SEPTOPAG varnish: the deadliest enemy of bacteria, fungi, and algae

The Institute of Ecotechnologies has recently developed biocidal varnish Septopag that finds applications in various fields. The waterproof organosoluble varnish Septopag can help to solve efficiently and reliably such problems as drinking water preservation, protection of surfaces from biofouling, disinfection of indoor premises, protection of timber, etc.

Vast numbers of various bacteria, viruses, fungi, algae, molluscs, and other micro- and macroorganisms inhabiting air and water environment cause biofouling and biocorrosion. Humans and animals suffer most from the implications of biofouling. They are those that are most susceptible to dangerous infectious diseases with respiratory and contact transmission paths (in the latter case contamination occurs on contact with the biofouled surfaces inhabited by the pathogens).

Many intestinal, respiratory, and purulent diseases belong to this dangerous group, as well as hepatitis, tuberculosis, and other diseases. Drinking water is often the source of pathogens. This occurs when the treated water suffers secondary microbial contamination on contact with atmospheric air and becomes unsuitable for drinking.

The activity of microorganisms causes rapid decay of various engineering structures and technological equipment made of metals, concrete, brickwork, wood, and polymeric materials. Vital activity of mould fungi, nitrifying and thionic bacteria can cause various destructive changes of the surfaces. These changes include pigmentation, buckling, scabbing, and peeling of the painted or plastered layer, and also dust-like deposit formation, cracking, loosening, and repelling of plaster and brickwork.

Rapidly multiplying bacteria are usually the first to inhabit the solid surfaces submerged in water. They excrete substance (such as acids, alcohols, and ketones) having corrosion activity against metals. Bacteria together with diatomaceous algae and protozoa form the primary slimy film on the underwater surfaces.

This film facilitates precipitation and propagation of biofouling macroorganisms (other algae, water plants, sponges, Crustacea, molluscs, etc.). Biofouling causes operating efficiency reduction of heat exchange systems, decrease of water pipeline flow capacity, reduction of watercraft velocity, increase of wear in machines and mechanisms, fuel consumption increment, and failure of navigational and scientific equipment.

The Institute of Ecotechnologies has developed organosoluble biocidal varnish Septopag to prevent various types of biofouling and biocorrosion. The active biocidal agents of the Septopag varnish are various polyalkylene guanidine (PAG) derivatives chemically bound to the polymeric film-forming base. The Septopag varnish is able to form strong waterproof coatings on the treated surfaces that preserve their biocidal properties in air and water environment.

The possible applications of the water-resistant biocidal varnish are manifold. These include disinfection of indoor surfaces, timber protection from mould and colouring fungi, protection of equipment working in long-term contact with water from biofouling and biocorrosion, and drinking water conservation.

Disinfection of indoor surfaces

Dust particles carried by the air accumulate a vast number or microorganisms. Dust precipitates in all the locations of living quarters (including the least accessible ones) forming potential sources of various pathogens.

Nowadays wet cleaning of indoor premises is one of the most widespread techniques for preventing infection propagation in medical and care facilities as well as in household. Water solutions of disinfectants are used to enhance the antimicrobial efficiency of wet cleaning. The most often used disinfectants are those containing active chlorine, phenol, quaternary ammonium compounds, and other toxic chemicals. This disinfection technique allows reducing the bacterial contamination of the treated surfaces by 93-97%. However, within 3-4 hours after the treatment the contamination level increases up to the initial value.

The Septopag varnish can be used both for indoor and outdoor applications: the coating does not lose its biocidal properties under the impact of atmospheric precipitation.

The IET has developed PAG-based water-soluble biocides Biopag and Phosphopag that remain on the treated surface for as long as 6 months, which is proven with X-ray photoelectronic spectroscopy (XPS). These biocides retain at least 84% of their initial antimicrobial activity by the end of this term.

The Institute has also developed biocidal paints and varnishes that have a more prolonged activity. These include the Septopag varnish and various paints of the Biokrapag series, which are also based on polyalkylene guanidines.

Organosoluble varnish Septopag is a waterproof coating material that contains Biopag chemically bound to the film-forming hydrophobic base. The varnish can be applied to the wall surface with a brush or roller; it forms a strong waterproof polymeric coating on the treated surface after drying. The biocidal activity of such coating is stable for at least 18 months. There is no need to apply other disinfectants to this surface during this term; dust can be washed off the polymeric coatings using conventional detergents and water.

The Disinfectology Research Institute of the Public Health Ministry of Russian Federation performed efficiency tests of the Septopag varnish. These tests have shown that the varnish coatings causes complete deactivation of bacteria within 60minutes, of yeast-like fungi within 2hours, and of tuberculosis mycobacteria within 24hours.

High antimicrobial efficiency of the coatings remains even after multiple repeated contamination of the test surface with microbial culture, and also when dry test culture was used or protein pollution was present. After treatment of surfaces contaminated with mould fungi, development of mould under the coating stops. An essential property of the coating is that after drying it is absolutely safe for humans and can therefore be used even in the sick wards.

The Septopag varnish can be used for long-term preventive disinfection of premises intended for accommodation of large number of people, rooms with moist air, and also rooms for some reason or other unsuitable for everyday treatment (prison cells, hospital rooms for insane patients, etc.). In all cases the varnish coating ensures a long-term (at least 18 months) protection of the treated surfaces from microbial attacks, reduces concentration of microorganisms in air, allows to save disinfectants, and reduces the workload of the personnel.

The possible applications of the water-resistant biocidal varnish are manifold. These include disinfection of indoor surfaces, timber protection from mould and colouring fungi, protection of equipment working in long-term contact with water from biofouling and biocorrosion, and drinking water conservation.

The biocidal additive in the Septopag varnish is chemically bound to the polymeric base and cannot be leached from the coating by water. Therefore this varnish can be used both indoors and outdoors: the coating does not lose its biocidal properties under the impact of the atmospheric precipitates. Yet another advantage of the Septopag varnish is that it can be applied at any time, and not only during the redecoration.

Timber protection

The Septopag varnish forms a water-resistant coating with a natural yellowish tint on the surface of the treated wooden objects. This coating protects the treated surfaces from mould and coloring fungi. Efficiency tests of the Septopag varnish were performed at the Senega lab for wood protection. Based on the results of these tests the Septopag varnish was characterised as a high-efficiency chemical for protection of dry timber

The efficiency of the varnish can be enhanced if the wood is pre-treated with water-soluble biocidal biocides (e.g., of the PAG group), which can penetrate the bulk of the wood. The varnish can also be used as a biocidal primer before decorative painting of wood.

The Septopag varnish is recommended for bioprotection of wooden structures used in moist, closed, poorly ventilated indoor premises or outdoors under the impact of atmospheric precipitates.

A remarkable property of the Septopag is a complete lack of toxicity of the varnish coating, whereas most chemicals currently used for wood protection contain heavy metals and other highly toxic substances that pollute the environment.

Drinking water conservation and protection of surfaces from biofouling

The non-fouling coatings of the following two types are mostly used for protection of surfaces exploited in a long-term contact with water:

  • coatings consisting of a soluble film-forming base and biocide;
  • coatings consisting of non-soluble film-forming base and soluble biocide (the latter type is called contact or diffusion type).

Self-polishing coatings belong to the soluble type. These are based on carboxyl-containing organotin polymers, which become water-soluble via hydrolysis and evolve biocide. Such coatings are effective only in case of dynamic conditions (e.g., when the watercraft is under way, so that the evolving biocide neutralises the biofouling microorganisms that are washed away by the water flow together with the eroding polymer). Under static conditions (e.g., when the watercraft is at anchor), however, such coating cannot prevent biofouling.

In coatings of the contact (diffuse) type the biocide is also gradually leached from the coating. Transport of biocide from the inner layers of the coating in this case is due to diffusion in the capillary channels formed in this coating. The requirements to the coatings (polyvinyl chloride resin, chlorinated rubber, Nairit (polychloroprene rubber), polyisobutylene, butyl rubber, epoxy resins, etc.) are the following.

It should have high mechanical strength, low swelling factor in water, and be able to contain large amount of biocide (40-60 volume%) and neutral filling substances, and, on the other hand, form coatings with high enough penetrability so as to allow biocide leaching by water.

A common belief is that the biocide contained by the coating can act on the biofouling microorganisms only when it is dissolved in water and ensures in the near-wall laminar layer of water the saturating concentration determined by its solubility. To ensure a guaranteed protection, this concentration should exceed the lethal dose for the microorganisms.

Environmental safety requirements impose strict limitations on the biocides. Copper compounds (copper protoxide) answer the requirements best. Application of organotin compounds is also permissible, because they can be transformed into non-toxic substances under the action of atmospheric factors.

The following compounds have repellent properties: acrylamide, benzoic, barbituric, and tannic acids, indole, tetramethylethylene diamine, thiourea, and phenylthiourea. Coatings containing oxyethyl cellulose, polyethylene oxide, hydrophilic acrylic resins, fluorinated graphite, vaseline oil and paraffin-based mastic compounds reduce the adhesion of biofouling organisms to the treated surface. However, adhesion-reducing coatings have low efficiency without biocides.

Following the environment safety considerations, application of biocides containing highly toxic compounds of mercury, arsenic, and lead in non-biofouling coatings is forbidden. These compounds are accumulated in the organisms of hydrobionts and can easily get into the human organisms via food chain.

A principally new approach to the creation of non-biofouling coatings of contact type was used in developing the Septopag varnish. This approach allowed solving the problem of developing effective anti-fouling coatings meeting the environmental safety requirements.

This approach consists in cross-linking the water-soluble polymeric biocide of the PAG family to the hydrophobic polymer used as the film-forming base of the varnish via an interpolymer chemical reaction. This results in chemical binding between the macromolecules of the film-forming polymer and the PAG derivative. These bonds are sufficiently strong to prevent biocide leaching and washing away by the water flow, on the one hand.

On the other hand, these bonds are rare enough to leave many unreacted guanidine groups that explain the biocidal activity of PAGs. Thus the composite polymer forms strong coatings with biocidal properties. The coating that Septopag varnish forms on the treated surface has high adhesion and water resistivity characteristic for the hydrophobic film-forming polymer, and high biocidal properties of PAGs.

Tests of Septopag coatings in water environment were performed as follows. A steel plate covered with the varnish was put into an experimental tank filled with tap water. Another plate exactly like the first one, but without coating, was put into the control water tank. Microbiological and chemical analysis of water from the tanks was performed regularly over several months. The total microbial number (TMN) was also measured in the probes taken from the surface of the test and control plates and the walls of both tanks.

Figures1-3 show that a rapid increase of the TMN occurred both in water and on the submerged surfaces in the control tank. The presence of the plate coated with the Septopag varnish inhibits essentially the increase of the TMN both on the surfaces and in water. At the same time, the chemical analysis of water in the test tank did not show any presence of free biocide (PAG) in the water of the test tank.

According to the microbiological and chemical characteristics, the water in the test tank continued to comply with the requirements for drinking water for a long time.

The results of the performed experiments show that the Septopag varnish can be used for conservation of drinking water, and also for prevention of biofouling of surfaces exploited in water environment for a long time.

Irina VOINTSEVA,

Dr.Sci. (chemistry)

Alexander DITYUK,

Ph.D. (physics)

Deputy director of the

Institute of Ecotechnologies

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