PPS Injection Moulding: Properties, Grades & Design Guide
PPS (polyphenylene sulphide) is the most cost-effective semi-crystalline high-performance thermoplastic for applications requiring continuous service above 180°C combined with broad chemical resistance. It is routinely used in automotive under-bonnet components, SMD electronic connectors, and industrial fluid-handling parts where nylon, POM, and polycarbonate cannot survive the environment. Nordmould processes PPS primarily as glass or mineral-filled grades, where the material's inherent tendency to brittleness is significantly improved.
What are the mechanical and thermal properties of PPS?
PPS is a semi-crystalline sulphide-backbone polymer. Its properties depend significantly on crystallinity achieved during moulding, which is governed by mould temperature. Unfilled PPS is brittle and rarely used in structural applications; filled grades — with 40% GF being the industry standard — are the practical choice.
| Property | Unfilled PPS | 40% GF PPS | 40% GF + Mineral PPS | Test Standard |
|---|---|---|---|---|
| Tensile Strength | 65–80 MPa | 150–190 MPa | 130–160 MPa | ISO 527 |
| Flexural Modulus | 3,900 MPa | 13,000–16,000 MPa | 12,000 MPa | ISO 178 |
| Izod Impact (notched) | 15–25 J/m | 55–80 J/m | 50–70 J/m | ISO 180 |
| Heat Deflection Temp (1.82 MPa) | 110–130°C | 260–270°C | 250°C | ISO 75 |
| Continuous Use Temp | 200–220°C | 200–220°C | 200°C | — |
| Density | 1.34 g/cm³ | 1.64 g/cm³ | 1.75 g/cm³ | ISO 1183 |
| Mould Shrinkage (flow) | 0.7–1.0% | 0.1–0.3% | 0.1–0.2% | ISO 294-4 |
| Water Absorption (24 h) | 0.03% | 0.02% | 0.02% | ISO 62 |
| Flame Rating | UL 94 V-0 | UL 94 V-0 | UL 94 V-0 | UL 94 |
The near-zero water absorption is critical in electronics applications: connectors and relay housings maintain dimensional stability and electrical properties across humidity cycles that would degrade nylon or PC significantly.
Where is PPS injection moulding used?
PPS's thermal stability, chemical resistance, dimensional precision, and inherent flame retardance without halogenated additives put it in a well-defined set of demanding applications.
Automotive under-bonnet: Throttle bodies, EGR valves, coolant system housings, fuel injector components, transmission sensor housings, and oil pump parts. PPS tolerates the combination of elevated temperature, aggressive fluids, and vibration that defines the engine bay environment.
Electronic connectors and relay housings: PPS is the dominant connector housing material for SMD components that pass through 260°C reflow soldering. Its dimensional precision in filled grades holds pin-to-pin spacing within the tight tolerances required by IEC connector standards.
Industrial pumps and valves: Pump impellers, valve seats, metering valve bodies, and chemical dosing system components. PPS's solvent resistance at elevated temperatures makes it the default choice where PVDF and other fluoropolymers are cost-prohibitive.
Electrical motor components: Brush holders, commutator insulators, and motor housings that must maintain dimensions and insulation properties at motor operating temperatures.
Aerospace and defence: Fluid connectors, brackets, and electrical components in environments where both temperature and chemical resistance are required simultaneously.
What are the moulding characteristics of PPS?
PPS is processable but technically demanding. Unfilled PPS flows very well at melt temperature; filled grades are more viscous and require higher injection pressures. The main process risks are embrittlement from low mould temperature, corrosion from sulphur species released at degraded melt temperatures, and warp from anisotropic shrinkage in heavily glass-filled grades.
Melt temperature: 300–340°C. Temperatures above 360°C cause thermal degradation, producing corrosive by-products including sulphur dioxide. Barrels and screws must be made from corrosion-resistant alloys — a bimetallic barrel with a nickel-alloy lining is standard. Processing equipment must be compatible with the corrosive nature of PPS at melt temperature.
Mould temperature: 120–160°C. Achieving semi-crystalline microstructure requires adequate mould temperature. Below 100°C, unfilled and lightly filled PPS forms predominantly amorphous parts that are brittle and dimensionally unstable. Oil-heated or electrically heated moulds are required for large tools.
Drying: 120–150°C for 3–4 hours in a dehumidifying dryer. Regrind should be dried separately.
Corrosion: PPS releases corrosive sulphur compounds at melt temperature and more severely on degradation. All tooling, barrel, screw, and hot-runner components in contact with PPS melt must be specified in corrosion-resistant materials. Maintenance intervals are shorter than with neutral polymers.
Warp: The primary process challenge with 40% GF PPS is anisotropic shrinkage — flow-direction shrinkage is approximately 0.1–0.3% while cross-flow can reach 0.8%. This differential causes warp in flat, unsupported geometries. Gate positioning to balance flow, use of mineral-glass hybrid fillers, and careful cooling circuit design are the main mitigation strategies.
Draft and ejection: Filled PPS is stiff and rigid at ejection; minimum 1.5° draft angles and polished core surfaces are recommended to avoid part damage during ejection.
Which PPS grades and variants are available?
| Grade | Filler / Modification | Primary Application |
|---|---|---|
| 40% Glass-filled PPS | Standard GF grade | Connectors, valve bodies, structural |
| 40% Glass + Mineral PPS | Reduced warp, improved isotropy | Flat components, enclosures |
| Carbon-fibre PPS | Maximum stiffness, thermal conductivity | Aerospace, heat sinks |
| PTFE-blended PPS | Low friction, improved wear resistance | Bearing surfaces, seal components |
| Conductive PPS | Carbon black or CNT loaded | ESD-safe components, shielding |
| High-purity PPS | Low extractables, semiconductor grade | Wafer handling, chemical equipment |
Mineral-filled hybrid grades have become increasingly important because they dramatically reduce the warp that limits pure GF PPS in thin flat components, while preserving the thermal and chemical performance of the base polymer.
What are PPS's advantages and limitations?
Advantages:
- Continuous use temperature of 200–220°C — cost-effective alternative to PEEK for many applications
- Broad chemical resistance: no known solvent dissolves PPS below 200°C
- Inherent UL 94 V-0 flame retardance without halogenated additives
- Very low water absorption (<0.03%) — stable electrical and mechanical properties across humidity cycles
- High stiffness in filled grades — suitable for precision-tolerance components
- Good dimensional stability at elevated temperatures; suitable for SMD reflow soldering
Limitations:
- Unfilled PPS is brittle — almost all applications require filled grades
- Anisotropic shrinkage in glass-filled grades causes warp in flat, unsupported parts
- Corrosive at melt temperatures — specialised corrosion-resistant equipment required
- High mould temperature requirement (120–160°C) increases tooling and energy cost
- Lower impact resistance than PEEK or PC — not suitable for high-impact applications
- Opaque in all standard grades
When should you choose PPS over alternative materials?
PPS vs Nylon (PA66): Choose PPS when the application requires higher continuous temperature (above 150°C), lower water absorption, or inherent flame retardance. Choose nylon when impact resistance is the primary requirement, or when material cost is constrained and temperature stays below 130°C.
PPS vs PEEK: PPS is the economic choice for applications up to 200–220°C with no biocompatibility requirements. PEEK is justified when temperature continuously exceeds 230°C, when impact resistance matters, or when implant-grade certification is needed.
PPS vs PEI (Ultem): PEI offers higher impact resistance and is amorphous (no crystallisation control issues), at a lower cost than PEEK. Choose PPS for better chemical resistance, higher continuous temperature, or when the inherent UL 94 V-0 rating without additives is required. Choose PEI for complex thin-walled geometries where amorphous material simplifies the moulding process.
PPS vs LCP: LCP achieves higher precision in very thin walls and ultra-fine connector pitches. PPS is preferred for structurally loaded components where LCP's flow-direction anisotropy would be a reliability risk.
Is PPS recyclable?
PPS is not collected in municipal recycling streams. Industrial regrind from clean production scrap is reusable in non-critical applications at up to 20–25% blend with virgin material; higher regrind levels reduce impact strength further. End-of-life recovery requires specialist facilities equipped for high-temperature processing of sulphur-containing polymers. The long service life of PPS components in automotive and industrial applications — typically 10–20 years before end-of-life questions arise — partially offsets this. Nordmould can advise on regrind use policies and alternative materials where sustainability requirements are relevant.
Frequently asked questions
What is the continuous use temperature for PPS injection-moulded parts?
Unfilled PPS has a continuous use temperature of 200–220°C. Glass and mineral-filled grades maintain structural integrity at the same temperatures with significantly higher stiffness. Heat deflection temperature (at 1.82 MPa) reaches 260–270°C for 40% glass-filled PPS — suitable for under-bonnet and reflow-soldering applications.
Does PPS need to be dried before injection moulding?
Yes. PPS is mildly hygroscopic. Drying at 120–150°C for 3–4 hours in a dehumidifying dryer is standard practice. Moisture levels above 0.05% cause splay, surface defects, and reduced mechanical performance. Regrind should be dried separately and blended conservatively with virgin material.
What are the melt and mould temperatures for PPS injection moulding?
PPS melt temperature is typically 300–340°C. Mould temperature should be 120–160°C for filled grades to achieve proper crystallisation. Lower mould temperatures produce amorphous, brittle parts. High mould temperature also reduces flash tendency and improves surface replication in fine-featured parts.
What makes PPS a good choice for electronic connectors?
PPS combines a UL 94 V-0 flame rating (inherent, without halogenated additives), dimensional stability at soldering temperatures (260°C reflow peak), very low water absorption (under 0.03%), tight moulding tolerances on glass-filled grades, and good electrical insulation. These properties together make it standard for SMD connectors and relay housings.
How does PPS compare to PEEK in cost and performance?
PPS raw material costs roughly 5–15× less than PEEK. PPS is the rational choice for applications with continuous temperature requirements below 200–220°C and broad chemical resistance demands. PEEK is justified when temperature exceeds 230°C continuously, when biocompatibility certification is required, or when impact resistance is critical.
Is PPS injection moulding chemically resistant?
PPS has outstanding broad-spectrum chemical resistance. It is unaffected by most organic solvents, acids, and bases at elevated temperatures — no known solvent dissolves it below 200°C. It is attacked by concentrated nitric acid, concentrated chlorine, and some halogenated solvents at high temperatures. It is widely used in fluid-handling, pump, and valve components.
What are the main filled grades of PPS available for injection moulding?
Common grades include 40% glass-filled PPS (standard high-stiffness grade), 40% glass + mineral-filled PPS (reduced warp, improved surface quality), carbon-fibre-filled PPS (maximum stiffness and thermal conductivity), and PTFE-blended PPS (bearing and seal grade with improved tribological properties).
Submit your STEP file to Nordmould for a free DFM review — our engineers will confirm whether PPS is the right specification and highlight any warp, gate, or tooling corrosion risks early in your design process.