Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

Polyimide - The Ultimate Champion Among Polymers

When we first started processing high-performance plastics, it seemed impossible for anything to match the versatility and high-performance capabilities of PTFE. However, when we developed PEEK, we realized that while PTFE does have a significant range of unmatched characteristics, PEEK surpassed it on out-and-out strength parameters. For a while, it did seem like PEEK was a good as it got with regards to robust polymers capable of withstanding immense loads at high temperatures.

When we explored further along high-performance polymers, however, we found that the universe of such materials is constantly expanding, yielding newer polymers that slowly become more mainstream. Standing out among these, is polyimide.

Not to be confused with polyamide – which is the name for nylon – polyimide is more commonly known by its trade names, such as Vespel and Kapton. Polyimide, a versatile polymer, has gained significant attention in various industries due to its exceptional properties and wide-ranging applications. 

This article delves into the processing methods employed for polyimide, explores its key properties, and highlights the advantages that make it a sought-after material in numerous fields.

Polyimide processing Method:

Polyimide can be processed using several techniques, including:

Solution Casting: This method involves dissolving the polyimide in a solvent to create a solution that can be cast into various shapes. Solution casting offers flexibility in producing thin films, coatings, and fibres, making it suitable for applications in electronics, aerospace, and flexible displays.

Compression Moulding: Compression moulding involves placing polyimide granules or powder into a mould and applying heat and pressure to create the desired shape. This technique is commonly used in the production of high-strength, high-temperature-resistant components such as gears, seals, and electrical insulation. A similar process is employed in making PEEK; however, the exception is that by using higher pressures (in excess of 3000 Bar), the polyimide powders can be compressed like PTFE and sintered in batches in an oven. This significantly increased productivity as compared with PEEK, where a single bush or rod can take anywhere from three to five hours to mould.

Film Extrusion: Polyimide pellets or powder are melted and extruded through a die to form continuous sheets or films. Film extrusion enables the production of thin, uniform polyimide films, widely utilized in the electronics industry for flexible circuits, insulating layers, and display components.

Injection Moulding: This method involves melting the polyimide and injecting it into a mould under high pressure. Injection moulding allows for the production of intricate and complex shapes, making it ideal for manufacturing components like connectors, switches, and automotive parts. However, the processing conditions for polyimide require high temperatures and the release of corrosive gases. Hence, care needs to be taken on the mould development, the equipment used for moulding, and the overall handling of the material.

Properties of Polyimide polymer:

Thermal Stability: Polyimide possesses excellent thermal stability, retaining its mechanical and electrical properties at high temperatures, typically up to 500°C (932°F). This property makes it suitable for applications in aerospace, automotive, and electronics industries.

Chemical Resistance: Polyimide is highly resistant to a wide range of chemicals, including solvents, acids, and bases. This resistance enables its use in harsh environments, such as chemical processing, where resistance to corrosive substances is crucial.

Mechanical Strength: Polyimide exhibits exceptional mechanical strength and rigidity, making it resistant to deformation and capable of withstanding high loads. Its strength allows for the production of lightweight yet durable components.

Electrical Insulation: With its excellent electrical insulation properties, polyimide serves as an effective dielectric material in applications requiring insulation against high voltages and frequencies, such as electrical motors, transformers, and circuit boards.

Advantages of Polyimide material:

High Temperature Resistance: Polyimide maintains its stability and mechanical integrity at elevated temperatures, enabling its use in demanding applications where other materials would degrade or fail.

Low Outgassing: Polyimide exhibits low outgassing properties, making it suitable for applications in the aerospace industry, where off-gassing could affect the performance of sensitive equipment.

Lightweight: Polyimide's high strength-to-weight ratio makes it an attractive choice for industries that require lightweight materials without compromising on mechanical performance.

Dimensional Stability: Polyimide demonstrates minimal dimensional changes under varying conditions, ensuring consistent performance and reliability over time.

Versatility: Polyimide can be formulated into various forms, including films, fibres, coatings, and adhesives, enabling its use in a wide range of applications, from electronics and aerospace to medical devices and automotive components.

A key issue with polyimide – as with so many high-performance polymers – is that it is expensive. Even compared with PEEK – which costs between 12-50X what a regular polymer like polypropylene or Nylon 6 might cost – polyimide is pricey. Its price can range from 10-15X the price of PEEK. This premium is the reason that it has remained a niche polymer, restricted to thin films and smaller components. However, like PEEK, PTFE, and so many other high-performance plastics, applications that call for polyimide can use nothing else. It is likely that as time goes on and adoption continues, the price of polyimide will gradually reduce, making more suitable for more mainstream applications.

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Injection Moulding High-Performance Polymers

For the most part, injection moulding is seen as a well traversed process. It is a widely used manufacturing process that allows for the mass production of complex plastic parts with excellent dimensional accuracy and mechanical properties. Unlike machined components, injection moulded parts can be easily produced, with a single part taking only about a minute to make, where the same part may have required anywhere from a few minutes to a few hours to machine, depending on complexity. The downside for injection moulding is that the up-front costs are far higher. An injection moulding die might cost anywhere from a few thousand dollars to many tens of thousands, again depending on how complex the part is or how many cavities are needed. The trade-off is therefore made along the lines of cycle-time and consumption per part (both which tend to be lower with moulding), set against the mould cost, which needs to be amortized over a high volume of parts to offset the increase in the per part rate as against machining.

However, even if moulding is a viable option, there exist limitations depending on the type of polymer we are looking at. Regular injection moulding polymers would include polypropylene, poly-ethylenes (HDPE and LDPE), nylons, and polyacetal. Each of these has been extensively worked with such that any experienced moulder would know the methods of working with them. However, once we move into the realm of high-performance polymers, the matter becomes more complex.

Before we go further, let us look at the polymers in question. 

PEEK (Polyether Ether Ketone)

PEEK is a high-performance, semi-crystalline thermoplastic known for its excellent combination of mechanical properties, chemical resistance, and thermal stability. PEEK components offer exceptional strength, stiffness, and dimensional stability even at elevated temperatures. Its resistance to chemicals, including harsh acids and bases, makes it suitable for applications in the chemical processing, oil and gas, and medical industries. PEEK's inherent biocompatibility also makes it a valuable material in medical implants and devices.

PPS (Polyphenylene Sulfide aka Ryton)

PPS is a semi-crystalline, high-temperature thermoplastic renowned for its excellent chemical resistance, dimensional stability, and flame retardancy. PPS parts exhibit superior resistance to a wide range of chemicals, including solvents, fuels, and acids. Its low moisture absorption, excellent electrical properties, and high thermal resistance make it an ideal choice for electrical and electronic components, automotive parts, and industrial applications.

PVDF (Polyvinylidene Fluoride and Kynar)

PVDF is a highly versatile thermoplastic known for its excellent chemical resistance, UV stability, and fire retardancy. PVDF components exhibit exceptional resistance to harsh chemicals, such as acids, solvents, and chlorinated compounds, making it suitable for applications in the chemical processing, semiconductor, and electrical industries. Its inherent UV stability and flame-retardant properties also make it a popular choice for outdoor applications and fire-safe products.

PEI (Polyetherimide aka Ultem)

PEI is an amorphous, high-temperature thermoplastic that offers outstanding dimensional stability, excellent electrical properties, and inherent flame retardancy. PEI parts exhibit remarkable mechanical strength, stiffness, and resistance to creep, even at elevated temperatures. PEI's excellent electrical insulation properties make it suitable for electrical connectors, switches, and semiconductor components. It is also commonly used in aerospace, automotive, and healthcare applications due to its flame-retardant nature and biocompatibility.

Polyimide (PI aka Kapton)

Polyimide is a high-performance, semi-crystalline thermoplastic renowned for its exceptional thermal stability, excellent electrical insulation properties, and resistance to wear and chemicals. Polyimide components offer exceptional dimensional stability, high strength, and excellent resistance to creep, making them ideal for demanding applications in the aerospace, automotive, and electronics industries. Polyimide's ability to withstand extreme temperatures and harsh environments has made it a material of choice in applications such as insulation, aerospace composites, and high-temperature electronics.

PAI (Polyamide-Imide aka Trolon)

PAI is a high-performance thermoplastic known for its exceptional mechanical properties, high temperature resistance, and excellent chemical resistance. PAI parts exhibit exceptional dimensional stability, high strength, and excellent resistance to wear and creep, even at elevated temperatures. Its inherent flame retardancy, low outgassing properties, and resistance to a wide range of chemicals make it suitable for aerospace, automotive, and industrial applications.

The superior properties of these polymers make them vital in several industries. However, there are drawbacks to moulding these polymers. For one, high-performance polymers tend to be far more expensive than regular polymers, often in the range of 20-50X the price. This makes moulding a challenge, as a new mould usually requires some trial and error before it is production ready. The second issue is that these polymers only melt at elevated temperatures, usually in excess of 300°C. Adding to the complexity is that when in a molten state, these polymers will give of effluents that can be highly corrosive to regular injection moulding equipment. As a result, the entire injection moulding machine and the mould itself need to be made of higher-grade metals and have high-temperature heating elements to ensure that the equipment can handle the process.

Because of these challenges, there exist very few moulders that will take on parts in these polymers. However, as the demand for these polymers increases, so too will the demand for processors that have focused their efforts on developing these plastics.

In 2023, Poly Fluoro embarked on a venture to develop an injection moulding machine tailored to moulding high-performance plastics. The addition of this equipment will make Poly Fluoro one of the very few polymer companies world-wide that can take on high-volume injection moulded parts in these high-performance polymers. We look forward to yet again being pioneers in our field and moving to areas that others would otherwise hesitate to go.

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2. Expanded PTFE (ePTFE) Vents

3. PTFE in Brake Cables

PTFE Machined Conduits

The versatility of PTFE as a material is only matched by its difficulty to process and fabricate. The properties of PTFE mean that it is invaluable in certain applications. However, as PTFE cannot be injection moulded or melt-processed in any way, there lie certain challenges in creating the shapes needed by the end applications. As always, the work around these challenges is what makes PTFE such an interesting polymer to manufacture.

Specifically, when making PTFE conduits, the requirement for a monolithic part with multiple entry and exit ports results in a complex machining problem. While not insurmountable, this problem is usually solved by a combination of moulding, shaping, and machining using a variety of tools and techniques.

PTFE is a high-performance fluoropolymer known for its excellent chemical resistance, low friction coefficient, and wide temperature range. It is non-reactive to most chemicals, including corrosive substances, and its low friction coefficient ensures smooth fluid flow. Moreover, it can withstand extreme temperatures, ranging from cryogenic conditions to high heat environments. These properties make it an ideal material for conduits in various industries.


PTFE machined conduits offer numerous advantages over traditional conduit materials. Firstly, their chemical inertness ensures compatibility with a broad range of aggressive chemicals and solvents, making them suitable for applications in the chemical, pharmaceutical, and food processing industries.

Secondly, PTFE's low friction coefficient significantly reduces pressure losses and minimizes energy consumption. This characteristic makes PTFE conduits highly desirable in fluid transfer systems, improving efficiency and reducing operational costs.

Thirdly, PTFE conduits exhibit excellent electrical insulation properties, making them suitable for applications requiring electrical or thermal insulation. They are widely used in the electrical and telecommunications industries to protect wires and cables from environmental factors and potential damage.

The usefulness of PTFE machined conduits enables their utilization in various industries:

Automotive: In the automotive sector, they are used for fuel and brake systems, thanks to their resistance to corrosive fuels and high-temperature performance

Aerospace: PTFE conduits also find applications in the aerospace industry, where they are employed in hydraulic and fuel transfer systems due to their lightweight nature and ability to withstand extreme temperature fluctuations.

Medical: PTFE conduits are extensively used in the medical field for applications such as catheters, endoscopes, and fluid transfer systems. Their biocompatibility and resistance to chemicals and high temperatures make them ideal for medical devices.

Semi-conductors: PTFE machined conduits are also employed in the semiconductor industry, where they are utilized for chemical delivery systems and in corrosive gas handling. Their resistance to aggressive chemicals and high-purity characteristics ensures the integrity of the manufacturing process.

Machining PTFE conduits

Because of the challenges to melt-process PTFE, the conduits must be machined out of a single block. This can often be costly, as the extensive removal of material results in a lot of wastage. Furthermore, the more the part is machined, the higher the cycle time. Add to this that the part itself might require multiple operations and the compounded effects of material wastage, cycle time, and setting and programming can result in an expensive final component. Typically, the machining time for a single part can range from as low as 15 minutes, to as high as 2 hours. Manufacturers – such as Poly Fluoro – spend a significant amount of time optimising this process, creating special moulds such that the ‘stock shape’ is as close to the final shape as possible. Furthermore, 4-axis and 5-axis capabilities increasingly allow parts to be machined in fewer settings, thereby reducing the set-up time, and increasing the accuracy of the final component’s dimensions.

Regardless of the methods used, the process of making a PTFE conduit is difficult and can defeat most that are unfamiliar with PTFE machining and its peculiarities. Nonetheless, there are applications where nothing but PTFE will do and in such cases, it falls to the experts to step in and show how it can be done.

Read More

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2. PTFE in Brake Cables

3. Graphene in Polymers - The Way of the Future