Influence of UV radiation on the properties of polyethylene. Does polycarbonate transmit UV rays? What are the ranges of ultraviolet radiation

There were times when tanned skin was considered a sign of low birth, and noble ladies tried to protect their faces and hands from the sun's rays in order to maintain an aristocratic pallor. Later, the attitude towards tanning has changed - it has become an indispensable attribute of a healthy and successful person. Today, despite the ongoing debate about the benefits and harms of insolation, the bronze skin tone is still at the peak of popularity. But not everyone has the opportunity to visit the beach or the solarium, and in this regard, many are interested in whether it is possible to sunbathe through the window glass, sitting, for example, on a glazed loggia or attic heated by the sun. According to the site http://onwomen.ru

Probably, every professional driver or just a person who spends a long time behind the wheel of a car noticed that his hands and face become covered with a light tan over time. The same applies to office workers who are forced to sit at an uncurtained window for the entire shift. On their faces, you can often find traces of sunburn even in winter. And if a person is not a frequenter of solariums and does not make a daily promenade through the parks, then this phenomenon cannot be explained otherwise than by tanning through glass. So does glass transmit ultraviolet light and is it possible to tan through a window? Let's figure it out.

The nature of tanning

In order to answer the question of whether it is possible to get a tan through ordinary window glass in a car or on a loggia, you need to understand exactly how the process of darkening of the skin takes place and what factors influence it. First of all, it should be noted that sunburn is nothing more than a protective reaction of the skin to solar radiation. Under the influence of ultraviolet light, the cells of the epidermis (melanocytes) begin to produce the substance melanin (dark pigment), due to which the skin acquires a bronze tint. The higher the concentration of melanin in the upper layers of the dermis, the more intense the tan.

However, not all UV rays cause such a reaction, but only those in a very narrow wavelength range. Ultraviolet rays are conventionally divided into three types:

• A-rays (long wavelength)- are practically not delayed by the atmosphere and freely reach the earth's surface. Such radiation is considered the safest for the human body, since it does not activate the synthesis of melanin. All it can do is cause a slight darkening of the skin, and then only with prolonged exposure. However, with excessive insolation with long-wave rays, collagen fibers are destroyed and the skin becomes dehydrated, as a result of which it begins to age faster. And some people are allergic to the sun because of A-rays. Long-wave radiation easily overcomes the thickness of window glass and leads to gradual fading of wallpaper, furniture surfaces and carpets, but it is impossible to get a full tan with its help.
• B-rays (medium wave)- linger in the atmosphere and reach the Earth's surface only partially. This type of radiation has a direct effect on the synthesis of melanin in skin cells and contributes to the appearance of a quick tan. And with its intense exposure to the skin, burns of varying degrees occur. B-rays cannot penetrate through ordinary window glass.
• C-rays (shortwave)- represent a great danger to all living organisms, but, fortunately, they are almost completely neutralized by the atmosphere, before reaching the surface of the Earth. Such radiation can only be encountered high in the mountains, however, even there its effect is extremely weakened. Physicists distinguish another type of ultraviolet radiation - extreme, for which the term "vacuum" is often used due to the fact that waves of this range are completely absorbed by the Earth's atmosphere and do not fall to the earth's surface.

UV is radiation with wavelengths from 400 nm to 10 nm. It is divided into 4 ranges:
A: 400-315 nm
B: 315-280nm
C: 280-100 nm
Extreme: 121-10 nm.

Different materials have different transparency to ultraviolet rays depending on the wavelength. For the extreme range, even air is opaque! The window pane allows band A to pass through, but does not pass the other 3.
You can verify this by looking at the graph.

The graph is verified by a simple experiment. We shine a 365 nm UV LED through ordinary glass with a thickness of 6 mm on an invisible inscription that glows only under ultraviolet light.

There is no noticeable decrease in brightness. You can take glass several times thicker, but the inscription will continue to glow, ultraviolet passes very well!

Glass transmission of 400-315 nm is especially important to consider when choosing high-quality sunglasses, because most of the ultraviolet present on the street passes through a glass lens without a protective layer: in Moscow from 301 nm, in temperate latitudes from 295 nm, in the world from 286 nm .

If you say that air does not transmit ultraviolet, it will be a half-truth, just like saying that glass does not transmit UV. You should always mention the specific ultraviolet range so that such dangerous half-myths do not appear.

• Can you tan through glass?

  Whether it is possible to get a tan through window glass or not depends on what properties it has. The fact is that glasses come in different types, each of which is affected by UV rays in different ways. Thus, organic glass has a high transmission capacity, which allows the passage of the entire spectrum of solar radiation. The same applies to quartz glass, which is used in tanning lamps and room disinfection devices. Ordinary glass, used in residential premises and cars, transmits only long-wave rays of type A, and it is impossible to sunbathe through it. Another thing, if you replace it with plexiglass. Then it will be possible to sunbathe and enjoy a beautiful tan almost all year round.

  Although sometimes there are cases when a person spends some time under the sun's rays passing through the window, and then finds a light tan on the exposed skin. Of course, he is in full confidence that he got tanned precisely by insolation through the glass. But it is not so. There is a very simple explanation for this phenomenon: the change in shade in this case occurs as a result of the activation of a small amount of the residual pigment (melanin) produced under the influence of type B ultraviolet radiation, located in the skin cells. As a rule, such a “tan” is temporary, that is, it quickly disappears. In a word, in order to get a full-fledged tan, you must either visit a solarium or regularly take sunbaths, and it will not work to change the natural skin tone towards a darker one through ordinary window or car glass.

• Is it necessary to defend?

Worrying about whether it is possible to get a tan through glass is only for those people who have very sensitive skin and a predisposition to the appearance of age spots.

They are advised to use special means with a minimum degree of protection (SPF) at all times. Apply such cosmetics should be mainly on the face, neck and décolleté. However, it is still not worth protecting yourself too actively from ultraviolet, especially long-wave, because the sun's rays in moderation are very useful and even necessary for the normal functioning of the human body.

May 28, 2016
Specialization: a professional in the field of construction and repair (a full cycle of finishing work, both internal and external, from sewerage to electrics and finishing work), installation of window structures. Hobbies: see column "SPECIALIZATION AND SKILLS"

The question of whether linoleum is harmful to health, I was asked quite often. The opinion about the toxicity and allergenicity of this flooring is widespread, and therefore, when choosing materials for interior decoration, many are skeptical of linoleum. Well, if there are small children in the house, then the level of suspicion must be multiplied by at least two.

In fact, a significant part of the claims about the dangers of this material for health are either greatly exaggerated or refer to low-quality varieties. And yet, it is simply necessary to figure out where is the truth and where is fiction. That is why I analyzed the main sources describing the harm of linoleum, and I suggest that you familiarize yourself with my conclusions.

Material analysis

Natural and synthetic coatings

Before you understand whether linoleum is harmful or not, you need to specify in advance what material we are talking about. As anyone who has even a little experience with flooring knows, linoleums are different, but in this aspect, the division into natural and synthetic coatings will be most relevant.

It is convenient to compare them using the table:

natural linoleum

Synthetic linoleum

the basis of the material is a jute cloth - burlap of rare weaving; jute is impregnated with a composition based on linseed oil (linum oleum, hence the name of the material, by the way) with the addition of turpentine (also mostly natural); wood flour, lime flour, resins, pigments, etc. are used as fillers.

the base of the roll is foamed PVC, which is responsible for compensating for irregularities in the base, providing heat and sound insulation; a reinforcing layer can be laid on top of the base - fiberglass, which gives the coating strength and elasticity; on top is a decorative layer of polyvinyl chloride with a pattern applied to it; an abradable material can be applied over the pattern - a transparent coating based on polyurethane or the same PVC.

As you can see, in natural linoleum, in principle, there are no components that can cause health problems. The coating is non-toxic, does not emit volatile substances, and contains practically no synthetic components.

Therefore, if the price (rather high, it must be admitted - from 1000 rubles per square or more) does not bother you, then buy it. If you are still limited in funds, or you need a more moisture-resistant and wear-resistant material, then you will have to put up with some of the disadvantages of synthetic linoleum.

Potential threats from linoleum

So, back to our thesis that the harmfulness of linoleum mainly concerns its synthetic varieties.

What are the potential threats?

1. Polyvinyl chloride, which acts as a binder (a replacement for linseed oil, cheaper and more accessible), is itself almost completely inert. If it is not taken as food, then its toxicity will be zero, so the harm from it is still a myth.

PVC does release toxic chlorine gases when burned.
But I think that this situation is already beyond the scope of the issue under discussion: if linoleum is on fire, then in any case it poses a threat.
On the other hand, polyvinyl chloride itself ignites very reluctantly, in addition, where necessary, the instruction recommends laying special fire-resistant linoleum.

1. The reinforcing material - fiberglass - also does not contain volatile substances that can have a negative impact on health. There is nothing to fear here either.

1. The main source of danger are additives - stabilizers and plasticizers. They are introduced into the composition of PVC so that it is both durable and elastic. Some manufacturers use cheap raw materials with low environmental friendliness, and therefore, immediately after laying, the material actively emits toxic volatile phenols. For an adult, staying in a room with "fresh" linoleum can cost a headache, and even provoke poisoning in a baby.

1. Pigments should also be included here: if cheap paint was used for decoration, and even the manufacturer saved on the thickness of the abradable layer, then after two or three years of operation, particles of coloring substances will begin to enter the atmosphere. They may not cause any particular harm to health, but they can provoke an allergic reaction in a person with a predisposition.
2. Another threat is associated with the decomposition of polymers under the influence of ultraviolet radiation. If filtering additives were not introduced into the polyurethane coating to create a protective layer, then under bright sunlight (for example, in a living room with large windows), the coating will begin to decompose, and some of the decomposition products will enter the atmosphere.

1. Finally, you should not lay commercial and semi-commercial varieties of coatings in the house (especially bedrooms and children's rooms). Quite different requirements are put forward for their composition, so that even in high-quality models, the content of potentially hazardous components can be high.

Glue as a harmful factor

Another factor that causes harm from linoleum, and which is often forgotten, is glue.

Its influence should be taken into account for the following reasons:

1. Many themselves contain large amounts of volatile toxins. Of course, linoleum manufacturers do not recommend using such mixtures for installation, but quite often craftsmen (either self-taught or simply not responsible enough workers) work with what they have.

1. The active components of the adhesive, even if they are not toxic in themselves, can react with polyurethane, causing both its decomposition and the dissolution of additives (plasticizers, stabilizers, pigments). In addition to reducing the strength and reducing the service life of the coating, the result is the ingress of not very useful "chemistry" into the air.
2. Particular attention should be paid to the choice of glue if the linoleum is laid on a warm floor: when heated, chemical reactions are activated, and the risk of getting at least an unpleasant odor, and at the most serious intoxication, increases significantly.

Briefly summarizing, I still note: unlike common situations, most of the statements about the dangers of linoleum are not myths. They simply do not concern all products on the market, but only products from the economy segment: trying to reduce costs, material manufacturers sometimes violate a number of standards.

What can be done, I will tell below!

How to make the floor as safe as possible?

Since we figured out that a significant part of the talk about the dangers of linoleum is not a myth, and at least has a rational justification, then it’s worth considering what can be done with this information.

It is quite possible to protect yourself, and I recommend following these rules (they are quite simple):

1. We choose only high-quality coatings. Linoleum must have a certificate of compliance with sanitary standards. If there is no such certificate, then even the lowest price should not become an argument in favor of the purchase.

For children's rooms, we buy only specialized coatings, to which much more stringent requirements are put forward.

1. Smell the roll before buying. A strong chemical odor is a sign of high levels of toxins. Of course, any linoleum will “smell”, but you can easily identify frankly substandard options.

1. After installation, ventilate the room well.. It is desirable that at least five to seven days pass between finishing the floors and settling in: during this period, the concentration of toxins in the air will just decrease.
2. And when doing the installation with your own hands, and when contacting professional finishers, we pay attention to the adhesive composition used. Let you have to overpay a little, but it's better to take really high-quality safe glue.

1. When cleaning, we use only those detergents that do not destroy the floor covering..
2. Timely replacement of linoleum, without waiting for its wear due to the complete destruction of the abradable layer under the influence of pedestrian load and ultraviolet radiation.

Conclusion

Having figured out how harmful linoleum is, and having understood which factors are dangerous, it will be quite simple to prevent unpleasant consequences. The recommendations I have given, based on practical experience, and the video in this article and comments in which you can ask me questions on all aspects of the topic will help you with this.

Many types of protective film for greenhouses and greenhouses have been created at home and abroad. Let's try to understand this diversity.

Types of polymer film

Polyethylene film. At present, ordinary unstabilized polyethylene film (GOST 10354-82, recipe 10803-020) is widely used in vegetable growing in our country. It is obtained from natural gas.

The polyethylene film is slightly bluish and has a slightly matte tint, highly elastic. Its strength is the same in length and width and is equal to more than 100 kg1cm2. With decreasing temperature, the strength of the film increases.

In the first period of operation, it retains its qualities at a temperature of -65 degrees. However, it has been established that for a film that has been in operation, frost resistance decreases even at a temperature of minus 5-10 degrees. she becomes fragile. Therefore, a plastic film that has served the summer cannot be used for shelter in winter or late autumn.

The polyethylene film slightly changes its linear dimensions depending on the temperature, which makes it possible to fasten it rigidly to structural elements.

Under the action of ultraviolet rays and elevated temperature, the film “ages”, and as a result, its tensile strength, light transmission and frost resistance deteriorate. When using a 0.05 mm thick film as a screen in glazed greenhouses, it lasts from 3 to 5 years, while a similar film, being exposed to direct ultraviolet rays, wears out within 3-4 months.

The durability of a polyethylene film depends on the thickness, operating conditions and applied structures.

A thinner film is cheaper, but for tunnel shelters it must be at least 0.08-0.1 mm thick. At the same time, it is believed that it is unprofitable to use a film with a thickness of more than 0.15 mm for shelters on unheated ground.

Polyethylene film is produced in rolls with a web (sleeve) width of 1.2-3 m.

Plastic film usually transmits 80-90% of sunlight. But in special designs with film, where there are fewer shading bindings, the illumination is even higher than under glass.

It should be noted that the polyethylene film used in vegetable growing was not specially created for these purposes and, of course, has significant drawbacks: short service life (4-5 months); a hydrophobic surface that reduces the flow of light as a result of pollution and the formation of a reflective screen due to small droplets of water condensate; a high degree of transparency for infrared radiation, which worsens the thermal regime in shelters at night.

For reusable shelters, it is better to use light-stabilized polyethylene film (GOST 10354-83, recipe 108-08 or 158-08). The stabilization of the film is achieved by introducing into its composition substances that prevent the destruction of the polymer under the influence of atmospheric conditions. The service life of this film in continuous operation reaches one year, and on tunnel shelters it can be used for 2-3 seasons. Outwardly, it does not differ from unstabilized and can be identified by the label on the roll.

The Leningrad Research and Production Association "Plastpolymer" and the Agrophysical Institute have developed a recipe for obtaining a new hydrophilic film (GOST 10354-73, formulation 108-82). The composition of this film includes light and heat stabilizers, which increase its service life by 2-3 times compared to the usual one. The surface of the film is hydrophilic, it is little polluted, moisture condensate is formed in the form of a continuous layer, which increases light transmission and eliminates "drops". The ability of the new film to transmit infrared (thermal) radiation has been reduced from 80 to 30-35%. In production tests, the yield of vegetables in greenhouses covered with a hydrophilic film increased by 10-15%.

Heat-retaining polyethylene film (GOST 10354-83, recipe 108-143G or 158-143G) transmits infrared rays much less, as a result, the temperature under it is 1.5-2 degrees. higher than under conventional polyethylene film. The improved thermal regime under the new film allows you to increase the early harvest of vegetables. The production of a heat-retaining film requires less polyethylene due to the filler (kaolin).

Currently, the industry produces heat-retaining film under the SIK brand.

Foamed film, which consists of two layers: monolithic and foamed, has special properties. It transmits 70% of the visible spectrum of sunlight in diffuse form, as a result, the air temperature under the film decreases slightly during the day and is maintained at a higher level at night. "Foamed" film is recommended for tunnel-type shelters and greenhouses, as well as for vegetative propagation of plants. In its manufacture, polyethylene is saved up to 20% due to its foaming.

Polyethylene photodestructible (GOST 10354-82) film has the ability to collapse after a certain period of operation. Depending on the formulation, this film has the following average terms for the onset of destruction:

formulation 108-70 with radiation exposure - 20 days;

- "- 108-70 without irradiation - 45 days;

- «- 108-71 without irradiation - 60 days.

Photodegradable film is recommended for mulching and as frameless shelters. For these purposes, it is made with a thickness of 0.04-0.06 mm, and before use it is perforated with round or slit-like holes.

PVC film (GOST 16272-79, recipe C). In appearance, it resembles cellophane. PVC film is highly transparent, it transmits up to 90% of visible light and about 80% of ultraviolet radiation. Unlike polyethylene, it almost does not transmit infrared (thermal) rays. Due to this, it is warmer at night under the shelter of a PVC film than under a polyethylene one. This film differs in the big durability in operation reaching 2-3 years. At the same time, it is 2-3 times more expensive than polyethylene. At the same time, it should be taken into account that the PVC film is characterized by relatively low frost resistance (brittleness temperature -15 degrees C), therefore it cannot be left in winter on unheated structures.

Black polyethylene film (GOST 10354-82 formulation 108-157 or 158-157) due to stabilization with soot is practically opaque even at a thickness of 0.04 mm. It is designed for mulching the soil of vegetable and other crops. It improves the hydrothermal regime of the soil in the root layer and suppresses weeds, as a result, the yield increases and labor costs for care are reduced.

For mulching during one season, it is recommended to use a black film 0.04-0.05 mm thick, for two years - 0.06-0.08 mm thick, three or four - 0.1 - 0.12 mm.

The pages of this information resource have already noted the need to protect products made of polyethylene, in particular semi-finished products (polyethylene rods, sheets, plates, etc.) made of polyethylene of various grades, as well as other materials of the polyolefin family, from the harmful effects of UV radiation during operation outdoor products.

The harmful effect of UV - radiation is expressed in a change in the color of the material (fading), as well as in a change in its mechanical properties - the material becomes brittle and cracks, even without mechanical stress.

It should be noted that these processes (fading and change in mechanical properties) are not related to each other - fading characterizes, first of all, the durability of dyes used in the production of materials, and therefore the loss of the original color of the product does not always mean a change in the mechanical properties of the material.

As noted above, to make polyolefins resistant to UV radiation, special UV stabilizers (HALS - inhibitors) are introduced into their composition during the production process.

In general, it can be said that the resistance of a material to UV radiation, and therefore the service life of products, depends on the amount and effectiveness of the UV stabilizers used, as well as on the intensity of UV radiation - at higher latitudes, the intensity of UV radiation is lower, than in the lower ones. Additionally, the intensity of UV - radiation can enhance, for example, its reflection from the water surface.

The combination of stabilizers and dyes added to the material can also have a significant impact on the life of products, for example, the carbon black dye added to polyethylene products is itself a good UV stabilizer, so the service life of black polyethylene products is the longest. .

Leading manufacturers of engineering thermoplastics regularly test their materials to determine the effect of UV radiation on their properties. In general, it can be said that the target indicator for the period during which there should not be a significant change in the properties of materials is 10 years.

However, taking into account the fact that, as noted above, the intensity of UV radiation for different climatic zones is different, for places with high radiation intensity, the actually achievable value of this indicator can be much lower.

On the other hand, for products containing a soot-based dye, the service life can be much longer - up to 20 years on average, without significant changes in the properties of the material.

Separately, it is worth dwelling on the issue of fading of the material. This effect can be observed to a greater or lesser extent, depending on the intensity of UV - radiation and the durability of the dyes used. At the same time, the resistance of recently used organic dyes, as a rule, is significantly lower than the resistance of dyes based on heavy metals (for example, cadmium). Therefore, not always more modern materials are more resistant to fading.