Pall Corporation

Irving B Joffee

Peter J Degen

Thomas C Gsell

David B Pall

Ioannis P Sipsas

Warren M Foss

Isaac Rothmann

Frederick A Baltusis

A heat-treated, hydrophobic, polyvinylidene difluoride membrane is provided having uniform crystallinity as evidenced by a difference in crystallinity over the membrane of less than about 10 percent. Also provided is a hydrophilic, polyvinylidene difluoride membrane prepared from a heat-treated, hydrophobic, polyvinylidene difluoride membrane which remains hydrophilic after heating to a temperature as high as about 121.degree. C.

Uniform polyvinylidene difluoride membranes

A method is provided for enhancing the characteristics of a hydrophobic polyvinylidene difluoride membrane which comprises heating the membrane to a temperature of at least 80.degree. C. but less than the temperature at which the membrane softens and deforms for a time sufficient to achieve a state such that, when the membrane is subsequently hydrophilized, the membrane has substantially uniform hydrophilic properties.

Method for making uniform polyvinylidene difluoride membranes

A method is provided for filtration of particulates from a fluid medium which includes passing the medium through a surface modified, skinless, hydrophilic, microporous, alcohol-insoluble polyamide membrane derived from an alcohol-insoluble hydrophobic polyamide resin having a ratio of CH.sub.2 :NHCO of methylene CH.sub.2 to amide NHCO groups within the range of from about 5:1 to about 7:1. The membrane is characterized by (1) the surface properties thereof being substantially controlled by functional polar groups of a membrane surface-modifying polymer having a molecular weight of 20,000 or greater, (2) the membrane surface-modifying polymer being homogeneously distributed in the membrane, and (3) having the capability of reacting or interacting in a controlled manner with (a) particulate matter in a fluid, (b) non-particulate matter in a fluid, or (c) both (a) and (b).

Polyamide membrane with controlled surface properties

A polyvinylidene difluoride structure with a critical surface energy of at least about 80 dynes/cm and a method of making such a structure comprising the steps of contacting a polyvinylidene difluoride structure with an alkalized solution, such as potassium hydroxide, to form activated sites on the surface of the structure; rinsing the activated structure to remove residual alkali; contacting the rinsed, activated structure with a solution of a polymerization initiator, such as potassium peroxydisulfate, and a polymerizable vinylic monomer, such as acrylic acid; and polymerizing and grafting the monomer to the activated structure to form a polyvinylidene difluoride structure with a critical surface energy of at least about 80 dynes/cm.

Method of making polyvinylidene difluoride structure

Polyvinylidene difluoride structure

Filter media comprised of charge modified, resin coated inorganic microfibers are prepared by mixing inorganic microfibers with an aqueous solution of a water soluble, noncolloidal cationic thermosetting binder resin to form a dispersion, following which a precipitating agent is added to precipitate the binder resin and coat the microfibers. The coated microfibers may be used in the dispersed or suspended form as a filter aid. Preferably they are formed into a filter sheet which is then dried and cured to form a filter sheet of narrowly distributed pore size, pore sizes as small as one-half micron, and having a positive zeta potential in alkaline media. Glass is the preferred microfiber and polyamine-epichlorohydrins the preferred resins. By providing the normally negative zeta potential microfibers with a positive zeta potential the binder resins used to coat the microfibers substantially enhance particulate removal capabilities of the microfiber filter sheet.

Charge-modified microfiber filter sheets

Surface modified, skinless, hydrophilic, microporous, polyamide membranes with controlled surface properties are prepared by the steps of preparing a casting solution comprised of (A) a casting resin system comprised of (a) an alcohol-insoluble polyamide resin, and (b) a water-soluble membrane surface modifying polymer having functional polar groups and a molecular weight of 10,000 or greater, and (B) a solvent system in which the casting resin system is soluble; inducing nucleation of the casting solution by controlled addition of a nonsolvent for the casting resin system under controlled conditions to obtain a visible precipitate of casting resin system particles, thereby forming a casting composition; spreading the casting composition on a substrate to form a thin film; contacting and diluting the film of the casting composition with a liquid nonsolvent system for the casting resin system, thereby precipitating the casting resin system from the casting composition in the form of a thin, skinless, hydrophilic, surface modified, microporous, polyamide membrane; and washing and drying the membrane. The membranes of this invention are characterized by having fine pore ratings, the surface properties thereof being substantially controlled by functional polar groups of a membrane surface modifying polymer and having the capability, through the functional polar groups of the modifying polymer, of reacting or interacting with particulates and/or nonparticulates in a fluid.

Surface modified, skinless, hydrophilic, microporous, polyamide membranes are formed by preparing a casting solution comprised of (A) a casting resin system comprised of (a) an alcohol-insoluble polyamide resin, and (b) a cationic, water-soluble, quaternary ammonium, thermosetting, membrane surface modifying polymer, and (B) a solvent system in which the casting resin system is soluble; inducing nucleation of the casting solution by controlled addition of a nonsolvent for the casting resin system under controlled conditions to obtain a visible precipitate of casting resin system particles, thereby forming a casting composition; spreading the casting composition on a substrate to form a thin film; contacting and diluting the film of the casting composition with a liquid nonsolvent system for the casting resin system, thereby precipitating the casting resin system from the casting composition in the form of a thin, skinless, hydrophilic, surface modified, microporous, polyamide membrane; and washing and drying the membrane. The membranes of this invention are characterized by having fine pore ratings, the surface properties thereof being substantially controlled by cationic, quaternary ammonium groups of a modifying polymer thereby providing a positive zeta potential in alkaline media, and for those with moderate or low levels of surface modifying polymer present, a time to reach an effluent resistivity of 14 megaohms/cm under the Resistivity Test of 10 minutes or less. They have greatly enhanced filtration efficiency over a broad pH range with a variety of contaminants, including very fine negatively charged particles, bacteria and endotoxins.

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Huntington, NY, United States of America

Irving B Joffee