Selection and evaluation of biocides for aqueous metal-working fluids

Selection and evaluation of biocides for aqueous metal-working fluids J.L. Shennan*

Uncontrolled microbial contamination of cutting fluids can cause a dramatic reduction in effective life and lead to production problems such as corrosion and blocked filters. One method of controlling such contamination is the use of biocides. This paper reviews types of biocide, primarily for use in soluble oil emulsions, and discusses factors affecting their selection and use; laboratory test methods are discussed. Keywords: microbiological resistance tests, preservatives, cutting fluids Aqueous metalworking fluids are used on machine tools to cool and lubricate the cutting edge and to remove swarf from the interface. These cutting fluids are commonly 'soluble oil emulsions', milky dispersions of mineral oil in water. In addition to the lubricant base oil, soluble oil formulations contain emulsifiers, corrosion inhibitors and various other ingredients which may include emulsion co-solvents, emulsion stabilizers, antifoams, buffers and extreme pressure additives t . The products are sold as concentrates to be diluted, by 1 : 10 to 1 : 100 depending on the fluid and the application, with water at the factory site to form the cutting oil emulsion. During the working day the fluid is continually circulated over the workpiece, typically at 15-25 litres/min, and returned to a sump, containing say 2 5 - 2 5 0 litres, at the base of the machine. Large machine shops have centralized cutting fluid systems circulating from a common sump of typically 2 5 - 3 0 m 3 capacity. All these systems are open to microbial contamination and the working life of a soluble oil emulsion depends on the intrinsic resistance of the product to spoilage and the microbial challenge it receives in use. A soluble oil emulsion undergoing biodeterioration is a complex dynamic system. The microbial population changes quantitatively and qualitatively during the lifetime of a fluid and may differ in both aspects in different fluid types used under different in-service conditions. The nutrient status of the fluid changes as contaminants deplete c~rbon sources or degrade formulation ingredients to provide growth substrates for other organisms. New sources of nutrient, both mineral and carbonaceous, may be added from detritus of all types and from the lysed cells of dead microorganisms as contamination levels build up. As buffer chemicals are depleted through demand from acidic microbial metabolites, the pH of the fluid falls. The aerobic status of the fluid fluctuates with the circulation regime used. Depending on the design of the machine system and the degree of metal swarf accumulation, microaerophilic or anaerobic conditions will occur in stagnant areas. The principal spoilage agents of soluble oil emulsions are Gram-negative bacteria. Pseudomonads are usually present in emulsions with low to moderate levels of contamination (up to 10 s/ml). Once spoilage is actively under way, with counts rising to 108/ml or above, the facultatively anaerobic fermentative enterobacteria may dominate the population with sulphide producing bacteria present at lower levels 103 - 10 s/ml). During the final stages of biodeterioration, *British Petroleum Company plc, BP Research Centre, Sunbury on Thames, Middlesex TW16 7LN, UK

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characterized by fall in pH and incipient splitting of the emulsion, many different Gram-negative bacteria can be isolated, including species ofAcinetobacter, Achromobacter and Alcaligenes. Yeasts and filamentous fungi are often present in spoiling soluble oil emulsions at low counts (10 2 - 1 0 3/ml) and can develop to dominate the population if the competing bacteria are brought under control by use of a bactericide. If uncontrolled, microbial contamination in the circulating fluid will lead to the formation of surface slimes, sludges associated with accumulated swarf, or floating mats of fungal hyphae. Although such aggregations of biomass may be partly removed by swarf separators or filters, heavy contamination usually leads quickly to emulsion breakdown, especially if the emulsifier has been used as a growth substrate. Chronic contamination of a machine system using unprotected cutting fluids can shorten the effective life of a given product charge from several months to a matter of days. Some soluble oil emulsions, however, can sustain a high bacterial count without loss of performance. In these cases, the 'Monday morning smell' of hydrogen sulphide, disengaged from anaerobic swarf-laden sumps when the circulation system is switched on after the weekend shutdown, will call for action if no other indication of spoilage has appeared Metal working fluid biodeterioration was first described over 40 years ago by Lee and Chandler 2 who recommended control through 'good housekeeping' and the use of phenolic biocides. The main groups of contaminating organisms were later identified and the various and changing parameters of the microbial ecosystem involved described 3-s . Detailed case histories were published, by Lindert 9 and Sonntag 1° , dealing with control methods in the workshop, combining the use of antimicrobial chemicals, good quality make-up water and improvements in workshop practice. Of the biocides available in the late 1950's, Bennett et al x1-13 found phenolic derivatives and nitroparaffins to be most effective in cutting fluids. Recently the control of cutting fluid spoilage has again become a problem, commanding the attention of the applied microbiologist and fluid formulator alike. Increased awareness of the potential effects of certain chemicals on occupational health and on the environment has led, in the lubricant industry, to major changes in soluble oil formulations, in both the base oils and the additives used. For example, comparatively bioresistant naphthenic base oils have been replaced by paraffinic types and the common inclusion of inhibitory phenolic components has been

0301-679X/83/060317-14 $03.00 © 1983 Butterworth & Co (Publishers) Ltd

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Shennan- Biocides for aqueous metalworking fluids discouraged. As a consequence the new, acceptable products are often more susceptible to microbial spoilage. While every effort to improve safety in the use of industrial products must be made, many manufacturers are faced with the conundrum of controlling biodegradation in a product which has been designed to be safe to handle (non-toxic) and readily disposable in the environment (biodegradable). While the introduction of new antimicrobial chemicals has helped to resolve this problem, a number of factors have to be taken into account in the choice of a suitable biocide for soluble oil emulsions. Many different products have been recommended for use and methods for evaluating their effectiveness in the laboratory have been developed. These topics are reviewed below. Although soluble oil emulsions comprise the bulk of the cutting fluid market today and are the products most prone to biodeterioration, contamination can also occur in 'synthetic' fluids, based on petroleum derived organic chemicals, or 'semi-synthetics' containing 10-15% by volume mineral oil. The choice of appropriate biocides for all coolant products follows the same general principles to be described for soluble oil emulsions.

Biocide selection for metalworking fluids While the purpose of chemical control of cutting fluid contaminatian is the protection of the fluid, great care is required in the selection and use of biocides to maximize their antimicrobial effect without presenting a health hazard to workers operating the machines and without contaminating the environment with a toxic chemical. The initial choice of a biocide is, therefore, determined by the following factors: • toxicological profile • environmental impact • efficacy in use A battery of submissions under these headings and registration for a specific application is necessary for legal use in the USA of a biocide under the Federal Pesticide Act of the Environmental Protection Agency (EPA) 14. In the United Kingdom and the European Economic Community registration is not required. Instead, it is the responsibility of the manufacturer to ensure that his product 'shall not be harmful under intended conditions of use'. If that product is a cutting fluid formulated from several ingredients, the manufacturer of each component provides data on toxic properties and the conditions under which it may be harmful. This information is required for all components, including biocides, whether added to the concentrate at source or incorporated in the fluid following dilution. With ttte information now available on biocides it is possible to make a reasoned selection prior to testing; attention given to toxicological data early in the process of biocide selection will prevent waste of effort in evaluating the efficacy of products that might eventually prove to be too dangerous to use. Once an apparently acceptable biocide is found to be effective in a given formulation, the potential health hazards of the total composite product, both as a concentrate and at the in-use dilution, should then be assessed. Health criteria include acute and chronic toxicity, skin and eye irritancy, inhalation reaction and potential allergic effects. Account is also taken of possible synergism and offter interactions between formulation components. For instance, a surfactant may enhance skin penetration of an oily material.

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Information on the long-term effects of the use of biocides is available for the older classes of product. The phenoi derivatives have been in use for many applications for over a century and their toxicity is well understood. Safetyinformation on more modern biocides is now being Compiled. Industry, health authorities and environmental agencies are now alert to potential mutagenic and carcinogenic consequences of using relatively unknown chemicals and methods of assessing such effects are being developed and refined. Contact dermatitis due to the detergent and defatting action of water soluble coolants is the most common health hazard in individuals exposed to cutting fluids!~171 Skin irritation can also be caused, however~ by other ingredients , such as emulsifiers and corrosion inhibitors or heavy metal salts, particularly of nickel or chromium, originating from the machined material. Several biocides, known to be skin and eye irritants in the concentrated form, are safe to use when diluted and handled as recommended by tl-/e manufacturers. Instances of sensitization to biocides ate usuatiy traced to some departure from norton1 practicelS-!9 o

En vironmen tal considerations Industrial codes of good practice, for example that published by the Institute of Petroleum 2° , indicate that the manufacturer of a cutting fluid formulation should provide adequate information to allow for safe disposal of the used product. This is usually based on biodegradability data from the .... suppliers of biologically active ingredients. Many chemicals can be safety disposed of by dilution and local water authorities often impose strict limits on phenol levels discharged in aqueous effluents. An advantage of some modern biocides is that the active molecule is released from an unstable condensate and is not persistent:

Effectiveness Once safety and environmental factors have been satisfied in the choice of a biocide, its effectiveness in the intended product and its cost have to be assessed. (Table 1)i Theterm 'biocide' is ofte n applied to all chemicals which inN.bit microbial activity. In practice the distinction between biocidal and biostatic action is often merely a function of concentration, the same compound being biocidal at high concentrations and biostatic at low levels. In addition, biocides may support or even stimulate growth at yet lower concentrations. Some antimicrobial chemicals used in soluble oit emulsions have a broad spectrum of activity

Table 1 Requirements for a soluble oil biocide An ideal biocide for use in aqueous metal working fluids should : Have low human toxicity and irritancy Be disposable Show a broad antimicrobia[ spectrum Be compatible with normal soluble oil additives Not be inactivated by soluble oil components Be chemically stable Preferably be water soluble Not be inactivated by organic matter Be non-corrosive Be economical in use Ha~e EPA registration (in USA)

December 1983 Voi 16 Number 6

Shennan- Biocides for aqueous metalworking fluids

while others are chosen for selective action against specific groups of microorganisms. In choosing a biocide for soluble oil emulsions, compatibility with the formulation is a major consideration. Biocides must maintain their activity in the presence of various formulation ingredients under in-service conditions. Most cutting fluids are alkaline and biocides must theretore be stable at pH 9.5 10.5. Biocides have to act in the water phase of the oil-in-water emulsion. Oil soluble biocides will partition preferentially into the oil phase and exert little effect on the contaminating organisms present in the aqueous phase. Salts of oil soluble biocides are, however, water soluble. Chemical instability can cause loss of biocide during blending and storage and some biocides may only be suitable for addition to the diluted emulsion 21 . The presence of the biocide must not adversely affect the function of the formulation ingredients, particularly the emulsifier and corrosion inhibitor. The biocide must not itself be corrosive. Information provided by the biocide manufacturer on a new product should include data on specificity, killing curves and effective concentrations. These may require amplification if the organisms used to obtain results for a product data sheet were irrelevant to the particular inservice spoilage or contamination problem to be controlled by the biocide. Data may also have been obtained under relatively favourable conditions, in water, saline solution or nutrient media. Although, with experience, a reasonable amount of prediction can be made on effectiveness, no one biocide will fulfil all the criteria listed in Table 1. The only satisfactory answer is to test the candidate biocide in the formulation with an inocululn and under experimental conditions which model closeb those found in the workshop. This is the critical stage in the selection of suitable biocide.

In soluble oil emulsion spoilage only a few characteristics will be common to all fluids in all situations. In practice each fluid-site combination has to be considered as capable of producing some new factor which could not be predicted from laboratory testing. Field trials are required, therefore, under in-service conditions to define addition levels, top-up rates or to highlight any unforeseen problems.

A ccop tobility Finally, the biocide incorporated in the cutting fluid must be acceptable to the machine operator. If, for instance, the product smells unpleasant, it will not be tolerated by the work force, however safe and effective the biocide may be.

Biocide evaluation

Laboratory selection and testing methods used by different workers fall into three categories described below. Details of techniques, including the microbial groups monitored and methods used for their detection and enumeration, are to be found in the references indicated.

Test-tube screening methods The pioneers in the selection of antimicrobial chemicals for the control of cutting fluid spoilage used classical bacteriological test-tube screening methods, determining percentage survival of the inoculated population 2'22 . Later methylene blue reduction was proposed as a quick screening method for test tube assays of biocides 2a . These simple methods are useful for the biocide manufacturer in screening broad classes of candidate compounds for biocidal activity in model cutting fluids ~'2s and for determining optimum concentration ranges 26 . These techniques, however, yield little useful information in the selection of

Table 2 Summary of biocide evaluation methods for soluble oil emulsions Method

Type

Challenge

Use of iron chips

Aeration

Inoculum level

Duration

Reference

A

Aerated bottle

Repeated: weekly

No

Constant

~ 2 x 10 s/ml

Up to 4 months

27

B

Aerated bottle

Single

Yes

Off at weekend

5 x 10V/ml

2 weeks

26

C

Aerated bottle

Single

Yes

Off at weekend

5 x 10V/ml

8 weeks

26

D

Recirculating

Twice

External circulation over chips

Constant

10 ml spoiled fluid in 3600 ml test fluid

1 month

23

E

Recirculating

Repeated: thrice weekly

Fluid circulated up through chips in reservoir

Off overnight and at weekend

5 x 10S/ml

1 month

32

F

Recirculating

Repeated: as needed

External circulation with hold-up under anaerobic conditions

Constant

2 x 106/ml

36 days

33

G

Recirculating

Repeated: as needed

External circulation : chips also in reservoir

Off at weekend

~ 106/ml

Up to 4 months

34

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Shennan- Biocides for aqueous metalworking fluids biocides for use in cutting fluid control as they do not reproduce the actual conditions under which these products spoil.

Air

Aerated bottle tests Test regimes using large aerated culture bottles are the basis of experimental and evaluation methods developed by two of the main research groups in the field of cutting fluid miv.robiology. Techniques of this type have been accepted as standard methods by committees on metal working fluid methodology of the American Society for Testing Materials (ASTM) and the American Society for Lubrication Engineering (ASLE). The method developed by Bennett and his co-workers (see for example Izzat and Bennett 27) is based on large wide mouthed 1 litre capacity glass containers, vigorously aerated by a capillary tube to give a uniform 'rolling' of the coolant (Table 2, Method A). The test fluids are prepared with tap water of 1 2 0 - t 6 0 ppm hardness. The final coolant content of each unit is 600 ml, including all additions. During the course of the experiment, the liquid level -is made up weekly by adding distilled water to avoid build-up of inorganic salts. As in atl cutting fluid test methods, the ingredients are not sterilized and the units are open to aerial contamination. Aeration in Bennett's method is constant and does not, therefore, simulate overnight and weekend down-times. The units are inoculated with 2 ml of a combined bacterial and fungalinoculum (~ 2 x 10 s/ml final cell concentration) and reinoculated each week with 1 ml of a similar mixed culture. The two inoculum populations are maintained separately, the bacteria in a soluble oil emulsion, the fungi in a synthetic coolant, both of which are aerated and known to be degradable. Every week 75% of each culture is discarded and the remainder made up to volume with freshly prepared coolant. The units are sampled once each week and tested for content of viable bacteria and moulds. The tests can be continued for up to four months or until spoilage is apparent, that is when the count exceeds 10 s/ml on two consecutive weeks or visible slimes develop. The method does not include the use of metal chips. An investigation into the effects of various metals on cutting fluid biocides 28 showed that metals generally interfered , ~ _ _ _ . ~ F l o w of emulsion

with

~ . r . ~

air

Funnel holding3g iran chips

~

Wire mesh

~i!

!',

i', ,"i

il U.

I I

support

3 oo , o,

--t -emu's

i!l~

I

Ii I i i~ii

~.--Gal,on~le I

il l

i,lt!

I

I

I

r

__--II-',,nl ........ I \,. ~'- f

Fig i Circulating system for testing biocides in aqueous metal working fluids 23 (Table 2, Method D) 320

o

11

Cutting fluid err.;Ulsia0

A q u a r i u m circulatoraM aeratar

Fig 2 Circulating system for testing biocides in aqueous metal working fluids 32 (Table 2, Method E) with the action of antimicrobial agents, in some cases enhancing their activity. As iron adversely affected the antimicrobial action of most biocides tested, it was argued that the practice of including iron fines in similar test methods could result in the elimination of biocides which might be favourably affected by other metals. A 'Two-week Bioresistance Test' (Table 2, Method B) has been adopted as ASTM Standard Method D 3946-80 after consideration by a joint ASTM/ASLE task force (D2/LI) on bioresistance of aqueous metaiworking fluids 291 it is based on a procedure developed by Rossmoore and his cow o r k e r s 26,3°"

Compressed__.~ air

--7 iitre fermenterjar

Large glass containers of 1 litre total capacity are used. These are charged with 10 g of ferrous chips, 100 m! of inoculum and made up to 1000 ml with the cutting fluid° After mixing, 50 ml is removed and a capillary aeration tube inserted. The inocu!um is prepared from spoiled fluid incubated with an equivalent quantity of a peptone based broth for 48 hours. The final cell concentration in ~he test fluid is ~ 5 x 107/ml. The tests are carried out at ambier~t temperature. Samples are withdrawn for bacterial and fungal counts at intervals of 0, 5, 7 and 12 days, the fluid levels being made-up with distilled water during the course of the experiment. Aeration is suspended for the equivalent of week-end shut-downs. This test is designed to test biocidai rather than biostatic activity, the criterion of successful 'control' being reduction of viable bacterial and fungal counts from the unprotected control levels of ~ 109/ml and 10 s/ml respectively to less than 100/ml. Use of a biocide to prevent lower contamination levels reaching high counts is not assessed. The high count of the microbial challenge and the organic nutrients introduced with the culture broth used to prepare the 1(3% by volume inoculum would mimic some of the very worst conditions encountered in a machine shop.

December 1983 Vol 16 Number 6

Shennan- Biocides for aqueous metalworking fluids The "Eight-week Biocide Evaluation' test (Table 2, Method C) is a six-week extension of the bioresistance method described above z6 with minor variations, mainly in the use of a selected defined inoculum (discussed later). It has been adopted by ASTM Committee E35 as Standard Procedure E686 for the evaluation of anti-microbial agents in aqueous metalworking fluids.

Recirculating tests Recirculating rig methods, favoured by many workers, attempt to simulate the conditions under which a cutting fluid will be used in service. The soluble oil emulsions containing biocide are circulated over iron chips or other metal fines if specific machining operations are planned 31 . The test systems are usually subjected to repeated challenges using a mixed flora of contaminants. Although used in many industrial laboratories, only a few of these systems have been described in the open literature. The first method of this type was developed by Pivnick and Fabian 23 (Table 2, Method D). The apparatus, shown in Fig 1, is based on a one gallon jar containing 3600 ml cutting fluid. A flow of compressed air enters the system through a J-shaped tube at the base of the reservoir, forcing the emulsion up the flow tube into the funnel containing 3 g of iron chips. The fluid trickles down through the bed of chips to re-enter the main reservoir. The biocide-containing emulsion is continuously circulated and after one week a 10 ml inoculum (count unspecified) is added from a mixture of spoiled fluid samples. Samples are then taken for counts and at 1,10 and 18 days thereafter. Fluids which are still 'sterile' at 18 days are reinoculated at 22 days and a final count made at 29 days. The system, therefore, receives two, possibly mild, microbial challenges. In the method of Himmelfarb and Scott 32 (Table 2, Method E) the quantity of test fluid is increased to 5 litres and a circulating/static cycle is introduced by discontinuing

Air lift

Swart

Air vent

Air

Fig 4 Circulating system for testing biocides #7 aqueous metal working fluids 34 (Table 2, Method G) aeration overnight and at weekends. The apparatus (Fig 2) is based on a 7 litre fermentor jar containing 5 litres of test fluid, aerated by an aquarium aerator packed with 5 g of iron chips. Immediately the system has been charged, the fluid circulation is started and an inoculum (~ 5 x l0 s/ml final concentration) of mixed bacteria isolated from spoiled emulsion samples is added. Samples are taken for plate counts and the tanks reinoculated three times each week. The tests are continued for 24 days. As the circulation of the fluid in this method is entirely within the confines of the reservoir container, the metal fines, which represent the workpiece and swarf, are not exposed to air, a contrast with real machining operations. Hill et al's apparatus 33 (Fig 3) is fitted with a recirculating device to aerate and lift the fluid from the base of the reservoir to trickle back over swarf held in a separate container (Table 2, Method F). The fluid is trapped in the swarf-containing tube until the level rises sufficiently to allow it to siphon out and back into the main'reservoir. Metal chips are also present in the base of the fluid container, representing the sump in a machine system. The inoculum (1 ml), added to 3 litres of cutting fluid, is a mixed suspension of bacteria, yeast and fungi isol~/ted from cutting fluids (~ 2 x 106/ml final concentration). Twice weekly samples are taken for microbial counts and the flasks reinoculated with a further 1 ml of mixed cell suspension. The fluids are circulated continuously but the holdup of fluid in the smaller swarf filled reservoir and the swarf collected at the base of the flasks allows local areas of anaerobic growth to occur.

Fig 3 Circulating system ]br testing biocides in aqueous metal working fluids 33 (Table 2, Method F)

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In a further version of the recirculating technique s4 , the basic unit (Fig 4) consists of a 1 litre tall beaker containing 800 ml of test fluid and 10 g of mild steel chips (Table 2,

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Shennan- Biocides for aqueous metalworking fluids Method G). The fluid is circulated by the inlet airflow from the aeration tube to be discharged over mild steel millings in a funnel supported above the beaker. A battery of units is hetd in a water bath at constant temperature (22°C) in a fume cupboard to minimize any potential hazard from oil mists or aerosols. The air flow is shut off at weekends. Each beaker is inoculated with 5 ml of a mixed microbial population prepared from isolated cutting fluid contaminants mixed with spoiled fluid from industrial samples. The final count in the test fluid is ~ 5 x 106/ml bacteria and "" 103/ml fungi. Samples are withdrawn as required for microbial counts, pH and emulsion strength measurements. The fluid levels are made up with distilled water and the units reinocutated weekly.

Field trials The field trial marks the final stage in selection before a new cutting fluid is marketed or a biocidal additive recommended for an existing product. Ideally, three sites are chosen to represent good, moderate and bad workshop conditions. The machines to be used are sampled for microbiological counts before and after cleaning to establish baseline data. The machine systems are thoroughly cleaned of old fluid and swarf using an appropriate system cleanser compatible with the fluid and the new biocide. A full programme of tests is devised and samples of fluids are taken regularly once or twice each week to be despatched, as quickly as possible, to the testing laboratory if there are no suitable facilities on site.

Defined inoculum for biocide evaluation A standard inoculum has been proposed for biocide testing using the ASTM standard methods for aqueous metalworking fluids 3s . Six strains isolated from spoiled cutting fluids are used, Pseudomonas aeruginosa and Ktebsiella pneumoniae from soluble oil emulsions, Pseudomonas fluorescens andProteus mirabilis from synthetic fluids and Cephalosporium sp. and Fusarium sp. from semi-synthetic fluids. The individual cultures are grown in a mixture of cutting fluids and nutrient broth ~ and combined to give a count in the inoculum of ~ 109/ml for each bacterial species and "~ 10S/ml for the fungi. While biocide manufacturers and the metal working fluid formulator may find a defined inoculum from a culture collection bank useful in comparative screening tests and for compliance with EPA registration requirements in the USA, no universally suitable inoculum can b'e devised. The fluid formulator is ultimately concerned with the performance of a product under machine shop conditions and wilt, therefore, wish to challenge a new formulation during laboratory screening with spoiled fluids taken from the working environment or with organisms recently isolated from and maintained in similar fluids.

Biocide types Biocides for soluble oil emulsions must be nontoxic, environmentally acceptable, compatible with common formulation ingredients and effective, mainly against Gramnegative bacteria, under normal conditions of use. These requirements rule out the use of some major groups of industrial, pharmaceutical, medical or food preservatives. Inorganic or organo-metallic antjmicrobial compounds containingheavy metalions, although effective and compatible,

322

are unsuitable for use in cutting fluids. They are relatively toxic and environmentally persistent with strong resistance to biodegradation. Traditionally, however, the metalwork. ing industry has made use of the antimicroNal effect of copper through the practice of adding some spent fluid from yellow metal machinin8 systems to fresh charges of cutting fluid. Medical bactericides are safe and well documented, but are often expensive and may- have narrow activity spectra. However, several products, including some formaldehyde release agents, developed principally for use as cosmetic offwater emulsion preservatives, have a!so been tried in cutting fluids. Acids and esters would destroy the alkaline status of~ne fluids. The oxidizing agents, hydrogen peroxide and ozone, are reactive and potentially corrosive. Chlorine donors are also chemically reactive and do nor exert any effect until the free, uncombined chlorine levels exceed 0.3 ug/mt. High levels of sodium or calcium ions introduced as hypochlorite salts would affect emulsion stability. While the quaternary ammonium compounds (qac) are valuable biocides for many applications, they are most effective against Gram-positive bacteria which are seldom a problem in cutting fluids. Qac are chemically incompatible with a wide range of compounds found in soluble oil formulations, for example anionic and non-ionic surfactants, phospholipids.and fats. The principal antimicrobial agents for metal working fluids used experimentally or in service ate listed in Appendix [ with examples of commercially available products~'. The iist is not exhaustive, but illustrates the chemical types which have been used. Additional information on dose rates, handling, toxicology, etc, is to be found inthe references given in Appendix 1, in general reviews of industrial biocides 36-38 and in the manufacturers' literature on individual products,

Phenolic derivatives Phenols have been in general use as chemical disinfectants for over a hundred years and, although many derivatives exist, they generally have a common mode of action, destroying or inactivating the normal enzymic or transpolX mechanisms of the cell. In general they are not readily inactivated by organic matter and have a wide microbial spectrum. They are relatively inexpensive and their use caa therefore be cost effective. The major disadvantages of the phenolic derivatives Iie in their toxicity and potential for skin irritancy and odour; they are relatively unpleasant to handle. During use, biocidat activity can be diluted rapidly to sublethal levels and resistant populations can develop after prolonged exposure. Halogenated derivatives, especially some chlorophenylphenols, have come increasingly under scrutiny because of their recalcitrance to biodegradation when discar'Jed. Combined environmental and human safety considerations have led to the withdrawal from the USA market of some phermt derivatives which had been widely used; these include 2,4,6trichlorophenol and 4-chloro-2-phenytpheno!39 , both of which were proposed as cutting fluid biocides in early papers ~,23 . ~Mention o f any biocide by chemical, trivial or product name does" not imply endorsement by BP Co, plc for use in that company products.

December 1983 Vo~ 16 Number(}.

Shennan- Biocides for aqueous metalworking fluids In phenols, halogenation generally decreases water solubility but increases activity, the antimicrobial specificity depending partly on the degree and type of substitution of the basic phenol. The chlorophenols have a greater tendency to be inactivated by organic matter. Monochlorophenols and monochlorocresols show moderate control of Gram-negative Pseudomonas species in soluble oil emulsions u , but can be inactivated by non-ionic surfactants. In general, however, phenolic derivatives such as the sodium salt of 4-chloro-3methylphenol, are useful for control of fungal growth in synthetic cutting fluids and, in combination with a chemically compatible bactericide, in soluble oil emulsions. The bis-phenol, dichlorophene, has been recommended for use with cutting fluids but its effectiveness against Gramnegative bacteria is variable and it can show poor compatibility with certain soluble oil formulations. A common non-chlorinated phenolic biocide, 2-phenylphenol, is the only phenol derivative to have EPA registration in 1981 for use with cutting fluids in the USA v~.

F o r m a l d e h y d e release biocides Formaldehyde(formalin) was proposed for the control of metal working fluids by Lithbertson in 19433 . It has a full spectrum of antimicrobial activity causing cell lysis and reaction with cell proteins and is very economical in use. It is, however, volatile, has a pungent odour and is highly toxic with a threshold lethal value of 2 ppm. In 1956 tris(hydroxymethyl)nitromethane was found to be effective in controlling cutting fluid spoilage 4° and it was observed that this might be due to the slow release of formaldehyde from the molecule. By 1970 a number of formaldehyde release agents were available for use as preservatives and were soon being evaluated in cutting fluids 41,42 " The formaldehyde-release biocides have proved to be particularly useful in soluble oil emulsions. While their spectrum of activity is not as wide as that of formaldehyde itself, this is more than compensated by a great reduction in the irritancy and toxicity associated with formalin. They are non-volatile and act through the slow release of active formaldehyde 'on demand' from the condensate at acid pH, sufficient to kill cells without swamping the system with free formalin. Formaldehyde donors, suitable for use as cutting fluid biocides, are stable in alkaline or neutral conditions but break down under acid pH to release the active formaldehyde. While this release can be triggered by acidity in the free aqueous emulsion, formaldehyde is also thought to be liberated at the cell boundary under the localized conditions of low pH following the excretion of acidic products from normal cell metabolism. Formaldehyde release agents are linear and cyclic reversible polymers of formaldehyde with a variety of organic molecules 24'38'43 . Further modifications of chemical structure have been synthesized to improve solubility in hydrocarbon systems and the rate at which molecular breakdown occurs. A slow continual supply over a period of time rather than a sudden release of the active formaldehyde is the aim. Many of these biocides, especially condensates of formaldehyde and amines, appear to possess antimicrobial activity due to the polymer complex in addition to that attributed

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solely to their formaldehyde content. An explanation offered by Kallen and Jencks ~ for the enhanced biocidal activity of amine complexes is the establishment of equilibria between formaldehyde and amines in aqueous solution, with the formation of highly reactive imines as intermediates. The imines are susceptible to nucleophilic attack and will react with cell components containing nucleic acids or amino acids. Another putative equilibrium compound with inhibitory activity is oxazolidine ~s . in general, the formaldehyde condensates seem to be less prone than formaldehyde itself to select for resistant organisms following prolonged use 24 . The formaldehyde donors do have some disadvantages. They are much less active against fungi and their importunate use in soluble oil emulsions may lead to the appearance of intractable fungal infections. Their chemical reactivity is high and resinous compounds can be formed with a large number of materials commonly used in cutting fluid formulations. Some of the most widely used formaldehyde-release agents are derivatives of triazine. These are cyclic, saturated symmetrical molecules which have been outstandingly successful in the control of soluble oil spoilage. They are based on hexahydro-1,3,5-trie thyl-s-triazine and hexahydro-1,3,5-tris (2-hydroxyethyl)-s-triazine. The triethyl derivative (a condensate of ethylamine and formaldehyde) is used to preserve latex paints and pigment slurries in addition to metal working fluids. It has broad spectrum activity against both bacteria and fungi, has good oil and water solubility, and is stable in most cutting fluid concentrates. It has low intrinsic toxicity and is usually non-irritant at the dilutions used in the workplace. The tris(2-hydroxyethyl) version is sold almost exclusively for the protection of soluble emulsion oils. It is also stable, but rather less effective against fungi than the triethyl derivative. Due to their widespread use, the tris(2-hydroxyethyl) derivatives have been the subject of investigations into contact dermatitis associated with their u s e 1 9 ' 4 5 4 8 . It appears that these chemicals can act as contact sensitizers under some circumstances and not under others 49 , but claims of allergic sensitization do not appear to have been substantiated. lmidazole biocides are used for the preservation of cosmetic oil/water emulsions. The derivative 1,3-di(hydroxymethyl)5,5-dimethyl-2,4-dioxoimidazole is active over a wide pH range but the rate of formaldehyde release is higher at alkaline pH values 3a . In cutting fluids, the imidazoles are reported to be non-toxic, non-irritant and compatible with emulsion ingredients and proteins s° . A chloro-imidazole (containing the =N-C1 group)hydrolyses in water to produce an imido-(=NH) group. Its activity may be increased under acid conditions 3a . Oxazolo-oxazoles, formed by reacting formaldehyde with tris(hydroxymethyl)methylamine, have been recommended for several uses including the preservation of cutting fluids. They are mild skin irritants but can cause severe eye irritation. Hexamine (1,3,5,7-triaza-1-azonia adamantane) has been used as a urinary antiseptic for over 80 years. Although the quaternized hexamine derivatives are structurally similar to the qac biocides, they act through the release of formaldehyde. They are not inactivated by proteins and are not

323

Shennan- Biocidesfor aaueousmetalworking fluids surface active, but they have a poor storage life and are unsuitable for use in concentrates. They are relatively stable at alkaline pH, are highly water soluble and can be added when needed to alkaline systems. Several antimicrobial products, apparently based on chloracetamide, have been recommended by different manufacturers for use in aqueous metalworking fluids, although detailed chemical formulae are not available. A mixture of 2-chloro-N-(hydroxymethyl)acetamide and sodium tetraborate is especially effective at mould control in synthetic fluids.

Aliphatic derivatives Tris(hydroxymethyl)nitromethane has largely been superceded as a cutting fluid biocide by more efficient formaldehyde release agents. It is poorly compatible with most concentrates and must be added directly to the diluted fluids. Although economical in use, it is relatively inactive as a fungistat. A number of other nitro- or bromo-nitro-aliphatic compounds have been proposed as cutting fluid control agents n'~2 , but no evidence is available to support formaldehyde release as the active principle. The bromo-nitrogen product, 2-bromo-2-nitropropan-1,3-diol is unaffected by anionic or non-ionic surfactants or proteins. It is active over a wide pH range and acts by binding to thiol groups of enzymes. Another similar chemical, 2,2-dibromo-3nitrilopropionamide, has EPA approval for use as a cutting fluid biocide. As it is unstable in alkaline solutions, it is added continuously to the diluted fluid.

Organosulphur-nitrogen compounds A number of sulphur-nitrogen biologically active chemicals have been used with success for the control of cutting fluid spoilage. Several derivatives of the 5-membered ring, 3-oxyisothiazole, have been developed as industrial biocides. The compound 1,2-benzisothiazol-3-one, primarily used as a preservative for latex paints and plastics emulsions, has also been used in metal working fluids. The chemical has low mammalian toxicity but can have marked skin irritancy in sensitized individuals sl's2 . A mixture of 2-methyl4-isothiazolin-3-one (2.6%) with its 5-chloro-substituted form (8.6%) is active at very low concentrations (2-9/ag/ml active ingredient) against a wide microbial spectrum including pseudomonads ~6 . It is compatible with most emulsifying agents but may be inactivated by sulphides and primary amines. It is water soluble, degrades to non-toxic metabolites and is non-irritant at in-service concentrations. Competition by the active isothiazolone moiety with thiazole in the assembly of thiamine is thought to be the mode of action 36 . Another biocidal mixture, prepared from 2-mercaptobenzothiazole and dimethyl dithiocarbamate and used as a paper mill slimicide, has been proposed for use with cutting fluids. A substituted dithiocarbamate has been shown to have some effect in soluble oil emulsions, possibly functioning as a competitor for sulphydryl enzyme groups. By condensing dithiocarbamate with acetamide to form a thiadiazine, biocidal activity is enhanced 24 . 1,5-dimethyltetrahydro 1-2thiadiazine was found to be compatible and effective in aqueous metalworking fluids42 but has been used more extensively in adhesives, coatings and slurries. Hydrolysis of

324

one molecute of thiadiazine is thought to release ~:wo molecules of formaldehyde, but may also yield the active thiocarbamate. Chlorinated pyridine derivatives have been tested in aqueous metalworking fluids sa but they are unstable at alkalihe pH; their biocidal action is slow-acting and they have iow Water solubility. A second class of pyridine derivatives, the pyridinethiones or omadines, are much more effective, especially against fungi. Zinc omadine is neither toxic nor irritant, finding wide use as an anti-dandruff agent. The putative mode of action of the omadines, discussed by Rossmoore 36 , is thought to !ie in interference with transport and integration of cations into essential cellular metabolic processes. A mixture of sodium omadine and a substitutedtriazine is marketed as a wide spectrum cutting oil biocide.

Miscel/aneous compounds A mixture of morpholines is effective at control of both bacteria and fungi in synthetic water-based cutting fluids and soluble oil emulsions. While the product is highly irritant at high concentrations and must be handled with care, it is suitable for incorporation into soluble oil concentrates as it is soluble both in water and hydrocarbon solvents. The activity of dimethoxane is attributed partly to its aldehyde content and partly to the 1,3-dioxane moiety. It is reasonably effective in controlling fungal spoiiage of synthetic cutting fluids. The biocides have a marked odour as they hydrolyse to acetaldehyde; they are compatible with non-ionic surfactants but will cause discoloration in formulations containing amides or amines. A mixture of monocyclic oxyazolidines, originally intended as a corrosion inhibitor, has also been used as an effective biocide in soluble oil emulsions. Polymeric hexamethylene biguanide, a cleansing agent ir the food industry, is effective at controlling fungi in synthetic fluids. It is of limited use as a biocide for soluble oil emulsions as it is cationic (although not surfactant) and its activity is reduced in the presence of organic matter.

New biocida/ products New antimicrobial agents recentiy developed for use in soluble oil emulsions include 2-mercaptobenzamide s4 , nitro-oletin substituted quinoxaline dioxides ss , 2,2'-bis (methylaminocarb onyl)diphenyldisulphide s6 ,and i ,2-dibromo-2,4-dicyanobutane s~ . Closer study of the resistance of certain soluble oil formula' tions to biodeterioration has identified ingredientswhich have inhibitory activity in addition to their primary function as co-solvents, anti-rust additives, etc. A series of triazole corrosion inhibitors have been evaluated for antimicrobiaI properties in a range of cutting fluids s8 . Benzotriazole, 5-chlorobenzotriazole and tolyltriazole were effective against a mixed population and. were all compatible with other popular cutting fluid biocides:

Biocide mixtures and synergistic effects In systems relying solely on restricted spectrum, nonoxidizing biocides it is good practice to use two chemically different biocides alternately. Buitd-up of bacteria resistant

December 1.983 Vol "~6 Number 6

Shennan - Biocides for aqueous metalworking fluids

to one biocide type will therefore be prevented. Growth of unaffected micro-organisms may be encouraged merely through the removal of competition, exemplified by the vigorous development of a fungal population in certain cutting fluid systems, following control of bacterial contamination. Several of the cutting fluid biocides listed in Appendix 1 are mixtures of chemicals, usually a formaldehyde release bactericide combined with a compatible fungicide 4:'s3 . These have a wider antimicrobial spectrum or show synergistic effects allowing active ingredients to be incorporated at lower dosage rates in the fluid. Additional advantages are cost saving in the use of expensive biocides or decrease of potential irritancy or environmental toxicity of the spent cutting fluid. Striking synergism in mixtures of benzylhemiformals (benzylalcohol reacted with formaldehyde) and phenols has been noted by Paulus 24 but the pH must be kept below 9.5 to prevent interaction. In mixtures of amine-formaldehyde condensates(triazines) and phenols, benzylamines are probably formed as reaction products. This is also thought to be the effect of combining triazines with omadines 26 . A more extensive investigation into biocide combinations has been made by Bennett and his group 31'59 . Various formaldehyde release agents, thiazoles, phenols, aldehydes and morpholines were tested in dual combinations in a synthetic fluid and a petroleum oil based soluble oil emulsion. Although certain combinations showed synergistic effects, the authors found they were unable to draw many general conclusions from their results. The chelating agent ethylenediaminetetracetic acid (EDTA) had a potentiating effect on a number of chemically unrelated biocides 27'3~'s9-61 . It was concluded that one biocide used with EDTA could be more effective than mixtures of biocides. Inorganic cations play an important role in maintaining the integrity of plasma membranes and the additional antimicrobial effect of EDTA and other chelators may be due to their ability to combine with divalent cations in the membrane structure. Synergistic effects of physical and chemical treatments for cutting fluids can occur, probably through damage of the cell membrane by relatively mild heat treatments, sub-lethal levels of radiation or ultrasound. This renders the Cell more permeable to biocidal chemicals and results in control at lower biocide dose rates. However, this increase in effectiveness wot~ld have to be considerable to offset the additional capital and running costs of physical treatments.

The biocide in use There are many ways of reducing the contamination load in the system to be treated by biocides and delaying their inactivation by organic matter or adsorption onto accumulated metal swarf. The Code of Practice for Metalworking Fluids published by the Institute of Petroleum 2° summarizes the various aspects of contamination control that can be put into effect at the workshop. The soluble oil concentrate as delivered to the workshop has a low water activity and is free from all but adventitious contamination. The microbial inoculum comes from the water and utensils used during make-up of the diluted emulsion and from any residues of old fluid in the newly charged machine system. However clean the machine

TRIBO LOG Y international

system may be, the coolant fluid is continually challenged during its working life by bacterial and fungal cells in compressed and entrained air and the detritus and general filth that can find its way into a circulating cutting fluid system. Good design of machines and centralized coolant systems can alleviate many problems. The principal aim is to minimize stagnant areas in a circulating fluid system. Dead legs of pipework, sagging pipe runs and inaccessible, undrainable sumps can be eliminated. Rapid removal of swarf prevents the sequestering of chemical additives, including biocides, on the large surface area of metal fines. Organic matter, added from extraneous sources or from the build-up of contamination biomass, can also adsorb biocides and reduce the active concentration in the free fluid. Good housekeeping practices are therefore essential for ensuring good coolant management. Improvement of workshop hygiene is a matter of education, persuasion, supervision and management. Attention to machine maintenance will reduce the leakage of hydraulic, gear or lubricating oils into the soluble oil emulsion. This 'tramp oil' may itself be contaminated, may act as yet another growth substrate for the cutting oil microflora, or may add sulphur or phosphorus ions from additives into the coolant mixture. Both the microbiological and chemical quality of the water supply used at the factory to dilute the soluble oil emulsion can influence the ultimate life of the fluid, ldeally distilled water or deionized water from units which are frequently regenerateo should be used to eliminate this potential source of inoculum. If good quality potable water is available, adequately clean supplies will be obtained by drawing water directly from a flowing main. Water hardness affects both the chemical and biological status of a cutting fluid a°'62'63 . The effectiveness of many different antimicrobial chemicals may be reduced in the presence of hard water 64 although the reasons are not clearly understood. Unprotected fluids prepared with hard water spoil more quickly than the same emulsion prepared in purified water. Water of suitable hardness, between 100-200 ppm, is usually obtained by blending naturally soft or deionized water to the required hardness with added salts 6s,66 . Con t r o l o f b i o c i d e a d d i t i o n

In a clean, newly charged system, a basic decision is whether to treat the system with high concentration 'shock' doses at intervals or to maintain an effective biocide concentration at all times. With inherently biodegradable cutting fluids, maintenance of an effective level ofbiocide (often in the range 500-2500 ppm formulated product) by frequent small additions is favoured. Excessive concentrations ofbiocide may approach levels which are unacceptable for health reasons. The wasteful use of an expensive product is to be avoided as are difficulties in disposal or inactivation once the fluid is spent. For economic and safe management of biocide addition, analytical procedures for determining the residual concentration of biocide in cutting fluid samples are required 67 . Test kits for the rapid assessment of residual formaldehyde levels in cutting fluids are available, but biocides other than the formaldehyde donors cannot be monitored as easily. A further decision is to include a biocide from the outset with the first charge of fluid or introduce it only when

325

Sherman - Biocides f o r aqueous metalworking fluids

danger signs appear. Delaying biocide addition requires some effective means o f monitoring contamination levels in the fluid. In a typical workshop, microbiological laboratory facilities are unlikely to be available and other less exact methods are needed to allow at least some estimation of microbial numbers to be made on the shop floor to anticipate Spoilage rather than to recognize it once it is too late to take action. Characterization o f the successive microbial populations dominating the different stages o f contamination in m a n y metal working fluids would allow the introduction o f differential diagnostic tests which could anticipate the onset of serious spoilage problems. Although advances are being made towards this objective through research and field experience, such methods are still n o t available. Pending new rapid methods for product monitoring at the workplace, reliance has been placed on dipslide techniques 3a'ss,69 which give adequate indication of contamination 'alarm' levels in soluble oil emulsions. Other rapid methods for determining incipient spoilage include the estimation o f microbial hydroperoxidases 7° , monitoring pH and dissolved oxygen decrease or depletion o f specific formulation ingredients 71'72 .

Conclusions The extensive use o f biocides must be looked on as a shortterm solution to the problem o f soluble oil spoilage. In the longer term the answer is to reformulate soluble oil emulsions using ingredients with greater intrinsic resistance to biodegradation or to formulate completely new products which are microbially less susceptible. The restricted addition o f biocides will probably remain as a necessity since some inherent biodegradability o f a metal working fluid m a y be unavoidable. Radical improvements, however, should be possible. Other factors contribute to the limitation o f fluid life, including swarf accumulation, atmospheric oxidation and exhaustion of active chemicals. Keeping contamination under control, therefore, rather than attempting elimination may be a good practical aim, Even a 10 or 100-fotd reduction in count could make the difference between a product which is contaminated b u t acceptable and one which is unserviceable. A useful target could be the control o f particular groups o f bacteria, for example those which utilize hydrocarbons or emulsifiers as carbon sources or which produce hydrogen sulphide gas. The user m a y be prepared to p u t up with recalcitrant contamination if malodorous bacterial products are not released, the cutting fluid performs well and user safety is n o t impaired. The most cost effective solution would be attained when the limit o f use, as determined b y biodegradation, coincides with fluid life determined by other performance criteria.

Acknowledgements The author wishes to thank BP Co, plc, for permission to publish this paper. The literature reviewed forms a background to active research and advisory work on metal working fluids carried out in that Company and the author would like to thank her many colleagues for their collective experience on the subject. Finally, the author thanks Professor J.D. Mandtestam and Professor F. Gibson for constructive criticism o f the manuscript.

326

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4.

Fabian F.W. and Pivnick H. Growth of bacteria in soluble oil emulsions. AppL MicrobioL, 1953, 1, ]99-203 Bennett E.O. and Wheeler H.O. Survival of bacteria in eutfirig oil.AppL MicrobiaL, 1954, 2, 368-37] Bennett E.O. The role of sulfate reducing bacteria inlthe deterioration of cutting emulsions. Lub. Eng;, 195 7, !3, 215-219

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Kitzke E.D. and McGray RJ. Coolant microbiology: the roie of industrial research. Proc. 14th ASLE Mtg., 1959, paper No 59AM34 Lindert A.N. Some problems encountered in the use of soluble oils. Lubr. Eng., 1951, 7. 223-227 Sonntag W. Bacterial decomposition of soluble oil emulsions. Lubr, Eng., 1952, 8, 234 Bennett E.O., Adamson C.L. and Feisal V.E. Factors involved in the control of microbial deterioration. I. Variation in sensitivity of different strains of the same species. AppL MicrobioL 1959, 7, 368-3 72 Bennett E.O. and Futch H.N. Nitroparaffin inhibitors for cutting fluids. Lubr. Eng., 1960, 16, 228-230 Carlson V. and Bennett E.O. The relationship between the oilwater ratio and the effectiveness of inhibitors in oil-soluble emulsions. Lubr. Eng., 1960, 16, 572-574 Ro~moore H.W. Antiwderobial agents for water-based metaiworking fluids. J. Occup. MecL, 1981, 23(4), 24 7-254 Smith T.H.F. Toxicological and microbiologicalaspects of cutting fluid preservatives, lncL Med, 1970, 39, 2 9 - 3 7 Cronin E. Contact Dermatitis. Churchill-LivingstonG (l 980] Rycroft R.J.G. Bacteria and soluble oil dermatitis. Contact Dermatitis, (1980), 6, 7-9 Roberts D.L, Messenger A.G. and Summedy R. Occupational dermatitis due tO 1,2-benzisothiazolin'-3-one in the pottery industry. Contact Dermatitis, 1981, 7, 145-147 Schneider W., Huber M., Kwoczek J.J., Popp W., Schmitz R. mid Tronnier H. Further studies on the skin tolerance of highly diluted coolants. Berufs-dermatosen, 1965, 13, 65-85 Institute of Petroleum Code of practice foi metalworking fluids. Heyden & Son, (19 78) Onyekwelu I.U., Bennett E.O. and Gannon J.E. The effective life of preservatives in cutting fluid concentrates. TriboL Int., 1981, 14, 7-9 Westveer W.M. Cutting oil disinfection. Modern Sanitation, 195l, 3, 31 Pivniek H and Fabian F.W. Methods for testing the germicidal value of chemical compounds for disinfecting soluble off emulsions.AppL MicrobioL, 1953, 1, 204-207 Paulus W. Problems encountered with formaldehyde releasing compounds used as preservatives in aqueous systems, espeeially lubficoolants - possible solutions to the problems. Proc. 3 r d Int. Biodeterior. Syrap., 1976, 1075-1082 Singer M. Laboratory procedures for assessing the potenffal of antimierobial agents as industrial biocides. Process. Biochem, 1976, l l, Jul/Aug, 3 0 - 3 5 Rossmoore H.W., Siecldaans J.F., Rossmoore L.A. and Defonzo D. The utility of biocide combinations in controlling mixed microbial populations in metalworking fluids. Lubr. Eng., 19 79, 35, 559-563

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December 1983 Vol 16 Number 6

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Bennett E.O., Gannon J.E. and Onyekwelu I.U. The effects of metals upon the inhibitory activities of cutting fluid preservatives. Int. Biodeterior. Bull., 1982, 18(1), 7-12

53. Rossmoore H.W., deMare J. and Smith T.H.F. Anti- and promicrobial activity in hexahydro-1,3,5-tris(2-hydroxyethyl)-striazine in cutting fluid emulsions. Proc. 2nd Int. Biodeterior.

Syrup. (19 72) pp 286- 293 54. Abbott Laboratories Biocidal additive for cutting fluids. US

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29. SharpeU F.H. Development of test protocols for anti-microbial agents by the ASTM. Dev. Ind. Microbiol, 1979, 20, 73 80

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56. Imperial Chemical Industries Ltd. Combating microorganisms. GB Patent 1532984 (1978)

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58. Bennett E.O., Onyekwelu I.U., Bennett D.L. and Gannon J.E. Inhibitory activities of triazole compounds in metal working fluids. Lubr. Eng., 1980, 36(4), 215-218

32. Himmelfarb P. and Scott A. Simple circulating tank test for evaluation of germicides for cutting fluid emulsions. AppL Microbiol., 1968, 16, 1437 1438 33. Hill E.C., Gibbon O. and Davies P. Biocides for use in oil emulsions. TriboL Int., 1976, 9(3), 121-130 34. Rawlinson A.P. and Shennan J.L. Paper in preparation 35. Rossmoore H.W. and Rossmoore L.A. The identification of a defined microbial inoculum for the evaluation of biocides in water based metalworking fluids. Lubr. Eng., 1980, 36(1),

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42. Bennett E.O. Formaldehyde preservatives for cutting fluids.

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60. Izzat I.N. and Bennett E.O. The potentiation of cutting fluid preservatives by EDTA. Lubr. Eng., 1979, 35, 153 159 61. Izzat I.N. and Bennett E.O. Effect of varying concentrations of EDTA on the antimicrobial properties of cutting fluid preservatives. Microbios, 1978, 26, 37-44 62. Feisal E.V. and Bennett E.O. The effect of water hardness on the growth of Pseudomonas aeruginosa in metal working fluids.

J. Appl. Bacteriol., 1961, 24(2}, 125 130 63. Bennett E.O. The effect of water hardness on the deterioration of cutting fluids. Society of Mechanical Engineering Technical

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BlackweU (1982) pp 343-351 51. Slovak H.J.M. Contact dermatitis due to benzisothiazolin in a works analytical team. Contact Dermatitis, 1980, 6, 187-190 52. Alomar A. Contact dermatitis from benzoisothiazolone in cutting oils. Contact Dermatitis, 1981, 7(3), 155-156

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F o r A p p e n d i x 1 - Biocides used in cutting fluids - see over

327

Shennan- Biocides for aqueous metalworking fluids A p p e n d i x 1 Biocides used in cutting fluids

Chemical

Formulae

Examples of commercial products

ManuReference facturert

2-phenylphenol

DOWICIDE 1

1

sodium 2-phenylphenol

DOWlCIDE A*

1

PHENOLIC DERI VA TI VES Non-chJorinated phenols

OH

Chlorinated phenols

2-chlorophenol

[~cl

OH

OH Cl~ CI Cl

4-chlorophenol 2,4,5-trichlorophenol

cl

OH

4-chloro-3-methylphenol (p-chloro-m-cresol)

CH~

4-chloro-2-methylphenol (p-chloro-o-cresol)

OH

!1 DOWlCIDE 2

1

23,40

PREVENTOL CMK

2

23,38

./CH3

cl

OH CI

4-chloro-3,5-dimethylphenol (p-chloro-m-xylenol)

PCMX

H~c'~CH3 Cl

OH 3-chloro-2-phenylphenol

11,14,21, 37,39,40,74 39

@

B/s-phenol

@

74

MCOPP

cl

2,2'-methylene-bis(4chlorophenol) (5,5Ldichloro-2,2 L dihydroxy-diphenylmethane), (dichlorophene)

OH

HO

CI

PANACIDE C PREVENTOL GD

2

VANCIDE TH* BACTOCI DE THT

4 5

14,27,37,60

GROTAN BK*

6

13,!4,21, 27~39,42, 60.64

GLOKILL 77 ONYXIDE 200*

7 8

CINON

9

DANTO I N

10

37,38

GERMALL 115

11

38

HALAN E

12

40

3

13,38 "

CI

FORMALDEHYDE RELEASE AGENTS

~ 2H5

Triazines

hexahydro-1,3,5-triethyls-triazine

/N--.. fN.~

H5C2

hexahydro-1,3,5-tris (2hydroxy-ethyl)-s-triazine

Ca

C2H5

/Nx /N.~

HOH4Ca Ce

CaH40H

"monocyclic arninal" containing formaldehyde and ethylamine lmidazoles

1,3-di (hydroxymethyl)5,5-dimethyl-2,4dioxoimidazole

CH~ O / H3C HOH2C-Nv N-CH20H tl 0

N,N'-methylene bis-[5'- (1hydroxymethyl)-2,5-dioxo4imidazolidinyl urea] CH~ O 1,3-dichloro-5,5-dimethylH~C~F - T d hydantoin (1,3-dichloro-5,5dimethyl-2,4-imidazolidinedione) cI- N v N -CI I| o 328

H O~ N

c'T

//NH 0~''

CH20H I N .//O NH

HaC\NH O~.~r.____NH H

14,39

I CH2OH

December 1983 Vol 16 Number 6

Shennan - Biocides for aqueous metalworking fluids

Examples of commercial products

ManuReference facturert

NUOSEPT 95

13

38

DOWlClL75*,200*

1

14,21,27 36-39,60

PREVENTOL D2

2

PREVENTOL D3

2

"amine-formaldehyde condensation product as a cyclic amino-acetal"

BAKZID

9

"semiacetal"

BODOXlN

9

TRIS-NITRO*

14

ONYZIDE 500 MYACIDE Sl

8 15

64,73

XD 8254 DPNPA

1

14,37

PROXEL CRL*, XL*

16

14,21,27 37,39,60

KATHON 886*

17

14,31, 36-38

BUSAN 85*

18

14

BIOClDE 223

19

36,42

DOWlClL S-13

1

36

Formulae

Chemical

Oxazolo-oxazole

5-hydroxymethoxymethylI-aza-3,7-dioxa bicyclooctane

o@o CH 2 (OCH 2 ) n O H

Hexamine derivatives

cis 1-(3-cischloroallyi)-3,5,7triaza-1 -azoniaadamantane chloride (N-(3-chloroallyl) hexamine)

H2C

CHz

CH 2

"benzyl hemiformal" derivative

Ha

Acetamides

n-hydroxymethylchloroacetamide

CI.CHz. CO.NH.CH z OH

A L IPHA TIC DERI VA TI VES

NO2

i HOCH2- C - CHzOH

tris(hydroxymethyl)nitromethane (2-hydroxymethyl2-nitro-1,3-propanediol)

i

CH20H

N%

2-bromo-2-nitropropane1,3-diol

HOCH z - C - CH20H i

Br

2,2-dibromo-3nitrilopropionamide

N--C- C-C- NH 2 i

11,13,14, 21,27,37, 39,60,75

Br

ORGAIVOSULPHUR-NITROGEIV COMPOUNDS Thiazoles

1,2-benzisothiazolin-3-one / /0

2-methyl-4-isothiazolin-3-one + 5-chloro-2-methyl-4isothiazolin-3-one Dithiocarbamate

potassium dimethyldithiocarbamate Thiadiazine

1,5-dimethyltetrahydro-2thiadiazine

CH3 S H3C\ N ~:. -

CI/~s/N\cH

S.K

HsC /

3

F--s-..l~S N H3C/ V

N -.,CH3

Pyridine derivatives

2,3,5,6-tetrach Ioro-4(methyl-sulfonyl) pyridine

TRIBOLOGY international

CL[~IS02CH ~cr3 CI/"~ N ~/~CI

329

Sherman.- Biocides for aqueous metalworking fluids Chemical

Formulae

Examples of commercial products

ManuReference facturert

Zn O M A D I N E *

20

Na O M A D I N E *

20

BIOBAN P1487"

14

14,21 ;27, 36,37,39, 60

GIV-GARD D X N * DIOXIN (R)

21 22

t4,37 38

BIOBAN CS1135

14

36

VANTOCI L 1B

16

hexahydro-1,3,5-tris (2hydroxyethyl)-s-triazine + sodium omadine

T R I A D I N E 10"

20

14,31

2-chloro-N- (hydroxymethvl) acetamide + sodium tetraborate

GROTAN HD I1"

6

14,21,31

n-hydroxymethylchloroacetamide + "o-formal of benzylalcohol"

PARMETOL K50

sodium 2-mercaptobenzothiazole + sodium dimethyldithiocarbamate

VANCIDE 51 *

4

14,36,37

sodium 2-mercaptobenzothiazole + potassium NhydroxymethyI-N-methyl dithiocarbamate

BUSAN 52

18

37

1 -hydroxy-2(1 H)pyridine thione (2-pyridinethiol-1oxide): zinc or sodium complexes

\sJ

14,21,28, 36,37,39 2-1,27,36, 37,39,53, 60

MISCEL LANEOUS Morphol ines 4-(2-nitrobutyl)morpholine + 4,4-(2-ethyl-2-nitrotdmethylene)dimorpholine

~

r•CH•

Dioxanes

za5

,,cooc.soh.c,

2,6-dimethyl-1,3-dioxan4-ol acetate (6-acetoxy-2,4dimethyt-1,3-dioxane); (dimethoxane)

%/0

I

CH3

~H~

~ H3

Azolidines

NH

4,4-dimethyloxyazolidine + 3,4,4-trimethvloxyazolidine

Polymeric biguanide

H3CI~---~/N-CH~

NH I|

hexamethylene biguanide HCI

-

[-(CH2)sNH.C.NH.C.NH.(CH2)3 -], NH.HCl

MIXTURES

*Registered13 for use in cutting fluids by EPA. tManufacturers 1. Dow Coming, Reading, UK 2. Bayer (UK), Bury St. Edmunds, UK 3. BDH Chemicals,Poole, UK 4. R.T. Vanderbilt, Norwalk, CT, USA 5. Cochraneand Keen (Chemicals), Rochdale, UK 6. Sterling Industrial, Sheffield, UK •7. ABM Chemicals,Stockport, UK

330

8. Onyz Chemical Co., Jersey City, NJ, USA 9. Bacillofabrik Dr. Bode, Hamburg, FRG 10. Glyco, Greenwich, CT, USA 11. Chemag 12. BASF, Cheadle,UK 13. TennecoOrganics, Bristol, UK

14. 15. 16, 17. 18.

IMC, Des PJaines,IL, USA Boots,Nottingham, UK ICI, Manchester, UK Rohm & Haas, Philadelphia, PA, USA Buckman Laboratories,Memphis, TN, USA 19. Drew Chemicals, Boonton, N J, USA 20. Olin Corp:, Stamford, CT~USA 21. Givaudan,Whyteleafe, UK

December 1983 Vol 16 Number 6