Wet spinning of asymmetric hollow fibre membranes for gas separation

This thesis describes the spinning and characterizatin of hollow fibre membranes for gas separation. The type of fibres studied here are made by a wet spinning process. A homogeneous solution is prepared, consisting of a polymer in a suitable organic solvent, and extruded as a hollow fibre. Both the inside (the bore) and the outside of the solution are contacted with a nonsolvent for the polymer. Due to an exchange of solvent and nonsolvent the polymer precipitates and a structure with a certain degree of porosity is formed. Such a structure usually is assymmetric. This means that only a very thin layer on the outside and/or the inside has a densified structure (a toplayer), while the remainder of the fibre wall has a considerably higher porosity (the sublayer). To obtain good gas separation properties it is essential that the toplayer is pore-free. The subjets described in this thesis may be divided into three categories. Firstly, the influence of various spinning parameters on the fibre gas separation properties is studied, as determined by the microscopic structure. Secondly, the relation between the spinning parameters and the macroscopic fibre structure (diameter, roundness, porosity of the sublayer, macrovoid formation, etc.) is investigated. Thirdly, it is investigated how additional information can be obtained about the properties of the (usually) dense toplayer. This is done by using an etching technique.