COPPER SOAPS
I11 still reveal a wide variation in iron and tin pickup. For this reason it is customary to include six to twelve cans as one sample for examination at any one date. The problem of adequate sampling received considerable attention in the planning of experiments in the current nutrition program on commercially canned foods ( 1 5 ) . The decisions reached as to the methods of procedure and sampling to be used were made after full consideration of the problem by the collaborating laboratories at universities and in the industry. I n the belief that these sampling methods may prove of service to other investigators, the salient points of procedure are listed:
As Rot-Proofing Agents on Fabrics
1. STATISTICAL DETERMINATIOKS OF RANGESIN NUTRITIYE
VALUESOF COMMERCIALLY CANNED FOODS.Only commercial samples of known history are to be examined. A sample is to be composed of six retail size cans packed in the same cannery on the same day. These six are to be composited and assays made on the composite. I n most instances samples are to be taken from each cannery on three days during different times in the season. 2. OVER-ALL CANNING EFFECTS a. As a raw stock control a 2-kg. sample from a well-mixed 300-pound batch comparable to the material appearing in the processd product is collected. b. The final product sample consists of twelve retail size cans; six are composited and sampled for assay immediately after cooling, and six are returned to the laboratory for food inspection measurements. c. Ascorbic acid determinations are made in the field on both raw and processed samples. d. Samples for B vitamin assays are pureed (in the field) with sulfuric acid to give a pII of 3 or below, chloroform and toluene added, and the samples held under refrigeration until assayed. e . Samples for carotene assay are pureed with alcoholic potassium hydroxide and held under refrigeration in the dark until assayed. f. Samples for moisture determination are weighed into cans, known amounts of distilled water added, the cans closed and heat-sterilized. 3. SPECIFICCANNERY OPERATIONS a. As in section 2a, the initial control is composed of a 2-kg. sample taken from the well-mixed material as it enters the operation. b. As in section 2b, the sample emerging from the specific operation is 2 kg., collected from various portions of the batch. c. Samples for ascorbic acid, B vitamins, carotene, and moisture aye treated as under 2c, d, e, and f.
U. S. Department of Agriculture, Beltsville, Md. a
Copper naphthenate prevents rotting of cotton fabric in soil at lower concentrations on the fabric than do coppep oleate, copper “talla te”, or copper hydrogenated resinate. Several methods have demonstrated that the high preservative capacity of copper naphthenate in contact with soils is related to the fact that naphthenic acid itself is a potent fungicide. Various factors affecting the behavior of copper preservatives in contact with soils are studied. They include solubilization by acid hydrolysis and b y complex formation, and deactivation by chemical combination. Data from pure culture test procedures are contrasted with the results obtained by exposure to soils.
T
HE present emergency has intensified interest in methods for the prevention of rotting and mildewing of fabrics. Sandbags, tents, jungle hammocks, insect netting, and other articles of military importance are commonly subject to severe deterioration by microorganisms. This is particularly true in moist, warm climates. This report deals with the fabric-preservative values of four copper soaps and with the utility of certain laboratory procedures for the estimation of mildew-proofness or rot-proofness of fabric. The term “mildew” i s here used in a broad sense to refer to either fungal or bacterial mirroorganisms, regardless of whether they produce actual tendering of fabric, An organism which may grow on fabric without causing tendering is here termed a “superficial” organism. “Rot” refers to the tendering of fabric by microorganisms. Many chemical compounds have been used as mildew and rot preventives for fabrics. Jarrell, Stuart, and Holman (15) report the effectiveness of copper compounds. Furry, Robinson, and Humfeld (10) find preservative value in various commercial preparations, including copper, mercury, and phenolic materials; they propose also the use of a cadmium treatment. Bertolet (4) discusses a large number of fabric preservatives, including several of recent development. Several attempts have been made by various workers to develop rapid, accurate, and reproducible methods for estimating the value of mildew-proofing treatments. Important advances have been made along this line. However, laboratory test methods have not yet developed to such a stage that their results alone may be used as accurate predictions of the resistance tu mildewing or rotting of a treated fabric under all of the varied service conditions to which i t may be subjected. The field performance of any particular protective agent depends not only on its initial germicidal value, but also on i t s reaction to those environmental agencies which tend to cause it to be deactivated, dissipated, or destroyed. Use of different test methods has resulted in apparently conflicting data and much confusion as to the actual value of each preservative. I t was thought that some clarification of this perplexing situation might result from a closer examination of the causal factors operating in
LITERATURE CITED
(1) American Can Co., Canned Food Reference Manual, 2nd ed., 1943. (2)
PAUL B. MARSH, GLENN A. GREATHQUSE, KATHARINA BOLLEKBACHER, AKD MIPRY L. BUTLER
Bessey, 0. A . , and King, C. G., J . Biol. Chem., 103, 687-98 (1933).
Booher, L. E., Hartzler, E. R., and Hewston, E. M., U. S. Dept. Agr., Circ. 638 (1942). (4) Clifcorn, L. E., and Heberlein, D. G., IND.ENG.CHEM.,36,
(3)
171 (1944).
(5) Clouse, R. C., J . Am. Dietet. Assoc., 19, 496-504 (1943). (6) Farrell, K. T., and Fellers, C. R., Food Research, 7 , 171-7 (1942).
(7) Fixsen, M. A. B., Nutrition Abstracts & Revs., 8 , 281-307 (1938).
( 8 ) Hauck, H. M., J. Home Econ., 35, 295-300 (1943). (9) Kohman, E. F., Natl. Canners Assoc., Bull. 19-L (1937). (10) Lueck, R. H., and Pilcher, R. W., IND. ENC.CHmr., 33, 292-300 (1941).
Maclinn, W. A., and Fellers, C. R . , Mass. Agr. Expt. Sta., Bull. 354 (1938). (12) McHenry, E. W., Can. Pub. Health J . , 26, 124-7 (1935). (13) Musulin, R. R., and King, C. G., J . Biol. Chem., 116, 409-13 (11)
(1936).
Stern, R. M., and Vavich, M.P., private communication. Stewart, J. A., and Pilcher, R. W., Chem. Eng. News, “Can Makers Wartime Problems”. (16) Theriault, F. R., and Feilers, C. R., Food Research, 7 , 503-8
(14) (15)
(1942). PRESEN~E before D the Division of Agricultural and Food Chemistry at the AN SOCI~TY, Pittsburgh, Pa. 106th Meeting of the A M ~ R X CCHEMICAL
176
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1944
the case of a particular type of preservative. Accordingly, a group of four copper soaps was selected-copper naphthenate, copper oleate, copper "tallate", a?d a copper hydrogenated resinate. The use of copper soaps in preventing microbiological deterioration of fish nets is apparently older than the application of such materials to woven fabric. Taylor and Wells (28, 24), Atkins (2, S), Conn (e),and Robertson and Wright (19) report the use of such materials as copper oleate, copper resinate, and copper naphthenate. Elkin and White (7) present limited data on copper napthenate and copper oleate treatments for jute fabric; Armstrong (1) lists copper naphthenate, copper oleate, and copper stearate among the better preservatives for jute sandbags. Copper tallate, derived from tall oil, a by-product of the manufacture of paper from southern pine, seems not to have been mentioned previously in the literature although it is a t present marketed as a preservative in the United States. Three different methods for estimating the mildew-proofness of a treated fabric were in common use a t the time this work was begun. Probably the oldest of these is the so-called soil burial test. While many modifications have been used, the essential feature is that the fabric being tested is buried in soil and examined a t intervals for observation of the amount of rotting. Breaking strengths of the fabric may or may not be determined. Soil burial tests have been used by the Army Engineers Corps, by the Office of the Quartermaster General, by commercial companies, and by workers in England. The Southern Regional Laboratory of the United States Department of Agriculture is currently conducting extensive soil burial tests to determine the rot-proofness of treated fabrics. A culture test method with the fungus Chaetomium globosum, Kunze is now in use in many laboratories. The method was originally developed by Thom, Humfeld, and Holman (26), and slightly modified by Humfeld and co-workers (10, 20). The method has obvious merits in that the fungus employed is a common cellulose decomposer, is easily handled in culture, and produces relatively rapid breakdown of cotton and jute fabric. The utility and limitations of the method are discussed in a later paragraph. Greathouse, Klem+me, and Barker (11) introduced the use of a glass-cloth substratum and a modified nutrient medium for the fungus in place of agar, and the sodium nitrate salt medium as a method for the study of cellulose decomposers. The fungus Metarrhizium sp. was found to be an extraordinarily active cellulose decomposer; although the method was not used in the evaluation of preservative treatments, the possible utility of the technique for this purpose was suggested. MATERIALS AND METHODS
The fabric used was a bleached %ounce duck with an average breaking strength in the warp direction of 123.6 pounds. It had 58 two-ply yarns per inch in the warp and 41 in the filling. Breaking strength determinations were made with a Scott tester by the approved A.S.T.M: strip method. The fabric was di ped into solutions of the copper soaps in a 3 to 1 mixture (by vorume) of Stoddard's solvent and acetone, and run through a household clothes wringer provided with metal rollers. The desired concentration of copper on the fabric waa obtained by adjusting the conkentration of the cop er soap in the solvent and by maintaining a fixed pressure on %e rolls of the
177
wringer; the concentration of copper on the fabric was checked by analysis. Comparative data on inorganic copper treatments were obtained with fabric treated by J. D. Dean, of the Southern Regional Laboratory. This fabric was an Osnaburg with 34 yarns inch in the warp direction; its average breaking strengt in the warp direction was 63 pounds. The cop er naphthenate was a semiviscous green fluid concopper. It was composed of 65% total solids and taining 35% petroleum vehicle. The copper tallate was similar in appearance and contained 7% copper. The copper oleate was a green solid with 10% copper. The copper hydrogenated resinate was a thick viscous li uid, a commercial sample secured through S. Department of Agriculture; it conWiley Smith of the tained 6% of copper. The naphthenic acid was a dark brown liquid with an acid value of 200. The tall oil was a commercial material obtained through Wiley Smith, as was also the hydrogenated resin. The oleic acid was a Droduct of J. T. Baker Chemical Comaanv. Confirmatory experiments with naphthenic acid were carried out on a sample from a second source and also with a second sample of tall oil.
88
8.
TABLE I. CHEMICAL AND MECHANICAL" ANALYSES OF SOILS Soil No.
1
SoilTypeb Composted
-
preenhnnae o_ -- -
Clay,
Silt,
Organic
%
%
15.5
32.7
C, % o 3.16
Moisture Equiva-
.
lent. % d 28.3
~ € 3 6.95
Silt loam 11.1 52.2 0.86 18.4 4.85, Loam 12.6 42.1 2.70 23.2 4.25, Clay loam 21.8 40.3 8.53 50.0 4.18 Carried out by the pipet method described by Olmstead et al. (f8). b Soil 1 had been used for fabric tests for several months before these experiments were started; the other soils had not been used before. c Determined by combustion and moisture equivalent by method of Briggs and McLane (6). d Moisture retained by soil under specified conditions against B force of 1000 times gravity.
2 3 4
The preparation and properties of naphthenic acids have been presented by Gurwitsch and Moore ( l a ) , Ellis (8), Shipp (E?), and Littmann and Klotz (17). Hastings, Pollak, and Wafer (19) describe the production and properties of tall oil, and West (26) gives an extensive annotated bibliography on the material. Copper analyses were made by the usual iodometric method, following the procedure described by Kolthoff and Sandell (16). Analyses of the soils used are given in Table I. Soil burial and culture tests were carried out in a room maintained a t approximatel 85' F. and 90-100% relative humidity. The soil waa placeB in rectangular enameled containers the size of ordinary dish pans. The soil moisture was maintained at a level such as mi h t be used in the growing of plants. The samples were 6 X inches, cut with the long dimension in the warp direction, raveled to exactly one inch in width, dipped into a mineral salt solution, and planted in a vertical direction in the soil with about a/4 inch projecting above the soil line. After 9-day incubation, the samples were removed from the soil, washed, dried, conditioned for 18-24 hours a t 70' F. and 65% relative humidity, and broken. Etcept as otherwise stated, each breaking strength figure represents the average of determinations on five experimental strips. The nutrient salt medium applied to the strips a t the time of planting contained 0.003 M magnesium sulfate, 0.008M potassium monohydrogen phosphate, and 0.0125 M ammonium nitrate. This medium is designated as 3-salt medium A, Untreated control strips of the 8-ounce duck used in this study rotted rapidly when subjected to the soil burial procedure. Soils 1, 2, 3, and 4 required 6, 6, 8, and 8 days, respectively, ta reduce untreated control strips to zero tensile strength. Metarrhizium tests were made according t o the procedure described by Greathouse, Klemme, and Barker (11),employing 3-salt medium A, except as otherwise indicated in the text, This method involves planting a sterilized strip of fabric in a
11j
TABLE11. RESIDUALSTRENQTH OF COPPER-TREATED COTTONDUCKAFTER 9-DAYEXPOSURE TO 9011,s Copper Treatment Naphthenate Oleate Tallate Hyd. resinate 0 Per cent copper.
7 -
0.050 0 0 0
0
Soil 1 0.1 0.2
68 0 0 0
85 0 2 16
0.4 97 0 2 10
0.14
23 2 9 17
Soil 2 0.2 0.4
Soil 4
Soil 3 0.2 0.4
0.8
0.1"
0.2-
0.4
0.8
Breaking afrenglh as % ' of original rtrength 65 84 99 86 98 94 45 80 2 32 46 1 48 73 40 6 84 30 35 45 29 14 21 22
97 47 43 19
95 23 33 32
85 40 53 69
99 57 50 75
100 87 83 86
0.8
0.1"
178
Vol. 36, No. 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
The culture bottles were the same as those used for other test organisms. The incubation period was 3 days. COMPARISON O F COPPER SOAPS
From the standpoint of rotting, one of the most severe conditions to which a fabric may be exposed is contact with moist soil. Armstrong (1) points out that sandbags are often placed in direct contact with the ground and may cont'ain soil as well as other filling materials. Many other mildew-proofed fabrics may be expected to come in contact with soil for longer or short,er periods during storage or use. Cotton duck strips treated with copper naphthenate, copper oleate, copper tallate, and copper hydrogenated resinate were placed in moist soils a t 85' F. according to the procedure described, and the strengths of the fabrics at the end of a 9-day period are recorded in Table 11. Under the conditions of this experiment copper naphthenate provided effective protection a t lower copper concentrations on the fabric than did any of the other three copper soaps, Similar burial tests were made in soil 1 with fabric treated with copper naphthenates made from naphthenic acids from different original sources. Fabric treated with a copper naphthenate made from a naphthenic acid of West Coast origin retained the following percentages of the original strength after the soil burial test on the 0.1, 0.2, 0.4, and 0.8% copper samples, respectively: 38, 76, 83, and 85. Fabric treated with copper naphthenate made from naphthenic acid of Mexican origin retained 19, 76, 85, and 94y0 of the original st,rengths for the same copper concentrations on the fabric; fabric similarly treated with copper naphthenate made from a naphthenic acid of South American origin retained 40, 71, 85, and 86% of the original strength. Since this superiority of copper naphthenate was so clear-cut and could be demonst,rated repeatedly in the soil burial test, experiments were devised to determine its cause. Investigating further into the fungicidal caControl Naphthenic Oleic Tall Hydroggnated acid acid oil resin pacity of copper naphthenate, it was found that Figure 1. Fungicidal Value of Organic -4cid Radicals against the material had good protective power against Penicillium sp. and Aspergillus niger (lye of Each Compound growth of the copper-tolerant fungus, Aspergillus on the Fabric) niger. Fabric strips treated with each of the four copper compounds were placed on glass wicks in culture bottle on a glass wick substratum saturated with a salt culture bottles a i d inoculated with spores of the f&us. Threemedium, inoculating the strip with the spores of Xetarrhizium salt medium supplemented o,25yo glucose and o.25% sp., and incubating a t 85' F. for 7 days. The strain of Metarpeptone was provided for the nourishment of the organism, Tkizium used was designated as 1334.2. which is not a true cellulose decomposer. The fungus grew The Chaetomium test was carried out according to a procedure similar to that described by Rogers, 'VC'heeler, and Humfeld ($01, well on the 0.2, 0.4, and 0.8% copper levels of each of the four and later used by Robinson) Humfeld (I0) and by treatments except the naphthenate; on this treatment it did many commercial laboratories. Fabric strips cut and raveled as not grow a t all. A simple explanation of the observed high prodescribed for the soil burial test were steam-sterilieed in an autotective value of copper naphthenate would be a t hand if we could olave a t 15 pounds for 15 minutes, planted on mineral salts-agar in culture bottles, pipet-inoculated with ascospores of Chaetomium globosum, and incubated at 85" F. The strips were removed from the culture bottles, washed briefly in water, dried, conditioned, and O F ORGANIC ACIDSON DETERIORATION OF COTTON TABLE III. EFFECT broken as previously described. ~h~ c. globosum FABRIC I N SOIL BURI.4L AKD FUNGCS TESTS culture was a subculture from the original isolate Metarrhiziun sp., 7 Days Choetonium, 14 D a y s Soil Burial, 9 Days used by Thom, Humfeld, and Holman (20'). I n culture tests with Aspergillus niger van Tieghem 0.25a 0.50 1 . 0 2 . 0 0.25a 0 . 5 0 1.0 2 . 0 0 . 2 5 a 0 . 5 0 1 . 0 2 . 0 and with Penicillium sp., the test strips were planted Breaking strength as % of original strength on a thin mat of absorbent cotton placed in culture bottles and saturated with a liquid medium. The Naphthenio 21 26 46 67 24 90 92 95 30 32 64 104 acid 10 91: medium contained 3-salt medium A supplemented Oleic acid I 3 o 4 13 3 4 5 4 5 6 5 Tall oil with 0.25% glucose and 0.25% peptone, lvith the exception that the glucose concentration was raised Hyd.resin lo l6 lo 44 a Per cent of organic acid on the fabric. toO.8% in order to increase the severity of the test in t h e case of the samples photographed for Figure 1.
and
2"
*
; ; ;
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1944
TABLE IV. RESIDUAL PRESERVATIVE VALUEIN COPPERTREATED FABRICS AFTER ACIDLEACHING . Copper Treatment Naphthenate Oleate Tallate Hyd. resinate
FfE:
Leaching 0.083 0.043 0.060 0.47
Growth of A. niger None Heavy Heavy Heavy
Breaking Strength after Burial, % of Original Strength Soil 1 Soil 2 Soil 3 Soil 4 70 70 77 105 1 2 8 19 8 6 10 20 8 25 26 24
TABLE v. RESIDUALSTRENGTH O F COPPER-TREATED FABRIC AFTER EXPOSURE TO Chaetomium alobosum AND TO Metarrhizium SP.
Copper Treatment
-Chaetomiuma0.025C 0.05
0.10
-Metarrhiziumb----0.025C 0.05
Breaking strength as % of original strength 66 45 83 80 17 Naphthenate 66 34 68 Oleate 23 91 85 23 64 32 86 Tallate 24 20 73 67 10 Hyd. resinate 5 Method of Rogers, Wheeler, and Humfeld ($0). b Method of Greathouse, Klemme, and Barker (11). 0 Per cent copper.
0.10 84 90 83 80
establish that copper naphthenate contains some additional effective fungicidal constituent besides copper.
179
Although no final conclusion may be drawn from a single experiment, it is interesting to note that in a 9-day soil burial test fabric treated with naphthenic acid retained about the same strength as one treated with zinc naphthenate-i.e., 21, 26, 46, and 67 pounds for the 0.25, 0.50, 1.0, and 2.0y0 applications of the naphthenic acid as compared with 21, 29, 50, and 73 pounds for the same concentrations of zinc naphthenate. In view of the possibility of variation between samples from different sources, it is worthy of mention that a naphthenic acid sample from a second source showed good preservative value in soil burial tests and against A. niger. Tall oil from a second source showed no protective value in soil or against Aspergillus, Chaetomium, or Metarrhizium. When naphthenic acid was subjected to vacuum distillation, he first material to distill over was a relatively nonviscous, traw-colored fluid. F ric treated with 4y0of this material retained 52% of its strength after a 9-day soil burial test (soil 1). Fabric containing 4% of the residue retained 65% of its strength in the same test. A second distillation was discontinued a t a later stage; the heavy residue, accounting for 16% of the original material, was applied to the fabric. Tested in parallel with the two previously mentioned samples, this material was less effective; the fabric retained only 22% of its original strength.
EFFECT OF ORGANIC ACID RADICALS
No quantitative data were a t hand with regard t o any fungicidal properties which might be attributed to naphthenic acid. Therefore the relative merits of the organic acid radicals of the copper soaps were investigated. Figure 1 shows that naphthenic acid is highly effective in preventing the growth of A. niger and Penicill i u m sp. The organic constituents of each of the other copper soaps were ineffective. Our experiments have shown that a s low as 0.5% of naphthenic acid on fabric prevents growth of Aspergillus niger completely, whereas 2% of any of the other organic constituent materials of the copper soaps allows luxuriant growth. The results in Table I11 demonstrate that naphthenic acid is effective in preventing deterioration by cellulose decomposers such as Chaetomium globosum and Metarrhizivm sp., and that it affords distinct protection against rotting in soil. If further evidence were necessary to prove that the fungicidal power of copper naphthenate is due in part to naphthenic acid, one additional experiment seemed to certify this conclusion. Fabric treated with copper naphthenate was leached free of essentially all its copper in a 0.00316 Nnitric acid bath. After a subsequent soil burial test, however, it still showed evidence of decided residual protective power on the fabric and resistance to the mowth of AsDeraillus niaer. As Table IV shows. none of the other " Copper oleate Copper tallate treatments gave this residual protection after similar acid leaching. Figure 2- Copper- Solubilizing Effect of Aspergillus niger If, as has been indicated, the superiority of copper naphthenate on Copper-Treated Fabrics over other soaps in soil contact tests is attributable, a t least in Fabric washed free of growth; n o t e decolorized zones at sites of fungus part, to the fungicidal properties of napthenic acid, other metal colonies. naphthenates might be expected to be similarly superior to the corresponding metal oleates, tallates, and resinates. I n this connection, a soil burial exTABLE VI. LOSS O F COPPER FROM COPPER-TREATED FABRICS UNDER VARIOUS periment has brought out the distinct superiority of CONDITIONS zinc naphthenate over zinc tallate, zinc oleate, and Treatment % pH Time Naphthenate cu Oleate cu Tallate Cu Cu Resinate Hyd. zinc resinate. The fabric breaking strengths in percentages of the original strength for treatments cal-Copper content reduced from 0.8% to:-. culated to deposit 0.1,0.2,0.4, and O.Syoof zinc on the Soil burial .. 6.95 Qdays 0.41 0.22 0.20 0.74 fabrics were, respectively: zinc naphthenate 23, 38, Soil paste .... 66 .. 98 5 24hr. 7days 0.16 0.09 0.15 0.38 Soil extract 0.052 0.039 0.039 0.082 71, and 93%; zinc oleate 14, 12, 16, and 30%; zinc Extd. soil ... 3days 0.69 0.72 0.74 0.81 tallate 3, 7, 12, and 30%; zinc resinate 15,7, 14, and Peat moss 3.2 2days 0.14 0.10 0.10 0.13 3days 0.02 0.01 0.04 0.09 267& These tests were carried out in soil 1 by the 1 5.8 2hr. 0.04 Glycine 0.05 0.12 0.72 1 hr. 0.16 Gallic acid 2 5.1 0.23 0.29 0.16 method used for the copper compounds. When the Aspartic acid 1 6.8 1 hr. 0.14 0.09 0.30 0.70 same four zinc soapswereappliedto fabric a t the O.Syo Glutamic acid 1 6.5 1 hr, 0.33 0.23 0.51 0.72 Gluconic acid 1 6.4 1 hr. 0.62 0.56 0.61 0.76 zinc level and inoculated with Aspergillus niger in 0.09 0.07 0.63 4.0 2 hr. 0.11 Acetate buffer tn i NI culture flasks, all treatments except the naphthenate 2hr. 0.30 0.22 0.27 0.60 allowed abundant growth of the fungus, while the naphthenate allowed no growth.
-
....
..
.. ...
INDUSTRIAL AND ENGINEERING CHEMISTRY
180
Vol. 36, No. 2
TABLE VII. REMOVAL OF COPPERFROM TREATED FABRICSO BY LEACHING AGENTS Copper Compound Naphthenate Oleate Tallate Hyd.resinste
15 30 Citric acid 0.5’%, 0.33 0.24 0.32 0.18 0.42 0.24 0.62 0.49
% Residual Copper after Following No. of Minutes: 90 120 neutraliaed to pH 5.6 0.15 0.09 0.07 0.09 0.05 0.03 0.20 0.09 0.04 0.49 0.49 0.47
15
60
Acetic acid 0.1 N , pH 3.0 Nsphthenate 0.39 . 0.28 0.14 0.08 Oleate 0.55 0.30 0.20 0.18 Tallate 0.60 0.50 0.39 0.31 Hyd.resinste 0.78 0.69 0.58 0.52 4 Original copper content, 0.8% in all cases.
0.11 0.15 0.27 0.46
30
60
90
120
0:&9
30 Lactic 0.36 0.28 0.33 0.61
acid 370, 0.26 0.18 0.40 0.54
0.16 0.09 0.06 0.52
0.41 0.20 0.51 0.65
Ammonia 0.54% 0.31 0.26 0.19 0.15 0.12 0.12 0.58 0.45 0.44 0.58 0.85 0.65
K tartrate 3’%, neutralized to pH 5.8 0.60
0.35
0.45 0.52 0.68
0.53 0.24 0.42 0.66
0.61 0.57 0.60 0.73
Nitric acid 0.41 0.42 0.50 0.70
FACTORS M I N I M I Z I N G P R O T E C T I O N B Y C O P P E R
I n comparative tests with the three other copper soaps investigated, the relative superiority of the copper naphthenate might be expected to be accentuated by factors tending to minimize the protective value of copper. For example, copper might be leached off the fabric, it might be adsorbed by soil particles, or it might be rendered inactive by precipitation in an extremely insoluble form. Comparison of results obtained by the Chaetomium method (Table V) with those from soil burial (Table 11) shows soil burial to be a more severe test than these Chaetomium and Metarrhizium procedures. Copper-treated samples subjected to soil burial may lose major amounts of copper to the soil. Samples buried in soil by the usual procedure were analyzed for copper with the results recorded in Table VI. The amount of copper lost by the sample depends in part upon the continuity of the moisture film between soil and sample. When enough water was added to the soil to bring it to a pasty consistency, the copper losses (Table VI) were even higher. Before copper can be lost from a fabric, it must pass into solution. Since each of the lour copper soaps is highly insoluble in water (ranging from 15 to 50 p.p.m. of copper), it appears that t h e soil must have some capacity for solubilizing copper. When an extract of soil 1 was made with 2’34 sodium hydroxide and the extract neutralized, the solution obtained was highly effective in dissolving copper from treated fabrics (Table VI). The extracted soil was ineffective in solubilizing copper from treated fabrics. Attention was then directed to the question of what type of .material in soils might cause solubilization of copper. It was noted first that acid materials--for example, peat moss-may cause it. Even an acetate buffer of pH 4 caused considerable copper loss from the fabric (Table VI). As previously stated, however, the active soil extracts had been neutralized before use. A t this point it was found that neutralized solutions of a variety .of naturally occurring hydroxy and amino acids are capable of solubilizing copper from copper-treated fabrics; these data are .also shown in Table VI. Table VI1 presents more detailed data on the rate of copper solubilization from treated fabrics. I n these experiments five test strips of treated fabric (6 X 1 1 / 2 inches) w r e shaken in a 1-liter volume of each of the solutions, and single strips were withdrawn after different intervals. I n all cases the fabrics originally contained 0.87, copper. The soil factors which bring about solubilization of copper may well be of microbiological origin. If Aspergillus niger spores are planted in isolated spots on strips of fabric treated with copper tallate or copper oleate, a bleached zone results in which copper has been solubilized. Figure 2 shows the phenomenon. The first strip of each pair was incubated 2 days, and the second strip 3 days. Copper which has passed into solution from the solid protective .film on a fiber is then available for the poisoning of a microorganism. However, certain other factors may intervene to prevent this. The copper may be washed away by rain water, with
0.16
0.37 0.64
0.34 0.12 0.11 0.63
0.32 0.10
0.00316 A’, pH 2.5 0.32 0.22 0.23 0.12 0.34 0.26 0.62 0.58
60
90 120 neutralized to pH 0.20 0.14 0.04 0.07 0.25 0.25 0.48 0.41
180
5.0 0.07 0.03 0.19 0.38
0.11 0.11 0.20 0.74
the eventual result of a major loss of copper from the fabric and then susceptibility to bacterial or fungal attack. The soluble copper may be adsorbed by the soil. Jamison (14.) pointed out the unusual capacity of soils for adsorption of copper. The soluble copper may even be precipitated in a highly insoluble, and therefore fungicidally inactive, chemical combination. An attempt was now made to demonstrate under controlled conditions how these dissipating and deactivating influences might affect the resistance of copper-treated fabrics t o decay by organisms.
TABLE VIII. RESIDUAL STRENGTH OF COPPER-TREATED FABRIC AFTER Chaetomium AND Metarrhizium INCUBATION IN THE PRESENCE OF CYSTIKE Copper Treatment
----Chaetomium0.4%Cu
Naphthenate Oleate Tallate Hyd. resinate Untreated
102 47 30 14 7
0.8%Cu
--Metarrhizium---. 0.4%Cu 0 8%Cu
Breaking strength as
102 91 91 54
7oof
original 103 52 65 21 3
103 91
96 91
Table VI11 presents data on a n attempt to deactivate copper treatment by producing ra highly insoluble precipitate. I n this experiment 0.057, of the sulfur-containing amino acid cystine was added to the 3-salt medium used in the Metarrhizium tests (Table V); in other respects the tests were identical, Considerable deactivation occurred, and in the presence of cystine, as in soil burial, copper naphthenate was distinctly superior to the other copper compounds. When Chaetomium spores were used instead of Metarrhizium spores in the same cystine-glass wick procedure, the fabric breakdown was not so striking, but was sufficient to enable differentiation between the copper naphthenate and the other three copper soaps. Data from comparative tests of a copper soap treatment along with two inorganic copper treatments are reported in (Table IX).
TABLEIX. COMPARATIVE TESTSOF COPPER NAPHTHENATE WITH INORGANIC COPPERTREATMENTS Copper Treatment Copper naphthenate
Cuprammonium carbonate
Cuprammonium fluoride
Breakinz as 3 ’ % of Orizinal Break - Strennth - afteii Cu Content of Fabric, soil burial Metarrhizium- Ch. globosum (T-1452) 6days 9 d a y s cystine % 16 0 4 57 0.00 28 9 7 67 0.125 0.26
0.50 1.0 0.06 0.125 0.25 0.50 1.0 1.5 0.06
0.126 0.25 0.50 1.0
74 77
46 101 104
0 0 26 39
0 0
..
.. ..
0 0 17 47
..
0 9 58 100 0 0 0 25 78
13 88 94 7 9
9 11 21 83 0
9 11 22 77
80 81 79 3 74 76 80 82 86 18 55 83 81 86
February, 1944
INDUSTRIAL AND ENGINEERING CHEMISTRY
Data from the Metarrhizium-cystine test run more closely in accord with soil burial results than do the results obtained by the T-1452 test with Chaetomium globosum. I n both series of culture tests the fabric was washed for 24 hours in cold running water before incubation; 0.1% of cystine was used in the Metarrhizium culture medium. PRESERVATIVE VALUE OF COPPER SOAPS
The relative protective values of different copper soaps may be expected to vary with the conditions of exposure of the treated fabrics. I n view of the adsorptive and insolubilizing capacities of soils, i t is not difficult to understand why a compound such as copper hydrogenated resinate which is highly insoluble in water and in various solutions (Tables VI and VII) is unsuited to protection of a fabric in contact with soils. The relatively small amount of fungicidally active copper released into solution is, presumably, readily deactivated by adsorption or chemical insolubilization. Fabric may contain high amounts of total copper as copper hydrogenated resinate and still be disintegrating in soil (Tables I1 and VI); this is likewise true in the cystine culture method. Copper oleate, copper tallate, or copper naphthenate, on the other hand, releases fungicidally active ionic copper into solution more readily than does copper hydrogenated resinate. Of the three more readily soluble compounds, copper naphthenate possesses the additional advantage of fungicidal capacity of the anion as well as in the cation of the compound. It seems possible that for above-ground exposures (in which adsorption and chemical insolubilization might be expected to be a t a minimum) copper hydrogenated resinate might release sufficient soluble copper to provide good protection. As Table V shows, the initial germicidal value of the compound is rather good. I n t h e case of above-ground exposures with conditions of heavy rainfall, the relatively low solubility and consequent slow rate of loss of total copper from the fabric might be a distinct advantage. The length of the service life of a treated fabric exposed to attack by microorganisms may also be influenced by mechanical stresses, by photochemical deterioration, by direct chemical reactions between the preservative and the fabric or between the preservative and other finishing agents, and by other factors. I n warm humid climates or in such cases as fabric tests in contact with soil, dway by microorganisms may often be the most important deteriorative influence. I n consideration of the experimental results described here, certain suggestions will indicate those factors which are important in determining the length of the service life of a copper-treated fabric exposed to severe attack by microorganisms in soils: 1. The initial copper content of the fabric. 2 . The rate of loss of copper from the fabric. 3. The presence or absence of residual fungicidal capacity in t h e treatment after loss of all or most of the copper. 4. Deactivation of soluble copper by formation of fungicidally ineffective insoluble compounds. SUMMARY AND CONCLUSIONS
Copper naphthenate prevents rotting of cotton fabric at lower concentrations than do copper oleate, copper tallate, or copper hydrogenated resinate. The high preservative value of copper naphthenate is related t o the fact that naphthenic acid itself is a potent fungicide; this conclusion is based on the following experimental observations: 1. Of the four soaps, copper naphthenate alone is able to prevent the growth of the copper-tolerant fungus Aspergillus niger. 2. Naphthenic acid is effective in preventing the growth of Aspergillus niger, Penicillium sp., Chaelomium globosum, and Metarrhizium sp., and in preventing fabric deterioration in soil. Tall oil, oleic acid, and hydrogenated resin show no protective value in any of these cases. 3. Fabric treated with copper naphthenate, which has been *drasticallyleached with dilute nitric acid until essentially free of
181
all copper, still has enough residual protection to prevent growth of A! ergillus niger; i t is likewise protected against deterioration in soif Fabrics treated with copper oleate, copper naphthenate, and copper tallate lose copper readily at the points where the fabric is in contact with soil. Each of these compounds is highly insoluble in water but may be solubilized by acid hydrolysis or by reaction with materials which form soluble copper complexes. A neutralized sodium hydroxide extract of soils will bring copper soaps into solution. Neutralized solutions of a variety of naturally occurring hydroxy and amino acids are also effective in this regard. Copper hydrogenated resinate is highly resistant t o leaching under the conditions listed above. I t s relatively poor protective power in contact with soils may be in part due t o the low availability of ionic copper, The relative superiority of copper naphthenate in comparative tests with the other three copper soaps here studied is accentuated by soil factors tending to minimize the preservative value of copper-via., leaching, adsorption, and chemical deactivation. ACKNOWLEDGMENT
The authors wish to express their thanks to H. D. Barker, U. S. Department of Agriculture, for helpful comments during the course of the investigation and to Marcus Jaeger for the preparation of the photographs. Thanks are due also to the following companies for supplying experimental materials: Socony-Vacuum Oil Company, Inc., The Shepherd Chemical Company, Nuodex Products Company, Inc., Union Oil Company of California, and West Virginia Pulp and Paper Company. BIBLIOGRAPHY
Armstrong, E. F., Chemistry &Industry, 60, 668-74 (1941). Atkins, W. R. G., J . Marine Biol. Assoc. United Kingdom, 15, 219 (1928). Ibid., 16, 583-8 (1930). Bertolet, E. C., Am. Dyestuff Reptr., 33, 214 (1943). Briggs, J. L., and McLane, J. W., U. S. Dept. Agr., Bur. Soils, Bull. 45, 1-23 (1907). Conn, W. T., U. 9. Bur. Fisheries, Document 1075 (1930). Elkin, H. A., and White, W. A. S., J . Tertile Inst., 30, 340-6 (1939). Ellis, Carleton, ”Chemistry of Petroleum Derivatives”, New York, Chemical Catalog Co., 1934. Furry, M. S., and Robinson, H. M., Am. Dyestuff Reptr., 30, 504 (1941). Furry, M. S., Robinson, H. M., and Humfeld, H.. IND.ENG. CEEM.,33, 538-45 (1941). Greathouse, G. A., Klemme, D. M., and Barker, H. D., IND. ENQ.CHEM.,AN.4L. ED.,14, 614-20 (1942). Gurwitsch, L., and Moore, H., “Scientific Principles of Petroleum Technology”, London, Chapman and Hall, 1932. Hastings, R., Pollak, ‘A., and Wafer, J. M., Soap Sanit. Chemic a l ~6, , 24-7, 70 (1943). Jamison, V. C., Soil Sci., 53, 287-97 (1942). Jarrell, T. D., Stuart, L. S., and Holman, H. P., Am. Dyestuf Reptr., 26, 495-505 (1937). Kolthoff, I. M., and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis”, p. 604, MacMillan Co., New York, 1936. Littmann, E. R., and Klotz, J. R. M., Chem. Rev., 30, 97-111 (1942). Olmstead, L. B., Alexander, L. T., and Middleton, H. E., U. S. Dept. Agr., Tech. Bull. 170, 1-22 (1930). Robertson, A. C., and Wright, W. H., U. S. Bur. Fisheries, Document 1083 (1930). Rogers, R. E., Wheeler, H. G., and Humfeld, H., U. S. Dept. Agr., Tech. Bull. 726, 1-35 (1940). Roszkowski, Jan, 2.anorg. Chent., 14, 1-20 (1897). Shipp, V. L., Oil Gas J., March 19, 1936, pp. 56-8. Taylor, H. F., and Wells, A. W., U. S. Bur. Fisheries, Document 947, 1-73 (1923). Ibid.,998, 409-37 (1925). Thom, C., Humfeld, H., and Holman, H. P., Am. Dye Reptr., 23, 581-6 (1934). West, C. J., Inst. Paper Chem., Bibliographic Series 133-5, 1-84 (1942).
