Processing of polysulphones

When processing polysulphones there are four main points to bear in mind  

For extrusion and blow moulding the polysulphones used are of higher molecular weight. Melt temperatures for blow moulding are of the order of 300-360°C with mould temperatures about 70-95°C. 

The polysulphones tend to be used in applications when requirements cannot quite be met by the much cheaper polycarbonates and possibly aromatic polyethers. In many of the fields of use they have replaced or are replacing ceramics, metals and thermosetting plastics rather than other thermoplastics. 

The generally very good electrical insulation properties coupled with heat resistance and non-burning behaviour indicate usage in coil bobbins, printed circuit boards (which resist heat of soldering), lamp bulb bases and TV 

more recently developed, uses include microwave oven parts, transparent pipelines, chemical plant pumps and coffee machine hot water dispensers. One exceptional use has been to produce, by an extrusion moulding process, very large rollers for textile finishing for use where cast nylons cannot meet the specification. Also of growing interest are medical equipment applications that may be repeatedly steam-sterilised at 134°C, filtration membranes and cartridges for ink-jet printers. 

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The process of blending with another glassy polymer to raise the heat distortion temperature is not restricted to polycarbonate, and the polysulphones are obvious candidates because of their higher Tg. One blend has been offered (Arylon T by USS Chemicals) which has a higher softening point than the ABS-polycarbonates. 

Several blends based on polysulphone materials have been marketed. Probably the most well known is Mindel, originally produced by Uniroyal, acquired by Union Carbide, but now marketed by Amoco. Whilst not exhibiting the heat resistance of the unblended homopolymer, Mindel materials, which are blends of polysulphone and ABS, are lower in cost, easier to process and have higher notched impact strengths. The Mindel A materials are unreinforced, the Mindel B grades contain glass fibre, and the Mindel M grades contain other mineral fillers. A related polysulphone/SAN blend has been marked as Ucardel. 

Alternative approaches were developed by Rose and his colleagues at involving polyetherification reactions, in principle very similar to the polyetherification processes that they had developed earlier for the manufacture of polysulphones (Table 21.3), either by self-condensation of products such as IV or reaction between intermediates V and VI (Figure 21.8). 

These plastics are processable by injection moulding, blow moulding, extrusion and sheet forming and can be plated. Applications include electronic connectors, TV components, printed circuitry, projector lamp housings, and filter bowls. Produced in the USA, it is worthwhile monitoring the availability of polysulphones as applications are planned. 

As the author pointed out in the first edition of this book, the likelihood of discovering new important general purpose materials was remote but special purpose materials could be expected to continue to be introduced. To date this prediction has proved correct and the 1960s saw the introduction of the polysulphones, the PPO-type materials, aromatic polyesters and polyamides, the ionomers and so on. In the 1970s the new plastics were even more specialised in their uses. On the other hand in the related fields of rubbers and fibres important new materials appeared, such as the aramid fibres and the various thermoplastic rubbers. Indeed the division between rubbers and plastics became more difficult to draw, with rubbery materials being handled on standard thermoplastics-processing equipment. 

The simplest aromatic polysulphone, poly-(p-phenylene sulphone) (formula I of Table 21.3) does not show thermoplastic behaviour, melting with decomposition above 500°C. Hence in order to obtain a material capable of being processed on conventional equipment the polymer chain is made more flexible by incorporating ether links into the backbone. 

The Ar and/or Ar group(s) will contain sulphone groups and if Ar = Ar then identical products may be obtained by the two routes. Polyetherification processes form the basis of current commercial polysulphone production methods. These will be discussed further below. 

As with the polysulphones, the deactivated aromatic nature of the polymer leads to a high degree of oxidative stability, with an indicated UL Temperature Index in excess of 250°C for PEEKK. The only other melt-processable polymers in the same league are poly(phenylene sulphides) and certain liquid crystal polyesters (see Chapter 25). 

Polymers with very good heat resistance (both in terms of deformation and of heat aging resistance) but which may be processed by conventional techniques, e.g. polysulphones and poly(phenylene oxides). 

A wide variety of thermoplastics have been used as the base for reinforced plastics. These include polypropylene, nylon, styrene-based materials, thermoplastic polyesters, acetal, polycarbonate, polysulphone, etc. The choice of a reinforced thermoplastic depends on a wide range of factors which includes the nature of the application, the service environment and costs. In many cases conventional thermoplastic processing techniques can be used to produce moulded articles (see Chapter 4). Some typical properties of fibre reinforced nylon are given in Table 3.2. 

Membranes used for the pressure driven separation processes, microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO), as well as those used for dialysis, are most commonly made of polymeric materials. Initially most such membranes were cellulosic in nature. These ate now being replaced by polyamide, polysulphone, polycarbonate and several other advanced polymers. These synthetic polymers have improved chemical stability and better resistance to microbial degradation. Membranes have most commonly been produced by a form of phase inversion known as immersion precipitation.11 This process has four main steps ... 

As part of a downstream processing sequence, 10 m3 of a process fluid containing 20 kg m 3 of an enzyme is to be concentrated to 200 kg/m3 by means of ultrafiltration. Tests have shown that the enzyme is completely retained by a 10,000 MWCO surface-modified polysulphone membrane with a filtration flux given by ... 

The membrane permeation was tested for separation of HTO from water at INCT [114]. Membranes made from regenerated cellulose, polysulphone, and polytetrafluoroethylene were used. Separation factors anio/HTO obtained in membrane process were not higher than 1.04 for cellulose and 1.02 for polysulphone, while for PTFE membranes were as high as 1.06-1.22. 

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