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SPECIALTY PLASTICSPolyphenylene sulfide

(PPS)

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General DescriptionBenzene rings and sulfur atoms form the backbone of the symmetrical macromolecule and characterize the properties:

- high strength, stiffness and hardness,- high heat distortion temperature,- low moisture absorption,- favorable flow properties,- high dimensional stability,- high chemical resistance,- high weathering & radiation resistance - low flammability (without additives).

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Structure and General Properties PPS has a symmetrical structure and is only slightly branched

So it is highly crystalline; degree of crystallinity, and thus the properties of moldings, depend on the thermal history to a very great extent.

melting temperature is 285°C

toughness of the brittle basic material is improved by the addition of glass fiber and mineral fibers.

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AdditivesAmong 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.

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Availability

Four basic grades of PPS compounds are:• glass-reinforced • glass- & mineral filled • pigmented glass- & mineral filled and• 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.

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Thermal Properties

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

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

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

• 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

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Resistance to Chemicals

• Excellent chemical resistance, better than other advanced engineering plastics

• No known solvents below 200°C

• Inert to steam, strong bases, fuels and acids

• Minimal moisture absorption

• Very low coefficient of linear thermal expansion

• Stress-relieving manufacturing

• PPS ideally suited for precise tolerance machined components

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Resistance to Chemicals

At room temperature PPS is resistant to• dilute mineral acids,• alkaline solutions, • aliphatic and aromatic hydrocarbons, • ketones, • alcohols • chlorinated hydrocarbons, • oils, • fats, • water and hydrolysis

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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.

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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.

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Processing

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%.

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Processing

• 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

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Joining

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

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

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Typical Applications

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.

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Typical Applications

valve & compressor parts

HPLC COMPONENTS

SOCKET ASSEMBLY

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New applications:• High pressure liquid chromatography

components, • Wafer retaining rings for CMP polishing, • Hydrocarbon pump, valve & compressor

parts • Oil field parts, • Aerospace components• Medical and diagnostic device parts• Electronic device encapsulation,• Microwave cookware, • Thick-walled mechanical parts, • High arc resistance, • High modulus anti-friction devices.

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Typical Applications

• PPS is also used in the coatings industry.

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

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

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MANUFACTURERS

Celstran® (Ticona)Comshield® (A. Schulman Inc.)Larton (LATI S.P.A.)NOVAPPS® (Mitsubishi Engineering-Plastics Corp)RTP Compounds (RTP Company)Ryton® (Chevron Phillips Chemical Co.)SUPEC* (GE Advanced Materials Asia Pacific)Techtron® (Quadrant Engineering Plastic Products)TEDUR® (Albis Plastics Corporation)Thermotuf* (LNP Engineering Plastics Inc.)Torelina® Alloy (Toray Resin Company)TOYOBO (TOYOBO America, Inc.)Xtel(TM) (Chevron Phillips Chemical Co.)

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Further Reading

1. BRYDSON J.A, Plastics Material, Butterworth Heinemann, oxford, New Delhi (2005)

2. DOMININGHAUS H., Plastics for Engineering, Hanser publishers, Munich, New York (1998)

3. CHARLESS A . HARPER, Modern Plastics Hand Book McGraw –Hill, New York (1999)

4. MARGOLIS J. M., Engineering Thermoplastics, Marcel-Dekker, New York (1985)

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Table –I Guide values of properties of PPSProperties Units PPS R 4 R10Density g/cm3 1.67 1.60 1.90Water absorption (23°C, 24h) % - 0.05 0.03Tensile strength N/mm2 121 116 83

Elongation at break % 0.9 0.5

Tensile modulus of elasticity N/mm2 114700 12400

Impact strength (Izod) J/m 69 175 132

Impact strength (Charpy) kJ/m2 12.8 6.1

Notched impact strength J/m 5.8 53

Notched impact strength kJ/m2 6.6 4.2

Rockwell hardness scale R 123 R123 R 120

Melting Point °C 285

Service temperaturein air without mechanical loading long-term °C 200 200

Glass transition temperature 93 88 88

Heat deflection temperature °C 260

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Table –I Guide values of properties of PPSProperties Units PPS R 4 R10

Vicat ISO Method A °C 243 245

Coefficient of linear expansion mm/mm/°C 2.9x105 22.10-6 22.10-6

Thermal conductivity W/mK 0.25 0.25

Volume resistivity cm 4.6.1016

Surface resistance 4.5.1016 2.1015

Dielectric constant 106 Hz 3.8 3.8 4.8-6.1

Dissipation factor 50 Hz 0.0014 0.01-0.08

Dielectric strength kV/mm 17.2

Power Factor 0.0014

Fire performance to UL 94 class V-0 V-0

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