POROUS MEMBRANE BASED ON A POLYMER-FILLED FIBROUS STRUCTURE

Abstract

A porous membrane structure includes a fibrous host material, which defines a plurality of inter-fiber voids, and a porous guest polymer that fills at least a subset of the plurality of inter-fiber voids of the fibrous host material. The porous guest polymer facilitates selective transport of materials across the porous membrane structure and provides selective barrier properties to the porous membrane structure. The porous membrane structure may be configured as a protective barrier material for use across a range of applications.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. nonprovisional patent application of, and claims priority under 35 U.S.C. §119(e) to, U.S. provisional patent application Ser. No. 61/493,630, filed Jun. 6, 2011, which application is expressly incorporated by reference herein in its entirety.

APPENDIX AND INCORPORATION THEREOF BY REFERENCE

Each of the following publications and descriptions is incorporated herein by reference in its entirety:

• • a) Jung, Kyung-Hye et al., “Structure-property relationships of polymer-filled nonwoven membranes for chemical protection applications,” made available Jun. 12, 2010 in the Journal of Membrane Science, a copy of which is attached as Appendix A;
  • b) Jung, Kyung-Hye et al., “Chemical protection performance of polystyrene sulfonic acid-filled polypropylene nonwoven membranes,” made available Jul. 1, 2010 in the Journal of Membrane Science, a copy of which is attached as Appendix B; and
  • c) Jung, Kyung-Hye et al., “Synthesis and Characterization of Polymer-Filled Nonwoven Membranes,” submitted to Journal of Applied Polymer Science, a copy of which is attached as Appendix C.
    The disclosure of each of the foregoing publications and descriptions is intended to provide background and technical information with regard to the invention described hereinbelow.

COPYRIGHT STATEMENT

All of the material in this patent document is subject to copyright protection under the copyright laws of the United States and other countries. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in official governmental records but, otherwise, all other copyright rights whatsoever are reserved.

BACKGROUND OF THE PRESENT INVENTION

1. Field of the Present Invention

The present invention relates generally to a porous membrane structure, and, in particular, to porous membrane structures prepared from fiber-based structures and functional polymers that fill the voids within the fiber-based structures.

2. Background

In recent years, there has been growing interest in selective separation membranes and selective barrier membranes for a wide range of military, industrial and consumer applications. Such applications include: supported membranes for use in a wide range of industrial and pharmaceutical processing applications; protective clothing for military and industrial use; personal outerwear and related garments; and batteries and fuel cells. Interest in membrane structure has focused on controlling the pore structure, controlling pore size, controlling the structure of the porous medium to improve selective separation, providing a membrane structure that is both strong and resilient under use conditions, and providing a membrane structure that has a long use life.

Traditional materials used to provide a selective separation membrane structure include hydrogels, polyelectrolytes (namely, ionic polymeric materials of various types, such as anionic, cationic or betaine polymers), blocked hydrophilic non-ionic copolymers, and related polymers. These materials typically swell in water and have generally poor strength and mechanical properties. To address this issue, industry has moved toward two types of structures.

The first such type of membrane structure involves polymer-filled membrane technology consisting of a highly porous, robust, polymeric membrane that functions as the “host” structure and functional “guest” polymers that are used to fill the internal structure of the host film. The host film provides the necessary strength and mechanical properties, and the guest polymers, within the internal structure of the film, provide the functional micro-porous medium. Together they provide a functional membrane that can be optimized for specific applications, including the specific selective material separations or specific selective barrier properties. Examples of technologies that have attempted to address specific needs utilizing this approach are set forth in the following patents and published patent applications:

• • U.S. Patent Application Publication No. to Isomura et al. US 2010/0279204 A1 which is directed to the preparation of a separation membrane for fuel cells that include a porous film, where the pores are filled with a polymeric ion exchange composition that is generated by polymerizing selected monomers within the pores and then functionalizing the polymers;
  • U.S. Pat. No. 7,868,051 to Fukuta et al., which is directed to the preparation of a membrane for fuel cells by filling the voids of a porous membrane with a cross-linking ion exchange resin;
  • U.S. Pat. No. 7,824,820 to Yamaguchi et al., which is directed to the preparation of an electrolyte membrane based on filling the pores of a porous film with a polymer that is capable of conducting protons;
  • U.S. Pat. No. 7,749,629 to Hommura et al., which is directed to the preparation of an electrolyte membrane based on filling the pores of a porous melt-moldable fluoro-chemical resin film with an ion exchange polymer; and
  • U.S. Pat. No. 7,674,349 to Hiraoka et al., which is directed to a method for the continuous production of a functional membrane film based on filling the pores of a porous resin sheet with polymeric precursors that are then polymerized to generate the membrane film.

While polymer-filled, highly porous membranes have much higher strength and mechanical properties as compared against simple unsupported polymer membranes, a significant deficiency in current filled-membrane technologies involves long-term durability, which remains poor. In polymer-filled, highly porous membranes, the host membrane experiences large stresses while suppressing the swelling of the functional guest polymer. As a result, the system often loses its integrity during use, especially in applications where the membranes face repeated hydration and dehydration (i.e., repeated swelling and contraction). Furthermore, the system's ability to function is dictated completely by the volume capacity of the filled pores that provide a complete path through the membrane structure. The system's ability to separate effectively is a function of the guest polymer's ability to selectively transport materials across the filled voids within the membrane structure. The volume percent of “completed paths” through the structure is often limited.

The second type of membrane structure involves supported membranes, which include technologies where the membrane film itself is supported through the use of an external structure. Such structures include a wide array of external support structures ranging from porous metal plates to various types of fabrics. In these membrane structures, the functional membrane provides the desired performance while the external structures provide support and protection for the membrane. Examples of technologies that have attempted to address the development of specific membranes of this type are set forth in the following patents and published patent applications:

• • U.S. Patent Application Publication No. US 2010/0075101 A1 to Tang, which is directed to the preparation of supported separation membranes for gas and liquid materials based on a membrane applied directly to a tricot fabric;
  • U.S. Pat. No. 7,569,616 to Kotera et al., which is directed to the generation of electrolytic ion exchange membranes for fuel cells based on the use of a reinforced inner layer of a fluoro-polymer-based non-woven fabric structure;
  • U.S. Pat. No. 6,919,026 to Hama et al., which is directed to the preparation of specific nonwoven materials to be used as supports for membrane materials;
  • U.S. Pat. No. 6,645,420 to Beck, which is directed to the preparation of a membrane structure based on the incorporation of a unitary, formed carrier fabric to provide support for the formed membrane; and
  • U.S. Pat. No. 6,484,887 to Fukutomi et al., which is directed to the preparation of ion-selective membranes that are supported by woven fabric shaped backings.

While external supports in current supported membrane technologies provide improved stability for the functional membrane structure, such supports, at the same time, tend to restrict flow through the membrane. There are also serious issues with bonding of the membrane to the support structure and maintaining the stability of the bonded structure through the swelling and contractions associated with functional membrane structures. While these types of structures tend to provide for higher transport of materials through the membrane, when one considers interference or diffusion requirements for materials through the external support structures, the net effect is a low-performing and short-lived membrane.

Accordingly, there remains a need for improved, selective separation and selective barrier membranes that provide high strength and long-term structural stability, a high level of permeability, and a high level of selectivity functionality. This and other needs are addressed by one or more aspects of the present invention.

SUMMARY OF THE PRESENT INVENTION

The present invention comprises a porous membrane structure comprising a fibrous host material and a porous guest polymer.

Broadly defined, the present invention according to a first aspect includes a porous membrane structure that includes a fibrous host material and a porous guest polymer. The fibrous host material provides structure to a membrane and defines a plurality of inter-fiber voids. The porous guest polymer fills at least a portion of the inter-fiber voids of the fibrous host material.

In features of this aspect, the fibrous host material may include a woven material; the fibrous host material may include a nonwoven material; and the fibrous host material may include a knit fabric material.

In further features of this aspect, the porous guest polymer may facilitate selective transport of materials across the membrane; and the porous guest polymer may provide selective barrier properties across the membrane.

In still further features of this aspect, the fibrous host material may comprise approximately 3% to approximately 40% of the total weight; the fibrous host material may comprise approximately 5% to approximately 30% of the total weight; the fibrous host material may comprise approximately 10% to approximately 25% of the total weight; the porous guest polymer may comprise approximately 60% to approximately 97% of the total weight; the porous guest polymer may comprise approximately 70% to approximately 95% of the total weight, and the porous guest polymer may comprise approximately 75% to approximately 90% of the total weight.

In still further features of this aspect, the porous guest polymer may include a polymer based on free-radical polymerizations of vinyl, acrylate, or methacrylate intermediates that are chain-extended or cross-linked with di- or poly-functional intermediates; the porous guest polymer may include a polymer based on pre-polymers and reactive intermediates; and the porous guest polymer may include a polymer based on pre-formed polymers that can be applied from solvents or water.

In still another feature of this aspect, the fibrous host material may be a flexible material.

Broadly defined, the present invention according to a second aspect includes a membrane structure substantially as shown and described.

Broadly defined, the present invention according to a third aspect includes a membrane that includes a fibrous host material and a porous guest polymer. The porous guest polymer is configured to provide selective transport of materials across the membrane or selective barrier properties across the membrane.

Broadly defined, the present invention according to a fourth aspect includes a membrane that includes a fibrous host material and a porous guest polymer. The fibrous host material comprises approximately 3% to approximately 40% of the total weight, and the porous guest polymer comprises approximately 60% to approximately 97% of the total weight.

In a feature of this aspect, the fibrous host material may comprise approximately 5% to approximately 30% of the total weight, and the porous guest polymer may comprise approximately 70% to approximately 95% of the total weight. In another feature of this aspect, the fibrous host material may comprise approximately 10% to approximately 25% of the total weight, and the porous guest polymer may comprise approximately 75% to approximately 90% of the total weight.

Broadly defined, the present invention according to a fifth aspect includes a protective barrier material that includes a porous membrane structure. The porous membrane structure includes a fibrous host material, which defines a plurality of inter-fiber voids, and a porous guest polymer that fills at least a subset of the plurality of inter-fiber voids of the fibrous host material. The porous guest polymer facilitates selective transport of materials across the porous membrane structure and provides selective barrier properties to the porous membrane structure.

In features of this aspect, the fibrous host material may include a nonwoven material; and the fibrous host material may be a flexible material.

In further features of this aspect, the fibrous host material may comprise approximately 3% to approximately 40% of the total weight of the porous membrane structure; the fibrous host material may comprise approximately 5% to approximately 30% of the total weight of the porous membrane structure; and the fibrous host material may comprise approximately 10% to approximately 25% of the total weight of the porous membrane structure.

In still further features of this aspect, the porous guest polymer may comprise approximately 60% to approximately 97% of the total weight of the porous membrane structure; the porous guest polymer may comprise approximately 70% to approximately 95% of the total weight of the porous membrane structure; and the porous guest polymer may comprise approximately 75% to approximately 90% of the total weight of the porous membrane structure.

In still further features of this aspect, the porous guest polymer may facilitate transfer of water vapor across the porous membrane structure and may provide barrier properties against a toxic chemical; the porous guest polymer may include a PAMPS polymer; the porous guest polymer may include a PSS polymer; and the porous guest polymer may include a PMA polymer.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, embodiments, and advantages of the present invention will become apparent from the following detailed description with reference to the drawings, wherein:

FIG. 1 is a graph illustrating tensile properties of porous membranes based on polymer-filled fibrous structures;

FIG. 2 is a graph illustrating vapor permeability of PAMPS membranes with respect to moisture transport and transport of chemical warfare agent simulants (represented by the transport of dimethyl methyl phosphate (DMMP)).

FIG. 3A is a graph illustrating water vapor permeability of membranes based on polymer-filled fibrous structures; and

FIG. 3B is a graph illustrating DMMP vapor permeability of membranes based on polymer-filled fibrous structures.

DETAILED DESCRIPTION

As a preliminary matter, it will readily be understood by one having ordinary skill in the relevant art (“Ordinary Artisan”) that the present invention has broad utility and application. Furthermore, any embodiment discussed and identified as being “preferred” is considered to be part of a best mode contemplated for carrying out the present invention. Other embodiments also may be discussed for additional illustrative purposes in providing a full and enabling disclosure of the present invention. Moreover, many embodiments, such as adaptations, variations, modifications, and equivalent arrangements, will be implicitly disclosed by the embodiments described herein and fall within the scope of the present invention.

Accordingly, while the present invention is described herein in detail in relation to one or more embodiments, it is to be understood that this disclosure is illustrative and exemplary of the present invention, and is made merely for the purposes of providing a full and enabling disclosure of the present invention. The detailed disclosure herein of one or more embodiments is not intended, nor is to be construed, to limit the scope of patent protection afforded the present invention, which scope is to be defined by the claims and the equivalents thereof. It is not intended that the scope of patent protection afforded the present invention be defined by reading into any claim a limitation found herein that does not explicitly appear in the claim itself.

Thus, for example, any sequence(s) and/or temporal order of steps of various processes or methods that are described herein are illustrative and not restrictive. Accordingly, it should be understood that, although steps of various processes or methods may be shown and described as being in a sequence or temporal order, the steps of any such processes or methods are not limited to being carried out in any particular sequence or order, absent an indication otherwise. Indeed, the steps in such processes or methods generally may be carried out in various different sequences and orders while still falling within the scope of the present invention. Accordingly, it is intended that the scope of patent protection afforded the present invention is to be defined by the appended claims rather than the description set forth herein.

Additionally, it is important to note that each term used herein refers to that which the Ordinary Artisan would understand such term to mean based on the contextual use of such term herein. To the extent that the meaning of a term used herein—as understood by the Ordinary Artisan based on the contextual use of such term—differs in any way from any particular dictionary definition of such term, it is intended that the meaning of the term as understood by the Ordinary Artisan should prevail.

Furthermore, it is important to note that, as used herein, “a” and “an” each generally denotes “at least one,” but does not exclude a plurality unless the contextual use dictates otherwise. Thus, reference to “a picnic basket having an apple” describes “a picnic basket having at least one apple” as well as “a picnic basket having apples.” In contrast, reference to “a picnic basket having a single apple” describes “a picnic basket having only one apple.”

When used herein to join a list of items, “or” denotes “at least one of the items,” but does not exclude a plurality of items of the list. Thus, reference to “a picnic basket having cheese or crackers” describes “a picnic basket having cheese without crackers,” “a picnic basket having crackers without cheese,” and “a picnic basket having both cheese and crackers.” Finally, when used herein to join a list of items, “and” denotes “all of the items of the list.” Thus, reference to “a picnic basket having cheese and crackers” describes “a picnic basket having cheese, wherein the picnic basket further has crackers,” as well as describes “a picnic basket having crackers, wherein the picnic basket further has cheese.”

Referring now to the drawings, the preferred embodiments of the present invention are next described. The following description of one or more preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

In accordance with one or more embodiments of the present invention, structured membranes can be generated by using a fiber-based “host” matrix, where the voids within the fiber-based host matrix are filled with a functional “guest” polymer. These fiber-based, filled membrane structures address many of the deficiencies that are prevalent in the current membrane technologies. Membrane structures in accordance with the present invention have high long-term structural stability, a high concentration of effective paths through the functional guest polymer (i.e., higher level of transport through the membrane), and an interactive mechanism between the structural component of the membrane and the functional guest polymer that enhances the ability of the functional guest polymer to provide effective separation (i.e., tortuosity).

In these structured membranes, the fabric structure provides membrane strength and mechanical properties while supporting membrane integrity during its use life. Further, these membrane structures provide a novel, flexible matrix for the functional guest polymers. Still further, these membrane structures support a high level of transport by providing a high concentration of effective paths through the functional guest polymer and by also providing a level of tortuosity, within the fiber-based structure, which has been shown to enhance the separation efficiency of the functional guest polymer. Membranes in accordance with the present invention thus may have significant advantages over current membrane technology in terms of being able to supply desirable properties such as high levels of material transport, high performance in selective separations, structural strength, mechanical stability, and a range of tunable properties including flexibility, chemical resistance, and penetration resistance.

Fiber-based structures suitable for this application include a wide range of woven, non-woven and knit fabric structures. The wide range of fiber-based structures that can be used in this application provides for a wide, diverse range of membrane structures, which results in a wide range of performance properties that can be generated. In addition, by controlling the structure of the fiber structure and the diameter of the fibers used in the structure, it is possible to generate controlled levels of tortuosity within the final membrane structure, which can significantly modify the selective character of the separation that is generated using the membrane. The flexibility of the fiber-based structures can be matched to that of the guest polymer that is used to fill the voids within the structure and, in this way, a product can be designed that has sufficient internal flexibility to withstand repeated swelling and contractions associated with the guest functional polymer, thereby providing separation membranes that have long-term mechanical and material stability.

Advantages associated with using a fiber-based matrix as the host framework for a polymer filled membrane include:

• • the fiber-based structure can provide strength together with the flexibility needed to support long term mechanical and functional stability within the membrane structure;
  • the fiber-based structure has a high internal capacity for the guest functional polymer, thereby generating high levels of transport across the membrane structure;
  • the host framework can be constructed from a wide range of different polymers that can be selected for desirable secondary properties such as chemical resistance, low ion interaction, or structural flexibility;
  • the host structure can be designed to improve the performance of the guest functional polymer by providing tortuosity within the structural matrix, which can be used to generate improved separation properties;
  • the thickness and the ratio of fiber-based host matrix to functional guest polymer within the membrane can be precisely controlled;
  • the functional and mechanical properties of the fiber-based structure can be tuned by controlling the volume fraction of the guest functional polymer occluded in the pores of the host framework; and
  • the nature of the system provides a high level of flexibility in the types of functional guest polymers that can be considered, thereby generating the technology for supporting a full range of membrane applications.

The present invention includes a fibrous structure (the “host” structure) that has been filled with a hydrophilic polymer composition (the “guest” polymer). The composition of the guest polymer can then be matched to the properties of the host structure and to the requirements of the application that is being envisioned for the membrane. Together, the host structure and guest polymer can provide a high-performance membrane product.

The fibrous host structure can be constructed from a wide range of fibrous materials depending on the specifics of the application. Such fibrous material may include, but are not limited to: polyolefin polymers, such as polyethylene and polypropylene; condensation polymers, such as the wide range of polyester and nylon polymers that are commercially available; high-performance polymers such as polyphenylene sulfide, KEVLAR or NOMEX; solution or solvent spun polymers, such as acetates, acrylics and rayon; natural fibers, such as cotton, wool and silk; highly polar polymers, such as polyvinyl alcohol and modified polyvinyl alcohol polymers; and other specialty polymers, such as elastaines, flame-retardant polymers, or fibers based on polymer structures specifically designed for a membrane application. The present invention is not limited to the nature of the polymer used in the fiber, the selection of which may be significant to particular applications.

Fibrous host structures can also be selected from a wide range of fabric structures that are available. Such fabric structures may include, but are not limited to: woven materials of various structures, including various weaves and modified woven structures, woven materials prepared using fine denier and micro-denier fibers, and 3-D woven structures; knit structures of various types; and nonwoven materials, including carded and point bonded fabrics, carded and powder bonded or fiber bonded fabrics, spunbond, SMS or related bonded fabrics, spun lace or needled fabrics, air lay or wet lay fabrics, and the like. The present invention is not limited to the nature of the host fabric structure that is used to support and provide tortuosity within the membrane, the selection of which may be significant to particular membrane applications.

The guest polymer composition can also be selected from a wide range of available polymeric structures. Such polymers may be applied as monomers and then reacted within the fibrous matrix to generate the guest polymer. Such polymers may also be applied as pre-polymers and then chain-extended and/or cross-linked within the fibrous matrix to generate the guest polymer. Additionally, specific polymers may be applied as a solvent solution that is deposited within the fibrous matrix as the solvent is removed. There are a wide range of guest polymeric materials that can be utilized to generate functional membrane materials that fill the voids within the fiber-based structure.

For instance, guest polymeric materials may include hydrogels or polyelectrolytes. Additionally, guest polymeric materials may include polymers that are based on free-radical polymerizations of vinyl, acrylate, or methacrylate intermediates that are cross-linked with di- or poly-functional intermediates. Such materials are applied as monomers and then free-radical polymerized within the matrix. The inclusion of di- or-poly-functional materials in the formulation, appropriate to the reactive system, function to cross-link and stabilize the membrane final structure.

Further, guest polymeric materials may include functional pre-polymers that are prepared and applied to the fiber-based structure along with chain extension and/or cross-linking materials based on reactive, poly-functional intermediates. For hydroxyl or amine functional pre-polymers, suitable reactive cross-linking materials can include epoxy, blocked urethane, or similar functional intermediates. Conversely, the pre-polymer may be reactive functionalized (such as epoxy, blocked urethane or the like) and the chain extending/cross-linking material would be a di- or poly-functional pre-material or polymer having functional groups suitable to extending and cross-linking the polymeric material. In either case, polymerization would be completed by a heating process to generate the stabilized membrane.

Still further, guest polymeric materials may include polymers that are prepared and applied to the fiber-based structure as solvent- or water-based solutions and that then generate a stable membrane structure once the solvent/water is removed.

For functional activity, the polymers generated are typically polar structures with a high concentration of ionic or polar non-ionic structures. By cross-linking the structures, one obtains a stable, water-swellable membrane structure that is then the basis for selective movement of materials across the membrane. The present invention is not limited to the nature of the guest polymer that provides the functional medium within the membrane, the selection of which may be significant to particular membrane applications.

In accordance with the present invention, advantages can be obtained from the generation of membrane structures that are based on a host fibrous structure and a guest polymer that fills the voids within the host fibrous structure. Utilizing this technology leads to significant and previously unexpected advantages as compared with existing membrane technologies. Such advantages include, but are not limited to: membranes that have high strength and avoid many of the issues that shorten the working life or reduce the efficiency of other membrane structures; membranes that have very high material transfer rates that are not limited by the structure of external secondary supporting materials or by the volume of porous channels within a host structure; and membranes that have enhanced separation characteristics based on the development of tortuosity within the host-guest structure, which provides improvements in the separation of materials based on polarity, molecular size, molecular weight, or combinations of these properties. Such membrane structures are highly functional and are understood to represent a significant improvement in the development of new membrane structures.

Membranes in accordance with one or more aspects of the present invention may be those where the structure is based on a host fibrous structure that makes up approximately 3% to 40% of the weight of the final membrane and a guest porous polymer that fills in the inter-fiber voids within the host structure and makes up approximately 60% to 97% of the weight of the final membrane. Additionally, membranes in accordance with one or more aspects of the present invention may be those with structures based on a host fibrous structure that is then filled with a functional guest polymer to generate the membrane structure.

The present invention according to a preferred embodiment includes a membrane composed of a fiber-based structure as a host fibrous structure, where the voids within that structure are filled with a porous polymer material as a guest polymer.

In preferred aspects, the host fiber-based structure may be selected from the materials summarized below.

• • Materials may include woven fabrics based on various polymer types, fiber diameters and cross-sections, weaves, and constructions.
  • Materials may include nonwoven fabrics based on the range of nonwovens processes including spun-bonded, melt-blown, card and needle punched, card and bond with thermal or polymer bonding agents, card and spun lace, air lay, wet lay, along with various composite nonwoven processes and the like.

In preferred aspects, the porous guest polymer may be selected from the classes summarized below.

• • Polymers may include polymers based on free-radical polymerizations of vinyl, acrylate, or methacrylate intermediates that are chain-extended and/or cross-linked with appropriate di- or poly-functional intermediates.
  • Polymers may include polymers based on pre-polymers and reactive intermediates. In these formulations, the reactive intermediates of various types serve to create a stable high molecular weight polymer material through chain-extension and cross-linking mechanisms. Desirable pre-polymers are low molecular weight materials with available functionality in the form of amine or hydroxyl groups, and desirable reactive intermediates are monomers of low molecular weight polymers with reactive functionality (such as blocked urethanes, epoxy, or a similar reactive structure).
  • Polymers may include pre-formed polymers that can be applied from solvents or water to form a stable membrane structure as the solvent/water is removed.
    The first two classes of materials may be combined with the host structure in such a way that the polymeric intermediates that will be used to generate the guest polymer penetrate the host fiber-based structure and fill the voids of that structure and are then polymerized by chain-extension and/or cross-linking to generate the stable porous guest polymer. The latter class is applied and the functional polymer is deposited as the solvent is removed.

In a preferred embodiment of such porous membrane structures, the fibrous host structure makes up approximately 5% to 30% of the weight of the final membrane structure, and the porous guest polymer makes up approximately 70% to 95% of the weight of the final membrane structure. In another preferred embodiment, the fibrous host structure makes up approximately 10% to 25% of the weight of the final membrane structure, and the porous guest polymer makes up approximately 75% to 90% of the weight of the final membrane structure.

EXAMPLES

Outlined below are examples of the preparation of membranes in accordance with the present invention. The following examples are provided for illustrative purposes and do not limit or otherwise impair the scope of the present invention.

Example 1

Polystyrene Sulfonic Acid (PSS) Filled Fabric Based Membrane

Polymer materials used in the preparation of the PSS-based membrane are as follows:

• • Sodium 4-vinylbenzenesulfonate (NaVBS)
  • 2,2′-Azobis(2-methyl proprionitrile) (AIBN) (free radical initiator)
  • Divinyl benzene (DVB) (cross-linking agent)
  • Dimethyl sulfoxide (DMSO)

The PSS membrane was synthesized by free-radical polymerization from the monomer blend of NaVBS and DVB, followed by post-polymerization ion-exchange of the Na⁺ with H⁺ in a 30 gram nonwoven fabric (polypropylene card and bond).

Preparative steps are summarized as follows. 1.0 mole/1 NaVBS, 0.1 mole/1 AIBN & 0.1 mole/1 DVB were dissolved in DMSO. Polypropylene nonwovens were soaked in the DMSO solution mixture and placed between Teflon plates. The plates were heated at 60° C. under vacuum for 4 hours. The resulting PSS-filled membranes were washed in distilled water and vacuum-dried for 24 hours. To obtain compact, thinner membranes, the dried PSS-filled nonwoven membranes were compressed using hot pressure under 17 MPa at 95° C. for 1 minute. The membrane was then subjected to ion-exchange to provide the acid form of the membrane.

The chemical structure of the polymer used to generate the PSS-based membrane is as follows:

Example 2

Poly(2-Acrylamido-2-Methyl-1-Propanesulfonic Acid) (PAMPS) Based Unsupported Membrane

Materials used in the preparation of the PAMPS-based membrane are as follows:

• • 2-Acrylomido-2-methyl-1-propanesulfonic acid (AMPS)
  • 2,2′-Azobis(2-methyl proprionitrile) (AIBN)
  • Ethylene glycol dimethacrylate (EGDM)
  • Dimethyl sulfoxide (DMSO)

The PAMPS-based membrane was synthesized by free-radical polymerization of AMPS and EGDM to generate an unsupported film.

Preparative steps are summarized as follows. 1.0 mole/1 AMPS, 0.10 mole/1 AIBN and 0.10 mole/1 of EGDM were dissolved in DMSO. The solution mixture was placed, with a spacer, between two TEFLON plates. The plates were heated at 60° C. under vacuum for 4 hours. The resulting unsupported PAMPS membranes were washed in distilled water and vacuum-dried for 24 hours. To obtain compact, thinner membranes the dried unsupported PAMPS membranes were compressed using hot pressure under 17 MPa at 95° C. for 1 minute.

The chemical structure of the polymer used to generate the PAMPS-based membrane is as follows:

Example 3

Poly(2-Acrylamido-2-Methyl-1-Propanesulfonic Acid) (PAMPS) Filled Fabric Based Membrane

Materials used in the preparation of the PAMPS-based membrane are as follows:

• • 2-Acrylomido-2-methyl-1-propanesulfonic acid (AMPS)
  • 2,2′-Azobis(2-methyl proprionitrile) (AIBN)
  • Ethylene glycol dimethacrylate (EGDM)
  • Dimethyl sulfoxide (DMSO)

The PAMPS-based membrane was synthesized by free-radical polymerization of AMPS and EGDM in a 30 gram nonwoven fabric (polypropylene card and bond).

Preparative steps are summarized as follows. 1.0 mole/1 AMPS, 0.10 mole/1 AIBN and 0.10 mole/1 of EGDM were dissolved in DMSO. Polypropylene nonwovens were soaked in the solution mixture and placed between 2 Teflon plates. The plates were heated at 60° C. under vacuum for 4 hours. The resulting PAMPS-filled membranes were washed in distilled water and vacuum-dried for 24 hours. To obtain compact, thinner membranes the dried PAMPS-filled nonwoven membranes were compressed using hot pressure under 17 MPa at 95° C. for 1 minute.

The chemical structure of the polymer used to generate the PAMPS-based membrane is as follows:

Example 4

Polymethyl Acrylic Acid (PMA) Based Membrane

Materials used in the preparation of the PMA-based membrane are as follows:

• • Methacrylic acid (MA)
  • Potassium peroxodisulfate (PPS)
  • Ethylene glycol dimethacrylate (EGDM)
  • Distilled water

The PMA membrane was synthesized by free-radical polymerization from the monomer MA and EGDM in a 30 gram nonwoven fabric (polypropylene card and bond).

Preparative steps are summarized as follows. 1.0 mole/1 MA, 0.10 mole/1 PSS and 0.10 mole/1 of EGDM were dissolved in distilled water. Polypropylene nonwovens were soaked in the solution mixture and placed between 2 Teflon plates. The plates were heated at 60° C. under vacuum for 4 hours. The resulting PMA-filled membranes were washed in distilled water and vacuum-dried for 24 hours. To obtain compact, thinner membranes the dried PMA-filled nonwoven membranes were compressed using hot pressure under 17 MPa at 95° C. for 1 minute.

The chemical structure of the polymer used to generate the PMA-based membrane is as follows:

FIG. 1 is a graph illustrating tensile properties of porous membranes based on polymer-filled fibrous structures. As shown in FIG. 1, the unsupported membranes are very weak, and the filled membranes are generally stronger then the non-woven fabric itself.

Membranes were evaluated as potential barrier fabrics. Barrier fabrics are designed to provide high moisture transport along with low transport of chemical warfare agent simulants (represented in the following data by the transport of dimethyl methyl phosphate (DMMP), a simulant for the nerve gas agent Sarin). FIG. 2 is a graph illustrating vapor permeability of PAMPS membranes with respect to moisture transport and transport of chemical warfare agent simulant DMMP. The membranes provided a high level of moisture transport with relatively low values for DMMP transport. As further shown in FIG. 2, while the unsupported membrane did provide high moisture transport and relatively low DMMP transport, the filled membranes yielded lower values in both measurements and the reduction in DMMP transport is clearly higher than that of water. This is believed to be due to the tortuosity effect introduced by the fabric structure, which is understood to be a significant enhancement of membrane performance.

FIG. 3A is a graph illustrating water vapor permeability of membranes based on polymer-filled fibrous structures, and FIG. 3B is a graph illustrating DMMP vapor permeability of membranes based on polymer-filled fibrous structures. The PSS, PAMPS and PMA based membranes were also evaluated as protective membranes. As shown in FIGS. 3A and 3B, all three polymer classes are relatively consistent in performance, showing that the membranes generated according to the invention yielded both high moisture transport and low transport of the nerve gas simulant DMMP (thereby indicating a high ability to transfer moister while functioning as a barrier to nerve gas). The data also illustrates that the filled fabric membranes provide significantly improved barrier properties against DMMP with minimal reduction in moisture transport results. As noted above, these results are believed to be the effect of tortuosity introduced by the fabric structure.

As shown in the data, membranes in accordance with the present invention have significantly enhanced separation properties (i.e., selective blocking of materials) while maintaining optimal performance with respect to water vapor permeability. In particular, water vapor transfer capabilities and performance of membranes in accordance with the present invention is at or near 100% of such capabilities for known membrane structures.

Membranes in accordance with the present invention may be tuned for a wide range of particular applications. These membrane structures may have utility as barrier membranes for military and industrial chemical protection applications, breathable barrier fabrics for a range of personal clothing applications, or as separation membranes for a range of different applications, such as water treatment, mineral extraction, bio-separations, filters, sensors, biocatalysts, supercapacitors, data storage, energy generation, micro-electronics and semiconductors, drug delivery, pharmaceutical purification, artificial blood vessels, tissue growth, environmental processes, ultra-filtration, materials synthesis, batteries and fuel cells, as well as various other applications.

Based on the foregoing information, it will be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those specifically described herein, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing descriptions thereof, without departing from the substance or scope of the present invention.

Accordingly, while the present invention has been described herein in detail in relation to one or more preferred embodiments, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for the purpose of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended to be construed to limit the present invention or otherwise exclude any such other embodiments, adaptations, variations, modifications or equivalent arrangements; the present invention being limited only by the claims appended hereto and the equivalents thereof.

Claims

1. A porous membrane structure comprising:

(a) a fibrous host material for providing structure to a membrane, the fibrous host material defining a plurality of inter-fiber voids; and

(b) a porous guest polymer that fills at least a subset of the plurality of inter-fiber voids of the fibrous host material.

2. The porous membrane structure of claim 1, wherein the fibrous host material includes a nonwoven material.

3. The porous membrane structure of claim 1, wherein the porous guest polymer facilitates selective transport of materials across the membrane.

4. The porous membrane structure of claim 1, wherein the porous guest polymer provides selective barrier properties to the membrane.

5. The porous membrane structure of claim 1, wherein the fibrous host material comprises approximately 3% to approximately 40% of the total weight.

6. The porous membrane structure of claim 5, wherein the fibrous host material comprises approximately 10% to approximately 25% of the total weight.

7. The porous membrane structure of claim 1, wherein the porous guest polymer comprises approximately 60% to approximately 97% of the total weight.

8. The porous membrane structure of claim 7, wherein the porous guest polymer comprises approximately 75% to approximately 90% of the total weight.

9. The porous membrane structure of claim 1, wherein the fibrous host material is a flexible material.

10. A protective barrier material comprising:

(a) a porous membrane structure, the porous membrane structure including a fibrous host material, which defines a plurality of inter-fiber voids, and a porous guest polymer that fills at least a subset of the plurality of inter-fiber voids of the fibrous host material;

(b) wherein the porous guest polymer facilitates selective transport of materials across the porous membrane structure and provides selective barrier properties to the porous membrane structure.

11. The protective barrier material of claim 10, wherein the fibrous host material includes a nonwoven material.

12. The protective barrier material of claim 10, wherein the fibrous host material is a flexible material.

13. The protective barrier material of claim 10, wherein the fibrous host material comprises approximately 3% to approximately 40% of the total weight of the porous membrane structure.

14. The protective barrier material of claim 13, wherein the fibrous host material comprises approximately 10% to approximately 25% of the total weight of the porous membrane structure.

15. The protective barrier material of claim 10, wherein the porous guest polymer comprises approximately 60% to approximately 97% of the total weight of the porous membrane structure.

16. The protective barrier material of claim 15, wherein the porous guest polymer comprises approximately 75% to approximately 90% of the total weight of the porous membrane structure.

17. The protective barrier material of claim 10, wherein the porous guest polymer facilitates transfer of water vapor across the porous membrane structure and provides barrier properties against a toxic chemical.

18. The protective barrier material of claim 17, wherein the porous guest polymer includes a PAMPS polymer.

19. The protective barrier material of claim 17, wherein the porous guest polymer includes a PSS polymer.

20. The protective barrier material of claim 17, wherein the porous guest polymer includes a PMA polymer.