Document ZBGErVa7wxZ21a3odpoQk1B78

f: Biocides in Adhesives and Sealants BY M. C. HUANG CHEMICAL DIVISION ABBOTT LABORATORIES NORTH CHICAGO, ILLINOIS Since the term "biocide" has not been The two most important questions Usually, the only microbes which used widely in the adhesive and seal concerning the spoilage problem are: thrive in an air-tight container are bac ants industry, its meaning may not be clearly understood. In its literal defini tion, biocide means a substance which kills life, both plant and animal! Ob viously, this is not a good working def Has the microbial attack occurred before the user opens a fresh container of your product, or does it occur after he has applied it? teria; the so-called anaerobic bacteria do not require air for their source of oxygen. (Most fungi'--- the mold or mildew types of organisms -- need air as their oxygen source.) In-can spoil inition because of its connotations What is the nature of the offending age can usually be attributed either to concerning your life and mine. It is microbe -- is it bacterial or fungal, or bacteria or to the enzymes that certain preferable to define biocide as a both? Or is it an enzyme synthesized bacteria secrete. These enzymes can "chemical or system of chemicals by the microbes, which may now be hydrolyze organic materials, thereby which either kills microorganisms either living or dead? rendering the adhesive ineffective. (microbes) or inhibits their normal Separation of an animal glue or a growth." "In-Can" Preservation starch paste into distinct water and sol For the adhesives and sealants in If the attack has occurred by the id phases is a familiar example of en dustry. this means that a biocide time the user opens his container, the zyme attack against emulsifiers. should prevent the growth of microbes organism was already in the adhesive Enzymes, once formed, are not which might 1) hurt the adhesive prop or sealant when the container was inhibited by many biocides. The mod erties of an adhesive or sealant prod filled. There are two possible sources ern approach to the enzyme problem is uct. 2) spoil its appearance, or 3) im of microbes leading to this condition. to prevent microbial growth by proper part an offensive odor to it. One is your manufacturing plant; a biocide selection to preclude the syn In an Adhesives Age editorial ("On warm, humid environment creates thesis of enzymes. the Positive Side." February, 1973, ideal conditions for microbial growth page 6) B. J. Kotsher defined biocides, and sporulation. The other possible "Post-Application" Preservation gave examples of types used, discussed source is the numerous raw materials In many cases, microbial attack Federal regulatory developments, and which go into your formulations. Cer occurs after application of the adhe encouraged the adhesives and sealants tain raw materials are particularly sus sive or sealant. Unlike in-can spoilage, industry "to become more familiar ceptible to microbial contamination. the culprit in these cases is usually a with all the facets of the (biocide selec As with larger organisms, microbes fungus (mold), whose spores either are tion) problem and with all the oppor which present problems to the adhe in the air or are dormant in the can tunities presented in finding solu sives and sealants industry usually feed until the presence of air and moisture tions." on organic matter -- proteinaceous enables their rapid growth. Examples The purpose of this article is to ex materials such as gelatin, casein, or of this include: pand on the editorial by providing zein -- or cellulosic materials such as The familiar blackening of bathtub more detail -- hopefully by 1) giving thickeners, starch, or dextrin. Beyond chalk results from Aspergillus niger the -adhesives and sealants technical these obvious "foods," numerous other (a black mold), which feeds on the director a broader perspective on the organic chemicals or binders can be caulk or on the adhesive behind the problem and some guidelines for its metabolized T>y microbes. These in tiles. -- solution, -and 2) discussing related environmental issues. clude plasticizers, surfactants, certain synthetic latex systems, and so forth. Splotches of Aspergillus niger or Aspergillus oryzae.(green mold) xome- feT THWESIVES AGE, ytJLV 1975 -T - -- DSW 586874 STLCOPCB4092208 w protection/100 gallons, 14 oz. protection/100 gallons, 12 oz. protection/100 gallons, 16 oz. times show through wallcoverings (especially nonporous types like vinyls, which cause the paste to remain moist for extended periods, thus promoting mold growth). Black mold or red slime (another mold) are sometimes problems in ready-mixed gypsum wallboard joint compounds. Here, because the "glue line" is pretty thick, drying can be slow. Spores of these vigorous molds will grow rapidly into unsightly colo nies which can show through-a coat of paint. Corrugated boxboard has been known to show mold growth in humid, tropical climates; this results from mold feeding on the corrugating adhesive, or possibly on the board it self. Figure 1 -- Microbiological evaluations run with Amical mildewcides in adhesive and sealant formulations to determine optimum concentrations to use on a cost/use basis. Abbott-modified ANSI test; test organism, A. niger; 14 days. Figure 2 -- Another series of microbiological evaluations, ANSI test, 6/74. unprotected sample -- substantial over growth 0.10% A-48 dispersion -- clear zone of inhibition 0.05% A-48 dispersion -- clear zone of inhibition 0.15% A-48 dispersion -- clear zone of inhibition. The Market for Biocides There are no published statistics on the use of biocides in adhesives and sealants. Based on field interviews with technical and purchasing managers at numerous large, medium, and small adhesives and sealants companies, we estimated the 1972 biocide consump tion at $1.4 million, broken down as follows: : End use $ Millions Construction, including joint compound Packaging Sealants All other Total $0.6 0.3 0.2 0.3 $1.4 Source: Abbott Laboratories field market analysis At the time the analysis was done (late 1972). the leading type of biocide was the mercurial. Other types range from inexpensive chemicals like for maldehyde and phenol, to the parabens and chlorinated phenols, to the higher priced nonmercurial specialty bio cides. Mercurials may no longer be the leading type of biocide, since we know of several companies which have since replaced mercurials with nonmer curials. including Abbott's Amical 48 and Amical 48 Dispersion. DSW 586875 Biocide Cost/Use Economics . Accustomed to using biocides which range in price from $0.10 to $2.50 per pound, both technical and purchasing people in the adhesives and sealants in dustry tend to react negatively to pecialty biocides which may cost $6 o $17 per pound or more. 24 ADHESIVES AGE, JULY 1975 STLCOPCB4092209 The real key to biocide economics is cost per unit protection -- not cost per pound of biocide. We refer to this con cept as "cost/use economics." The same concept has elsewhere been dubbed "cost/benefit ratio." "efficacy per unit cost" (which is the inverse), and so forth. Here is a simple example of the application of the cost/use factor A starch packaging adhesive is well protected by a SO.50/lb biocide, used at the 0.3 percent weight level. The cost/use factor in this case is 0.5 x 0.3 = 0.15. Suppose that a S6.00/lb biocide will provide equivalent protec tion when used at the 0.01 percent level. In this case, the cost/use factor would be only 6 x 0.01 = 0.06. The adhesive maker would actually save 60 percent by using the apparently more "expensive" biocide. To keep the concept simple, we as sign no units to the cost/use factor. As long as two biocides are compared in identical units -- dollars/batch, cents/can. etc. -- it makes no dif ference what units are used. The Environmental Issuei MIC vs. LD,,, ' Early industrial biocides were heavy metal compounds which were well- known poisons. We can point to the mercurials, arsenicals. and lead com- ... pounds as examples. The objective was to applv them in such a way that man suffered the least and the pests suffered the most. As the chemical, pharmaceutical, medical, and environmental communi ties became more knowledgeable and more concerned, there evolved bio cides which were selectively more poisonous to microbes while being less poisonous to mammals, birds, and fish. Classical examples were phenol and its derivatives in the industrial field and quinine and its derivatives in the human and animal health field. Notice now the trend away from compounds based on heavy-metal elements. Indeed, the commercial antibiotic today (penicillin, tetracycline, erythro mycin. streptomycin, etc.) is a biocide with a specifically high toxicity to disease-causing microbes and a low toxicitv to the host organism (the pa tient). In other words, they are biocides with a low MIC value and a high LD50 value. The terms MIC and LD50 are worth discussing. MIC stands for minimum inhibitory concentration, and it refers to the con centration of biocide (usually ex pressed as parts per million) in a con trolled medium (such as nutrient agar) which will inhibit growth of a specific microbe. The lower the MIC, the better the biocide. For example, a compound showing an MIC of 1 ppm against Aspergillus niger is likely to be a better bathtub-caulk biocide than a compound showing an MIC of 20 ppm against that same organism. The word "likely" is emphasized because the MIC values of the two compounds were determined in a controlled medi um in the laboratory. In an actual caulk formulation, their effective usage levels may or may not be in a ratio of 1 to 20. LD5n stands for lethal dosage, and it refers to the quantity of a biocide which a group of mammals can with stand ithrough skin absorption or. more commonly, when administered orally l and statistically have a 50-50 chance of surviving. This test, also carried out in the laboratory, is ad ministered to a variety of test animals, particularly to rats (in which LD50 val ues correlate closely with human LD5n values). LD50 is usually expressed in milligrams of compound per kilogram of body weight. The higher the LD50. the safer the biocide. Thus, a biocide with an LD50 of 10.000 mg/kg will be substantially safer to workers in the plant than a biocide with an LD50 of 200 mg/kg. Finally. TL50 data are now required by the Environmental Protection Agency for biocides used in a number of industries where the plant effluent may be deleterious to fish life. TL50 stands for median toxic limit, and it refers to the biocide concentration, in parts per million in water, at which a certain species of fish (usually fresh water fish) will statistically stand a 50 50 chance of surviving. The higher the TL50. the safer the biocide. Working With Your Biocide Supplier In our experience, most adhesives and sealants firms do not have microbiologists on their technical staffs. This is understandable, because microbial spoilage problems are I) minor in relation to the problems of adhesion or sealing, and 2) generallv more effectively solved by companies with microbiological facilities and per sonnel. M icrobiological testing can be costly, and it is not usually precise to the "nth" degree. You may derive some benefit from asking one or two competitive biocide suppliers to evalu ate the efficacy of biocides in your formulations. Doing this excessively. ADHESIVES AGE. JULY 1975 however, can only lead to unnecessary overhead expenses for the biocide sup pliers. resulting inevitably in higher prices for the biocides. You and your supplier will get the maximum mutual benefit if vou will first discuss your microbiological problem with a representative of vour biocide supplier. He may want to com municate with his home office before he commits them to perform tests. As suming mutual prior agreement, you should then submit a reasonable number, of samples always including both a blank control (containing no biocide) and a standard production control. Whenever possible.-stick with standard ASC. ASTM. MIL tests, etc. If not. arrive at a mutual under standing of the test parameters before tests are initiated. Code the samples, and request a written and pictorial report of the results. After the tests are complete and you have reviewed the report, discuss the results openly and frankly- with the biocide supplier's sales or technical representative. Summary Biocides are chemicals or systems of chemicals which either kill or inhibit microorganisms. These microbes, if not inhibited, frequently damage the esthetic or engineering properties of adhesives and sealants. An adhesive or sealant manufacturer having microbial problems should pinpoint whether they are "in-can" problems, "post application" problems -- or both. In 1972. the adhesive and sealant in- dustrv consumed approximatelv 51.4 million of biocides, mainly in con struction and packaging adhesives and in sealants. Biocide economics should be based not on the price of the biocide alone, but on its cost/use factor. Sometimes a high priced biocide will prove less expensive to use. Environmental issues are becoming important in the choice of biocides for adhesives and sealants. The ideal biocide has 1) a numerically low MIC value against your problem organism. 2) a high oral ED.-,,, value in mammals, and 3) a high TLS,, value in fresh-water fish. When vou ask your biocide supplier to help you evaluate the etticacy ot a biocide, you wall get the best results if vou are 1 I specific in stating the problem and possible test methods. 2i reasonable in your expectations, and 3) candid in discussing the test results with the biocide supplier who did the evaluation . DSW 586876 STLCOPCB4092210 Switching to water-based systems? We have the thickener. Emulsifier and suspending agent, too. All from Carbopol resins. In a vast number of water-based, industrial formulations Carbopol resins offer excellent suspension, viscosity stability, and a broad range of flow properties. STLCOPCB4092211