by Irina VOINTSEVA, Dr. Sc. (Chem.), senior researcher,A. Nesmeyanov Institute of Hetero-Organic Compounds, RAS; Genrich TSEITLIN, Dr. Sc. (Chem.), Head of Chair of Chemistry and Polymer Film-Forming Materials; Russian Chemical- Technological University named after D. Mendeleyev; Olga SKOROKHODOVA, Cand. Sc. (Tech.), Director of EVTMA firm
Fighting microbes causing dangerous infections in people and animals has been, and remains, one of the most "ancient" and vital areas of research.
Concerning what we call "biological damage" to materials and equipment it is caused by various bacteria and viruses and also fungi, algae, and molluscs which are present in vast amounts in our environment. Given favourable conditions, they can change, often beyond recognition, the appearance and physical-mechanical properties of materials lacking "biological resistance". The targets of such damage in building construction, for example, are wood, bricks, masonry, concrete, metal and polymer articles. Damage to their surface caused by mold, nitrifying and thionic bacteria manifests itself in the form of powder-like coatings, pigmentation, swelling, peeling and scaling off of paint and plastering.
The main method of prevention consists in the use of water solutions of desinfectants (chloractive,
Disinfection of surfaces by INTERCIDE varnish (1) as compared with control samples (2) at the Research Institute of Transplantology of the RF Ministry of Health.
phenolic, ammonium and such like compounds). These help reduce by 93 - 97 percent bacterial "pollution" of surfaces. However, as often as not, the contamination is restored in a matter of 3 to 4 hours and almost at the original level.
PAINT-AND-VARNISH MATERIALS WITH BIOCIDAL ADDITIONS
The main requirements for biocidal compounds are high efficiency at low concentrations, broad spectrum of applications and low toxicity for warm-blooded organisms. These substances should also be colorless, non-volatile, fit for storage, compatible with various paint-and-varnish components as well as inexpensive. Unfortunately, many of them lose their fungicidal * properties when in contact with paint. The few available domestic preparations of this kind are produced either on the basis of phenols, banned a few years ago, or ecologically harmful polymers with admixtures of low-molecular stannic-organic compounds. The most promising biocidal additions to paints and varnishes which meet the above requirements are salts of polyhexamethyleneguanidine (PHMG) whose polymer chain links contain positively charged guanidine clusters of three NH-groups at the central carbon atom. These salts are high-molecular analogs of the commonly known preparation chlorhexine, but they are more effective and less toxic than low-molecular ones. Polyguanidine mixtures were produced in Russia for the first time in the late 1960s by Dr. Pyotr Gembitsky at the Institute of Petrochemical Synthesis named after A. Topchiev of the USSR Academy of Sciences.
In principle, guanidine compounds are very common in nature and find applications as physiologically active substances. They include, for example, arginine, folic and nucleic acids and numerous proteins. The guanidine group is an active component of many preparations (sulfaguine, ismeline, pharingocept), including antibiotics (streptomycin, blasticidine and mildomicin). The aforesaid PHMG synthetic salts are well known for their bactericidal virulecidal, fungicidal, algicidal, pesticidal and insecticidal effects.
* Fungicides - agents that destroy fungi or inhibit their growth. - Ed .
INTERCIDE varnish (1) for wood protection in 100 %-moisture conditions as compared with polycept (2).
Preparations on the basis of PHMG are produced in this country under different trademarks, like polycept, phogucide, biophage, phosphophage, anavedin, Bior-1, etc.
Specialists of the Institute of Ecologo-Technological problems have developed a range of BIO-KRAPAG paints and varnishes on the basis of alkyd * and water-dispersion materials. They have passed microbiological and climate tests including those in medical establishments, food and agro-industrial enterprises.
The use of biocidal BIOKRAPAG paints for indoor applications ensures complete antimicrobic protection (for no less than one year) of the walls, ceilings and equipment without any additional disinfection... Painting of offices and living premises with biocidal paints and varnishes makes it possible to rapidly normalize what we call sanitary conditions, prevent spreads of infections and contamination of premises with mold fungi.
WATER-RESISTANT BIOCIDAL COATINGS
Of great complexity (because of stringent ecological requirements) is the problem of producing biocidal paints for the protection of the surfaces of materials and equipment in humid environment. Processes of what we call biocorrosion overgrowing actively manifest themselves upon river and marine hydrotechnical structures, ship hulls, instruments and mechanisms which are in constant contact with water. While occurring both in salt and fresh water, they are most intense on the former, causing serious maintenance problems and breakdowns. They affect the performance of heat exchangers and water pipes, slow down ships, cause increased wear of machinery and equipment, increase fuel consumption and interfere with the normal functioning of navigational and scientific instruments.
The first "settlers" on hard surfaces in water are bacteria which secrete corrosive substances (acids, alcohols and ketones ** ). Together with diatomic (single- cell) algae and protozoa bacteria they form a primary mucous film which promotes the sedimentation and development of microorganisms on the surface (algae, sponges, worms, crustaceans, molluscs, etc.).
The main method of protection of river and marine transport and equipment consists in applying protective paint and varnish coatings in many layers. The best fillers and fast-drying knotting varnishes can protect marine vessels from bioovergrowing for 2 to 3 years. Protective coatings include those with soluble film-forming base and biocide and insoluble film-forming and soluble biocide (coatings of "contact" or diffusion type). The former include self-polishing coatings produced on the basis of carboxil-containing tin-organic polymers. In the process of hydrolysis they release biocides and become soluble in water. Such materials are effective
* Alkyd resins-thermoplastic or thermosetting synthetic resins made by heating polyhydroxy alcohols with polybasic acids and used for protective coatings. - Ed .
** Ketone - organic compound with a carbonyl group attached to two carbon atoms. - Ed.
INTERCIDE effect for protection from bio-overgrowing of surfaces in stagnant water: 1 - plate treated with preparation, 2 - wall of tank with water over plate with the preparation, 3 - wall of control tank with water.
only when a vessel is moving, when the friction of its hull against water is reduced and the liberated biocides neutralize micro- and macroorganisms which are washed off the surface together with dissolved polymer. In that case, however, the overgrowing of hulls is increased during stops.
The biocide, however, is leached out from coatings of the contact (diffusion) type. That is why the film-forming base of the latter (epoxy and perchlorovinyl resins, chlorinated rubber, Nairit, polyisobutylene, butyl rubber, etc.) must possess high mechanical strength, slightly swell in water, contain large volumes of biocide and neutral fillers, and, at the same time, produce coatings with the necessary permeability for seawater which leaches out the biocide. For the formation of what are called transport capillaries it is necessary to add to the paint colophony which is readily soluble in salt water. The level of water-soluble biocide in paint should amount to 40 - 60 percent.
Chemical agents introduced into non-overgrowing coatings are divided into biocidal ones and repellants. The latter are more preferable as having a lesser impact on the biosphere.
The main varieties include copper peroxides and tin components. But meeting best the modern requirements of ecological safety and protection of the environment are the former ones. Banned are highly toxic compounds of mercury, lead and arsenic as being accumulated in hydro-biota and easily getting into human organism through food chains.
Possessing repellant effect are: acrylamide, benzoin, barbituric and tannic acids, indole, tetramethylen-diamine, thiourea and phenylthiourea. Ethoxycellulose, polyethyleneoxide, hydrophilic acrylic resins, fluorinated graphite, mastics on the basis of paraffin and mineral oil reduce the adhesion of micro- and macroorganisms to the surface and the friction when a vessel is in motion. But all of these substances are of little effect without the addition of biocides.
It has to be stressed that anti-overgrowth properties of paint coatings can be boosted by the administration of several preparations. To suppress the growth of algae zink oxide is added to the paint because it is effective algicide which increases the rate of dissolution of copper thus boosting its preventive effect. To improve cer-
Effectiveness of INTERCIDE for water conservation: 1 - water over plate with preparation, 2 - water in control tank.
tain technological characteristics one can add to the paints and varnishes derivatives of carbamic and salicylic acids, thio- and isocyanides which possess bactericidal effect.
The biocide present in a coating impacts microorganisms only when passing into an aqueous medium and building up in the near-wall laminary layer of water in a sufficient concentration equal to the solubility factor of this preparation which should be lethal for microorganisms.
FROM POLYMERS TO NANOPARTICLES
The most promising and safe are coatings of contact type in which the hydrophilic biocidal preparation is chemically linked with the hydrophobic film-forming material. In this case the harmful biocidal component is not leached out in water and does not get into the environment. But low-molecular substances cannot be used for such coatings because their biocidal properties are lost in any chemical reaction.
As a result of studies by Dr. Irina Vointseva of the Institute of Hetero-Organic Compounds named after A. Nesmeyanov it has been possible to develop and patent INTERCIDE biocidal varnish containing highly biocidal PHMG hydrophilic polymer. Its film-forming base is hydrophobic polyethylene whose repeated links contain functional groups which interact with the guanidine PHMG groups. The substance is a solution of interpolymer in an organic solvent. Left after its evaporation is a colorless waterproof coating with good adhesion to wood, plastics, concrete, tiles and other materials. Laboratory microbiological and toxicological tests of INTERCIDE conducted at the Scientific Research Institute of Desinfectology of the RF Ministry of Health have demonstrated its efficiency in the air: bacteria of golden staphylococcus are completely deactivated in one hour, Candida fungi in 2 hours and the most resistant tuberculosis bacteria in 24 hours. The effect of the preparation is preserved after the repeated administration of microbes upon the treated surface.
In vivo tests of the varnish have been conducted in several institutes of the RF Ministry of Health and Medical Academy with different levels of bacterial contamination (including autoclave chambers, washrooms for microbiologically contaminated dishes, hospital corridors, rooms for the processing of diagnostic samples from tuberculo-
sis patients, etc.). At the Scientific Research Institute of Transplantology of the RF Ministry of Health, for example, levels of pathogenic microflora were measured for several months from experimental and control surfaces. It was established that the share of "positive" results from varnished surfaces was much smaller than on the control ones, with a minimal levels of microorganisms on the former. Deliberate contamination of this coating with colon bacillus conducted after six months of its operation in ordinary conditions demonstrated its high antiseptic effect.
Similar results were obtained in prolonged tests of INTERCIDE at the Institute of Tuberculosis of the Russian Medical Academy: in natural conditions 92 percent of "wash-off did not contain any pathogenic microflora; during artificial contaminations of the surface with the clinical strain of tuberculosis bacteria only isolated colonies (1 - 4) were observed while on the control surfaces this growth was massive (50 - 100 colonies).
These findings led the researchers to this conclusion: varnish coating is much more effective against bacteria of tuberculosis than the widely used chloramine. And it was not accidental than the RF Ministry of Health has registered INTERCIDE as desinfectant "number one" and recommended it "for treatment of surfaces in curative- preventive centers and in premises with large numbers of patients threatened with bacterial (including tuberculosis) and fungous infections".
The list of new preparations of this kind includes the water-dispersion composition EPOCIDE on the basis of epoxy oligomers and PHMG which do not contain toxic solvents and which form waterproof biocidal coatings of increased strength.
Recent tests of this preparation proved its high efficiency for protecting different kinds of equipment from bacterial contamination.
In recent years our experts have been experimenting with nanoparticles of some metals as one of the components of paints and varnishes. Their high bactericidal effect gives us hopes for new effective methods of antibacterial protection for the future. The very first tests with nanoparticles of silver have demonstrated their bactericidal potential. The same is expected from nanoparticles of zink oxide. But the appropriate technological solutions are still at the development stage.
Illustrations provided by the authors
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