PRODUCT REVIEW
n
Summit, New Jersey 07901
the rlastics nesearcn ana veuelopment venter or tne Celanese Plastics Company in Summit, N . J. He received a B.S. in Chemical Engineering from Columbia University in 1965 and M.S. and Ph.D. degrees in Chemical Engineering in 1969 and 1972, respectively, from Worcester Polytechnic Institute. He joined the Celanese Plastics Company as a research engineer in the New Products Exploration Department and is currently conducting process and product deuelopment work on engineering molding resins. Dr. Bierenbaum has published papers on molecular sieve catalysis and holds patents on microporous polymer film technology. He is also adjunct instructor in Chemical Engineering at the Newark College of Engineering.
Robert B. Isaacson received his B.S. in Chemistry from the City College of New York in I956 and his Ph.D. in Physical-Organic Chemistry from the Uniuersity of Maryland i n 1961. He joined the Celanese Plastics Company in 1965 as a Senior Chemist after previous employment with the ESSOResearch and Engineering Company. He is presently the Technical Manager of Resins R&D for the Celanese Plastics Company. Dr. Isaacson has numerous patents and publications in the fields of polymer synthesis, catalysis, and structure-property relationships.
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Ind. Eng. Chem., Prod. Res. Develop..Vol. 13, NO. 1, 1974
!mica1 bngmneering m lYti2, his M.S. in Chemical Engineering in 1964, and his Doctor of Engineering Science Degree in 1968. All were received from the Newark College of Engineering (N.C.E.), Newark, N. J. He taught at N.C.E. as a teaching assistant and instructor of chemical engineering from 1962 until 1967, when he joined the Celanese Research Company as a Research Engineer. In 1970, he was promoted to Group Leader of Process and Product R&D for the Celanese Advance Engineering Composites Venture. Dr. Druin is presently the Group Leader of New Products Exploration for the Celanese Plastics Company. He is the author of patents and papers in the fields of structure-property relationships and of graphite fiber and microporous polymer film technology. Dr. Druin is also an adjunct instructor in the Chemical Engineering Department of N.C.E. Steven G. Plovan received his B.S. in Chemistry from Wayne State University in 1954 and his Ph.D. from Kansas State University in 1960. He joined the Celanese Research Company in 1967 as Research Associate, after prior experience with the Du Pont Company and General Motors Research Laboratories. He is presently a Section Head in the Celanese Coatings and Specialty Chemicals Company. Dr. Plouan has several patents and papers in the fields of microporous films, adhesives, and organic synthesis.
Investigations, dealing with films of crystalline polymers formed by extrusion at conditions of high stress on the polymer melt, have resulted in the discovery of a unique group of materials. Annealing the extruded film resulted in an elastic crystalline polymeric material. Immediate length recoveries of greater than 90% from strains of 50-100% were observed. Deformation of the annealed material parallel to the extrusion direction followed by elevated temperature stabilization of the elongated film resulted in a substrate characterized by a large number of submicroscopic pores (typically 2000 by 200 A ) . Pore size distribution was found to be a function of extent of the film deformation. The micropores are discrete, slightly tortuous channels which extend from one film surface to the other. They allow for the rapid flow of gases, vapors, and some liquids but are small enough to restrict transport of colloids or bacteria. Film surface area of 50’m2/g and apparent density reduction of 30% are characteristic of the microporous structure. Chemical properties of the porous film (e.g., resistance to attack by acids and bases) remain similar to those of the parent polymer. The formation of micropores is related to the placement of polymer chains into microcrystalline lamellae which are in turn aligned in rows parallel to the extrusion direction. This placement of chains largely occurs during the high melt stress extrusion process and is perfected during annealing. The elastic properties of the annealed film are believed due to the ability of the rows of lamellae to exert a restorative force during macroscopic deformation. Micropore formation results from lamellae spreading during film elongation with the interlamellar areas becoming micropores.
1. Introduction Thin porous structures are of great commercial interest. Among the major end uses has been that of separators in energy systems such as batteries. More recently, extremely fine porous or microporous materials have also found increasing use in other applications such as blood oxygenation, microfiltration, and other separation processes. Porous compositions are of two basic types: in the first t h e pores are not interconnected (foams a r cellular plastics), and in the second type tortuous paths extend from surface to surface of the structure. Compositions of the second type are used in many of the above-mentioned applications. The development of thermoplastic materials possessing outstanding physical and chemical properties has resulted in extensive research and development designed to utilize these desirable characteristics in porous structures. One such area of research has treated changes in the morphology of crystalline polymers, as a result of macroscopic stresses. While much of this work has been designed to predict material failure (e.g., fracture and crack propagation), a long-range scientific goal is development of a complete theory of the solid state of crystalline polymers. This paper details an additional and highly useful result of these efforts-development of a new group of engineering plastic films with unique microporous structures with commercial applicability.
11. Literature Survey Many studies have dealt with deformation of crystalline polymers (15, 16). While results have been difficult to generalize, it is apparent that the response of a polymeric material to deformation is frequently determined by the manner in which it was formed. A key stratification in formation of polymeric structures is the amount of stress applied to the molten material prior to its solidification to a shaped article such as a film or a fiber. High stress on molten polymers is generated by rapidly drawing a thick, slow-moving cross section to a thin, rapidly traveling cross section. In the discussion which follows, it will become apparent that application of high stress to a molten polymer undergoing crystallization can result in a solid structure which exhibits unique properties before, during, and after macroscopic deformation. In general, the responses of crystalline polymers to applications of stresses are of two kinds: (1) brittle fracture
(high rate of loading, low temperature) and (2) ductile fracture after plastic deformation (low rate of loading, high temperature). Much work has been done on the plastic deformation mechanism of polyethylene (26, 30, 31) and polypropylene (23, 32) by Peterlin and coworkers. As films of these crystalline polymers were slowly drawn, the microscopic crystalline spherulites were gradually transformed into a fiberlike structure. Before drawing, these spherulites consisted of arrays of folded polymer chains called lamellae. These lamellae were arranged in a radial fashion around the center of the spherulite. Figure 1 is a representation of a single, folded polymer chain lamella. Figure 2 shows how lamellae are believed arranged in a microcrystalline spherulite (24). In contrast to the spherulitic structures, it was reported by Keller that in polyethylene, lamellae could also be aligned in rows parallel to the stress direction (18). In these rows, the surface planes of the lamellae were perpendicular to the stress direction. This type of morphology is referred to as a row lamellar structure and,is depicted (33)in Figure 3. Similar structures in blown films of polyoxymethylene were reported in detail. along with electron micrographs (12). A detailed study dealing with the effects of stress on molten polyethylene (19) showed that during crystallization at high stress, row lamellar structures were produced. The existence of a fibrous microstructure which acted as muclei for lamellae growth was suggested. Crystallization at low stress produced twisted lamellae similar to those found in certain types of spherulites. However, stress measurements in this study were not exact. It was also reported that row lamellar structures were observed near the surface of injection moled bars of polyoxymethylene (4). The proposed nuclei of the rows were fibrils formed as a consequence of the high stress ( 4 ) . Evidence for the existence of these fibrils in blown films of polyoxymethylene is given (11). In a n interpretive review of this subject, the suggestion was made that the presence of these fibrils determines “whether the polymer will crystallize spherulitically or in a ‘row structure’ morphology” ( 7 ) . Support for this hypothesis is presented in a study on polypropylene films where graphite fibers served as nucleants for row lamellar structures (13). A number of reports delineated crystallization kinetics and resultant morphology of fibers and films of crystalline polymers formed under stress (2, 10, 37). At low and modInd. Eng. Chem., Prod. Res. Develop., Vol. 13,No. 1, 1974
3
Figure 1. One folded polymer chain lamella.
A report showed that molecular orientation existed in stressed polyethylene melts well before the onset of crystallization (17). In addition, evidence was presented to illustrate that i t was the stress rather than a radial thermal gradient which was chiefly responsible for the unusual orientation of the resultant crystallites. A thermodynamic analysis of the behavior of a stressed polymer melt ( I ) indicated that the degree of spherulite flattening is “determined by the difference in critical .~.. free perpendb to nucleation energy a t angles equal to and perpendicular the stress direction. The existence of even slight molecular m orientation leads to the appearance of flattened spherulites and its increase rapidly causes their degradation into degradat lamellae.” The exact nature of the molecular structure connecting cor >. . the subject > . , of,some controversy (34). ,n,\ is The termilamellae nology most frequently used to describe these structures has been varied, e.g., “intercrystalline links” (201, “interlamella ties” (81,and “bridging structure” (35). Use of the “bridging structure” phrase has been adopted as more general and entirely adequate for the purpose of this paper (36). A detailed study (35) of the nature of interlamellar material in cold drawn, stress-crystallized polyethylene and poly(ethy1ene oxide) showed that this fibrillar microstructure was of two basic types: one type being the microfiber formed upon initial stress crystallization and the other type formed from disrupted lamellae as depicted by Peterlin (25). Unusual results with melt spinning (extrusion) of poly(3 methylhutene) fiber under conditions of high melt draw ratio (high stress) were reported (29).It was found that while these fibers were highly crystalline, they exhibited elastic (immediate) recovery from large extensions. This was unusual in that classical elastomers and other materials displaying elastic behavior are generally noncrystalline or amorphous. The elasticity in the poly(3-methylbutene) fiber was postulated as due to the ability of the crystalline lamellae themselves, “joined together in stacks, to deform (probably bend) elastically.” It was also reported that in addition to poly(3-methylbutene), other polymers such as polypropylene and polyoxymethylene could be melt spun to form crystalline, elastic fibers under conditions of high stress (28). These fibers developed very large amounts of accessible internal volume (micropores) and a high surface area on stretching. It was suggested that this result was due to the spreading or “splaying apart” of the lamellae in the fiber. The mechanical, optical, and thermodynamic properties of these unusual fibers are provided (33) along with a suggested mechanism for lamellae spreading. A figure depicting this mechanism (33) is reproduced as Figure 4 in this paper. Other explanations for the source of t h e elastic restoring force have appeared. One theory (33) is that the row lamellar structure functions as a “leaf spring.” As the film or fiber is elongated, the lamellae are “peeled apart,” i.e., separated. In the separated state, the lamellae network can exert an elastic spring action (leaf spring). Variablelength interlammellar bridging structures limit interlamellar separation and prevent failure. An alternative mechanism for the elasticity has been proposed ( 5 ) . This mechanism involves shearing of lamellae between interlamellar bridging structures. In this theory, the lamellae are depicted as sliding past their neighbors by a distance less than the yield strain of the crystal. A number of patents dealing with elastic fibers and films of crystalline polymers have been cited ( 6 ) . ~~~~~~~~~~~
~~~
~~
I
Figure 2. Stacks of parallel lamellae in a microcrystalline spherulite (24). (Reprinted by permission of Interscience Pub-
lishers.)
Y-
INTERLAMELLAR REGON BRIDGING STRUCTURE
t
STRESS DIRECTION
‘Foldd polymer C h i n Perp4ndiCUIor M tlrm bindion.
Figure 3. Stacks of parallel lamellae.
erate amounts of “jet stretching” (the ratio of take-up speed to initial melt velocity) it was shown that spherulite size decreased and spherulite flattening increased: i.e., the morphology exhibited similarities to the row lamellar structure described above. These phenomena were ohserved with fibers of polypropylene (2) and both fibers and films of polyethylene (10,37). Another study dealing with polypropylene fibers formed by crystallization under stress ( l o a ) disputed the previously summarized assertion (of ref 2) that spherulite structures existed at all. Rather, it was suggested that the light-scattering properties originally attributed to spherulites (2) could be caused by “the magnitude of orientation fluctuations” in the (row) lamellar morphology. Other authors (21) have reported that molecular orientation in polypropylene and polyethylene fibers greatly iucreased with increasing melt draw ratio (take-up velocity divided by extrusion rate). Large increases in the crystalline region contribution to birefringence were observed at high melt draw ratios (above 80). It was stated “the unusual orientation of crystallites, which was first found by Keller (18) . . . is the main cause of this unusual change of birefringence.” 4
Ind. Eng. Chem.. Prod. Res. Develop..Vol. 13, No. 1, 1974
.
..
--20.0
EXTENSIGN RATE: 1OOY. I MIN. TEMPERATURE: 23.C .Break Stress
u1
v
n
INTERLAMELLARR G I O N BRIDGING STRUCTURE MICROPORES
Figure 4. Spreading apart of lamellae to form micropores.
It is of singular importance that the row lamellar structure is believed to be responsible for the elastic property. In the films which are described in this paper, it is also the row lamellar structure which results in the novel micr oporosity .
111. Process Description A. Material Selection. The basic process for developing these unique microporous structures is dependent on forming the row lamellar morphology described previously. Thus, polymer systems which develop this morphology upon crystallization under stress lend themselves most readily to the technology. Significant among these polymers are the crystalline polyolefins, polyamides, polyesters, and polyoxymethylenes. Much of our work has centered on commercially available isotactic polypropylene and the discussion which follows will deal with results obtained with this material. B. Process Outline. The production of the microporous films involves a number of critical process steps. The crystalline polymer is first extruded into a thin film under conditions which enhance stress on the molten polymer. Generally, temperatures close to the melting point, coupled with a rapid drawdown of the melt (Le., application of a high melt stress) as it exits from the extrusion die, have been found to yield the needed morphology. It is often desirable to anneal the film at this stage in an untensioned state to perfect the necessary crystalline structure. This film, the precursor to the final microporous film, has a n unusual stress-strain behavior. It also exhibits very high immediate recovery from deformations of up to 50-100% similar to the crystalline fibers discussed previously. Figure 5 illustrates the stress-strain behavior of t h e precursor film as compared to a conventional polypropylene film. Engineering stress is plotted as a function of film extension, up to the break stress. Figure 6 is indicative of the elastic recovery of the precursor from smaller deformations. The precursor is then elongated in the machine direction of the film. This represents one of the most critical steps in the process and one in which a great deal of control over the pore size and pore size distributed may be exercised. During the extension of up to 300%, the lamellar structure is deformed to produce an interconnecting network of slitlike voids. The film a t this point is opaque and is of greatly reduced apparent density. The density reduction affected by the drawing operation is illustrated in Figure 7 . Density reduction was measured by mercury intrusion ( 2 7 ) . The deformation process may be used to control the pore size and pore size distribution as shown in Figure 8. Pore sizes were estimated by comparing electron micrographs of subsequent samples with those pressures a t which mercury intrusion occurred. Size denotes the long dimension of the elliptical pore. Thus, films subjected to elongations of 300% have a maximum number of pores below 1000 A while those undergoing deformation of only 100% have a bimodal distribution with a large num-
CONVENTIONAL POLYPROPYLENE FILM
-600
% EXTENSION
Figure 5. Stress-strain properties of precursor film prepared from
isotactic polypropylene. EXTENSION: 1 0 0 % MIN. TEMPERATURE: 23*C 9.0 I I I
-
0
I
I
1
40
50
60
Precursor Film
10
20 */e
30 EXTENSION
Figure 6. Recovery of precursor film from high elastic deformation.
c)
E
0
I
I
1
100
200
300
EXTENSION. *I.
Figure 7. Apparent density of microporous polypropylene film as
a function of extension. ber of pores greater than 1500 A. These larger pores appear to offer the most accessible paths between the film surfaces. Solvent imbibition and gas permeability are directly related to the pore size distribution and can be conInd. Eng. Chem., Prod.
Res. Develop., Vol. 13, No. 1, 1974 5
I
-
% EXTENSION
==-
100
-
300
v)
s"
0
15 # ETHANOL :
0
0
0
1000
2000
ESTIMATED PORE DIAMETER.
i I
:E,
0
50
100
EXTpE)IoN.
x
50
100
150
200
250
300
Figure 10. Solvent sorption of microporous polypropylene films.
I
\I
YCLOHEXENE
EXTENSION. X
Figure 8. Pore size distribution in microporous polypropylene films. I
PYRIDINE
10 2
0
o'20r-----l
1so
0.161
STRETCHHG TEMPERATURE. 'C
Figure 9. Gas permeability of 0.0025 cm thick microporous polypropylene films.
Figure
trolled by the extent of the film deformation. Figures 9 and 10 indicate these effects. The temperatures at which the deformation occurs can also play an important role in the process of pore formation. Temperatures close to, but below, the crystalline melting point can be employed. The limit of temperature is controlled by the previous annealing temperature; e.g., for polypropylene it has been found that stretching the film at a temperature above loo" after annealing at 120" does not lead to the desired porous structure. Figure 11 depicts how the reduction of density ( i e . , void formation) for this case is sharply reduced at elevated stretching temperatures. A final important step in the process involves the stabilization of the pore structure. This is accomplished by heat setting the film while maintaining it in a tensioned state. The heat setting temperature is generally chosen close to, but below, the crystalline melting point. For polypropylene, this temperature is between 140 and 155". The stabilization step prevents relaxation of the porous structure during conditions of storage and use. The film at this point is hydrophobic, with a critical surface tension of 35 dyn/cm and can be rendered hydrophilic by coating with a surfactant. To summarize, the process involves a number of interrelated steps: (1) extrusion of film under conditions of low melt temperature and high melt stress; (2) annealing of this extruded film in a relaxed or untensioned state; (3) uniaxial stretching of the precursor film to develop the desired void structure; (4) heat treating the porous film in a tensioned state to stabilize the void structure; ( 5 ) coat-
ing the hydrophobic film with a surfactant to produce a hydrophilic film (optional).
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Ind. Eng. Chem., Prod. Res. Develop.. Vol. 13,No. l , 1974
11. Density reduction of microporous polypropylene film.
IV. Physical and Chemical Properties Using refinements of the technology previously described, the authors and colleagues have developed a series of thin microporous films (0.025 cm thick) under the trademark of Celgard (9, 14) (Celanese Plastics Co., Plastics Research Center, Summit, N. J.). Figure 12 is a transmission electron micrograph which shows the lamellae and the micropores which resulted from spreading the lamellae during elongation of the precursor. Bridging structure can also be seen connecting lamellae. This figure also shows the size relationship and uniformity of the pores in Celgard compared to that of other porous compositions. One result of this ultrafine pore structure is an extremely high film surface area, 50 m2/g of film. The pores in Celgard are discrete, slightly tortuous channels which extend from one surface to the other. These pores allow for the flow of gases, vapors, and, under certain conditions, liquids as well. The microporous structure is unlike that found in conventional membranes and porous materials. The pores are generally less than 0.2 ~r(2000 A) in length and 0.02 I.( (200 A) in width, dimensions significantly smaller than those of other structures. This allows Celgard to function uniquely as a separator. In most filter materials, for example, separation is accomplished because the flow paths are interconnected, highly tortuous channels which entrap or preferentially restrict passage of selected mixture components. In other types of conventional membranes, sepa-
*
INIT!ALWATER F M RATE AT 2 0 1 CELGARO 244001
2
4 6 B PRESSURE. Am.
~~
Figure 12. Transmasum electron rnmograph of Celgard film. Table I. Typical Physical Properties of Celgard Film PI'operty
Tensile strength MD* TDb Tensile modulus, MD Elongation, M D Tear initiation, M D M I T fold endurance Mullen burst
Value
Test method
!0,000 psi f!,000 psi 2 X lo5 psi
ASTM D882 ASTM D882
40% 1Ib 106 20 points
ASTM ASTM ASTM ASTM
M D = machine direction. 6 TD direction.
=
D882 D1004 D643 D774
transverse to machine
ration occurs because of a thin coating placed on one surface of the material. This coating allows for separation of mixture components on the basis of their different sorptive and diffusive properties, Celgard, on the other hand, acts as a barrier to certain compounds because of the small size of the pores. Figure 13 summarizes many of the transport properties of Celgard films which are regulated by the microporous structure. Celgard 2400 refers to the standard, hydrophobic film. Celgard 2400W and K-72-4 refer to hydrophilic variants of the base film. Table I lists mechanical and other physical properties of the film. The outstanding mechanical feature of Celgard films is their high strength, particularly in the machine direction. Because of the porous nature of the film, it has a lower density (0.6 us. 0.9 g/cm3) than that of other polypropylene articles. The films are capable of withstanding the chemical effects of a wide variety of chemical solvents. Table I1 qualitatively summarizes the many chemical compounds which are compatible with Celgard. These films can be used a t temperatures from -62 to +70" witbout special design considerations. Above 70" they shrink in the length direction with some reduction in porosity. If the film is constrained, it can be used to temperatures up to 120"without loss of porosity. Table III shows data on the separator resistance of hydrophilic Celgard films usable in aqueous electrolytes. It is apparent that immersion of greater than 26 weeks in
laale 11. Lompantmty of Celogard r ~ h wlth n Various Compounds*
Acids HSOl (coned) Alcohols Ethyl alcohol Ethylene glycol Isopropyl alcohol Ether alcohols Butyl Cellosolve (2-butoxyetbanol) Methvl P.. dI_ l_m ~lve .....--__ _." (2-methoxyetbanol) Bases KOH (40%) Ethers 1,kdioxane Fuels Gasoline Kerosene
A
A A A
B A ._
A
B B B
Halogenated Hydrocarbons Carbon tetrachloride C Tetrachloroethylene C (perchloroethylene) Hydrocarbons Benzene B Hexane B Toluene B Ketones A..a+n..a
-.-.-""I.-
Methyl ethyl ketone . (3ils 10W30 motot' oil IMiscellaneous N,N-Dimethvlnw+---.. amidle N,N-D 'imethylfomamid Nitrobb..,,,, Tetrahydrofuran Freon TF
.. A A
B A. .
B B B
* T h e compatibility statements are based on 72 hr of exposure a t room temperature (25"). Key: A, good (no effect);B, slight swell; C, teristies should be evaluatea. highly caustic or acidic solutions has resulted in little or no deterioration of the microporous structure since separator resistance would have changed if this had occurred.
V. End Use Applications These unique properties lend themselves to a variety of potential end uses, summarized in Table IV. The acid, alkali, chemical, and thermal stability of the film, the pore size, and the low electrical resistivity of Celgard make it an ideal battery separator. In aqueous electrolyte batteries, chemically treated wettable films are employed (Celgard 2400W and K-72-4) but nonaqueous systems can be accommodated with untreated film (Celgard 2400). Electron transport is unrestricted, while particulate matter cannot pass through the film. Ind. Eng. Chem., Prod. Rfs. Develop., Vol. 13, No. 1. 1974
7
Table IV.Potential End Use Applications for Celgard Films
Table 111. Separator Resistance0 of Hydrophilic Celgard Film (mn cmz)
Immersion time Electrolyte and concn 25% 31% 40% 45% 40% 28%
KOH KOH KOH
25% 31% 40% 45% 40% 28%
KOH KOH
KOH
KOH H&O4
KOH KOH
KOH HpSO4
Temp, “C 22 22 22 22 59 22 22 22 22 22 59 22
1
1
1
hr
day
week
26 weeks
60.6 63.9 69.0 413.0 60.0
40.6 38.7 53.5 78.0 54.8
38.7 45.2 52.2 78.0 49.0
35.4 45.2 47.1 52.9 71.0
Celgard 2400W 83.9 371.0 208.0 108.0 OLb 1160.0 OL 1730.0
Celgard K-72-4 32.2 64.5 61.9 45.2 50.3 52.2 92.9 80.6
Functional medical
Burn dressings Endotracheal tube cuffs Nonadherent dressings Alkaline battery separators Bacteria filters Dialysis Industry-laboratory ultrafiltration Lead-acid battery separators Oxygenation and membrane supports Reverse osmosis supports Water purification Degassing Acoustical film Mattress ticking Sleeping bag fabric tarpaulins Tent fabrics Thermal blankets Sterile packaging Diaper covers Disposable protective clothing, industrial and military O.R. pack and drape Apparel linings Fashion raincoats Plastic raincoats Reusable protective clothing Shoe linings Travel bags Upholstery fabric backing Agricultural produce wrap Cable wrap Capacitor wrap Controlled-environment packaging Industrial tape Nonfogging packaging film Controlled-release desiccant for anhydrous fluids
Membrane and ultrafiltration
Industrial processing Insulation and protective barriers
35.4
-+
Sterile packaging commonly used for hospital syringes and catheters can take advantage of the permeability of the film to gases and vapors such as ethylene oxide or steam. Outgassing ethylene oxide from sterilized packages is generally the slow step in the process, and the film permits a greatly accelerated rate. Contamination of a sterilized package is prohibited by the pore size of the film which is too small for penetration by bacteria. The barrier properties of the film toward bacteria, polymeric substances, and liquid water, as well as its permeability toward water vapor, recommend use in medical dressings (3) where the film behaves like a “synthetic skin.” Laminates of Celgard and polyurethane foam have been used to treat severely burned patients. The laminate acts as a barrier t o bacteria while promoting growth of new epithelia. The transport of gases through the film is a flow phenomenon, not a diffusion process. Consequently, there are a variety of applications where transport of gases is a critical parameter. In addition to sterile-packaging mentioned above, processes such as blood oxygenation and life support systems make use of the gas transport properties. Wettable microporous films can find use in reverse osmosis and other membrane systems as supports for active layers such as Loeb membranes. Sulfonated poly(phenylene oxide) (SPPO) membranes for reverse osmosis have been developed (22) which utilize Celgard as the substrate. The high mechanical strength and high porosity of the Celgard support the SPPO reverse osmosis membrane without impeding water flux. A variety of packaging applications take advantage not only of the porosity but also of the thermoplastic nature of the film which permits sealing by conventional heat and ultrasonic techniques. Desiccant and fumigant packages where controlled release of chemical species is desired are examples. The film can be laminated to fabrics, nonwovens, open scrims, and other open porous materials with up to 90% retention of porosity, for end use applications where high impact and tear resistance are required. FDA-approved grades of resin can be processed to give the desired microporous structure and then used in contact with food or the human body. Because of the high surface area of the film, it is receptive to printing and adhesive bonding without further treatment. Ind. Eng.
Applications
38.7
Falk, S. U., Salkind, A. J., “Alkaline Storage Batteries,” p 260,Wiley, New York, N. Y., 1969. OL = instrument overload 1290 ma cm2.
8
Category
Chem., Prod. Res. Develop., Vol. 13, No. 1, 1974
Sterile packaging Disposables
Apparel
Household furnishings Tape, wrap, and packaging
VI. Summary Results of investigations into the responses of crystalline polymers to macroscopic stresses have led to discovery of a unique group of microporous films. The structure of these films is characterized by submicroscopic pores (2000 by 200 A) of striking uniformity. Films produced by the technology described in this communication retain the desirable properties of thermoplastics, such as resistance to chemical attack and high mechanical strength, while exhibiting rapid gas, vapor, and liquid transport rates. Acknowledgment A grateful acknowledgment is extended to Dr. I. L. Hay, Celanese, for many helpful suggestions on polymer morphology and for the electron micrograph. Literature Cited (1) Baranov, V. G., Frenkel, S. Ya., Gromov, V. I . , Volkov, T. I . . Zurabian, R. S., J . Polym. Sci., Part C, No. 38, 61 (1972), ( 2 ) Baranov, V. G., Volkov. T. I., Farshyan, G. S., Frenkel, S. Ya., J. Polym. Sci., Part C. No. 30,305 (1971). (3) Bierenbaum, H. S., Isaacson. R. B., Lantos, P. R., U. S. Patent 3,426,754 (Feb 11, 1969) (4) Clark, E. S.. SPE (Soc. Plast. Eng.) J., 23, 246 (1967). (5) Clark, E. S.. paper presented at the Borden Award Symposium of the American Chemical Society, Boston, Mass., 1972. See Clark, E. S . , Polym. Sci. Techno/., 1 , 279, 280 (1973). (6) Clark, E. S., Polym. Sci. Techno/.. 1 , 282 (1973). (7) Clark, E. S. Garber. C. A . , Int. J. Polym. Mater., 1 , 31 (1971).
(8) Davis, H. A.. J. Poiym. Sci.. PartA-2, 4, 1009 (1966):
(9) Druin. M. L.. Loft, J. T.. Plouan, S. G . . U. S. Patent 3.679.538 (July 25. 19721. (10) 'Farshyan, G. S.. Baranov, V. G.,Frenkel. S. Ya., Vysokomoi s b din., Ser. A, 12, 1574 (1970). (loa) Fung. P. Y.-F., Orlando, E., Carr, S. H.. Poiym. Eng. Sci., 13, 295 llq7RI ~...-,.
(11) Garber.C.. Clark, E., J. Macromoi. Sci., Phys., 4,499 (1970). (12) Geil, P. H.. Polymer Single Crystals." p 441 ff. Interscience, New York. N. Y.. 1963. (13) Hobbs. S.Y . . Nature (London), Phys. Sci., 234.13 (1971). (14) Isaacson, R. B.. Bierenbaum, H. S., U. S. Patent 3,558,764 (Jan 26,1971). (15) J. MacromoiSci.. Phys., 4,467-759 (1970) (16) J. MaierSci.. 6,451-59, 6 (1971). .. . . 1111 Katayama, K.. ma no, T., Nakamura, R.. Koiioid-Z. 2. Poiym., 226, 125 119681. (18) Kkiler. A..J. Poiym. Sci., 15, 31 (1955). (19) Keller. A.. Machin. M. J.. J. Macromoi. Sci., Phys., 1, 41 (1967). (20) Keith. H. 0.. Padden, I. J.. Jr.. Vadimsky. R. G.. Science, 150, i w f i it9fisi ,.---,. (21) Kitao. T., Ohya, S.. Furukawa, J., Yamashita, S., J. Poiym. Sci., PartA-2, 11.1091 (1973). (22) LaConti. A. B.. Chludzinski, P. J., Fickett. A. P., in "Reverse Os~
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Receiuedforreuiem April 18,1913 Accepted November 23, 1973
Acid Leaching of Ilmenite into Synthetic Rutile f Thomas S. Mackey Associated Metals and Minerals Corporation, Texas Crty. Texas 77590
Dr. Thomas S. Mackey, a Technical Consultant, re. ceiued a B.S. Degree from Manhattan College, anM.S. Degree in Engineering from Columbia Uniuersity, and a Ph.D. from Rice University. He has been employed by the Wah Chang Corp. and is currently a consultant to Associated Metals and Minerals Corp., the Indonesian State Tin Enterprise Co., Taiwan Metal Mining Co., and others. He is a Fellow of the American Institute of Chemists, Institution o f Mining and Metallurgy, Sigma Pi Sigma, Sigma Xi, and Sigma Gamma Epsilon. He is a Registered Professional Engineer in Texas and serues as State Director. He is a Certified Professional Geologist. Dr. Mackey is the current Chairman of the Lead, Zinc, Tin Committee of the American Iwtitute of Mining, Metallurgical and Petroleum Engineers. He is a member of the American Chemical Society. Dr. Machey has authored over a dozen scientific journal publications in English, Spanish, and French and is a member of many scientific organizations.
Introduction About 15% of the total world supply of titanium now comes from the mineral rutile, and since the reserves of rutile are limited while the demand increases, it is expected that in the next few years a need will continue to develop alternate sources for titanium dioxide. Today, the coatings pigment industry accounts for approximately 95% of the total annual titanium mineral consumption. The balance is used in the welding rod, ceramics, and refractory and in other miscellaneous applications such as a weighting agent in concrete. The predominant mineral of titanium is ilmenite (assaying 50-6070 TiOa), found in adequate supply throughout the world. Most of the ilmenite mined today is consumed to make pigments, uia the sulfate process, for the paint, paper, and plastic industries, and metal. During the past 20 years, there has been a trend to produce pigments uia the chloride process, which has traditionally used rutile assaying over 95% Ti02 as a feed material. In the sulfate process, ground ilmenite is digested with strong sulfuric acid, yielding a titanium sulfate solution which is later hydrolyzed and precipitated to form a Ti02 pigment and a solid waste consisting mostly of ferrous sulfate septahydrate crystals. The ilmenite is treated with strong sulfuric acid and the solid reaction cake is dissolved in water by the reaction
-ilmenite + sulfuric FeO.TiO,.Fe,O,
+
acid
~
5H,SO,
titanvl sulfate ?See the Literature Cited section at the end O f this article for a comprehensive list Of referencespertinent to this Work.
+ iron sulfates + water
+ Fe,O, + Fe(SO,), + 5H,O ~~
TiO(S0,)
ind. Eng. Chem., Prod. Res. Develop.. Vol. 13, No. 1, 1 9 7 4 9
