Polyurethane foam
At Termyson we know our trade very well. That is why we carry out our insulation works with polyurethane foam , since it is the best thermal insulator and offers a number of advantages and facilities in its application and durability.
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Advantages of polyurethane
- Solves leak problems
- It is not flammable.
- It can be painted.
- Seal any area safely.
- Product of very long duration.
- It does not allow condensation to occur.
- Extends the useful life of the treated surfaces.
- Controls dilatations in concrete structures.
- It acts as a vibration damper.
- Energy saving used in cooling or heating.
Forms of application of polyurethane
- In situ by projection or projected polyurethane : it is obtained by simultaneous pulverization of the two components on a surface, partitions, naves, roofs, terraces, farms, etc.
- In situ by casting, or injected polyurethane : in which the two components are mixed and introduced through a hole previously made in the partition, for expansion. Isolating in this way all the space between the two partitions of the house. It is the method used in houses already built that do not have insulation.
Properties of polyurethane foam
The rigid polyurethane foam is a duroplastic synthetic material, highly spatially crosslinked and non-fusible. In the usual densities, for thermal insulation, the foam contains only a small part of the volume of solid matter (with a density of 35 kg / m³ , only about 3% of the volume is solid matter).
Next, we detail the properties of polyurethane foam.
Cell structure
The rigid polyurethane foam obtained by projection has a predominantly closed cell structure. The percentage of closed cells is above 97%.
Density
The density of the rigid polyurethane foam by projection for thermal insulation is included and standardized in Standards UNE 92120-1 and 92120-2 according to the application, between 30 and 55 kg / m ³ . Although, for special applications, higher densities (100, 200, etc.) or lower densities (acoustic foams: 10, 12, 15, etc.) can be used.
Thermal conductivity
The high insulating capacity of rigid polyurethane foam by projection is not achieved in the construction with any other known insulating material. This special feature is due to the very low thermal conductivity of the foaming gas occluded inside the closed cells.
In this way, the rigid polyurethane foam produced "in situ" can reach a thermal conductivity value of 0.022 W / m • K. Because the cells do not completely prevent the diffusion of gases through their walls, this conductivity value increases slightly with time until it finally stabilizes. In practice, the thermal conductivity value of the foam is considered to be that obtained after 9 months of aging (UNE 92120-1), 0.028 W / m • K.
By applying coatings that prevent the diffusion of gases (vapor barrier) it is possible to achieve that the thermal conductivity of the foam does not show appreciable alterations with time, maintaining values of 0.023 W / m • K.
Water absorption
The absorption of water by the rigid polyurethane foam by projection occurs as a function of environmental conditions and may take place by wetting or diffusion and condensation of the steam. It is influenced mainly by density.
The absorption of water by short-term partial immersion of the rigid polyurethane foam according to the test is less than 0.13 kg / m². It must be borne in mind that the greater amount of water considered is due to the one remaining in the cells that are broken when making the cut to make the test piece.
By vapor diffusion and subsequent condensation, the isolations can absorb water depending on their situation and the temperature and humidity to which they are subjected. In practice, it is necessary to avoid reaching unwanted limits of humidity by diffusion of water vapor modifying the constructive solution. It can be done by increasing the density of the foam or in very extreme cases by placing a vapor barrier on the surface adjacent to the interior of the room (hot side of the insulation).
Resistance to the transmission of water vapor
The values that characterize the resistance to water vapor are the dimensionless mu, or, the resistivity to the diffusion of water vapor.
For rigid polyurethane foam by projection for thermal insulation, in densities 30-60 kg / m ³ , the resistance to the transmission of water vapor ranges between 330-825 MN • s / g • m, being the dimensionless factor, of resistance to the transmission of water vapor from 60 to 150. These values guarantee - in the majority of thermal insulation solutions by rigid polyurethane foam and depending on the density that we adopt - the absence of interstitial condensation, allowing its time the perspiration of the enclosures. Understanding that the transpiration of the enclosures in the building is the most beneficial effect both to avoid pathologies of all kinds, hygiene, health, comfort, etc.
In applications with high levels of steam and / or temperature (for example, cold rooms) it will be necessary to place a vapor barrier on the hot side of the insulation to avoid condensation. In residential buildings the most critical values are usually manifested in flat roofs because waterproofing prevents transpiration.
Stability / Resistance
The rigid polyurethane foam obtained by projection is resistant to the materials commonly used in construction.
In addition, rigid polyurethane foam by projection is:
- - Resistant, to a great extent, to the solvents normally used in adhesives, paints, bituminous pastes, preservatives for wood and sealants.
- - Resistant to aging, against the action of roots and inert. Biochemically, for example, against molds.
- - Stable against fuels, mineral oil and diluted acids and alkalis.
- - Resistant against the action of the exhaust gases or the more aggressive industrial atmosphere.
- - Imputrescible, stable before detritus. Inodora and physiologically does not present disadvantages.
- - It's chemically neutral. Fire behavior: the rigid polyurethane foam has an M3 fire classification. Thermal expansion: the thermal expansion of rigid polyurethane foam by projection due to temperature is a function of density and substrate fixation.
Closed cells and open cells
Each material has a certain variation in its dimensions when the temperature varies. In addition, in the case of rigid polyurethane foam, there is a gas enclosed in its cells that causes a drop in pressure, with cold, and an overpressure, with heat. Therefore, by shrinkage a contraction occurs and by heating a dilation of the cellular structure.
With the usual density, 35 kg / m³, the coefficients of contraction, or expansion of the rigid polyurethane foam, are between 5 and 8 x 10-5 K-1.
The open cell foams, by not using gases of low thermal conductivity, have a cost of raw material approximately 20% lower. In addition, as the applied density of the product is lower, the required amount of material per m² is reduced between 15% and 30%. However, the implementation in order to obtain the minimum benefits required by the project and the current legislation implies additional costs. The application of an open cell polyurethane system, in direct replacement of a closed cell one, without the necessary corrections (greater thickness, mortar plastering, vapor barrier, etc.) can cause multiple problems:
- Breach of project and / or legislation.
- Poor insulation and higher energy consumption.
- Absorption of water in the insulation and deterioration of the insulating properties.
- Appearance of humidity and mold (unhygienic).
- Water filtrations. Both the manufacturer and the installer have the obligation to adequately inform their client of the type of product and its suitability for the different constructive solutions.