Novel Membranes for the Separation of Small Molecules: Preparation, Characterization, and Evaluation

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This is a novel method for processing polymer films to make gas separation membranes. A polymer sheet is simultaneously stretched and compressed by pulling it through a roller (roll-truding). The purpose of the prior work was to produce higher strength polymer sheets. However, the flux of gases through the resultant films has been round to be very high, approximately 1000 times what one would expect for the unprocessed films. It is suggested this has occurred because there has been an alignment and segregation of microcrystalline domains within rubbery domains of the film, thus making the diffusion path through the film less tortuous. Further, the domain size separating the crystalline domains is of angstrom dimensions, and can be controlled by the roll-truding process and by subsequent annealing. If still thinner films can be produced, domain sizes might be used in conjunction with differences in diffusion rates and solubilities to add a stearic selectivity to a gas separation process. If the films can be used for gas separations, this will constitute a major breakthrough in gas membrane separations, as a very wide variety of polymers, which could not previously be used for gas separations, can be turned into gas separation membranes by this process. Though it is probably not possible to produce hollow fiber membrane modules by roll-truding, the process should be ideal for making spiral-wound modules.