| abstract |
The invention relates, on the one hand, to a method for the production of hollow fibre membranes, which are suitable, for example, for gas separation and have a dense, non-porous top layer and a porous under layer, with the aid of a one-step process using a spinning head which has three concentrically arranged outlet openings, either a non-solvent for the relevant polymer, which instantaneously demixes the polymer solution, or a mixture of such a non-solvent and a solvent for the polymer, which mixture, depending on the solvent content, imparts to the polymer solution a behaviour which ranges from instantaneous demixing behaviour to delayed demixing behaviour, being fed through the innermost opening; a polymer solution being fed through the intermediate opening and a non-solvent which gives 'delayed' demixing of the polymer solution being fed through the outermost opening, after which the three streams are directed together into a coagulation bath which contains a precipitation medium which instantly demixes the polymer solution, after which the resulting membrane is obtained. On the other hand, the invention relates to a method for the production, in the abovementioned manner, of hollow fibre membranes which are suitable, for example, for ultrafiltration and have both a porous top layer and a porous under layer, with which method - in contrast to the abovementioned method - a non-solvent which produces 'instantaneous' demixing of the polymer solution is fed through the outermost opening. |