Acrylic in architecture

The most beautiful architectural structures are created from acrylic glass - transparent roofs, facades, road barriers, awnings, canopies, gazebos. All these structures are used in outdoors under constant exposure to sunlight. A reasonable question arises: can acrylic structures withstand the "onslaught" of the rays of the scorching sun, while maintaining excellent performance, gloss, transparency? We hasten to please you: there is no reason for concern. Acrylic structures can be safely used outdoors under the constant influence of ultraviolet radiation, even in hot countries.

Comparison of acrylic with other plastics in terms of UV resistance

Let's try to compare acrylic with other plastics. Today, for the manufacture of facade, roof glazing and protective structures, a large number of different transparent plastics are used. At first glance, they are no different from acrylic. But synthetic materials, similar to acrylic in their visual characteristics, lose their visual appeal after a few years of operation in direct sunlight. No additional coatings and films are able to protect low-quality plastic from ultraviolet radiation for a long time. The material remains sensitive to UV rays, and, alas, there is no need to talk about the reliability of all kinds of surface coatings. Protection in the form of films and varnishes cracks and peels off over time. It is not surprising that the warranty against yellowing of such materials does not exceed several years. Acrylic glass from the Plexiglas brand behaves quite differently. The material has natural protective properties, therefore, does not lose its excellent characteristics for at least three decades.

How does acrylic sun protection technology work?

UV resistance of Plexiglas is provided by the unique Naturally UV Stable comprehensive protection technology. Protection is formed not only on the surface, but throughout the entire structure of the material at the molecular level. The plexiglass manufacturer Plexiglas provides a 30-year warranty against yellowing and clouding of the surface during continuous outdoor use. This warranty applies to transparent colorless sheets, pipes, blocks, rods, corrugated and ribbed plates made of Plexiglas brand acrylic glass. canopies, roof coverings, transparent acrylic facades, arbors, fences and other plexiglass products do not acquire an unpleasant yellow tint.

The diagram shows changes in the acrylic light transmission index during the warranty period in various climatic zones. We see that the light transmission of the material is slightly reduced, but these are minimal changes, imperceptible to the naked eye. A decrease in the light transmission index by several percent can only be determined with the help of special equipment. Visually, acrylic remains pristinely transparent and shiny.

On the graph, you can trace the dynamics of changes in the light transmission of acrylic in comparison with ordinary glass and other plastics. First, the light transmission of acrylic in its original state is higher. It is the most transparent plastic material known today. Over time, the difference becomes more noticeable: low-quality materials begin to darken, fade, and the light transmission of acrylic remains at the same level. None of the known plastics, except acrylic, can transmit 90% of the light after thirty years of operation under the sun. That is why acrylic is preferred modern designers and architects when creating their best projects.

When we talk about light transmission, we are talking about the safe spectrum of ultraviolet rays. Acrylic glass delays the dangerous part of the solar radiation spectrum. For example, in a house under an acrylic roof or in an airplane with acrylic windows, people are under reliable protection of the glazing. To clarify, let's look at the nature of ultraviolet radiation. The spectrum is divided into short-wave, medium-wave and long-wave radiation. Each type of radiation has a different effect on the world. The most high-energy radiation with a short wavelength, absorbed by the ozone layer of the planet, can damage DNA molecules. Medium-wave - with prolonged exposure causes skin burns and inhibits the main functions of the body. The safest and even most useful is long-wave radiation. Only a part of the dangerous medium-wave radiation and the entire long-wave spectrum reaches our planet. Acrylic allows the useful spectrum of UV radiation to pass through, while blocking dangerous rays. This is a very important advantage of the material. Glazing at home allows you to keep maximum light in the room, protecting people from the negative effects of ultraviolet radiation.

Enamel resistance to fading

Conditional lightfastness was determined on samples of dark gray RAL 7016 enamel on REHAU BLITZ PVC profile.

The conditional light fastness of the paintwork was determined in tests in accordance with the standards:

GOST 30973-2002 "Polyvinyl chloride profiles for window and door blocks. Method for determining resistance to climatic influences and assessing durability". p. 7.2, tab. 1, approx. 3.

Determining the conditional light fastness at a radiation intensity of 80±5 W/m 2 was controlled by changing the gloss of the coatings and color characteristics. The color characteristics of the coatings were determined on a Spectroton device after wiping the samples with a dry cloth to remove the formed plaque.

The change in the color of the samples during the test was judged by the change in color coordinates in the CIE Lab system, calculating ΔE. The results are shown in table 1.

Table 1 - Change in gloss and color characteristics of coatings

	Holding time, h			Gloss loss, %	Color coordinate - L	Color coordinate - a	Color coordinate -b	Color change Δ E to standard
		Before testing	After testing

Samples 1 to 4 are considered to have passed the test.

The data are given for sample No. 4 - 144 hours of UV irradiation, which corresponds to GOST 30973-2002 (40 conditional years):

L = 4.25 norm 5.5; a = 0.48 norm 0.80; b = 1.54 norm 3.5.

Conclusion:

The power of the light flux up to 80±5 W/m 2 leads to a sharp drop in the gloss of the coatings by 98% after 36 hours of testing as a result of plaque formation. With continued testing, no further loss of gloss occurs. Light fastness can be characterized in accordance with GOST 30973-2002 - 40 conditional years.

The color characteristics of the coating are within acceptable limits and comply with GOST 30973-2002 on samples No. 1, No. 2, No. 3, No. 4.

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. As the polymer degrades, it breaks chemical bonds and oxidation of the material. 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 surface degradation and crystal structure 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 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, 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 raw 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. In this method, the complete 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 at 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 pressing. 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 due to 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 in priority areas of 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"

Polymers are active chemical substances, which 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 unfavorable 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 harmful Sun 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.

Experiments are also carried out 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 for changes in chemical composition 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. Big number such components contribute to the spread of microorganisms.

Consequences destructive impact can be noticed quite quickly, because:

• 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.

Conducted 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 adverse influence 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 is highly corrosive to metal surfaces, which can not be said about acrylic. Another distinguishing feature with a minus sign y silicone sealants their environmental friendliness appears. 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 high and reliable protection against ultraviolet radiation. Oils with a UV filter are successfully used for outdoor applications, allowing the material to retain all its essential 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.