CA2003205A1 - Fabric reinforced composite membrane - Google Patents

Abstract

Fabric Reinforced Composite Membrane ABSTRACT OF THE DISCLOSURE
An abrasion-resistant, tear-resistant, multilayer composite membrane, useful in electrolysis, is provided comprising a continuous perfluoro ion exchange polymer film attached to a reinforcing fabric by means of a porous, expanded polytetrafluoroethylene (EPTFE) interlayer. The fabric and EPTFE are rendered hydrophilic and non-gas-locking by coating the interior and exterior surfaces thereof with a perfluoro ion exchange resin of equivalent weight less than 1000.The composite preferably is treated with an ionic perfluoro surfactant. Also provided is a multilayer composite according to the above in which the continuous perfluoro ion exchange film is itself a multilayer construction of a perfluorosulfonate polymer and a thin layer of perfluorocarboxylate polymer in which the perfluorosulfonate polymer interfaces with the EPTFE and the interior and exterior surfaces of the EPTFE and fabric are coated with perfluoro-sulfonate polymer. Also provided are a method of making the composites and methods of use for these fabric reinforced thin membrane structures as separators in electrolytic cells, and as selective barriers in permeation separation and facilitated transport operations.

Description

F~bric ~ejn~orced Composi~e aqe~
BACKGROUND OF THE INVENTION
1. Field of the Invention 'rhe inventicn rela~es to a comp~6ite membrane useful in electrolytic 5 processes snd other chemical separations.

2. D~;cription of Related Art In electrolytic processes such as the electrolysis o brine or hydrogen chloride, or In the electrowinning o~ various me~al~, it i~ impor~ant to provide~ separator between anode and cathode compartrnent3. Chemic~lly ~table ion 10 exchange membranes made from perfluorosulfonic acid poly ner, as de~cribed inUS. Patents 3~282,875; 3,718,627; 4,358,545; and 4,329,434, or from perflllor~
carboxylic ~cid polymer, ~s described in U.S. Patent~ ~,131,7~0 and 4?734,170, h~ve ~ound broad use as separators. For the elecerolysis of brine to produce concentrated caustic, d multilayer membrane involving both perf~uorosulfonic 15 acid polymer and perfluorocarboxylic dcid polymer has been u~ed as described in J~panese Pstent Appllcation Disclosure No. 52/3B589.
For reason3 of guali~y, eîficiency, cost e~ec~Jv~nes~ and often safety it is impol tant that the separator be tear-, abr~sion-, punctur~ and scratch-resistant, yet not so th~ck or r~inforced ~h2t its resi~tAnce to ionic conduction 20 And concomitant power consumption Are excessively high.
Unr~inforced perfluoro ion exchange resin membranes ~re mechanically weak, especlally when swollen in aqueou~ medi~. ~or example, characteristic Elmendorf tear stren~th for a 5 mil, 1100 squivalent weight film i5 about 80 gr~ms when d~y and con~lderably less when satursted with wat~r. As ~ con-25 sequen~e, r~inforcement mech~nisms have been devised in which a fabric,usu~lly m~d~ trom polytetrafluoroethylene (PTF~) fiber~, h~ been psrtially or wholly ~n~apsul~ted by the perIluoro lon exchange polymer. Commercial products r~tl~et thi~ approach. ~owever, it requires about fl 5-10 mil thicknessof ion exchange rnembr~ne to effectively bond to and encapsulate the fabric.
30 Thinner membranes are unsatisfactory since ~hey may not completely csver the fabrio on both ~ides and the integrity of thg membrane i~ ~mpaired. T~e electrical res~stance in aqueous me~ia of t~is reinforoed S-10 mil struc~ure is considerably higher than that of ~n unreinforced thinner membran~ because of the increased thickness ~nd the reduced effective cross-section available for ion 35 transport because of the encapsulated fabric.
13.S. Patent 4,60~,170, in an attemp~ to addres~ this problem, discloses a cornposite of a relatiYely thin con~inuo~ perfluoroionom~r membrane with a .

32~i porous, expanded polytetrafluoroethylene ~PT~E) structure rendered hydrophili¢
by a number of means to provide ~n electroly~ie membrsne with low resistance to lonic conduction ~nd moderate tear strength. High l~vels of tear strength ~ndcut-through and abrasion resistance are not provided by thi approach, howeYer.
5 High levels of tçar strength and abrasion resistance are not provlded by ~ny known prior EPTFE structure which is sufficiently porous to provide ~cceptsbly low voltage operation.
U5. Patent 4,B04,17û also claims the use ot a multilayer membrane consisting of perfluorosulfonic acid polymer and perfiuorocarboxylic acid 10 polymer which Is larninated to porous EPTF13 for use in brine electrolysis to reduce hydroxyl ion back migr~tion.
Japanese Patent Applica~ion Disclosure No. 62-230231 describ~ a re-inforced membrane structure involving a continuous perfluoro ion exchange fllm lam inated to a porous body. The porous body is described as a thre~l~yer lS laminate jnvolving a fabric or scrim made from a fluorine containing polymer whlch has been sandwiched and encapsulated between two EPTFE sheet~. To provided hydrophilicity and some measure of cohesion, the EPTFE sheets and the ~abrie are impregnated with a solution of the acidic form of perfluorosul$onic acjd polymer. After drying, the porous body sandwich structure is heat 20 laminated with the continuous perfluoro ion exehange sheet. This eonstruction provides an EPrFE interlayer between the abric and the continuous ion exchange membrane. However, the bond provided by the perfluoroionomer is low, e.g., less than 60 gms/ln. peel strength for a 20 strand per inch scrim, and degrades to essent~ally no strength, e.g., less than 20 gmstin~ peel strength, dfter 25 immersion in hot water for 24 hours.
Japane3~ Patent Applicatisn Disclosure No. 62-280230 describes 8 com-posite structur~ in whlch a scrim or open fabric is heat lam~ated and encap-sulated be~wcen a continuous perfluoro ion exchQnge membrane ~nd an EPTFE
sheet, thus irnparting tear strength to the struc~ure. This method of mech~nical30 enhancem~nt i9 deficient ~n that relatively thlck ion exchang~ membranes or high equivalent weight membranes must be used to penetrate through the fabric and bond to the EPTFE sheet in order to avoid pinholes and thereby loss of elecSrolytic integrity. Thi~ker membranes or high equivalent weight membrdnes result in higher voltage operation. Also this method Is not applicable to 35 composites having more tightly woven fabrics, which in some applications may be desirable to protect ~he membrane from cutting or abr~ive damage.
'rhe presen~ inven~ion overcomes mos~ of the mech~nical deficiencies of pr~violls membranes and, surprisingly, provides a membrane having a lower ~32~5 r~sistance to ionic conduction which approache~ tl at of very thin"Jnreinforced perfluoro ion exch~nge polymer membranes.
In the separation of fluids, membran*3 through which fluids have different permeation rates have been useful in separating mixtures of those fluid~. Such 5 films have. been wound with macroporous separating meshes which permit free flow Qf fluids to and from the membrane'~ surfaceq and modules h~ve been constructed. Thin perfluoroionomer films have a very high persneability to w~terand some other polar molecules. but effective permeation separation modules can not be built from these thin, fragile perfluoroionomer filme.
Facilitated transport is a relsted separation technîque wherein a con-tinuous membrane is pl~sticized or swollen with a liquid. The dissolved liquid complexes with one of the fluidc to be separated and selectively f~cil;tates itstransport across the membrane. Again, thin perfluoroionomer film~ offer some unique opportunities for fscilitated transport, as, for example, in the separation 15 of amino ~cids in aqueous media, bl~t the thin perfluoroionomer is not suffi-ciently strong ~o undergo module constru¢tion or withstand operating pressure differentials. U.S. Petent 4,194,041 provides for ~ waterproof article which permlts the p~ssage of water vapor and includes ~ hydrophilic layer. Specific claims are drawn to a perfluoroionomer, which permits the passage of water 20 vapor and which i9 composited with a hydrophobic ~PTFE l~yer which prevents the p~ssage of liquid water. However, the ~bility to transport aqueous liquids is important not only in electrolytic processes but ~Iso in perme~tion separ~tion and facilit&ted transport operations.
The composlte~ of the present invention overcome the mechanical 25 ~trength limitations of thin perfluoroionomer films without signific~ntly reducing the high p~rme~tion and transport r~tes possible with these thin perfiuoroion-omer films. In ~ddition, the composites of this invention provide for ~n EPTFE
l~yer whioh is rendered hydrophili~ by coating the interior and exterior surfaces of the EPTF~ with a perfluoroior~omer without destroyin~ its porosity. In this 30 way, ga~ locking of the EPrFE structure, which blocks the flow of ~gueous liguid~ ~o or from the continuous membrane's surface, is avoided~
The structure of the present invention involves the flow and/or mech~
icQl Interlocking of the fiber Qf the fabri~ into the por~s of the EPTFE sheet, resulting ~ strong bonds, e.g., varying from 80 to ~00 gms/in. peel strength, in35 the absence of Qn adhesive, which remain essentially unchangcd even after long exposure in boiling w~ter. Indeed, in some cases where extsnsive penetration of the surface layer of the polymer into the sheet is 1chieved, the EPT~ sheet fsils cohesiYely before the fabric/EPTFE interfaee CAIl be ~eparated.

2~ 05 -.4-SUMMARY OF THE INVENTIC)N
A multilayer composite membrane is provided comprising ~ synthetio fabric bonded ~o one surface of a layer of porsus, expanded polytetrafluoro-ethylene (EPTFE), the EPTF~ layer havlng a ccntinuous perfluoro ion exch3nge 5 polymer film laminated thereto on the surfaee opposite the one surface, ~he fabric and porous EPTFE having a coating on at least a portion of the internal and external surfaces thereof of a perfluoro ion exchange re~in, The bond between the synthetic fabric and EPTFE is believed to be a me~hanical ~ond formed at points o~ ~on~act between the fabric and the EPTFE layer.
~lso provided is a multilayer compoæite membrane comprising a continu-ous perfluoro ion exchange polymer lilm having a synthetic f~bric layer bonded to both surfaces oY the perfluoro ion exchang~ polymer film in sandwiclt-like configuration by means of an EPTFE interlayer intsrposed between the ~on exchan~e polymer film and e~ch synthetic fabric layer, the fabri~ ~nd porou~
15 I~PTYE h~ving a coatin~ on a~ least a portion of the internal uld external surface~ thereof of a perfluoro ion exchange resin, the bond ~etween the ~ynthetic fabric and EPTFE being at lea~t partially a me¢hanloal bond ~ormed at polnts of conta~ between the fabric and the EPTF~ l~yers. The f~bric prefer~ly is made from halogen containing synthetie polymer fibers such a~
20 polytetrafluoroethylene, a perfluoro copolymer of tetrafllJoroethylene or poly-tetrafluoroe~hylene flber~ coated with perfluoro ~opolymers of tetrafluoro-ethylene. The Yabric may be woven or nonwoven. The ~ontinuous perfluoro ion exehange polymer fllrn preferably is perfluorosulfonate or perfuoroearboxylate.
The intcrior and exterior surfaces of the ~PTF~ and fabric preferably are coated25 wlth p¢rfluorosulfonic acid polymer of equivalent weight les~ than 1000 or perfluorocarboxylie scid po~mer of equivnlent weight less than 1000. The f~bric and EPrFE preferably are impregnated with sn ionic perfluorosurf~ctant.
The composlt~ may be used as a reinforced thin selectlve barrier in chemie81 s~p~rations, pro~iding mechsnical strength without ~crificing low 30 resistance to ~clectiv~ transport inherent in a thin continuous per~luoro ion exchange p~lymer f ilm ~lone. The composite may be employed as an electrolytic separator between anode and cathode comp~rtments in ~n electro-lyzer, providing low voltage operation, ~nd as a thin continuous barrier in permeation separ~tions and in facilit~ted transport operation~, whereby s~id ~5 fabric provides mech~nical support and the spac~s between fibers provide avenues o~ passage o~ fluids to and from the continuous membr~ne's surfaces without substantially sacrificing the hi6h selective permeation rates to water 3;2:~S
~.~

and other hydrophilic msterials inherent in the thl n continuou~ perfluoro ion exchange polymer l'ilm.
Also provid~d l~ a process for makin8 the multilayer oomposite of the invention.
BRJEF DESCR~PTION OF T~}E D~AWIN~3S
Fig. 1 ~ a perspective cross-sect~on~l view of on~ embodirnent of the composite of th~ invention.
Fig. 2 i~ a cro~s-sectional view of a s~cond embodiment of the compssite of the invention.
Figs. 3 to 6 are photo~icrographs taken st v~rious magnificfltions showing the composite laminates according to the invention.
D~TAILED DESCRlPrlON OF THE INVENTION
AND PREFERRED ~MBODIM~Nr5 WlT~
REFE~ENCE TO THE DRAWINC;S
A mechanically strong multilayer composite membr~ne with low r~sis-tance to ionic conduction in electroly~iG processes and ~llowing high perme~tionra~es in perme~tion separation and facilitated transport op~ration3 is provided,comprising a continuou~ perfluoro ion exchange polymer film ~ttached on one or both sides to a reinforcing fabric by means of an EPTF~ interl~yer, wherein the ao f~bric(s) and EPT~E interlayer(s) are rendered hydrophilic ~nd non~as-locking by coating at l~ast a part or ~11 Or the interior ~nd exterior surfac~ the~eof wltha perfluoro ion exch~n~e resin, pr~ferably of e~uivalsnt weight ~2SS ~han 1000.
Initilll wetting i~ assur~d by trea~ment ot the fabric(s) and EPTFE interl~yer(s) wlth a water soluble ionic surfactant such a~ ammonium perfluorooct~no~te.
The continuolls perfluoro ion exchange membran~ may be perfluorosulfonic acid polymer or perfluQrocQrboxyli~ ~cid polymer and the perfluorosulfonic acid polymer i~ pre~erred.
In el8C~lrOlyS39 proce~ses producing caustie exceeding 20% in concentrs-tion, a continuou~ bil~yer ion ex¢hange membrane comprisinB~ ~ thin 12yer of perfluoroc~rboxyl~te polymer on one sur~s~e of perfluorosulfonate ion exchange polym~r film (as described in V.~. P~tent ~,~87,668, Eng~nd ~t ~l ~DuPont)) is incorporated in the composite of this invention with the thin sulfonQte layer interfacin~ with the EPTFE ~nd with the carboxylate layer providing a barrier to bsck migra~ion of the hydroxyl ions.
For prooe~ses producing lower strength caustic from brine, ~ thin 1500 equivalent weight perîluorosulfonate layer may be in~orporated in the composite of ~his invention to provide ~ barrier to hydroxyl ion back migration. ~or electrolysis of sodium or potassium choride~ the oa~ion exchange layer may be Z~ 3;~:~5 coated with a non~lectrode layer to reduce eell voltage. The nature and appli-cation of such layers are àescribed in U.K. Patent 206468~.
The ~PTFE layer of the present invention serves as an interl~yer between a nonporous ion exchange membrane and ~ reinforeing fabrlc which: (a~ provides S meahanicul anchoring sites wher2by both the perfluoroionomer membrane and the f~bric are firmly bonded to the EP~FE by interlocking nf surface polymer ~rom both the fabric and the perfluoroionorner membrane into ths por~ of the EPTFE; (b) provides a support preventing the relatively thin (e.g., 0.5-3 mil) ion exchange membrane from being ruptured between the fibers of the tsbric in a 10 laminati~n process ~nd thereby preserving the integrity of the membrane; and,(c) by virtue of the thinness and high poro6ity of the ~ FE does not greatly reduce the effective cross sec~ion of the membrane for ionic conduction. In thisway, sturdy fabrlcs can be used to mechanically reinforce or armor thin perfluoroionomer membranes without greatly increasing the low resistance to 15 ionic flow inherent in the unreinforced ion exch~nge membr~nes.
Correspondingly, the composites of the present invention c~n also be used ~n permeation separation and facilitated ~ransport separnltion processes and devlces. The fabric provides mechanical ~trength and support and the spwes between the fibers provide ~venues ~or rel~tlvely unencumbered passage of fluids20 to and from the continusus membrane surface withouS subst~ntial1y sacrifieingthe hi~h selective permeati4n or facilita~ed transport rates possible wi~h thin perfluoroionomer membranes. Co~ting the interior and exterior surfaces of the EPTF~ with per~luoroionomer render~ the EPTFE 3tructure 3ufficiently hydro-philic to avold ~s loc~cing which would block the free passage of aqueous liquids 25 So the membrRne surfaee. In addition, the external and internal coating provides an inert rein~orcement of the EPTFE qtructure against compression and collapse under 2 subst~ntJ~l pressure gradient.
The invent~on ~lso provides for the combination of perfluoroionomer membranes wlth any polymeric fabric or ceramic fiber fabric ~oated with 30 polymer th~t ~an w}thstand the chemic~l and thermnl constrain~ of electrolyti~
or other seæaration syst@ms. Accordingly, h&logen eontaining polymers arld polymeric fibers ~re preferred. These include polytetrafluoroethylene and teerafluoroethylene copolymers, PVC and chlorin~ted PVC.
As useà in this ~pplic~tion, the term "synthetic îlb~r" means ~11 synthetic 35 fibers which h~ve a polymeric surface lsyer, to include, but not be limited to, EPTFE f iber, TeflonQD PFA fluoroc~rbon resin monofilament, Teflon~ FEP
fluorocarbon resin monofilRment, polyvinylchloride (PVC) monofilament, chlori-n~ted PVC monofilfiment, o~her polymeric fibers, polymeric fîbers with a surf~ce 32~S
~7--coat o~ ~nother polymer, glass fiber co~ed with a polymer9 ~nd oeher ceramic ~ibers costed with ~ polymer, The term "fabri~' in this disclosure reâer~ to fa~ric~ woven from these fibers and ~Iso non-woven webs and sheets o~ these fibers l&id down ~y ~ varietyS o~ techniques. W ithin the intent of thl~ disclosure~ the term "abric" also includes polymeric netting, meshes and screens f~bricated as one web or by cutting holes in a sheet, in which the intersection~ betweel~ Iiber~ or strengthmembers are eompletely ~used.
The term "bond" between f~bric and EPTFE sheet in thi~ disclosure refers 10 to a unron ~et~een the ~iber or strength member o~ the fabrie with the EPTFE
sheet, the union being lar~ely, but not necessari~ exclusively, mechanical and involving the intermingling of surface components of the ~iber with the fibrils and nodsl structure of the EPTFE sheet. (See, e.g., US. Patent 3,953,566 or a discussion of nodes ~nd fibrils in porous ~PTF~.~ Thus the term "bond" in this15 disclosure ~mbrAces both the union effected by the entanglement of the nodes and fibrils of the EPTF~ sheet with those of the ~iber and the union effected by the ~low of the surf~ce layer of a polymeric fiber or a polymer co~ted fiber into the fibrils and nodal structure of the EPTFl~ sheet. The introduction of anRdhesive materl~l to effect the bond beyond those present i~n the ~iber or in the 20 ~PTFE sheet is not contemplated.
A detsiled description of the composite membranes of the invention and preferred embodiment is best provided with reference to the accompanying drawings wherein ~ig. 1 is a perspective cross-sectional view of one embodiment of the compo ite of the invention. The multilayer ~mposite 10 comprises 25 synthetic fabri~ 16 bonded to one surface of a sheet Or porous EPrFE 14. T~s EPTPE layer 14 has ~ continuous perîluoro ion ~xchange polymer ~ilm 12 lamln~ted to i~s other surface as shown. Both the fabric 16 and the EPrFE layer 14 h~va a ~o~ting on at least a portion of their internal and external surfaces o~ e perfluoro Jon exch~nge resin. The bond 18 betYveen the synthetic f~bric and30 the ~PrF13 i3 believed ~o be a mechanical bond at the points of contact between tha f~bric ~nd the EPT~E.
In another embodiment aecording to the inven~ion, shown in Fig. 2, ~
multilayer composite membrane 20 i~ provided comprising a continuous pernuoro ion exchange polymer film 22 having fabric layers 26, 26 bsnd to both surfaces 35 of film 22 in s~ndwich-lik~ configuration by means of p~rou~ EPTFE interlayers 24, 24 interposed between film 22 and fabric lRyers 26, aB~ The fabric and porous EPrFE have a coating on at least a portion of their ~nternal and externalsurfaces of a perfluoro ion exchange resin. T~e bond 28 between the synthetic z~s fabric 26 and the ~PIFE 24 is believed to be a mPohanical bond formed at the points of contact b~tween the f~bric and the EPrFE~
The ~abric 16, 26 is preferably made frorn h&logen cont~ining synthetic polymer ~ibers such a~ polytetrafluoroethylene, a perfluoro copolymer of tetra-S fluoroethylene or polytetrafluoroethy~ene. fibers coated with perYluoro copoly-mers of tetrafluoroethylene. The fabric may be woven or nonwoven ~abric. The extern~l ~rface of the tibers of the fabric is prefer~bly non-ionomerlc. TJ'~e continuous perfluoro ion exchflnge polymer film 12, 22 may be perfluorosulforlate or perfluorocarboxyl~te. The perfluoro ion exchange polymer ~ilm may also be 10 a bilayer comprising n layer of perfluorosulfonate bonded to a layer of pernuoro-ca~oxylate, wherein the perfluorosulfsJlate is adjacent the EPT~E layer.
The interior and exterior surfaces oî the EPTF~3 and fabric ~re costsd with perîluorosulonic acid polymer, preferably of e~uivalent weight 1es5 than 1000 or perfluorocarboxylic acid polymer, also of equiv~lent weight less th~n 15 1000. The fabric and EPTFE~ preferably are impregn~ted with an ionic per-fluoro6urfactflnt.
The EPrPE l~yer is about 0.2 to ~bout 5 mils thick. The fabric andporous ~PTFI3 may have ~ coating on all internal and external surfaces thereof of ~ perfluoro ion exchange resin. The peel strength oî the bond between the 20 ~abr~c an~ EPTFE layer o~n exceed 30 grams per inch of width ~fter immersion of the ~omposite in water maintained a~ 90-100C for over 22 hours.
The composite may be used as a reinlorced, thin selectlve barrier in chemical separations, a~ an electrolytic ~parator between anode and cathode compartments in an electrolyzer, ~hereby providing low voltage operRtion, ~s a 25 thin continuous b~rrier in permeation seL~aration operstlons, or as a thin continuous barrier in facUitated tFansport oper~tion3, whereby the ~bric provldes mechan~cal ~upport and the spaces between ïibcrs provide avenues for passag~ for ~ s to and trom the continuous membrane'~ suriaces without substsntially saorifieing the high eransport r~tes inherent In thin facilitated 30 transport systems Involving thin perfluoro Jon exchange polymer films, Fig~. 3 to ~ ~re scannin~ electron microgrsphs, tak~n at magnlfications of 90X, 210X, 1500X and 500CX, respectively of ths multil~yer composite membrane depicted schematically in Fig. 1.
In Figs, 3 ~o 6, the synthetic fabric 16 is seen bonded to one surface of 35 a sheet of porous ~TFE 14. The EPTFE layer 14 has the continuous perfluoro ion exchange polymer film 12 laminated to its o~her surface. Both the fsbric 16 and the EPTFE layer h~ve ~ coating on at least ~ portion o their internal ~nd external sur~aces of a per~ll30ro ion exchan~e resin. The bond 18 between 2~ 5 _9 _ the ~ynthetic fabric strands and th~ EPTFE is in~ic~ted ~o be ~ mechanical interaction ~t the polnts of cont~ct between fabric ~nd EPI~.
The preferred process for ~he m~nufac~ure of a three-l~yer, fabri~
reinforced composite membr~ne involve a selies of ~teps:
(l) . Thermal lamlnfltion of fabric and EPTFE to form an intermedi~te lamin~ted sheet;
(2) Melt extrusion of the precursor of the perfluorin~ted lonomer to form a film. This pr~cursor polymer m~y be the sulfonyl ~luoride copolymer or the carboxylester copolymer. Both materials may be coextruded to form a bil~yer film coatainirlg a l~yer of each polymer;
(3) Lamination of the pre~ursor film to the intermed1~te laminate;

(4) Impregnation o~ th~ ineermediate laminate with 8 dllute (e.g., 2%) llquid composition of low e~uivalent weight ionomer (~ di~losed ~n V5. Paten~
4,453,991), ~Lnd dlying. (It is important ~o render the EPT~E layer hydrophili~
lS at this st~qge to &void bl~stering during the next hydrolysis step (5));
(53 lHydrolysis o~ the precursor film layer to the perfluoroionomer form in ~n alkaline water polsr organic solvent mixture, rinslng with water, and drying; ~nd, preferably, (6) Impregnation of the intermediate l~minate with ~n ionic surfact~nt and drying.
~aoh step of the process csn be performed on a sepAr~te p~ece of continu ously operatlng equipment with a roll wind~p. However, to prepar~ 8 composite Involving a very thln continuous ionomeric film layer, and also for economics athlgh product~on levels, steps (2) and (3) cAn be combined. The Intermedi~te laminate prep~red in ~tep (l~ c~n be melt ~odted wlth th~ precur~or po~mer to lay down ~ sub-mil thi~kness of the continuolJs ~ilm layer. 5tep (4~ ~ould beintegrated with step (3) by spraying or otherwise impregnating the trilayer lsminste as it ~omes off the laminator (or melt ~oater) And drying before win~
up.
The tw~side armored fiv~layer compo~i~e ~s shown in Fig. 2 is prepared by following steps (I) and (2) to yield a three-lay~r lamin~te and ~hen repe~ting step (2) in applying a second intermediate laminate (as prep~red in s~ep (1)) tothe o~her side oî the con~inuous film l~yer.
AlternatJvely, the continuous perfluorosulfonic acid polymer membrane can be applied to the EPrFE membrane by co~ting the ~3~rFE membrane with a liquid composition of llO0 EW perfluorosulfonic acid polymer in A solYent sys~em that forms a thin, even layer of liquid on the ~PTFE surface, but does not substantially penetrate into the EPrFE structure. This step replaces steps t2) and (3) ~bove Qnd ellminates the need for step (-5~.

~3`;~5 --Aecording to ~he above process, rolls of fabric ~nd EPT~F~ are to be fed to a continuous lAminator provided with ei~her ~ series of he~te~ n;p rolls or aheated large roll with a wi~3e stainless s$eel band on l~. The webs ~re fed around rolls and through the nips or between the band and the large roll to maintain 5 contact at l~mindting temperature for a îew seconds (eg., 1-lO seoonds).
The rolls or band on the fabric side are pr~ferably to b8 maintained at least 20-30C below the temperature at which the fibers in the f~bric st~rt to shrink, melt or deform, or suffer a significant permanent loss in physical properties during the few seconds of contact tirne. For fabri~ mad~ from 10 EPIFE fiber, this temper~ture can be as high as 400C for a few second~. For fabrics rn~de from EPrFE fl~er coated with Teflon~D ~EP fluorQearbon resin, Gl' for fabric~ made from glass fiber coated with Tenon~ FEP flusrocarbon resin, it is preferable to mainta~n the temperature below 250C.
The rolls or band on the EPTFE side are m~intainzd at a temperature 15 sufficiently high to echieve rapid bonding at the EP'rFE/fiber interfQce, but not so high ~s to degrade the EPIF~ or f~bric during the time of eontact. This can be ~00C or higher depending on line speed and the partieular EPTFE and fabri~
involved. Such high temper~tures are re~uired ~o rapidly bond the EPTFE fiber to th~ EPrFE sheet. However, for fabrics made from fibers with sn ~EP resin 2û ooating, the roll or band temperature on the EPT~E side preerably should be in the 300-375C range, depending on line speed and the particular EPTEE and f~brio involved~ Similarly, EPTFE can be laminated to fabrics mad~ from less thermally stable fibers (e.g., PVC monofilament), with corresponding adjustment of the band or roll temperatures on each slde of the ~omposite, depending on 25 line speed and the therm~ T~chanical propertics of the fiber.
The precursor polymer is ~xtruded at R temperature less than 300C to form a film of 0.5 to 5 mils in thicknes3. This film can be of sulfonyl nuoride polymer, cArboxylester polymer, or a multll&yered strueture of su~fonyl îluoridepolyrners, carboxylestc~ polymers or both, where the different p~lymers form 30 distinct layers h the coextruded film. Alternatively, ~ multilflyer film can be made by extrud}ng separate films an~3 "blocking' the fllms together, i.e., put~ing the films together under low pressure and heat so that they ~dhere together thr~gh the lamination process.
Laminatlon of th~ film (single or multilayer) to the s;de of the in~er 35 mediate l~rnin~te opposite the fabric, with the sulf~nyl fluoride side of a bifilm placed in contact with the EPTFE, takes place wi~h surface temperstures (two surfaces) less than 280C ~nd under a pressure differenti~ of not more than 760 mm mercury, with the prefçrred method being to apply a vacuum of no greater --than 500 mm mercury to the f~bric side of the composite while keeping the ~ilm side at atmosphsric pressure. The contact time to he~t and v~cuum is to be less than 90 seconds.
The composite should be coated with a liquid compositioll of ionomer prior S to hydrolysis in a primarily ~queous medi~ therwise, the ionsmer film will swell but the hydrophobic EPr~E will not a~ow the release of the hydrostatic pre~sure from the swelling, c~using the structure to delamin~te.
The aliphatic alcohol w~ter liquid composition of the ~cidic form of th0 920 EW perfluorosulfonic acid po1ymer is heated under parti~l vacuum at less th~n 8aC to remove most of the liguid component leaving a residue of at least 30% solids. This residue is diluted ~t atmospheric pressure in a polar organic solvent, preferably a lower aliphatic alcohol, such ~s ethanol, to 1-6% solids, by weight. Thi~ liquid composition is sprayed or coated onto the ~abric side of thelaminate in an amount sufficient to eompletsly impregn~te the EPI~ wi~h the liquid composit1On. Th~ EPTF~ becomes translucent and nearly transparent upon complete Impregn~tion. The laminate is dried at less th~n the boiling point of the solvent in the liquld comp~sition.
Th~ composit~ thus formed is hydrolyzed to ionomeric form as described In U.S. P~tent 4,584,071, e.g., 50-lO0C solu~ion of 6-aO% KO~ (preferred) or other soluble hydroxide~ 5-40% polar org~nic solvent (DMSO, preisrred) and 50-90% water with H contact t~me of at least 5 minutes. The composite Is next rinsed w1th water for nt le~st 10 minutes resulting in the potassium salt form of the perfluorosulfonate polymer. If.desired, the polymer c~n be exch~nged to the desired ionic form by cont~cting a ~ath of at least 1% of ~ salt of ~he de~ired catlon, or ~n ~cid i~ the hydrogen form ~ desired, rinsed agsin with water ~nd dri~d.
If desired, the dry lamin~te is impregnated by spr~ying, immersion or coating w1~h ~ ~olution 50.2-5%) of an ionic surfactdnt in water or a salt/w~terolutiorl, and drled.
Alternatively, hydrolysis c~n ~8 c~rried out prior to coating EPrFE with ionomer if the water content of the hydrolysi~ bath is low enough so that th~
bath solution will fully penetrate the EPTFE, thus preventing delamination from occurring. Tnis would involve hydrolyzing the structure irnmediately after lamination of the polymer fllm in a solution of 5-23% alk~i met~l hydroxide, 3 9096 polar organic solvent and 0-60% wRter, the ~olution ~ing such ~hat it wi~
en~er into the EPTFE portion of the composite to completely fil~ the porous structure, at 50-100C with a contact time of ~t least 5 minutes. The s~ructure is rinsed in water ~nd dried. The aforementioned 1-6% liquid ~omposition of 920 21D~;205 E~ ~cid form of the perfluorosulfonic acid polymer in a polar organic solvent is then sprayed or coated onto ehe EPTFE side of the struc~ure in the s&me manner as above. The surfac~ant, if desired, and salt, if deslred, ean be applied with the polymer solution~
The exAmple~ which follow ~re in~ended ~o be ;llustr~tlve of ~he com-posites according to the invention and the met~od of its prepar~tion snd use, but should not be construed as limiting the scope of the claim~ in any way.

~æos EXAMPLE I
An expanded PIFE sheet structure, as dis~lo~ed in U3. Patent 3,953,5~6, which is incorporated herein by ref~renee, here designated as EPTFE-l and having thç following physical characteristics was used: air flow wa 710 second~
as measured by ~3urley Densometer ASTM D726-5$; thickness was between .0025 and .0045 inches; appnrent density was between 0.27 and 0.33 gms/ec and pore size was about 0.~5 microns a3 indicated by methanol bubble point (measured by AS~M ~316-80) which was between 9.5 and 12.5 psi. Also used was an expanded PTFE sheet structure here designated as EPTFE-2 which h~d the ~ollowing physical.~characteristics: air flow was 3.5-4.5 seconds as measured by Gurley Densometer; thickness W~5 .0030-.003~ inches; apparent density was between 0.20 and 0.25 ~ms/cc and pore size was about 1 micron as indic~ted ~y the methanol bubble point test, which was measured by A~TM ~316-80, and was between 5.5 and 8.5 psi.
A 20-s~rand per inch by 20-strand per inch pl~in weave f~bric of 400 denier EPTFE fiber, tenacity ~xceedin~ 1200 gram ,;here designated as ~20x20, was used. Also used ~nd here designated F8x8 was an ~strand per inch by ~
strand per ineh plain weave fabric of Teflon~ 100 FEP Yluorocarbon resin coated 200 denier ~PTFE fiber, tenacity exceeding 600 gr~ms. W. L. Gore l~ Associ~tes, Inc. prepared and provided the 200 denier EPTFE fiber wlth a 1.25 mil thick coating of ~eIlon~ FEP. Teflon~ 100 F13P fluoro~arbon resin is ~ copolymer of polytetrafluoroethylene ~nd hexafluorQpropylene commercially available from E, I. duPont de Nemours ~ Co., Inc.
One turn of G20x20 was wrapped on a 3-inch diameter aluminum mandrel.
This was covered by one turn of EPTl~`E-1 and the assembly clamped at the ends of the mandrel and along the seflm to prevent unraveling. T}'le assembly was then immersed in a 370C ~alt bath for one minute, removed to ~5C ambient temperature ~r 5 minutes ~nd then cooled rapidly by Immersion ~n 25C water.
Removal from the mandrel yielded an intermediate laminate in which a bond between the ¢20x20 fabric and the EPTFE was establ~shed. ~ on~ mil film of 1500 equiv~lent weight of the sulfonyl fluoride form of perfluorosulfonic ~cid polymer was then melt laminated to the EPTFE side of the intermediate Isminate by vacuum lamination at 240C.
The fabric/EPT~E side of the thre~ply composJte wus spraye~ with a liguid composition of 2%, 920 equivalent weigh~ ~EW) hydrolyzed perfluoro~
sulfonic acid polymer (as disclosed in DuPont UK Y~tent 1,2B6,589) in a 5%
water-ethyl alcohol mixture until the EPrFE bec&~me translucent, and then dried at 2SG for 1 hour. The entire structure was then exposed to a 14% potassium ~3~
--.l 3--hydroxide, 3096 dimethyl sulfoxide solution in water at 80C for I hour to hydrolyze the continuous membrsne to the potassium sQl~ form. ~inally, the fabri~ side wa5 sprayed with 8 2% solution of lmmonium perfluQrooet~noate in water and dried. This structure is here designated Composite A.
A three-ply Composite B was preparsd using îabrlc C320x20 snd EPTF~-2 to prepare the intermediate laminate. Th8 rest of the steps were th~ ssme as for Comp~;ite A.
A five ply Composite C, a membr~ne armored on both sides by fabric, w~s prepared by sequenti~lly melt l~minating a a20x20/~PTFE-1 intermodiate laminate to îirst one side of the sulfonyl nuoride form of a one miL 1500 equivalent weight perfluorosulfonic acid polymer and then to the other~ Prior to hydrolysis, the five-ply composite w~s spreyed on both sides with a liquid composition of 2%, 920 equivalent weight perfluorosulfoni¢ acid polymer. After hydrolysis, both sides were sprayed as before with 2% smmonium perfluor~
octanoate solution in water.
Intermediate laminates of F8x8 fabric with EPTFE-1 were prepered by wrspping a 3-inch diameter mandrel with aluminum îoil, th~n one wrap of F8x8 fabric, then one wr~p of EPTFl~-1, clamping, immersion in ~ 370C s~lt bath for 40 seconds and cooling. The aluminum ~oil facilltAted removal of the intermediate laminate from the mandrel Rnd then the foil could be stripped from the intermedlate lamlnate. A thres-ply laminate with one mil, 1500 equivalent weight perfluorosulfonate polymer film was then prepared by ~ procedure similar to that used for Composites ~ and B. This composite is here designated Composite D.
A three-ply Composite E w~s prepared using fabric ~8x8 and EPTFE-1 by the same procedures for Composite D but only ~ 20 second lamination time in a 370C salt bath. Then a 3.2 mil coextruded bifilm consisting of 0.8 mils of the carboxylester form of the perfluorocarboxyl~e (C~3 polymer ~djacent to 2.4 mils of the ~ulfonyl nuoride form of the perfluorosulfon~te (XR) polymer w~s melt lamin~ted to the EPTFE side of the intermedi~te laminate by va~uum lumin~tion at 230C; ~he perfluorosulfona~e side oî the bifilm w~s oriented tow~rds and lamin~ted to the ~PTF~3. 1'he rest of the steps were the ssme as for Composite A.
A two-ply Composite F, repeating ~he approach described in U.S. Patent 4,604,170, w~s prepared by melt l~minating a one mil film of 1500 EW of the sulfonyl fluoride form of perfluorosulfonic acid polymer to EPTFE-1 on ~ vQcuum laminator at 230C. The EPTFE side of this composite was sprayed as before with a liquid compositlon of 2%, 920 EW hydrolyzed perfluorosulfonic acid polymer and the rest of the steps were the s~me as Composite A.
In the same manner, two-ply Composite G WQS prepalied using EPT~-2 and a one mil film of lS00 EW perfluorosulfonic a~id polymer.
Also evalu~ted were ~ one mil film OI unsupported hydrolyzed perfluoro-sulfonic acid polymer, Nafion$ 324 perfluorlnated membrsne, and Nafion~ 90209 perfluorinsted membrane. N~fion~ 32~ (hereafter N3243 is a o~mmerci~lly ~vailable six mil perfluorosulfonic acid polymer stru~ture which consists of a one mil layer of 1500 EW (equivalent weight) perfluorosulfonate polymer as a hydroxyl ion barrier and a 5 mil supporting layer of 1100 EW perfluorosulfonate polymer in which a 24x24 ~rand per inch reinforcing fabrie ~ PTFE is embedded. Nafion~ 90209 is a eommercial mernbrane for finite gap operation in 3296 caustic production. It is a bimembr~ne of a perfluorosulfonate po~mer and a perfluorocarboxylate polymer in which ~ 15x15 strand per inch plain weave 200 denier GORE T~X~D fiber is embedded. TJ~le membranes sre availabie îrom the E. 1. E)uPont de Nemours ~ Co., Wilmington, DE and C:O~E-TEX~ f~ber B
an ~PTF~ fiber avail~ble from W. L. Gor~ ~ As~ociQtes, Inc., Newark, DE.
Tear strength of these composites were then evaluated on ~n Elmendorf Tear Tester (ASTM D-1424~. For ea~h structure, a tear me~surement w~s mads in each of the two fabric dire~tions and then aver~ged. ~Result9 Al'e shown in Tabla 1.
Table 1 Tesr ~trength, De~ignation ~ ~L_ as l-lsnoxR 1 mil 1500 EW perfluorosulfonic 130 ~cid polymer 1-llOOXR S mil 1100 EW perfluorosulfonic 80 ~cid polym¢r N-324 6 mil 24x24 Teflon~ fiber ~bric 2620 reinforced Nafion~
N90209 6.5 mil 15x15 GORE-TRX~ fib~r f~bric 6û80 rein~oP~d Nafion0 Composite A G20x20/EPTFE~ 1500XR 512û
CompQsit~ B G20x20~EP'~FE-2/1-1500XR 4030 Composite C G20x20/l~PTFE-1/1-1500XR/EPTFE-1/a 2ûx20 5800 Composite D F8x8/EPTFF-1/1-1500XR 3710 C:omposit~ ~ F8x8/:EPTFE-1~2.4-1100XR/0.8CR 2620 Composite F l~PTFE-1/1-1500XR 30 Composite G EPTFE-2/1-1500X~ 30 ;~3~

Thus, through an EPI~E interlayer one mil per~luorosulfonic Rcid polymer membrane can be fabric reinforced to enhance tear strength by over an order of m3gnitude- Tear strength of these composites/ ~re QISO an ordeP of magni-tude higher than the membrane/EP'rFE composites of ~l.S. Patent 4,604,170, 5 represented here by 5Omposites F and G, and of the same order of magnitude as thick commercial composites where f~bric is embedded in the membrane.
EXAMPLI: II
Relative scratch resistance of the composites of this ~nvention compared to an unreinforced perfluorosulfonic acid polymer was demonstrated 8S follows:
10 Composite A from Example I w~s placed with the fabric side up on El hard flatsurfaoe,and was stroked with rnoderate pressure 100 times with the round end of a 1-7/8 inch x S/16 inch paper clip. It was str~ked 25 time~ in eaeh of the fabric directions and 25 times in each of the bias direceions. No visible holes in the reverse continuous membrane side were noted nor was any &ir flow detected In ~he aurley densometer. In oontrast, a one m31 film of 1500 equiv~lent weight perfluorosulfonic acid polymer was strdsed once and a ~cr~tch Qnd visible holes were produced. Gurley densometer mea urement on this scr~tched s~mple was six seconds for 100 ml air flow.
Thus, the utiljty of thc composite o~ ~his invention to armor a fragile, ~3 thin ion exchange membrane against scratehing or abrQsion Is demonstrQted~
Composite C of Example I would provide protection on both side~ of the membrane.
EXAMPL13 m Composite A, Composite D and Composite F were prepared as described ln ~xample I. These composites were immersed for one-half hour in a 2%
solution of ammonium perfluorooctanoate in water th~t ha~ been satura~ed with sodium chloride at room temper~ture. NRfion0 N3~4, a commercially av&ilable membrsne, was soaked in fl 2% sodium hydroxide solution in w~ter ovemight at room temperature.
Each membrAne was placed in an electrochem;cal ~ell with an active area of 45cm2 ~3" di~meter). The ~node compartments were made of glass and fitted with rlattened DSA anodes o~t2~ned from Eltecn Systems Corp. of Chardon, QH.
The cathode compartments were made of polymethylmethacrylate and were fitted with a mild steel expanded metal c~thode. ln each cell ~he anode was placed in contact with the membrane and 3mm ~ap was maintained between the membrane and the cathode. In each case, the 1500 EW layer was oriented towards the ca~hode.

3~C~S

The cells were operated under the following conditions: cell temperature wa~ 85-90C; tot~l current was 14 amperes for a current density OI 3.1 kiloamperes per square meter; the concentration of the sodium chloride ~ed solution was 23.5-24% by w~ight and it was fed at 3-3.5 ml peP minute; the 5 concentration of the sodium hydroxide produced was controllsd to 15-18% by weight by constant wster addition to the catholyte; one foot he~d on the cathodecompartment was maIntain~.
Operating results after ste&dy state was reached are tabulated in Table ~ along with Elmendorf tear strength value~. Current efficiencies (C.E.~ were 10 obtained by relating the amount of sodium hydroxide produced to the number of coulombs used.
Table II
T~ar Strength %NaO}~ %C.E.Volts KWH/MT~ (grams) _ N324 16.5 88.û 3.722933 262û
Composiee A 15.9 86.03.29 a564 5120 Composite D lS.6 87 3.56 2740 3270 ~Kilo watt hours/metrie ton of ssdium hydroxide Thus, the compa6ites of this invention offer ubout 7-14% improvement ~n energy con~umption over the ~ommercial membr~ne for this use, and a 25-95%
20 Improvement in tear ~trength.
EXAMPLE IV
Cornposite B w~s prepared as described in Exampl~ l. TAis oomposite was soaked for one-half h~ur In 0.2% solution of ammonium perfluorooctanoate in water at room temperature. Nafion~ N324, the commercially available 25 m¢mbrane, was soaked in 2% sodium hydroxide soIutisn in water overnight at room temperatur~.
Esch membrane was placed in an electrochemical cell with an active ~re~
of 45cm2 (3" dlsmeter). .The anode compartments were made of glass and fitted with flattened DSA anodes obtained from Eltech System~ Corp. of Chardon, OH.
30 The cathode compartments were made of polymethylmethacryl~te and were fitted with B rnild steel exp~nded metal cathode. In each ceil, the anode was plaeed ~n contact with the membrane and 3mm g~p W8S maintained between the membr~ne and the cRthode. In each csse, the 1500 I~W Iayer was oriented towQrds the cath~e.

3~5 The c~lls were operated un~er the following conditions: cell temperature was 85-90C; total current was 14 amperes for A current density oY 3.1 kiloamperes per square meter; the ¢oncentration of the potassium chloride feed solution was 23.5-24% by weight Qn-d it w~s fed at a rate of 3.5-4 ml per minute;
S the concentration of the pot6ssium hydroxide produced was controlled to 16-19%by weight by constant water addition to the catholyte; ~e foot head on the cathode compartment w~s msintained.
Operating results aîter ste~dy state was reached ~re tabulated in Table m elong with ~lmendorf tear strength values. Current efficieneies (C.E.) were 10 obt~ined by relating the amount ratio of potassium hydroxide produced to the number of coulombs used.
Table III
.
Te~r Strength Desi~nation 96KOH %C.E. Volts KWH/MT~
N324 18.8 82.0 4.82 2810 2620 15 Composite B 18.æ 81.0 4.~2 2726 4030 ~Kilo watt hours/metric ton to caustic potassium hydroxide Thus, Composite B of ~his invention offers about 3% improvement in energy consumption ovcr ~he commercial membrane for this use and more than 50% improvement in tear strength.
EXAMPLE V
_ Composite E was prepared 8S described in Example I. These composites were soaked for one-half hour in 0.2% solution o~ ammonium perfluorooctanoate in water at room ~emperature. Nafion~ N90209, the stsndard commercial membrane for finlte gap operation in 32% caustic production, wa~ soaked in 2%
sodium hydroxide solution in water overnight at room temperature.
Each membr~ne was placed in an electrochemical cell with an sctive area of 45cm2 (3~r diameter). The anode compartments were made of glass an~ fitted with fl~ttened DSA anodes obtained from Eltech Systems ~:orp., of Chardon, OH.
The csthode compartments were made oY polymethylmethacrylate and were tltted with Q mlld steel expanded steel cathod~. ~ each cell, the anode was placed in contact with the membrane and 3mm gap w~ main~aine~ between the membr~ne and the cathode. In each case, the 1$00 EW layer was oriented towards the c~thode.
The cells were operated under the following conditions: eell temperature was 85-90C; total current was 14 arnperes for a current density of 3.1 kiioamperes per square meter; the concentration of the sodium chloride feed 2~)~03~5 solution was 23. 5-24% by weight and it w~s fed at a rate of 3.1-3.3 ml per minute; the coneentration of the sodium hydroxide produeed was controlled to 30~35% by weight by cons~ant w~ter addieion to the catholyte; one foot head on the cathode compartment was maintained.
Operating results after steady state was reached sre t~bulated in Table IV ~long with Elmendorf tear strength values. Current e~ficiencies (C.E.) were obt~ined by rel~ting the amount of sodium hydroxide produced to the number of coulombs used.
T~b e nt Tear Strength Desi~nation %NsOH %C E. VoltsKWH/MT~ (grams)_ ;
N90209 32 95.8 3.46 24206030 Composite E 31.8 95.5 3.36 2358 2~20 ~Kilo watt hours/metri~ ton of sodium hydroxide Thus, the composites of this invention offer about 2.5% improvement in energy consumption over the commercial membrane for this use and tear ~trength at an ~ccepta~le level.
EXAMPLE VI
Composite A and Composite D, were prep&~red as d~scribed in Example I.
In the case of Composlte 1), a one-inch wide strip of two mil Kspton~ po~rimide f~lm (obtained from the DuPont Company~ was inserted between the fabric ~nd EPTFl~-l to prevent bsnding in that area, thus providing means to run peel strength tests.
Composite H was prepared similarly to that described in Jap~nese Patent Application Disclosure No. 62 280231 dated December 5, 1987. Sheet structure 2S EPIFE-1 w~s impregn~ted with ~ 3% liquid composition oî 920 EW perfluoro-sulfonic flCid polymer in ethyl alcohol and dried at 25C. F~bric G20x20 w~s impregn&ted with ~ 5% liquid composition of 1100 EW perfluorosulfonic acid polymer in a mixture of water and lower aliphatic ~lcohols; this solution w~s obtflined from Sohltion Technology, Mendenh~ll, PA. The impregnated f~bric w~ dried at 25C. Tne ~mpregnated G20x2û f~bric was then ~andwiched between two layers of the impregnated EPrFE-I and hest l~min~t~d at 150-160C for lS minutes, The plies of this intermediate lamin~te flre held togetherby the perfluoro ivn exchange resin impregnant. A one mil continuous membrane of 1500 EW sulfonyl fluoride form o~ perfluorosulfonic acid polymer w~s then melt lamin~ted to thiS intermediate laminate by vacuum lsmination at 230C.

3~

-1~

The entire structure was then exposed to a 14% potassium hydroxide, 30%
dimethyl sulfoxide solution in w~ter at 80C for one hour to hydrolyze the continuouAs membrane to the potassium ion form.
Also similar to ehat described in Jspanese Patent Application Disclosure No. ~2-280231, Composite J was prepared like Composite H except that EPrFE-2 was used and impregnated with a 2% liquid compssition of 1100 EW per~luoro-sulfonic acid polymer in ~ mixture of water ~nd ~liphatic alcohols and dried at 25C. This composite was heat laminated at 210-~20C for 15 minutes. The rest of the steps are similar to those for Composite H.
C~mparison of peel strength of these composites was made as follows: A
two-inch wide strip was cut from each o~` tne composites. The outer layer of the composite located opposit~ to the con~inuous ion exchange ~ilm was separated from the rest of the composite for about one inch.
The composite part containing the membrane W&S hung in a suspended clamp which gripped the entire two-inch width. Another clamp with an attached basket w~s clamped onto the 1" long x 2" wide separated portion of the outer l~yer gripping the entire width. The outer layer was the fabric I yer in the cases of Composites A and D. In the case of Composites H and J, representing the type structure disclosed in Japanese Patent Applieation Disclosure No. 62-280231, the peel valucs recorded are those for peeling the fabric alon~ with theouter EPTFE layer from the rest of the composite.
Increasing weights were ~dded to the basket hanging from the separated lay~r until peel initiAted and continucd to completlon. Peel tests were run 8t room temperature on the composite as prepared, and immediately after joaking for a2 hours in gn-100C water. Results rounded to the nearest 5 grams ~re tflbulated in Table V. Two peel values are recorded ~or each condition. The lower value indicates either the highest load at which no peel was observed or the lowest lo~d at which peel progresscd one inch but then halted. The higher value is the level ~t which peel propagated ~hrough 2.5 inches of strip length.

'Q~

Table V
Peei Strength (gms/~" width) Composite After 22 hrs. in Operatir~
Desi~nation Description As Yrepared 90-100~C H2O Volta~e ~ . _ _ .
A G20x20/EPTFE- 160-175 85-160 3.29 honded intermedi~te DF8x8/EPTFE-1/1- 925-1225 590~90 3.56 1500XR FEP melt bonded intermediate HEPTFE-1/G20x~0/ 100-120 30-40 Over-EPTFE-1/1-1500XR voltage ionomer bonded intermediate J EPTFE-2/G20x20/ 40-60 40-60 Over-EPTFE-2/1-1500X~ voltage ionomer ~onded intermediate The bonds effected by ionom r impregnant of Composites H and J (the composites of the type described in Japunese Patent Application Disclosure No.

6~-280231) are quite we~k. Bond strengths drop to nearly zero after hot water exposure. In contrast, the bond of Composite A is stron~er and relatively unnffected by extended hot water exposure. 'rhe melt bond of Composite D is very strong, both in the as prepared sample and in the specimen that had been exposed 22 hours in 90-100C wa~er. Indeed, with Composite D, peel of the fabric from the me mbrane takes place by the cleavage of the EPTFE-l Interlayer, not by failure of the fabric/EPTFE bond.
In addition, the low voltage clairns- m~ds for the relatively thick, heavjly impregnated str~ctures of Japanese Patent Application Disclosure No. 62-280231 as represented by Composites H and J could not be verified under conditions clescribed in Example ~1. VoltAges were so hi~h that the ele~trolytic cells could not operate. The low voltage levels required for Composites A and D, as determined in Example IlI, are recorded here ag~in for contrast with the H and J type composites described in Japanese Patent Application Disclosur~ No. 62-2~0231.
EXA~PLE Vll .
Several fabric rcinforced composite membrane construetions were evaluated for permeability to waler using ASTiVI E36 ~ (invcrted cup) to measurc their moisture vapor transfer rate (MVT~. Two samples were prepared in a manner 40 similsr tu that for Composite A or B of Example 1 and comprised three layers:a thin one mil membrane of 1080 EW perfluorosulfonic acid polymer; ~ layer of 2~3~

EPTFE-l or EPTFE-2 sheet; and a fsbric of G20x20 fiber fsbric rsinforcement.
The fabric ~nd EPTFE sheet side of the construction was sprayed with a liquid ccmposition of 2% 920 EW perfluorosulfonic acid polymer in 9596 ethanol to coat the interior and exterior surfaces of the fine fibril and node structure. As a 5 final treatment, the EPI`FE membrane side of the construction was impregnated with a 2.;~% solution of ammonium perfluorooc~anoate in 15% isopropyl alcohol, ~5% water to sid in initinl wetting of the structure. These two semples are designated as sample 7A and sample 7B.
~wo more samples were prepared which were similar to samples 7A and 7B
10 except that the EPTFE membrane side of each construction was not sprayed with 920 EW liquid composition and was no~ treated with ammonium perfluoro-octanoate solution. These two samples sre example composites disclosed in US.
Patent 4,194,041 and are designated as sample 7C and 7D.
In addition, an unsupported one mil membrane of 1080 EW perfluorosulfonic 15 acid polymer was evaluated.
All perfluorosulfonic ~cid membranes and composites were tested in the potnssium ion form.
Testing was c~rricd out in a contro~ed environment &S preseribed by ASTM
E96-80. Samples 7A, 7B, 7C and 7D were placed in the ~est cups so th~t the 20 water would contact the EPTFE side of ths constructiorl snd the perfluoro-sulfonic acid polymer layer was exposed to the air stream. Test conditions were as follows: room temperature was 22.9C; relative humidity was 50%; snd the air flow velocity passing across the membrane samples was S50 ft. per minute.
In All cases, ~h~ test was run for two hours. Results of this testing can be seen in Table Vl.
Table Vl Designation Descr_ption MYTR (g/mal24 hrs.) Sample 7A G20x20/EPTFE-1/1-1080XR/920EW~APFO 9465 S~mple 7B G2Ux20tEPlFE-2/1-lU80XR/920EW/APFO 10913 Sample 7C ~320x20tEPTFE-l/1-1080XK 7236 Sample 7D G20x20/EYTFE-2/1-1080XR 5~71 1 mil 1080 1 mil 1080EW perfluorosulfonic acid polymer 8631 The data in Table VI show that semples 7A and 7B which were sprayed with a 2% liquid composition of 920 EW perfluorosulfonic acid polymer, as in Example 35 I, to render the EPTFE hydrophilic had si~nificantly higher MVTR values than ssmples 7C and 7D, similar constructions which had not been sprayed with 920 EW perfluorosul~onic ac~d polymer liquid composition.

Samples 7A and 7B h~d MV'rR values compnrable to or higher thPn the one rnil 1080 E~Y unsupported membrane while the 7C~ and 7D samples h~d MVTR
va~es signifieantly lower th~n ~he one mil 1080 EW unsupported membrane.
This demonstretes thRt the moisture vapor transfer propertie~ of the one mil 5 1080 EW membrane are nst diminished when the EP'I`FE membrane ~nd fabrie r~inforcement are ettached in accordance with the present invention. However, the moisture vapor transfer properties oî the one mil 1080 EW membrane are significantly diminished when EPTFE membrane snd fabrie reinforcement are attached us disclosed in U.S. P~tent 4,194,041.
. EXAMPLE VIII
Two samples of membrane were evaluated for permeability to water using ~ modification of the desiccant methsd described in A3TM E9~-80. The first sample (designsted 8A) was prepsred by first l~minating C;20x20 EPTFE
fiber fabric eo EPTFE-l membrane as d~scribed in Example I. This intermediate 15 laminate WQS restr~ined and coa~ed on the EPTFE membrane qide with a 1,3%
liquid composition of 1100 EW perfluorosulfonic acid polym¢r In ~0% water, 40%
1-methoxy-2-propanol. The solvent makeup of this liquid compositioll was intended to provide a uniform layer of liquid which adhered to, but did not substantially penetr~t~, the EPTFE membr~ne. The liquid composition was 20 allowed to dly ~t 23C. Two more co~ts of liquid composition were applied ~y this pro~edure. The resultllnt coating was 0,2 mil thick as determined by optical metho~;.
The fsbric/EPT~E side of the lQminate was then tre~ted with a û.5%
liquid ~omposition of 920 EW perfluorosulfonic acid polymer in a solution comprising 84~6 water; 14% eth~nol; and ~.0% ammonium perfluorooctanoate, and wss allowed to dry at 23C, This liquid composition was designed to fully wet th~ fabric/EPTFE ~ide of the laminate without disturbing the continuous 1100 EW membrane on ehe opposite side.
The second sample (designated 8B3 was Nafion~ 417, a commereially ~vailable, f~bric-reinîorced, 7 mil thick perfluorosulfonjc acid polymer mem-bran~ obtained from DuPont.
Both samples were tested in the acid form of the perfluorosulfonic acid polymer.
The wat~r permeation test requires that 8"x8" specimens be placed in a supporting ring and floa$ed ~fabric side down) in A controlled temperature, distilled water bath at 23C ~ 0.2C. A 70 ml aliquot of a slurry of potassium a~tate u~ distilled w~ter ~5 to 1 ratio~ was added to each of several desiccant cups (4.~ oz. capacity, 6.5 cm i.d. opening). an EPTFE membrane wns sealed 2~32~3S

over each desiccant cup opening to contain the desiccant. This membr~ne was part number #S10831 and W8S o~tained from W. L. Gore & Associ~tes, Inc.
Desiccant cups were weighed to an sccuracy of + O.OOlg and were immediately placed onto their respeetive samples. Th0 desiccant cups were allowed to absorb 5 moisture through the samples for exactly 10 minutes. After the lO minutes had elapsed, the cups were removed from the samples and reweighed. Moisture vapor transmission rate was calculated directly from the desiccarlt ClJp weight gain, surface aree o~ sample and elapsed time of the test. Results of this te~ting can be seen in T~ble VII.
Table VII
Description MVTR t~ /24 hrs.) Sample 8A C;20x20tEPlFE-1, 0.2 mil, Cast llOOE~W 132,054 Membrsne, 920EW/APFO
Sample ~B Nafion~ 417, 7 mil, 1lOOEW Nafion~/24x24 17,450 Teflon ~iber Fahrie Reinforced Membrane The da~a in Table Vll show that ssmple 8A had greater than 7 times higher moisture Yapor transmission rate than sample BB, the commercially available perfluorosulfonic acid membrane. This difference is attributed to the fact that commercial membranes with embedded reinforcing fabrics require 5 ~o 20 10 mils of thickness to remain continuous while the composite in accordance with this invention allows for the fabrication of a very thin, continuous perîluorosulfonic acid polymer lnyer in the composite.
Whlle the invention has been disc~osed herein in connection with certain embodiments ~nd detailed descriptions, it will be clear to one skilled in the art ~5 $hat modifications or variations of such details can be made w3thout deYiating from the gist of this invention, and such modifications or variations are considered to be within the scope of the claims hereinbelow.

Claims (35)

1. A multilayer composite membrane comprising a synthetic fabric bonded at points of contact to one surface of a layer of porous, expanded polytetrafluoroethylene (EPTFE), said EPTFE layer having a continuous per-fluoro ion exchange polymer film laminated thereto on the surface opposite said one surface, said fabric and porous EPTFE having a coating on at least a portion of the internal and external surfaces thereof of a perfluoro ion exchange resin.

2 A multilayer composite membrane comprising a continuous perfluoro ion exchange polymer film having a synthetic fabric layer bonded at points of contact to both surfaces of said perfluoro ion exchange polymer film in sandwich-like configuration by means of an EPTFE interlayer interposed between said ion exchange polymer film and each said synthetic fabric layer, said fabric and porous EPTFE having a coating on at least a portion of the internal and external surfaces thereof of a perfluoro ion exchange resin.

3. The composite of claim 1 or 2 wherein said fabric is made from halogen containing synthetic fibers.

4. The composite of claim 1 wherein said fabric is made from synthetic fibers selected from the class consisting of polytetrafluoroethylene, a perfluoro copolymer of tetrafluoroethylene or polytetrafluoroethylene fibers coated with perfluoro copolymers of tetrafluoroethylene.

5. The composite of claim 2 wherein said fabric is made from synthetic fibers selected from the class consisting of polytetranuoroethylene, a perfluorocopolymer of tetrafluoroethylene or polytetrafluoroethylene fibers coated with perfluoro copolymers of tetrafluoroethylene.

6. The composite of claim 1 or 2 wherein said fabric is woven fabric.

7. The composite of claim 1 or 2 wherein said fabric is nonwoven fabric.

8. The composite of claim 1 or 2 wherein the external surface of the fibers of said fabric is non-ionomeric.

9. The composite of claims 1, 2, 3 or 4. wherein said continuous per-fluoro ion exchange polymer film is perfluorosulfonate.

10. The composite of claims 1, 2, 3 or 4 wherein said continuous perfluoro ion exchange polymer film is perfluorocarboxylate.

11. The composite of claim 1 wherein said perfluoro ion exchange polymer film is a bilayer comprising a layer of perfluorosulfonate bonded to a layer of perfluorocarboxylate, wherein said perfluorosulfonate is adjacent said EPTFE layer.

12. The composite of claim 1 or 2 wherein the interior and exterior surfaces of the EPTFE and said fabric are coated with perfluorosulfonic acid polymer of equivalent weight less than 1000.

13. The composite of 1 claim 2 wherein the interior and exterior surfaces of the EPTFE and said fabric are coated with perfluorocarboxylic acid polymer of equivalent weight less than 1000.

14. The composite of claim 1 or 2 wherein said fabric and EPTFE are impregnated with an ionic surfactant.

15. The composite of claim 1 or 2 wherein said fabric and EPTFE are impregnated with an ionic perfluorosurfactant.

16. The composite of claim 1 or 2 wherein said EPTFE layer is 0.2 to 5 mils thick.

17. The composite of claim 1 wherein said fabric and porous EPTFE
have a coating on substantially all internal and external surfaces thereof of perfluoro ion exchange resin.

18. The composite of claim 2 wherein said fabric and porous EPTFE
have a coating on substantially all internal and external surfaces thereof of a perfluoro ion exchange resin.

19. The composite of claim 1 or 2 wherein the peel strength of said bond between said fabric and EPTFE layer exceeds 30 grams per inch of width.

20. The composite of claim 1 or 2 wherein the peel strength of said bond between said fabric and EPTFE layer exceeds 30 grams per inch of width after immersion of said composite in water maintained at 90-100°C for over 22 hours.

21. The method of using the composite of claim 1 or 2 reinforced thin selective barrier in chemical separations.

22. The method of using the composite of claim 1 or 2 as an electrolytic separator between anode and cathode compartments in an electrolyzer.

23. The method of using the composite of claim 1 or 2 as a thin continuous barrier in permeation separation operations.

24. The method of using the composite of claim 1 or 2 as a thin continuous barrier in facilitated transport operations.

25. A process for making a multilayer composite membrane comprising:
(a) laminating a fabric to a sheet of EPTFE to form an intermediate laminate;
(b) extruding a polymeric film of a precursor of a perfluorinated ionomer;
(c) laminating the EPTFE sheet side of said intermediate laminate to said precursor film;
(d) impregnating said intermediate laminate with a liquid compo-sition of low equivalent weight isomer followed by drying; and (e) hydrolyzing said precursor film to the perfluoroionomeric form followed by drying.

26. A process for making a multilayer composite membrane comprising:
(a) laminating a fabric to a sheet of EPTFE to form an inter-mediate laminate;
(b) forming a thin polymeric film of a precursor of a perfluorinated ionomer on the EPTFE sheet side of said intermediate laminate;
(c) impregnating said intermediate laminate with a liquid compo-sition of low equivalent weight ionomer followed by drying; and (d) hydrolyzing said precursor film to the perfluoroionomeric form followed by drying.

27. The process of claim 25 or 26 wherein said hydrolyzing and drying step is followed by impregnating the intermediate laminate with an ionic sur-factant and then drying.

28. The process of claim 25 or 26 wherein said precursor film is sulfonyl fluoride polymer.

29. The process of claim 25 or 26 wherein said precursor film is carboxyl ester polymer.

30. The process of claim 25 or 26 wherein said precursor film is a bilayer film of sulfonyl fluoride polymer and carboxyl ester polymer.

31. The process of claim 25 or 26 wherein said fabric is made from halogen containing synthetic fibers.

32. The process of claim 25 or 26 wherein said fabric is made from synthetic fibers selected from the class consisting of polytetrafluoroethylene, a perfluoro copolymer of tetrafluoroethylene or polytetrafluoroethylene fibers coated with perfluoro copolymers of tetrafluoroethylene.

33. A process for making a multilayer composite comprising:
(a) laminating a fabric to a sheet of EPTFE to form an inter-mediate laminate;
(b) depositing a thin continuous polymeric film of a perfluorinated ionomer on the EPTFE surface of the intermediate laminate by treating it with A liquid composition of greater than 1000 equivalent weight perfluorinated ionomer, the liquid composition having a surface tension sufficiently high to preclude substantial penetration of the liquid composition into the pores of theEPTFE; and (c) impregnating said intermediate laminate with a liquid com-position of low equivalent weight ionomer, followed by drying.

34. The composite of claim 1 or 2 wherein the interior and exterior surfaces of the EPTFE and said fabric are coated with a salt form of a per-fluorosulfonate polymer of equivalent weight less than 1000.

35. The composite of claim 1 or 2 wherein the interior And exterior surfaces of the EPTFE and said fabric are coated with a salt form of a per-fluorocarboxylate polymer of equivalent weight less than 1000.