EP0593515A1 - Article pour separation et purification et methode de controle de sa porosite - Google Patents

Article pour separation et purification et methode de controle de sa porosite

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Publication number
EP0593515A1
EP0593515A1 EP92912441A EP92912441A EP0593515A1 EP 0593515 A1 EP0593515 A1 EP 0593515A1 EP 92912441 A EP92912441 A EP 92912441A EP 92912441 A EP92912441 A EP 92912441A EP 0593515 A1 EP0593515 A1 EP 0593515A1
Authority
EP
European Patent Office
Prior art keywords
article
particulate
particles
ptfe
sorptive
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP92912441A
Other languages
German (de)
English (en)
Inventor
Donald F. Hagen
William V. Balsimo
Robin E. Wright
Craig G. Markell
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
3M Co
Original Assignee
Minnesota Mining and Manufacturing Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Minnesota Mining and Manufacturing Co filed Critical Minnesota Mining and Manufacturing Co
Publication of EP0593515A1 publication Critical patent/EP0593515A1/fr
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
    • B01J20/28033—Membrane, sheet, cloth, pad, lamellar or mat
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28002—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their physical properties
    • B01J20/28011—Other properties, e.g. density, crush strength
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
    • B01J20/28016—Particle form
    • B01J20/28021—Hollow particles, e.g. hollow spheres, microspheres or cenospheres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
    • B01J20/28028—Particles immobilised within fibres or filaments
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J20/28069—Pore volume, e.g. total pore volume, mesopore volume, micropore volume
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J20/28078—Pore diameter

Definitions

  • This invention relates to a porous particle loaded sheet of fibrillated polytetrafluoroethylene (PTFE) comprising a combination of sorptive particles and energy expandable or expanded polymeric particles, and a process therefor.
  • PTFE polytetrafluoroethylene
  • U.S. Patent No. 4,990,544 teaches a gasket comprising a fibrillated PTFE resin and a fine inorganic powder dispersed therein.
  • U.S. Patent No. 4,985,296 teaches an expanded, porous PTFE film containing filler material which is purposely compressed to provide thin films where space reduction is desirable.
  • 4,971,697 teaches a chromatographic article comprising a PTFE fibril matrix having enmeshed therein a mixture of non-swellable sorptive particles and hydrated silica flakes.
  • Hagen, et al. "Membrane Approach to Solid Phase Extractions", Analytica Chimica Acta. 236 (1990) 157-164, relates to particle loaded PTFE matrices useful in extraction applications.
  • U.S. Patent No. 4,460,642 teaches a water- swellable composite sheet of microfibers of PTFE and hydrophilic absorptive particles enmeshed therein which is useful as a wound dressing.
  • U.S. Patent No. 4,923,737 discloses a method for a "metal cloth" prepared from fibrillated PTFE containing metal or other particles entrapped in the fibrils.
  • fibrillated PTFE has also been combined with a polyamide to provide articles by extrusion blow-molding (U.S. Patent No. 4,966,941) and with an elastomer to provide articles with increased durability (U.S. Patent No. 4,962,136).
  • U.S. Patent No. 4,945,125 teaches a process of producing a
  • U.S. Patent No. 4,914,156 describes a blow moldable composition comprising a polyether, an epoxide polymer, a source of catalytic cations, and a fibrillatable PTFE.
  • U.S. Patent No. 4,914,156 describes a blow moldable composition comprising a polyether, an epoxide polymer, a source of catalytic cations, and a fibrillatable PTFE.
  • 4,902,747 discloses a polyarylate composition
  • U.S. Patent Nos. 4,199,628 and 4,265,952 relate to a vermicular expanded graphite composite blended with a corrosion resistant resin such as PTFE with improved impermeability to corrosive fluids at high
  • U.S. Patent No. 4,483,889 discloses the method of making a composite material comprised of a fibrous matrix, expandable polymeric microbubbles, and a formaldehyde-type resin involving distributing the expandable microspheres (either expanded or unexpanded) into the fiber matrix, expanding the polymeric bubbles by application of heat (in the case where unexpanded microbubbles were used), and impregnating the resulting porous matrix with a curable formaldehyde-type resin to give a foam.
  • the present invention provides a
  • composite sheet-like article useful in at least one of separations and purification applications comprising:
  • the weight ratio of PTFE to total particulate is in the range of 2:98 to 50:50, more preferably 5:95 to 25:75.
  • the weight ratio of sorptive is preferferably, the weight ratio of sorptive
  • particulate to energy expanded or expandable polymeric particulate is in the range of 3:1 to 1000:1, more preferably 5:1 to 500:1.
  • this invention provides a method of controlling interstitial porosity in a composite sheet-like article useful in at least one of separations and purification applications.
  • the amount of energy expandable particulate in the fibril matrix controls interstitial porosity in the expanded sheetlike article.
  • “sorptive” means microporous and capable of being active in separations and purification applications.
  • FIG. 1 is a plot of time vs. distance traveled for a solvent front in thin layer chromatography (TLC) in articles of the invention in which the proportion of expanded particulate to sorptive particulate is varied;
  • FIG. 2 is a plot of a TLC solvent front rate vs. percent unexpanded particulate and vs. percent expanded particulate;
  • FIG. 3 is a plot of percent numbers of pores vs. pore size in unexpanded and expanded articles of the invention
  • FIG. 4 is a plot of flow rates vs. percent
  • FIG. 5 is an enlarged perspective view of a portion of an unexpanded article of the invention
  • FIG. 6 is an enlarged perspective view showing an article of the invention in use in a column
  • FIG. 7 is a cross-sectional view, greatly
  • FIG. 8 is a cross-sectional view, greatly
  • FIGS. 1-4 see Example 1, below.
  • FIG. 5 is a perspective view of partially rolled sheet 10 of the article of the invention. Energy expandable particulate 12 and sorptive particulate 14 are enmeshed in PTFE fibril matrix 16.
  • FIG. 6 is an enlarged perspective view showing packed column 20 containing article 10 of FIG. 5 which has been rolled up, placed in chromatographic column 22, and subjected to energy to expand article 10 so that it snugly fills a portion of the interior cavity 24 of column 22.
  • FIG. 7 shows one embodiment of a cross-sectional view, greatly enlarged, of the sheet like article 30 of the invention having PTFE fibrils 32 in which are enmeshed sorptive particulate 34 and energy expandable particulate 36.
  • FIG. 8 shows sheet-like article 40 provided after application of energy to the article of FIG. 7.
  • Fibrils 42 have expanded particles 44 and sorptive particles 46 enmeshed therein.
  • Controlled interstitial porosity in sheet-like articles comprising a fibrillated PTFE matrix and sorptive particulate enmeshed therein can be achieved by further incorporating therein in the range of 0. 05 to 25 weight percent of energy expandable or expanded hollow polymeric particles.
  • Expandable particulate material useful in the present invention can be swellable or non-swellable in aqueous or organic liquid, and preferably is
  • the expandable particulate is not
  • Expandable particulate includes those materials comprised of a polymeric shell and a core of at least one other material, either liquid or gaseous, most preferably a liquid at room temperature, in which the polymeric shell is essentially insoluble.
  • a liquid core is advantageous because the degree of expansion is directly related to the volume change of the core material at the expansion temperature.
  • the volume expansion expected can be approximated from the general gas laws.
  • expandable particulate comprising liquid core material offers the opportunity to provide much larger volume changes, especially in those cases where a phase change takes place, i.e., the liquid volatilizes at or near the expansion temperature.
  • Gaseous core materials include air and nonreactive gases and liquid core materials include organic liquids.
  • Preferred energy expandable particulate also called microbubbles, microballoons, and microspheres
  • shells comprising copolymers of vinyl chloride and vinylidene chloride, copolymers of vinyl chloride and acrylonitrile, copolymers of vinylidene chloride and acrylonitrile, and copolymers of styrene and
  • methacrylate and copolymers of methyl methacrylate and up to about 70 percent by weight of orthochlorostyrene.
  • the unexpanded microspheres contain fluid,
  • a blowing agent which is conventional for microspheres of the type described here.
  • the blowing agent is 5 to 30 percent by weight of the microsphere.
  • the microspheres can be added in different manners, as dried particles, wet cakes, or in a suspension, e.g., in an alcohol such as isopropanol.
  • the microspheres can also be added in a pre-expanded form.
  • the unexpanded particulate desirably is in the size range of from about 0.5 micrometer to about 200 micrometers, preferably from 1 micrometer to 100 micrometers, most preferably from 3 micrometers to 50 micrometers.
  • the volume of the expandable particulate increases by a factor of at least 1.5, preferably a factor of at least 5, and most preferably a factor of at least 10, and may even be as high as a factor of about 100.
  • Expancel polymeric microspheres (Nobel Industries, Sundsvall, Sweden) expand from an approximate diameter of 10 micrometers in the
  • V f and r f are the final volume and radius of the expandable particulate, respectively, after expansion, and V i and r i are the corresponding initial values for the unexpanded particulate.
  • Expanded particulate provides increased interstitial porosity in the sheet material.
  • compositions that are useful as expandable particulate can be found in U.S. Patent No. 3,615,972. A further description of compositions useful as expandable particulate in the present invention is given in U.S. Patent No. 4,483,889.
  • expandable hollow polymeric microspheres useful in the present invention include those made of poly(vinylidene chloride-co-acrylonitrile) such as ExpancelTM 820, ExpancelTM 642, ExpancelTM 551, ExpancelTM 461, and
  • blowing or raising agents may be incorporated within the polymerization process. They can be volatile fluid-forming agents such as aliphatic hydrocarbons including ethane, ethylene, propane, propene, butene, isobutene, neopentane, acetylene, hexane, heptane, or mixtures of one or more such aliphatic hydrocarbons preferably having a number average molecular weight of at least 26 and a boiling point at atmospheric pressure about the same
  • blowing agents are halocarbons such as perfluorobutanes, perfluoropentanes,
  • dichlorodifluoromethane chlorotrifluoromethane, trichlorotrifluoroethane, heptafluorochlorocyclobutane, and hexafluorodichlorocyclobutane
  • tetraalkyl silanes such as tetramethyl silane, trimethylethyl silane, trimethylisopropyl silane, and trimethyl-n-propyl silane, all of which are commercially available.
  • the shape of the expandable particulate is the shape of the expandable particulate.
  • spherical i.e., it may be irregular. Other shapes can easily be envisioned such as urnlike as described in U.S. Patent No. 3,615,972.
  • the shape and orientation of the expandable particulate in the composite article determine the anisotropy of the expansion step. Where essentially spherical expandable particles are used, heating leads to isotropic expansion of the composite, i.e., there is no preferred direction of expansion and all three axes expand uniformly so that the overall shape of the article does not change, only its size. Other physical constraints that may have been imposed on the article, such as during processing or by
  • anchoring one part of the article prior to expansion may lead to less than perfect isotropic expansion where essentially spherical expandable particulate is used.
  • the volume of the composite article increases.
  • the percent volume increase is dependent on a number of factors such as the loading of expandable particulate in the composite and the molecular weight of the polymeric shell of the expandable particulate.
  • the decrease in article density is inversely
  • Thickness of the composite article prior to expansion can range from about 0.0127 cm to about 0.32 cm, preferably from about 0.018 cm to 0.25 cm, most preferably from about 0.025 cm to about 0.127 cm. When the article is too thin, it has very little structural integrity while articles having thicknesses outside of the given range may be difficult to form. Thickness after expansion is dependent on several factors, as stated above. Thinner articles can be made by
  • particulate useful in the sheet-like articles of the present invention are disclosed therein.
  • the sorptive particulate material (which can be one material or a combination of materials) useful in the present invention is non-swellable in aqueous and organic media and is substantially insoluble in water or the elution solvent. Not more than 1.0 gram of particulate will dissolve in 100 g. of aqueous media or elution solvent into which particulate is mixed at 20°C.
  • the sorptive particulate material can be carbon, an organic compound, a polymer, or an inorganic oxide such as silica, alumina, titania, zirconia, and other ceramics, or it can be ion exchange or chelating particles.
  • Preferred particulate material are silica and zirconia, with silica being particularly preferred because of the ease in bonding a variety of hydrophobic and semi-hydrophobic coatings onto its surface and because they are commercially available.
  • Silica is available from Aldrich Chemical Co.
  • Zirconia is available from Z. Tech Corporation (Bow, NH).
  • Other inorganic oxides are available from Aldrich Chemical Co.
  • Suitable sorptive particles for the purposes of this invention include any particle which can be coated with insoluble, non-swellable sorbent material or the surface (external and/or internal) of which can be derivatized to provide a coating of insoluble,
  • non-swellable sorbent material non-swellable sorbent material.
  • Preferred supports for such coatings include carbon and inorganic oxide particles, most preferably silica particles. Such particles having coated surfaces are well known in the art, see, for example, Snyder and Kirkland,
  • crosslinking of polymers or the coatings can be any crosslinking of polymers or the coatings.
  • Sorptive coatings which can be applied to silica particulate can be either thin mechanical coatings of insoluble, non-swellable polymers such as crosslinked silicones, polybutadienes, etc. or covalently bonded organic groups such as aliphatic groups of varying chain length (e.g., C 2 , C 8 , and C 18 ) and aliphatic or aromatic groups containing amine, nitrile, hydroxyl, chiral, and other functionalities which alter the polarity of the coating.
  • the silica, or other support particle acts primarily as a carrier for the organic coatings and the particles are
  • the variation in chemical composition of the coatings provides selectivity in molecular separations and polarity.
  • the sorptive particulate material may have a spherical shape, a regular shape or an irregular shape.
  • Sorptive particulate material which has been found useful in the invention has an apparent size within the range of 0.1 to about 600 micrometers, preferably in the range of 1 to 100 micrometers. It has been found advantageous in some instances to employ particulate materials in two or more particle size ranges falling within the broad range. As an example, particles having an average size in the range of 0.1-30
  • micrometers and even up to 100 micrometers having chromatographic activity may be employed in combination with particles having an average size in the range 1 to 250 micrometers acting as a property modifier.
  • Particles useful in the present invention have water sorptive capacity less than 10% by weight, preferably less than 1% by weight. As noted above, particles which undergo dimensional changes due to water swellability are less desirable. In view of the teachings of U.S. Patents 4,565,663 and 4,460,642, it is surprising that hydrophobic particles and other non-swellable particles enmeshed in PTFE provide superior chromatographic articles compared to
  • the active sorbent particles useful in the present invention can be pre-mixed with a property modifier which can function, for example, as a
  • non-swellable property modifiers can be coated particles (e.g., cation exchange resins), calcium carbonate, ammonium carbonate, kaolin, sugar, polyethylenes, polypropylenes, polyesters, polyamides, polyurethanes, polycarbonates, zeolites, chitin, vermiculite, clay, ceramics, ion exchange and chelating particles, and the like.
  • coated particles e.g., cation exchange resins
  • calcium carbonate e.g., ammonium carbonate, kaolin, sugar, polyethylenes, polypropylenes, polyesters, polyamides, polyurethanes, polycarbonates, zeolites, chitin, vermiculite, clay, ceramics, ion exchange and chelating particles, and the like.
  • These property modifier materials can be present in an amount in the range of 0 to 28.99 parts per part of PTFE, preferably 0 to 9.00 parts per part of PTFE, provided that the sorbent non-
  • modifier particulate can include chromatographically inactive materials such as low surface area glass beads or bubbles to act as property modifiers and processing aids. It is
  • particulate can be added at low levels (up to 10 weight percent of particulate) to aid in visualizing sample components to be separated.
  • component bands can be useful for diagnostic purposes.
  • a limited amount of water-swellable property modifiers can be useful as a processing aid.
  • Representative swellable property modifiers include starch, chitosan, modified starches such as SephadexTM and SepharoseTM starches (Pharmacia, Sweden), agarose, polymethacrylates,
  • styrene-divinylbenzene copolymers polyacrylamides, cellulosics, and coated particles (e.g., silica coated with a polyacrylamide).
  • coated particles e.g., silica coated with a polyacrylamide.
  • Water-swellable materials may be used as a thin coating on non-swellable particulate.
  • the preferred method of manufacture of the article of the invention utilizes an emulsion of PTFE with a masking agent added to modify the hydrophobic particle surface/water interaction and allowing rapid wetting of the surface of the hydrophobic particulate.
  • Preferred masking agents are polar organic compounds such as alcohols, amines, acids, etc. with the preferred group being alcohols due to their efficacious removability as by solvent extraction or drying after formation of the article.
  • the PTFE composite sheet material of the invention is prepared by dry blending the
  • particulate/masking agent mixture to form a mass having a putty-like or dough-like consistency.
  • the sorptive capacity of the solids of the mixture is noted to have been exceeded when small amounts of water can no longer be incorporated into the mass without separation. Care should be taken to ensure that the ratio of water to masking agent does not exceed 3:1. This condition should be maintained throughout the entire mixing operation.
  • the putty-like mass is then subjected to intensive mixing at a temperature maintained below the expansion temperature of the expandable particulate for a time sufficient to cause initial fibrillation of the PTFE particles. Minimizing the mixing at the specified temperature is essential in obtaining optimal
  • Mixing times will typically vary from 0.2 to 2 minutes to obtain the necessary initial fibrillation of the PTFE particles.
  • Initial fibrillation causes partial disoriented fibrillation of a substantial portion of the PTFE particles.
  • Initial fibrillation will be noted to be at an optimum within 60 seconds after the point when all components have been fully incorporated together into a putty-like (dough like) consistency. Mixing beyond this point will produce a composite sheet of inferior separations and chromatographic properties.
  • the devices employed for obtaining the necessary intensive mixing are commercially available intensive mixing devices which are sometimes referred to as internal mixers, kneading mixers, double-blade batch mixers as well as intensive mixers and twin screw compounding mixers.
  • the most popular mixer of this type is the sigma-blade or sigma-arm mixer.
  • Some commercially available mixers of this type are those sold under the common designations Banbury mixer, Mogul mixer, C. W. Brabender Prep mixer and C. W. Brabender sigma blade mixer.
  • Other suitable intensive mixing devices may also be used.
  • the putty-like mass is then transferred to a calendering device where it is calendered between rolls maintained below the expansion temperature of the expandable particulate, preferably at room temperature, to cause additional fibrillation and consolidation of the PTFE particles, while maintaining the water level of the mass at least at a level of near the absorptive capacity of the solids, until sufficient fibrillation occurs to produce the desired chromatographic sheet material.
  • the calendering rolls are made of a rigid material such as steel.
  • a useful calendering device has a pair of rotatable opposed calendering rolls each of which may be adjusted toward the other to reduce the gap or nip between the two.
  • the gap is adjusted to a setting of about 10 millimeters for the initial pass of the mass and, as calendering operations progress, the gap is reduced until adequate consolidation occurs.
  • the sheet is folded and then rotated 90° to obtain biaxial fibrillation of the PTFE particles. Smaller rotational angles (e.g., 20 to less than 90°) may be preferred in some chromatographic or separations applications to reduce calender biasing, i.e., unidirectional fibrillation and orientation.
  • the calendered sheet is then dried under
  • the preferred drying temperature range is from 20°C to about 50°C.
  • the most convenient drying method involves suspending the composite sheet at room temperature for at least 24 hours. The time for drying may vary depending upon the particular composition, some particulate materials having a tendency to retain water more than others.
  • the resulting composite sheet has uniform porosity (homogeneous throughout) and a void volume of at least 30% of the total volume and up to 80%, preferably 40 to 60 percent.
  • the PTFE aqueous dispersion employed in producing the PTFE composite sheet of the invention is a
  • the PTFE aqueous dispersion will contain about 20% to about 70% by weight solids, the major portion of such solids being PTFE particles having a particle size in the range of about 0.05 to about 0.5 micrometer.
  • Commercially available PTFE aqueous dispersions may contain other ingredients, for example, surfactant materials and stabilizers which promote continued suspension of the PTFE particles; these dispersions are less desirable for separations and purification applications.
  • TeflonTM 30 and TeflonTM 30B contain about 59% to about 61% solids by weight which are for the most part 0.05 to 0.5 micrometer PTFE particles and from about 5.5% to about 6.5% by weight (based on weight of PTFE resin) of non-ionic wetting agent, typically octylphenol
  • TeflonTM 42 contains about 32 to 35% by weight solids and no wetting agent. FluonTM PTFE, having reduced surfactant levels, is available from ICI, Exton, PA.
  • the polytetrafluoroethylene fibrillated network be tight enough to support the enmeshment of the expandable particulate and sorptive particulate so that the final composite has sufficient structural integrity to be handled.
  • the sorptive particulate and energy be tight enough to support the enmeshment of the expandable particulate and sorptive particulate so that the final composite has sufficient structural integrity to be handled.
  • expandable particulate do not easily dislodge from the final composite, i.e., they do not fall out of the article when the article is handled.
  • PTFE fibrillated network is that PTFE fibrils are able to flow or draw out as the expandable particulate expands, thereby maintaining the structural integrity of the article.
  • the poor bonding of PTFE to the expandable particulate also allows the fibrils to "slide" from a given
  • microbubble's surface during the expansion step i.e., there is poor adhesion of the fibrils to the polymeric shell of the microbubble.
  • the useful range of fibrillated polymer in the final composites can be from about 2% to about 50% by weight, preferably from 3% to 40%, and most preferably from 5% to 25%, based on the total weight of the composite.
  • Energy can be provided to the composite article to cause expansion of the expandable particulate by any of a number of means, including thermal energy from a heat source such as an oven, steam, or a heat gun, radiant energy such as that given off by an infrared light bulb and a laser such as a carbon dioxide laser, and other means known to those skilled in the art.
  • a heat source such as an oven, steam, or a heat gun
  • radiant energy such as that given off by an infrared light bulb and a laser such as a carbon dioxide laser
  • a laser such as a carbon dioxide laser
  • expansion step are dependent on the type of polymer used in the microbubble and on the particular blowing agent used. Typical temperature ranges are from about 20°C to about 200°C, preferably from 50°C to 175°C, most preferably from 70°C to 160°C. Nobel Industries provides a series of expandable bubbles which expand at different temperatures. A more complete description of various polymers and blowing agents can be found in U.S. Patent No. 3,615,972. Further discussion of blowing agents in general can be found in U.S. Patent Nos. 4,640,933 and 4,694,027.
  • the length of time required for full expansion of the composite article to occur is dependent on the particular blowing agent, the nature of the polymeric shell of the bubble, and the efficiency of heat
  • polymeric shell is sufficient to allow full expansion. In cases where heat transfer to the article is much more efficient, such as with the use of steam as a heat source, expansion can occur much more quickly,
  • the present invention provides sheet-like articles which have great utility in separations and purification applications by controlling porosity by use of expandable particulate.
  • porosity greatly enhances the utility of chromatographic and separations articles.
  • Two types of porosity are involved: 1) the internal porosity of the sorptive particles and 2) the flow through or interstitial porosity of the composite article.
  • Proper choice of the sorptive particle porosity depends on the intended application, typically 60 to 100 Angstrom pores for small molecules such as drugs, pesticides, pollutants, etc., and 200 to 1000 Angstrom pores for large biomolecules.
  • Type of particulate includes both organic and inorganic materials and determines the sorptive or reactive specificity of the composite article. Interstitial porosity controls the distance between sorptive particles which determines the
  • the present invention typically utilizes 8-10 micrometer sorbent particles with 60 Angstrom internal pores and high surface area, e.g., 100-500 m 2 /gm, for efficient separations. Interstitial porosity controlled by the expandable polymeric particulate determines the rate at which fluids can be passed through the composite
  • Typical interstitial porosity for separation articles of the present invention range between 0.1 and 10 micrometers.
  • the resultant composite article has great utility in rapid and efficient processing of fluids to isolate pollutants, drugs, and biomolecules in
  • the articles of the present invention are uniquely suited in separations devices where elimination of voids and channels is desirable at confining surfaces, such as in cylindrical tubes or columns between flat restraining plates, or in any confined geometric space.
  • the article either in the form of a flat sheet (round, square, or any geometric shape) or roll, can snugly fill and conform to the shape of a confined volume.
  • a chromatograph column or cartridge can be loosely fitted with a rolled sheet, then energy applied to the composite column or
  • a group of seven chromatographic sheets comprising a PTFE fibrillated matrix and a combination of TLC silica (Aldrich Chemical Co.) and Expancel 551DU polymeric particles enmeshed therein was prepared as follows:
  • Varying ratios of Expancel 551 DU microspheres and TLC grade silica were dry blended to obtain a range from 0% to 50% by weight Expancel microspheres with respect to silica particulate.
  • Sample 1 the 0% sheet, was made by mixing 20 g silica with 7.1 g Fluon PTFE emulsion containing 27.9 weight percent solids.
  • isopropanol:water was then added and blending occurred to obtain a mass with dough-like consistency.
  • the mass was then calendered with a roll temperature of 38 °C. and a gap between the rolls of 0.38 cm.
  • the sheet is folded and rotated 90 degrees to obtain biaxial fibrillation of the PTFE particles.
  • the gap between the calendering rolls was reduced in increments of 0.13 cm and the sheet
  • microspheres silica were 0.04:19.96, 0.20:19.80,
  • FIG. 1 shows the effect of the weight percent of Expancel microspheres on TLC elution rates after expansion.
  • the amounts of Expancel microspheres were varied from 0.2 to 50% and a standard TLC test dye mixture (IV 30-04, available from Analtech, Inc., Newark, DE) was used to determine the effect of
  • FIG. 1 shows the TLC solvent front rate for samples B, C, D, and E, listed above at a solvent front distance of 40 mm before expansion (plot G) and after expansion (plot H).
  • the upper curve for the unexpanded article shows a slight increase in solvent front rate as the percentage of Expancel microbubbles with respect to silica is increased. This may be due to the enhanced "wetting" characteristics of the
  • Expancel particles The lower curve for the expanded article shows the unexpected parallel relationship between unexpanded and expanded articles over the 1 to 20% concentration range. The increased rate is not directly proportional to the Expancel particulate concentration. This indicates that the more preferred range of Expancel particulate concentration is from 1 to 10% and the most preferred range for TLC
  • FIG. 3 is a plot of the interstitial porosity before (plot J) and after (plot K) thermal expansion of one of the formulations (6% Expancel microspheres in TLC silica).
  • the unexpanded article had a mean pore size of 1.7 micrometers while the article after expansion had a mean pore size of 5.8 micrometers as measured with a Coulter PorometerTM
  • Table 3 shows the data obtained for the thickness of the various formulations before and after thermal expansion at 120°C for 3 minutes.
  • microspheres and C 18 bonded silica to obtain a range from 1% to 50% by weight Expancel with respect to silica particulate.
  • Sample 8 the 1% sheet, was made by mixing 0.25 g Expancel microspheres and 24.75 g C 18 silica with 8.9 gm Fluon PTFE emulsion from ICI
  • Example 1 containing 27.9 weight percent solids. Twenty-six g of 50:50 volume percent isopropanol:water was then added and the mix blended to obtain a mass with dough-like consistency. The mass was then calendered at a roll temperature of 38°C. After the initial calendering, the sheet was folded and rotated 90 degrees to obtain biaxial fibrillation of the PTFE particles. The gap between the calendering rolls was reduced as in Example 1 and the sheet recalendered. Folding, rotating the sheet, reducing gap, and recalendering was repeated according to Example 1 until the composite sheet thickness was 0.05 cm. This procedure was repeated for samples 9, 10, and 11 with the exception that the weights of Expancel:C 18 silica were 1.25:23.75,
  • the four composite sheets then contained 1.0, 5.0, 20.0, and 50.0 weight percent Expancel microspheres with respect to C 18 silica particulate.
  • the composite sheets were dried at room temperature for 24 hours.
  • FIG. 4 is a plot (L) of the flow data in Table 4. It is to be noted that the flow rates were not a linear function of the expanded Expancel microbubble concentration. Table 5 illustrates the relationship observed between levels of Expancel microbubbles and ability of the composite articles to extract hydrophobic
  • pollutants such as phthalates from water.
  • One liter water samples containing trace levels (100 ppb) of dimethyl-, diethyl-, and dibutyl-phthalates were filtered through sample articles 8 through 11. The phthalates were then recovered from the sample
  • the expanded column article efficiently trapped the dye at the top of the column with little evidence of voids or channeling between the original individual layers or the particle-wall interface which is commonly observed with conventional particle packed columns. It is known in the art to collapse flexible wall columns inward by external radial compression to help eliminate voids and channels at the column wall interface.
  • the composite sheet of this invention which comprises a combination of sorptive particles and expandable microspheres in a PTFE matrix expands radially outward to eliminate voids and
  • the unexpanded composite article of this invention can be placed in a variety of confining geometrical structures and subsequently expanded to conform to the geometry of the confining structures to provide devices useful in the separation and purification sciences.
  • Forced flow planar chromatography is known in the art and consists of a sorbent sheet material clamped between a rigid plate and a flexible plate which is akin to a bladder, see, for example, L. Botz et al., Journal of Liquid Chromatography, 13(14), 2809-2828 (1990).
  • the side edges are sealed and fluid pressure is applied to the flexible plate compressing the sorbent sheet material between the plates to prevent channeling and eluant/solvent flow over the surfaces of the sorbent sheet.
  • Elutant is forced into the edge of the sheet through an inlet port using a constant flow pump.
  • this invention provides rigid plates (such as glass) between which are sandwiched a PTFE fibril composite comprising expandable microspheres and sorptive particulate enmeshed therein.
  • Formulations of silica or C 18 bonded silica, as in Examples 1 and 2 can be used to effect specific separations.
  • a wide range of other sorptive particulate described in the art can also be used.
  • Use of a composite article of the invention in such a device eliminates the need to apply external pressure and the need for a flexible plate.
  • the internal pressure generated between the two rigid plates as a result of expansion of the expandable particulate in the composite article of the invention is dependent on both the amount of expandable
  • the present invention provides an efficient means of performing forced flow planar chromatography.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Analytical Chemistry (AREA)
  • Organic Chemistry (AREA)
  • Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)

Abstract

Article composite comprenant, sous sa forme non expansée, une matrice en PTFE fibrillée et une combinaison de particules polymères creuses expansibles et de particules à sorption. Lorsqu'on lui applique de l'énergie comme de la vapeur, de la chaleur, ou un laser, cet article subit une expansion et présente un volume des vides supérieur et une densité inférieure. Ces articles sont poreux et sont efficaces pour les opérations de séparation et de purification. Sous une forme plate ou laminée, l'article composite peut être utilisé dans des dispositifs de séparation.
EP92912441A 1991-06-28 1992-05-18 Article pour separation et purification et methode de controle de sa porosite Ceased EP0593515A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US72266591A 1991-06-28 1991-06-28
US722665 1991-06-28
PCT/US1992/004121 WO1993000163A1 (fr) 1991-06-28 1992-05-18 Article pour separation et purification et methode de controle de sa porosite

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EP0593515A1 true EP0593515A1 (fr) 1994-04-27

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JP (1) JPH06508792A (fr)
CN (1) CN1068065A (fr)
AU (1) AU653414B2 (fr)
BR (1) BR9206221A (fr)
CA (1) CA2110156A1 (fr)
IL (1) IL102060A0 (fr)
MX (1) MX9203621A (fr)
WO (1) WO1993000163A1 (fr)

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US5429869A (en) * 1993-02-26 1995-07-04 W. L. Gore & Associates, Inc. Composition of expanded polytetrafluoroethylene and similar polymers and method for producing same
US5468314A (en) * 1993-02-26 1995-11-21 W. L. Gore & Associates, Inc. Process for making an electrical cable with expandable insulation
US5391298B1 (en) * 1993-03-05 1997-10-28 Minnesota Mining & Mfg Method for performing a solid-phase extraction under pressurized conditions
US5876918A (en) * 1993-03-08 1999-03-02 Hydros, Inc. Aligned fiber diagnostic chromatography with positive and negative controls
US5403489A (en) * 1993-06-24 1995-04-04 Minnesota Mining And Manufacturing Company Solid phase extraction method and apparatus
WO1995008661A1 (fr) * 1993-09-21 1995-03-30 W.L. Gore & Associates, Inc. Materiau isolant gonfle et ses procedes de fabrication
US5504281A (en) * 1994-01-21 1996-04-02 Minnesota Mining And Manufacturing Company Perforated acoustical attenuators
EP0741766B1 (fr) * 1994-01-24 1998-09-09 W.L. Gore & Associates, Inc. Joint d'etancheite elastique reutilisable
US5700375A (en) * 1996-04-29 1997-12-23 Minnesota Mining And Manufacturing Company Particle loaded membranes as oxidant scavengers
US5945217A (en) * 1997-10-14 1999-08-31 Gore Enterprise Holdings, Inc. Thermally conductive polytrafluoroethylene article
JP5162476B2 (ja) * 2006-02-13 2013-03-13 ドナルドソン カンパニー，インコーポレイティド ファインファイバーおよび生物活性微粒子を含有するウェブならびにその使用
US8389425B2 (en) * 2010-01-29 2013-03-05 3M Innovative Properties Company Bonded mat and method for making

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US4153661A (en) * 1977-08-25 1979-05-08 Minnesota Mining And Manufacturing Company Method of making polytetrafluoroethylene composite sheet
IL57710A (en) * 1978-07-07 1982-11-30 Klein Max Mats for adsorption and filtration of liquids
SE8204595L (sv) * 1982-08-05 1984-02-06 Kema Nord Ab Forfarande for framstellning av hartsimpregnerade fiberkompositmaterial
US4496461A (en) * 1983-06-17 1985-01-29 Amf Incorporated Chromatography column
US4540625A (en) * 1984-01-09 1985-09-10 Hughes Aircraft Company Flexible air permeable non-woven fabric filters
US4810381A (en) * 1987-12-28 1989-03-07 Minnesota Mining And Manufacturing Company Composite chromatographic article

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WO1993000163A1 (fr) 1993-01-07
AU2008892A (en) 1993-01-25
AU653414B2 (en) 1994-09-29
CA2110156A1 (fr) 1993-01-07
BR9206221A (pt) 1995-03-14
JPH06508792A (ja) 1994-10-06
IL102060A0 (en) 1992-12-30
MX9203621A (es) 1992-12-01
CN1068065A (zh) 1993-01-20

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