About polyurethane foam, otherwise, polyurethane foam, heard today not only professional builders. Perhaps anyone who thought about the insulation of their own homes, considered this material as one of the good options. After all, it is not only effective, but also very convenient for installation - it is enough just to spray it on the right place. And the long service life and excellent quality of the PUF have already made it a kind of standard among heaters. Let us see what is so remarkable polyurethane foam, consider its characteristics, list the advantages, and also find out if it has any flaws.
This material is one of the varieties of plastic. It has a cellular foam structure, with a gaseous substance prevailing in the composition of polyurethane foam - from 85 to 90 percent. The gas is filled with numerous tiny cells isolated from each other. The remaining few percent of the volume falls on the hard part - the thin walls of these cells.
German scientists from the company IG Farben invented polyurethane foam, supervised by the famous Otto Bayer. However, in those days, this name is not thundering. So, in the laboratory of the city of Leverkusen, after a series of experiments, a new material was obtained, the properties of which turned out to be unique. It became clear that this substance is waiting for a lot of opportunities for use.
Various types of polyurethane foams are in great demand today - after all, they are very simple to manufacture, and immediately on the construction site. At the same time two liquid components, mixing, enter into a chemical reaction. At observance of the necessary proportions, the polymer is synthesized, which is a hardened foam. By altering the recipe of preparation, you can get polyurethane foam, which differ in properties from each other. Some of them are suitable for insulation of windows and doors, others - for insulation of houses made of brick or reinforced concrete, and others - for a variety of pipelines.
So, depending on the proportion of the starting materials, we get polyurethane foams at the exit with cells of different sizes, whose walls have a different thickness and, accordingly, strength. We will not list all types of PU foam that can be obtained by changing the recipe. Let us dwell on the two most popular materials in this group.
1. All familiar foam rubber, scientifically called elastic polyurethane foam, has a density of from 5 to 35 kilograms per cubic meter. We meet this material every day in the form of scourers and sponges, a filler of chairs and sofas, lining in shoes and clothes, as well as shock-proof packaging.
2. Not so long ago, rigid polyurethane foam began to be used in construction work. But today, scientists can already say that it will be with him in 30 or 50 years - the material is being investigated and tested. In addition, in some laboratories, experiments were conducted in which PPU was subjected to the procedure of artificial aging. And those and other results were the same. It is safe to say that the insulation polyurethane foam does not like contact with mineral acids and organic solvents. But he is not afraid of water and oil products at all.
In our country, a sufficiently large number of grades of rigid PU foam is used - about 30. They are used both separately and in various combinations with each other. It all depends on the purpose of the application - it can be warming the house, protecting it from noise, creating an insulating layer on the refrigeration equipment. This material has received such wide applications due to its wonderful properties.
Spraying polyurethane foam over a heat-insulated surface.
We will talk about rigid polyurethane foams - they are used during construction work. They perfectly keep the heat, practically do not let in steam and water, they are not afraid of corrosion, radiation and aggressive chemical environment. In addition, they are very durable, withstand large temperature drops and weather disasters.
The properties of the PUF as a heat insulator depend on the size of its constituent cells. The thermal conductivity of rigid polyurethane foams is in the range of 0.019 to 0.035 watts per meter per Kelvin. To make it clear that this is an excellent indicator, we give examples of comparison. For expanded clay gravel, this parameter ranges from 0.12 to 0.14 watts per meter per Kelvin, and for gas glass and foam glass - as much as 0.84 watts per meter per Kelvin. Inferior polyurethane foam and mineral wool with a thermal conductivity of 0.045-0566 watts per meter per Kelvin.
The material's absorption of noise is determined by several parameters: elasticity, the ability to pass air, and the thickness of the insulation and its damping properties.So, for polyurethane foam, the ability to delay sounds depends on how rigid the frame of the material is and what the frequency of sound vibrations is. The friction force that occurs when particles are transported between neighboring cells, as well as the absorption of sound waves by air from the cells, is also important. By experiments, it was found that it best protects against the noise of semi-elastic polyurethane foam.
In relation to aggressive chemicals, polyurethane foam is more stable than expanded polystyrene. PUFs cannot destroy caustic chemical vapors (the concentration of which does not exceed the permissible). This heater is not afraid of gasoline, oils, alcohols, diluted acids and plasticizers. He is quite persistent with the ketoc esters. Even concentrated acid is not always able to damage it.
If you apply a layer of polyurethane foam on a metal surface, it does not rust. After all, at the same time triple protection will work - both the polyurethane itself and the two films, outside and inside, arising from the polymerization of the material. One of the films will adhere to the metal, and the second will come into contact with the external environment. Depending on the brand of PU foam, the protective layer may be more or less effective.
The moisture absorption of this material is one of the lowest - in a day it can reach from 1 to 3 percent of the original volume. This figure depends on the recipe of PPU. The thicker the insulation, the less water it can absorb. And still the special substances introduced into the composition of polyurethane foam increase the water resistance. One of these water repellents, which reduces moisture absorption by 4 times, is ordinary castor oil.
Polyurethane foam can belong to three groups: С (self-extinguishing), TS (non-combustible) and TV (difficultly flammable). As you can see, the combustibility of polyurethane foam is quite low. And to increase its fire resistance helps either the introduction of special additives, or a change in the chemical formula of the recipe. The second option is expensive, so they often use the method of introducing fillers. These can be phosphorus compounds, as well as halogens. It is possible to put on a regular polyurethane foam only a thin layer of fire-resistant polyurethane foam containing additives. In industrial premises where the danger of fire is high, such a coating applied from two layers would be quite appropriate.
The density of this insulation varies from 30 to 80 kilograms per cubic meter. This figure depends on what technology used in the production of the material. In principle, this is not bad - when weatherization, more rigid and softer materials may be required. It all depends on the specific task. Therefore, sometimes it is possible to obtain substantial savings by applying cheaper PPU of lower density.
The life of polyurethane foam is declared by manufacturers not less than 20-30 years. But there is already evidence that the real numbers are much greater. In American, German, Swedish and Japanese cities, the buildings built in the seventies of the last century are now being dismantled. At their construction polyurethane foam was used for warming. After examining his samples taken from pipes, walls and roofs, experts concluded that the material remained unchanged in all respects. Nine-tenths of all the cells remain isolated, still allowing you to conserve heat well. The chemical state also has not changed. Both laboratory and industrial tests in unison confirm this.
After 10–20 seconds, during which the material hardens, polyurethane foam becomes absolutely safe. If it is heated to a temperature of more than 500 degrees, then the emission of two gases will start: carbon dioxide and carbon monoxide. But if you put wood or rubber in place of the PPU, then at the same temperature they will be more dangerous. Experiments on mice confirmed this.
|Parameters||Minimum and maximum values |
|Heat conductivity, W / m at Kelvin||0.019 - 0.035|
|Density, kg / m||from 26 to 300|
|Tension at which the material begins to collapse, MPa|| at compression from 0.15 to 1.0 |
at bending from 0.35 to 1.9
|Water absorption,% of volume||from 1.0 to 5.0|
|Flammability group of material||GOST-12 . 1. 044 (slow-burning)|
Arguing not about the abstract technical characteristics of polyurethane foam, but about its specific use, we can distinguish the following Advantages of this heater:
1. PPU perfectly “sticks” to any materials, be it brick, glass, wood, concrete or metal.The shape of the surface, its deviation from straightness does not matter. Due to the good adhesive properties, there is no need to subtilize with the device of additional fasteners. By the way, the plane before spraying is not necessary to process anything.
PU foam has excellent adhesion to almost all construction materials.
2. This insulation is made right on the spot, and the volume of the original components is minimal. Therefore, transportation costs are low.
3. Polyurethane foam differs in unusual ease, it does not make heavier a surface. When roof insulation is very important.
4. When applying a layer of polyurethane foam, we not only insulate walls and partitions, but also make them more durable.
5. The polyurethane foam coating does not react to warming and cooling during the year. It feels great at temperatures from minus 200 to plus 200 degrees Celsius.
6. In contrast to panel and sheet insulation, this type of thermal insulation is a single whole, tightly fitting the structure. Nowhere is there a joint or a small seam where a cold wind can blow.
You can install the PUF anywhere and without the use of fasteners.
This article is by no means an advertisement, therefore we will list the negative properties of polyurethane foam. However, there are very few of them, more precisely, two.
1. Negative exposure to ultraviolet radiation may lead to rapid deterioration of the material. In order to prevent the destruction of insulation, it is necessary to provide for its protection. In this capacity, plaster, various panels or ordinary paint can serve, which not only protects from the sun, but also makes the surface of the PU foam more attractive.
2. As already mentioned, polyurethane foams are considered to be combustible materials. By classification, they have a flammability group G-2. This means that when exposed to high temperature ignition does not occur, but the insulation will begin to fester. This process will stop immediately as soon as the material is cooled. But where the surface heats up too much or it can catch fire, you should not use PPU.