RICHARD T. ROSS and STANLEY J. BUCKMAN Buckrnan Laboratories, Inc., Memphis, Tenn.
Microbiological Deterioration of Water-Thinnable Coatings
. Uninoculated
750 325 310 355
and cellobiose. The third had a high RF value, not yet identified. I t has been assumed that resins are not subject to microbial attack. Attempts have been made to synthesize resins which would not require stabilizers, thus making paints containing such resins immune to microbiological spoilage. Although elimination of proteinaceous and carbohydrate materials would significantly reduce the nutritional value of emulsion paints, the experiments indicate that poly(viny1 acetate), styrenebutadiene, and acrylic resins are themselves subject to microbial deterioration. A basal medium was prepared containing 1.O% of ammonium nitrate, 1.O% of potassium monohydrogen phosphate, and one of four synthetic resins as supplied by the manufacturers as a carbon source : one styrene-butadiene, one acrylic, and two poly(viny1 acetate) resins. One milliliter of an aqueous suspension of washed cells of each of three bacteria most frequently isolated from spoiled emulsion paints was used as an inoculum: Aerobacter sp., Proteus sp., and Flavobacterium sp. After 48 hours' incubation at room temperature, aliquots of each culture were streaked on nutrient agar plates. These were incubated a t 28' C. Each microorganism grew in media containing any one of the four synthetic resins as a sole source of carbon. Such growth was confirmed using the resin alone as the growth medium, without added ammonium nitrate and potassium phosphate. Viscosity measurements before inoculation and after inoculation and incubation for 30 days at 28' C. show that viscosity was reduced as the result of growth of bacteria. T o determine the initial mechanism in degradation of vinyl resins by bacteria, each resin, uninoculated and inoculated, was added until the saturated bromine water was decolorized. The fact that approximately one half as much inoculated resin was required to decolorize the bromine water indicates that microbial activity is in part associated with the unsaturated ethylene linkage of vinyl resins. This is in keeping with similar activity in certain unsaturated triglycerides, and indicative of enzymatic-catalyzed oxidations (5). Further investigation is needed to establish mechanisms and pathways of utilization.
Uninoculated
9.5 4.6 5.4 6.0
Disfigurement of Emulsion Paint Films
M I c R o B I o m C I c A L deterioration ofwater-thinnable coatings falls into two general categories, spoilage of emulsion paints in the container and disfigurement of paint films. The former is the result of metabolic degradation of resins and emulsion stabilizers, usually by bacterial rather than fungal activity. Disfigurement is the result of mold growth, alone or with soil particles trapped and entrained by vegetative structures. The form of microbial attack in the container is dependent on the nature of the paint itself. Paper partition chromatographic analyses of spoiled paints containing stabilizers have been used to determine the mechanism of attack. Paints containing casein or alpha-protein were analyzed, employing phenol and butanol-acetic acid-water as solvents and ninhydrin as an indicator. Chromatographic paper treated with either material revealed the presence of various amino acids, including tryptophan, indicative of active proteolysis. The microflora was identified as predominantly Proteus sp. It is logical to assume that the putrid odors emitted by these paints were the result of further metabolism of the amino acids, specifically tryptophan, which may be ultimately degraded to skatol and indole. I n chromatographic analyses of spoiled paints known to contain methylcellulose and carboxymethylcellulose as protective colloids, butanol-acetic acid-water was used as a solvent and ammoniacal silver nitrate as an indicator. Sugar and sugar derivatives appear as black spots on the chromatographic paper strips. Two spots were identified as glucose
Alterations in Viscosity of Synthetic Resins as a Result of Bacterial Activity" Visc., Resin Microorganism Cp. Poly(viny1 acetate) 1
Poly(viny1 acetate) 2
Styrenebutadiene
Acrylic
Uninoculated
Proteus sp. Aerobacter SP. Flavobacterium sp. Uninoculated
Proteus sp. Aerobacter sp. Flavobacterium sp. Proteus sp. Aerobacter SP. Flaeobacterium sp. Proteus sp. Aerobacter SP. Flusobacterium sp.
0
800 250 220 255
620 120 145 150
Measured with Ostwald viscometer.
1 16
Disfigurement of emulsion paint films by growth of mold is essentially the same
INDUSTRIAL AND ENGINEERING CHEMISTRY
as that of any paint film (7-4, 6). The microflora varies with the environment ; a much greater variety ofmold is involved in the disfigurement of interior paint films than exterior surfaces. Considerable differences in the kind and quantity of mold are observed on the interior of food plants, breweries, homes, and offices. To ensure adequate sampling, isolations were made from paint test fences in Memphis, Tenn., Chicago, Ill., San Francisco, Calif., Miami, Fla., Wilmington, Del,, and Sayville (L.I.), K. Y . Eleven known genera of fungi and three bacteria were isolated from emulsion paints. Many of these were isolated infrequently and may have been chance inhabitants. At least four molds and two bacteria were isolated in sufficient numbers to be considered the normal microflora of paint films: Pullularia pullulans, Phoma glomerata, Cladosporium sp., Alternaria sp.. Flavobacterium sp., and Bacillus subtilis. r o t all the molds were
encountered in each geographical area, and definite differences in the proportion of their occurrence were observed. Pullularia pullulans was observed more frequently in all areas but Delaware and New York, where another black mold later identified as a species of Cladosporium was observed as frequently. Approximately one third of the observable disfigurement of panels examined in California was the result of growth of Phoma glomerata. The greatest variety of microorganisms was isolated in Miami. Microorganisms may also play a significant role in the degradation of emulsion paint films, as Ross ( 5 ) has reported for oil paint films. Indications of similar deterioration of emulsion paint films remain empirical, despite demonstration of the ability of bacteria to use emulsion resins as a partial or complete source of nutrition. Test fence exposures suggest that microorganisms are significant in emulsion paint film degradation. Literature Cited (1) Buckman, S. J., Stitt, W. D., A m . Paint J. 49 (39), 80-116 (1957).
(2) Drescher, R. F., Zbid., 42 (27), 80-102 (1958). (3) Goll, M., Coffey, G., Paint, Oil Chem. Rea. 111,14,16, 17, 30 (1948). (4) Klens, P., Lang, J. F., J. Oil Colour Chemists' Assor. 39 (12), 887-99 (1956). (5) Ross, R. T., 0 8 6 . Diq. Federation Paint @ Varnish Production Clubs 30 (399), 377-91 (1958). (6) Rothwell, F. M., Zbid., 30 (399), 368-76 (1958).
RECEIVED for review May 20, 1958 ACCEPTED November 12, 1958
