UV stabilizers are a necessary additive in polymeric materials. Acrylic UV resistance UV resistance

Polymers are active chemicals that have recently gained wide popularity due to the mass consumption of plastic products. Every year, the volume of world production of polymers is growing, and materials made using them are gaining new positions in the household and industrial sectors.

All product tests are carried out in laboratory conditions. Their main task is to determine the factors environment, which have a devastating effect on plastic products.

The main group of adverse factors that destroy polymers

The resistance of specific products to negative climatic conditions is determined taking into account two main criteria:

• the chemical composition of the polymer;
• type and strength of external factors.

In this case, the adverse effect on polymer products is determined by the time of their complete destruction and the type of impact: instant complete destruction or subtle cracks and defects.

Factors affecting the degradation of polymers include:

• microorganisms;
• thermal energy of varying degrees of intensity;
• industrial emissions containing harmful substances;
• high humidity;
• UV radiation;
• x-ray radiation;
• an increased percentage of oxygen and ozone compounds in the air.

The process of complete destruction of products is accelerated by the simultaneous action of several adverse factors.

One of the peculiarities of conducting climatic tests of polymers is the need for test expertise and study of the influence of each of the listed phenomena separately. However, such evaluation results cannot accurately reflect the picture of the interaction of external factors with polymer products. This is due to the fact that under normal conditions, materials are most often subjected to combined effects. In this case, the destructive effect is markedly enhanced.

Effect of ultraviolet radiation on polymers

There is a misconception that plastic products are particularly damaged by the sun's rays. In fact, only ultraviolet radiation has a destructive effect.

Bonds between atoms in polymers can be destroyed only under the influence of rays of this spectrum. The consequences of such adverse effects can be observed visually. They can be expressed:

• in the deterioration of the mechanical properties and strength of the plastic product;
• increased fragility;
• burnout.

In laboratories, xenon lamps are used for such tests.

They also conduct experiments to recreate the conditions of exposure to UV radiation, high humidity and temperature.

Such tests are needed in order to draw conclusions about the need to make changes in the chemical composition of substances. So, in order for the polymer material to become resistant to UV radiation, special adsorbers are added to it. Due to the absorbing ability of the substance, the protective layer is activated.

The stability and strength of interatomic bonds can also be increased by introducing stabilizers.

The destructive action of microorganisms

Polymers are substances that are highly resistant to bacteria. However, this property is typical only for products made of high quality plastic.

In low-quality materials, low molecular weight substances are added that tend to accumulate on the surface. A large number of such components contribute to the spread of microorganisms.

The consequences of the destructive impact can be noticed quite quickly, since:

• aseptic qualities are lost;
• the degree of transparency of the product is reduced;
• brittleness appears.

Among the additional factors that can lead to a decrease in the performance of polymers, it should be noted elevated temperature and humidity. They create conditions favorable for the active development of microorganisms.

The ongoing research has made it possible to find the most effective method preventing the growth of bacteria. This is the addition of special substances - fungicides - to the composition of polymers. The development of bacteria is suspended due to the high toxicity of the component for the simplest microorganisms.

Is it possible to neutralize the impact of negative natural factors?

As a result of the research, it was possible to establish that most of the plastic products on the modern market do not interact with oxygen and its active compounds.

However, the mechanism of polymer destruction can be triggered by the combined action of oxygen and high temperature, humidity, or ultraviolet radiation.

Also, when conducting special studies, it was possible to study the features of the interaction of polymeric materials with water. Liquid affects polymers in three ways:

1. physical;
2. chemical (hydrolysis);
3. photochemical.

Additional simultaneous exposure to elevated temperature can accelerate the process of destruction of polymer products.

Corrosion of plastics

In a broad sense, this concept implies the destruction of the material under the negative influence of external factors. Thus, the term “polymer corrosion” should be understood as a change in the composition or properties of a substance caused by an adverse effect, which leads to partial or complete destruction of the product.

Processes of targeted transformation of polymers to obtain new material properties do not fall under this definition.

We should talk about corrosion, for example, when polyvinyl chloride comes into contact and interacts with a chemically aggressive environment - chlorine.

Most oils and sealants are used with equal success for interior decoration, as well as for the external one. True, for this they must have a certain set of properties, for example, such as moisture resistance, thermal insulation and resistance to ultraviolet radiation.

All these criteria must be met without fail, because our climatic conditions are unpredictable and constantly changing. It may be sunny in the morning, but by afternoon clouds will already appear and heavy rain will begin.

With all of the above in mind, experts advise choosing UV-resistant oils and sealants.

Why a filter is needed

It would seem, why add a UV filter when you can use silicone or polyurethane sealant for outdoor work? But all these tools have certain differences, which does not allow them to be used in absolutely all cases. For example, you can easily restore a seam if an acrylic sealant was used, which cannot be said about silicone.

In addition, the silicone sealant has a high aggressiveness to metal surfaces, which cannot be said about acrylic. One more hallmark with a minus sign for silicone sealants is their non-environmental friendliness. They contain solvents that are hazardous to health. That is why some acrylic sealants have begun to use a UV filter to expand their range of applications.

Ultraviolet radiation is the main cause of degradation of most polymeric materials. Given the fact that not all sealants are UV resistant, you need to be extremely careful when choosing a sealant or oil.

Substances resistant to ultraviolet radiation

There are already a number of UV resistant sealants on the market for sealants and coatings. These include silicone and polyurethane.

Silicone sealants

The advantages of silicone sealants include high adhesion, elasticity (up to 400%), the possibility of coloring the surface after hardening, and UV resistance. However, they also have enough disadvantages: non-environmental friendliness, aggressiveness to metal structures and the impossibility of the restoration of the seam.

Polyurethane

They have even greater elasticity than silicone (up to 1000%). Frost-resistant: they can be applied to the surface at air temperatures down to -10 C °. Polyurethane sealants are durable and of course UV resistant.

The disadvantages include high adhesion not to all materials (it does not interact well with plastic). Used material is very difficult and expensive to dispose of. Polyurethane sealant does not interact well with a humid environment.

Acrylic sealants with UV filter

Acrylic sealants have many advantages, including high adhesion to all materials, the possibility of seam restoration and elasticity (up to 200%). But among all these advantages, one point is missing: resistance to ultraviolet rays.

Thanks to this UV filter, acrylic sealants can now compete with other types of sealants and make it easier for the consumer to choose in certain cases.

Oils with a UV filter

Colorless coating agent wooden surfaces has a high and reliable protection from ultraviolet radiation. Oils with a UV filter are successfully used for outdoor work, allowing the material to retain all its basic positive properties, despite external influences.

This type of oil allows you to slightly delay the next planned surface coating with oil. The interval between restorations is reduced by 1.5–2 times.

Rigid (non-plasticized) polyvinyl chloride was the first to appear on the Russian advertising market, and, despite the increasing range of polymeric materials offered every year, it continues to steadily maintain its leading position in some areas of advertising production. This is due to the fact that PVC has a complex of properties necessary for solving various problems and meeting the most stringent requirements for structural materials of this type.

PVC is characterized by natural resistance to UV radiation, chemical attack, mechanical corrosion and contact damage. For a long time of operation on the street does not lose its original properties. It does not absorb atmospheric moisture and, accordingly, is not prone to the formation of condensate on the surface. Among all other plastics, it has a unique fire resistance. Under normal operating conditions, it does not pose a danger to either humans or the environment. Easily machined, formed (compact material), welded and glued. With film application, there is no need to think about "pitfalls" - PVC without human intervention will not present "surprises".

The conditional disadvantages of polyvinyl chloride include:

• short-term resistance of color modifications to sunlight (this does not apply to materials with additional UV stabilization);
• the possible presence of materials of unknown origin surface release agents that require removal;
• limited frost resistance (up to -20 °C), which is far from always confirmed in practice (subject to all technological rules for the manufacture of structures and their installation, in the absence of significant mechanical loads, PVC behaves stably even at lower temperatures);
• a higher coefficient of linear thermal expansion compared to many other polymeric materials, i.e. a wider range of dimensional distortions;
• insufficiently high degree of light transmission of the transparent material (approx. 88%);
• increased requirements for disposal: smoke and combustion products are dangerous for humans and the environment.

Rigid polyvinyl chloride is produced in various modifications only by extrusion. A wide range of PVC, including sheets:

• compact and foamed;
• with a glossy and matte surface;
• white, colored, transparent and translucent;
• flat and embossed;
• standard version and increased bending strength,

allows you to use this material in almost all areas of advertising production.

Tatiana Dementieva
process engineer

1

Composite materials based on polypropylene resistant to UV radiation have been obtained. To assess the degree of photodegradation of polypropylene and composites based on it, IR spectroscopy was the main tool. When the polymer is degraded, chemical bonds are broken and the material is oxidized. These processes are reflected in the IR spectra. Also, the development of polymer photodegradation processes can be judged by the change in the structure of the surface exposed to UV irradiation. This is reflected in the change in the contact angle of wetting. Polypropylene stabilized with various UV absorbers was studied by IR spectroscopy and contact angle measurements. Boron nitride, multi-walled carbon nanotubes, and carbon fibers were used as fillers for the polymer matrix. The IR absorption spectra of polypropylene and composites based on it have been obtained and analyzed. Based on the data obtained, the concentrations of UV filters in the polymer matrix, which are necessary to protect the material from photodegradation, were determined. As a result of the research, it was found that the used fillers significantly reduce the degradation of the surface and crystal structure of the composites.

polypropylene

UV radiation

nanotubes

boron nitride

1. A. L. Smith, Applied IR Spectroscopy. Fundamentals, technique, analytical application. – M.: Mir, 1982.

2. Bertin D., M. Leblanc, S. R. A. Marque, D. Siri. Polypropylene degradation: Theoretical and experimental investigations// Polymer Degradation and Stability. - 2010. - V. 95, I.5. - P. 782-791.

3. Guadagno L., Naddeo C., Raimondo M., Gorrasi G., Vittoria V. Effect of carbon nanotubes on the photo-oxidative durability of syndiotactic polypropylene // Polymer Degradation and Stability. - 2010. - V.95, I. 9. - P. 1614-1626.

4. Horrocks A. R., Mwila J., Miraftab M., Liu M., Chohan S. S. The influence of carbon black on properties of orientated polypropylene 2. Thermal and photodegradation // Polymer Degradation and Stability. - 1999. - V. 65, I.1. – P. 25-36.

5. Jia H., Wang H., Chen W. The combination effect of hindered amine light stabilizers with UV absorbers on the radiation resistance of polypropylene // Radiation Physics and Chemistry. - 2007. - V.76, I. 7. - P. 1179-1188.

6. Kaczmarek H., Ołdak D., Malanowski P., Chaberska H. Effect of short wavelength UV-irradiation on aging of polypropylene / cellulose compositions // Polymer Degradation and Stability. - 2005. - V.88, I.2. - P. 189-198.

7. Kotek J., Kelnar I., Baldrian J., Raab M. Structural transformations of isotactic polypropylene induced by heating and UV light // European Polymer Journal. - 2004. - V.40, I.12. - P. 2731-2738.

1. Introduction

Polypropylene is used in many areas: in the production of films (especially packaging), containers, pipes, parts of technical equipment, as an electrical insulating material, in construction, and so on. However, when exposed to UV radiation, polypropylene loses its performance characteristics due to the development of photodegradation processes. Therefore, various UV absorbers (UV filters) are used to stabilize the polymer, both organic and inorganic: dispersed metal, ceramic particles, carbon nanotubes and fibers.

To assess the degree of photodegradation of polypropylene and composites based on it, the main tool is IR spectroscopy. When the polymer is degraded, chemical bonds are broken and the material is oxidized. These processes are reflected in
IR spectra. By the number and position of the peaks in the IR absorption spectra, one can judge the nature of the substance (qualitative analysis), and by the intensity of the absorption bands, the amount of the substance ( quantitative analysis), and, consequently, to assess the degree of degradation of the material.

Also, the development of polymer photodegradation processes can be judged by the change in the structure of the surface exposed to UV irradiation. This is reflected in the change in the contact angle of wetting.

In this work, polypropylene stabilized with various UV absorbers was studied by IR spectroscopy and contact angle measurements.

2. Materials and experimental technique

As source materials and fillers were used: polypropylene, low viscosity (TU 214535465768); multilayer carbon nanotubes with a diameter of no more than 30 nm and a length of no more than 5 mm; high-modulus carbon fiber, grade VMN-4; hexagonal boron nitride.

Samples with different mass fractions of filler in the polymer matrix were obtained from the starting materials by extrusion mixing.

Fourier IR spectrometry was used as a method for studying changes in the molecular structure of polymer composites under the action of ultraviolet radiation. The spectra were recorded on a Thermo Nicolet 380 spectrometer with an attachment for implementing the frustrated total internal reflection (ATR) Smart iTR method with a diamond crystal. The survey was carried out with a resolution of 4 cm-1, the analyzed area was in the range of 4000-650 cm-1. Each spectrum was obtained by averaging 32 passes of the spectrometer mirror. The comparison spectrum was taken before taking each sample.

To study the change in the surface of experimental polymer composites under the action of ultraviolet radiation, we used the method of determining the contact angle of wetting with distilled water. Contact angle measurements are carried out using the KRÜSS EasyDrop DSA20 drop shape analysis system. The Young-Laplace method was used to calculate the contact angle of wetting. V this method the full contour of the drop is estimated; the selection takes into account not only the interfacial interactions that determine the contour of the drop, but also the fact that the drop is not destroyed due to the weight of the liquid. After successful selection of the Young-Laplace equation, the wetting angle is determined as the slope of the tangent at the point of contact of the three phases.

3. Results and discussion

3.1. Results of studies of changes in the molecular structure of polymer composites

The spectrum of polypropylene without filler (Figure 1) contains all the lines characteristic of this polymer. First of all, these are vibration lines of hydrogen atoms in the functional groups CH3 and CH2. The lines in the region of wave numbers 2498 cm-1 and 2866 cm-1 are responsible for the asymmetric and symmetric stretching vibrations of the methyl group (CH3), and the lines 1450 cm-1 and 1375 cm-1, in turn, are due to the bending symmetric and asymmetric vibrations of the same group . Lines 2916 cm-1 and 2837 cm-1 refer to the lines of stretching vibrations of methylene groups (CH2). Stripes on wave numbers 1116 cm-1,
998 cm-1, 974 cm-1, 900 cm-1, 841 cm-1 and 809 cm-1 are commonly referred to as regularity bands, that is, lines due to polymer regularity regions, they are also sometimes called crystallinity bands. It is worth noting the presence of a low-intensity line in the region of 1735 cm-1, which should be attributed to vibrations of the C=O bond, which may be associated with a slight oxidation of polypropylene during the pressing process. The spectrum also contains bands responsible for the formation of double bonds C=C
(1650-1600 cm-1) that arose after the sample was irradiated with UV radiation. In addition, it is this sample that is characterized by the maximum intensity of the C=O line.

Figure 1. IR spectra of polypropylene after UV resistance testing

As a result of exposure to UV radiation on composites filled with boron nitride, C=O bonds (1735-1710 cm-1) of various nature (aldehyde, ketone, ether) are formed. The spectra of UV-irradiated samples of pure polypropylene and polypropylene containing 40% and 25% boron nitride contain bands, usually responsible for the formation of C=C double bonds (1650-1600 cm-1). The bands of regularity (crystallinity) in the range of wave numbers 1300-900 cm-1 on the samples of polymer composites subjected to UV irradiation are noticeably broadened, which indicates a partial degradation of the crystalline structure of polypropylene. However, with an increase in the degree of filling of polymer composite materials with hexagonal boron nitride, the degradation of the crystalline structure of polypropylene decreases. UV exposure also led to an increase in the hydrophilicity of the surface of the samples, which is expressed in the presence of a broad line of the hydroxo group in the region of 3000 cm-1.

Figure 2. IR spectra of a polymer composite based on polypropylene with 25% (wt.) hexagonal boron nitride after UV resistance testing

The spectra of polypropylene filled with a 20% (wt.) mixture of carbon fibers and nanotubes before and after testing practically do not differ from each other, primarily due to the distortion of the spectrum due to the strong absorption of IR radiation by the carbon component of the material.

Based on the data obtained, it can be judged that there are a small number of C=O bonds in the samples of composites based on polypropylene, carbon fiber VMN-4 and carbon nanotubes, due to the presence of a peak in the region of 1730 cm-1, however, it is reliable to judge the amount of these bonds in the samples is not possible due to the distortion of the spectra.

3.2. Results of the Study of Changes in the Surface of Polymer Composites

Table 1 presents the results of a study of changes in the surface of experimental samples of polymer composites filled with hexagonal boron nitride. An analysis of the results allows us to conclude that the filling of polypropylene with hexagonal boron nitride increases the resistance of the surface of polymer composites to ultraviolet radiation. An increase in the degree of filling leads to less degradation of the surface, which manifests itself in an increase in hydrophilicity, which is in good agreement with the results of studying changes in the molecular structure of experimental samples of polymer composites.

Table 1. Results of changing the contact angle of the surface of polymer composites filled with hexagonal boron nitride as a result of testing the resistance to ultraviolet radiation

Filling degree BN	Wetting angle, gr
	Before the test	After the test

An analysis of the results of studying changes in the surface of experimental samples of polymer composites filled with a mixture of carbon fibers and nanotubes (Table 2) allows us to conclude that filling polypropylene with carbon materials makes these polymer composites resistant to ultraviolet radiation. This fact is explained by the fact that carbon materials actively absorb ultraviolet radiation.

Table 2. Results of changing the contact angle of the surface of polymer composites filled with carbon fiber and nanotubes due to the test of resistance to ultraviolet radiation

Degree of filling UV+CNT	Wetting angle, gr
	Before the test	After the test

4. Conclusion

According to the results of studying the resistance of composites based on polypropylene to ultraviolet radiation, the addition of hexagonal boron nitride to the polymer significantly reduces the degradation of the surface and crystal structure of the composites. However, carbon materials actively absorb ultraviolet radiation, thereby providing high resistance of composites based on polymers and carbon fibers and nanotubes to ultraviolet radiation.

The work was carried out within the framework of the federal target program "Research and development on priority areas development of the scientific and technological complex of Russia for 2007-2013”, State contract dated July 08, 2011 No. 16.516.11.6099.

Reviewers:

Serov GV, Doctor of Technical Sciences, Professor of the Department of Functional Nanosystems and High-Temperature Materials, National University of Science and Technology "MISiS", Moscow.

Kondakov S. E., Doctor of Technical Sciences, Senior Researcher, Department of Functional Nanosystems and High-Temperature Materials, National University of Science and Technology "MISiS", Moscow.

Bibliographic link

Kuznetsov D.V., Ilinykh I.A., Cherdyntsev V.V., Muratov D.S., Shatrova N.V., Burmistrov I.N. STUDY OF THE STABILITY OF POLYPROPYLENE-BASED POLYMERIC COMPOSITES TO UV RADIATION // Contemporary Issues science and education. - 2012. - No. 6.;
URL: http://science-education.ru/ru/article/view?id=7503 (date of access: 01.02.2020). We bring to your attention the journals published by the publishing house "Academy of Natural History"

Having collected a significant collection of dark-colored hyphomycetes isolated from different habitats, we began to study the relationship of natural fungal isolates to UV radiation. Such a study made it possible to reveal differences in UV resistance among species and genera of the Dematiaceae family widely distributed in the soil, to determine the distribution of this trait within each biocenosis, and its taxonomic and ecological significance.

We have studied resistance to UV rays (254 nm, dose intensity 3.2 J/m species of 19 genera) soils. When studying the UV resistance of Dematiaceae cultures isolated from the flat saline soils of the south of the Ukrainian SSR, we proceeded from the assumption that with an increase in unfavorable living conditions due to soil salinity, a greater number of resistant species of dark-colored hyphomycetes will accumulate in it than in other soils. In some cases, it was not possible to determine UV resistance due to the loss or sporadic sporulation in the species.

We studied natural isolates of dark-colored hyphomycetes; therefore, each sample was characterized by an unequal number of cultures. For some rare species, the sample size did not allow for appropriate statistical processing.

The widespread and frequent genus Cladosporium is represented by the largest number strains (131), in contrast to the genera Diplorhinotrichum, Haplographium, Phialophora, etc., isolated only in isolated cases.

We conditionally divided the studied mushrooms into highly resistant, resistant, sensitive and highly sensitive. Highly resistant and resistant were those whose survival rate after 2-hour exposure to UV rays was more than 10% and from 1 to 10%, respectively. Species whose survival rate ranged from 0.01 to 1% and from 0.01% and below, we classified as sensitive and highly sensitive.

Large fluctuations in the UV stability of the studied dark-colored hyphomycetes were revealed - from 40% or more to 0.001%, i.e. within five orders of magnitude. These fluctuations are somewhat smaller at the level of genera (2–3 orders) and species (1–2 orders), which is consistent with the results obtained on bacteria and tissue cultures of plants and animals (Samoilova, 1967; Zhestyanikov, 1968).

Of the 54 studied species of the Dematiaceae family, Helminthosporium turcicum, Hormiscium stilbosporum, Curvularia tetramera, C. lunata, Dendryphium macrosporioides, Heterosporium sp., Alternaria tenuis, and a significant part of Stemphylium sarciniforme strains are highly resistant to long-term UV irradiation at 254 nm. All of them are characterized by intensely pigmented, rigid cell walls and, with the exception of Dendryphium macrosporioides, Heterosporium sp. and Hormiscium stilbosporum, belong to the Didimosporae and Phragmosporae groups of the Dematiaceae family, characterized by large multicellular conidia.

A significantly larger number of species are resistant to UV rays. These include species of the genera Alternaria, Stemphylium, Curvularia, Helminthosporium, Bispora, Dendryphion, Rhinocladium, Chrysosporium, Trichocladium, Stachybotrys, Humicola. Distinctive features of this group, as well as the previous one, are large conidia with rigid, intensely pigmented walls. Among them, fungi of the Didimosporae and Phragmosporae groups also occupied a significant place: Curvularia, Helminthosporium, Alternaria, Stemphylium, Dendryphion.

23 species of dark-colored hyphomycetes are classified as UV-sensitive: Oidiodendron, Scolecobasidium, Cladosporium, Trichosporium, Haplographium, Periconia, Humicola fusco-atra, Scytalidium sp., Alternaria dianthicola, Monodyctis sp., Peyronella sp., Curvularia pallescnes, etc. Note that A. dianthicola and C. pallescens, whose conidia are less pigmented, are sensitive to UV rays, although other species of these genera are resistant and even highly resistant.

According to the accepted division, species of the genus Cladosporium, which is widespread and represented in our studies by the largest number of strains, are classified as sensitive (C. linicola, C. hordei, C. macrocarpum, C. atroseptum. C. brevi-compactum var. tabacinum) and highly sensitive (C. . elegantulum, C. transchelii, C. transchelii var. semenicola, C. griseo-olivaceum).

Species of the genus Cladosporium belonging to the first group were distinguished by fairly dense, intensely pigmented, rough cell membranes, in contrast to the second group of species, the cell walls of which are thinner and less pigmented. Sensitive species whose survival rate after irradiation with a dose of 408 J/m 2 was less than 0.01% are Diplorhinotrichum sp., Phialophora sp., Chloridium apiculatum, etc. There were no large-spore dark-colored hyphomycetes in this group. Species highly sensitive to UV irradiation had small, weakly pigmented or almost colorless conidia.

In some species of Dematiaceae, the morphology of conidia formed after irradiation with a dose of 800 J/m 2 was studied. The conidia of Cladosporium transchelii, C. hordei, C. elegantulum and C. brevi-compactum formed after irradiation are usually larger than those of non-irradiated species. This trend was especially clear in the basal conidia. Noticeable changes in the morphology of conidia were also observed in large-spore, UV-resistant species Curvularia geniculata, Alternaria alternata, Trichocladium opacum, Helminthosporium turcicum, they were detected only after irradiation with high doses of UV rays of the order of 10 3 J/m 2 . At the same time, the conidia of Curvularia geniculata noticeably elongated and became almost straight; in the conidia of Alternaria alternata, the number of longitudinal septa decreased until they completely disappeared, and they themselves became larger than the control ones. On the contrary, the conidia of H. turcicum became smaller, the number of septa in them decreased, sometimes the septa became curved. In the conidia of Trichocladium opacum, the appearance of individual, unusually swollen cells was observed. Such changes in morphology indicate significant disturbances in the processes of growth and division in irradiated fungi.

The study of natural isolates of fungi of the Dematiaceae family confirmed a certain dependence of UV resistance on the size of conidia and pigmentation of their membranes. As a rule, large conidia are more resistant than small ones. It should be noted that the index chosen by us - the survival rate - of melanin-containing fungi after irradiation with a dose of 408 J/m , Kumita, 1972). It is quite obvious that the nature of this phenomenon needs further study with the involvement of highly resistant and resistant species of the Dematiaceae family.

We studied the distribution of the UV resistance trait in dark-colored fungi isolated from floodplain-meadow, saline and high-mountain soils, which was depicted graphically. The resulting curves resembled normal distribution curves (Lakin, 1973). The survival rate of the majority (41.1 and 45.8%) of crops isolated from meadow and saline soils of Ukraine, respectively, was 0.02-0.19% after a dose of 408 J/m 2 (2-hour exposure), and resistance to this factor was distributed within 6 orders of magnitude. Consequently, the assumption of increased resistance to UV irradiation of dark-colored hyphomycetes from saline soils was not confirmed.

The UV resistance of alpine species of the Dematiaceae family differed markedly from that described above, which was reflected in the change in the position of the peak of the curve and the range of distribution.

For 34.4% of cultures, the survival rate was 0.2-1.9%. The survival rate of 39.7% of isolates exceeded 2%, i.e., the distribution curve of the UV resistance trait is shifted towards increased resistance to UV radiation. The distribution range for this property did not exceed four orders of magnitude.

In connection with the revealed differences in the distribution of the trait of UV resistance in lowland and high-mountain species and genera of the Dematiaceae family, it seemed appropriate to check how they occur: due to the predominant occurrence of highly resistant and UV-resistant species of dark-colored hyphomycetes in mountain soils, or there is an increased resistance to UV radiation of high-mountain strains of the same species or genus compared to lowland strains. To prove the latter, we compared cultures of the Dematiaceae family isolated on the surface of plain and high mountain soils, as well as from surface (0–2 cm) and deep (30–35 cm) horizons of plain meadow soils. Obviously, such mushrooms are in extremely unequal conditions. The samples we used made it possible to analyze 5 common genera of the Dematiaceae family isolated on the surface of plain and high mountain soils on the basis of UV resistance. Only strains isolated from alpine soils, species of the genus Cladosporium and Alternaria are significantly more resistant than strains isolated from plain soils. On the contrary, the UV resistance of strains isolated from lowland soils was significantly higher than that of highland soils. Consequently, differences in the microflora of areas with increased insolation (alpine soils) in relation to UV rays are determined not only by the predominant occurrence of resistant genera and species of Dematiaceae, but also by their possible adaptation to such conditions. The last provision is obviously of particular importance.

Comparison of UV resistance of cultures of the most common genera of dark-colored hyphomycetes isolated from surface, exposed to light, and deep soil horizons showed the absence of statistically significant differences between them. The range of changes in the trait of resistance to UV rays in natural isolates of widespread Dematiaceae species was mostly the same in lowland and high-mountain isolates and did not exceed two orders of magnitude. The wide variability in this trait at the species level ensures the survival of a stable part of the species population in environmentally unfavorable conditions for this factor.

The conducted studies confirmed the exceptionally high UV resistance of the species Stemphylium ilicis, S. sarciniforme, Dicoccum asperum, Humicola grisea, Curvularia geniculata, Helminthosporium bondarzewi revealed in the experiment, in which, after an irradiation dose of about 1.2-1.5 ∙ 10 3 J/m 2 to 8-50% of the conidia remained alive.

The next task was to study the resistance of some species of the Dematiaceae family to biologically extreme doses of UV radiation and artificial sunlight (ISS) of high intensity (Zhdanova et al. 1978, 1981).

A monolayer of dry conidia on a gelatinous substrate was irradiated according to the Lee method modified by us (Zhdanova and Vasilevskaya, 1981), and comparable, statistically significant results were obtained. The source of UV radiation was a DRSh-1000 lamp with a UFS-1 light filter that transmits UV rays of 200–400 nm. The light flux intensity was 200 J/m 2 s. It turned out that Stemphylium ilicis, Cladosporium transchelii and especially its Ch-1 mutant are highly resistant to this effect.

Thus, the survival of S. ilicis after a dose of 1 ∙ 10 5 J/m 2 was 5%. A 5% survival rate for Ch-1 mutant, C. transchelii, K-1 and BM mutants was observed after doses of 7.0 x 10 4 ; 2.6 ∙ 10 4 ; 1.3 ∙ 10 4 and 220 J / m 2, respectively. Graphically, the death of irradiated dark-colored conidia was described by a complex exponential curve with an extensive plateau, in contrast to the survival of the BM mutant, which obeyed an exponential dependence.

In addition, we tested the resistance of melanin-containing fungi to high-intensity ISS. The source of radiation was a solar illuminator (OS - 78) based on a DKsR-3000 xenon lamp, providing radiation in the wavelength range of 200-2500 nm with a spectral energy distribution close to that of the sun. In this case, the share of energy in the UV region was 10–12% of the total radiation flux. Irradiation was carried out in air or under vacuum conditions (106.4 μPa). The radiation intensity in air was 700 J/m 2 s and in vacuum - 1400 J/m 2 s (0.5 and 1 solar dose, respectively). One solar dose (solar constant) is the value of the total flux of solar radiation outside the earth's atmosphere at an average Earth-Sun distance, incident on 1 cm 2 of the surface in 1 s. Measurement of specific irradiance was carried out according to a special technique at the position of the sample using a luxmeter 10-16 with an additional neutral light filter. Each strain was irradiated with at least 8-15 successively increasing radiation doses. Irradiation time varied from 1 min to 12 days. Resistance to ISS was judged by the survival rate of fungal conidia (number of formed macrocolonies) in relation to non-irradiated control, taken as 100%. A total of 14 species of 12 genera of the Dematiaceae family were tested, of which 5 species were studied in more detail.

The resistance of cultures of C. transchelii and its mutants to ISS depended on the degree of their pigmentation. Graphically, it was described by a complex exponential curve with an extensive resistance plateau. The LD value of 99.99 upon irradiation in air for the mutant Ch-1 was 5.5 10 7 J/m 2 , the initial culture of C. transchelii - 1.5 10 7 J/m 2 , light-colored mutants K-1 and BM - 7.5 ∙ 10 6 and 8.4 ∙ 10 5 J / m 2, respectively. Irradiation of the Ch-1 mutant under vacuum conditions turned out to be more favorable: the resistance of the fungus increased markedly (LD 99.99 - 2.4 ∙ 10 8 J/m 2 ), the type of dose survival curve changed (multicomponent curve). For other strains, such exposure was more detrimental.

When comparing resistance to UV rays and high-intensity ISS of cultures of C. transchelii and its mutants, many similarities were found, despite the fact that the effect of ISS was studied on “dry” conidia, and an aqueous suspension of spores was irradiated with UV rays. In both cases, a direct correlation was found between the resistance of fungi and the content of melanin pigment PC in the cell wall. A comparison of these properties indicates the participation of the pigment in the resistance of fungi to ISS. The mechanism of the photoprotective action of the melanin pigment proposed later makes it possible to explain the long-term resistance of melanin-containing fungi to total doses of UV rays and ISS.

The next stage of our work was the search for cultures of melanin-containing fungi more resistant to this factor. They turned out to be species of the genus Stemphylium, and the resistance of S. ilicis and S. sarciniforme cultures in the air is approximately the same, extremely high and described by multicomponent curves. The maximum radiation dose of 3.3 ∙ 10 8 J/m 2 for the mentioned cultures corresponded to the value of LD 99 . In a vacuum, with more intense irradiation, the survival rate of Stemphylium ilicis cultures was somewhat higher than that of S. sarciniforme (LD 99 is 8.6 ∙ 10 8 and 5.2 ∙ 10 8 J/m 2, respectively), i.e., their survival almost the same and was also described by multicomponent curves with an extensive plateau at the survival rate of 10 and 5%.

Thus, a unique resistance of a number of representatives of the Dematiaceae family (S. ilicis, S. sarciniforme, C. transchelii Ch-1 mutant) to long-term high-intensity ISS irradiation was found. In order to compare the obtained results with the previously known ones, we reduced the values ​​of sublethal doses obtained for our objects by an order of magnitude, since the UV rays (200–400 nm) of the OS-78 facility amounted to 10% in its luminous flux. Consequently, the survival rate of the order of 10 6 -10 7 J/m 2 in our experiments is 2-3 orders of magnitude higher than that known for highly resistant microorganisms (Hall, 1975).

In the light of ideas about the mechanism of the photoprotective action of the melanin pigment (Zhdanova et al., 1978), the interaction of the pigment with light quanta led to its photooxidation in the fungal cell and, subsequently, to stabilization of the process due to reversible electron phototransfer. In an argon atmosphere and in a vacuum (13.3 m/Pa), the nature of the photochemical reaction of the melanin pigment remained the same, but photooxidation was less pronounced. The increase in UV resistance of conidia of dark-colored hyphomycetes in vacuum cannot be associated with the oxygen effect, which is absent when “dry” samples are irradiated. Apparently, in our case, vacuum conditions contributed to a decrease in the level of melanin pigment photooxidation, which is responsible for the rapid death of the cell population in the first minutes of irradiation.

Thus, a study of the resistance to UV radiation of about 300 cultures of representatives of the Dematiaceae family showed significant UV resistance to this effect of melanin-containing fungi. Within the family, heterogeneity of species on this basis has been established. UV resistance presumably depends on the thickness and compactness of the arrangement of melanin granules in the cell wall of the fungus. The resistance of a number of dark-colored species to sources of high-power UV rays (DRSH-1000 and DKsR-3000 lamps) was tested and an extremely resistant group of species was identified, which significantly exceeds such microorganisms as Micrococcus radiodurans and M. radiophilus in this property. The peculiar nature of the survival of dark-colored hyphomycetes was established according to the type of two- and multi-component curves, which were first described by us.

A study was made of the distribution of the trait of resistance to UV rays of dark-colored hyphomycetes in the high-mountain soils of the Pamir and Pamir-Alay and in the meadow soils of Ukraine. In both cases, it resembles a normal distribution, but UV-resistant species of the Dematiaceae family clearly predominated in the mycoflora of alpine soils. This indicates that solar insolation causes profound changes in the microflora of the surface soil horizons.