Production of asymmetric track membranes with a high permeability and separation selectivity

An investigation of the structure and surface properties of poly(ethylene) terephthalate track membranes (PET TM) with a changed pore profile subjected to the plasma RF-discharge is performed. It was arranged that effect of the nonpolymerizing gas plasma on the membranes of researched sample leads to formation of asymmetric membranes possessing a higher flow rate. Choice of optimal discharge parameters allows one to etch the membrane in its layer. In this case in the membrane layer not affected by plasma, the mean pore diameter remains at its initial level. Preserving the initial (nominal) pore diameter allows one to perform the filtration processes with no decrease of separation selectivity. It is shown that the introducing of the polymerizing gas, cyclohexane, into the composition of plasmaforming gas provides improved hydrodynamic properties of asymmetric membranes.

The investigations have allowed us to make the following conclusions. The effect of the nonpolymerizing gas plasma on PET TM with a changed pore profile leads to formation of asymmetric membranes possessing a higher flow rate. The choice of optimal discharge parameters allows the etching of the membrane in its layer, in this case in the membrane layer not affected by plasma; the mean pore diameter remains at its initial level. Preserving the initial (nominal) pore diameter allows one to perform the filtration processes with no decrease of separation selectivity. The introduction of cyclohexane into the plasma-forming gas provides the improved hydrodynamic properties of asymmetric membranes. In this report we have considered only effects of RF-discharge plasma treatment on the structure and surface properties of the PET TM with a changed pore profile and, hence, they cannot be used as a basis for rationalizing particular chemical mechanisms of plasma modi-fication of the polymer under study. To clarify these problems, it is necessary to employ the techniques capable of detecting transient and final products of the chemical reactions occurring during plasma treatment. Nevertheless, the observed effects show a possible way for manufacturing of asymmetric composite track membranes for nanofiltration and reverse osmosis possessing a higher productivity that can be the subject of further, more detailed studies aimed at optimizing the plasma discharge parameters for controlling the properties of manufactured membranes.