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(3) Brown, W. E., and Peterson, W. H., IND. ENG.CHEM.,42, 1823 (1950). (4) Clutterbuck, P. W., Lovell, R., and Raistrick, H., Biochem. J . , 26, 1907 (1932). (5) Cram, D. J., J . Am. Chem. Soc., 70, 4240 (1948). (6) Cram, D. J., and Tishler, M., Ibid., 70, 4238 (1948). (7) Gailey, F. B., Stefaniak, J. J., Olson, B. H., and Johnson, M. J., J . Bact., 52, 129 (1946). (8) Higuchi, K., Jarvis, F. G., Peterson, W. H., and Johnson, M. J., J . Am. Chena. SOC.,68, 1669 (1946). (9) Johnson, &I. J., J . Biol. Chem., 137, 575 (1941). (IO) Karnovsky, M. L., and Johnson, M. J., A n a l . Chena., 21, 1125 (1949). (1:)
National Research Council, Canada, Radio and Electrical Engineering Division, Rept. E.R.A.-166 (February 1949).
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(12) Peterson, W, H., Harvey Lectures, Ser. XLII, 276 (1946-47). (13) Raper, K. B., Mycologia, 44, 1 (1952). (14) Rivett, R. W., Johnson, M. J., and Peterson, W. H., IND.ENG. CHEM.,42, 188 (1950). (15) Schmidt, W. H., and Moyer, A. J., J . Bact., 47, 199 (1944). J . Biol. Chem., 100, 695 (1933). (16) Shaffer, P. A., and Somogyi, -M., (17) Somer, P. de, Bull. SOC. chim. biol., 29, 364 (1947). (18) Stahmann, M. A , , and Stauffer, J. F., Science, 1 0 6 , 3 5 (1947). (19) Stodola, F. H., Wachtel, J. L., Moyer, A. J., and Coghill, R. D., J . Biol. Chem., 159, 67 (1945). (20) Taira, T . , Yamatodani, S.,Fujii, S., Komatsu, H., and Takamoto, I., J . Antibiotics ( J a p a n ) , 4 , 103 (1951). (21) Woodruff, H. B., and Larsen, A. H., U. S. Patent 2,532,980 (Dec. 5, 1950). RECEIVED for review June 16, lS52.
ACCEPTED
January 2, 1953.
NYLON-COATED LEATHER FRED LEONARD, T. B. BLEVINS, W. S. WRIGHT, AND M. G. DEFRIES Army Prosthetics Research Laboratory, Walter Reed Army Medical Center, Washington, D . C .
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E A T H E R is used extensively in fabricating prostheses. The leather is usually worn in direct contact with the skin during use of the prosthesis and is subject to acid and alkaline sweat and bacterial skin flora. Experience has indicated that uncoated leather causes clothing stains, retains odors, and undergoes cracking, discoloration, and degradation. These effects are especially noted during summer months, and in certain instances the useful life of samples of chrome-tanned horsehide harnesses has been as short as 4 weeks. Any coating t o be considered as a protective coating for leather in this application should possess the following attributes: Act as a n osmotic membrane, allowing diffusion of water vapor, b u t be an effective barrier t o bulk sweat, larger nitrogenous molecules, and proteolytic bacteria Have sufficient strength and flexibility to withstand repeated flexings without cracking from the leather Be resistant t o sweat of varying p H Show qood adhesion Be easily cleansible after wear Be easily applied Show good abrasion and scuffing resistance
Of the commercially available plastic materials which were considered for this application, it appeared that a n alcoholsoluble type nylon designated FLM-6501(I), manufactured by D u Pont, showed most promise. Bull et al. (8) have described the use of a n alcohol-soluble type nylon in occlusive dressings for wounds and burns, and their data indicate t h a t this type film was water vapor permeable and acted as an effective barrier against microorganisms. This paper describes the use and properties of FM-6501 S y l o n ( I ) as a protective coating for leather in contact with the skin. FM-6501 Nylon has been used to coat leather worn next t o the skin of amputees. The results indicate t h a t the coated leather is far superior t o uncoated leather in this application. EXPERIMENTAL
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The nylon solution is prepared PREPARATION OF SOLUTION. by allowing 20 grams of Nylon FM-6501 t o dissolve with stirring in 200 cc. of 85% 2-propanol-water solution heated t o 170' F. Once dissolved, the nylon remains in solution for several days, after which the solution gels. T o redissolve the nylon, it is merely necessary to reheat the solution t o 170' F. COATINGTHE LEATHER. The leather in either the fabricated or "as received" form is first wiped clean with alcohol and dried in a circulating-air oven a t 60' C. for 5 minutes. It is then carefully brush-coated with five coats of nylon solution, allowing approximately 5 minutes to elapse between each application.
Following this technique, a transparent coating of approximately 0.008 inch is obtained. ilfter the final coat the sample is allowed to dry in a circulating-air oven a t 60" C. for 15 minutes. ABRASIONRESISTANCE.The abrasion resistance was measured with a Taber Abrasor, Research Model, Taber Instrument Co., North Tonawanda, New York, using a CS-8 wheel and a 250-gram u-eight. The samples were allowed to run for 3000 cycles. FLEXERE.The nylon-coated leather samples were flexed by fixing one end of the sample t o a rigid support and the other end of the sample t o a horizontally reciprocating rod. At each pull stroke the sample received a slight stretch; on the return stroke, the sample was flexed. The machine was operated at a speed of 65 cycles per minute for 40,000 cycles. SIIIULTANEOUS FLEXING AND ABR4DING I N SYNTHETIC SWEAT MEDIUM. A strip of nylon-coated leather was placed on a glass tray in a Gardner washability machine No. 105 (Henry 8. Gardner Laboratories, Inc., Bethesda, Md.). The trough of the machine was filled with a synthetic sweat medium until the nyloncoated sample was immersed. The brush was allowed t o move over the surface of the sample and arranged so t h a t the action of the brush caused the leather to flex while being abraded. The synthetic sweat ( 3 ) was composed of the following ingredients: Sodium chloride, 57 millimoles Lactic acid, 3280 mg. Urea, 390 mg. Creatinine, 10 mg. Uric acid, 15 mg. Water, qs. t o make 1 liter RESISTAKCE TO SYNTHETIC SWEAT. A weighed sample of the nylon pellets was placed in 250 cc. of the synthetic sweat composition at 40' C. for 7 days. After immersion, the sample was washed with water, filtered, dried, and reweighed. STRESS-STRAIN PROPERTIES. Tensile strength and ultimate elongation were measured with a Scott L6 rubber tester in accordance with A.S.T.M. Method D-142, using die C. WATERVAPORPERMEABILITY. Ointment jars, 2-ounce capaoity, with metal screw tops were used. The inside diameter of the tops was 1.85 inches. Circular specimens of the leather samples were cut t o this diameter. Iloles 34 mm. in diameter were cut out in the center of each lid. Thus, when the circular specimens were inserted inside the tops and the caps screwed in place, an square meters of the specimen surface was area of 9.07 X exposed. The diffusion jars were filled within inch of the top with Drierite. The diffusion jars were placed in a desiccator containing acid sweat at 40" C. At regular intervals a jar was removed, weighed, and replaced in the desiccator. The gain
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in weight was reported as a function of time. At the end of 24 hours the test was terminated. Specimen thickness of nyloncoated leather was 0.037 inch. Thickness of nylon coating was approximately 0.008 inch.
TABLE 11. STRESS-STRAIK PROPERTIES O F CHROME-TANSBU HORSEHIDE Treatment
RESULTS AND DISCUSSION
ABRASIOX RESISTANCE.At the end of 3000 cycles on the Taber Abrasor the nylon-coated sample showed only faint signs of wear, whereas an uncoated leather sample had been badly abraded. Through this treatment the sample coated with nylon had been reduced in thickness 27& whereas the uncoated sample was reduced 68%.
HOURS
Figure 1. Water Vapor Permeability of NylonCoated Leather
FLEX RESISTANCE.Using the test described in the experimental section, visual examination of the nylon-coated sample after 40,000 cycles showed no surface cracks. flaws, or peeling. REsIST-4NCE T O IMLIRIERSION I N SYSTHETIC SWEAT. L4fter immersion in synthetic svieat for 1 week a t 40" C. the nylon pellets were free-flowing and did not show anv tendency to adhere to each other, After washing with water, filtering, mashing, drying, and reweighing, 99% of the original sample weight had been recovered. STRESS-STRdIN TESTS. The results Of these tests on a nylon film cast from 2-propanol-water solution are shown in Table I . The findings indicate that the films are humidity sensitive. With increasing exposure to higher humidity the tensile strength falls and the ultimate elongation increases. Under conditions of use the nylon film will be expsed in essentially vapor saturated atmosphere, and under these conditions the stress-strain properties anticipated are those given in the third section of Table 1-1981 pounds per square inch ultimate tensile strength and 484% elongation a t break.
Vol. 45, No. 4
Dried a t 60' C., 20 hr. 100% relative humidity, 1 week
Tensile Lb./Sq. Strength, In.
Elongation, %
3596 2936
57
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WATERABSORPTIOU.Weighed samples of leather, one uncoated and the other coated with nylon on all surfaces, were immersed in distilled water a t 25" C. for 48 hours. After carefully LT iping 17 ith gauze to remove adhering droplets, the samples were reweighed. The nylon-coated sample had gained 17yo by weight, whereas the uncoated sample had gained 150%. WATER VAPORPERMEABILITY. The data are summarized in Figure 1. The diffusion of water vapor through the nyloncoated sample varied linearly M ith time during the 24 hours of the test. The assembly of nylon on leather (0.037-inch thick) permits diffusion of nater vapor a t the rate of 32.6 grams of water per 1.8 square meters per hour, with a partial pressure difference of approximately 50 mm. of mercury. This permeability m a y b e compared n i t h the hourly water loss from the total surface of the human body (approximately 1.8 square mpters) of 20 to 25 grams of insensible perspiration. FIELDTESTING.Field tests of the effectiveness of the nylon coating on leather harnesses worn bv more than 50 amputees have indicated that the coating inhibits deterioration of the leather harnesses for periods greater than 1" vear. Figure 2 shoFTs two harnesses, one uncoated (left harness) and worn for approuimstel\- 2 months during the summer, and another, nylon-
PROPERTIES OF NYLON FILx TABLE I. STRESS-STRAIS Treatment Dried a t 60' C 20 hr. 50% relative h&idity, 1 week 72 hrs. immersion in water
Tensile Strength, Lb./Sq. In. 3470 2028 1981
Elon ation,
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50 395 484 ~~
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Unsupported nylon films conditioned for 1 week a t 50% relative humidity and 25" C. showed an ultimate elongation of 395%. However, a t extensions over 20%) the material does not exhibit simple elastic behavior. Fifteen minutes after the removal of the load required t o stretch the film 257,, a 5% residual set was noted. A racking phenomenon similar t o that demonstrated by nylon fibers was observed a t higher elongations. At the breaking point, a sample having an original thickness of 0.008 inch reduced to 0.002 inch. The stress-strain properties of the chrome-tanned horsehide used in these experiments are given in Table 11. Compared with Table I, the data indicate that, with the nylon bonded t o the leather, it should be possible to strain the leather up to its ultimate elongation without rupturing the nylon.
Figure 2.
Inhibited Deterioration of Leather Harnesses
Uncoated, worn for 2 summer months (left); nylon-coated, worn for 2 years ( r i g h t )
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coated and worn for over 2 years. The uncoated harness has become badly deteriorated and unfit for further usa, whereas t h e coated socket of the second harness, while beginning to show signs of cracking, was still usable. In addition, the problem of clothing stains attendant upon the use of uncoated leather next t o the skin was eliminated. All leather portions of prostheses worn by amputees are now being routinely nylon-coated. SOLUBILITY CHARACTERISTICS OF COATING SOLUTION. Nylon solutions made up as described remain clear for a period of about 3 days, after which time the solution begins to gel. Further investigation revealed that solutions could be stabilized for periods of several months by compounds containing loosely bound
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hydrogen atoms-e.g., phenol, picric acid, other substituted phenols, and lactic acid. Further work on the use of stabilized solutions is in progress. LITERATURE CITED (1) Brubaker, M. H., Hanford, W. E., and Wiley, R. H., U. S. Paterlt 2,285,009 (June 2, 1942). (2) Bull, J. P., Squire, J. R., and Jopley, E., Lancet, 213-15 (Aug. 7, 1948). (3) Mickelsen, C., and Keys, A . , report to the National Research
Council Laboratory of Physiological Hygiene, University of Minnesota, Minneapolis, Minn., May 13, 1943.
RECEIVED for review September 4, 1952.
ACCEPTED January 1 , 1953.
Development of Thiokol Polymer Protective Coatings for Steel ANTHONY P. MASSA', HERMAN COLON2, AND W. FRED SCHURIG Polytechnic Institute of Brooklyn, Brooklyn 2, N . Y .
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OR a number of years polysulfide types of polymers have been known t o be effective barriers against water and solvent permeation, and hence they would appear to be useful as protective coatings for steel and other metals or surfaces attacked by water or water-related media or solvents. This investigation was conducted to develop polysulfide protective coatings effective against not only water and weather exposure, but also against marine and solvent immersion. The development program involved work with systems containing water or solvents as the dispersing medium, and other polymers and resins as adjuncts to the polysulfide polymers themselves t o increase the value of the coating compounds. Extensive water vapor permeability tests have indicated that there are decided differences between polymer structures. These tests also demonstrated t h a t work on the improvement of methods of film preparation offered more possibilities for better coatings when the optimum in combination of coating materials was reached.
The results of these preliminary experiments indicated t h a t some work would have to be done on pigments and solvents, in addition t o the resins studied, in order t o develop satisfactory coating compositions. The tests indicated t h a t the development of Thiokol-type coatings from water systems was a definite possibility. WATER DISPERSIONS
Thiokol-type latices are effective in protecting steel and other metal surfaces from corrosion on exposure to a great majority of organic solvents. However, with prolonged exposure of these coatings to aqueous media, some blistering and black spots develop. Subsequently, rusting takes place a t these black spots. The elimination of these black spots would make Thiokol latices per se very useful for anticorrosive coatings. A number of tests were conducted to determine the cause of the black spots. Analytical and other tests indicated that the black spots were iron sulfide formations which resulted from the interaction of free sulfur contained in the polymer with the steel SUMMARY O F PRELIMINARY TESTS of the base metal. The inclusion of a small amount of soluble Initial experiments with coatings made from water dispersions chromate salt in the latex temporarily eliminates black spot gave poor test results. Corrosion and permeability tests as formation. However, the chromate salt is eventually extracted well as theoretical considerations demonstrated that the emulsiand black spot formation occurs as before. In this respect, fiers and dispersing agents were responsible for the failure of the Thiokol polymers are not as effective as phosphate steel primer coatings. Attempts were then coatings which contain a solumade to eliminate or deble metal phosphate, free crease the amount of waterphosphoric acid, and an oxidiextractable materials in the zing agent (9). Here the systems. chemicals react with the iron surface t o form a n Methods were found t o anticorrosive phosphate coatdisperse polysulfide polymer ing which adheres to the latices in resin solutions of base metal. The complexity many types, so that a great of phosphate and other metal number of these resins and primer systems and the polymers, in combination fact that there are usually with Thiokol-type l a t i c e s , several different irregular were studied for appiication interfaces on the protected as protective coatings. surface has led t o a large 1 Present address, H. K. Fergunumber of independent theoson Co., New York, N. Y. ries of the inhibition mechFigure 1. Accelerated Corrosion Test, Constant * Present address, Federal Adheanism ( 5 ) . Temperature Bath sives Corp., Brooklyn, N. Y .
