SOLVENT-FREE PRODUCTION OF POROUS POLYMER STRUCTURES

Abstract

A method for manufacturing of porous polymer structures, in particular membranes, the method comprising the steps of providing a mixture of one or more polymers and one or more salt nano- and/or microparticles, primary shaping said blend, and removing said one or more salt particles, wherein at least part of the one or more salt nano- and/or microparticles is one or more solid acids, and whereby the ratio of polymer-to-particle is in the range of 3:1 to 1:10 by weight. Also provided are mixtures suitable to obtain such porous polymer structures, porous polymer structures as described herein, shaped articles containing such structures, and the use of such porous polymer structures, shaped articles and mixtures.

Claims

1-17. (canceled)

18. A method of manufacturing a porous polymer structure having a pore size of 1 to 5000 nm, comprising the steps of: a) providing a mixture comprising: 1 to 90 wt. % of at least one of one or more polymers and oligomeric precursors thereof, 0.5 to 95 wt. % of at least one of salt nanoparticles and salt microparticles having primary particle sizes between 1 and 50,000 nm, wherein at least part of one or both of said one or more salt nanoparticles and salt microparticles is one or more solid acids, and wherein the ratio of polymer to particles is in the range of 3:1 to 1:10 by weight; d) primary shaping said mixture; and i) removing said one or more salt particles with a non-organic solvent.

19. The method according to claim 18, further comprising step f) subjecting the obtained material to at least one of a drying step and a cooling step.

20. The method according to claim 18, further comprising step g) subjecting the thus obtained material to at least one of further reshaping and further processing.

21. The method according to claim 18, further comprising step h) subjecting the thus obtained material to a polymerization or cross-linking step.

22. The method according to claim 18, further comprising step j) removing the obtained porous polymer structure from said substrate.

23. The method according to claim 22 wherein said step (j) is performed prior to step (i) and, if present, prior to any of a step f), a step g), and a step h).

24. The method according to claim 18, wherein 40 to 85 wt. % of said at least one of the one or more salt nanoparticles and salt microparticles is one or more solid acids.

25. The method according to claim 18, wherein the primary shaping in step (d) is performed by extruding said mixture through a dye to form porous polymer structures with a constant cross section.

26. The method according to claim 18, wherein the primary shaping in step (d) is performed by casting said mixture to form parts with a non-uniform cross section.

27. The method according to claim 18, wherein one or more of the method steps are performed continuously.

28. The method according to claim 18, further comprising step e) coating a substrate with said mixture, wherein said coating step (e) is selected from the group consisting of spraying and roll-to-roll processes.

29. The method according to claim 18, wherein a) one or both of said nanoparticles and microparticles are selected from the group consisting of oxides, carbonates, sulphates, halogenides, nitrates and phosphates; and/or b) one or both of said nanoparticles and microparticles have a particle size of 1 to 50000 nm.

30. The method according to claim 18, wherein said solid ac-id(s) is/are selected from the group consisting of at least one of i) carboxylic acids; and/or ii) sulfonic acids; and iii) phosphonic acids; and iv) pyrophosphoric acid; and v) amino acids; and vi) Lewis acids; and derivatives thereof.

31. The method according to claim 18, wherein said polymer(s) is/are selected from the group consisting of at least one of polysulfones, polyethersulfones, polycarbonates, polystyrenes, polyacrylates, polysiloxanes, polyarylates, polyurethanes, polyesters, polyethers, polyimides, polyamides, halogenated polyolefins, cellulose acetates, liquid crystal polymers, and polymers that can be cross-linked.

32. The method according to claim 18, wherein a) said support material is made of polymer(s), rubber(s), metal(s), ceramic(s) and glass(es); and/or b) wherein said support material is a film, a woven or non-woven textile; and/or c) wherein said support material has a two-dimensional or a three-dimensional shape.

33. The method according to claim 18 comprising an additional step k) exposing an inner bulk material of the primary shaped mixture; wherein step (k) is performed after step (d). and prior to step (i) and, if present, prior to any of a step e) coating a substrate with said mixture, a step f) subjecting the obtained material to at least one of a drying step and a cooling step, a step g) subjecting the thus obtained material to at least one of further reshaping and further processing, and a step h) subjecting the thus obtained material to a polymerization or cross-linking step; or wherein step (k) is performed after step (d) and, if present, after any of a step e) coating a substrate with said mixture, a step f) subjecting the obtained material to at least one of a drying step and a cooling step, a step g) subjecting the thus obtained material to at least one of further reshaping and further processing, and a step h) subjecting the thus obtained material to a polymerization or crosslinking step, and prior to step (i).

34. A mixture for manufacturing porous polymer structures, wherein the mixture comprises: 1 to 90 wt. % of one or more polymers; and 0.5 to 95 wt. % of at least one of salt nanoparticles and salt microparticles having primary particle sizes between 1 and 50,000 nm; wherein at least part of one or both of said one or more salt nanoparticles and salt microparticles is one or more solid acids, and wherein the ratio of polymer:nanoparticle is in the range of 3:1 to 1:10 by weight.

35. The mixture according to claim 34, wherein 40 to 85 wt. % of said at least one of the one or more salt nano-particles and salt microparticles is one or more solid acids.

36. A kit of parts for manufacturing a mixture according to claim 34, wherein a first part comprises at least one of one or more types of salt nanoparticles and one or more types of salt microparticles, wherein at least part of said one or more salt nanoparticles and said one or more salt microparticles is one or more solid acids, and a second part comprises one or more polymers.

37. The kit of parts according to claim 36, wherein 40 to 85 wt. % of said one or more salt nanoparticles and said one or more salt microparticles comprised in said first part is one or more solid acids.

Description

[0177] The present invention is further explained in more detail by means of figures. Unless stated otherwise, like reference numerals are used to refer to the same or similar elements.

[0178] FIG. 1: Schematic view of methods of manufacturing porous polymer structures according to the invention;

[0179] FIG. 2: Schematic illustration of the variability in porous polymer structures obtainable by using different dyes;

[0180] FIG. 3: SEM images of a poly(propylene) membrane not according to the invention;

[0181] FIG. 4: SEM images of a poly(ethylene) membrane according to the invention;

[0182] FIG. 5a: Schematic illustration of a method as disclosed herein comprising a step of exposing the inner bulk material of the primary shaped mixture;

[0183] FIG. 5b: SEM images of a poly(propylene) membrane obtained by the method described in FIG. 5a.

[0184] One embodiment of the inventive method of manufacturing a porous polymer membrane 1 is illustrated in the left column in FIG. 1. In a first step (a), a mixture 2 is provided which contains salt nano- and/or microparticles, wherein at least part of the one or more salt nano- and/or microparticles is one or more solid acids, and a polymer. In a next step (b), the moisture content of mixture 2 is optionally adapted and the components are thoroughly mixed in step (c) to afford a homogeneous blend which is used to coat a substrate 3 in steps (d) and (e). The thus obtained bi-continuous structured network of a polymer and a salt 4 is optionally subjected to a drying and/or cooling step (f) and may be further reshaped and/or processed in step (g). Optionally, the coating 4 can be subjected to a polymerisation or cross-linking step (h). Finally, the nano- and/or microparticles are removed from the coating 4 by a washing solvent in step (i) to afford a substrate-supported porous material 5. The porous polymer film 5 is then removed from the supporting material 3 in step (j) to give membrane 1.

[0185] The right column in FIG. 1 illustrates an alternative embodiment of the inventive method of manufacturing a porous polymer membrane 1, wherein step (j), i.e. the separation of the salt/polymer composite film 4 from the substrate 3, is performed prior to steps (f) to (i). Thus, an unsupported, “free-standing” bi-continuous structured network of a polymer and a salt 5 is obtained first and dissolution of the salt particles in step (i) to afford the porous membrane 1 is performed afterwards.

[0186] FIG. 2 illustrates the variability of the primary shaping step (d) of the mixture 2 comprising polymer, salt nano- and/or microparticles, and at least one solid acid when using different primary shaping techniques. Dye processes (d1) and (d2) can be used to produce continuous structures with constant cross-sections, such as flat films or tubes, respectively. It may be desirable that the part comprises impermeable areas 6 and/or that the part is comprised of more than one material and/or that the part features a non-uniform cross-section. This circumstance is taken into account in FIG. 2 (d3) by the fact that the edges 6 of the exemplary shown hollow cuboid are represented differently from side faces of said cuboid. Such structures can for example be obtained by 2K injection moulding. FIG. 2 further illustrates that the porous structure 1 is then formed by dissolving the extruded or moulded parts in process step (i) to obtain said inventive porous membrane 1 in the form of flat films, tubes or parts comprising multiple materials with different properties.

[0187] To further illustrate the invention, the following examples are provided. These examples are provided with no intent to limit the scope of the invention.

[0188] I. Preparation of Starting Materials

[0189] The preparation of the salt nanoparticles is described in WO2005/087660. The synthesis of calcium carbonate (denoted as CaCO.sub.3), barium carbonate (denoted as BaCO.sub.3), strontium carbonate (denoted as SrCO.sub.3), potassium carbonate (denoted as K.sub.2CO.sub.3) and sodium carbonate (denoted as Na.sub.2CO.sub.3) nanoparticles is shortly described below; an FSP apparatus as described in WO2005/087660 is used.

[0190] a) Preparation of CaCO.sub.3 Nanoparticles:

[0191] Ca-2-Ethylhexanoate in 2-ethylhexanoic acid (Molekula) was diluted with tetrahydrofuran (THF) to a final calcium content of 3.9 wt. %. This precursor is fed (9 ml/min, HNP Mikrosysteme, micro annular gear pump mzr-2900) to a spray nozzle, dispersed by oxygen (9 l/min, PanGas Tech.) and ignited by a premixed methane-oxygen flame (CH.sub.4, 1.2 l/min; O.sub.2, 2.2 l/min). The off-gas is filtered through a glass fibre filter (Whatman Ltd., USA) by a vacuum pump (Busch S. A., Switzerland). The resulting powder is collected on the glass fiber filter and removed by a spatula.

[0192] b) Preparation of BaCO.sub.3 Nanoparticles:

[0193] Ba-2-Ethylhexanoate in 2-ethylhexanoic acid (AlfaAesar) was diluted with tetrahydrofuran (THF) to a final barium content of 4.6 wt. %. The precursor is fed (5 ml/min, HNP Mikrosysteme, micro annular gear pump mzr-2900) to a spray nozzle, dispersed by oxygen (5 l/min, PanGas Tech.) and ignited by a premixed methane-oxygen flame (CH.sub.4, 1.2 l/min; O2, 2.2 l/min). The off-gas is filtered through a glass fibre filter (Whatman Ltd., USA) by a vacuum pump (Busch S. A., Switzerland). The resulting powder is collected on the glass fibre filter and removed by a spatula.

[0194] c) Preparation of SrCO.sub.3 nanoparticles: Sr-2-Ethylhexanoate in 2-ethylhexanoic acid (Strem Chemicals) was diluted with tetrahydrofuran (THF) to a final strontium content of 4.7 wt. %. The precursor is fed (5 ml/min, HNP Mikrosysteme, micro annular gear pump mzr-2900) to a spray nozzle, dispersed by oxygen (5 l/min, PanGas Tech.) and ignited by a premixed methane-oxygen flame (CH.sub.4, 1.2 l/min; O2, 2.2 l/min). The off-gas is filtered through a glass fibre filter (Whatman Ltd., USA) by a vacuum pump (Busch S. A., Switzerland). The resulting powder is collected on the glass fibre filter and removed by a spatula.

[0195] d) Preparation of K.sub.2CO.sub.3 nanoparticles: 20 wt. % of K-2-Ethylhexanoate (AlfaAesar) was dissolved in 2-ethylhexanoic acid and further diluted with tetrahydrofuran (THF) to a final potassium content of 3.5 wt. %. The precursor is fed (5 ml/min, HNP Mikrosysteme, micro annular gear pump mzr-2900) to a spray nozzle, dispersed by oxygen (5 l/min, PanGas Tech.) and ignited by a premixed methane-oxygen flame (CH.sub.4, 1.2 l/min; O.sub.2, 2.2 l/min). The off-gas is filtered through a glass fibre filter (Whatman Ltd., USA) by a vacuum pump (Busch S. A., Switzerland). The resulting powder is collected on the glass fibre filter and removed by a spatula.

[0196] e) Preparation of Na.sub.2CO.sub.3 Nanoparticles:

[0197] 20 wt. % of Na-2-Ethylhexanoate (Aldrich Fine Chemicals) was dissolved in 2-ethylhexanoic acid and further diluted with tetrahydrofuran (THF) to a final sodium content of 2.4 wt. %. The precursor is fed (5 ml/min, HNP Mikrosysteme, micro annular gear pump mzr-2900) to a spray nozzle, dispersed by oxygen (5 l/min, PanGas Tech.) and ignited by a premixed methane-oxygen flame (CH.sub.4, 1.2 l/min; O.sub.2, 2.2 l/min). The off-gas is filtered through a glass fibre filter (Whatman Ltd., USA) by a vacuum pump (Busch S. A., Switzerland). The resulting powder is collected on the glass fibre filter and removed by a spatula.

[0198] II. Preparation of Polymer Membranes

[0199] a) Preparation of a Poly(Propylene) Membrane (not According to the Invention):

[0200] 30 wt. % poly(propylene) resin (Aldrich Chemestry, USA) was heated in a ceramic beaker until the polymer was completely molten.

[0201] 70 wt. % ZnO particles (Hongwu, China) were added under through stirring until a pasty molasses has formed. Said molasses was casted onto a hot metal plate using a metal roller to obtain a thin film. Said film has been left to cool off for 5 min. Finally, the salt particles are dissolved in 1M hydrochloric acid (denoted as HCl) for 10 minutes to reveal the porous structure.

[0202] The formation of porous structure has been confirmed by scanning electron microscopy (Nanosem 450, FEI). As can be seen in FIG. 3, dissolution of the ZnO particles in hydrochloric acid resulted in a porosity which is visible on both the upper side of the membrane (FIG. 3, top left) and the lower side facing the substrate (FIG. 3, top right). The apparent hole sizes are due to the size of the ZnO particles used (50 to 100 nm), whereby not completely dispersed particles, i.e. agglomerates, led to the formation of larger pores in the porous material. The membrane cross-sections shown in the lower line in FIG. 3 show residual ZnO particles in the poly(propylene) matrix (left side) and interconnected pores after repeating the dissolution step (right side).

[0203] b) Preparation of a Poly(Ethylene) Membrane According to the Invention:

[0204] 33 wt. % polyethylene resin (CleanHDPE, Polytechs) was cycled in an extruder (HAAKE MiniLab) at 180° C., 60 rpm. 33 wt. % CaCO.sub.3 particles (Solvay, USA) were gradually added to polymer, running in closed loop mode in the extruder. 33 wt. % sulfamic acid were gradually added to the composite, running in closed loop mode in the extruder. The final composite was extruded and pressed to form a flat film. This film was left to cool off for 5 min. Finally, the salt particles were dissolved in 1M hydrochloric acid (denoted as HCl) for 10 minutes to reveal the porous structure.

[0205] The formation of porous structure has been confirmed by scanning electron microscopy (Nanosem 450, FEI). As can be seen in FIG. 4, dissolution of the CaCO.sub.3 particles in hydrochloric acid resulted in a porosity which is visible on both the upper side of the membrane (FIG. 4, top left) and the lower side facing the substrate (FIG. 4, top right). The apparent hole sizes correlate well with the size of the CaCO.sub.3 particles used (500 to 1000 nm). The membrane cross-section shown in the lower line in FIG. 4 shows a network of interconnected pores which were obtained without repeated washing.

[0206] FIG. 5a shows a schematic illustration of a method as disclosed herein comprising a step (k) of exposing the inner bulk material of the primary shaped mixture. In this embodiment, primary shaping (d) of the mixture comprising polymer and particles by extrusion 7 and calibration 8 leads to a sandwich-like sheet 9 with solid upper and lower surfaces featuring relatively closed pores and at least partially molten polymer in its center. Such a membrane could also be considered symmetrical with respect to its longitudinal section. Two chilled rollers 10 with opposite direction of rotation, as indicated by arrow 11, are installed downstream of the extruder 7 to split the extruded sheet 9 into two parts 12, wherein the temperature of the chilled rollers 10 is set to at most half the temperature of the last zone at the exit of the extruder. Due to the cooled rollers 10, the material adheres to their surface and opens the still warm, “liquid” center of the extruded sheet 9. After cooling and removal of the salt particles with 1M hydrochloric acid, the two membranes 12 thus obtained each have an asymmetrical longitudinal section, with a pore structure that is rather closed on the respective roller side B and rather open on its opposite side A, as confirmed by the scanning electron microscopy images of the respective sides shown in FIG. 5b. The asymmetry of the longitudinal sections of the membranes 12 greatly facilitates and accelerates the complete removal of the salt particles in that the aqueous solvent can easily penetrate the material, especially from the open-pore A side, and produce the porous polymer structure.