Polysulphones commercially available

Commercially available plate- and frame- type ultrafiltration equipment are used for exopolysaccharide concentration. The membranes are polysulphone or polyvinylidine fluoride with molecular weight cut-off between 20-60,000. There is a relatively low eneigy requirement (1-2 kWh m 3) for pumping the fluid through the filtration unit at the desired pressure. Pressure difference across the membrane is of the order 2-14 atmospheres. 

The hollow fibre is the most crucial part of the microdialysis probe. It acts as a membrane, and its characteristics affect performance in the sampling step as well as the probe s suitability for the selected application. Hollow fibres are commercially available in different materials, the most common being polycarbonate (PC), regenerated cellulose (Cuprophan, CU), cellulose acetate (CA), polyacrylonitrile (PAN), polyethersulphone (PES), polysulphone (PE), and polyamide (PA). Generally, the fibres have an outer diameter between 200... 

In g eral terms it is likdy that the three commercially available polysulphones will not con >ete with each other for... 

Therefore, most commercial polysulphones are available as amorphous materials, which consequently are transparent after melt processing. There is an exception in the family, which does not possess the kinked feature (iv) this is a crystalline polymer having a melting point exceeding 500°C, at which temperature it will be also starting to degrade ... 

Polyethersulphone is the term given to certain polysulphones of improved heat resistance introduced by ICI. (In fact all commercial polysulphones are polyethersulphones.) Commercial polymers now have values of ranging from 190 to 285°C, but the cost generally increases sharply with T, and those at the higher end of the range may only be available to special order. 

Although the amount of thermoplastic polymer used with reinforcement is still small there is an increasing interest in the use of reinforcements with thermoplastic as the matrix to provide improved properties, particularly strength, stiffness, dimensional stability, shrinkage and heat resistance. Virtually all thermoplastics have been reinforced and a great many are now available commercially. The best known is nylon but it is expected that great advances will be made in the use of styrenes, olefins and some of the more specialised polymers, such as polycarbonate and polysulphone. 

The sulphone group is highly polar and polymers containing both sulphone and p-phenylene groups might be expected to have high softening points. In fact, the simplest polymer of this kind, poly(p-phenylene sulphone) (Fig. 12.1A) melts at 520°C with decomposition and so is not a useful thermoplastic material. In order to obtain a material which can be processed on conventional equipment it is necessary to make the polymer chain less stiff and in all currently available commercial polysulphones this is achieved by the incorporation of ether links. 

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