Properties and characteristics of polyurethane foam its advantages and disadvantages
Not only professional builders have heard about polyurethane foam, or PU, today. Perhaps, anyone who thought about warming their own home, considered this material as one of the good options. After all, it is not only effective, but also very convenient for installation – it is simple enough to spray it on the right place. A long service life and excellent quality of PU has already made it a kind of standard among heaters. Let's see what is so remarkable about polyurethane foam, consider its characteristics, list its advantages, and find out whether it has any disadvantages.
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What is polyurethane foam and what is it like?
This material is a type of plastic. It has a cellular foamy structure, and the composition of polyurethane foam is dominated by a gaseous substance - 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 solid part-the thin walls of these cells. German scientists from the company IG Farben, led by the famous Otto Bayer, came up with polyurethane foam. However, in those days, this name was not yet booming. So, in the laboratory of the city of Leverkusen, after a series of experiments, a new material was obtained, the properties of which were unique. It became clear that this substance is waiting for a lot of opportunities for use. Various types of PU are in great demand today – because they are very easy to make, and immediately on the construction site. In this case, two liquid components, mixing, enter into a chemical reaction. If the necessary proportions are observed, a polymer is synthesized, which is a solidified foam. Modifying the recipe, you can get polyurethane foams that differ in properties from each other. Some of them are suitable for thermal 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 at the output of polyurethane foam with cells of different sizes, the walls of which have different thickness and, accordingly, strength. We will not list all types of PU that can be obtained by changing the recipe. Let's focus on the two most popular materials of this group. 1. All familiar foam, scientifically called elastic polyurethane foam, has a density of 5 to 35 kilograms per cubic meter. This material is found daily in the form of washcloths and sponges, the filler of chairs and sofas, the lining in shoes and clothing, as well as shockproof packaging. 2. Rigid polyurethane foam has recently been used for construction work. But today, scientists can already tell what will happen to it in 30 or 50 years – the material is being investigated and tested. In addition, some laboratories conducted experiments in which the PPU was subjected to an artificial aging procedure. Both results were the same. It is safe to say that the polyurethane foam insulation 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, we use a fairly large number of brands of rigid PU – 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 opportunities of application due to its wonderful properties.
Thermal conductivity
The properties of PU as a thermal insulator depend on the size of its constituent cells. The thermal conductivity of rigid polyurethane foams ranges from 0.019 to 0.035 watts per meter per Kelvin. To make it clear that this is an excellent indicator, let's give examples of comparison. In expanded clay gravel, this parameter is from 0.12 to 0.14 watts per meter per Kelvin, and in gas glass and foam glass-as much as 0.84 watts per meter per Kelvin. Inferior to polyurethane foam and mineral wool with a thermal conductivity of 0.045-0.056 watts per meter per Kelvin.
On the technical characteristics
We will talk about rigid polyurethane foams – they are used during construction works. They keep heat perfectly, practically do not pass steam and water, are not afraid of corrosion, radiation and aggressive chemical environment. In addition, they are very durable, withstand large temperature changes and weather disasters.
Relation to chemical media
Polyurethane foam is more resistant to aggressive chemicals than Styrofoam. Pups can not destroy caustic chemical vapors (the concentration of which does not exceed the permissible). This insulation is not afraid of gasoline, oils, alcohols, dilute acids and plasticizers. It is quite resistant to ethers with ketones. Even concentrated acid is not always able to damage it. If you apply a layer of PU on a metal surface, it will not rust. After all, this will work triple protection-as the polyurethane itself, and two films, outside and inside, arising from the polymerization of the material. One of the films will be adjacent to the metal, and the second will be in contact with the external environment. Depending on the brand of PU, the protective layer may be more or less effective.
The sound-absorbing ability
The material's absorption of noise is determined by several parameters: elasticity, air permeability, as well as 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. Also important is the friction force that occurs when particles are transferred between neighboring cells, as well as the absorption of sound waves by air from the cells. It was found out by experiments that the best protection against noise is a semi-elastic type of foam.
Combustibility of polyurethane foam
Polyurethane foams can belong to three groups: C (self-extinguishing), TC (difficult to burn) and TV (difficult to ignite). As you can see, the combustibility of polyurethane foam is quite low. And to increase its fire resistance, either the introduction of special additives or changing the chemical formula of the recipe helps. The second option is expensive, so more often use the method of introducing fillers. These can be phosphorus compounds, as well as Halogens. You can apply only a thin layer of fire-resistant PU containing additives to ordinary polyurethane foam. In industrial premises where the risk of fire is high, such a coating applied from two layers will be quite appropriate.
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Density
The density of this insulation varies from 30 to 80 kilograms per cubic meter. This indicator directly depends on what technology was used in the production of the material. In principle, this is not a bad thing – when warming, you may need both harder and softer materials. It all depends on the specific task. Therefore, sometimes you can get significant savings by using a cheaper foam of lower density.
Environmental safety and human impact
After 10 — 20 seconds, during which the material hardens, the polyurethane foam becomes absolutely safe. If it is heated to a temperature of more than 500 degrees, then two gases will be released: carbon dioxide and carbon monoxide. But if you put wood or rubber in place of the foam, they will be more dangerous at the same temperature. Experiments on mice confirmed this.
Durability
The service life of polyurethane foam is declared by manufacturers not less than 20-30 years. But there is already evidence that the actual numbers are much higher. In American, German, Swedish and Japanese cities, buildings built in the seventies of the last century are being dismantled. During their construction, polyurethane foam was used for insulation. After studying its samples taken from pipes, walls and roofs, experts concluded that the material remained unchanged in all respects. Nine-tenths of all cells remain isolated, allowing you to still save heat well. The chemical state has not changed either. Both laboratory and industrial tests confirm this in unison.
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Table of properties of polyurethane foam
| Parameters | Minimum and maximum values |
| Thermal conductivity, W / m per Kelvin | 0,019 — 0,035 |
| Density, kg / m | from 26 to 300 |
| The stress at which the material begins to break down, MPa | when compressed from 0.15 to 1.0 when bent from 0.35 to 1.9 |
| Water absorption, % of volume | from 1.0 to 5.0 |
| Group of combustibility of the material | GOST-12.1.044 (difficult-to-burn) |
About the pros
Talking not about abstract technical characteristics of polyurethane foam, but about its specific application, we can highlight the following advantages of this insulation: 1. PPU perfectly "sticks" to any materials, whether it is a brick, glass, wood, concrete or metal. The shape of the surface and its deviation from the straightness do not matter. Due to its good adhesive properties, there is no need to use any additional fasteners. By the way, the plane does not need to be processed before spraying. PPU has excellent adhesion to almost all building materials. 2. This insulation is made right on the spot, and the volume of the original components is minimal. Therefore, transport costs are low. 3. Polyurethane foam is extremely light, it does not weigh down the surface. When insulating the roof, this 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. 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 insulation is a single unit, tightly fitting the structure. There is no joint anywhere, no small seam where a cold wind can blow. To install the PPU can be anywhere and without the use of fasteners.
About cons
This article is not advertising, so we will list the negative properties of polyurethane foam. However, there are very few of them, or rather, two.
1. Negative effects of UV radiation can lead to rapid wear and tear of the material. To prevent the destruction of the insulation, it is necessary to provide its protection. This can serve as a plaster, various panels or ordinary paint, which not only protects from the sun, but also makes the surface of the foam more attractive.
2. As already mentioned, polyurethane foams are considered difficult-to-burn materials. According to the classification, they have a combustibility group G-2. This means that when exposed to high temperatures, the fire will not occur, but the insulation will begin to smolder. This process will stop immediately as soon as the material is cooled. But where the surface is too hot or may catch fire, PU should not be used.