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البولى يوريثان(polyurethanes)

البولى يوريثان(polyurethanes) Polyurethane foam is undoubtedly an excellent insulating and sealing material. Polyurethane foam has been known in construction for many years. Excellent insulating properties result directly from the structure of foam as a porous material containing an open and closed-cell system. Due to the very low thermal conductivity coefficient, it is ideally suited as thermal insulation for a variety of applications. Foam is also characterized by a very low water absorption coefficient. Thanks to this, it is used, among others, in waterproofing of foundations, terraces, and many other surfaces.

Polyurethane foams and their properties

Polyurethane is substantially made of two raw materials — isocyanate and polyol, which are derived from crude oil. After mixing those two process-ready liquid components of the system and various auxiliary materials, such as catalysts, foaming agents, and stabilizers, a chemical reaction starts.

The history of polyurethane dates back several generations. At first, there was a technology of producing rigid (hard) foam, then flexible foam, and finally semi-rigid foam.

What properties does PUR foam have? Above all, it demonstrates good thermal parameters — it is resistant to a wide range of temperatures (from –200°C to +135°C). Average thermal conductivity coefficient of polyurethane foam is 0.026 W/m2, and the most favourable apparent density after the curing of rigid foam is usually 35 – 50 kg/m³.

The greatest advantage of PUR foam is its excellent thermal insulation properties. Polyurethane foam is also resistant to relatively high loads, as well as fungi and mould. Thus, it is undoubtedly an ideal material for any construction and renovation works, such as thermal and acoustic insulation, and — in the case of flexible polyurethane foam — fitting and sealing.

Open- and closed-cell foams

Polyurethane foam is divided into two basic types — open-cell and closed-cell. The former is intended for indoor use, particularly for insulating walls and roofs as well as increasing acoustic comfort of a room, as polyurethane foam — besides thermal insulation properties — has a very high noise reduction coefficient. Open-cell foam is vapour-permeable, so that we can say that a surface covered with it “breathes.” Sprayed from the inside, directly on the roof, it can be easily used on a membrane or boarding.

When it comes to technical parameters — open-cell foam has density of 7–14 kg/m³, while its thermal conductivity coefficient ranges from 0.034 to 0.039 W/(m*K). Among the types of open-cell polyurethane foam, there are materials with different fire rating. The best ones are rated E.

Another group — closed-cell polyurethane foam — due to its high water resistance, higher rigidity, and strength, is used outdoors and in rooms with high humidity.

Its structure contains more than 90% of closed cells and its density ranges from 30 to 60 kg/m³. Thermal conductivity coefficient of closed-cell polyurethane foam ranges from 0,02 to 0,024 W/(m*K).

Closed-cell foam types differ in parameters depending on their application. On the one hand, it is perfect for insulating foundation walls, ceiling structures, roofs, and floors. On the other hand, it can be used in industrial and agricultural buildings, for example to insulate production floors, warehouses, cold stores, or livestock buildings.