Among the most difficult polymers to process, Polyphenylene Sulfide (PPS) is nonetheless a challenge worth undertaking.
Often called by its trade name “Ryton®”, Polyphenylene sulfide (PPS) is a high-performance thermoplastic polymer known for its exceptional mechanical and thermal properties. The polymer finds extensive use across various industries due to its unique combination of characteristics such as chemical resistance, heat resistance, dimensional stability, and electrical insulation.
However, processing PPS requires a deep understanding of the material’s behaviour, and a significant amount of time and effort needs to be spent to achieve a consistent end-product.
Properties of Polyphenylene Sulfide
PPS is distinguished by a unique combination of mechanical, thermal, chemical, and electrical properties. Let’s take a closer look at these key characteristics:
1. Thermal Stability: PPS has excellent thermal stability, with a continuous service temperature of up to 200°C (392°F). It can withstand short-term exposure to temperatures as high as 260°C (500°F), making it suitable for high-temperature environments such as automotive engine compartments and industrial processes. This thermal resistance is attributed to its aromatic backbone structure, which provides rigidity and stability even under extreme conditions.
2. Chemical Resistance: One of the most outstanding features of PPS is its resistance to chemicals. It is virtually impervious to acids, alkalis, organic solvents, and oxidizing agents. PPS also demonstrates high resistance to hydrocarbons, fuels, and oils, which makes it particularly well-suited for applications in the chemical, automotive, and oil and gas industries. This chemical stability is one of the key reasons why PPS outperforms many other engineering plastics in aggressive chemical environments.
In terms of properties and even feel, PPS is often compared with PEEK. However, while PEEK exhibits superior mechanical and thermal properties, PPS outranks PEEK on chemical resistance. Specifically, as PEEK is affected by Sulphuric Acid, PPS is used in environments where this acid is prevalent.
3. Mechanical Strength and Dimensional Stability: PPS exhibits excellent mechanical properties, including high tensile strength, rigidity, and dimensional stability. The material retains its mechanical strength even under elevated temperatures, making it suitable for structural components. Its low coefficient of thermal expansion (CTE) ensures that PPS parts maintain their dimensional stability over a wide range of temperatures, which is critical for precision components such as gears, bearings, and other load-bearing parts.
While these properties can be attributed to PPS, they are nearly impossible to achieve using pure PPS. In order to achieve its mechanical strength, PPS needs to be reinforced with fillers of glass and even PTFE. Glass is especially important – most PPS grades are in fact PPS+40% Glass – in that it allows the polymer the necessary ‘fibre’ to hold its shape and form. Pure PPS will have a tendency to shatter and splinter (often in sharp shards that can cut), so it is rarely used in this form.
4. Electrical Insulation: PPS is an outstanding electrical insulator. It has a high dielectric strength, low dielectric constant, and low dissipation factor, making it a preferred material for electrical and electronic applications. PPS is used in electrical components that require high insulation resistance and stability in harsh environments, including connectors, switches, and printed circuit boards (PCBs).
5. Low Water Absorption: PPS has low water absorption rates, making it dimensionally stable even in humid or moisture-laden environments. This property enhances its reliability and durability in outdoor applications and environments with varying humidity levels.
6. Flame Retardancy: PPS is inherently flame-retardant due to its aromatic structure. It exhibits excellent self-extinguishing properties, which is a significant advantage for applications where fire safety is a concern. Its flame resistance makes it suitable for electrical enclosures, automotive components, and aerospace applications.
Advantages of Polyphenylene Sulfide
The combination of the aforementioned properties results in numerous advantages that make PPS a sought-after material in various high-performance applications.
1. High Temperature Tolerance: PPS's ability to withstand high temperatures without losing mechanical strength or dimensional stability is one of its most significant advantages. Components made from PPS can function reliably in high-heat environments where other materials would degrade or deform. This high-temperature tolerance expands the range of applications, from engine components to electrical housings that are exposed to heat during operation.
2. Chemical and Corrosion Resistance: PPS is almost universally resistant to chemicals, offering superior corrosion resistance compared to metals and other plastics. This advantage reduces the need for protective coatings or special surface treatments, making PPS a cost-effective solution for applications in chemical processing, oil and gas, and automotive industries. Its chemical resistance also ensures long-term durability and reduced maintenance requirements.
3. Dimensional Stability: The low coefficient of thermal expansion (CTE) of PPS, combined with its low water absorption, ensures that components maintain their dimensions under varying environmental conditions. This advantage is particularly important in precision applications, such as electronics and precision instrumentation, where even minor dimensional changes could lead to performance issues.
4. Ease of Processing: Although challenging to process at first, PPS can be processed through injection molding, extrusion, or compression molding, making it highly adaptable for manufacturing complex shapes and parts with tight tolerances. The polymer can be reinforced with fillers such as glass fibers, carbon fibers, or minerals to enhance its mechanical properties, further broadening its application potential.
|
Property (Unit) |
Test Method |
Unfilled |
Glass Reinforced |
Glass-Mineral Filled* |
|
Filler Content (%) |
|
- |
40 |
65 |
|
Density (kg/l) |
ISO 1183 |
1.35 |
1.66 |
1.90 - 2.05 |
|
Tensile Strength (Mpa) |
ISO 527 |
65-85 |
190 |
110-130 |
|
Elongation at Break (%) |
ISO 527 |
6-8 |
1.9 |
1.0-1.3 |
|
Flexural Modulus (MPa) |
ISO 178 |
3800 |
14000 |
16000-19000 |
|
Flexural Strength (MPa) |
ISO 178 |
100-130 |
290 |
180-220 |
|
Izod notched Impact Strength (KJ/m2) |
ISO 180/1A |
|
11 |
5-6 |
|
HDT/A (1.8 Mpa) (°C) |
ISO 75 |
110 |
270 |
270 |
5. Flame Resistance: The inherent flame retardancy of PPS adds another layer of safety in applications where fire hazards are a concern. This property makes it a preferred material in electrical and automotive industries, where flame-resistant materials are critical for ensuring safety and compliance with fire safety standards.
6. Lightweight: Compared to metals, PPS is lightweight, which is a significant advantage in industries such as automotive and aerospace. Replacing metal components with PPS helps reduce overall weight, which can improve fuel efficiency and reduce energy consumption in vehicles and aircraft.
Applications of Polyphenylene Sulfide
Given its impressive properties and associated advantages, PPS is used in a wide array of applications across multiple industries. Below are some of the key application areas where PPS excels:
1. Automotive Industry: PPS is extensively used in the automotive industry for under-the-hood components, particularly those exposed to high temperatures and corrosive fluids. Common applications include:
-
Engine Components: PPS is used in manufacturing components such as water pumps, fuel systems, oil pumps, and engine housings, which require both heat and chemical resistance.
-
Transmission Components: The polymer’s dimensional stability and mechanical strength make it ideal for transmission gears, bearings, and other precision components.
-
Electrical Connectors: PPS’s excellent electrical insulation properties make it a preferred choice for connectors and switches within automotive electrical systems, ensuring reliability even in harsh conditions.
2. Electrical and Electronics Industry: PPS is widely used in the electrical and electronics sector due to its electrical insulation properties, flame retardancy, and dimensional stability. Applications include:
-
Connectors and Housings: PPS is commonly used in electrical connectors, switches, and housings for electronic components, providing excellent insulation and heat resistance.
-
Printed Circuit Boards (PCBs): The polymer’s heat resistance and low dielectric constant make it an ideal substrate material for PCBs used in demanding environments, such as aerospace and telecommunications.
-
Insulating Films and Tapes: PPS films and tapes are used for insulation in high-temperature electrical applications.
3. Aerospace Industry: The aerospace industry demands materials that offer a high strength-to-weight ratio, chemical resistance, and flame retardancy. PPS meets these requirements, and its applications in the aerospace industry include:
-
Structural Components: PPS is used in various structural components that require high strength and dimensional stability under varying temperature and pressure conditions.
-
Electrical Insulation: The material is also used in insulating components for avionics and other high-performance electrical systems, where maintaining electrical integrity is crucial.
4. Industrial Applications: PPS finds extensive use in industrial applications, particularly in environments that involve exposure to chemicals, high temperatures, or wear. Examples include:
-
Chemical Processing Equipment: Due to its resistance to corrosive chemicals, PPS is used in components such as valves, pump housings, and seals in the chemical processing industry.
-
Filter Bags and Membranes: PPS is used to manufacture filter bags and membranes for high-temperature filtration systems in industrial processing plants, especially those handling hot gases or corrosive fluids.
-
Mechanical Bearings and Gears: The polymer’s mechanical strength and wear resistance make it suitable for gears, bearings, and other load-bearing components that operate under high stress and temperature conditions.
5. Medical Industry: In the medical industry, PPS is valued for its biocompatibility, chemical resistance, and dimensional stability. It is used in various medical devices and components, such as:
-
Surgical Instruments: PPS’s ability to withstand high-temperature sterilization methods, such as autoclaving, makes it a suitable material for surgical instruments and components.
-
Medical Device Housings: The polymer’s chemical resistance and electrical insulation properties make it a reliable material for housings of sensitive medical equipment.
6. Oil and Gas Industry: The oil and gas industry requires materials that can endure exposure to harsh chemicals, extreme temperatures, and high pressures. PPS is used in:
-
Seals and Gaskets: The chemical resistance and thermal stability of PPS make it ideal for seals and gaskets in oil and gas pipelines, valves, and pumps.
-
Downhole Components: PPS is also used in various downhole components, where its mechanical strength and resistance to corrosive environments are critical.
Conclusion
Polyphenylene sulfide (PPS) stands out as one of the most versatile and high-performance thermoplastic polymers available today. Its exceptional properties—such as high temperature and chemical resistance, mechanical strength, dimensional stability, electrical insulation, and flame retardancy—allow it to excel in a wide range of demanding applications. Industries such as automotive, electronics, aerospace, and chemical processing have embraced PPS for critical components that require long-term reliability and performance in harsh environments.
As industries continue to demand materials that offer higher performance and greater durability, PPS is poised to play an increasingly important role. Whether in automotive components, electrical connectors, or industrial filtration systems, PPS’s unique set of advantages ensures that it will remain a key material in modern engineering applications for years to come.
Note: Ryton® is the registered trademark of Solvay
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