Scrapers
Rod seals
Piston Seals
Guide rings
Back-Up rings
O-Rings / X-Rings
Flat seals
Spring-loaded seals
Radial shaft seals
Rotary seals
High pressure seals
Sealing sets
O-ring measuring towers
Turned parts
Milled parts
Turned and milled parts
Bushes or bearings
Moulded parts
Large format 3D printing
Post-processing of 3D printed parts
Heat-resistant 3D printed components
Plastic Components with Flame Retardancy
PPS (Polyphenylene Sulfide)
Definition and Classification
PPS stands for polyphenylene sulfide. It is a thermoplastic — that is, a plastic that can be plastically deformed by heating and solidifies again on cooling. PPS belongs to the semi-crystalline engineering plastics. “Engineering plastic” here means a technical plastic designed for loaded components, where dimensional stability, stiffness, and resistance matter more than pure processing or cost aspects.
In sealing technology, PPS usually becomes of interest when a component close to the seal must permanently maintain its shape and function. This concerns, for example, guide, back-up, and wear parts in pumps, valves, or compressors. The task of such parts is rarely “sealing” in the narrow sense. Frequently, they stabilize the gap, guide moving components, or protect softer sealing materials against extrusion and wear.
What Does “Semi-Crystalline” Mean, and Why Is It Relevant?
Semi-crystalline means that the polymer chains in the material are partly ordered (crystalline) and partly disordered (amorphous). This morphology affects practice directly in many cases: the crystalline portion supports stiffness and dimensional stability, and it often contributes to chemical resistance. For sealing assemblies, this is relevant because fits, gaps, and preloads can change with temperature and media contact. A semi-crystalline material like PPS frequently remains more stable than strongly amorphous plastics.
Temperature Behavior and Dimensional Stability
PPS is a high-temperature thermoplastic with a melting temperature on the order of approx. (depending on standard, measurement method, and grade). This value describes when the crystalline portion melts. However, it does not yet say at which temperature a component can be safely used in continuous operation.
For sealing technology, the more important question is therefore how stiff and dimensionally stable PPS remains at elevated temperatures. In guide and back-up elements, this decides surface pressure, gap behavior, and thereby friction, leakage paths, and wear. Particularly with tight tolerances, it pays to look at the overall system: temperature profile, assembly condition, mating partner, and mechanical loads determine whether dimensional stability remains stable in operation.
| Parameter (classification) | What it answers | Relevance near the seal |
|---|---|---|
| Melting temperature (≈ 280 °C) | When the material melts | Limit orientation, not a continuous-use approval |
| Stiffness at temperature | How much the component yields under load | Gap and guidance accuracy, contact pressure |
| Thermal expansion | How much dimensions rise with temperature | Tolerances, binding or clearance in guides |
Chemical Resistance, Moisture, and Hydrolysis
PPS is considered broadly chemical-resistant and is frequently used where media are aggressive or change. In addition, a very low water absorption is described (as a guideline, an order of magnitude around ~0.02 % is often cited, depending on test conditions and grade). In practice, this matters because moisture absorption leads in many plastics to dimensional changes and altered mechanical properties. PPS frequently remains comparatively stable under moist conditions, which makes guide and back-up functions more reliable.
When it comes to media, the question is typically: which fluid actually applies, at which temperature, and over what time? In fluid technology, these are frequently hydraulic oils, fuels, water or steam, and cleaning chemicals. PPS is often a good candidate for these, but the specific resistance depends on recipe, temperature, and exposure time. Therefore, for demanding applications, a system test is set up that reflects the real media list and temperature profile.
Water Absorption vs. Hydrolysis: Practical Significance
Water absorption means that water physically enters the material and thereby affects dimensions or properties. Hydrolysis, by contrast, is a chemical breakdown by water that can split polymer chains. PPS is frequently described as hydrolysis-resistant, which can be a relevant advantage for components in contact with hot water or steam. Near the seal, this directly affects service life and dimensional stability, because guide elements must retain their function even after many temperature and media cycles.
Friction, Wear, Fillers, and Material Distinction (PEEK/PTFE)
PPS can be used in sliding and wear contacts but does not automatically reach the best tribological performance in every pairing. Tribology describes friction and wear in the contact of two surfaces. In sealing technology, not only the material decides but also the system: mating surface (hardness, roughness), lubrication or medium, surface pressure, and speed. In practice, modified PPS grades are therefore frequently used.
Common modifications are fillers and additives. Glass fiber typically increases stiffness and strength but can stress the mating partner more. Mineral fillers often improve dimensional stability and temperature behavior. Solid lubricants such as PTFE content reduce friction and can lower stick-slip. As a result, PPS materials are particularly interesting as guide, back-up, and wear rings, while pure sealing lips or very low-friction slide seals frequently use other material concepts.
Suitable Functions Near the Seal (Static vs. Dynamic)
In many assemblies, the question is what the PPS part should specifically deliver. For purely static sealing functions, PPS is rarely chosen as the main sealing material. More frequently, PPS takes over supporting tasks that first make a seal function — for example by preventing extrusion or stabilizing guidance.
In dynamic systems, PPS is also used indirectly: as a filler in PTFE compounds, it can improve wear resistance. When PPS is used as a stand-alone slide component, it usually requires a tribological design that considers PV loading (pressure × velocity) and the mating partner.
Fillers: Benefits and Trade-Offs
| Modification | Typical benefit | Possible trade-off |
|---|---|---|
| Glass fiber | Higher stiffness and strength | Can act more abrasively on the mating surface |
| Mineral fillers | Better dimensional stability, more stable temperature behavior | Properties depend strongly on the recipe |
| Solid lubricants (e.g., PTFE additives) | Lower friction, less stick-slip | Mechanical parameters can drop |
PPS vs. PEEK vs. PTFE: Brief Comparison for Material Selection
For material selection in sealing technology, PPS is often classified between PTFE and PEEK. PTFE offers very low friction but is mechanically soft and tends to cold flow (time-dependent deformation under load). PEEK is mechanically and thermally very capable and is frequently used in heavily loaded applications but is often more cost-intensive. PPS in many cases combines good heat and chemical resistance with dimensional stability and is therefore frequently chosen for guide and back-up functions when the system places high demands but does not need the extreme performance reserve of PEEK.
In the end, the specific application nevertheless decides: medium, temperature, mating surface, and loading determine whether PPS, a PPS compound, or an alternative material is the most robust solution. For critical applications, specialized material and system assessment is sensible.
