challenged the traditional understanding that metals conduct electricity while plastics do not. The conductive polymers developed by MacDiarmid, Heeger, and Shirakawa had significant applications in microelectronics, including flexible plastic transistors and electrodes, plastic batteries, and electromagnetic interference shielding.
The three scientists first met by chance when MacDiarmid visited the Tokyo Institute of Technology and gave a lecture on (SN)x, an inorganic polymer. Shirakawa, who was researching polymer chemistry, showed MacDiarmid a sample of a silvery polymer that he and his colleagues had accidentally created. This polymer, polyacetylene (PAC), was known to exist as a black powder, but the addition of too much Ziegler-Natta catalyst to acetylene resulted in the creation of a silvery film that exhibited metallic properties. Recognizing that substances with a metallic sheen often conduct electricity, MacDiarmid invited Shirakawa to the University of Pennsylvania to collaborate with him and Heeger.
Through their collaboration, MacDiarmid, Heeger, and Shirakawa succeeded in increasing the conductivity of the plastic by adding iodine to the polymer. This discovery led to the presentation of the Nobel Prize in Chemistry in 2000, one of the most prestigious awards a natural scientist can receive. Their work opened up new avenues of research and applications in the field of conducting and semiconducting organic polymers.
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Conductive plastics are made with conductive additives
Conductive plastics, also known as plastic conductors, are a class of conductive polymeric materials. They are made by introducing a pi-conjugated system to a polymer, resulting in a polymer with overlapping pi electron systems. This process imparts electrical conductivity to the plastic, allowing it to conduct electricity.
There are two main types of plastic conductors: structural plastic conductors and composite plastic conductors. Structural plastic conductors are inherently conductive due to the conductive carriers (electrons or ions) provided by their polymer structure. The conductivity of these plastics can be significantly increased by mixing them with dopants, which can be chemical or physical. For example, doped polyacetylene, a typical structural conductive plastic, can increase its conductivity by adding iodine or arsenic pentafluoride. These plastics can be used to create high-power plastic batteries, capacitors, and microwave-absorbing materials.
On the other hand, composite plastic conductors do not conduct electricity on their own. Instead, they act as binders and are easy to prepare and highly practical. They are commonly used in switches, pressure-sensitive components, connectors, electromagnetic shields, and solar cells. The development of composite plastic conductors has led to applications in anti-static additives, anti-electromagnetic screens for computers, and smart windows.
Conductive plastics are designed to meet specific design requirements, such as the need to dissipate static build-up or transfer an electrical charge. They offer flexibility in product design, allowing designers to create products based on their desired material requirements, part complexity, and volume demand. For instance, thermoset polyurethanes can be made as strong and rigid as metal or as soft and flexible as a foam cushion, while also achieving a specific level of conductivity.
The preparation of conductive polymers involves various methods, with oxidative coupling of monocyclic precursors being the most common. To address the low solubility of polymers, researchers employ techniques such as adding solubilizing functional groups to monomers or forming nanostructures and surfactant-stabilized conducting polymer dispersions in water. The desired properties of conductive polymers can often be achieved with lower molecular weights compared to conventional polymers.
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Metal salt technology can be used to make plastics conductive
Plastics are typically considered to have poor electrical conductivity, which is why they are often used for insulating cable covers. However, scientists have discovered that conductive plastics can be created by mixing plastics with a high concentration of stringy carbon black and a coking compound. This creates a plastic that combines the electrical conductivity of metals with the various properties of plastics.
One such method to make plastics conductive involves the use of metal salt technology, or "doping", which involves sprinkling different atoms or electrons through the plastic material. This process can significantly increase the conductivity of plastics, with some even reaching the conductivity of metals. This type of conductive plastic is known as a structural plastic conductor, where the conductive carriers (electrons or ions) are provided by the polymer structure.
The University of Chicago's scientists have made a breakthrough in this area by discovering a material that can be made like plastic but conducts electricity like metal. This material, described as "like conductive Play-Doh", can be moulded into place while still conducting electricity. This discovery opens up new possibilities for designing a whole new class of materials that are easy to shape and robust in everyday conditions.
The process of creating conductive plastics using metal salt technology offers several advantages. Firstly, it eliminates the need for melting metals to shape them into chips or devices, as the plastic can be moulded at room temperature. Secondly, it provides new options for devices that need to withstand heat, acid, alkalinity, or humidity, as the conductive plastic is very stable and resistant to these elements. Finally, conductive plastics can be used in a wide range of applications, including switches, pressure-sensitive components, connectors, electromagnetic shields, and solar cells, enabling the development of smaller and faster computers.
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Conductive plastics can be used in medical devices, food processing systems, military and industrial applications
Conductive plastics have a wide range of applications in various industries, including medical devices, food processing systems, military equipment, and industrial contexts.
In medical devices, conductive plastics offer several advantages. They can be used to create strong, thin-walled sterilizable components, as well as flame-retardant, pre-colored parts that can be electrostatically painted. Conductive plastics are also used in instrument handles and holders, microfiltration devices for immunoassays, reusable syringe injectors, respirators, nebulizers, prosthesis packaging, sterilizer trays, and dental tools. Liquid-crystal polymers, for example, possess high strength and stiffness, and can be sterilized using common methods, making them ideal for dental tools, surgical instruments, and sterilizable trays. Conductive thermoplastics also provide superior electrostatic discharge (ESD) protection and electromagnetic interference (EMI) shielding compared to other materials, such as metals.
Food processing systems also benefit from the use of plastics, including conductive varieties. Food-grade plastics are designed to meet stringent regulations and standards, such as those set by the EU and US, to prevent any adverse effects from substance migration. PEEK (polyether ether ketone) plastics are commonly used in food processing due to their high-temperature performance, mechanical properties, and chemical resistance. They are suitable for direct contact with food during filling, mixing, and portioning processes, as well as in equipment like closing dies, filler nozzles, scrapers, valves, blenders, and mixing paddles. Acrylic or polymethyl methacrylate (PMMA) is another plastic used in food processing, valued for its strength, stiffness, and optical clarity, enabling advanced vision systems and physical inspections.
In military applications, plastics, including conductive varieties, play a crucial role in enhancing stealth capabilities and protecting personnel. Polymer matrix composites, for instance, are used in domes on military ships and aircraft to shield detection equipment and dampen position-revealing vibrations. Military helicopters are equipped with polymer foam blades and Kevlar-carbon fiber structural materials, providing multi-spectral stealth capabilities against radar, infrared, and acoustic detection. Additionally, polymer matrix-based coatings are applied to military vehicles to thwart visual detection, both in normal and thermal conditions.
Conductive plastics also find utility in industrial applications. They can be used in switches, pressure-sensitive components, connectors, electromagnetic shields, resistors, and solar cells. Their combination with nanotechnology is expected to revolutionize molecular electronics, leading to faster and smaller computers. Conductive polymers are also promising for organic light-emitting diodes, flexible transparent displays, chemical sensors, and biosensors.
Overall, conductive plastics offer unique advantages and find diverse applications across medical devices, food processing systems, military equipment, and industrial technologies.
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Frequently asked questions
Plastics are generally considered insulators and not electrical conductors. However, under certain circumstances, plastics can be made to conduct electricity. For example, conductive plastics are engineered materials that are filled with conductive additives like carbon black, graphite, or metal salts to attain a specific level of conductivity.
There are several ways to make plastics conductive. One method is to add conductive additives such as carbon fillers or metal salts to the plastic. Another method is to add iodine to the polymer, increasing the conductivity of the plastic by making the electric charge carriers less dense and more agile.
Conductive plastics have two main uses in product design. Firstly, they can play a conductive role in electro-mechanical mechanisms. Secondly, they can help dissipate unwanted static from a machine. Conductive plastics are used in medical devices, food processing systems, military and defense applications, and industrial applications.
