Polyphenylsulfone (PPSU)

Polyphenylsulfone (PPSU) is an amorphous, highly heat-resistant, inherently flame-retardant, and naturally transparent high-performance thermoplastic.

Contents

1, History
2. Production
3. Properties
4. Applications
5. Example Properties

1. History

PPSUs have been in use for over 40 years. Union Carbide first commercialised heat- and hydrolysis-resistant polysulfone (PSU) under the trade name Udel in 1965. Imperial Chemical Industries (ICI) and 3M also filed patents for the chemistry at about the same time. These characteristics were amplified with the development of PPSU in the early-to-mid 1970s.

2.  Production

PPSU can be produced by the reaction of p-dichlorobenzene with sodium sulphide in a polar solvent.  It can also be formed by the polymerisation of p-halothiophenoxide metal compounds both in the solid state and in solution, or via the condensation of p-dichlorobenzene with elemental sulfur in the presence of sodium bicarbonate.

3.  Properties

The biphenylene ether unit in PPSU increases its impact strength markedly and reduces its notch sensitivity, resulting in notched (Izod) impact values that exceed those of other polysulfones. It also contributes to the ease with which PPSU can be injection moulded or extruded on conventional equipment. High mould temperatures of 140-180°C, and even higher for glass fibre-reinforced grades, will be required, however. 

PPSU is prized for its high toughness, and outstanding flexural and tensile strengths, excellent hydrolytic stability and good resistance to heat, being able to operate continuously in temperatures of around 180°C. It is also resistant to chemicals. For example, it is highly resistant to aqueous mineral acids, bases, and oxidising agents and most solvents. It should be noted, however, that exposure to aromatic and oxygenated solvents, such as ketones and ethers, can create some stress cracking.

4.  Applications

PPSU is therefore an excellent choice for the manufacture of components that will be exposed to high temperatures and corrosive media. Most (unfilled) grades of the thermoplastic cannot be used for outdoor applications, however, because of its limited resistance to weathering, ozone and ultraviolet radiation (UV).

In the medical industry, PPSU has been used as a strong, lightweight alternative to metal in sterilisation cases and trays, handles for surgical instruments, as it can absorb significant impacts without cracking or breaking, even after prolonged and repeated exposure to high temperatures, chemical disinfectants, hot water and steam. Grades of PPSU can be steam sterilised over 1000 times without significant detriment to their properties, making the thermoplastic an excellent choice for the manufacture of reusable medical devices.

The hydrolytic stability and toughness of PPSU, coupled with its high deflection temperatures and resistance to environmental stress cracking make the material suitable for the production of membrane electrode assembly subgaskets in proton exchange membrane (PEM) fuel cells.

PPSU is also widely used in place of brass in plumbing parts exposed to pressurised hot water applications, as it can be injection moulded to tight tolerances and exhibits low creep under sustained loads at elevated temperatures.

The inherent flame-retardance of PPSU, meanwhile, makes it an appealing choice for the production of parts used in aircraft interiors and specialist PPE for firefighters. It is increasingly specified for use in additive manufacturing and injection moulding production processes.

5.  Example properties