WO1997028898A1

WO1997028898A1 - Improved filled porous polymers with surface active agents and methods of making same

Info

Publication number: WO1997028898A1
Application number: PCT/US1996/020399
Authority: WO
Inventors: John L. Dennison; C. Bradford Jones; William P. Mortimer, Jr.; Eric K. Propst
Original assignee: W.L. Gore & Associates, Inc.
Priority date: 1996-02-07
Filing date: 1996-12-27
Publication date: 1997-08-14
Also published as: AU1341097A

Abstract

The present invention is an improved method for incorporating a functionalized surface agent into a porous polymer support structure and improved, novel articles made by this method. The present invention is particularly applicable to those instances where the porous support structure must undergo harsh processing conditions that might alter or damage the functionalized surface agent if it were present during the harsh processing.

Description

TITLE OF THE INVENTION

IMPROVED FILLED POROUS POLYMERS WITH SURFACE ACTIVE AGENTS AND METHODS OF MAKING SAME FIELD OF THE INVENTION The present invention relates to methods of producing filled polymer materials, and especially filled porous polymer materials, having surface active agents incorporated therein.

BACKGROUND OF THE INVENTION Surface modified powders (or "functionalized surface agents") are currently used for a variety of applications, including sorption (i.e., adsorption or absorption) processes, reaction precursors, reactants, and catalysts. Despite providing excellent active characteristics, powders alone are typically difficult to handle and process. For example, possible air entrainment of fine powders makes them a health concern and requires special handling equipment and procedures for metering, contacting and separating. Powders can also be difficult to employ mechanically because they cannot be formed readily into convenient strong shapes without sacrificing exposed surface area using sintering or binders.

To relieve problems associated with surface active powders, the powder can be incorporated into a porous support material. By adhering the powder to a support material, the powder can be more easily handled and used. Other advantages of incorporating a filler into a porous support material include reduced channeling as compared to a packed bed; lower pressure drop (high flow rate) through the structure as compared to a packed bed; and more convenient incorporation into devices.

U.S. Patent No. 3,824,150, is directed to immobilization of enzymes by mechanical entrapment within a semi-permeable carrier such as a membrane, or by chemical coupling through an intermediate agent to natural or synthetic polymeric materials including cellulosic materials in the form of filter paper. The use of cellulosic filter paper and similar organic carriers having enzymes coupled or otherwise bonded thereto suffer from disadvantages inherent in such support materials inasmuch as the latter are usually fragile, are subject to microbial attack and cannot be easily sterilized without damage.

U.S. Patent No. 4,102,746, to Goldberg, is directed to proteins such as enzymes which are immobilized on a microporous binder or matrix having finely divided filler particles dispersed throughout the binder. The proteins are coupled to the filler particles, and the microporous binder provides both larger surface area and greater stability than would otherwise be available via a cellulosic material support However, the surface area available is still limited by the attachment of the filler particles to the microporous binder

U S Patent Nos 5,071 ,610, 5,147,539 and 5,207,915, all in the name of Hagen et al , are directed to controlled pore composite polytetrafluoroethylene articles and methods for their manufacture and use, whereby a polytetrafluoroethylene (PTFE) fibril matrix is prepared having insoluble, non-swellable sorptive particles enmeshed in said matrix, the ratio of non-swellable sorptive particles to PTFE being in the range of 40 1 to 1 4 by weight These articles are beneficial in a number of filtration applications based on the inert nature of the PTFE and the ability to enmesh the particles within the PTFE fibrils However, due to the thermal and chemical sensitivity of the surface functional sorptive particles, processing techniques are limited to those which will not destroy the functionality of the particles Consequently these articles are limited to close-packed PTFE structures which limit the flow of liquid during filtration and the like

U S Patent No 5,248,915, in the name of Hagen et al , attempts to overcome the problem of a close-packed structure by providing energy expandable hollow polymeric particles along with the sorptive particles within the PTFE matrix which, upon introduction of energy, expand to provide an expanded article having increased void volume and decreased density

However, such materials still suffer from the problems associated with close- packed PTFE structures

All of this activity is based on a growing need for practical support structures for various surface active agents Because surface active agents are themselves often very fragile and can often be damaged by the processing requirements of various support structures, much of the activity to date has been limited to simple structures that, while providing less than optimum physical characteristics such as strength, flow characteristics, available surface area of the active agent, etc , at least can be fabricated without damaging the agent Accordingly, there has been a long-felt need in the field of reaction and separation systems for strong, stable support structures which provide a maximum surface area of at least one functionalized surface agent, while still providing the flexibility of a sheet or three-dimensional unit for maximum design flexibility DISCUSSION OF COMMONLY OWNED PATENTS

One material which has shown good potential as a support structure for such applications is a strong, flexible, thermally stable, inert, highly porous material such as an expanded polytetrafluoroethylene (PTFE) as disclosed in U.S. Patent Nos. 3,953,566, 3,962,153, 4,064,214, 4,096,227, 4,187,390 and 4,902,423, all of which are specifically incorporated herein by reference. This expanded PTFE material comprises a microporous structure of microscopic polymeric fibrils (i.e., thread-like elements) interconnecting polymeric nodes (i.e., particles from which the fibrils emerge). As the term "expanded PTFE" is used herein, it is intended to include any PTFE material having a node and fibril structure, including in the range from a slightly expanded structure having fibrils extending from relatively large nodes of polymeric material, to an extremely expanded structure having fibrils merely intersecting with one another at nodal points.

Expanded PTFE has a number of important properties which make it particularly suitable as a support for functionalized materials. First, PTFE is of very high purity and does not require the use of thermal stabilizers, anti¬ oxidants, anti-blocking agents, slip additives or plasticizers which can migrate out and contaminate any systems in which the support materials are being utilized. Second, PTFE is a highly inert material that is hydrophobic. Accordingly, the material is resistant to interactions with materials which it may come into contact with during use. Additionally, by expanding PTFE in the manner taught by U.S. Patent No. 3,953, 566 to form the node and fibril structure, the material undergoes a significant increase in tensile strength and becomes highly flexible. Moreover, the expanded PTFE provides an extremely effective support structure due to its expanded structure which allows entrapment of materials within the node and fibril "cages", thus providing a maximum surface area of functionalized material available for reaction. While it is possible to add a functionalized filler to the expanded PTFE after formation, this tends to provide a weaker bond between the expanded PTFE support material and the functionalized filler, weaken the support structure itself and/or to reduce the exposed active surface area of the agent due to the need, for example, of an adhesive or other binder material to attach the agent thereto. The post-formation filling of porous expanded PTFE is particularly troublesome due to PTFE's inert nature (making it more difficult to adhere material to it) and the tortuous microporous nature of the expanded PTFE membrane (making it more difficult to transfer particles into the depth). Incorporation of a filler into an expanded PTFE matrix during the PTFE processing is possible, such as disclosed in U.S. Patent No. 4,985,296, which is specifically incorporated herein by reference. This technique maintains access to surface area of the filler by suspending filler particles by fine strands of PTFE. Handling is simplified owing to the flexible nature of the expanded

PTFE/filler composite. Finally the material can be formed in many convenient to use forms, such as tapes, membranes, tubes, rods, beading, etc. These forms can be used to generate novel reactor and separation configurations. Unfortunately, to take advantage of the expanded PTFE/filler composite, the filler must be compatible with the often extremely harsh processing conditions that are encountered in the processing of the expanded PTFE support material. For example, the filler must be chemically compatible with processing fluids and survive high temperature processing conditions (i.e., up to 350°C or more) used to achieve many of the expanded PTFE/filler composites of interest.

The surface active component of many fillers typically will not meet these criteria. Either the surface active filler will react with typical processing fluids or become modified or degraded during high temperature processing. Accordingly, the ability to provide active fillers in a highly porous polymer, such as an expanded PTFE polymer, has been limited by the processing limits of the filler.

Accordingly, it is a primary purpose of the present invention to provide a method for creating a filled polymer structure having functionalized surface agents contained therein whereby the surface agents are protected from harsh processing conditions that would otherwise damage their functionality.

Moreover, it is another primary purpose of the present invention to provide a filled polymer support structure wherein suspension of the filler within the support structure provides a high surface area of filler for functional surface active agent attachment, thus enhancing the efficiency of the system. Another primary purpose of the present invention is to provide filled polymers wherein the composition, placement and loading of the surface active agents suspended in the filled polymer may be tailored to provide unique structures.

A further primary purpose of the present invention is the formation of materials comprising surface active agents supported on a stable, inert, filled porous polymer which permit significant flexibility in designing a virtually unlimited number of reactor and separator systems. These and other purposes of the present invention will become evident based upon a review of the following specification.

SUMMARY OF THE INVENTION The present invention is an improved method for incorporating at least one functionalized surface agent into a porous polymer support structure and improved, novel articles made by this method. The present invention is particularly applicable to those instances where the porous support structure must undergo harsh processing conditions that might alter or damage the functionalized surface agent if it were present during the harsh processing.

As the term "harsh conditions" is used herein, it is intended to encompass any processing conditions for the support structure that would be expected to impair or destroy functionalized surface agents which are sensitive to such conditions. In addition, harsh conditions may encompass processing conditions in which the presence of the functionalized surface agent may negatively impact the processing of the support structure.

The method of he present invention comprises first providing a porous support structure exhibiting a node and fibril structure and having at least one relatively robust filler contained therein. As used herein, the term "node and fibril structure" refers to a range from a slightly expanded structure having fibrils extending from relatively large nodes of polymeric material, to an extremely expanded structure having fibrils merely intersecting with one another at nodal points. Typical support structures of the present invention may include nonwoven structures, solvent extracted polymer structures, thermally induced phase separated polymer structures, and expanded polymer structures which exhibit node and fibril characteristics. Specific examples may include ultra high molecular weight polyethylenes, expanded polytetrafluoroethyienes, polyethylene-coated polyester fiber nonwovens.solvent extracted polysulfones, and the like. Limited only by the tolerances of the support structure and the filler, the filled support structure can be readily processed under harsh conditions (e.g., involving exposure to certain chemicals and/or processing temperatures or pressures, etc.) that might otherwise damage functionalized surface agents which are sensitive to such harsh conditions. Following processing under such harsh conditions, a sensitive functionalized surface agent is applied to the filled polymer so as to bind the surface agent to the filler.

In this manner, the support structure can be processed in virtually any suitable manner without fear that the functionalized surface agent will be in any way compromised or destroyed The presence of the at least one filler in the porous support structure serves a number of important functions

First, the filler can be selected to provide an extremely effective binding site for the functionalized surface agent A polymer support material, such as expanded PTFE, that has been selected for its structural characteristics or chemical inertness may be less than optimum, and in some cases may be totally inadequate, as a bonding site for a desired functionalized agent Incorporating a filler allows much greater flexibility in design of the finished product by allowing independent selection of a support structure for its physical characteristics and a surface active filler for its bonding characteristics Thus, by first placing the filler within the support structure and then using the filler as the binding site for the functionalized surface agent, effective attachment of the functionalized surface agent within the support structure is achieved with greatly reduced risk of separation of the surface agent during use Second, the suspension or entrapment of the filler within the support structure can also provide a high surface area of the filler which is available for surface agent attachments and, correspondingly, a high surface area of surface active agent for sorption, etc , processes This feature significantly enhances the efficiency of the filled porous polymer as a component of a reaction or separation system relative to conventional materials

A particularly preferred embodiment of the present invention comprises providing a support structure of expanded PTFE having a robust filler, such as a silica, trapped within its node and fibril structure Ideally, the filler and PTFE are combined during the initial processing of the PTFE so that the filler is intimately enmeshed within the porous expanded PTFE structure Benefits to using PTFE include high temperature and chemical stability, as well as its tendency to minimally occlude filler surface area after combining the PTFE and filler In contrast, other polymer supports which do not exhibit a node and fibril structure may tend to coat the filler and block filler surface area during composite formation Since composite formation processing involves relatively high temperatures, and may further include exposure to aggressive chemicals, many functionalized surface agents cannot be safely processed in this manner

Following formation of the filler/polymer composite support structure, the surface of the filler may be functionalized using any of a broad range of solid surface modification chemistries or processes such as organosilanes, acyl chlorides, anhydrides, isocyanates, ion exchange, doping, leaching, reduction, plating, or mechanical coating The chemistries can be applied using any convenient environment for reaction, which optionally may involve solvents and may take place in the liquid or gas phase. As a result of the surface modification reaction, the filler surface may be at least partially covered (e.g., chemically bonded, coated, or doped) with one or more desirable functionalized surface agents, including a polymeric, organic, organometallic, metallic, metal oxide, catalytic, ionic, acidic, basic, anionic, cationic, enzymatic, protein, or biocellular material so as to bind the functionalized surface agent to the filler. Moreover, functionalized surface agents of different compositions may be combined on a single support structure or multiple layers of support structures having different surface agents may be combined in a desired setup. The present invention provides a distinct improvement in the processing of functionalized surface agents into usable structures. Moreover, the present invention allows for the effective combination of a wide variety of functionalized surface agents, including extremely vulnerable agents such as enzymes, proteins, biological cells, organic or organometallic moieties, into very strong and forgiving materials, such as those materials described in more detail herein. The invention also allows the processing of highly reactive materials such as catalysts which may be poisoned or cause undesirable reactions during the support processing. The present invention also provides the ability to tailor the composition, loading, and the like, of the surface active agents on the support structures. As a result, the present invention can be used to create many exciting new materials and systems that can be easily handled and used.

DESCRIPTION OF THE DRAWINGS

The operation of the present invention should become apparent from the following description when considered in conjunction with the accompanying drawings, in which:

Figure 1 is a scanning electron micrograph (SEM) of a commercially available dried PTFE material containing C-18 bonded silica; and

Figure 2 is an SEM of a material processed in accordance with the present invention showing an open structure containing C-18 bonded silica.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an improved method for incorporating at least one functionalized surface agent into a porous polymer support structure that is particularly applicable to those instances where the porous support structure must undergo processing under harsh conditions that might alter or damage the functionalized surface agent if it were present during the harsh processing. Moreover, the present invention is also applicable to instances wherein the functionalized surface agent may produce hazardous conditions during and/or interfere with the processing of the porous polymer support structure.

Examples of harsh conditions may include, for example in the case of PTFE processing, high processing temperatures (e.g., in excess of about 150°C, and especially very high temperatures such as those encountered in expanded PTFE processing at up to 350°C or higher), high pressure (e.g., about 14000 Kpa or higher), aggressive chemical exposure (e.g., alcohols, molten salts, etc.), as well as any other conditions which would tend to render the functionalized surface agents ineffective for the desired application. However, the present invention also encompasses conditions which are less severe than those involved with PTFE processing, but which nonetheless detrimentally affect the sensitive functionalized surface agents.

The method of the present invention comprises first providing a porous support structure having at least one relatively robust filler contained therein. Examples of suitable porous support structures that can be employed with the present invention include those polymers which exhibit a node and fibril structure, such as nonwoven structures, solvent extracted polymer structures, thermally induced phase separated polymer structures, and expanded polymer structures which exhibit node and fibril characteristics. Specific examples may include ultra high molecular weight polyethylenes, polyethylene-coated polyester fiber nonwovens, solvent extracted polysulfones, expanded polytetrafluoroethyienes (PTFE), and the like, which can incorporate such robust fillers within their matrices.

The "robust" fillers that can be employed in the present invention comprise any particulate that will withstand harsh processing conditions and is capable of bonding to functionalized surface agents. As used herein, the term "particulate" is meant to include particles of any aspect ratio and thus includes particles, chopped fibers, whiskers and the like. Examples of suitable "robust" fillers that can be employed with the present invention include silica (xerogel, aerogel, fumed, gelled, fused, amorphous, crystalline), glass, titanates (barium, calcium, etc.), metal oxides (aluminum, titanium, tin, lead, etc.), carbides (silicon, etc.), nitrides (boron, etc.), zeolites, metals, and polymers.

Limited only by the tolerances of the support structure and the filler, the filled support structure can be readily processed under harsh conditions that might otherwise damage certain functionalized surface agents. Following processing under harsh conditions, a functionalized surface agent is then applied to the filled support structure so as to bind the surface agent to the filler. The present invention can be employed with a wide variety of functionalized surface agents. As the term "sensitive functionalized surface agents" is used herein, it is intended to include any material that provides chemically active surfaces and that will not withstand harsh processing conditions. These include: polymeric, organic, organometallic, metallic, metal oxide, catalytic, ionic, acidic, basic, anionic, cationic, enzymatic, protein, or biocellular materials.

The precise mechanism for binding of the functionalized surface agent to the filler will depend upon the type of surface agent and filler being employed. Suitable methods include any of a broad range of filler surface modification chemistries or processes such as organosilanes, acyl chlorides, anhydrides, isocyanates, ion exchange, doping, leaching, reduction, plating, or mechanical coating. The chemistries may be applied using any convenient environment for reaction, which may involve solvents and may take place in the liquid or gas phase.

A novel feature of the present invention is that the filler/support structure may be processed in virtually any suitable manner without fear that the functionalized surface agent will be in any way compromised or destroyed.

A further novel feature of the present invention is that the suspension of the filler within the support structure provides a high surface area of filler for functional surface active agent attachment, thus enhancing the efficiency of the system.

Another novel feature of the present invention is the ability to tailor the composition, placement and loading of the surface active agents suspended in the filled polymer support structures.

A further novel feature of the present invention is that the use of surface active agents supported on a stable, inert, filled porous polymer permits significant flexibility in designing a virtually unlimited number of reactor and separator systems. A particularly preferred embodiment of the present invention comprises providing a support structure of expanded PTFE having at least one robust filler, such as a silica, trapped within its node and fibril structure. Ideally, the filler and PTFE are combined during the initial processing of the PTFE so that the filler is intimately adhered within the expanded PTFE structure. In this preferred embodiment, the support material may be created by first combining the at least one filler and the PTFE by dry blending, wet blending, or coagulation with dispersion. The filler/PTFE coagulum or powder is then lubricated and processed by, for example, extruding and/or calendering and/or molding to form a desired geometry such as a tube, sheet, shape, rod, fiber, tape, or the like. The structure is then typically expanded at an elevated temperature in one or more directions, in series or in unison, for one or more times. The lubricant may be removed from the extrudate, if desired, prior to expanding by stretching. The structure may then be sintered at a temperature at or above about 350°C, and, optionally, expanded and/or calendered again after sintering.

Since such processing involves relatively high temperatures, and may further include exposure to aggressive chemicals, many functionalized surface agents cannot be safely processed in this manner. Following formation of the filler/PTFE composite structure, the surface of the filler may be functionalized using any of a broad range of filler surface modification chemistries or processes, such as organosilanes, acyl chlorides, anhydrides, isocyanates, ion exchange, doping, leaching, reduction, plating, or mechanical coating so as to bind the functionalized surface agent to the filler. The chemistries may be applied using any convenient environment for reaction, which optionally may involve solvents and may take place in a liquid or gas phase. As a result of the surface modification reaction, the filler surface is at least partially covered (chemically bonded, coated, or doped) with a polymeric, organic, organometallic, metallic, metal oxide, catalytic, ionic, acidic, basic, anionic, cationic, enzymatic, protein, or biocellular material.

It is generally understood that to function properly a surface active agent, such as a catalyst or the like, typically needs open access to the surface of the filler. Significant differences exist between previously available filled materials and materials made in accordance with the present invention, as can be seen, for example, in Figures 1 and 2. Figure 1 is a scanning electron micrograph (SEM) of a commercially available dried PTFE tape containing C-18 bonded silica sold as EMPORE™ by Minnesota Mining and Manufacturing (St. Paul, MN). As can be seen in Figure 1 , the particles of treated silica appear "glued" together by PTFE fibril "mortar", thus severely limiting the openness of the structure and severely restricting fluid flow. In addition, critical surface area of the C-18 bonded silica is blocked by contact with the PTFE fibril mortar, thus severely reducing the efficiency of the C-18 bonded silica in the desired application.

By contrast, Figure 2 is an SEM of a filled, expanded PTFE structure containing C-18 bonded silica which was processed in accordance with Example 1. The open structure shown in Figure 2, in which the silica filler particles are suspended by a web of very thin, -strong PTFE fibrils attached between nodes, is characteristic of expanded PTFE. Analysis of expanded PTFE structures by differential scanning calorimetry over a temperature range of 30° to 450°C at a heating rate of 10°C/min. characteristically results in a first endothermic peak in the temperature range 325°C to 350°C and a second endothermic peak in the temperature range 370°C to 390°C.

If the silica filler had been treated with the C-18 prior to mixing with the PTFE, the C-18 would be expected to decompose during the processing conditions required to create this unique, expanded PTFE structure. Instead, as outlined in Example 1 below, the silica and PTFE were first processed to form the unique structure shown, and then the C-18 was bonded to the silica after the harsh processing of the expanded PTFE was completed. The resulting product has significant advantages when compared to the commercially available, non-expanded product shown in Figure 1 , including a much lower resistance to fluid flow and a larger available surface area of the C-

18 bonded silica.

The present invention provides a distinct improvement in the processing of functionalized surface agents into usable structures. The present invention allows for the effective combination of a wide variety of functionalized surface agents, including extremely vulnerable agents, into very strong and versatile support materials such as expanded PTFE. As a result, the present invention can be used to create many exciting new materials that can be easily handled and used. Possible structures that can be formed from the material of the present invention include membranes, tapes, beads, filaments, tubes, etc. Moreover, different surface active agents may be present on a single support structure to further enhance the efficiency of structures and/or multiple structures may be combined to provide more effective reactor and separator systems.

Without intending to limit the scope of the present invention, the following examples illustrate how the present invention may be made and used:

EXAMPLE 1

Approximately 1.8 kg of silica (10 micron silica gel with 60 Angstrom Pores, available from Grace Davison Chemical Co.) were mixed with about 20 liters of water. To this mixture was added about 17.3 pounds (7.8 kg) of 23.1 % solids PTFE dispersion and about 1.2 pounds (1.8 kg) of 0.4% cationic polyacrylimide solution (available from BASF). Mixing was continued until coagulation occurred. The coagulum was dried to a powder by heating at 165°C for 21 hours, then frozen below 0°C for 24 hours and screened through a 1/4 mesh wire screen.

The resulting powder was lubricated with a water containing surfactant lubricant at a lubricant to filled polymer weight ratio of 0.95, then formed into a cylindrical pellet and ram extruded to form a 2030 micron tape. The tape was then unidirectionally calendered to 635 microns.

The tape was steam cleaned and then dried on a drum dryer. The tape was then heated to a temperature of about 250°C and expanded in both the machine direction and the transverse direction by about 2.3:1 at a rate of 1000%/second, then subjected to an amorphous locking step at about 380°C for a period of time.

The formed silica/PTFE membrane was humidified at about 70°C at

100% relative humidity for about 18 hours, then dried in a convection oven at about 120°C with no humidity control. In a 1000 ml round bottom flask, about 3.77 g of membrane, 200 ml of toluene (solvent) and about 1.8 g of dimethyloctadecylchlorosilane (Approx. 1 :1 based on the weight of filler) were combined and refluxed for about 19 hours.

The membrane was then rinsed 6 times with toluene and 2 times with hexane, then dried at about 120°C for 4 hours.

Elemental Analysis

Elemental analysis of the formed membrane was performed by Galbraith

Laboratories, Inc., Knoxville, TN, measuring percent carbon with and without the use of the surface treatment agent. Ten micron gelled silica with 60 angstrom pores is known to react with dimethyl n-octadecylchlorosilane (C18) to yield a carbon loading on the silica of 12 to 17%, depending on reaction conditions. One strong open structure was reacted with the silane compound, and the other sibling was treated identically except that C18 silane was not present. Assuming a 15% carbon loading on the silica and a 50% silica/50% PTFE initial composite, the carbon loading of the untreated material should be

11.5 %, and after surface treatment the value should be 17.6 %, giving a difference of 6.1 %.

The untreated sample had an 11.8% carbon loading, while the treated sample had a carbon loading of 16.8%. These values agreed quite well with the theoretical values and showed that the surface treatment reaction occurred as expected. Solid Phase Extraction

The retention and flow characteristics of :

1. C18 bonded silica in an open PTFE membrane

2. Untreated silica in an open membrane 3. Commercially available C18 bonded silica in PTFE matrix

(EMPORE™ membrane) were compared in application as solid phase extraction media. In this test, water was doped with three organic molecules (phenol, benzaldehyde, dimethyltolumide) to a known concentration. The water was drawn through each sample solid phase extraction disk. The nonpolar organic molecules were expected to be retained on the nonpolar C18 bonded silica, with greater retention associated with the least polar molecules. The target molecules retained on the solid phase extraction disk were then removed by flushing with a strong solvent (methanol). The quantity of target molecules in the water (not retained) and in the methanol (retained) was determined using liquid phase chromatography, a standard analytical procedure.

The flow rate at which the initial doped water was drawn through the extraction disk was controlled by maintaining a vacuum in the collection flask. The higher the vacuum, the greater the resistance to flow through the membrane.

The following table shows the performance of the three samples.

Sample g silica/cnrr Flow Rate Vac. Pressure Phenol* Benz *^* DET^*** ml/min KPa

Treated 0.045 4.0 53.2 38 100 100

Untreated 0.045 4.0 53.2 22 14 80

EMPORE™ C18 0.033 2.6 60 37 85 100

^* Phenol: % Phenol retained in the membrane

^**Benz: % benzaldehyde retained in the membrane. ^***DET: % dimethyltolumide retained in the membrane.

The strong, open expanded PTFE membranes offered about 53% higher flow rate at lower pressure drop with about 36% greater C-18 bonded silica per unit area. Retention of the nonpolar organic molecules by the treated PTFE membrane was comparable to the commercially available material, indicating the successful application of the C-18. EXAMPLE 2

Approximately 5.4 kg of silica (10 micron silica gel with 60 Angstrom pores, available from Grace Davison Chemical Co.) were mixed with about 20 liters of water in a low shear mixer. To this mixture was added about 1.8 kg of 23.1% solids PTFE dispersion (available from E. I. duPont de Nemours and

Co.) and about 1.6 kg of 0.4% cationic polyacrylimide solution (available from BASF), and mixing was continued until coagulation occurred, then the mixer was stopped. The coagulum was dried, frozen and screened as in Example 1. The resulting powder was lubricated with a 2:1 propylene glycol: isopropyl alcohol mixture at a filled polymer to lubricant ratio of 1.2, then formed into a 10 cm diameter cylindrical pellet and extruded to form a 3050 micron tape. Two layers of tape were stacked to form a two-layer sheet which was unidirectionally calendered to 1500 microns and dried on a drum dryer. The tape was then heated to a temperature of about 250°C and expanded in the machine direction on draw rollers heated to 235°C at a draw ratio of about

2.76x at a speed of 13.7 m/min, then amorphously locked under tension at about 380°C. A second sample of the tape was heated and drawn in the same manner as the 2.76x tape, except that the draw ratio was about 1.9x. The formed silica/PTFE membranes were humidified at about 70°C at 100% relative humidity for about 18 hours, then dried in a convection oven at about 120°C.

The following procedure was carried out for both the 2.76x membrane and the 1.9x membrane. In a 1000 ml round bottom flask, about 150 g of membrane, 500 g of toluene (solvent) and about 100 g of octadecyltrichlorosilane were combined and refluxed for about 19 hours. The membrane was rinsed 3 times with hexane, then dried at about 100°C for 1 hour. The dried membrane was then hydrolyzed with 500 ml of 50/50 acetonitrile/water solution for thirty minutes at room temperature and dried at about 100°C for one hour. The membrane was placed in a flask with 500 ml of toluene and 100 g of trimethlychlorosilane, and the mixture was refluxed for about 4 hours. The tape was then rinsed 3 times with hexane and dried for 1 hour at about 100°C.

Elemental Analysis Elemental analysis was performed by Galbraith Laboratories, Inc.,

Knoxville, TN, on percent carbon with and without the use of the surface treatment agent. The reaction of 10 micron gelled silica with 60 angstrom pores is known to react with dimethyl n-octadecylchlorosilane (C18) to yield a carbon loading on the silica of 12 to 17% depending on reaction conditions. One strong open structure was reacted with the silane compound, and the other sibling was treated identically except that C18 silane was not present. Assuming a 15% carbon loading on the silica and a 72% silica/28% PTFE initial composite, the carbon loading of the untreated material was expected to be approximately 8% and after surface treatment the value was expected to be approximately 19%.

The untreated sample had an 8.5 % carbon loading, while the treated sample expanded at a 2.76x ratio had a carbon loading of 20.5% and the treated sample expanded at a 1.9x ratio had a carbon loading of 20 %. These values agree quite well with the theoretical values and showed that the surface treatment reaction occurred as expected.

Flow Through Membrane Analysis UUssiinngg aa 00..77 ccmm²² ffllooww ccrroossss--sseection, the flow rate of 10 ml of water though the post bonded composite was measured, as shown below.

Sample Draw Silica Thickness Flow Rate Vacuum

Ratio g/m² mil ml/min KPa

1 2.76 490 56 5.3 68

2 1.9 450 40 4.5 68

EMPORE™ 1.0 330 20 2.2 68

The expanded tape exhibited a 48% higher silica loading with 230% greater flow at a given pressure drop. The flow rate and loading may also be adjusted by varying the draw ratio used to manufacture the composite.

Sample SiO₂ Flow Vac. Pressure Phenol^* Benz.^** DET g/cm² ml/min KPa

1 0.047 3.3 10 38 86 98

2 0.074 3.5 11.3 48 94 97

EMPORE™ C18 0.033 3.6 29.3 37 85 100

^* Phenol: % Phenol retained in the membrane

^**Benz: % benzaldehyde retained in the membrane. ^***DET: % dimethyltolumide retained in the membrane. The above table compares the retention .and flow performance of the two expanded PTFE samples and the EMPORE™ membrane. At similar flow rates the retention was comparable. However, Samples 1 and 2 offered 42% and 124%, respectively, higher C-18 per unit area. Moreover, the amount of vacuum that was needed to maintain the liquid flow through Samples 1 and 2 was approximately 1/3 that necessary for the EMPORE™ membrane.

Expansion of the PTFE/silica composite at high temperatures allows the formation of structures that allow, among other things, higher silica loading, lower pressure drops and greater flow rates.

Provided below are examples of post treatment processes that may be used on a variety of fillers in a filled support structure, such as a PTFE matrix, for a range of applications. The chemical treatment methodologies, filler types, applications, and composite structures mentioned are merely representative of the wide applicability of the present invention and is not in any way all inclusive.

The post treatment processes are selected from published methodologies that resulted in specific surfaces with demonstrated successful performance. Owing to the inert characteristics of PTFE, it is expected that the reaction conditions used for the treatment of these powders may be used with little or no modification.

EXAMPLE 3

This example is directed to direct organometallic bonding to silica within a support structure of the present invention. This example demonstrates the use of an allyl treating reagent.

A PTFE/silica gel composite containing up to 99% silica is prepared using known processing methods to form a porous structure. The silica is then reacted with a rhodium allyl compound to form a bound rhodium ligand that is a catalyst for olefin hydrogenation activation. A PTFE/silica composite which contains about 1.8 g of silica is added to approximately 60 ml of toluene. About 160 g of Rh(allyl)3 is added dropwise, while stirring in a dry box, to the toluene bath containing the composite. Propylene evolution is expected to occur. The reaction mixture is stirred for 24 hours and filtered and dried in vacuum until a pressure of 1.3 Pa is attained. This results in an oxygen bond between the silica and Rh(allyl)2 complex.

The silica supported Rh(allyl)2 is reacted with hydrogen (101 kPa) in a 5000 ml flask and left for 3 days to insure completeness of reaction. The result is a chemically bonded Rh allyl hydride. This surface is able to catalytically hydrogenate olefins.

With regard to allyl treating reagents, it is usually necessary to incorporate the reagent in a post treatment step due to the presence of the allyl group in the Rh complex which is unstable at high temperatures associated with PTFE processing. Similarly, the use of any temperature sensitive bound ligand would limit the use of high temperature processing for PTFE filler composites.

EXAMPLE 4

This example demonstrates surface modification of a filler within a PTFE matrix using a Grignard reagent.

A PTFE/silica composite is prepared in any form, such as a tape, membrane, tube or rod, with the silica embedded in the porous PTFE structure. The surface hydroxyls of the silica in the PTFE matrix are replaced with

Cl using SiC -^*., TiCl4, or SOCI2. Ten grams of silica contained in the PTFE matrix are covered with dry pentane in a 1 liter flask, to which 10 grams of SiClφ TiCl or SOCI2 is added and refluxed for 1 hour, thus forming a silica-CI reactive surface. Fifteen ml of alpha-napthylbromide in 40 ml of dry ether is stirred under reflux with 2.5 grams of Mg until the metal dissolves. Fifteen ml of this reagent is added to the silica-CI. The product is filtered and washed repeatedly with water to hydrolyze the excess Grignard and remove salts. The powder is then rinsed with ether, chloroform, and acetone. The naptha-silica is then extracted with chloroform for at least 24 hours to remove traces of nonbonded organics.

The process results in a naptha surface functionality that is bonded directly to a silica atom (not through an oxygen linkage as with silane treatment chemistry). An expected advantage is greater hydrolytic stability between the functional group and silica.

EXAMPLE 5

This example demonstrates immobilized chelating functionality by showing the application of silane treated silica. In this example, a composite of silica bonded with a chelating agent is used to selectively extract and release heavy metal ions from solution based on solution pH.

A PTFE/silica composite is prepared in any form, such as a tape, membrane, tube or rod, with the silica embedded in the porous PTFE structure. A chelating functional group is immobilized on silica gel using a silylation reaction to remove trace metals from solution. The silica/PTFE structure containing 5 g of silica is placed in 10 ml of a 10% (N-beta-aminoethyl-gamma- aminopropyltrimethoxysilane) toluene solution at room temperature. After about 10 minutes the composite is rinsed with toluene and isopropyl alcohol, and the product is dried at about 80°C for 12 hours.

Based on the performance of chelating silica powder, metal ions (Hg⁺⁺, Cu⁺⁺, Zn⁺⁺, Pb⁺⁺) may be extracted from solution by the immobilized diamine groups. As the pH is reduced, the immobilized ions are released. Removal of ions on silated silica may be a commercial process for reducing residual ionic impurities or for recovery of metals from dilute solution on a commercial level. However, it is expected that such production will require high flow rates. The present invention provides novel materials which meet the demanding standards for such commercial production. Particularly, the processing of the present filled porous polymers, such as the high temperature PTFE processing, enable the formation of structures which allow high flow and intimate contact with the surface modified filler. Such composite structures may be used to design novel extraction systems.

EXAMPLE 6

This example is directed to surface modified tin oxide, thus demonstrating the use of a filler other than silica within a porous polymer membrane.

While silica is a desirable substrate for many surface active fillers, the use of other oxides, as well as nitrides, carbides, ceramics, and other like materials may be required. It has been demonstrated that surface treated tin oxide has potential value in electrochemical applications. Thus, it is expected that the photoelectrochemical properties of tin oxide would be useful if contained in a PTFE composite matrix.

A PTFE/tin oxide/conductive carbon composite is formed in any desired geometry and having a porous structure. Five grams of aminopropyltrichlorosilane are reacted with 5 g of tin oxide in dry, deaerated benzene. The tin oxide is then reacted in a 10% solution of refluxing silane, under nitrogen, with several portions of fresh solvent. The tin oxide remains electrochemical ly active and offers the potential to selectively modify the tin oxide surface for tailorable electrochemical interactions. One application for such a component is as a surface active electrode. The flexibility of incorporating such materials into a PTFE or other suitable surface permits the use of such materials in novel electrode configurations. EXAMPLE 7

This example is directed to immobilization of enzymes, thus demonstrating the support of a bioactive material within a PTFE/filler matrix. This example also demonstrates sequential post treatment. A PTFE/silica composite containing 5 g of silica is prepared using a porous PTFE structure. The composite is added to 20 ml of dry toluene containing 3 ml of 3-aminopropyltriethoxysilane. The slurry is then heated under reflux for 10 hours while under agitation. After washing with toluene, acetone and chloroform, the resulting product is dried at about 190°C for 2 hours. The coupling of the aminopropyl modified carrier to glucose oxidase is performed using a 2.5% glutaraldehyde in 0.1 M sodium phosphate, pH 7. Five milliliters of the glutaraldehyde solution are added to 1 g of aminopropyl carrier. The suspension is rotated in a rotovapor for 1 hour, the first 30 minutes under reduced pressure. After washing with water, glucose oxidase (corresponding to 1200 units) is dissolved in 2.25 ml of cold 0.1 M sodium phosphate. After evacuation, the mixture is shaken for 2 hours and kept in a refrigerator at about 4°C overnight. The final product is washed with cold buffer and water and kept as a suspension in water at about 4°C prior to use.

The immobilized glucose oxidase is reacted with glucose to liberate hydrogen peroxide which can be detected. A detection limit of about 8x10^"7 M glucose is achieved demonstrating the activity of the supported enzyme and the potential application in trace detection.

Other enzymes could be supported to allow analytical testing, or catalytic production of specific enzymatic products. The enzyme supported on a filler in a PTFE matrix may be exposed to the solution environment where the enzyme carries out the desired reaction. The PTFE/filler composite can comprise any form and may be subjected to harsh temperatures and chemical treatment prior to bonding the enzyme to the surface. Enzymes are chemically and thermally sensitive and would not survive traditional PTFE processing, making post treatment essential.

Of potential interest is the support of a bioactive material for implantable applications. PTFE matrix material is biologically inert and currently used in biologically implantable applications. It is also known that control of the PTFE matrix pore structure can control the extent of in-growth of biological tissue. Control of in-growth with respect to the surface active filler may be required for successful application of these surface active fillers. EXAMPLE 8

This example is directed to whole cell immobilization, wherein a PTFE/silica composite is prepared having whole cells supported on the silica. Specifically, a porous PTFE membrane is processed so as to contain 5 g of silica. The resulting composite is added to 50 ml of anhydrous ethanol containing 1 g of octadecyltrichlorosilane. After about 5 minutes the ethanol is decanted and the composite washed with ethanol. The treated PTFE/silica composite is washed twice with 5g of 0.25M sucrose solution buffered with 5 mM phosphate to pH 7.4. The composite is then placed in 25 ml of sucrose solution. Three ml of rat liver mitochondria suspension is added and the mixture stirred gently for 5 minutes. The solution is then washed twice with 30 ml of sucrose solution and three times with distilled water. Based on oxygen uptake after addition of alpha-ketoglutaric acid and ADP to solution and the formation of ATP, the coupled oxidation with phosphorylation by the mitochondria is validated.

The use of active cellular material in conjunction with the support structures of the present invention, such as PTFE matrices, offers exciting possibilities in terms of bioreactor design flexibility. Also, it is well known that control of the pore structure of the PTFE matrix can be used to control the extent of in-growth associated with implantable devices. With the control of the

PTFE matrix morphology not limited by processing limitations, unique implantable PTFE/bonded cellular materials are possible.

EXAMPLE 9 This example is directed to the incorporation of a solid super acid catalyst on a PTFE/filler matrix, thus demonstrating post treatment as a method to avoid contact of reactive filler and typical PTFE processing fluids.

Solid acid catalysts such as mixed oxides (chalcides) have been used extensively for many years in the petroleum industry and in organic synthesis. Their main advantage compared with liquid acid catalysts is the ease of separation from reaction mixture, which allows continuous operation, as well as regeneration and reutilization of the catalyst. Furthermore, the heterogeneous solid catalysts can lead to high selectivity and specific activity. Super acids can be used to crack alkanes at room temperature. Consequently PTFE processing aids such as mineral spirits (alkane mixtures) may react with the filler in the course of processing rendering the processing fluid nonfunctional. Post treatment would avoid this problem. A PTFE filler composite is prepared using as a filler a ceramic composite composed of Tiθ2"Zrθ2 and formed into any porous structure using appropriate processing procedures.

The PTFE filler composite containing the Tiθ2"Zrθ2 ceramic is exposed to SbFs vapor at room temperature followed by degassing. The adsorption- desorption cycle is repeated a number of times and finally the catalyst is subjected to high vacuum to remove the last trace of SbFs- This process results in the formation of a super acid. A system with approximately 30% SbFs by weight exhibited a high activity for butane cracking at room temperature and for pentane and 2-methylpentane isomerization at 0°C with a selectivity of close to 100%.

If an alkane can be catalytically cracked at room temperature, then many traditional PTFE processing fluids may not be stable in the presence of this super acid. Post treatment avoids potential interactions with processing fluids.

EXAMPLE 10

This example is directed to sequential surface modifications involving the formation of a palladium polyacrylonitrile surface. A PTFE crystalline silica composite containing up to 99% silica is first prepared having a porous node and fibril structure.

The PTFE/silica composite structure is wet-out in a reactor containing butanol. A sufficient quantity of acrylonitrile is dissolved in butanol to coat the particle surface, then a sufficient quantity of benzoyl peroxide is added to initiate the polymerization. The solution is then stirred and refluxed for 24 hours. The composite is rinsed with butanol and dried at 120°C for 4 hours.

PdCl2 is reacted with the polyacrylonitrile surface, then the composite is wet- out with a water/isopropanol mixture. The wet composite is added to the reaction vessel containing an aqueous bath with a sufficient quantity of dissolved PdCl22H2O to react with the polyacrylonitrile surface. The water is then driven off by drying at 120°C. This results in the polyacrylonitrile coated particles with catalytically active palladium.

Experimental results on the powder indicate that this polymer complex is an active catalyst for hydrogenation of alkenes and can reduce nitrobenzene to aniline at about 100% yield at room temperature and under atmospheric pressure.

Novel filled polymer support structures offer virtually limitless possibilities for reactor configurations. Post-bonding in this example is used not only because the polymer complex would not survive high temperature processing, but also because catalytically active palladium may be a hazard when combined with PTFE processing components such as alcohols, diols, alkanes, and the like.

While particular embodiments of the present invention have been illustrated and described herein, the present invention should not be limited to such illustrations and descriptions. It should be apparent that changes and modifications may be incorporated and embodied as part of the present invention within the scope of the following claims.

Claims

The invention claimed is:

1. A method of producing a filled polymer having at least one sensitive functionalized surface agent contained therein, comprising: producing a support structure comprising a porous polymer structure exhibiting a node and fibril structure and having at least one robust filler embedded therein, including processing the support structure under harsh conditions that would otherwise damage the functionality of the surface agent if it were present during processing; following cessation of the harsh conditions, applying the at least one sensitive functionalized surface agent to the filled polymer so that the surface agent adheres to the filler.

2. The method of claim 1 , wherein said harsh conditions comprise at least one of elevated temperature, high pressure and chemical exposure.

3. The method of claim 1 , wherein said porous polymer structure comprises a material selected from the group consisting of nonwoven structures, solvent extracted polymer structures, thermally induced phase separated polymer structures, and expanded polymer structures.

4. The method of claim 1, wherein said polymer comprises expanded PTFE and said processing comprises expanding the PTFE in at least one direction at an elevated temperature to form a porous expanded PTFE matrix.

5. The method of claim 1 , wherein said at least one robust filler comprises at least one material selected from the group consisting of silica, glass, oxides, titanates, carbides, nitrides, zeolites, metals and polymers.

6. The method of claim 1 , further comprising providing as said at least one surface active agent at least one material selected from the group consisting of polymeric, organic, organometallic, metallic, metal oxide, catalytic, ionic, acidic, basic, anionic, cationic, enzymatic, protein or biocellular material.

7. The method of claim 1 , wherein said at least one surface active agent is applied by at least one surface modification technique selected from the group consisting of organosilanes, acyl chlorides, anhydrides, isocyanates, ion exchange, doping, leaching, reduction, plating and mechanical coating.

8. A method of producing a filled polymer having at least one sensitive functionalized surface agent contained therein, comprising: producing a support structure comprising expanded polytetrafluoroethylene (PTFE) having at least one robust filler embedded therein, including processing the support structure at temperatures greater than about 350°C which would damage the functionality of the surface agent if it were present during processing; following cessation of the processing, applying the at least one sensitive functionalized surface agent to the filled expanded PTFE polymer so that the surface agent adheres to the filler.

9. The method of claim 8, wherein said processing further comprises at least one condition selected from the group consisting of high pressure and chemical exposure.

10. The method of claim 8, wherein said processing comprises expanding the PTFE in at least one direction at an elevated temperature to form a porous expanded PTFE matrix comprising nodes and fibrils.

11. The method of claim 8, wherein said at least one robust filler comprises at least one material selected from the group consisting of silica, glass, oxides, titanates, carbides, nitrides, zeolites, metals and polymers.

12. The method of claim 8, further comprising providing as said at least one surface active agent at least one material selected from the group consisting of polymeric, organic, organometallic, metallic, metal oxide, catalytic, ionic, acidic, basic, anionic, cationic, enzymatic, protein or biocellular material.

13. The method of claim 8, wherein said at least one surface active agent is applied by at least one surface modification technique selected from the group consisting of organosilanes, acyl chlorides, anhydrides, isocyanates, ion exchange, doping, leaching, reduction, plating and mechanical coating.

14. A filled polymer having at least one sensitive functionalized surface agent contained therein, comprising: a support structure comprising expanded PTFE and at least one robust filler incorporated within said expanded PTFE; and at least one sensitive functionalized surface agent bound to at least a portion of said at least one robust filler.

15. The filled polymer of claim 14, wherein said at least one robust filler comprises at least one material selected from the group consisting of silica, glass, oxides, titanates, carbides, nitrides, zeolites, metals and polymers.

16. The filled polymer of claim 14, wherein said at least one sensitive functionalized surface agent comprises at least one material selected from the group consisting of polymeric, organic, organometallic, metallic, metal oxide, catalytic, ionic, acidic, basic, anionic, cationic, enzymatic, protein or biocellular material.

17. The filled polymer of claim 14, wherein said at least one robust filler is tethered by fibrils of PTFE.

18. A filled polytetrafluoroethylene (PTFE) polymer having a sensitive functionalized surface agent contained therein, said filled polymer when analyzed by differential scanning calorimetry over a temperature range of 30° to 450°C at a heating rate of 10°C/min. exhibits a first endothermic peak in the temperature range 325°C to 350°C and a second endothermic peak in the temperature range 370°C to 390°C.