What is PPS? Poly Phenylene Sulfide

Polyphenylene sulfide (PPS) is an aromatic, crystalline, opaque, high temperature polymer with simple chemical structure containing benzene and sulfur. PPS was initially synthesised in a laboratory by Macallum in 1948 via melt polymerisation by reacting sulphur, sodium carbonate, and dichlorobenzene. Macallum’s patents (US2513188 and US2538941) were sold to Dow in 1954. Further studies at Dow indicated that Macallum’s PPS synthesis route led to mixture of crosslinked and linear PPS structures. Further studies at Dow lead to alternative polymerisation routes, however, difficult by-product extraction hindered commercial manufacturing of PPS at Dow.

First large-scale commercial manufacturing process was developed around 1963 by Edmunds and Hill (Patent No.: US3354129A) at Philips Petroleum Company. However, this earlier version of PPS was low molecular weight materials and predominantly used in coating applications. Mouldings from low Mw PPS were made via chain extension and crosslinking to increase Mw. Low Mw PPS with crosslinking operation found to affect mouldability owing to high process temperatures and poor melt flow characteristics. This led to the development of high molecular weight linear PPS without any crosslinking reactions. High Mw Linear PPS found to have consistent flow behaviour, high elongation, high impact strength and better moulding characteristics. PPS is available in various grades and some of them are listed below:

Low Mw Coating Grade ‘Cross-linkable’ PPS
High Mw Moulding Grade ‘Cross-linked’ PPS
Low Mw Coating Grade ‘Linear’ PPS
High Mw Moulding Grade ‘Linear’ PPS (Predominantly used in fibre spinning process)
Elastomer toughened PPS
Glass fibre filled PPS & Carbon fibre filled PPS
Glass fibre/Mineral filled PPS
Lubricated PPS
PPS – Carbon Fibre UD tapes

Chemical Structure of PPS:

Linear PPS is manufactured by reacting dichlorobenzene with sodium sulfide. Linear PPS is tough, ductile, and has resistance in hot-wet conditions. Whereas crosslinked PPS is more rigid with better creep and heat resistance. Presence of phenyl ring and polar group increases thermal performance of PPS with continuous use temperature can be up to 230°C. Owing to semi-aromatic structure, PPS has high melting point typically in the range of 270-285°C. However, like PEEK, Tg is low in the range of 80-90°C.

Typical Material Properties:

Some of the properties are listed below. These values to be considered as indicative rather than accurate. As filled PPS grades are very common, properties of both unfilled and filled grades are shown below:

Material Property	Unit	Indicative Value Unfilled High Mw PPS	Indicative Value GF Filled PPS
Mechanical Properties
Tensile Strength	MPa	80-90	170-195
Tensile Elongation at Break	%	4-6	1.5-1.9
Tensile Modulus	MPa	3400-3500	13000-14700
Density	g/cm³	1.35	1.65
Notched Impact strength	kJ/m²	70-82	25-34
Rockwell Hardness (M)	D	90	100

Thermal Properties
Typical Melting Range	°C	270-285	270-85
Typical glass transition temperature	°C	80-90	80-90
Service Temperature	°C	Less than 200°C	Less than 240°C
CTE	10^-4 /°C	0.50-0.52	0.20-0.26
Deflection Temperature 1.8 MPa	°C	110-115	250-270

Electrical Properties
Dielectric Constant at 1 MHz		4.4-4.6	3.9-4.1
Dissipation Factor Tan δ at 1 MHz	E^-4	9-11	18-20
Dielectric Strength	kV/mm	17-18	28-31
Volume Resistivity	Ohm.m	1 x E⁹	>1 x E¹⁵

Typical PPS Processing Methods:

Injection Moulding
Compression Moulding
Extrusion
Fibre spinning
Composite moulding
Automatic tape lay-up / Automatic fibre placement

Unique Properties of PPS:

Outstanding heat resistance.
Relatively a low-cost material amongst high performance polymers.
High rigidity and chemical resistance
Low coefficient of friction
Melt processability
High creep resistance
Non-Flammable
Easy blendability leading to vast range of compounds

Limitations of PPS:

Outgassing at high temperature
Brittleness and low ductility
Opaqueness
Low glass transition temperature

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