Product Content
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Engineering Plastic-PPS
**PPS Overview:**
Polyphenylene sulfide (PPS) is a crystalline polymer with the chemical name polyphenylene sulfide. Its molecular structure consists of alternating benzene rings and sulfur atoms. The numerous benzene rings provide rigidity, while the sulfide bonds offer flexibility. PPS is characterized by its hardness, brittleness, high crystallinity, difficulty in flammability, excellent thermal stability, high mechanical strength, and superior electrical properties.
PPS is a crystalline (with a crystallinity of 55%-65%) high-rigidity white powder polymer that exhibits excellent heat resistance (continuous use temperature up to 240°C), mechanical strength, stiffness, flame retardancy, chemical resistance, electrical properties, and dimensional stability. It has good wear resistance, creep resistance, and self-extinguishing properties, achieving UL94 V-0 rating. It maintains excellent electrical properties at high temperatures, flows well during molding, and rarely shows sink marks or surface defects. PPS has good affinity with various inorganic fillers. For improved physical and mechanical properties and heat resistance (heat deflection temperature), it can be reinforced with materials like glass fibers, carbon fibers, aramid fibers, and metal fibers. Common inorganic fillers include talc, kaolin, calcium carbonate, silica, and molybdenum disulfide. PPS/PTFE, PPS/PA, and PPS/PPO alloys are commercially available, with PPS/PTFE improving toughness, lubricity, and corrosion resistance, and PPS/PA providing high toughness.
**PPS Characteristics:**
1. **General Properties:**
PPS is a white, highly crystalline, hard, and brittle polymer. Pure PPS has a density of 1.3 g/cm³, which increases after modification. PPS has an extremely low water absorption rate, typically around 0.3%. It is highly flame retardant, with an oxygen index as high as 44%, making it one of the most flame-retardant plastics (pure PPS has an oxygen index of 47%, PSF 30%, PA66 29%, MPP 25%).
2. **Mechanical Properties:**
Pure PPS has relatively low mechanical properties, especially impact strength. Glass fiber reinforcement significantly improves impact strength from 27 J/m to 76 J/m, increasing threefold; tensile strength increases from 6 MPa to 137 MPa. PPS has very high stiffness, with a flexural modulus of 3.8 GPa for pure PPS, reaching 12.6 GPa after inorganic filler modification. This is much higher than PPO (2.55 GPa) and PC (2.1 GPa). PPS has excellent creep resistance under load, high hardness, and wear resistance, with a wear loss of only 0.04g after 1000 revolutions. Adding F4 and molybdenum disulfide further improves these properties. PPS also has some self-lubricating properties, and its mechanical properties are less sensitive to temperature changes.
3. **Thermal Properties:**
PPS has excellent thermal properties, capable of short-term exposure to 260°C and long-term use between 200-240°C. Its heat resistance is comparable to PI and second only to PTFE among thermoplastics, which is rare even among thermosets.
4. **Electrical Properties:**
PPS has outstanding electrical properties. Compared to other engineering plastics, it has low dielectric constant and dielectric loss tangent, which remain stable over a wide range of frequencies, temperatures, and humidity levels. PPS has excellent arc resistance, comparable to thermosets, and is widely used as an insulating material in electrical applications, accounting for about 30% of its usage.
5. **Environmental Properties:**
One of PPS's key features is its excellent chemical resistance, second only to PTFE. It is stable against most acids, esters, ketones, aldehydes, phenols, aliphatic hydrocarbons, aromatic hydrocarbons, and oxyhydrocarbons but is not resistant to oxydibenzenes, oxidizing acids, oxidizers, aqua regia, hydrogen peroxide, and sodium hypochlorite. PPS has excellent radiation resistance.
**PPS Applications:**
1. **Automotive Industry:**
Carburetors, distributor components, electronic and electrical parts, throttle valves, sensors, etc.
2. **Electronics and Electrical Industry:**
Connectors, insulating partitions, terminals, switches, etc.
3. **Home Appliances:**
Structural components of tape recorders, diodes, various parts, etc.
4. **Aerospace Industry:**
PPS/PTFE can be used for anti-stick, wear-resistant components, and transmission parts such as shaft pumps.
**Processing Methods:**
1. **Processing Characteristics:**
PPS supplied by resin manufacturers is a low-molecular-weight (4000-5000), high-crystallinity (75%) white powder, unsuitable for direct plasticization. For plasticization, cross-linking modification is required to increase melt viscosity. Typically, the melt index should be 10-20; for glass-fiber-reinforced PPS, it can be higher but not exceed 200. Cross-linking methods include thermal and chemical cross-linking, with thermal cross-linking being predominant. Thermal cross-linking occurs between 150-350°C, with optimal conditions being 150-350°C. Chemical cross-linking requires cross-linking promoters like zinc oxide, lead oxide, magnesium oxide, cobalt oxide, phenolic compounds, hexamethoxymethylmelamine, hydrogen peroxide, and alkali or alkaline earth metal hypochlorites. Despite cross-linking, PPS retains good flowability, allowing scrap reuse up to three times. PPS has inherent release properties, eliminating the need for mold release agents. Post-processing can enhance crystallinity and heat deflection temperature, typically at 204°C for 30 minutes.
2. **Processing Methods:**
- **Injection Molding:** Standard injection molding machines can be used. For glass-fiber-reinforced PPS, a melt index of 50 is recommended. Injection molding parameters: barrel temperature 280-330°C for pure PPS, 300-350°C for 40% GFPPS, mold temperature 120-180°C, injection pressure 50-130 MPa.
- **Extrusion:** Use vented extruders with processing conditions: feed zone temperature <200°C, barrel temperature 300-340°C, adapter temperature 320-340°C, die temperature 300-320°C.
- **Compression Molding:** Suitable for large parts, using two-stage compression—initial cooling followed by hot pressing. Preheating temperatures: 360°C for 15 minutes for pure PPS, 380°C for 20 minutes for GFPPS. Compression pressure: 10-30 MPa, cool to 150°C before demolding.
- **Spray Coating:** Suspension spray coating or combined suspension spray and dry powder thermal spraying can be used, depositing PPS on metal surfaces followed by plasticization and quenching. Coating treatment temperature: above 300°C for 30 minutes.
