Biocidal blends

Also, many biocide products tend to operate effectively within only a fairly narrow band of operating conditions. Therefore, for any particular cooling system under consideration, it is necessary to review the specific properties of each of the potentially suitable biocides or biocide blends and match these with the reported or observed system problems. 

There are almost countless combinations of biocide blends being used around the world, each product using two or three or possibly more of the primary products discussed in the previous section. Many combinations were originally designed for the pulp and paper industry and have been later adapted for cooling water and other applications. 

If the tannin blend is made from spray-dried powders, the dilution water must be heated to 160 to 180 °F and the biocide only added when the temperature has cooled below 140 °F. 

In the CIT/MIT blend the chlorinated species has by far the greater biocidal efficacy but is also the less stable of the two components. Although MIT alone has relatively low antimicrobial performance it has recently been discovered that this compound has truly synergistic activity when combined with BIT and such a blend has several advantages over CIT/MIT products. 

Although the "ideal biocide" for the wet-state protection of paints still waits to be discovered the recent development of the methyl/benz-isothiazolinone blend offers many advantages over currently used preservatives. 

This study was designed to evaluate the performance of commonly used biocides against the performance of a new liquid blend. In order to choose an effective preservative package, the two main criteria the biocide must have, are (i) to be approved by the US Food and Drug Administration (FDA) under sections 21 CFR 176.170 and 21 CFR 176.180 which cover components of paper and paperboard in contact with foods and (ii) to be designated as a safe biocide (low toxicity, non-sensitiser, easy to handle). The three most commonly used products (i) 5-chloro-2-methyl-4-isothiazolin-3-one + 2-methyl-4-isothiazolin-3-one, (ii) 1,5-pentanedial and (iii) l,2-benzisothiazolin-3-one, currently meet the above criteria. The new liquid blend, l,2-dibromo-2,4-dicyanobutane -I- 2-bro-mo-2-nitropropane-l,3-diol was also designed to meet the criteria. 

Apart from sodium hypochlorite and sodium bromide solutions, almost all other liquid biocides (or biocide intermediates) are nonoxidizer types. Most nonoxidizers are manufactured by specialist chemical companies, who sell these branded products for scores of different sanitizing or disinfection applications, of which cooling water system treatment is only one. These chemicals may be merely renamed (according to subregistration permits) or they may be blended with other biocides or inhibitors to form new and different products with accordingly modified properties. Some biocides may only be available from the primary manufacturer, often as extremely concentrated and hazardous materials. These chemicals will then usually require some form of dilution, stabilization, and quality verification before being incorporated into a service company s product line. 

Since those days, various other bromine-based biocides and biocide intermediates have been introduced onto the global market or found renewed favor. The most notable are sodium bromide, isocyanurate/NaBr blends, and DBNPA (a nonoxidizer available as a powder or solution, and recently introduced in tablet form). Most bromine biocides employ chlorine in some form as an activator to produce the primary biocidal species hypobro-mous acid (HOBr). 

From the preceding, it can be seen that there is a wide range of individual nonoxidizing biocides and blends available. None of the individual products are especially effective under all operating conditions or water qualities, although the newer individual biocides tend to perform better than older materials. However, several of these newer biocides are generally offered only by one or two primary manufacturers (examples are DBNPA, gluteraldehyde, isothiazolinones) and consequently are often the most expensive materials to use, on a cost-per-application basis. 

As a consequence (and for the most effective microbiological control), biocide programs should either employ suitable blends of individual products or provide for the application of two or three individual microbiocides that jointly provide the functions required. This point is frequently a more important reason for the use of dual biocide programs than the often reported justification of minimizing the risk of resistant strains. 

These products tend to have the highest degree of surfactant action. The cationic nature permits neutralization of the typically anodic biofilm. Cationics should not be used with anionic biocides, such as chlorophenols. Formulations tend to be based on a blend of BCP, quat, or polyquat and silicone defoamer. 

Hard-surface, usually metal, cleaning in which very specific kinds of dirt need to be removed, such as grease on engines, rust on metal parts, or burned carbon on cooking surfaces. The detergents may also need to be biocidal, such as blended non-ionic and quarternary amine surfactants. 

A standard Paint Research Institute latex paint, provided by J. F. Matthews of DuPont, was the reference sample to which the biocidal latex polymers were compared. After two months both the unweathered and weathered samples showed moderate or moderate to heavy growth on the paint surface. The unweathered samples showed severe stain intensities on basswood. The weathered samples showed medium stain intensities on both. When coatings of an MMA/nBA latex blended with a MMA/nBA/8 terpolymer latex were tested, only trace growth of Aureobasidlum pullulans on the coatings was observed using pine or basswood substrates. 

Dimethylol-5,5-dimethylhydantoin (DMDMH) and 3-methylol-2,2,5,5-tetramethylimidazolidinone (MTMIO) were mixed in different ratios in textile finishing systems for cellulose fabrics. The mixtures of 2,2,5,5-tetrame thylimidazolidinone (TMIO) and hydantoin rings on the grafted cellulose provided a combination of imide, amide and amine halamine stmctuies in different ratios after chlorination. These combinations improved both the power and stability of the biocidal properties of the treated cotton and polyester/cotton blend fabrics studied. Repeated laundering tests showed that even a small amount of added amine halamines could substantially reduce the loss of active chlorine and increase the power of the biocidal functions on the fabrics. The results were discussed. 12 refs. 

Cotton fabrics and cotton/polyester blend fabrics were treated in different finishing baths containing water repellent only, water repellent and a biocidal precursor (dihydro xymethyl-5,5-dimethylhydantoin, DMDMH), or DMDMH only. The antibacterial efficiency of the treated fabrics was tested against Staphylococcus aureus and Escherichia coh. Fabrics treated with water repellent only showed no antibacterial efficiency, whereas those treated with DMDMH either with or without water repellent showed excellent antibacterial efficiency. 4 refs. 

In many applications the additive consists of blends of different biocides to widen the biocidal spectrum. Biodispersants may be included in the blend. 

Blends of biocides (available from treatment companies) are usually supplied under a trade name. 

Some biocides and blends may be the subjea to patent protection. 

Carbendazim Antifungal performance Leach resistant Very cost effective Causes no colour shifts Good pH and heat stability Blends well with other biocides Efficacy gap against Altemaria sp. Future classification as Category n Mutagen Cannot have in clear systems... 

OIT Good broad spectrum fungicide No colour shift in coatings Can use in clear formulations Good stability in coatings Blends well with other biocides More expensive than carbendazim Labelling as a sensitiser at 500 ppm Can have leaching... 

IPBC Good broad spectrum fungicide Can use in clear formulations Blends well with other biocides Good stability in coatings Can cause colour shifts in coatings More expensive than carbendazim Some leaching possible Contains halogens Newly classified as a sensitiser... 

Diuron Good antialgal performance Does not cause colour shifts Very cost effective Can have in clear systems Blends well with other biocides Classified as a Category III mutagen Some leaching possible Halogen containing... 

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