PPS (polyphenylene sulfide) occupies an interesting slot in the engineering plastics lineup. It's not as strong as PEEK, not as chemically inert as PTFE, and not as heat-resistant as PI. What it does is deliver solid high-temperature performance at a price point that keeps your product budget under control.
We machine PPS regularly for customers who need the flame rating, the chemical resistance, or the thermal stability but can't justify PEEK pricing. Here's what you need to know about the material.
What makes PPS tick
PPS is a semi-crystalline thermoplastic with sulfur atoms alternating with aromatic rings in the polymer backbone. This structure gives it:
- Inherent flame retardance. PPS is V-0 rated at 0.8mm without any flame-retardant additives. The material chars rather than burning. This alone makes it the default choice for many electrical and electronic applications.
- Good chemical resistance. Below about 200°C, PPS resists virtually all solvents, most acids, and most bases. Strong oxidizing acids (nitric, concentrated sulfuric) attack it above 150°C. Short of that, it's remarkably inert.
- High continuous service temperature. Rated at 200-220°C under UL746B. Not PEEK territory, but well above most engineering plastics.
- Good mechanical properties. Tensile strength around 80-90 MPa unfilled, modulus around 3.8 GPa. Glass-filled (40% GF) pushes tensile to 150+ MPa and modulus to 12-15 GPa.
The good
PPS machines cleanly with standard carbide tooling. It produces dry, powdery chips that clear easily. Dimensional stability is better than PEEK or PTFE — PPS has low moisture absorption (<0.05%) and a relatively low, linear CTE, so parts hold their dimensions well across environmental changes.
The electrical properties are excellent: high dielectric strength, low dissipation factor, and arc resistance that exceeds PEEK. For electrical insulators, connectors, and high-voltage components, PPS is often the best choice technically as well as economically.
Cost-wise, 40% glass-filled PPS runs about 1/3 to 1/2 the price of unfilled PEEK. For applications within PPS's temperature and toughness envelope, that's a significant savings.
The not-so-good
PPS's biggest weakness is brittleness. Unfilled elongation is 1-3%, and even glass-filled grades don't improve on that. Parts with thin sections, sharp corners, or snap-fit features crack. This is not a tough material.
The high processing temperature (melt point ~285°C, mold temperature 130-150°C for injection molding) means PPS compounds need stabilizers to prevent degradation during processing. Off-spec material can have reduced mechanical properties from thermal history.
And PPS doesn't bond well. Overmolding, adhesive bonding, and ultrasonic welding are all challenging with this material. Design for mechanical fastening.
Where PPS shines
- Automotive under-hood. Coolant pump impellers, thermostat housings, EGR components. The combination of 200°C+ capability, glycol resistance, and cost-effectiveness is hard to beat.
- Electrical and electronic. Connectors, sockets, coil bobbins, switch components. The inherent V-0 rating simplifies the approval process.
- Chemical processing. Pump housings, valve bodies, filter components. Good chemical range below 200°C at a reasonable cost.
- Aerospace interiors. Low smoke, low toxicity, inherent flame retardance — PPS meets most aerospace FST requirements.
Machining tips
PPS machines more like a stiff, brittle plastic than a soft one. Key points:
- Carbide tooling, sharp edges. PPS is slightly abrasive (especially glass-filled grades), so tool wear is faster than with unfilled PEEK.
- Light, consistent chip loads. PPS chips rather than flowing, so getting the chip load right prevents edge chipping.
- Avoid excessive heat buildup. PPS's melt temperature is 285°C, and local overheating at the cutting zone can cause surface degradation.
- Coolant: dry cutting or light air blast. The chips are non-sticky and evacuate easily.
- For glass-filled PPS, diamond-coated tooling extends life significantly.
We stock PPS in unfilled and 40% glass-filled grades. If your application runs under 200°C, needs a flame rating, and doesn't see impact loads, PPS often makes more economic sense than PEEK. Send us your drawing and we'll tell you whether PPS is the right call.