Apart from PTFE, very few polymers command the respect of PVDF when it comes to chemical applications. However, Polyvinylidene fluoride, commonly known as PVDF, is a high-performance polymer with a remarkable combination of properties that make it invaluable in numerous different industries. This versatile material possesses unique characteristics, including excellent chemical resistance, high thermal stability, piezoelectric properties, and remarkable electrical insulation capabilities. 

While we at Poly Fluoro have always worked with PVDF by machining parts from extruded rods, we were recently presented with the opportunity to develop compression moulded and injection moulded parts using this amazing polymer. The results were more than satisfactory and put us in an exclusive league of companies that can make both large, machined components using compression moulding, as well as smaller intricate parts using our specially developed, high-temperature injection moulding press.

Before we delve any deeper into processing, let us look at some of the properties and applications of PVDF.

Properties of PVDF

1. Chemical Resistance

PVDF exhibits exceptional resistance to a wide range of chemicals, including acids, bases, and solvents. This property makes it ideal for use in corrosive environments, such as chemical processing plants and laboratories. It can withstand exposure to harsh chemicals without degrading or losing its integrity, ensuring long-term reliability.

2. High Thermal Stability

PVDF can operate at elevated temperatures without losing its mechanical properties. It has a high melting point, typically around 177°C (350°F), making it suitable for applications that involve exposure to heat. This thermal stability is particularly important in industries like aerospace, where materials must endure extreme conditions.

3. Piezoelectricity

One of PVDF's most intriguing properties is its piezoelectricity. When subjected to mechanical stress or pressure, PVDF generates an electrical charge. This property is crucial in various applications, such as sensors, transducers, and actuators, where the conversion of mechanical energy into electrical signals is necessary.

4. Excellent Electrical Insulation

PVDF is an outstanding electrical insulator, making it essential in the electronics industry. Its high dielectric strength and low dielectric constant allow it to insulate and protect electronic components from electrical interference and damage. This property is invaluable in the manufacturing of cables, capacitors, and electrical connectors. 

5. UV Resistance

PVDF is highly resistant to ultraviolet (UV) radiation, which can degrade many other materials over time. Its UV resistance makes it suitable for outdoor applications, such as solar panels, architectural cladding, and signage, where prolonged exposure to sunlight is inevitable.

6. Low Density

PVDF has a relatively low density compared to many other engineering plastics. It has a specific gravity of 1.8 compared to PTFE, which is at 2.25. This characteristic makes it lightweight, which is advantageous in industries like aerospace and automotive, where weight reduction is a critical factor in enhancing fuel efficiency and overall performance.

Applications of PVDF

1. Aerospace

In the aerospace industry, PVDF is used in a wide range of applications due to its exceptional properties. It is employed in aircraft components such as fuel lines, insulation for wiring, and lightweight structural parts. Its resistance to extreme temperatures and chemicals makes it suitable for aircraft exposed to harsh environments.

2. Electronics

PVDF's excellent electrical insulation properties make it a key material in the electronics sector. It is utilized in the manufacturing of cables, wire coatings, and printed circuit boards. Its piezoelectricity also finds application in sensors and transducers for detecting and measuring physical parameters.

3. Chemical Processing

PVDF's chemical resistance makes it a top choice for the chemical processing industry. It is used in the construction of pipes, valves, pumps, and storage tanks that transport and store corrosive chemicals safely. PVDF-lined equipment ensures the integrity of chemical processes and prevents contamination.

4. Renewable Energy

The solar energy sector benefits from PVDF's UV resistance. It is used as a protective material in solar panels, where it helps extend their lifespan and maintain their efficiency by shielding them from the harmful effects of UV radiation. PVDF's lightweight nature is also an advantage in solar panel design.

5. Medical Devices

In the medical field, PVDF is employed in various applications due to its biocompatibility and resistance to sterilization methods. It is used in medical tubing, catheters, and surgical instruments. Its piezoelectric properties are harnessed in ultrasound transducers for medical imaging.

6. Architectural Cladding

PVDF is a popular choice for architectural cladding materials in construction. It is used in the form of coatings on aluminium, steel, or other substrates to provide durable and aesthetically pleasing facades for buildings. Its UV resistance ensures that the cladding retains its colour and appearance over time.

7. Oil and Gas Industry

In the oil and gas sector, PVDF is used in applications that require resistance to harsh chemicals and high temperatures. It is utilized in the production of seals, gaskets, and liners for equipment used in drilling, refining, and transporting petroleum products.

8. Water Treatment

PVDF membranes are employed in water treatment processes, such as ultrafiltration and microfiltration. These membranes effectively remove contaminants and microorganisms from water sources, ensuring the production of clean and safe drinking water.

9. Automotive

PVDF's lightweight properties make it valuable in the automotive industry for reducing vehicle weight, thereby improving fuel efficiency and reducing emissions. It is used in components like fuel lines, engine components, and interior trim parts. The recent spike in electric vehicle manufacturing had put tremendous pressure on PDFV, as it happens to be ideal for use in a variety of areas essential to EV manufacturing.

Processing PVDF

PVDF can be extruded, compression moulded, or injection moulded. While it does require a higher temperature as compared with nylons, POM, or ethylenes, the temperature is still well below what it might take to process PEEK, PTFE, or PI (Vepel). Nonetheless, like all high-performance polymers, care needs to be taken on the selection of metals used in the moulding process, as these can very easily corrode when the polymer reaches its liquid state.

In its liquid state, PVDF is viscous enough that it tends not to leak out from a well-designed mould or die. At the same time, the viscosity is not so high that there are issues with cracks or blowholes. Provided enough pressure is given during the moulding (either compression or injection), the voids are easily removed, and the polymer generally behaves well. Unlike PEEK, which only melts at temperatures above 400°C and gives of effluents that need to be removed at high pressures of over 400Bar, PVDF melts at a far more sedate 200-250°C and at pressures of only 100Bar. Further, PVDF also has the option of being melted in a separate die and allows itself to be transferred to another die, where the pressure is applied to give it form. This makes it easier to process than PEEK, where it can sometimes take upwards of 4 hours to even mould a single piece.

Conclusion

Recent spikes in demand for PVDF (driven mainly by the EV boom globally), had pushed the price of raw materials up to the point where industrial applications were being priced out of the market. However, capacity expansions around the world have now brought the prices to more stable levels and the industry is once again looking poised for amazing things.

PVDF's unique combination of properties, including chemical resistance, high thermal stability, piezoelectricity, and excellent electrical insulation, means that it finds application in all corners of industry. From aerospace and electronics to renewable energy and medical devices, PVDF plays a pivotal role in enhancing the performance, durability, and reliability of numerous products and applications. As technology continues to advance, the versatility of PVDF will likely lead to even more innovative uses in the future, making it a material of enduring importance in the world of materials science and engineering.

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1. Air Permeability Testing and Water Entry Pressure Testing in Expanded PTFE Membranes

2. Polyimide - The Ultimate Champion Among Polymers

3. Injection Moulding High-Performance Polymers

The development of expanded PTFE (ePTFE) membranes unleashed a material that was unmatched in terms of properties. The breadth of applications that have been – and continued to be – found to benefit from ePTFE membranes is significant. With membranes, ePTFE’s exceptional properties such as chemical resistance, thermal stability, and high tensile strength were combined with micro-porosity to find applications in a wide range of fields, including filtration, medical devices, textiles, automotives, chemical plants, and many more.

The overarching tagline for ePTFE membranes is this: they repel dust and water but allow vapours and moisture to pass. This seemingly simple property can be further fine tuned to block not only water, but oils and mineral spirits as well, turning them from plain hydrophobic membranes to oleophobic membranes.

However, to understand how the membrane functions, and indeed to test the efficacy of the membrane, two fundamental parameters need to be considered.

The two important parameters that characterize the performance of ePTFE membranes are air permeability and water entry pressure. In this article, we will delve into the significance of air permeability testing and water entry pressure testing in expanded PTFE membranes.

Understanding Expanded PTFE Membranes

Expanded PTFE (ePTFE) is a remarkable material made by rapidly stretching extruded PTFE under high temperatures. The stretching process – which may be either uni-axial or bi-axial – imparts a micro-porosity to the material. These pores are much smaller than a molecule of water, but far larger than a molecule of steam. As a result, the membranes can act as a sort of valve, allowing only vapours through, but no liquids or dust. This feature – often called breathability – is somewhat unique to ePTFE and when combined with the ability to withstand high temperatures and corrosive chemicals, makes the material very useful.

However, to truly develop a tailored solution, one must be able to tweak the parameters to suit the end-application. While air and moisture can pass through the material, an application will have specific requirements as to the volume of air or moisture that should pass at a given pressure. Similarly, while water will be repelled by the membrane, certain applications would also have requirements pertaining to the pressure at which water might pass through the membrane.

Air Permeability Testing

Air permeability, also known as air porosity, is a crucial property of ePTFE membranes that influences their performance in applications where gas flow is involved. It refers to the ease with which air can pass through the membrane's pores. Air permeability testing is essential to assess the suitability of a membrane for specific applications, particularly in industries such as outdoor clothing, medical devices, and industrial filtration systems.

The air permeability test involves measuring the volume of air that passes through a unit area of the membrane under a defined pressure difference. The unit of measurement is usually cubic feet per minute per square foot (CFM/ft²) or litres per minute per square meter (LPM/m²). The test apparatus typically consists of a controlled air source, a sample holder, and a differential pressure gauge. The sample is securely clamped between two chambers, and air is allowed to flow through one side of the membrane while the pressure drop across it is measured. The standard ASTM D737 is used to test the material for air permeability.

The air permeability value provides valuable information about the membrane's breathability, which is crucial in applications like outdoor clothing and medical textiles. Membranes with higher air permeability values allow for better moisture vapor transmission while maintaining water resistance.

Water Entry Pressure Testing

Water entry pressure, also known as bubble point pressure or hydro testing, is another essential parameter in assessing the performance of ePTFE membranes, particularly in applications involving liquid filtration and moisture management. It determines the pressure at which liquid begins to pass through the pores of the membrane. Water entry pressure testing helps determine the membrane's resistance to liquid penetration and is crucial in applications like medical filtration devices, fuel filtration, and waterproof textiles.

To conduct a water entry pressure test, the ePTFE membrane is subjected to increasing pressure on one side while the other side is exposed to a wetting liquid, often water. As the pressure increases, the point at which liquid starts to penetrate through the membrane's pores is the water entry pressure. This pressure is usually measured in psi or bar. The standard ASTM D751 is used to test the material for water entry pressure.

A higher water entry pressure indicates that the membrane can withstand greater hydrostatic pressure before allowing liquid to pass through, making it suitable for applications that require liquid resistance. Conversely, membranes with lower water entry pressures are ideal for applications that require controlled liquid transport.

Importance of Testing

Air permeability and water entry pressure testing are vital for ensuring that ePTFE membranes meet the specific requirements of their intended applications. Different industries have different needs, and these tests help manufacturers and engineers select the most appropriate membrane for their products. 

For example, membranes used in automotive vents are required to have a very high-water entry pressure, as these vents protect the circuitry. Even under very harsh weather – including events where a vehicle might find itself partially submerged – the membrane cannot succumb to the pressure. Similarly, in case water does find a way into the circuitry, the heat within the system should be sufficient to turn the water into vapour so it can escape through the vent.

In medical applications, such as wound dressings or drug delivery devices, a balance between air permeability and water entry pressure is crucial to ensure optimal patient comfort and controlled liquid absorption. In industrial filtration, membranes with high air permeability and suitable water entry pressure values are chosen to maximize filtration efficiency and minimize pressure drop.

Conclusion

Expanded PTFE membranes have revolutionized various industries due to their exceptional properties. Understanding their air permeability and water entry pressure characteristics is crucial for their successful deployment. The ability to manufacture, test, and fine tune membranes is something that Poly Fluoro has been developing over the past few years. With in-house testing facilities for air permeability and water entry pressure, our engineering can pinpoint the exact process needed to ensure the end-properties are exactly what are needed by the end-user.

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1. Polyimide - The Ultimate Champion Among Polymers

2. Injection Moulding High-Performance Polymers

3. PTFE Machined Conduits

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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1. Injection Moulding High-Performance Polymers

2. PTFE Machined Conduits

3. Expanded PTFE (ePTFE) Vents