ULTRASONICALLY SURFACE MODIFIED POLYETHERSULFONE MEMBERS AND METHOD OF MAKING THEREOF

Abstract

The present disclosure provides a method for treating the surface of a microporous polymeric membrane, comprising immersing a microporous polymeric membrane in a liquid; and applying ultrasonic waves to the microporous polymeric membrane immersed in the liquid.

Claims

1. A method for treating the surface of a microporous polymeric membrane, comprising (i) Immersing a microporous polymeric membrane in a liquid; (ii) Applying ultrasonic waves to the microporous polymeric membrane immersed in the liquid.

2. The method according to claim 1, wherein the liquid is selected from organic liquids and/or water.

3. The method according to claim 1, wherein the polymeric membrane is selected from polymeric sulfone membranes, polyethylene membranes, polypropylene membranes, polyamide membranes, polyvinylidene difluoride membranes and polyacrylonitrile membranes.

4. The method according to claim 1, wherein the microporous polymeric membrane comprises a first surface, a second surface and an intermediate wall having a wall thickness disposed between the first surface and the second surface.

5. The method according to claim 1, wherein the microporous polymeric membrane comprises a separation layer.

6. The method according to claim 5, wherein the separation layer is located within the wall disposed between the first surface and the second surface.

7. The method according to claim 1, wherein applying ultrasonic waves in step (ii) comprises generation of cavitation in the liquid.

8. The method according to claim 1, wherein applying ultrasonic waves in step (ii) comprises application of sound power of at least 20 W, preferably of at least 40 W, more preferably of at least 50 W.

9. The method according to claim 1, wherein applying ultrasonic waves in step (ii) comprises application of sound power of up to 10,000 W, preferably up to 9,000 W, and more preferably up to 8,000 W.

10. The method according to claim 1, wherein applying ultrasonic waves in step (ii) is carried out over a period of time of at least 30 s, preferably of at least 1 min, more preferably of at least 5 min.

11. The method according to claim 1, wherein the ultrasonic waves are applied in a dose in the range of from 0.1 W/cm.sup.2 to 10 W/cm.sup.2, preferably from 0.2 to 8 W/cm.sup.2, more preferably from 0.4 to 6 W/cm.sup.2.

12. The method according to claim 1, wherein the method comprises modification of the membrane surface, preferably an increase of the filtration capacity of the membrane.

13. The method according to claim 12, wherein the method comprises increasing the surface porosity of the membrane.

14. A polymeric membrane, obtained by the method according to claim 1.

15. The membrane according to claim 14, wherein the filtration capacity was increased by at least 5%, preferably by at least 10%, more preferably of at least 15%.

Description

DESCRIPTION OF FIGURES

[0078] FIG. 1: SEM picture of 20000× magnification of the untreated roll side of a MicroPES 2FPH membrane (Comp. Ex. 1).

[0079] FIG. 2: SEM picture of 20000× magnification of the roll side of a MicroPES 2FPH membrane after the ultrasonic treatment as described in the experimental section (Ex. 1)

EXAMPLES

[0080] 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.

[0081] Test Methods

[0082] Surface Porosity:

[0083] A small piece of membrane is prepared for SEM-analysis by applying a thin gold coating layer with a sputter device. The sample is placed within the measurement chamber of a common SEM and at least three images are taken from both sides of the sample using a BSED-detector that ensures high contrast between sample surface and pores. These images are uploaded to an image-analysis-software (e.g. “Scandium”) where further data processing takes place. After setting a contrast threshold the software distinguishes between pores and polymeric surface area and differentiates the pore area into 10 discrete classes. This repeated three times per sample side provides a statistical value of surface porosity (pore-area divided by whole sample area) and furthermore a pore size deviation over the surface.

[0084] Volume Porosity:

[0085] 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. 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.

[0086] The volume porosity c is determined according to the following formula:

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

[0087] where: [0088] m.sub.dry=weight of the dry membrane sample after wetting and drying [g] [0089] m.sub.wet=weight of the wet, liquid-filled membrane sample [g] [0090] ρ.sub.liquid=density of the liquid used [g/cm.sup.3] [0091] ρ.sub.polymer=density of the membrane polymer [g/cm.sup.3]

[0092] Maximum Separating Pore:

[0093] 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

where σ.sub.B is a constant that is primarily dependent on the wetting liquid used during the measurement. For H.sub.2O, σ.sub.B is 2.07 μm.Math.bar at 25° C.

[0094] Nominal Pore Size

[0095] The nominal pore size in the separating layer is determined by perm porometry according to ASTM F 316-03 with the PMI Advanced Porometer CFP-1020-APLC-GFR (PMI, Ithaca, N.Y., US).

[0096] Transmembrane Flow (Water Permeability):

[0097] From a roll of flat sheet membrane a rectangular piece is cut and placed within the circular shaped mounting of a measurement chamber. Once it is closed a circular piece of membrane with a defined surface area of 43.20 cm.sup.2 is sealed within the chamber. After starting the measurement ultrafiltered and deionised water conditioned to 25° C. flows with a defined test pressure (approx. 0.6 bar) through the membrane. The filtrated water volume obtained over a measuring time of 1 minute, i.e. the permeate produced during the measurement, is determined gravimetrically or volumetrically.

[0098] The transmembrane flow TMF is calculated using formula (III)

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

[0099] where: [0100] V.sub.W=Water volume flowing through the membrane sample during the measuring time [ml] [0101] Δt=Measuring time [min] [0102] A.sub.M=Area of the membrane sample exposed to the flow (normally 30 cm.sup.2) [0103] Δp=Pressure set during the measurement [bar]

[0104] Through Put Test

[0105] A circular piece of membrane is cut from a membrane roll and placed in a flat sheet membrane test cell. In a separate pressurized vessel a solution of 0.2 g±10 mg soluble coffee in 5000 ml deionized water is prepared under constant stirring.

[0106] After venting the test cell containing the flat sheet membrane the solution is pressed through it for 10 minutes while the filtrate flow is constantly measured gravimetrically.

[0107] The cumulated permeate mass after 10 min of filtration is defined as the Through put measured in g.

[0108] Membrane Substrate

[0109] As substrate MicroPES 2FPH has been chosen as decent candidate since the retentive layer of this type is localized not on the outer surface but appears to be in the inner matrix of the membrane.

[0110] Ultrasonic Device

[0111] A regular ultrasonic bath with adjustable power from Bandelin (Model DK 156 bp, 35 kHz, 180 W) has been used.

[0112] Treatment Medium

[0113] An aqueous solution of 10 wt-% glycerol has been used to tailor the effect on the membrane. This medium was suitable in combination with the existing bath since pure water yielded high cavitation even on lower setting. This solution showed lower tendency to create cavitation bubbles and was more suitable for carrying out the experiments.

[0114] Treatment Procedure

[0115] Sheets from a MicroPES 2FPH roll (3M Company) have been placed between to glass plates in order to even more reduce the intensity of cavitation on the membrane surface and immersed in the water/glycerol solution. The device was then turned on at 10% intensity for 10 min. The membrane samples were then visually inspected. Since no defects could visually be detected bubble point, TMF and coffee through-put have been measured at five equally treated samples. The results are referenced against five untreated samples from the same membrane roll.

[0116] The properties of the membranes are summarized in table 1.

TABLE-US-00001 TABLE 1 Properties of the membranes according to the examples and comparative examples. Example 1 is the membrane treated as described above Comp. 1 is the untreated membrane. Ex. 1 Comp. Ex. 1 TMF [mL/cm.sup.2 min bar] 36.6 36.7 Bubble point in water [bar] 3.89 3.96 Coffee through put [g] 580 525

[0117] The experimental data showed that both TMF and bubble point were unaffected by the ultrasonic treatment. This demonstrates that the separation layer of the membrane as well as the general microporous structure of the membrane stayed intact during the ultrasonic treatment. The increase in throughput as demonstrated in the through put coffee test demonstrates that the surface porosity of the membrane was significantly increased by the ultrasonic treatment as described herein.