WO2002004083A2 - Membranes superficiellement modifiees et procedes de production - Google Patents

Membranes superficiellement modifiees et procedes de production Download PDF

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Publication number
WO2002004083A2
WO2002004083A2 PCT/US2001/021603 US0121603W WO0204083A2 WO 2002004083 A2 WO2002004083 A2 WO 2002004083A2 US 0121603 W US0121603 W US 0121603W WO 0204083 A2 WO0204083 A2 WO 0204083A2
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Prior art keywords
membrane
plasma
asymmetric
polymer membrane
ofthe
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PCT/US2001/021603
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WO2002004083A9 (fr
WO2002004083A3 (fr
Inventor
Ellen R. Fisher
Michelle L. Steen
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Colorado State University Research Foundation
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Priority to AU2001280496A priority Critical patent/AU2001280496A1/en
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Publication of WO2002004083A3 publication Critical patent/WO2002004083A3/fr
Publication of WO2002004083A9 publication Critical patent/WO2002004083A9/fr

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    • 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
    • B01D67/009—After-treatment of organic or inorganic membranes with wave-energy, particle-radiation or plasma
    • 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
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B01D69/125—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
    • B01D69/127—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction using electrical discharge or plasma-polymerisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C59/00—Surface shaping of articles, e.g. embossing; Apparatus therefor
    • B29C59/14—Surface shaping of articles, e.g. embossing; Apparatus therefor by plasma treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
    • B29K2995/0037—Other properties
    • B29K2995/0092—Other properties hydrophilic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2031/00—Other particular articles
    • B29L2031/755—Membranes, diaphragms

Definitions

  • the present invention relates to a membrane which has been modified using a plasma and methods for producing the same.
  • the present invention provides a polymer membrane which has been modified by a plasma and methods for producing the same.
  • one embodiment ofthe present invention provides a method for modifying a surface of a polymer membrane which comprises:
  • the method generally can also include
  • the overall direction of plasma flow is substantially perpendicular (or orthogonal) to the exterior surface (i.e., cross section) ofthe membrane.
  • the present invention can be used to increase the hydrophilicity or the hydrophobicity ofthe polymeric membrane depending on the surface modifying compound used.
  • Surface modifying compounds which increase the hydrophilicity of a polymeric membrane are well known to one of ordinary skill in the art.
  • Particularly preferred surface modifying compounds for increasing the hydrophilicity of a membrane include oxygen, air, water, hydrogen peroxide, ammonia, helium, argon, and mixtures thereof.
  • surface modifying compounds which increase the hydrophobicity of a polymeric membrane are well known to one of ordinary skill in the art.
  • Particularly preferred surface modifying compounds for increasing the hydrophobicity of a membrane include C,-C 10 alkane, C -C lQ fluoroalkanes, C r C 10 fluoroalkenes, fluorinated epoxides, siloxanes, and mixtures thereof.
  • the membrane comprises a polymer selected from the group consisting of polysulfone, polyethersulfone, polyethylene, polystyrene, polytetrafluoroethylene, polyester, poly(methyl methacrylate), polyacrylonitrile, polyvinylidene fluoride, and mixtures thereof. More preferably, the membrane comprises a polymer selected from the group consisting of polysulfone, polyether sulfone, and mixtures thereof. While membranes may be symmetrical, asymmetric membranes are preferred.
  • the plasma flow means comprises a vacuum.
  • Figure 1 is a schematic illustration of plasma reactor for surface modifying a polymer membrane
  • FIG. 2 is a SEM image ofthe cross-section of a untreated asymmetric PSf membrane (BTS55);
  • Figure 3 is a SEM images ofthe untreated (A) open (1000X) and (B) tight (9000X) sides of a BTS55 membrane;
  • Figure 4 is a graph showing bubble points as a function of treatment time for
  • BTS55 membranes treated with H 2 O plasma 25 W, 50 mTorr. Dashed line indicates bubble point for untreated BTS55. Error bars represent deviations in the bubble point measured for a minimum of three plasma-treated membranes;
  • Figure 5 is SEM images of BTS55 membranes treated with a 25 W H 2 O plasma (50 mTorr) for (A) two minutes and (B) ten minutes;
  • Figure 6 is a SEM image of a BTS55 membrane treated with a 100 W H 2 O plasma (50 mTorr);
  • Figure 7 is a graph showing bubble points as a function of time after plasma treatment for BTS55. Dashed line indicates bubble point for untreated BTS55. Treated samples stored in ambient conditions; a* ⁇ g / to ure 8 is a graphic representation of contact angle for plasma-treated BTS55 as a function of heat treatment. Treated membranes were heated in a conventional oven at 130 °C for a maximum of four hours. Contact angles were measured on both the open ( ⁇ ) and tight (A) sides ofthe membrane after heat treatment. Dashed line indicates contact angle for untreated BTS55; Figure 9 is a graph showing contact angles for plasma-treated BTS55 as a function of heat treatment.
  • Treated membranes were heated in a conventional oven at 130 °C (closed symbols) and 170 °C (open symbols). Data shown for membranes heated for a maximum of 15 minutes. Contact angles were measured on both the open ( ⁇ ) and tight (A) sides ofthe membrane after heat treatment. Dashed line indicates contact angle for untreated BTS55;
  • Figure 10 shows a graph of contact angles for plasma-treated BTS55 as a function of heat treatment. Samples were heated tight side up at 130 °C. Contact angles were measured on both the open ( ⁇ ) and tight (A) sides ofthe membrane after heat treatment. Dashed line indicates contact angle for untreated BTS55;
  • Figure 11 A is an optical emission spectrum of a 25 W H 2 O plasma (50 mTorr) without a BTS55 membrane in the reactor;
  • Figure 1 IB is an optical emission spectrum of a 25 W H 2 O plasma (50 mTorr) with a BTS55 membrane in the reactor;
  • Figure 12 is an environmental SEM image ofthe cross section of a treated PES membrane exposed to H 2 O vapor in the chamber ofthe SEM. The image is oriented with the tight side at the top.
  • membrane As used herein, the terms “membrane”, “polymer membrane” and “porous polymer membrane” are used interchangeably herein and refer to a porous polymer, which are useful in filtration (e.g., of biological fluids).
  • asymmetric membrane and "asymmetric polymer membrane” (e.g., asymmetric polysulfone membrane) are used interchangeably herein and refer to a membrane whose average pore size on one side ofthe surface (i.e., “rough surface side,” “rough side,” or “open side”) is larger than the average pore size on the other side ofthe membrane surface (i.e., “smooth surface side,” “smooth s fc ⁇ ? s tight side”).
  • cross section and “exterior surface” are used interchangeably herein and refer to the surface area ofthe membrane which is orthogonal to the general overall direction ofthe majority ofthe membrane's pores.
  • the polymer membranes ofthe present invention contain pores, which extend from the exterior surface into the bulk matrix.
  • the polymer membrane thus has pore surfaces, which are essentially the surfaces that surround and define the pores ofthe article.
  • the pore surfaces may sometimes be referred to as the "interstitial surface” because they surround the interstitial volume ofthe polymer membrane.
  • membrane surface modifying compound and “surface modifying compound” are used interchangeably herein and refer to a compound which is used to generate a plasma that modifies the surface property of a membrane such that the hydrophilicity or hydrophobicity ofthe membrane is increased.
  • Exemplary membrane surface modifying compounds include those described in the Summary ofthe Invention section above.
  • the term "permanent” when referring to the surface modification ofthe membrane refers to a time period for which the surface modification properties (or characteristics) last for at least about 1 month, preferably at least about 2 months, more preferably at least about 3 months, still more preferably at least about 4 months, and most preferably at least about 1 year.
  • the present invention will now be described in detail in reference to a method for producing a hydrophilic membrane, which is particularly preferred in many separation processes.
  • methods ofthe present invention can be used to produce a hydrophobic membrane (i.e., the resulting membrane is more hydrophobic than the untreated membrane) by selecting an appropriate surface modifying compound.
  • a hydrophobic membrane i.e., the resulting membrane is more hydrophobic than the untreated membrane
  • most polymers are hydrophobic; therefore, a separation of an aqueous sample typically requires a wetting agent to be applied to the membrane to make it more hydrophilic.
  • An additional problem frequently encountered with hydrophobic membranes is the lack of permanency ofthe wetting agent that is used to make them hydrophilic.
  • a reactor for producing an inductively-coupled, low density radio-frequency (rf) H 2 O plasma is the tubular glass reactor shown in Figure 1. Further description of this reactor appears in K. H. A. Bogart et al. "Plasma enhanced chemical vapor deposition of SiO 2 using novel alkoxysilane precursors", J. Vac. Sci. Technol. A 13(2), 476-480 (1995). It should be appreciated that the reactor need not be a tubular glass reactor, for example, the cross-section ofthe reactor can be in any shape including a circle, square, rectangle, rhombus, trapezoid, elipse and the like.
  • the reactor may be made of any of a variety of materials such as stainless steel, glass, plastics such as polycarbonates, and other materials known to those skilled in the art. When operated as described herein, this reactor is used to achieve flowing glow discharge to modify the surfaces of polymer membranes.
  • the reactor includes at least one cylindrical, holder (hereinafter “membrane holder,” which can be made of glass) to orient the polymer membrane perpendicular to the flowing discharge is illustrated in Figure 1 set forth herein, and may be operated as described below.
  • the present invention comprises a longitudinal oriented plasma reactor 10 formed from two sections, namely an inlet section 12 and an exhaust section 26.
  • Reactor 10 also comprises a separate cylindrical membrane holder (e.g., about 90 mm in length) 18, also preferably constructed from glass. One end ofthe membrane holder is threaded with a screw top (e.g., 30 mm dia.) and the opposite end is open to allow flow ofthe plasma through the membrane.
  • the membrane to be treated is placed in the membrane holder and substantially oriented perpendicular to the inductor coil (hereinafter "discharge region").
  • the membrane holder When operated as described herein, the membrane holder was situated in the exhaust section ofthe plasma reactor downstream from the discharge region (e.g., about 9 cm) to minimize plasma-induced damage to tne polymer membrane.
  • This perpendicular placement ofthe membrane cross-section to the plasma flow allows maximal exposure and penetration ofthe plasma through the thickness ofthe membrane.
  • this arrangement allows chemical modification ofthe entire membrane cross section.
  • the exhaust section ofthe plasma rector is in fluid communication with a vacuum pump via line 28 positioned therebetween.
  • a liquid N 2 cold trap may be positioned between the plasma reactor and the vacuum pump to avoid undesirable source gases or byproducts from entering the vacuum pump.
  • the exhaust section may also, or alternatively, be fitted with a replaceable fused silica window, allowing coaxial observation of emission from the plasma using an optical fiber, and may- s sS ted as described below.
  • Plasma emission may be imaged onto the 10 mm entrance slit of, for example, an Ocean Optics S2000 triple spectrometer equipped with three 1800 grooves/nm holographic gratings and three 2048 element linear charge coupled device-array detectors.
  • a Langmuir probe may also be attached to the exhaust section to measure electron and ion energies in the discharge region.
  • the length and geometry ofthe exhaust region may also be modified to accommodate "downstream” and "remote” treatments.
  • an exhaust section may be lengthened to 36 cm to perform treatments at increasing distances from the discharge region.
  • the longitudinal exhaust (or inlet) section can also be replaced with an L-shaped exhaust (or inlet) section to perform remote plasma treatments, in which the porous article is not directly exposed to the glow discharge.
  • the longitudinal exhaust section can also be replaced with a T-shaped exhaust section to perform remote plasma treatments, in which the porous article is not directly exposed to the glow discharge.
  • the reactor 10 further comprises an inlet line 42 through which the precursor to the reactive gas-phase radical (also termed "source gas” or "surface modifying agent”) may be introduced to the plasma reactor.
  • the source gas may be gas or liquid vapor.
  • a more preferred embodiment ofthe source gas is H 2 O vapor, which when operated as described herein may be introduced from a 100 mL Pyrex glass sidearm vacuum flask, which is operatively interconnected to the plasma reactor near the inlet section. Distilled water may be subjected to several freeze-pump-thaw cycles to remove dissolved gases prior to use. Water is then introduced into the plasma reactor through a Teflon stopcock 40, using a vacuum pump that draws water vapor through the plasma reactor.
  • the lines through which the water is admitted to the plasma reactor may or may not be heated to achieve the operating vapor pressure.
  • the vapor pressure is controlled using a Nupro bellows-sealed metering valve.
  • the pressure ofthe H 2 O vapor is allowed to stabilize prior to generating the glow discharge or to the addition of diluent inert gas (e.g. Ar) through an MKS mass flow controller.
  • the total pressure in the chamber is monitored with an MKS Baratron capacitance manometer which is insensitive to differing gas compositions and is stabilized to the desired value prior to generating the glow discharge.
  • the discharge generating apparatus (or “plasma generator”) comprises a power supply and an the source gas to a discharge.
  • Suitable power supplies include any radio-frequency (rf), microwave or direct current (DC) power supplies.
  • a suitable rf power supply may be obtained from, for example, Advanced Energy, and identified under their trade designation as an RFX-600 power supply.
  • 13.56 MHz rf power from the RFX-600 may be inductively-coupled to the source gas in the plasma reactor by an eight turn nickel plated copper coil and tuned with a Jennings 100 pF variable capacitor (also collectively termed "rf matching network"). This configuration may be used with any source gas ofthe present invention.
  • a pulsed rf power supply from, for example, RF Power Products (a subsidiary of Advanced Energy) and identified under their trade designation as an RF5S may also be used for any source gas ofthe invention, especially those that may polymerize in the plasma (also termed “polymer-forming plasmas"). Further description of pulsed plasma systems and their operation appears in N. M. Mackie et al. "Characterization of pulsed-plasma-polymerized aromatic films" Langmuir 14, 1227-1235 (1998), which is incorporated herein by reference in its entirety.
  • the plasma is generated by applying approximately 5-50 W, preferably about
  • CW continuous wave
  • Pressure within the reactor is maintained from about 20 mTorr to about 100 mTorr, preferably from about 40 mTorr to about 80 mTorr, and more preferably about 50 mTorr.
  • the treatment time is generally from about 0.25 minutes to about 10 minutes, preferably from about 1 minute to about 5 minutes, and more preferably about 2 minutes.
  • asymmetric polysulfone membranes US Filter
  • BTS55, BTS80 and UF membranes BTS55, BTS80 and UF membranes, distinguished by their nominal pore size distribution.
  • a non-porous polysulfone resin Westlake Plastics
  • asymmetric polyethersulfone membranes Millipore
  • distilled water underwent several freeze-pump-thaw cycles to remove trapped atmospheric gases.
  • Liquid samples were introduced into the reactor from a 100 mL Pyrex glass sidearm vacuum flask with Teflon ® stopcocks and the vapor pressure was controlled (within ⁇ 2%) using a Nupro bellows-sealed metering, valve.
  • the H 2 O pressure was allowed to stabilize prior to the addition of Ar (4.8 grade), which was added to the existing H 2 O flow through an MKS mass flow controller.
  • the amount of H 2 O admitted to the reactor was relatively constant ( ⁇ 2%).
  • the pressure in the chamber was monitored with an MKS Baratron capacitance manometer which is insensitive to differing gas compositions.
  • Preferred conditions for treating asymmetric PSf membranes were determined to be H 2 O (no additives), 25 " W applied rf power, 50 mTorr pressure for 2 minutes. These conditions were used in all experiments unless otherwise noted.
  • Bubble point analysis The nomenclature used to categorize asymmetric PSf membranes (Table I) corresponds to the nominal bubble point ofthe membrane. For example, BTS55 and BTS80 membranes have nominal bubble points of 55 psi and 80 psi, respectively.
  • the bubble point ofthe membrane is the pressure of air needed to expel liquid (e.g., water) from the pores of the membrane.
  • the bubble point provides information about the wetting properties with a particular liquid for a membrane with a known average pore diameter.
  • Bubble point measurements were obtained with an apparatus consisting of a sample holder (49 cm 2 ), a pressure gauge and a compressed air cylinder (4.8 grade).
  • the membrane Prior to obtaining a bubble point measurement, the membrane was immersed in 100 mL ofthe wetting liquid. Due to the hydrophobicity of polysulfone, the membrane was first wet with a 50:50 isopropylalcohol (IPA)/H 2 O solution. The aqueous EPA solution was gradually replaced with deionized water to effectively wet the pores with water. The wet membrane sample was placed in the sample holder between two protective metal screens with the tight side ofthe membrane upstream of air flow. The delivery pressure was then slowly increased until a breakthrough pressure was observed on the pressure gauge located downstream from the sample holder. This breakthrough pressure is the bubble point ofthe membrane. Unless otherwise noted, bubble points for plasma-treated membranes were measured within 24 hours of plasma treatment. Additional Analyses
  • Static contact angles were measured by the sessile drop method with a contact angle goniometer (Rame Hart Model 100). Measurements were taken on both sides of water drops at ambient temperature, immediately after 1 ⁇ L drops were applied to the surface and the needle tip was removed from the surface. The hysteresis ofthe water drop was evaluated by measuring the contact angle on both sides ofthe drop. In addition, measurements were made on both sides ofthe untreated and plasma-treated membranes. For each sample, three drops were placed at different locations on the sample. Reported contact angle measurements are the average ofthe measurements on each side ofthe membrane for at least three samples. Unless otherwise noted, contact angles were measured immediately after plasma treatment.
  • Plasma-treated membranes were exposed to extremes in heat and humidity to simulate "aging". To simulate hot, humid conditions, plasma-treated membranes were placed in a glass, cylindrical membrane holder modified to fit inside a conventional pressure cooker. The pressure cooker was then heated until the pressure inside reached ⁇ 15 psi above atmospheric pressure or -121 °C. Once these conditions were reached, the membrane was steam-treated for 15 minutes. Plasma-treated membranes were also exposed to high, dry temperatures by heating the membranes at 130 °C and 170 °C in a conventional oven for times ranging from minutes to hours. Scanning electron microscopy (SEM) images were obtained using a Phillips
  • the high-resolution C ls , O ls , and S 2p spectra were acquired at an analyzer pass energy of 25 eV and collected at a 55° takeoff angle, which is the angle between the surface normal and the axis ofthe analyzer lens.
  • Optical emission spectra from 425 to 713 nm for a 25 W H 2 O plasma (50 mtorr vapor pressure, with and without a PSf membrane in the reactor) were obtained from a plasma reactor modified with a replaceable fused silica window located at the downstream end ofthe reactor. The placement of this window allows coaxial observation of emission from the' plasma.
  • Plasma emission was imaged onto the 10 mm entrance slit of an Ocean Optics S2000 triple spectrometer using three optical fibers. The spectrometer is equipped with three 1800 grooves/nm holographic gratings and three 2048 element linear charge coupled device-array detectors. Emission signals were integrated for 2 s.
  • Asymmetric polysulfone membranes Asymmetric polysulfone membranes
  • Table I summarizes the types of asymmetric PSf membranes that are commercially available with average pore sizes ranging from 1.2 ⁇ m (BTS 5) to -0.01 ⁇ m (UF). Due to the asymmetry associated with these membranes, the actual pore size can vary widely from the average pore size ofthe membrane. For example, BTS55 has an average pore size of 0.2 ⁇ m; however, as a result ofthe asymmetry of BTS55, there is a pore gradient with gradual transition from much smaller ( ⁇ 0.1 ⁇ m) to much larger pores (>10 ⁇ m) across the thickness (i.e., bulk matrix) (125 ⁇ m) ofthe membrane. This distinct pore gradient can be seen in the cross-sectional SEM image for a BTS55 membrane ( Figure 2). This image also shows the tortuousity associated with the pores of asymmetric membranes contributing to the difficulties encountered in modifying the entire cross section ofthe membrane.
  • Table I shows the bubble points measurements for untreated asymmetric PSf membranes.
  • the bubble points measured were typically about 10 psi higher than the nominal bubble point for the material, except for BTS55 membranes.
  • BTS55 membranes were used in parameter space study of applied plasma power, H 2 O vapor flow rate (pressure) ariS. it ferment time.
  • Table I Bubble points measured for untreated asymmetric PSf membranes.
  • BTS55 membranes were treated with a 25 W H 2 O vapor plasma (50 mTorr total pressure) for times ranging from 15 seconds to 10 minutes.
  • Figure 4 shows there is a about 20-25 psi increase in the bubble point for all plasma treatment times examined (0.25-10 min). From equation (1), an increase in the bubble point could be a result of a decrease in the contact angle or a decrease in the overall pore diameter.
  • the observed change in the bubble point for plasma-treated BTS55 membranes may correspond to an increase in the hydrophilicity induced by plasma treatment or to adverse physical alteration in the membrane structure as a result of plasma treatment.
  • Applied plasma powers higher than 25 W also adversely affect the structural integrity ofthe membrane.
  • BTS55 membranes are damaged by a 100 W H 2 O plasma treatment ( Figure 6).
  • high applied rf powers and prolonged plasma exposure were avoided and typical treatments employed relatively low plasma powers (25 W) and pressures (50 mTorr) for short times (about 2 min).
  • changes in the pore diameter of asymmetric PSf membranes were quantified by porometry.
  • the results of porometry tests of plasma-treated BTS55 membranes are summarized in Table II. These results indicate that the average pore size or mean flow pore (MFP) of BTS55 membranes is negatively affected by plasma- treatment.
  • MFP mean flow pore
  • the pore sizes are about 35% larger than the pore sizes ofthe untreated BTS55; however, the pore sizes ofthe plasma-treated membranes are nearly identical to the values obtained for BTS55 membranes treated with a wetting agent. Therefore, plasma treatment ofthe present invention produces comparable results to those obtained by the convention of applying a wetting agent to make hydrophobic membranes hydrophilic. Table II. Porometry data for untreated and plasma-treated asymmetric PSf membranes.
  • the porometry results suggest that the observed increase in the bubble point for plasma-treated BTS-55 membranes may be the result of an increase in the pore diameter.
  • water contact angles were measured on both sides of plasma-treated membranes immediately after plasma treatment. Table III summarizes the results of these measurements before and after plasma treatment. As seen in Table III, the untreated membranes are hydrophobic with average contact angles of about 90° (BTS55). Despite the asymmetric structure, the average contact angle measured on the open side is similar to the average contact angle measured on the tight side for each membrane type. Table III. Contact angles" for untreated, plasma-treated and aged PSf materials.
  • a non-porous PSf resin was placed in the membrane holder and treated with identical plasma conditions.
  • Table III includes the results of contact angle measurements on both sides ofthe resin before and immediately after plasma treatment.
  • the side ofthe resin closest to the inductor coil (Side A) was more wettable after treatment than before treatment.
  • the downstream side (Side B) ofthe plasma-treated resin was not as wettable as the upstream side, suggesting that the complete modification of BTS55 membranes is related to its porosity.
  • Plasma-treated BTS80 membranes were also analyzed by porometry. The results obtained for these membranes before and after plasma treatment are similar to those obtained for BTS55 membranes (Table II). Overall, an increase in the pore sizes associated with BTS80 and BTS55 membranes was observed after plasma treatment. As noted above, this phenomenon is also observed for membranes treated with a chemical wetting agent. Permanence of hydrophilic membrane modification
  • FIG. 7 shows the effect that aging has on the average bubble point of plasma-treated BTS55 membranes.
  • the average bubble point, analyzed immediately after plasma treatment is about 75 ⁇ 2.2 psi (i.e., 0 days). As previously mentioned, this is about 20 psi higher than the average bubble point for untreated BTS55 membranes (57 ⁇ 3.3 psi).
  • Figure 7 illustrates that the average bubble points measured for samples aged for up to one month decrease slightly from the average bubble point of samples analyzed immediately after plasma treatment, but remain at about 20 psi higher than the average bubble point of untreated BTS55 membranes.
  • the permanence ofthe hydrophilic membrane modification was further tested by subjecting plasma-treated BTS55 membranes to accelerated aging. These experiments exposed the membranes to extremes in humidity and temperature. The humidity or temperature at which plasma-treated membranes revert to the same degree of hydrophobicity as the untreated membrane is correlated to the robustness ofthe modification. Treated BTS55 membranes were exposed to moist (e.g., steam) and dry heat. The permanence ofthe modification was then determined by measuring contact angles on both sides ofthe membrane after the wet or dry treatment. Bubble point measurements were also used for further comparison. Contact angle measurements for the steam-treated membranes indicated they were less wettable than plasma-treated membranes without steam treatment; however, a visible contact angle could not be measured on either side ofthe steam-treated membranes.
  • steam-treated membranes did not immediately absorb the water drop, but absorbed the drop in ⁇ 60 seconds. Although steam-treated BTS55 membranes do not lose hydrophilicity, steam treatment affects the wettability time of plasma-treated BTS55 membranes.
  • the average bubble point of plasma-treated BTS55 membranes analyzed after steam treatment (72 ⁇ 1.1 psi) is, however, essentially unchanged from the average bubble point measured immediately after plasma treatment (75 ⁇ 2.2 psi).
  • Plasma-treated membranes were steam-treated under the same conditions three times in succession. The membranes were allowed to dry between steam cycles. Contact angles were measured on each side ofthe membrane following the last steam treatment. The results obtained for two and three steam treatments were similar to those obtained for membranes steamed only once.
  • the steam-treated membranes did not immediately absorb the water drop but instead absorbed the drop in ⁇ 90 seconds.
  • the average bubble points obtained for membranes steamed two and three times are identical to the average bubble point obtained for membranes steamed only once. Therefore, repeated steam treatments do not cause further losses in hydrophilicity.
  • Table IV includes the results for two different experiments in which multiple BTS55 membranes were simultaneously plasma-treated for either 2 or 3 minutes.
  • the surfaces ofthe membrane closest to the inductor coil (Table IV, surfaces 1 and 2) were completely wettable after plasma treatment.
  • the open side ofthe second membrane (Table IV, surface 3) was also rendered completely wettable by plasma treatment.
  • the only way the surfaces on the interior ofthe stacked assembly (Table TV, surfaces 2 and 3) could be treated by the plasma is if the plasma penetrated the thickness of the membrane closest to the inductor coil.
  • Table IN Results for multiple membranes experiments.
  • the surface farthest downstream from the inductor coil (Table IV, surface 4) was less wettable than the other three surfaces ofthe membranes in the stacked assembly. Although surface 4 was not completely wettable, a decrease in the contact angle relative to the untreated BTS55 membrane was observed. It was found that by increasing the treatment time to 3 minutes, all four surfaces ofthe membranes in the stacked assembly were rendered completely wettable by plasma treatment. Therefore, increasing the treatment time achieves complete modification of both membranes.
  • Table IV summarizes the results of multiple membrane experiments performed for BTS80 and UF membranes at different treatment times.
  • both surfaces ofthe membrane closest to the inductor coil (Table IV, surfaces 1 and 2) are rendered completely wettable after a 2 minute plasma treatment.
  • both surfaces 3 and 4 ofthe BTS80 membranes were not completely wettable after a 2 minute plasma treatment.
  • surfaces 2, 3, and 4 in the UF experiment were not immediately completely wettable after a 2 minute plasma treatment.
  • the elemental composition for the untreated membrane is in agreement with the structure of PSf, Table V. In addition, no significant difference in composition was detected between the open and tight sides ofthe untreated BTS55 membrane.
  • the results in Table V for plasma- treated membranes indicate that H 2 O plasma treatment increases the oxygen concentration of asymmetric PSf membranes.
  • the oxygen content for both the open and tight sides of plasma- treated BTS55 membranes (-22%) is significantly higher than that for the untreated membrane (11.8 ⁇ 0.5%).
  • the increase in the high binding region ofthe C ls spectrum upon plasma treatment is believed to be consistent with the presence of ketone/aldehyde and carboxylic acid/ester groups.
  • Table VI provides the detailed results of the C ls spectrum for untreated and plasma-treated BTS55 membranes.
  • Negative derivatization control c. Positive derivatization control.
  • TFAA trifluoroacetic anhydride
  • FIG. 11 A shows an optical emission spectrum of a 25 W H 2 O vapor plasma (50 mTorr). This spectrum identifies the presence of OH radicals (at 306.95 and 309.14 nm), as well as H atoms (at 486.18 and 656.45 nm) in the H 2 O plasma. No emission from other species is observed.
  • Figure 1 IB shows the OES spectrum of a 25 W H 2 O vapor plasma (50 mTorr) when a PSf membrane (BTS55) was placed horizontally directly in the coil region ofthe plasma reactor. While emission from OH and H atoms is still evident in this spectrum, there are clearly strong emission lines at 282.68, 297.02, 312.71, 329.75, 483.17, and 519.48 nm. Less intense emission lines are also observed at 348.50, 450.75 and 560.67 nm. All of these new lines can be attributed to emission from CO in the plasma. See W. R. Harshbarger, R. A. Porter, T. A. Miller, P. Norton, Appl. Spectrosc, 1977, 31, 201.
  • a major advantage of methods ofthe present invention is that the entire membrane cross-section is modified. Penetration ofthe membrane modification by methods ofthe present invention is complete such that all surfaces ofthe membrane are treated. This is true for both microporous and ultrafiltration asymmetric PSf membranes. Without being bound by any theory, this extensive membrane modification by plasma treatment ofthe present invention is believed to be the result of allowing the plasma to flow through the pores ofthe membrane. Moreover, it is believed that the effectiveness of the H 2 O plasma treatment is not limited to microporous asymmetric PSf membranes, but is also effective for asymmetric membranes with smaller pore sizes.
  • Plasmas have often been used for temporary improvements in polymer wettability.
  • the wetting properties of poly(hydroxybutyrate-co-9% hydroxyvalerate) films were studied as a function ofthe type of plasma treatment (e. g. Ar, O 2 , H 2 O and H 2 O 2 plasmas).
  • H 2 O and H 2 O 2 were considered milder treatments, as they resulted in less surface etching and cross-linking ofthe polymer. It is believed the degree of crosslinking influences the permanence ofthe plasma treatment as H 2 O and H 2 O 2 plasma-treated films lost hydrophicility upon standing sooner than films treated with Ar and O 2 plasmas.
  • Loss of plasma-induced hydrophilicity is generally attributed to chain migration from the surface to the bulk to mimmize surface energy; hence, the degree of cross-linking affects the facility with which the chains can migrate from the surface into the bulk.
  • H 2 O plasma-treated membranes ofthe present invention are permanently hydrophilic upon standing. Indeed, plasma-treated samples ofthe present invention remain wettable with storage in ambient conditions for at least nine months. Exposure to environmental extremes such as heating in an oven or exposure to boiling H 2 O generally increases the hydrophobicity of plasma-treated membranes. In both cases, it is believed that chain motion is the cause of this loss in hydrophilicity for plasma- treated membranes exposed to high temperatures as heating polymers has been shown to increase chain motion. See, for example, T. R.
  • the permanency ofthe hydrophilic membrane modification ofthe present invention is related to the chemical changes in PSf as a result of plasma treatment. Incorporation of new, more hydrophilic functional groups that are covalently bound to the polymeric backbone results in permanent modification. Indeed, the oxygen concentration increases to more than 20% after plasma treatment (Table N) as new C-O x and a small number of OH groups are introduced by plasma treatment. This increase is observed for both surfaces ofthe plasma-treated membranes, further demonstrating that both surfaces are equally modified by plasma treatment.
  • Asymmetric PSf membranes have also been treated with inert gas/H 2 O plasmas (e.g., Ar/H 2 O); however, no additional benefit in adding inert gas to the H 2 O plasma was determined.
  • inert gas/H 2 O plasmas e.g., Ar/H 2 O
  • diluents can increase the fragmentation of H 2 O in the plasma (i.e., increase the amount of plasma-generated OH radicals), the addition of a diluent may also have a deleterious effect as it could lead to etching ofthe polymeric material.
  • All ofthe conditions employed in the present invention are relatively mild (low applied rf power and pressures as well as brief treatment times). Furthermore, the membrane is placed downstream from the inductor coil (e.g., about 9 cm), limiting exposure to energetic species. While membranes treated with methods ofthe present invention did not appear damaged by H 2 O plasma treatment on the scale ofthe SEM experiment, for plasma- treated BTS55, BTS80, and UF membranes an increase in average pore size, as determined by porometry, was generally observed. The increase in pore diameter resulting from plasma treatment is, however, comparable to the increase in pore diameter observed for membranes treated with a wetting agent.
  • Present inventors have identified the presence of excited state OH radicals in H 2 O plasma under the conditions used to process PSf membranes ( Figure 11 A) ofthe present invention. Moreover, present inventors have also identified the presence of additional species generated only during plasma modification of PSf membranes.
  • the OES spectrum in Figure 1 IB identifies the presence of excited state CO molecules, which are not observed in a 25 W H 2 O vapor plasma (50 mTorr) without a PSf membrane in the reactor. Thus, present inventors were able to detect reactive excited-state plasma species as well as excited-state products ofthe reaction with PSf.
  • Plasma-generated OH radicals can combine with atoms at the surface to produce C-O bonds by equation (3).
  • CO x groups such as aldehyde/ketone and carboxylic acid/ester groups.
  • these groups could be introduced by oxidation of alcohol groups plasma-generated by equation (3), oxidation can occur at other sites in the polymer backbone.
  • oxidation at position 2 yields an aldehyde, which can be further oxidized to yield a carboxylic acid group.
  • oxidation at the quaternary carbon (position 1) yields a ketone functionality.
  • a secondary oxidation pathway is at the sulfur (position 3) resulting in sulfate-like groups as seen in the high resolution S 2p spectra.
  • XPS results obtained by the present inventors indicate the presence of nitrogen on the plasma- treated samples suggesting the presence of amide-like groups, possibly at position (2). Therefore, the detailed chemical information obtained by the present inventors from the XPS shows concurrent reaction pathways.
  • asymmetric polyethersulfone (PES) membranes were also treated with the same plasma parameters used for the polysulfone membranes described above.
  • the untreated membranes had an average pore size of -10 ⁇ m (open side) and a contact angle of 90°.
  • the PES membranes were treated with a 25 W H 2 O vapor plasma (50 mTorr total pressure) for 2 minutes. Similar to the results for PSf membranes, contact angle measurements on the treated PES membranes were impossible to perform as the water drop immediately disappeared into the membrane (i.e., contact angle of 0°). Again, both sides of the plasma-treated membranes were completely wettable. This shows that the PES membranes were also rendered completely water-wettable as a result ofthe plasma treatment.

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Abstract

La présente invention concerne une membrane superficiellement modifiée et le procédé de production correspondant. Ce procédé nécessite d'une façon générale (a) de placer une membrane polymère en aval du courant d'un générateur de plasma, puis (b) de générer un plasma d'un composé de modification de surface, et enfin (c) de mettre en oeuvre un organe faisant passer le courant de plasma au travers de la surface intersticielle de la membrane de façon à produire une membrane polymère superficiellement modifiée. Selon un mode de réalisation particulier, l'invention concerne un procédé de production de membranes polymères hydrophiles à partir de polymères hydrophobes.
PCT/US2001/021603 2000-07-07 2001-07-03 Membranes superficiellement modifiees et procedes de production WO2002004083A2 (fr)

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WO2003097219A1 (fr) * 2002-05-17 2003-11-27 Millipore Corporation Membrane asymetrique a haut debit
WO2005007725A1 (fr) * 2003-07-11 2005-01-27 Pemeas Gmbh Feuille polymere asymetrique, procedes de fabrication et utilisation associes
WO2006044463A1 (fr) * 2004-10-13 2006-04-27 3M Innovative Properties Company Procede de preparation de membranes en polyethersulfone
GB2465652A (en) * 2008-08-28 2010-06-02 Gen Electric Processes for forming hydrophilic membranes from hydrophobic membranes using plasma
US7834131B2 (en) 2003-07-11 2010-11-16 Basf Fuel Cell Gmbh Asymmetric polymer film, method for the production and utilization thereof
US7942274B2 (en) 2000-05-24 2011-05-17 Millipore Corporation High-throughput asymmetric membrane
US8247039B2 (en) 2005-06-02 2012-08-21 Institut “Jo{hacek over (z)}ef Stefan” Method and device for local functionalization of polymer materials
CN109224876A (zh) * 2018-11-26 2019-01-18 迈凯特殊材料（苏州工业园区）有限公司 一种亲水性聚砜膜制备方法及其应用
CN110280137A (zh) * 2019-07-31 2019-09-27 郑州恒博环境科技股份有限公司 一种去除cod有机物专用超滤膜及其制备方法
WO2021072502A1 (fr) * 2019-10-16 2021-04-22 David R Mckenzie Traitement ionique de substrats par plasma
CN114566753A (zh) * 2022-03-04 2022-05-31 四川华能氢能科技有限公司 一种可提升离子迁移性能的制氢隔膜材料及其制备方法
WO2024050693A1 (fr) * 2022-09-06 2024-03-14 扬州纳力新材料科技有限公司 Procédé de préparation d'un film polymère modifié, film polymère modifié et son utilisation

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EP3092063A4 (fr) 2013-12-16 2017-10-11 SABIC Global Technologies B.V. Membranes polymères traitées à matrice mixte
US9492785B2 (en) 2013-12-16 2016-11-15 Sabic Global Technologies B.V. UV and thermally treated polymeric membranes

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Cited By (15)

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US7942274B2 (en) 2000-05-24 2011-05-17 Millipore Corporation High-throughput asymmetric membrane
WO2003097219A1 (fr) * 2002-05-17 2003-11-27 Millipore Corporation Membrane asymetrique a haut debit
US7834131B2 (en) 2003-07-11 2010-11-16 Basf Fuel Cell Gmbh Asymmetric polymer film, method for the production and utilization thereof
WO2005007725A1 (fr) * 2003-07-11 2005-01-27 Pemeas Gmbh Feuille polymere asymetrique, procedes de fabrication et utilisation associes
US7537718B2 (en) 2004-10-13 2009-05-26 3M Innovative Properties Company Hydrophilic polyethersulfone membrane and method for preparing same
WO2006044463A1 (fr) * 2004-10-13 2006-04-27 3M Innovative Properties Company Procede de preparation de membranes en polyethersulfone
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US8247039B2 (en) 2005-06-02 2012-08-21 Institut “Jo{hacek over (z)}ef Stefan” Method and device for local functionalization of polymer materials
GB2465652A (en) * 2008-08-28 2010-06-02 Gen Electric Processes for forming hydrophilic membranes from hydrophobic membranes using plasma
CN109224876A (zh) * 2018-11-26 2019-01-18 迈凯特殊材料（苏州工业园区）有限公司 一种亲水性聚砜膜制备方法及其应用
CN110280137A (zh) * 2019-07-31 2019-09-27 郑州恒博环境科技股份有限公司 一种去除cod有机物专用超滤膜及其制备方法
WO2021072502A1 (fr) * 2019-10-16 2021-04-22 David R Mckenzie Traitement ionique de substrats par plasma
CN114566753A (zh) * 2022-03-04 2022-05-31 四川华能氢能科技有限公司 一种可提升离子迁移性能的制氢隔膜材料及其制备方法
CN114566753B (zh) * 2022-03-04 2024-03-29 四川华能氢能科技有限公司 一种可提升离子迁移性能的制氢隔膜材料及其制备方法
WO2024050693A1 (fr) * 2022-09-06 2024-03-14 扬州纳力新材料科技有限公司 Procédé de préparation d'un film polymère modifié, film polymère modifié et son utilisation

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