Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0081—After-treatment of organic or inorganic membranes
  • B01D67/0093—Chemical modification
  • B01D67/00931—Chemical modification by introduction of specific groups after membrane formation, e.g. by grafting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0081—After-treatment of organic or inorganic membranes
  • B01D67/0088—Physical treatment with compounds, e.g. swelling, coating or impregnation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
  • B01D71/66—Polymers having sulfur in the main chain, with or without nitrogen, oxygen or carbon only
  • B01D71/68—Polysulfones; Polyethersulfones

Definitions

• the present disclosure relates to an improved efficient and effective method of manufacturing hydrophilic polyethersulfone (PES) membrane suitable for commercial applications and the resultant hydrophilic polyethersulfone (PES) membrane suitable for commercial applications produced thereby.
• PES hydrophilic polyethersulfone
• the hydrophobic membrane was prewetted with alcohol, and then soaked in aqueous solution that contained a hydrophilic monomer, a polyfunctional monomer (cross-linker) and an initiator of polymerization.
• the monomer and cross-linker were then polymerized using thermal or UV initiated polymerization, which formed a coating of cross- linked hydrophilic polymer on the membrane surface.
• U.S. Patent Nos. 6,193,077 Bl and 6,495,050 B2 proposed coating the PES membrane by soaking the membrane in an aqueous solution of hydrophilic polymer (polyalkylene oxide) and at least one polyfunctional monomer (cross- linker), then polymerizing a monomer. As described, a non-extractable hydrophilic coating was the resultant.
• hydrophilic polymer polyalkylene oxide
• cross- linker polyfunctional monomer
• U.S. Patent No. 4,943,374 proposed to blend PES in a solution with hydrophilic polymers (polyethylene glycol, PVA, polyacrylic acid, polyvinilpirrolidone, etc.). According to the patent, the resultant membranes obtained from the blended solutions were hydrophilic.
• U.S. Patent No. 6,071,406 disclosed the production of hydrophilic
• PES membranes by blending PES in a solution with a wetting agent (a block copolymer having hydrophilic and hydrophobic units).
• a wetting agent a block copolymer having hydrophilic and hydrophobic units.
• the hydrophobic units of the block copolymer were permanently attached to the hydrophobic matrix (PES) leaving the hydrophilic units on the membrane surface. Since, according to this patent, the wetting agent was permanently attached to the membrane and could not be leached, the resultant membrane possessed permanent hydrophilicity.
• U.S. Patent No. 5,178,765 disclosed the hydrophilization of PES membrane by blending PES with hydrophilic poly-2-oxazoline resin and polyvinylpyrrolidone resin. According to this patent, the membrane obtained thereby exhibited long-term water wettability.
• U.S. Patent No. 6,495,043 Bl disclosed a method for PES membrane hydrophilization by blending PES with hydrophilic ethylene oxide/propylene oxide copolymer. According to this patent, the resultant hydrophilic membrane had a reduced tendency toward fouling. As is known to those skilled in the art, the term "fouling" means clogging the membrane pores during the filtration process.
• U.S. Patent No. 6,039,872 disclosed a method of producing hydrophilic PES membrane by blending the PES with a hydrophilic monomer and an initiator for thermal polymerization. After blending, the polymer solution was heated to a temperature sufficient to start a polymerization of the blended monomer. The resultant polymer solution reportedly contained a blend of PES with hydrophilic polymer. The membrane produced from this resultant solution was reportedly hydrophilic.
• U.S. Patent No. 4,964,990 disclosed a method, which included a combination of blending PES in a solution with a hydrophilic additive, followed by a hydrophilic coating of the membrane.
• the PES was mixed in a solution with a hydrophilic polymer (polyethylene glycol or polyvinylpyrrolidone), and then the membrane was cast, quenched and dried. The dried membrane was post treated with an aqueous solution of polyvinyl alcohol and then cross-linked.
• the patent claimed that the resultant membrane possessed permanent wettability and stability after exposure to prolonged treatment in isopropanol or extended heat treatment.
• the hydrophilization of PES membrane was accomplished by treatment with low temperature plasmas. The following publications describe the application of plasma reactions for PES membrane hydrophilization:
• FIG. 1 One representative typical scheme for membrane coating is illustrated in Figure 1.
• the hydrophobic PES membrane 10 is prewetted in an alcohol solution 12, then washed with water 13, and soaked 14 in aqueous solution containing a hydrophilic monomer, cross-linker (polyfunctional monomer) and the initiator of polymerization. Then, the thus treated membrane is sandwiched between films 16 (usually Mylar films) and proceeds to the polymerization area 15.
• the polymerization process can be initiated by heat, UV radiation or ⁇ -radiation.
• the membrane In case of thermal polymerization, the membrane typically traverses along the surface of a hot plate 15, and the polymerization reaction is initiated at the temperature of about 8O 0 C to about 9O 0 C. In cases where the reaction is initiated by UV radiation or ⁇ -radiation, the sources of UV or ⁇ -radiation are installed instead of a hot plate 15, as would be appreciated by those skilled in the art. After polymerization, the membrane is washed with water at 17 and dried by conventional means at 18.
• U.S. Patent No. 5,178,765 shows that the amount of hydrophilic polymer poly-2-oxazoline resin blended with PES in solution is from 24 to 47% of the PES weight.
• U.S. Patent No. 6,071,406 shows that the amount of hydrophilic block-copolymer, blended with PES, is from 250 to 350% of the PES weight.
• U.S. Patent No. 6,495,043 Bl shows that the amount of hydrophilic additive (ethylene oxide/propylene oxide copolymer) is 80% of the PES weight.
• U.S. Patent No. 4,943,373 describes and claims a hydrophilic membrane formed from polyvinylidene fluoride (PVDF) wherein hydrophilic properties were imparted to the membrane by oxidation through the chemical treatment. Oxidation was performed through the treatment of PVDF membrane with a strong alkali solution (10 to 60 % NaOH) containing an oxidizing agent (potassium permanganate). According to the process description, under the action of strong alkali, conjugated double bonds are formed on the polyvinylidene fluoride as the consequence of the removal of hydrofluoric acid from the PVDF molecule, such formed double bounds are instantaneously oxidized producing hydrophilic polar groups.
• PVDF polyvinylidene fluoride
• the treatment included: a) heating the membrane at 60 to 300 0 C, b) Irradiating the membrane with a UV radiation source in the presence of oxygen for a time sufficient to surface oxidize the membrane.
• the treated membranes exhibited enhanced selectivity in gas separation and no information about changes of the membrane's hydrophilic properties was presented therein.
• Japanese Patent No. 137,487/83 discloses a process of regeneration of spent membranes from different polymers (including PES) with the aqueous solution containing a surfactant and an oxidizing agent (hypochlorite ion or hydrogen peroxide) in order to speed up the membrane regeneration process.
• the degree of a regeneration of spent membranes in the presence of an oxidizer was more complete (93.3%) than in the case when no oxidizer was used (66.7%); however, no information about changes of the membrane's hydrophilic properties was presented therein.
• One aspect of the present disclosure includes an improved method of manufacturing hydrophilic polyethersulfone (PES) membrane of the present disclosure comprising the acts of providing hydrophobic PES membrane; ⁇ rewetting the hydrophobic PES membrane in a sufficient amount of a liquid having a sufficiently low surface tension; exposing the wet PES membrane to a sufficient amount of aqueous solution of oxidizer; and after the exposing act, heating the hydrophobic PES membrane for a sufficient time at a sufficient temperature.
• PES polyethersulfone
• Another aspect of the present disclosure includes a method of manufacturing hydrophilic polyethersulfone (PES) membrane comprising the acts of: providing hydrophobic PES membrane; prewetting the membrane in alcohol; washing the membrane with DI water; immersing the washed membrane in an aqueous solution of about 2 to about 9 % ammonium persulfate; heating the solution with the immersed membrane from ambient temperature to about 80 to about 95 0 C and then maintaining the resultant membrane at about 8O 0 C to about 95 0 C for about 15 minutes; washing the membrane in water and then drying the resultant membrane.
• PES polyethersulfone
• Yet another aspect of the present disclosure includes a method of manufacturing hydrophilic polyethersulfone (PES) membrane comprising the acts of: providing hydrophobic PES membrane; prewetting the hydrophobic PES membrane in IPA; washing the resultant membrane with DI water; and immersing the resultant membrane in about a 12% aqueous solution of sodium hypochlorite for about 3 minutes at about 9O 0 C to about 95 0 C.
• PES polyethersulfone
• Still another aspect of the present disclosure includes a method of manufacturing hydrophilic PES membrane comprising the acts of: providing hydrophobic PES membrane; prewetting the hydrophobic PES membrane with about a 50% aqueous solution of methanol; washing the resultant membrane with DI water; immersing the resultant membrane in about a 20% solution of hydrogen peroxide (H 2 O 2 ); heating the hydrogen peroxide (H 2 O 2 ) solution at about 5O 0 C to about 7O 0 C for about 30 minutes; raising the temperature of the hydrogen peroxide (H 2 O 2 ) solution to about 98 0 C; maintaining the temperature of the hydrogen peroxide (H 2 O 2 ) solution at about 98 0 C temperatures for about 40 minutes.
• Another aspect of the present disclosure includes removing the membrane from the hydrogen peroxide (H 2 O 2 ) solution; washing the resultant membrane with DI water for about 10 minutes at a temperature of about 40 0 C; and drying the resultant membrane at about 6O 0 C for about 40 minutes.
• H 2 O 2 hydrogen peroxide
• Yet another aspect of the present disclosure includes during the immersing act, using an aqueous solution containing about 71% DI water, about 15% hydrogen peroxide and about 4% APS.
• Still another aspect of the present disclosure includes heating the membrane in the above aqueous solution at a temperature of about 50 0 C to about 7O 0 C for about 30 minutes; uniformly raising the temperature of the aqueous solution to about 92 0 C for about 20 minutes; and thereafter, maintaining the temperature of the aqueous solution at about 92 0 C for about 20 minutes.
• Another aspect of the present disclosure includes removing the resultant membrane from the above aqueous solution; washing the resultant membrane with DI water for about 15 minutes at a temperature of about 4O 0 C; and drying the resultant membrane at about 65 0 C for about 35 minutes.
• Another aspect of the present disclosure includes the use of gel membrane which has gone through phase inversion and washing but has not been dried. Such "gel” membrane will be treated in a similar way as described in this section
• Another aspect of the present disclosure includes a method of manufacturing hydrophilic polyethersulfone (PES) membrane comprising the acts of: providing gel PES membrane; exposing the gel PES membrane to a sufficient amount of an aqueous solution of oxidizer; and after the exposing act, heating the hydrophobic PES membrane for a sufficient time at a sufficient temperature.
• PES polyethersulfone
• Still another aspect of the present disclosure includes after the exposing act in the solution of oxidizer, operatively positioning the membrane between two films so that the membrane is sandwiched therebetween; and continuously moving the sandwiched membrane through at lest one heating zone.
• Yet another aspect of the present disclosure includes during the heating act, operatively positioning the membrane in a saturated water steam medium; and continuously moving the membrane through the saturated water steam medium.
• Figure 1 is a schematic representation of a typical representative prior art system for PES membrane coating to produce a hydrophilic PES membrane
• Figure 2 is a schematic representation of a representative dry membrane batch process system for the hydrophilization process of PES membrane according to the present disclosure
• Figure 3 is a schematic representation of a laboratory system for membrane oxidation using a sandwich method
• Figure 4A is a schematic representation of a representative method of heating uncovered, unsupported membrane in a steam medium
• Figure 4B is a schematic representation of a representative method of heating uncovered membrane on a transporting belt in a steam medium
• Figure 4C is a schematic representation of a representative method of heating uncovered membrane on a rotating drum in a steam medium
• Figure 5 is a schematic representation of a representative method of oxidizing uncovered "gel" membrane
• FIG. 6 illustrates protein binding results for various membranes
• Figure 7 is a schematic representation of a representative method of a representative two-cycle process of PES membrane oxidation.
• the present disclosure is directed to a new effective and economical method for the hydrophilization of PES membrane, which can successfully compete with all previously known methods and, quite possibly, exceed them.
• Ammonium persulfate is known to be a strong water soluble oxidizer: its standard oxidation potential is 2.01 volts. According to this potential APS is placed near the top of the oxidizers list.
• Example 1 illustrates the batch method of one process of the present disclosure.
• the first step involves the: preparation of hydrophobic PES membrane.
• the membrane was cast on the glass plate using the dope of following formulation: PES polymer (Radel polymer from Solvay) - 14%; l-Methyl-2-pyrrolidone (solvent) - 21%; Polyethylene glycol 400 (poroformer) - 65%.
• the cast membrane was air quenched inside a humidity chamber at a temperature of about 23 0 C and having an air humidity from about 65 to about 68% for about 25 minutes.
• the thus quenched membrane was then washed with DI water for about 30 minutes and then dried at about 80 0 C for about 15 minutes.
• hydrophobic PES membrane obtained as described above, was first used in the present Example and was also used in other Examples (Examples 2-5 below).
• a sample of hydrophobic PES membrane (about 10 cm x about 10 cm) was prewetted in isopropyl alcohol (IPA), washed with DI water and immersed in an aqueous solution of oxidizer (ammonium persulfate).
• oxidizer ammonium persulfate
• concentration of ammonium persulfate (APS) was about 3%.
• the solution was heated from ambient to about 9O 0 C - 95 0 C and maintained at about 9O 0 C - 95°C for about 15 minutes.
• the resultant membrane was cooled to ambient temperature, washed with water for about 10 to about 20 minutes in order to remove the remains of oxidizer and then dried at about 7O 0 C for about 40 minutes.
• Example 2 demonstrates the membrane hydrophilization process utilizing another oxidizer - Sodium Hypochlorite.
• a sample of hydrophobic PES membrane (about 8 cm x 40 cm) was prewetted in IPA, washed with DI water and immersed in about 12% aqueous solution of sodium hypochlorite for about 3 minutes. Then the membrane was taken out of the solution and wound into a roll with diameter of about 3 cm. The rolled membrane was again immersed in 12% aqueous solution of sodium hypochlorite, and the solution temperature was raised to about 97 0 C. The membrane was kept in the solution at this temperature for about 1 hour. Then the membrane roll was taken out of the solution, the membrane was unwound, washed with DI water for about 30 minutes and dried at about 70 0 C for about 30 min. The resultant membrane was hydrophilic: it was wetted in water instantaneously.
• hydrophilization process of the PES membrane performed as shown in examples 1 and 2, in accordance with the present disclosure, is simple, and can be applied in manufacturing conditions for the batch process of membrane treatment in the rolls, as shown in Figure 2.
• the hydrophobic PES membrane 30 is prewetted in alcohol solution 32, then washed in water 33, and soaked in aqueous solution of oxidizer at 34 and wound on the roll 35.
• the roll 35 is heated in the oven 36 (other heating methods are also possible, for example, microwave heating and other known processes) to the temperature of oxidation reaction for a sufficient time and is then the oxidized membrane 37 is processed through the washing 38 and drying 39 steps.
• the membrane continuously travels through the bath with alcohol for prewetting, then passes the water bath for washing, then passes the bath with APS solution and, after soaking in APS solution, the membrane is sandwiched between the films (preferably Mylar films).
• the heat treatment of the membrane is performed continuously between the Mylar films ⁇ for example by moving the "sandwich" along the surface of the hot plate, preheated to about 95-105 0 C. After the oxidation reaction is completed, the membrane is going out of Mylar films and then is washed and dried.
• a sample of hydrophobic PES membrane (about 8cm x about 24 cm) was prewetted with IPA, washed with DI water for about 5 minutes and soaked in about 3% APS solution for about 2 minutes.
• the membrane sample 45 after soaking in APS solution, was sandwiched between two bars of Mylar film 46. One end of the sandwich was connected to the roller 49, which pulled the sandwich at a speed of about 30 cm/min along the surface of a hot plate 47.
• the hot plate had a temperature regulation +/- I 0 C and was preheated to about 102 0 C.
• a piece of sponge 48 was placed on the sandwich surface to uniformly press the sandwich to the hot plate and also to prevent the membrane from cooling.
• the hot plate length was about 60 cm, and the speed of sandwich movement (about 30 cm/min) provided membrane heating on the hot plate for about 2 minutes. After heating, the membrane was taken out of the sandwich, washed in water for about 10 minutes, and dried at about 80 0 C for about 30 minutes.
• test A the treated membrane was instantaneously wetted in water and in NaCl solution having a concentration of about 20%.
• the membrane retained hydrophilicity after heating in water in an autoclave at about 124°C for about 1 hour. Because of the short oxidation time (about 2 minutes), the "sandwich" method can potentially be conveniently arranged as a continuous process for the large-scale manufacturing of hydrophilic PES membrane.
• the gel membrane is a membrane precursor, which was gone through the stages of casting, quenching and washing, but has not been dried.
• Oxidization of the membrane in the gel state is very interesting because the use of membrane in the gel state significantly shortened the manufacturing process of hydrophilic PES membrane suitable for commercial scale processing.
• the use of the membrane in the gel state approach eliminated the step of membrane drying (after the phase inversion and washing steps) as well as the steps of membrane prewetting with IPA and washing IPA off the membrane resulting in the efficient and effective method of manufacturing hydrophilic PES membrane suitable for commercial scale processing.
• the oxidation of the membrane in a gel state can have an additional advantage in that utilization of the gel membrane can significantly increase the efficiency of the oxidation process.
• membrane in the gel state has much higher porosity than a dried membrane.
• the membrane shrinks and, because of this shrinkage, it is believed that the number and the diameter of pores in the membrane can be significantly reduced. Due to a developed system of pores, the gel membrane is therefore believed to be more penetratable for different dissolved substances than for a dried membrane.
• the oxidizers utilized with the present disclosure can penetrate into the structure of gel membrane much faster and deeper, significantly increased degree of oxidation and hydrophilicity can be achieved by oxidation of the membrane in a gel state as compared to the oxidation of the previously dried membrane.
• the presently preferred manufacturing process for PES membrane in a "gel" state is described below in the Example 4.
• the resultant membranes produced using both type of samples, previously dried membranes and the membranes in the gel form showed high hydrophilicity.
• the resultant membranes were subjected to treatment in an autoclave at about 124 0 C.
• the hydrophilicity of all samples tested was not noticeably changed.
• the process of hydrophilization of "gel" membrane is significantly shorter since it does not include the operations of drying membrane after quenching and washing and the operations of membrane prewetting and washing before oxidation.
• the saturated water steam has the highest possible humidity at the certain temperature and cannot accept any additional amount of water. Because of this at the conditions of our experiment, the saturated steam medium reliably prevents the membrane from drying.
• the relatively low temperature of the oxidation process (below 100 0 C) facilitates the application of a steam treatment process without pressure.
• the process is safe and the required equipment is relatively simple and inexpensive, as compared to some prior art processes.
• Example 5 illustrates the hydrophilization of uncovered membrane (without Mylar films being utilized in the process):
• a sample of hydrophobic previously dried PES membrane about 5 cm x about 8 cm was prewetted in IPA, washed with water for about 10 minutes and soaked in about 6% APS solution for about 5 minutes.
• a sample of hydrophobic "never dried" PES membrane about 5 cm x about 8 cm was soaked in about 6% APS solution (without previous prewetting and washing). Both samples were placed on a piece on metallic net (about 10 cm x about 10 cm).
• a 2 L beaker was filled with water to about 1 A of its volume, and water was brought to boiling. The net with membrane samples was fixed inside the beaker approximately at about 10 cm above the water level.
• sample C in Table 3 below the hydrophobic, previously dried, PES membrane was prewetted, washed and soaked in APS solution the same way as it is described in the Process for the sample A and sample D of gel membrane was soaked in APS solution the same way as it is described in the Process for the sample B. Both samples (C and D) were placed without being placed between films on the surface of the metallic plate preheated to about 95°C and then were heated on this plate at about 95 0 C for about 6 minutes. Then the samples were washed and dried the same way as it was described in the Process 1.
• Table 3 below shows the hydrophilicity of the samples A, B, C and D obtained in Example 5 below.
• Figure 5 illustrates the presently preferred manufacturing method for hydrophilization of "gel” (never dried) membrane with application of the steam medium. As illustrated in Figure 5, this method is significantly shorter and simpler than the previous traditional process of membrane coating, as illustrated in Figure 1.
• FIG. 5 shows a roll of "gel" membrane at 80.
• the membrane 80 is connected to a rewind system (not shown). As the membrane 80 unwinds, it traverses through the first station 82 where the membrane soaks in aqueous solution of APS.
• the APS concentration in the solution can be, for example, about 3% to about 6% by Wt., the temperature about 20-30°C, soaking time about 2-4 minutes.
• the thus treated membrane 80 traverses a second station 83 (steam chamber) wherein the membrane is heated with saturated water steam in accordance with the diagram of Figure 4 A or Figure 4 B, or Figure C.
• the steam temperature can be about 9O 0 C to about 98 0 C and the time of membrane heating in the steam chamber can be about 2 to about 4 minutes.
• the treated membrane continues traversing to the third station at 84 (washing chamber) wherein the remains of oxidizer, which, possibly, can remain inside the membrane after the oxidation reaction is completed, are washed off with water.
• the membrane continues to the fourth Station 85 (drier) wherein the membrane is dried at the temperature, for example, about 70 to about 8O 0 C for about 5 to about 30 minutes. After drying at the station 85, the hydrophilization process is accomplished and the hydrophilic PES membrane according to the present disclosure is obtained.
• the membranes produced using the proposed method have low protein binding.
• the protein binding test was performed using fluorescein tagged
• Goat IgG protein (manufactured by Cedarlane Laboratories).
• the aqueous solution of protein (with a protein concentration of about 10 ⁇ g /ml) was pumped with a syringe pump through a disk of tested membrane with a diameter of about 13 mm at the flow rate of about 1 ml/min.
• a concentration of protein in the influent and effluent was measured using a Perkin - Elmer luminescence spectrophotometer.
• the amount of protein adsorbed by the membrane was calculated by multiplying a volume of the protein solution, pumped through the membrane, by the difference between the protein concentrations in the influent and effluent.
• Several membranes were tested for comparison including the oxidized membranes obtained in the Example 1 and several commercial membranes with different protein binding.
• FIG. 6 illustrates the protein binding results are presented in wherein the Protein binding of different membranes are prepared according to the following:
• Figure 6 illustrates that the protein adsorption of the oxidized PES membrane was close to the protein adsorption of the commercial membranes with low protein binding (Millipore 's PVDF membrane, Membrana PES; Millipore Express; Sartorius Sartopore) and was much lower than the protein adsorption of the membrane with high protein binding (nylon membrane).
• the obtained results show that the membrane, produced by the proposed hydrophilization method of the present disclosure, closely approximated the performance the group of those membranes known to exhibit low protein binding characteristics.
• a sample of hydrophobic PES membrane (about 5 cm x about 10 cm) is prewetted into about a 50% aqueous solution of methanol, washed with DI water and immersed in about a 20% solution of hydrogen peroxide (H 2 O 2 ).
• the membrane is heated in the hydrogen peroxide (H 2 O 2 ) solution at a temperature of about 50 0 C to about 70 0 C for about 30 minutes, then the temperature of the hydrogen peroxide (H 2 O 2 ) solution is raised to about 98 0 C and is maintained at about 98 0 C temperature for about 40 minutes.
• the membrane is washed with DI water for about 10 minutes at a temperature of about 40 0 C and dried at about 6O 0 C for about 40 minutes.
• the membrane oxidation process occurred at those conditions as follows: after the first membrane heating (at about 5O 0 C to about 7O 0 C) step, the membrane oxidation process is believed to be mostly completed and the hydrogen peroxide concentration in the solution is depleted. It is believed that the additional step of membrane heating at the elevated temperature (at about 98°C) is performed in order to fully complete the oxidation and to decompose the remaining H 2 O 2 . Since the products of H2O2 decomposition at the high temperature are water and oxygen, the resultant membrane, should not contain any hazardous substances.
• a sample of hydrophobic PES membrane (about 5 cm x about 10 cm) is prewetted and washed the same way as it is described in example 6 above.
• the sample is immersed in an aqueous solution containing the following ingredients: about 71% DI water, about 15% hydrogen peroxide (the first oxidizer) and about 4% APS (the second oxidizer).
• the membrane is heated in the above aqueous solution at a temperature of about 5O 0 C to about 7O 0 C for about 30 minutes. Then, the temperature of the aqueous solution is presently preferably uniformly raised to about 92 0 C for about 20 minutes, after which, the temperature of the aqueous solution containing the membrane is maintained at about 92 0 C for about 20 minutes.
• the membrane is washed with DI water for about 15 minutes at a temperature of about 4O 0 C and dried at about 65 0 C for about 35 minutes.
• H 2 O 2 functions as the only membrane oxidizer. APS does not appear to participate in the oxidation reaction since its working temperature is much higher
• a sample of hydrophobic PES membrane (about 8 cm x about 24 cm) is prewetted with IPA, washed with DI water for about 5 minutes, and soaked in about a 20% solution of hydrogen peroxide. Then the sample is sandwiched between two bars of Mylar film. The obtained sandwich is moved along the surface of hot plates.
• the scheme of this process is similar to the process shown in Figure 3; the only difference is that instead of one hot plate (as it is shown in Figure 3), two hot plates are used.
• the two hot plates have different temperatures with the first hot plate being preheated to a temperature of about 55 0 C to about 75 0 C, the second plate having a temperature of about 102 0 C.
• the length of each hot plate is about 60 cm; the speed of the sandwiched movement is about 30 cm/min.
• the membrane is heated on each hot plate for about 2 minutes.
• a sample of hydrophobic PES membrane (about 5 cm x 50 cm) is prewetted and washed the same way as described in the Example 6 above. This sample is placed on the bar of the Mylar film with the width about 7 cm. and the length about 4 meters. The ends of the sample are attached with the staples to the supporting Mylar film.
• the scheme of the laboratory system 90 which simulates a continuous hydrophilization process, is presented on the Figure 7.
• the Mylar film 91 with attached membrane sample 92 is pulled by the roller 93 and is going through the bath 94, containing a solution of the first oxidizer, then along the steam chamber 95, then through a bath 96 with a solution of the second oxidizer, then along the steam chamber 97, and finally is wound on the roller 92.
• the conditions of the oxidation process are as follows: ' The solution of the first oxidizer: aqueous solution of bleach (HClO) with a concentration of about 12%; the solution of the second oxidizer: aqueous solution of APS with a concentration of about 6%.
• the speed of the Mylar film movement is about 20 cm/minute; the length of the steam chambers is about 50 cm.
• the membrane sample After the membrane sample reaches the roller 92, it is detached from the Mylar film, washed in water at about 4O 0 C to about 5O 0 C and dried at about 65°C for about 30 minutes.
• the membrane oxidation experiment is performed the same way as it described in the Example 9, but the solution in the bath 94 is about 3% APS, and the solution in the bath 96 is about 6 % APS. It is presently believed that the resultant membrane, obtained after two oxidation cycles, will have a higher oxidation degree and higher hydrophilicity, compared to the membrane obtained after a single oxidation cycle.
• a sample of hydrophobic PES membrane (about 6 cm x about 6 cm) is prewetted into 50% aqueous solution of methanol and washed with DI water and immersed in aqueous solution, which contains about 95.8% water, about 4% APS, and about 0.2% of water soluble complex of Cu(II) (oxidation catalyst).
• complexes of transition metals including, but not limited to copper, zinc, iron etc. are water soluble substances, can be employed as catalysts for oxidation reactions and can significantly intensify the activity of oxidizers. Such complexes of transition metals are believed to lower the actuation energy barrier.
• the membrane is heated in the above described solution at a temperature of about 70 0 C for about 10 minutes, and then the membrane is removed from the solution, is washed with DI water for about 15 minutes at a temperature of about 40 0 C, and dried at about 70 0 C for about 40 minutes.
• a method of PES membrane hydrophilization by oxidation wherein a dried membrane (the membrane has completed all the stages of the manufacturing process, including, but not limited to: casting, phase inversion, washing and drying) is oxidized.
• a method of PES membrane hydrophilization by oxidation wherein, in order to make a hydrophilization process significantly simpler and shorter, a never dried gel membrane (the membrane after the stages of casting, phase inversion and washing, but prior to drying) is oxidized.

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