Work methods issues 488 INDEX

The ASTM is currently working on WK45948, New Test Method for Modified Fouling Index (MFI-0.45) of Water, to develop a companion procedure to the SDI for more accurate prediction of membrane fouling. Although there are devices on the market that automatically or semi-automatically measure both SDI and MFI-0.45, the MFI still has the following issues that need to be resolved ... 

The chemistry involved with crosslinking of diene-based systems is largely speculative. Since crosslinked systems, by their nature, are completely insoluble, all analytical procedures which require solutions of the polymers are unusable. IR spectroscopic techniques are of limited value because the spectrum of polystyrene blocks out most frequencies other methods are difficult in the solid state. Most work reported in this area is based on measuring the fraction of insolubles and some indication of how tightly crosslinked the insoluble component has become (by a swelling index test). The presence of occluded polystyrene in the gel fraction of typical rubber-modified plastics further complicates the issue, although Karam and Tien have attempted to allow for this problem through a modification of the Flory-Rehner equation. 

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