Additives of PPS

Additives of PPS:

- Among the high temperature resistant additives, the most important are glass fiber, carbon fiber & mineral fillers such as chalk, iron oxide and others

- Carbon fiber reduces surface resistance & in special cases achieves a desired electrical conductivity

- Mineral fillers improve processability, reduce shrinkage (particularly anisotropic shrinkage) and improve surface gloss

- Graphite increases the stiffness of molded material

- PTFE improves the friction and wear characteristics. 

Availability

Four basic grades of PPS compounds are:

1. glass-reinforced     

2. glass- & mineral filled 

3. pigmented glass- & mineral filled

4. carbon fiber-reinforced. 

40% glass-reinforced material has lower density and higher mechanical strength than glass- and mineral filled compounds which  offer a good balance of properties at a lower cost & the pigmented glass- & mineral filled grade offers competitive properties & attractive colour at an intermediate cost. 

Thermal Properties:

1. No appreciable weight loss in filled PPS below 500oC in N2 or air.

2. Coefficient of linear expansion is comparable to that of aluminium. 

3. Water absorption of PPS is low. After immersion in water for 31 days at 100 °C, the increase in weight was only 1.01 %.

4. Good Heat ageing resistance  - UL long-term temperature indices of 170 °C for 40% w/w glass reinforced PPS & 200 °C for 40% w/w  glass- and mineral filled PPS 

Resistance to Chemicals:

1. Excellent chemical resistance, better than other advanced engineering plastics

2. No known solvents below 200°C

3. Inert to steam, strong bases, fuels and acids

4. Minimal moisture absorption

5. Very low coefficient of linear thermal expansion

6. Stress-relieving manufacturing

7. PPS ideally suited for precise tolerance machined components 

At room temperature PPS is resistant to

1. dilute mineral acids,

2. alkaline solutions, 

3. aliphatic and aromatic hydrocarbons, 

4. ketones, 

5. alcohols 

6. chlorinated hydrocarbons, 

7. oils, 

8. fats, 

9. water and hydrolysis

Flammability

- PPS exhibits excellent fire retardancy (LOI = 53)

- When exposed to a flame, molded PPS extinguishes only after removal of the ignition source & then chars forming shiny black crust there is slight expansion

- It burns with a yellowish-orange flame giving off grey smoke with black traces and a smell of rotten eggs

- It does not drip.

Processing

- PPS is injection and compression molded. 

- Non-stick coatings are applied to metal parts by fluidized bed dipping or electrostatic spraying.

- Mold cavities should be well ventilated as air inclusions lead to weak flow lines.

Pre-drying

- The glass fiber reinforced grades require  drying only when stored in poor conditions.

- It is recommended that the mineral-filled grades are dried for 6 hours at 160°C.

- Regrind must be pre-dried. The excellent thermal stability of the material enables the proportion of regrind to be as high as 35%.

- Melt temperature is 340 to 370°C 

- Mold temperature 25 to 200°C. At 120°C, molding surfaces become smooth and shiny. The toughest moldings are obtained at 40°C

- Molding shrinkage is 1 % for unreinforced & 0.2% for glass fiber reinforced material

- Metal inserts cause stress cracking which can be avoided by selecting special purpose grades

Joining

1. Moldings can be joined by screws. Vibration welding provides higher strength joins than ultrasonic welding.

2. PPS can be bonded to itself and most other materials including metals with epoxide resin adhesives, cyanoacrylate and reactive monomeric acrylate systems.

Typical Applications

1. PPS is also used in the coatings industry. 

2. Slurry coatings can be applied by a spraying and baking operation. 

3. Release coatings are formulated from PPS along with small amounts of PTFE and appropriate pigments and applied by slurry techniques.

Pump Parts:

Housings, impellers, bushings, ball valves, pump vanes, end plates, oil well valves , oil well sucker rod guides and heat shields 

Electrical components: 

High voltage enclosures and sockets, coil bobbins, yokes and connectors, printed circuits for digital watches, relay housings, guides and switch relays, encapsulating of contacts and connectors.

New applications:

1. High pressure liquid chromatography components, 

2. Wafer retaining rings for CMP polishing, 

3. Hydrocarbon pump, valve & compressor parts 

4. Oil field parts, 

5. Aerospace components

6. Medical and diagnostic device parts

7. Electronic device encapsulation,

8. Microwave cookware, 

9. Thick-walled mechanical parts, 

10.High arc resistance, 

11. High modulus anti-friction devices.