CA2138078A1

CA2138078A1 - Reinforced particle-loaded fibrillated ptfe web

Info

Publication number: CA2138078A1
Application number: CA002138078A
Authority: CA
Inventors: William V. Balsimo; Lloyd R. White
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1994-01-10
Filing date: 1994-12-14
Publication date: 1995-07-11
Also published as: JPH07205321A; EP0664353A1

Abstract

A composite article including a particle-loaded fibrillated polytetrafluoroethylene web with a reinforcing screen or scrim partially embedded therein.

Description

~138078 Docket No. 49820CANlA

REINFORCED PARTICLE-LOADED FIBRILLATED PTFE WEB

A. Field of the Invention This invention describes a particle-loaded fibrillated polytenfluoroethylene web with a reinforcing screen or scrim at least partially embedded therein. Compared to an unreinforced web, this reinforced web can 0 resist a much greater pressure drop across it without deforming and displays greater strength against various mechanical stresses.
B. Description of Related Art Particle-loaded, non-woven, fibrous articles wherein the non-woven fibrous web can be compressed, fused, melt-extruded, air-laid, spunbonded, 15 mechanically pressed, or derived from phase separation processes have been disclosed as useful in separation science. Web products of non-woven webs having dispersed therein sorbent particulate have been disclosed to be useful as, for example, respirators, protective garments, fluid-ret~inin~ articles, wipes for oil and/or water, and chromatographic and separation articles. Coated, 2 o inorganic oxide particles have also been enmeshed in such webs. Such webs with enmeshed particles which are covalently reactive with ligands (including biologically-active m~teri~l~) have also been recently developed.
Numerous examples of PTFE filled with or entrapping particulate material are known in many fields. Mauly applications for PTFE filled with 25 electroconductive materials are known. These include circuit boards, oil leaksensors, electrical insulators, semipermeable webs, and various types of electrodes. Other such combinations have been used as gasket or sealing materials and wet friction materials. Still others have been used to produce high-strength PTFE films and webs with applications as structural elements and 30 electronic components. Where the particulate has catalytic properties, this type of combination provides a form which can be conveniently handled.

~138078 U.S. Patent No. 4,153,661 discloses various particulate distributed in a matrix of entangled PTFE fibrils as being useful in, among other things, electronic in~ul~tors and semipermeable webs.
Numerous combinations of PTFE and metals in which the metal is not 5 entrapped within a PTFE matrix are also known. These include PTFE webs completely or partially coated with metal and metal matrices with a network of fibrillated PTFE in the pores thereof. PTFE powder with metal filler has been used (in paste form) as a battery electrode and as a self-lubricating layer coated on bronze be~rin~. PTFE films coated onto metal films and plates are also 1 o known.
Methods of preparing fibrillated PTFE webs have been described in, for example, U.S. Patent Nos. 4,153,661, 4,460,642, and 5,071,610.
The physical pro~.Lies of such particle-loaded fibrillated PTFE webs are somewhat limited, however. They do not resist high pressure drops without 15 deforming and have limited strength against mechanical stresses created by, for example, fluid flow, tensile force, mechanical impact, and abrasion.

SUMMARY OF THE INVENTION
In one aspect, the present invention provides a composite article 2 o comprising a fibrillated polytetrafluoroethylene (PTFE) web having particulate entrapped therein and, at least parfially embedded in the web, means for reinforcing the web. Preferably, this reinforcing means is a screen or scrim.
In another aspect, the present invention provides a method for malting this article comprising the steps of providing a fibrillated PTFE web with 2 5 particulate entapped therein and pressure bonding to the web a means for reinforcing the web so that the reinforcing means is at least partially embeddedin the web.
Unless otherwise indicated, the'following definitions apply in this application:
"screen" means a reinforcing material with a regular geometric pattem of threads which can be polymeric, glass, metallic, etc.;

~138078 "scrim" means a non-woven web the fibers of which are not in a regular geometric pattem and which can be polymeric, glass, metallic, etc.; and "partially embedded" (when used in connection with a reinforcing means) means the reinforcing means is (a) at least partially depressed in the 5 web to which it has been pressure bonded so that the reinforced web, when viewed from an edge, shows only up to 95%, preferably up to 90%, more preferably up to 75 %, and most preferably up to 50 %, of the reinforcing means and (b) at least partially mechanically entangled with the web.
Embedding a reinforcing means in a fibrillated PTFE web provides the 10 web with mechanical strength and resistance to deformation when a pressure drop is applied across it. Use of such a reinforcing means also allows the web to be formed into configurations that were previously difficult, if not impossible to achieve.
The reinforcing means used in the composite article of the present 15 invention is at least somewhat porous, preferably very porous (i.e., at least50% voids), so as not to greatly interfere with the porosity of the fibrillated PTFE web. This reinforcing means is at least partially embedded in the fibrillated PTFE web. The PTFE fibrils appear to actually attach to or become mechanically entangled with the reinforcing means. This is further illustrated 20 by reference to the drawings described below.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. l is a scanning electron micrograph (SEM) of a fibrillated PTFE
web reinforced with a polymeric screen.
FIG. 2 is an SEM of the reinforced web from FIG. l with the screen partially pulled away from the web.
FIG. 3 is an SEM providing a inore m~gnified view of the reinforced web from FIG. 2.
FIG. 4 is an SEM of one screen thread of the reinforced web from 30 FIG. 3.

~138078 FIG. 5 is an SEM of a fibrillated PTFE web reinforced with a polymeric scrim.
FIG. 6 is an SEM of the reinforced web from FIG. 5 with the scrim partially pulled away from the web.
s FIG. 7 is an SEM providing a more m~gnified view of the reinforced web from FIG. 6.
FIG. 8 is an SEM of one scrim fiber of the reinforced web from FIG. 7.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 shows an SEM (60x m~gnification) of reinforced web 10 comprising particle-loaded fibrillated PTFE web 12 with screen 14 partially embedded therein. In this particular embodiment, fibrillated PTFE web 12 entraps activated carbon particulate. Any particulate, regardless of shape, thatcan be entrapped in a nonwoven polymeric web can be used in the reinforced 15 fibrillated PTFE web of the present invention. Representative examples of useful particulate include those listed in U.S. Patent Nos. 4,153,661, 4,460,642, 5,071,610, and 5,209,967 as well as U.S. Ser. No. 08/004,967, which lists are herein incorporated by reference. Particularly useful particulate m~eri~l~ include activated carbon, silica, derivatized silica, glass beads and 20 bubbles, chitin, and the like. In this particular embodiment, screen 14 is Nitex-37 nylon (TETKO, Inc.; Rolling Meadows, IL). Any porous screen can be used as a reinforcement means, although those with a very fine mesh can interfere with the porosity of the web and cause undesirable resistance to flow and channeling. Screen 14 can be pressed into web 12 by standard pleSSUle 25 bonding techniques as are well known in the art, optionally under elevated temperature.
FIG. 2 shows an SEM (15 x m~gnification) of fibrillated PTFE web 12 with screen 14 partially pulled away theleîlo--l. The screen pattem can be seen clearly in web 12.

21~8078 FIG. 3 shows a more m~gnified close-up SEM (35 x m~gnification) of that seen in FIG. 2. Again, the pattem of screen 14 can be seen clearly in web 12.
FIG. 4 shows an SEM (500X m~gnific~tion) of PTFE fibrils 16 from 5 web 12 (of FIGS. 1-3) still attached to screen 14 after screen 14 has been partially pulled away from web 12. That fibrils 16 become mechanically entangled with or attached to screen 14 threads while screen 14 is embedded in web 12 is readily apparent.
FIG. S shows an SEM (250X m~pnifit~tion) of reinforced web 20 10 comprising particle-loaded fibrillated PTFE web 22 with scrim 24 partially embedded therein. In this embodiment, fibrillated PTFE web 22 entraps silica, although, as mentioned above, many other types of particulate can be used. In this embodiment, scrim 24 is a nonwoven polypropylene web available from, for example, AMOCO Fabrics & Fibers Co. (Atlanta, GA). Any porous scrim 15 can be used as a reinforcement means, however.
FIG. 6 shows an SEM (35 x m~gnification) of fibrillated PTFE web 22 with scrim 24 partially pulled away therefrom. The scrim pattem can be seen clearly in web 22.
FIG. 7 shows a more m~gnified close-up SEM (lSOX m~pnific~tion) of 20 that seen in FIG. 6. PTFE fibrils 26 can be seen being pulled away from web 22 as scrim 24 is removed thererrol-l.
FIG. 8 shows a more m~gnified close-up SEM (330X m~gnific~tion) of that seen in FIG. 7. Silica particles 28 entrapped within fibrils 26 are apparent.
Once again, that fibrils 26 become mechanically entangled with or attached to 25 scrim 24 fibers while scrim 24 is embedded in web 22 is readily apparent.
To make the web in which are entrapped the active particulate, one begins with an aqueous PIFE dispersion. This milky-white dispersion contains about 20% to 705~ (by weight) of minute PTFE particles suspended in water.
A major portion of these PTFE particles range in size from 0.05 to about 0.5 3 o ~m. Commercially available aqueous PTFE dispersions may contain other ingredients such as surfactants and stabilizers that promote continued ~138078 sl~spel~ion. Examples of such commercially available dispersions include TeflonTU 30, Teflon~ 30B, and Teflonn' 42 (DuPont de Nemours Chemical Corp.; Wilmington, DE). Teflonn' 30 and Teflon~ 30B contain about 59 % to 61 % (by weight) PTFE solids and about 5.5 % to 6.5 % (by weight, based on 5 the weight of PTFE resin) of a non-ionic wetting agent, typically octylphenyl polyoxyethylene or nonylphenyl polyoxyethylene. Teflon~ 42 contains about 32 % to 35 % (by weight) PTFE solids and no wetting agent (but does contain a surface layer of organic solvent to prevent evaporation).
The particle-loaded fibrillated PTFE web preferably is prepalc~d as lo described in any of U.S. Patent Nos. 4,153,661, 4,460,642, and 5,071,610, theprocesses of which are incorporated herein by reference, by blending the desired reactive particulate into the aqueous PTFE emulsion in the presence of sufficient lubricant to approach or, preferably, exceed the sorptive capacity ofthe solids yet maintain a putty-like consistency. This putty-like mass is then 15 subjected to intensive mixing at a temperature preferably between 40" and lOOOC to cause initial fibrillation of the PTFE particles. The resulting puttylike mass is then repeatedly and biaxially calendered, with a progressive narrowing of the gap between the rollers (while at least maintaining the water content), until the shear causes the PTFE to fibrillate and enmesh the particulate and a 20 layer of desired thickness is obtained. Removal of any residual surfactant orwetting agent by organic solvent extraction or by washing with water after formation of the web article is generally desirable. The resultant web is then dried. Such webs preferably have thicknesses in the range of 0.1 to 0.5 mm.
Web articles with a thickness in the general range of 0.05 to 10 mm can be 2 5 useful.
If a web article with mulfiple particulate layers is desired, the component layers themselves are stacked on each other and calendered until they form a composite where the PTFE fibrils of the separate layers are entwined at the interface of adjacent webs. Such multilayer webs demonstrate 30 little boundary mixing between adjacent layers of particles. Multilayer articles preferably have thicknesses in the range of 0.1 to 10 mm.

~138~78 The void size and volume within such a web article can be controlled by regulating the lubricant level during fabrication as described in U.S. Patent No.
5,071,610. Recause both the size and the volume of the voids can vary directly with the amount of lubricant present during the fibrillation process, webs s capable of entrapping particles of various sizes are possible. For instance, increasing the amount of lubricant to the point where it exceeds the lubricant sorptive capacity of the particulate by at least 3 % (by weight) and up to 200 %(by weight) can provide mean void sizes in the range of 0.3 ~m to 5.0 ~m with at least 90% of the voids having a size of less than 3.6 ~m. This process can lo be used to create a web article with one or more kinds of reactive particulate enmeshed therein. The PTFE which forms the web within which particulate is to be trapped can be obtained in resin emulsion form wherein the PTFE and lubricant are already premixed (e.g., TeflonTY 30 or 30B, DuPont de Nemours;
Wilmington, DE). To this emulsion can be added additional lubricant in the 15 form of water, water-based solvents such as a water-alcohol solution, or easily-removable organic solvents such as ketones, esters, and ethers, to obtain the aforementioned desired proportion of lubricant and particulate.
Active particulate (i.e., those which perform a funtion such as chemical reaction with or sorption of a solute or conduction) useful in the present 20 invention includes any such pafticulate that can be immobilized in a non-woven, fibrous matrix. Representative sorptive particles include, but are not limited to, activated carbon, silica, derivatized silica, ion exchange resins, intercalated styrene divinylbenzene, and chitin. Conductive particles such as silver-coated glass spheres can also be used. Particulate material can be of regular (flat, 2s spherical, cubic, rod- or fiber-like, etc.) or irregular shape. Average diameters of useful particles are within the range of 0.1 to 100 ,um, more preferably within the range of 0.1 to 50 ,~4m, and most preferably within the range of 1 to10 ,um. Such particulate can be incorporated directly into the web article.
Particulate is generally distributed uniformly in the web article, but 3 o matrices which include combinations of particulate can be prepared.
Altematively, layers containing different particulate can be calendered into a 213~078 single matrix with distinct strata of particulate. Such multilayer composite articles show minim~l boundary mixing (between the various particulate) and retain good uniformity throughout each layer. Whether in a helelogeneous or homogenous form, this type of article can selectively sorb or react with one or 5 more chemical species to be removed from a fluid where these webs are to be used in chromatographic or separations applications.
Total particulate content of the web article can range up to about 97%
(by weight), (although particulate amounts in the range of 80 to 95% (by weight) tend to produce more stable web articles). The enm.oshing fibrils retain10 the enmeshed particulate, by entrapment or adhesion, within the matrix, and the enmeshed particles resist sloughing.
The web article of the present invention preferably comprises active particulate in an amount of at least 10% (by weight), more preferably comprises active particulate in an amount of at least 50% (by weight), and most 15 preferably comprises active particulate in an amount of at least 80% (by weight). High active particulate loading is desirable to maximize the sorptive capacity or chemical activity of the substrate.
Non-active adjuvant particles with average diameters in the same ranges as listed previously with respect to active particulate can be included.
20 Representative examples pf useful adjuvants that can be incorporated in the web article include property modifiers such as glass beads and/br bubbles, glass particles other than beads or bubbles, energy-expandable hollow polymeric particles such as Expancel~ microspheres (Nobel Industries; Sundsvall, Sweden) and mica. When present, such non-active particulate can comprise 25 from more than 0 to 95 % (by weight), preferably from more than 0 to 50%
(by weight), and most preferably from more than 0 to 10% (by weight) of the web article.
Particle-loaded fibrillated PTFE webs that have been reinforced in the above manner display improved resistance to ballooning and/or tearing and to 3 o shrinkage. This is very desirable in applications where the web must withstand a pressure drop caused by fluid flowing through it or must display dimensional stability. (Unreinforced fibrillated PTFE webs tend to shrink in the direction in which they were last machined.) Also, reinforced webs are easier to handle and less likely to be damaged during normal use.
If desired, a fibrillated PTFE web with particulate entlapped therein can 5 also be reinforced on both sides. In other words, reinforcement means can be partially embedded in both sides of the web. This can increase the composite article's resistance to the aforementioned undesirable properties. Additionally,multilayer web - reinforcing means composite articles also can be made. This might be desirable where each web layer contains a different type of 1 o particulate.
The reinforced particle-loaded fibrillated PTFE webs of the present invention can be used wherever unreinforced particle-loaded fibrillated PTFE
webs are useful, particularly in separation science (e.g., chromatographic and other separations as well as extractions).
Objects and advantages of this invention are further illustrated by the following examples. The particular materials and amounts thereof, as well as other conditions and details, recited in these examples should not be used to unduly limit this invention.

2 o EXAMPLES
Example I
The parficle-loaded fibrillated PTFE web described herein was made essenti~lly according to the procedure described in columns 3 to 6 of U.S.
Patent No. 4,153,661.
The following materials were added together and the mixture was mixed in a Ross~ mixer (Charles Ross & Son Co.; Hauppage, NY) at 30 rpm for 45 sec at 38C:
400 g dry super-activated carbon with a surface area of 2000 to 3000 m2/g and an average particle size of 30 ~m with a range of 3.9 to 200 ~m (Kansai Coke and Chemicals Co. Ltd.; Am~g~ki City, Japan) 2138~7~

312 g FLUONr~ PTFE emulsion, 22.6% PTFE in water (ICI
Americas, Inc.; Wilmington, DE) 894 g deionized water This mixing provided a doughy mass.
This dough-like mass was passed through a two-roll mill with an initial gap setting of 3.81 mm. The first few passes resulted in a web without enough strength to support its own weight; however, after a few more passes, the web was strong enough to maintain its integrity so that it could be folded into three layers and rotated 90 for its next pass through the mill. This biaxial lo calendering was followed for a total of ten passes. Thereafter, the gap was adjusted from 2.54 mm to 1.27 mm to 0.64 mm (with web passes through each gap) to produce a long web.
After the above three passes, the web was folded into eight layers and rotated 90. The gap was adjusted from 2.54 mm to 1.90 mm to 1.27 mm to 15 0.76 mm (with web passes through each gap). This process yielded a fibrillated PTFE web that was 1.14 mm thick which was dried by passing through a belt oven.
This web was reinforced by placing it between two layers of Naltex~
LWS filtration netting (Nalle Plastics, Inc.; Austin, TX) and passing this 20 composite article through a two-roll mill (gap = 0.89 mm, roll speed = 7.6 cm/sec). The tensile strength of the web-netting bond, measured by pulling the netting away from the web in a tensile tester (Thwing-Albert Instrument Co.;
Philadelphia, PA), was 0.18 N/cm.

Example 2 A particle-loaded PTFE web was prepared as in Example 1 with the exception that final web thickness was 0.76 mm. This web was reinforced as in Example 1 with the exception that gap width during reinforcement was 0.51 mm. The tensile strength of this web-netting bond was 0.33 N/cm.

2~38o78 Example 3 A particle-loaded PTFE web was prepared as in Example 1 with the excepfion that final web thickness was 1.52 mm. This web was reinforced as in Example 1 with the exception that gap width during reinforcement was 1.14 5 mm. The tensile strength of this web-netting bond was 0.21 N/cm.

Example 4 A particle-loaded PTFE web was prepared as in Example 1 except that extra calendering produced a final web thickness of 0.38 mm. This web was 10 sandwiched between two layers of 25 g/m2 basis weight polyethylene non-woven web, and this composite article was passed through a two-roll mill with a gap of 0.25 mm. The tensile strength of this web - non-woven web bond was 0.035 N/cm.

Example 5 A particle-loaded reinforced PTFE web was prepared as in Example 4 except that a polyester non-woven web with a basis weight of 45 gtm2 was used. The tensile strength of this web - non-woven web bond was 0.14 N/cm.

2 o Example 6 A particle-loaded reinforced PTFE web was prepared as in Example S
except that only one layer of reinforcement was used and the gap thickness during calendering was 0.64 mm.
This reinforced web and a similar unreinforced web were evaluated 25 three ways: 1) use as an absorbing means on a generic base, 2) tensile strength, and 3) ~hrink~ge.
Use with a ~eneric base: Generic bases for in-line filter holders are those designed for paper or paper-like webs. They are available from a wide variety of commercial sources such as Gelman Co. (Ann Arbor, MI) and Nalgene Co. (Rochester, NY). Unreinforced webs were soft and conformed to 2i38078 the contours of the generic bases. Thus, when a blue food coloring solution was passed through an unreinforced web, flow was restricted to those areas where the web was not in direct contact with the base, and the dye was absorbed only in those areas (i.e., channeling occurred).
When a similar dye solution was passed through a reinforced web supported on a generic base, no such conformation was observed, and the dye solution was evenly distributed throughout the web (i.e., ch~nneling, leaks, and/or breakthrough were not observed).
Tensile strength: The tensile strength of the reinforced webs were at least 10 an order of magnitude greater. The tensile strength of various reinforced webs is shown in Table I below.
Shrinkage: Shrinkage induced by mechanical stimulation and by long-term exposure to heat were both tested.
Disks (with diameters of 47 mm) of reinforced and unreinforced webs were biaxially shaken on a sieve shaker (C.E. Tyler Co.; Mentor, OH) for approximately 60 minutes. The unreinforced disks shrunk into an elliptical shape with a minor axis of about 42 mm (i.e., 30 about 10% shrink~ge). Essentially no shrinkage of the reinforced disks was observed.
Two disks (47 mm diameters) of reinforced web were placed in an oven at 71C for 51 days. No shr1nk~ge was observed. Under similar conditions, unreinforced webs would have shrunk by at least 10%.

Example 7 A particle-loaded fibrillated PTFE web was prepared using the same procedure as that described in Example 1. Instead of activated carbon, 30 however, the particulate was a C,8-derivatized silica a.T. Baker Co.;

Phillipsburg, NJ). The final thickness of the web was 0.51 mm. The web was 90% (by weight) particulate.
A layer of Naltex~ LWS filtration netting was placed between two of these webs. The layered composite was passed through a two-roll mill (gap =
5 1.27 mm).
A 50 mm x 50 mm square sample of this reinforced web was placed in a 47 mm manifold vacuum system (Millipore Corp.; Bedford, MA) with the supporting screen removed thererrolll. A liter of water with one drop of blue food coloring was pulled through the reinforced web. While removing dye 10 from the solution, the reinforced web did not balloon or tear and was not pulled into the vacuum flask.

Example 8 A large web with Cl8 as the entrapped particulate was p-epared using the 15 same procedure as in Example 1. Portions of this web were reinforced with various reinforcing materials, and these reinforced webs were tested against a comparative unreinforced web. The results are summarized in Table I below.
NITEXn' nylon screens are made by TETKO, Inc. (Rolling Meadows, IL). Monodur~ Nylon 475 and 850 screens a-re made by Industrial Fabrics 20 Corp. (Minneapolis, MN). Naltex~ filtration netting is made by Nalle Plastics, Inc. (Austin, TX). Celestra~ and PBN Ir non-woven webs are made by Fiberweb Inc. (Pensacola, FL). Brookings~ non-woven webs are made by Minnesota Mining and Manufacturing Co. (St. Paul, MN). Typar~ and 4dpf~
Straight non-woven webs are made by Reemay, Inc. (Old Hickory, TN).
25 CoverstockTM non-woven webs are made by Bonar Fabrics (Greenville, SC).
RFX~ non-woven webs are made by AMOCO Fibers and Fabrics, Inc.
(Atlanta, GA).

TABLE I
Type of Sample Tradename of p~ r ~ g Means Average Threads Thread Average Failure Stress (Ibs. Average Failure Strain (% linear 12~ r ,- ~ No. basis wt. per inch diameter per linear inch width of increase in length at peak stress) means (g/m~) (mils) material) Crossweb Downweb Crossweb Downweb NONE I N/A 323.7 N/A N/A 0.034 0.22 378.9 34.3 SCREEN 2 NITEX~ nylon 143.5 21 10 787 847 30 32 3 Monodur"' Nylon 475 116.3 37 7 973 786 28 46 4 Monodur Nylon 850 153.6 22 12 866 783 28 29 S Naltex~ filtration nening 53.6 15 N/A 3.11 1.64 193.9 24.0 6 Naltexn' filtration nening 166.3 44 N/A 11.63 13.97 168.0 44.0 SCRIM 7 Celestra~ .. .J . . web 19.2 N/A N/A 1.49 4.92 27.4 36.0 8 Brookings non-woven web 26.3 N/A N/A 1.25 5.92 34.9 24.6 9 Typar"' .... J._ web 44.9 N/A N/A 9.01 13.18 23.8 28.0 Fiberweb PBN II~ non-woven web 10.2 N/A N/A 1.94 4.34 46.9 50.3 I l Bonar G,. . ' ~ ..... ~, . . web 17.9 N/A N/A 11.83 2.46 23.4 43.4 0 12 Cerexn' ~ .. ~. web 50.9 N/A N/A 2.61 3.95 59.4 40.6 13 AMOCO RFX~ ....... J.. .web with AS 16.0 N/A N/A 0.66 1.35 259.4 27.4 14 Reemay 4dpf~ Straight .. ~.. web 23.7 N/A N/A 3.78 5.68 29.1 38.3 AMOCO RF~ .. web 17.0 N/A N/A 1.54 3.53 153.7 61.1 16 AMOCO RFX'Y non-woven web 33.9 N/A N/A 2.83 7.82 182.3 79.4 2l38o78 All samples other than No. 1 were reinforced. Stress and strain values for reinforcement means only are not shown but are of the same order of m~gnitl1de as for the corresponding reinforced webs.
Rec~llse samples 2-4 were illlplopelly cut, their stress and strain values 5 could be off by up to 30%; however, these numbers help to prove the overall conclusion that can be drawn from Table I, i.e., that reinforced webs, regardless of the type of reinforcement, are at least an order of m~gnitude stronger in both the crossweb and downweb directions than an otherwise identical unreinforced web.
Various modifications and alterations which do not depart from the scope and spirit of this invention will become a~alellt to those skilled in the art. This invention is not to be unduly limited to the illustrative embotlim~nt~set forth herein.

Claims

1. A composite article comprising:
a) a fibrillated polytetrafluoroethylene web having particulate entrapped therein; and b) means for reinforcing said web;
said reinforcing means being at least partially embedded in said web.

2. The composite article of claim 1 wherein said reinforcing means is a screen.

3. The composite article of claim 2 wherein said screen is metallic.

4. The composite article of claim 1 wherein said reinforcing means is a scrim.

5. The composite article of claim 1 further comprising a second fibrillated polytetrafluoroethylene web.

6. The composite article of claim 1 further comprising a second reinforcing means.

7. The composite article of claim 1 wherein said particulate is capable of chemical reaction with or sorption of a solute passing through said web.

8. The composite article of claim 7 wherein said particulate is selected from the group consisting of activated carbon, silica, derivatized 30 silica, intercalated styrene divinylbenzene, ion exchange resins, and chitin.

9. The composite article of claim 1 wherein said particulate is conductive.

10. A method of making a reinforced particle-loaded fibrillated polytetrafluoroethylene web article comprising the steps:
a) providing a fibrillated polytetrafluoroethylene web having particulate entrapped therein; and b) pressure bonding to said web a means for reinforcing said web so that said reinforcing means is at least partially embedded in said web.