Polyphenylene Sulphide (PPS)

POLYPHENYLENE SULPHIDE(PPS):

Polyphenylene sulfide (PPS) is a semi crystalline polymers, high temperature engineering thermoplastic. It is rigid and opaque polymer with a high melting point (280°C). It consists of para-phenylene units alternating with sulfide linkages..

The first commercial process for PPS was developed by Edmonds and Hill (US patent 3 354 129, Yr. 1967) while working at Philips Petroleum under the brand name Ryton.

Today, all commercial processes use improved versions of this method. PPS is produced by reaction of sodium sulphide and dichlorobenzene in a polar solvent such as N-methylpyrrolidone and at higher temperature [at about 250° C (480° F)].

Benzene 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).

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.

In the original process developed by Philips, the product obtained has a low molecular weight and can be used in this form for coating applications. To produce molding grades, PPS is cured (chain extended or crosslinked) around the melting point of the polymer in the presence of a small amount of air. This curing process results in:

1. Increase in molecular weight

2. Increased toughness

3. Loss of solubility

4. Decrease in melt flow

5. Decrease in crystallinity

A darkening in color (a brownish color in contrast to this linear PPS grades are off-white)

Over the period of time, modification to the process have been reported to eliminate curing stage & develop products with improved mechanical strength.

Regular PPS is an off-white, linear polymeric material of modest molecular weight and mechanical strength. When heated above its glass transition temperature (Tg ~85°C), it crystallizes rapidly. Main three types of PPS include:

Linear PPS

The MW of this polymer is nearly double as compared to regular PPS.

The increased molecular chain length results in high tenacity, elongation and impact strength

Cured PPS

Obtained from heating of regular PPS in the presence of air (O2)

Curing results in molecular chain extension & formation of some molecular chain branches increases the MW and provides some thermoset-like characteristics

Branched PPS

Has higher MW than regular PPS

The backbone of the extended molecule has extended polymer chin branched from it

Branched PPS has improved mechanical properties, tenacity and ductility.

PROPERTIES

1. Good fatigue, creep and dimensional stability

2. Continuous use at 240 Deg.C.

3. Non-burning

4. Very good chemical resistance even upto 190-200℃

5. Low water absorption

6. Good radiation resistance

APPLICATIONS

1.Electrical & Electronics

2. Connectors, sockets, coil formers, floppy disc heads, bush holders, insulating plates

3. Automotive

4. Valves, carburator parts, lamp sockets Industrial Pump components, metering equipment, medical/dental equipments.