UV-GRAFTING PROCESS FOR POLYMERIC FLAT-SHEET MEMBRANES

Abstract

The present disclosure is related to a polymeric membrane having a first surface and a second surface and a wall extending between the first and second surface, the membrane comprising pores on the first and second surfaces and throughout the wall, the membrane comprising a modified surface, the modified surface comprising acrylate and/or methacrylate polymers and/or copolymers, wherein the modified surface extends at least over the first and/or the second surface, and over the pores of at least 50% of the thickness of the wall. Furthermore, the present disclosure provides a method for producing such a membrane as well as a use of the membranes as disclosed herein for purification of aqueous media such as in biopharmaceutical applications.

Claims

1. A polymeric membrane having a first surface and a second surface and a wall extending between the first and second surface, the membrane comprising pores on the first and second surfaces and throughout the wall, the membrane comprising a modified surface, the modified surface comprising acrylate and/or methacrylate polymers and/or copolymers, wherein the modified surface extends at least over the first and/or the second surface, and over the pores of at least 50% of the thickness of the wall.

2. The polymeric membrane according to claim 1, wherein the polymeric membrane is selected from polymeric sulfone membranes, polyethylene membranes, polypropylene membranes and polyacrylonitrile membranes.

3. The polymeric membrane according to claim 2, wherein the polymeric membrane is a polymeric sulfone membrane.

4. The polymeric membrane according to claim 1, wherein the acrylate and/or methacrylate polymers and/or copolymers are obtained from monomers selected from at least one mono(meth)acrylate and at least one di(meth)acrylate, tri(meth)acrylate, tetra(meth)acrylate, penta(meth)acrylate and/or hexa(meth)acrylate and any combinations thereof.

5. The polymeric membrane according to claim 1, wherein the copolymers and polymers are grafted to the polymeric sulfone in the modified surface by irradiation with actinic radiation having wavelengths greater than 290 nm, preferably greater than 300 nm.

6. The polymeric membrane according to claim 1, wherein the membrane is a hydrophilic membrane.

7. The polymeric membrane according to claim 1, wherein the polymeric membrane exhibits an adsorption of the protein lgG as described in the experimental section of less than 30 μg/cm2, preferably of less than 25 μg/cm2, more preferably of less than 20 μg/cm2, even more preferably of less than 15 pg/cm2.

8. A method for modifying the surface of a polymeric membrane, comprising the steps (i) Providing a polymeric membrane; (ii) Applying a solution comprising monomers selected from acrylates and methacrylates and any combinations thereof to the membrane; (iii) Irradiating the membrane with actinic radiation having wavelengths greater than 290 nm.

9. The method according to claim 8, wherein irradiating with actinic radiation is carried out an irradiation dose of a mean value in the range of from 1 to 17 J/cm2, preferably in the range of from 3 to 15 J/cm2, more preferably in the range of from 5 to 13 J/cm2, even more preferably from 7 to 11 J/cm2.

10. The method according to claim 8, wherein irradiating with actinic irradiation is carried out at wavelengths greater than 300 nm, preferably at least 315 nm.

11. The method according to claim 10, wherein the actinic radiation is carried out at wavelengths in the range from 315 to 350 nm.

12. The method according to claim 8, wherein the polymeric membrane is selected from polymeric sulfone membranes, polyethylene membranes, polypropylene membranes and polyacrylonitrile membranes, preferably from polymeric sulfone membranes.

13. The method according to any one of claim 8, wherein the monomers are selected from at least one monoacrylate and/or at least one monomethacrylate and at least one diacrylate and/or at least one dimethacrylate.

14. Use of the polymeric membrane according to claim 1 for purification of liquid media, in particular aqueous media.

15. The use according to claim 14, wherein the use comprises pharmaceutical, biopharmaceutical or medical applications.

Description

DESCRIPTION OF FIGURES

[0045] FIG. 1 depicts an ATR-IR-spectrum of an UV-modified PES-based microfiltration membrane according to ex. 14 of the present disclosure (surface modified with a solution of 6% HPA/0.6% TEGDA at an irradiation set forth in the experimental section at a dose of 11 J/cm.sup.2) vs. an ATR-IR spectrum of an unmodified MicroPES sample (ex 3M).

[0046] FIG. 2 shows zeta-potentials of ex. 7, 9 and 11 as well as of comp. ex. 1. It shows that the larger the amount of polyacrylate applied to the membrane surface, the higher the gradient of the graphs. That means that the stronger the surface modification of a membrane with polyacrylates, the faster the zeta-potential rises to the neutral 0 mV line. Without wanting to be bound by theory, it may be assumed that the PEG-polyacrylate layer adsorbs more water and shields the basis PES membrane. It may be further assumed that this may also be the reason for the lower protein adsorption of the modified membranes as disclosed herein.

[0047] The present disclosure may further be exemplified by the following items:

[0048] Item 1: A polymeric membrane having a first surface and a second surface and a wall extending between the first and second surface, the membrane comprising pores on the first and second surfaces and throughout the wall, the membrane comprising a modified surface, the modified surface comprising acrylate and/or methacrylate polymers and/or copolymers, wherein the modified surface extends at least over the first and/or the second surface, and over the pores of at least 50% of the thickness of the wall.

[0049] Item 2: The polymeric membrane according to item 1, wherein the polymeric membrane is selected from polymeric sulfone membranes, polyethylene membranes, polypropylene membranes and polyacrylonitrile membranes.

[0050] Item 3: The polymeric membrane according to item 2, wherein the polymeric membrane is a polymeric sulfone membrane.

[0051] Item 4: The polymeric membrane according to any one of the preceding items, wherein the acrylate and/or methacrylate polymers and/or copolymers are obtained from monomers selected from at least one mono(meth)acrylate and at least one di(meth)acrylate, tri(meth)acrylate, tetra(meth)acrylate, penta(meth)acrylate and/or hexa(meth)acrylate and any combinations thereof.

[0052] Item 5: The polymeric membrane according to any one of the preceding items, wherein the copolymers and polymers are grafted to the polymeric sulfone in the modified surface by irraditation with actinic raditation having wavelengths greater than 290 nm, preferably greater than 300 nm

[0053] Item 6: The polymeric membrane according to item 5, wherein the actinic radiation have wavelengths in the range of from 315 to 350 nm.

[0054] Item 7: The polymeric membrane according to item 4 or item 5, wherein the treatment with actinic irradiation is carried out an irradiation dose of a mean value in the range of from 1 to 17 J/cm.sup.2, preferably in the range of from 3 to 15 J/cm.sup.2, more preferably in the range of from 5 to 13 J/cm.sup.2, even more preferably from 7 to 11 J/cm.sup.2.

[0055] Item 8: The polymeric membrane according to any one of the preceding items, wherein the polymeric sulfone is selected from polysulfone, polyethersulfone, and polyarylsulfone.

[0056] Item 9: The polymeric membrane according to item 7, wherein the polymeric sulfone is polyethersulfone.

[0057] Item 10: The polymeric membrane according to any one of the preceding items, wherein the membrane is a hydrophilic membrane.

[0058] Item 11: The polymeric membrane according to any one of the preceding items, wherein the monomers are selected from at least one monoacrylate and/or at least one monomethacrylate and at least one diacrylate and/or at least one dimethacrylate.

[0059] Item 12: The polymeric membrane according to item 10, wherein the monomers comprise at least one monoacrylate and at least one diacrylate.

[0060] Item 13: The polymeric membrane according to item 10, wherein the monomers comprise at least one monomethacrylate and at least one dimethacrylate.

[0061] Item 14: The polymeric membrane according to item 10, wherein the monomers comprise at least one monoacrylate and at least one dimethacrylate.

[0062] Item 15: The polymeric membrane according to item 10, wherein the monomers comprise at least one monoacrylate, at least one dimethacrylate and at least one diacrylate.

[0063] Item 16: The polymeric membrane according to item 10, wherein the monomers comprise at least one monomethacrylate and at least one diacrylate.

[0064] Item 17: The polymeric membrane according to item 10, wherein the monomers comprise at least one monomethacrylate, at least one diacrylate and at least one dimethacrylate.

[0065] Item 18: The polymeric membrane according to item 10, wherein the monomers comprise at least one monoacrylate, at least one monomethacrylate, at least one diacrylate and at least one dimethacrylate.

[0066] Item 19: The polymeric membrane according to item 10, wherein the ratio between the at least one monoacrylate and/or the at least one monomethacrylate on one side and the at least one diacrylate and/or the at least one dimethacrylate on the other side is in the range from from 20:1 to 1:1, preferably in the range of from 15:1 to 2:1, more preferably in the range of from 12:1 to 5:1.

[0067] Item 20: The polymeric membrane according to item 10 or item 18, wherein the monomers comprise hydroxypropyl acrylate.

[0068] Item 21: The polymeric membrane according to item 10, item 15 or item 18, wherein the monomers comprise hydroxypropyl acrylate and tetraethylene glycol diacrylate.

[0069] Item 22: The polymeric membrane according to item 10, item 12 or item 18, wherein the monomers comprise 2-hydroxy methacrylate and tetraethylene glycol dimethacrylate.

[0070] Item 23: The polymeric membrane according to item 10 or item 18, wherein the monomers comprise polyethylene glycol diacrylate.

[0071] Item 24: The polymeric membrane according to any one of the preceding items, wherein the polymeric membrane is a flat sheet membrane.

[0072] Item 25: The polymeric membrane according to any one of the preceding items, wherein the polymeric membrane is a hollow fibre membrane.

[0073] Item 26: The polymeric membrane according to any one of the preceding items, wherein the acrylate is selected from hydroxypropyl acrylate, the diacrylate is selected from diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, pentaethylene glycol diacrylate, the methacrylate is selected from 2-hydroxyethyl methacrylate, and the diemethacrylate is selected from diethylene glycol dimethacrylate, triethylene glycol diemethacrylate, tetraethylene glycol dimethacrylate, pentaethylene glycol dimethacrylate, and polyethylene glycol diacrylate.

[0074] Item 27: The polymeric membrane according to any one of the preceding items, wherein the polymeric membrane exhibits an adsorption of the protein IgG as described in the experimental section of less than 30 pg/cm.sup.2, preferably of less than 25 μg/cm.sup.2, more preferably of less than 20 82 g/cm.sup.2, even more preferably of less than 15 μg/cm.sup.2.

[0075] Item 28: A method for modifying the surface of a polymeric membrane, comprising the steps [0076] (i) Providing a polymeric membrane; [0077] (ii) Applying a solution comprising monomers selected from acrylates and methacrylates and any combinations thereof to the membrane; [0078] (iii) Irradiating the membrane with actinic radiation having wavelengths greater than 290 nm.

[0079] Item 29: The method according to item 28, wherein irradiating with actinic radiation is carried out an irradiation dose of a mean value in the range of from 1 to 17 J/cm.sup.2, preferably in the range of from 3 to 15 J/cm.sup.2, more preferably in the range of from 5 to 13 J/cm.sup.2, even more preferably from 7 to 11 J/cm.sup.2.

[0080] Item 30: The method according to item 28 or item 29, wherein irradiating with actinic irradiation is carried out at wavelengths greater than 300 nm, preferably at least 315 nm.

[0081] Item 31: The method according to item 29 or item 30, wherein the actinic radiation is carried out at wavelengths in the range from 315 to 350 nm.

[0082] Item 32: The method according to any one of items 28 to 31, wherein the polymeric membrane is selected from polymeric sulfone membranes, polyethylene membranes, polypropylene membranes and polyacrylonitrile membranes.

[0083] Item 33: The method according to any one of items 28 to 32, wherein the polymeric membrane is selected from polymeric sulfone membranes.

[0084] Item 34: The method according to item 33, wherein the polymeric sulfone is selected from polysulfone, polyethersulfone, and polyarylsulfone.

[0085] Item 35: The method according to any one of items 29 to 34, wherein the monomers are selected from at least one monoacrylate and/or at least one monomethacrylate and at least one diacrylate and/or at least one dimethacrylate.

[0086] Item 36: The method according to item 35, wherein the monomers comprise at least one monoacrylate and at least one diacrylate.

[0087] Item 37: The method according to item 35, wherein the monomers comprise at least one monomethacrylate and at least one dimethacrylate.

[0088] Item 38: The method according to item 35, wherein the monomers comprise at least one monoacrylate and at least one dimethacrylate.

[0089] Item 39: The method according to item 35, wherein the monomers comprise at least one monoacrylate, at least one dimethacrylate and at least one diacrylate.

[0090] Item 40: The method according to item 35, wherein the monomers comprise at least one monomethacrylate and at least one diacrylate.

[0091] Item 41: The method according to item 35, wherein the monomers comprise at least one monomethacrylate, at least one diacrylate and at least one dimethacrylate.

[0092] Item 42: The method according to item 35, wherein the monomers comprise at least one monoacrylate, at least one monomethacrylate, at least one diacrylate and at least one dimethacrylate.

[0093] Item 43: The method according to item 35, wherein the ratio between the at least one monoacrylate and/or the at least one monomethacrylate on one side and the at least one diacrylate and/or the at least one dimethacrylate on the other side is in the range from from 20:1 to 1:1, preferably in the range of from 15:1 to 2:1, more preferably in the range of from 12:1 to 5:1.

[0094] Item 44: The method according to item 35 or item 43, wherein the monomers comprise hydroxypropyl acrylate.

[0095] Item 45: The method according to item 35, item 40 or item 43, wherein the monomers comprise hydroxypropyl acrylate and tetraethylene glycol diacrylate.

[0096] Item 46: The method according to item 35, item 37 or item 43, wherein the monomers comprise 2-hydroxy methacrylate and tetraethylene glycol dimethacrylate.

[0097] Item 47: The method according to item 35 or item 43, wherein the monomers comprise polyethylene glycol diacrylate.

[0098] Item 48: The method according to item 35, wherein the acrylate is selected from hydroxypropyl acrylate, the diacrylate is selected from diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, pentaethylene glycol diacrylate, the methacrylate is selected from 2-hydroxyethyl methacrylate, and the diemethacrylate is selected from diethylene glycol dimethacrylate, triethylene glycol diemethacrylate, tetraethylene glycol dimethacrylate, pentaethylene glycol dimethacrylate, and polyethylene glycol diacrylate.

[0099] Item 49: Use of the polymeric membrane according to any one of items 1 to 27 for purification of liquid media, in particular aqueous media.

[0100] Item 50: The use according to item 49, wherein the use comprises filtration of beverages such as wine or beer and the clarification of vinegar.

[0101] Item 51: The use according to item 49, wherein the use comprises pharmaceutical, biopharmaceutical or medical applications.

[0102] Item 52: The use according to item 51, wherein the use is selected from hemodialysis, virus filtration, and sterile filtration.

EXAMPLES

[0103] The present disclosure is further described without however wanting to limit the disclosure thereto. The following examples are provided to illustrate certain embodiments but are not meant to be limited in any way. Prior to that some test methods used to characterize materials and their properties will be described. All parts and percentages are by weight unless otherwise indicated.

[0104] Test Methods

[0105] Volume porosity:

[0106] A sample of at least 0.5 g of the membrane to be examined is dry weighed. The membrane sample is subsequently placed in a liquid that moistens the membrane material, however without causing swelling, for 24 hours such that the liquid penetrates into all pores. For the present polyamide membranes, a silicone oil with a viscosity of 200 mPa s at 25° C. (Merck) is used. The permeation of liquid into the membrane pores is visually discernable in that the membrane sample changes from an opaque to a glassy, transparent state. The membrane sample is subsequently removed from the liquid, liquid adhering to the membrane sample is removed by centrifuging at approx. 1800 g, and the mass of the thus pretreated wet, i.e. liquid-filled, membrane sample is determined by weighing.

[0107] The volume porosity c is determined according to the following formula:

[00001]$\mathrm{Volume}\mathrm{porosity}\mathrm{.Math.}=\frac{\left(m_{wet}-m_{dry}\right)/{\rho }_{liquid}}{\left(m_{wet}-m_{dry}\right)/{\rho }_{liquid}+m_{dry}/{\rho }_{polymer}}$

[0108] where: [0109] m.sub.dry=weight of the dry membrane sample after wetting and drying [g] [0110] m.sub.wet=weight of the wet, liquid-filled membrane sample [g] [0111] ρ.sub.liquid=density of the liquid used [g/cm.sup.3] [0112] ρ.sub.polymer=density of the membrane polymer [g/cm.sup.3]

[0113] Maximum separating pore:

[0114] The diameter of the maximum separating pore is determined by means of the bubble point method (ASTM No. 128-99 and F 316-03), for which the method described in DE-A-36 17 724 is suitable. Thereby, d.sub.max results from the vapor pressure P.sub.B associated with the bubble point according to the equation

d.sub.max=σ.sub.B/P.sub.B

[0115] where σ.sub.B is a constant that is primarily dependent on the wetting liquid used during the measurement. For IPA, G.sub.B is 0.61 μm.bar at 25° C.

[0116] Determination of the transmembrane flow (water permeability) Disc-shaped membrane samples are stamped out of the membrane to be tested and then clamped fluid-tight at the perimeter in a suitable sample holder such that a free measuring area of 43.2 cm.sup.2 results. The sample holder is located in a housing that can be penetrated under pressure by water. The clamped membrane sample is then penetrated, from the side on which the surface of the membrane with the smaller pores is located, by deionized water conditioned to 25° C. at a defined pressure between 0.1 and 0.2 bar. The water volume that flows through the membrane sample during a measuring period of 60 s is determined gravimetrically or volumetrically.

[0117] The transmembrane flow, TMF, is determined according to formula (Ill)

[00002]$\begin{array}{cc}\mathrm{TMF}\left[\frac{l}{m^2.Math.h.Math.\mathrm{bar}}\right]=\frac{V_W}{\Delta t.Math.A_M.Math.\Delta p}.Math.600& \left(\mathrm{III}\right)\end{array}$

[0118] where: [0119] Vw=volume of water [ml] flowing through the membrane sample during the measuring period [0120] Δt=measuring time [min] [0121] Δ.sub.M=area of the membrane sample penetrated (43.2 cm.sup.2) [0122] Δp=pressure set during the measurement [bar]

[0123] Weight Gain

[0124] The weight gain of each sample after performing UV-grafting is calculated according to the following formula:

Weight gain=(Weight after grafting−Weight before grafting)/Weight before grafting)×100

[0125] The weight gain value represents the amount of Poly(meth)acrylate grafted on the membrane surface.

[0126] Water Permeability Test and determination of the water permeability reduction The water permeability was measured with a custom-made setup using deionized water. The membrane samples were cut in 43.2 cm.sup.2 circles and the roll side (shiny side) was used as upstream side. Measurements were performed at a transmembrane pressure of 0.6 bar at a temperature of 25° C. The permeate volume was recorded as a function of time for each sample.

[0127] The water permeability reduction is defined as:

Water permeability reduction =((TMF before UV grafting−TMF after UV grafting)/(TMF before UV grafting))×100

[0128] Protein Binding Test

[0129] Protein adsorption tests were conducted in phosphate buffered saline (PBS, SigmaAldrich Co. LLC) using the model protein IgG (from human blood, 99%, SigmaAldrich Co. LLC) at pH 7.4. The membrane samples (circles, 1 cm in diameter) were placed on a microwell plate and immersed in the IgG solution (4 g/L) for one hour on a shaker. Afterwards the protein solution was removed and the samples were washed with PBS buffer three times. Afterwards the amount of surface-bound IgG was determined with the help of the Pierce BCA protein assay kit (Thermo Fisher Scientific Inc., Waltham/USA). The BCA assay contains of bichincinonic acid and copper(II)sulfate, the reaction of the surface-bound protein with the copper(II)-complex leads to the formation of a distinct copper(I)-complex which can be photometrically detected at 562 nm.

[0130] Extraction

[0131] A harsh extraction test in deionized water/ethanol (70/30) for 4 hours at 60° C. was used to test the durability of the surface modification. The samples were immersed in that solution and dried in the oven at 60° C. overnight afterwards.

[0132] Zeta-potential analysis

[0133] The Zeta-potential of a membrane surface is a measure of its surface charge at the solid/fluid interface and was measured with the SurPass electrokinetic analyzer from Anton Paar (Graz, Austria). After cutting the membrane samples into two 20×10 mm pieces they were attached to both sample holders of the Adjustable Gap Cell with a double-sided adhesive tape. The gap height between the two samples holders was adjusted to 0.1 μm to form a streaming channel. After filling the system with 10.sup.−3 mol/L potassium chloride solution a pH titration was performed with 0.05 mol/L sodium hydroxide solution starting at pH 3. Then the pH was stepwise increased to 8. The Zeta-potential at each pH step was calculated according to Helmholtz-Smoluchowski equation:

ζ=(DI/DP)×(η/ε.sub.0 ε)×(L/Q)

[0134] with: η=Zeta-potential, DI/DP=slope of the streaming current against the pressure across the streaming channel, ε.sub.0=vacuum permittivity, ε=dielectric constant of the electrolyte solution, L=length of the streaming channel and Q=cross-section of the streaming channel.

[0135] UV-Grafting Procedure

[0136] All experiments were performed with MicroPES 2F microfiltration flat-sheet membranes (obtained from 3M). UV-irradiation trials were conducted with a Lighthammer LH-6 system from Heraeus GmbH, Hanau/Germany. Two “D”-Bulbs having an UV emission spectrum of between 250 and 380 nm were used. PET filters were employed such that only wavelengths greater than 315 nm could reach the membrane surface. The two “D”-Bulbs were placed behind each other to achieve UV-A doses up to 11 J/cm.sup.2.

TABLE-US-00001 TABLE 1 Overview of some of the (meth)acrylic monomers used for the UV-grafting experiments. Chemical name Purity/% Chemical structure Hydroxypropyl acrylate, mixture of isomers (HPA) 95 [00002] [00003] Tetraethylene glycol diacrylate (TEGDA) ≥87    [00004] 2-Hydroxyethyl methacrylate (HEMA) 97 [00005] Tetraethylene glycol dimethacrylate (TEGDMA) 95 [00006] Polyethylene glycol diacrylate, M.sub.n = 700 (PEG-Diacrylate) ≥92    [00007]

[0137] The membrane samples were cut into 18 x 25.4 cm pieces and stored in a Polyethylene (PE)-bag. The general procedure for sample surface modification is described as follows. The monomer solution was prepared by dissolving the required amount of pure monomer in deionized water. Afterwards the membrane sample was taken out of the PE-bag and immersed in the aqueous monomer solution and placed on a glass plate afterwards. A 50 μm thick PET (Polyethylene terephthalate) film (Hostaphan GN 50 4600 A from Mitsubishi) was used to cover the sample and the excess solution was squeezed out with the help of a rubber roller. For every experiment the roll side (shiny side) of the membrane was facing the PET film and the air side (matte side) of the membrane was facing the glass plate. Then the sample sandwich was transferred to the conveyor belt of the

[0138] Lighthammer system and the sample passed the two UV-“D”-Bulbs. After UV irradiation, the samples were washed three times with deionized water for 15 min each and then dried in an oven (30 min at 100° C.). Afterwards the samples were ready for further characterization and were stored in PE-bags again.

[0139] Table 2 shows the respective UV-A energies for every conveyor belt speed. These values were determined with the UV Power PUK II from EIT LLC, Leesburg/USA.

TABLE-US-00002 TABLE 2 Applied UV-A doses for the grafting experiments Conveyor belt Mean value UV- Mean value UV speed/m/min A dose/J/cm.sup.2 intensity mW/cm.sup.2 1.70 7.0 4500 2.75 11.0 4500

TABLE-US-00003 TABLE 3 Ex.1 to 6 and Comp. Ex. 1 Mean value Monomer (HEMA) UV-A dose concentration in grafting No. [J/cm.sup.2] solution [%] Ex. 1 11 12 Ex. 2 7 12 Ex. 3 11 6 Ex. 4 7 6 Ex. 5 11 1 Ex. 6 7 1 Comp. Unmodified Ex. 1 MicroPES 2F membrane

TABLE-US-00004 TABLE 4 Ex. 7 to 12 and Comp. Ex. 1 Mean value Monomer (PEG- UV-A dose diacrylate) concentration No. [J/cm.sup.2] in grafting solution [%] Ex. 7 11 12 Ex. 8 7 12 Ex. 9 11 6 Ex. 10 7 6 Ex. 11 11 1 Ex. 12 7 1 Comp. Unmodified Ex. 1 MicroPES 2F membrane

[0140] Weighing the membrane samples before and after the UV grafting procedure results in the weight gains as shown in Table 5 below:

TABLE-US-00005 TABLE 5 Weight gains of Ex. 1 to 12 after performing the UV grafting procedure No. Weight gain [%] Ex. 1 3.5 Ex. 2 1.7 Ex. 3 2.3 Ex. 4 1.2 Ex. 5 1.1 Ex. 6 1.1 Ex. 7 11.8 Ex. 8 9.0 Ex. 9 5.1 Ex. 10 4.1 Ex. 11 1.2 Ex. 12 0.8

[0141] The weight gain corresponds to the grafted amount of polyacrylate after UV irradiation.

[0142] Protein binding, i.e. IgG binding and water permeability reduction were determined for Ex.

[0143] 1 to 12 as well as Comp. Ex. 1. Binding tests were also conducted after the extraction tests have been carried out. The results are summarized in table 6.

TABLE-US-00006 TABLE 6 Results of IgG binding tests before and after extraction. IgG binding Water after permeability IgG binding extraction reduction/ No. [μg/cm.sup.3] [μg/cm.sup.3] [%] Ex. 1 7.0 8.2 3 Ex. 2 13.0 22.3 3 Ex. 3 5.7 7.9 4 Ex. 4 11.6 14.4 4 Ex. 5 11.0 23.5 2 Ex. 6 15.7 28.7 0 Ex. 7 4.3 4.7 57 Ex. 8 12.2 5.6 37 Ex. 9 9.3 4.8 16 Ex. 10 7.8 16.1 14 Ex. 11 21.9 23.4 5 Ex. 12 23.4 30.3 5 Comp. Ex. 1 23.0 50.6

[0144] For Ex. 13, the UV-grafting experiment of Ex. 3 was repeated with the dimethacrylate crosslinker TEGDMA on MicroPES 2F. The HEMA/TEGDA ratio was set to 10:1 and the monomer concentrations were 6% HEMA and 0.6% TEGDA dissolved in deionized water. Weight gain, IgG binding (before/after extraction) as well as water permeability reduction tests were performed for both Ex. 3 and Ex. 13. The results are summarized in table 76.

TABLE-US-00007 TABLE 7 Comparison between Ex. 3 and Ex. 13. Ex. 3 Ex. 13 Weight gain/% 2.3 4.8 IgG binding before extraction/ 5.7 11.4 μg/cm.sup.2 IgG binding after extraction/μg/cm.sup.2 7.9 13.0 Water permeability reduction/% 4 7

[0145] Similarly, for Ex. 14, the UV-grafting experiment of Ex. 13 was repeated with the difference that HEMA was changed to the acrylate HPA and TEGDMA was changed to the homologous acrylate TEGDA. Weight gain, IgG binding (before/after extraction) as well as water permeability reduction tests were performed. The results are summarized in table 8.

TABLE-US-00008 TABLE 8 Comparison between Ex. 13 and Ex. 14. Ex. 13 Ex. 14 Weight gain/% 4.8 4.2 IgG binding before extraction/ 11.4 5.3 μg/cm.sup.2 IgG binding after extraction/μg/cm.sup.2 13.0 6.5 Water permeability reduction/% 7 10

[0146] ATR-IR analysis

[0147] ATR-IR (Attenuated Total Reflection-Infra-Red) measurements were performed by using the FT-IR spectrometer Spectrum One equipped with the universal ATR accessory from Perkin Elmer. The analysis were carried out for the samples according to Ex. 1 to Ex. 6 and Ex. 7 to Ex. 12 in that the A% for both sides of the samples were measured. That is, for the roll side facing the UV lamp and for the air side ATR-IR analysis were carried out. The same experiments were carried out for Comp. Ex. 2 which was prepared analogous to Ex. 3, however, instead of UV-A lamp a germicidal UV lamp emitting 254 nm was used at an UV dose of 0.64 J/cm.sup.2. The results are summarized in table 9.

TABLE-US-00009 TABLE 9 A % values for roll-and air side of membranes according to Ex. 1 to 6 and Ex. 7 to 12 and Comp. Ex. 2. Sample A %.sub.Roll [%] A %.sub.Air [%] Ex. 1 7 3 Ex. 3 4.8 1.6 Ex. 5 1.5 1.3 Ex. 6 1.2 0.9 Comp. Ex. 2 23.7 0 Ex. 7 7.2 2.0 Ex. 8 5.1 2.2 Ex. 9 2.9 1.4 Ex. 10 4.0 2.2 Ex. 11 1.7 1.3 Ex. 12 1.4 1.3

[0148] This shows that in the membranes according to the present disclosure, not only the surface facing the UV source was modified. Rather, modification or grafting of the surface facing away the UV source was visible. That means that also the surface of the pores in the wall between the outer surfaces of the membrane was modified. This is in contrast to a membrane according to the state of the art where only the surface facing the UV source was modified. Accordingly, it was also demonstrated that the method according to the present disclosure comprising the use of UV irradiation with wavelengths greater than 300 nm was able to provide modification at least well into the thickness of the membrane, resulting in a higher modification of the total membrane surface.

[0149] Zeta-potential analysis was conducted on the roll side of samples from Comp. Ex. 1 and Ex. 7,9 and 11. The results are shown in FIG. 2.

[0150] Tensile strength/elongation at break analysis

TABLE-US-00010 TABLE 9 Mechanical test results. Tensile Tensile Elongation at Elongation strength strength break at break longitudinal transversal longitudinal transversal Sample (cN/15 mm) (cN/15 mm) [%] [%] Unmodified 1359 1201 59 76 6% PEG-Diacrylate, 1428 1289 51 67 7 J/cm.sup.2 + PET film (sheet, Lighthammer unit) 6% PEG-Diacrylate, 1006 1107 6 19 7 J/cm.sup.2 + Glass-filter (roll to roll, FLC unit)