Biocides face challenge of ever changing needs

06 January 1992 00:00  [Source: PCE]

Biocide formulations are constantly facing new challenges to enable customers' products to comply with environmental legislation, without compromising performance, writes Janet Dansie.

Paints and coatings, as a major market for biocide producers, has undergone change as a direct result of environmental awareness. The ecological effects of anti-fouling marine paints came to prominence several years ago. Since then environmental pressures to develop waterborne, rather than solvent-borne, paints, coatings and adhesives have increased. However, these products are still vulnerable to bacterial and fungicidal attack.

Environmental considerations are not the only headache. Dr Mike Parkin recently joined Nipa Laboratories (a member of the biocides division of BTP) as senior sales manager and has extensive experience in the development of industrial biocides for use in the polymer, paint, adhesive, metal working fluid and water treatment industries.

He says, 'Selecting an industrial biocide to preserve polymer emulsions, adhesives and paints can be fraught with difficulties. To begin with, there are often constraints placed on the manufacturer which are determined by the end application, or market forces. Indirect food contact applications will limit the choice to a handful of active ingredients.'

For instance, 'formaldehyde-free' is a common request in Europe today and it is certain that the list of favoured biocides will diminish, rather than grow, over the next five years. For these reasons, it is important to ensure that the biocide used will be acceptable to a wide customer base, not only now, but in the future.'

Biocides are reactive chemicals and under certain conditions they may be adversely affected by other raw materials in a formulation. There is no single active agent which is free from this problem and it is therefore important that the selection process takes into account biocide incompatibility and deactivation.

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Combining suitable active agents in a biocide formulation ensures these difficulties are minimised. It is often the case that the combination product offers greater cost-effectiveness, improved performance and a more diverse range of applications.

Isothiazolinone chemistry has been widely employed to preserve water-based emulsions, paints and PVA adhesives. Chlor-methyl-isothiazoline combined with formaldehyde-releasing condensates, such as N-methylochloracetamide and glycol-formals, results in an extremely potent and highly cost-effective biocide, says Parkin. Products of this type have been used, virtually without exception, by the paint industry until recent years.

Formaldehyde-free

The desire to remove formaldehyde has meant reformulation and problems for a number of manufacturers. Chlor-methyl-isothiazolinone is not without its problems - high pH and the presence of reductants may adversely affect activity. However, it remains an effective weapon against bacterial attack in many applications.

Benzisothiazolinone (BIT) has been widely accepted as an industrial biocide for a number of years and is often the preservative used when being formaldehyde-free, environmental acceptability, FDA/BGA approval, thermal stability and long term efficiency are prime requirements.

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Nipa Laboratories now produces and supplies BIT as 10% and 20% active solutions, a 33% pourable dispersion and as the active agent in the form of BIT pressed paste. Technical and production flexibility enables Nipa to combine BIT with a wide range of other well-known active agents, many possessing FDA/BGA indirect food contact approvals.

This market-led and industry-focussed initiative has optimised the benefits of BIT for specific applications, including PVA emulsions, SBR latices, emulsion paints and adhesives, resulting in a comprehensive selection of novel BIT-based biocides.

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ICI Biocides, which launched a solvent-free biocide, Promexal W50, for paints, adhesives and latex last year, has announced two new patented formulations, one for use in paints, the other in PVC.

Densil SP is designed for the preservation of solvent based paint films against both fungal and algal attack. Fungi occur both indoors and outdoors on paint films, especially under damp and humid conditions, both in domestic use, such as bathrooms and kitchens, and in industrial applications like breweries, dairies and food-processing plants. Water penetrating a damaged paint film and soaking a wooden substrate is likely to lead to the more serious economic threat of decay caused by wood-rotting organisms.

Algae require light to maintain their biological (photosynthetic) processes, so they tend to occur most frequently on exterior paint films, as well as concrete, stone and metal. The presence of algae is a cause of concern to the paint manufacturer because the large surface areas and light colours usually involved allow various coloured swathes of algae to show up very clearly. They can tolerate a wider range of acid and alkaline conditions than fungi and derive their energy from carbon dioxide in the air.

A suitable fungicide/algicide for dry film preservation must have specific properties to meet the needs of the paint manufacturer:

• Adequate control of micro-organisms associated with the defacement and/or degradation of paint films.
• No loss of anti microbial efficacy, due to leaching of relatively water-soluble preservatives from paint films.
• No discolouration of the paint film following light-induced degradation of the preservative.
• No adverse effects on dry film, causing incompatibility between the preservative and paint ingredients.
• Ease and safety of incorporation into the paint.

In contrast to most existing dry-film preservatives which are powders or pastes, ICI's Densil SP has been formulated as a free-flowing liquid in white spirit. This makes it easy to incorporate and it is completely pumpable, thus removing the handling hazards associated with the use of powders. It is claimed that the product has no adverse effect on the theological properties of solvent-based paints and has good storage stability.

Vulnerability

The other new product, Densil DOP, is a fungicide for PVC. Plasticised PVC is vulnerable to fungal attack in applications where it is exposed to moisture, sunlight, or both. These include car tops, flooring, pool linings, waterproof clothing, horticultural film and shower curtains.

Vulnerability is being increased as heavy metal stabilisers are phased out. Fungi do not attack the PVC itself. They use the plasticisers, fillers, pigments and other additives as nutrients. They convert the plasticiser into smaller, organic compounds, which can be used by both fungi and bacteria.

The degradation of plasticiser causes embrittlement, loss of tensile strength and PVC integrity, and destroys the appearance of the film by surface growth and the production of coloured metabolites. The most susceptible plasticisers are sebacates, epoxidised oils, polyethers and glycolates.

Most of the biocides currently in use have serious shortcomings, says ICI. Arsenic-based compounds, themselves open to environmental and toxicological concerns, are not light stable. Other non-arsenic based compounds easily leach out, providing only short-term protection.

ICI says that Densil DOP has been tailor-made to overcome these defects. It is not based on heavy metals and, being stable to heat, is unaffected by normal PVC processing conditions. A liquid formulation of the active ingredients in dioctyl phthalate, it differs from arsenic compounds, in that it is stable in UV light.

Both Densil SP and Densil DOP are liquid formulations, said to be easily pumped and dosed, minimising workers' exposure. The hazards of dealing with solid biocides, such as inhalation of fine particles, are eliminated and uniform distribution is achieved throughout the whole product batch.

Also aimed at the preservation of plasticised PVC, PU and sealants are the first two grades in a range of metal-free biocides recently introduced by Brussels-based Morton International. They are to be known as IT-3020 DOP and IT-4020 DOP. Further details will be available shortly.

Non-metallic fungicides are also the basis of Troy's Troysan range of products. Troysan Polyphase P100 is a powdered, broad spectrum fungicide/mildewcide (technical grade 3-iodo-2-propynyl butyl carbamate 97% min) for use with aqueous and solventborne interior and exterior paints, wood preservatives, metal working fluids, adhesives, paper coatings, inks, plastic coatings etc.

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Other fungicides, for similar areas of application, are in liquid form. Troysan Polyphase EC17 is an emulsifiable, freeze-stable concentrate, for use in aqueous systems such as latex paints and stains, leather and textile processing solutions, joint cements, caulks and sealants. The company also produces broad spectrum, non-metallic bactericides with a wide range of applications.

The negative impact of tributyltin compounds on the marine environment has prompted interest in the development of alternative antifouling agents for marine paints. Olin Chemicals has discovered that its zinc Omadine biocide, originally developed as an antidandruff agent, can also be used effectively in antifouling systems when used in combination with cuprous oxide or cuprous thiocyanate. It is said to have a broad spectrum of activity against bacteria, fungi and algae.

In tests against various other antifouling paints, including one based on TBTO copolymer, paints containing a combination of zinc Omadine antifoulant and a cuprous salt were shown to be virtually free of fouling after 12 months of exposure.

This combination was also said to be more effective than either biocide alone. It was demonstrated that surprisingly low levels of zinc Omadine antifoulant are effective, 3-5%, with 35-40% cuprous oxide, calculated on dry film weight.

Other applications

Zinc Omadine biocide can also be used in paint formulations to control mildew, would and other bacteria, and can help eliminate premature product degradation, discolouration and musty odours.

A non-metallic fungicide, said to be effective in non-aqueous coatings, is Fungitrol 11-50S, from Servo Delden. The product is supplied as a pumpable liquid, said to be easily added. Its principal features are that it is non-toxic and non-dermatitic at the recommended levels, highly-effective against a variety of micro-organisms and suitable for use in exterior and interior systems.

Dr Straetmans, the Hamburg-based formulator, represented by Ferguson & Menzies in the UK, offers protection agents for the paint industry; particularly the anti-fouling, low toxicity, ES-AF 40, which is an algicide/fungicide formulation for boat paints. Included in the range is Paint Additive MPA, a coalescing agent with antimicrobial and antifoaming properties, said to promote film formation at low temperatures.

Personal care and cleansing is another important area for biocides. Dr Straetmans has introduced SSL-664, a new fragrance combination with stabilising microbiological properties. This material possesses a broad spectrum of activity against organisms normally used in microbiological tests (Staph. aurea, Esch. coli, Ps aeruginosa, Cand. albicans, Asp. niger) and others casing problems in practice.

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This product is said to be skin friendly, as it is created from nature-identical ingredients which are biologically soft and degradable. They are also claimed to increase cleaning properties and act as organic solvents.

SL-664 is said to be especially useful to stabilise surfactant formulations, such as foam baths, gels, hair-care products and other personal cleaning preparations.

Antibacterial agents for personal care and beauty products are among the range from Angus Chemie, building on its basic nitroparaffins business. Biopan BNPD is recommended as a preservative for creams and lotions, specially those containing aloe, lanolin, jojoba and other natural products. It is soluble in water, alcohols, glycols and other polyols. It also retains its activity in the presence of most commonly used cosmetic and toiletry surfactants.

Biopan is said to be inhibitory to Pseudomonas, which is difficult to control with most antimicrobial agents and can develop resistance to preservatives. Angus Chemie asys that to date no strains of microorgansims have been reported that have acquired resistance to Biopan BNPD.

Oxaban A has been specifically designed for use in cosmetic products, being effective over a wide range of pH against a broad spectrum of micro-organisms. It is also claimed to be an effective alkaline pH buffering agent and a corrosion inhibitor in many aqueous systems.

In addition, the fatty acid salts of Oxaban A can function both as antimicrobial agents and as anionic surfactants for oil-in-water emulsification. The product is a cyclic substituted amine, containing no metal compounds or any organic derivatives of sulphur, phosphorous, halogens or boron. The chief ingredient is 4,4-dimethyl-1,3-oxazolidine.

Low-toxicity biocides

Bactria Laboratories currently produces over 40 low-toxicity biocides, widely used in synthetic latices, dispersions, aqueous-based emulsions, surfactant-based products and in sectors of the polymer and oil industries.

The chemistry of Bacteria Laboratories' biocides is broad-based, with both single active agent heterocyclic compounds and application-specific formulations; combining formaldehyde condensates, organo sulphur chemicals, N- & S- compounds, amine derivatives and isothiazolinone. As the physical form is important to certain customers, biocides are produced in both aqueous and solvent systems and in milled dispersions of insoluble actives.

The company has recently built a dedicated biocide manufacturing and formulation plant at Stallingborough UK, flexible enough to accommodate a diverse range of products while complying with challenging environmental demands.

Bactria's R&D effort is closely linked to customer requirements, developing precise formulations for the preservation of products such as a latex based adhesive, or a cutting fluid with particular properties. The company has the capability to take such a formulation from short test runs right through to production scale. Facilities include steam-jacketed reactors for pilot scale and bulk production, and fully-integrated blending vessels with sophisticated solids handling and dispersing equipment.

The Albright & Wilson Biocides Group has developed a range of products based on the active ingredient THPS, tetrakishydroxyme-thylphosphonium sulphate. The use of THPS has been patented worldwide by the company and is being developed for many applications.

Benefits

Among the benefits claimed for using THPS, compared with traditional products, are its broad spectrum of activity against microorganisms, rapid kill rate, compatibility with a wide range of water treatment chemicals and simple on-site measurement. It is said to be completely water soluble and insoluble in oils and many organic compounds, stable over I a wide range of pH, temperature and pressure and can be deactivated by a patented activated carbon method.

The chief reason for developing THPS has been to minimise environmental impact. It is said to have a low wildlife toxicity, to be inherently biodegradable (OECD 302B test) and, in its initial breakdown product, THPO, there is said to be an extremely low toxicity to mammals and fish.

The Tolcide PS range of products containing THPS, has been designed to meet certain identified market needs:

• 70%w/w THPS in a concentrate containing minimum amounts of additives. This allows formulation to suit end use applications.
• 70%w/w THPS in a formulated product which, on simple dilution with water, generates a ready-to-use product.
• 35%w/w THPS and lower active concentrations. All are fully formulated and suitable for direct use in a variety of applications.

The Tolcide PS range is claimed to be suitable for applications including the oilfield industry, industrial water treatment, pulp and paper manufacture, timber preservation, adhesives and coatings.

A recent development is Tolcide C60, a 60% concentrate of TCMTB, thiocyanomethylthiobenzothiazole, already known to be an effective biocide. This product had been developed to allow TCMTB to be used in a liquid form which is simple and safe to handle without the need for careful heating of the biocide containers. It remains liquid even at low ambient temperatures. Applications include leather, pulp and paper, water treatment, timber and coatings. As well as bactericidal and fungicidal properties, TCMTB is said to achieve good penetration into organic substrates, giving long term preservation.

Berol Nobel reports that in the quaternary ammonium compounds market the company is experiencing a continuous and increasing shift from benzalkonium chloride to twin chain quaternaries. Berol is increasing its level of activity in the industrial and institutional market and new product developments are expected as a result.

The Berol Nobel's Querton range has particular applications in areas where there is a need for very careful bacterial control. It includes Querton 210Cl-50 and its concentrated form, Querton 210Cl-80;, didecyldimethyl-ammoniumchlorides said to have a very strong bactericidal and fungicidal effect in foodstuffs, brewing and medical care. Querton 14 Br 40, a 40% active tetradecyltrimethyl-ammoniumbromide bactericide, is used in cosmetic and surgical scrub formulations.

Another biocide with medical applications has been launched recently by Hoechst UK's surfactants division. Dodigen 3519 is described as a powerful quaternary with a very broad range kill. This, combined with the absence of chloride ions, is said to make the biocide particularly effective for the sterilisation of surgical instruments, with no corrosion effects to V2A and V4A stainless steels. It can also be incorporated in cleaning formulations, particularly for high risk areas in hospitals and food preparation plants.

Two other recent products, Genapol 3520 and Genapol 3725, are low foaming, biodegradable, biocidal additives for industrial bottle washing. These products have undergoe extensive trials in Germany, in conjunction with the Bavarian State Brewery, Weihenstophen, with satisfactory results, according to Hoechst.

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