Abstract: A hollow fiber membrane is produced having an outer surface, and inner surface enclosing a lumen, and a continuous network of interconnecting pores extending from the outer surface to the inner surface, wherein substantially all of the pores have an elongated dimension and a shortened dimension, the elongated dimension being oriented substantially parallel to the axis of the hollow fiber, wherein the ratio of the elongated dimension to the shortened dimension is substantially constant from the outer surface to the inner surface, and wherein the pores change shape to increase the shortened dimension in response to a high pressure differential imposed across the membrane by increasing fluid pressure within the lumen.

Abstract: A method of making a porous polymeric material by heating a mixture comprising polyvinylidene fluoride and a solvent system initially comprising a first component that is a latent solvent for polyvinylidene fluoride and a second component that is a non-solvent for polyvinylidene fluoride wherein, at elevated temperature, polyvinylidene fluoride dissolves in the solvent system to provide an optically clear solution. The solution is then rapidly cooled so that non-equilibrium liquid-liquid phase separation takes place to form a continuous polymer rich phase and a continuous polymer lean phase with the two phases being intermingled in the form of bicontinuous matrix of large interfacial area, and cooling is continued until the polymer rich phase solidifies. The polymer lean phase is removed from the solid polymeric material.

Abstract: Extrusion of hollow membranes is improved by coextruding a coating fluid layer about the extrudate of heated polymer solution with its interior lumen forming extrudate. The coating fluid is disposed between the forming hollow fiber and a cooling fluid, and controls the rate of heat transfer to afford superior control over the structure and form of the hollow fiber produced in the invention. The coating fluid is typically the same material as the cooling fluid, and often is the same material as the solvent for the polymer in the heated polymer solution.

Abstract: A process for making a polymeric, porous hollow fibre (21) by heating a mixture of a thermoplastic polymer and a solvent to a temperature and for a time for the polymer and solvent to mutually dissolve, then introducing the molten mixture into an extrusion head (FIG. 1) adapted to shape the hollow fibre. The shaped fibre is then cooled in the extrusion head to a temperature so that non-equilibrium liquid-liquid phase separation takes place to form a bi-continuous matrix of the polymer and solvent in which the polymer and solvent form two intermingled separate phases of large interfacial surface area. Finally, the solvent is removed from the polymer.The extrusion head for forming the abovementioned polymeric, porous hollow fibre has an elongated body (17, 18) defining an axial passageway (11) for receiving a lumen-forming fluid (14) and a first annular passage (12) therearound for receiving the molten mixture (15) from which the hollow fibre (21) is formed.

Abstract: A method of making a porous polymeric material by heating a mixture of a thermoplastic polymer and a cationic or non-ionic surfactant having a hydrophilic-lipophilic balance range of 4.0 to 6.0 to a temperature and for a time sufficient for the polymer and surfactant to mutually dissolve. The mixture is then cooled to a temperature so that non-equilibrium liquid-liquid phase separation takes place to form a bi-continuous matrix of the polymer and surfactant so that the polymer and surfactant form two intermingled separate phases of large interfacial surface area. The surfactant is then removed from the polymer. The porous polymeric material produced by the above method has a lacey or filamentous structure consisting of a plurality of polymer strands connected together at spaced apart locations along each strand.

Abstract: A filter (10) has a shell (11) within which there is a bundle of microporous fibres (12). Pressurized feed suspension is introduced through inlet (15) and passes over the external walls of the fibers (12) with the clarified liquid being drawn from the lumens of the fibres (12) through outlet port (16) and the concentrated ffee being discharged through outlet (17). The solids retained within the shell are removed by a gaseous backwash cycle in which pressurized gas is introduced through the lumens and passes through the wall of the fibres (12) to dislodge solids retained on or in the fibre walls. The gaseous cleaning step is enhanced by varying the pressure within the housing (11) of the filter (10) while the gas is being introduced into the filter.