Mass Transfer in Polymers

The theories that describe diffusion in concentrated polymer solutions are approximate in nature. Among them, only one seems sufficiently developed to offer a good description of mass transfer in polymer-solvent systems the free-volume theory of diffusion. Though it affords good correlative success, it needs further testing. 

B. properties determining mass transfer in polymers, rheological properties of polymer melts, chemical, thermal and UV stability. 

The effect of pore size on CEC separation was also studied in detail [70-75]. Figure 9 shows the van Deemter plots for a series of 7-pm ODS particles with pore size ranging from 10 to 400 nm. The best efficiency achieved with the large pore packing led to a conclusion that intraparticle flow contributes to the mass transfer in a way similar to that of perfusion chromatography and considerably improves column efficiency. The effect of pore size is also involved in the CEC separations of synthetic polymers in size-exclusion mode [76]. 

Russell RJ, Axel AC, Shields KL, Pishko MV. Mass transfer in rapidly photopolymerized poly(ethylene glycol) hydrogels used for chemical sensing. Polymer 2001, 42, 4893 1901. 

This chapter summarizes the book with special emphasis on the future of migration modeling procedures for polyolefins and non-polyolefins in mono- and multilayer structures combined with modern analytical methods for measuring mass transfer in new polymer-migrant systems. 

One sign of progress is the extent to which sophisticated research on transport phenomena, particularly mass transfer, has penetrated several other fields, including those described in later papers of this volume. Examples include fundamental work on the mechanics of trickle beds [17] within reactor engineering studies of dispersion in laminar flows [18] in the context of separations important to biotechnology coupling between fluid flows and mass transfer in chemical vapor deposition processes for fabrication of semiconductor devices [19] and optical fiber preforms [20] and the simulation of flows in mixers, extruders, and other unit operations for processing polymers. 

The materials of the selective layer of the membranes dominating in the data are polymers. The polymers used can be both glassy and rubbery. It is therefore worthwhile to consider physicochemical regularities of hydrocarbon mass transfer across polymer membranes. 

As previously indicated, this discussion is organized for chromatograms from very narrow polymer standards for which we can consider that the effect of molecular weight distribution is negligible and for which the unique separation process is size exclusion. With these limitations, the contribution to band broadening is conveniently separated into extra column effects, eddy dispersion, static dispersion, and mass transfer. In the most classical chromatographic interpretation, extra-column effects are not discussed and the three other contributions are considered as Gaussian, so there is simply the addition of their variances. The number of theoretical plates is defined as N = VJaY and the influence of v, the linear velocity of the eluent, is summarized by the so-called Van Deemter equation ... 

Fig. 5B shows the separation of two stable proteins (lysozyme and myoglobin) by using a PEG IOOO/K2HPO4 polymer phase system at a flow rate of 1 mL/min, where they were well resolved in slightly over 5 hr. As suggested by the basic studies, the separation may be substantially improved by using the column II disk assembly, which provides a shallower channel to facilitate mass transfer in viscous polymer phases. 

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