POLYURETHANE (PUR)

As an efficient thermal insulation material, polyurethane has been used in buildings since 1950s. Polyurethane (PUR) sandwich panels are ever-increasingly preferred by more investors and designers all around the world. Having the best insulating values among the insulating materials used in buildings, polyurethane provides energy savings up to 40% in ever-increasing heating and air conditioning costs. Use of fossil fuels comprises 80% of CO2 emissions in the world. Use of polyurethane is a rational approach to help reduce CO2 emissions which is also the primary cause of global warming. Investors always seek high performance with low costs and the best solution to this expectation is polyurethane. Polyurethane is (plastic) polymers produced as a result of reactions between isocyanates in NCO group and polyols of OH group.

Contribution reaction is completely a polymerization reaction, and it is a sub-group of plastics. Polyurethane foam is produced by mixing the following 4 raw materials

:
  • Polyol
  • Isocyanate
  • Blowing gas (N-Pentane)
  • Catalyst

In addition to two fluids, i.e., isocyanate and polyol, the ideal closed cell polyurethane foam is produced as a result of chemical reactions of activators. Foam production rates are regulated by the catalyst. With the correct formulation of two raw materials and the control of the foam reaction, the following characteristics of polyurethane are determined:

  • Density
  • Mechanical Endurance
  • Closed Cell Structure
  • Heat Resistance
  • Resistance to Solvents
  • Reaction rate
  • Bonding strength

Roughly, chemical reactions can be described at 4 stages. The first stage consists of mixing Polyol formulation with isocyanate. In this case, a fluid is immediately produced, and foam begins to be produced at the second stage. At the third stage, the foam mixture creates heat and expands in volume by a factor up to 25 times more than its initial volume. At this stage, due to high adhesive properties of the foam, the foam tightly and continuously binds to various materials. At the fourth stage, free foaming creates a resistant layer on the exterior surface. In case there are still fluids at this stage, foaming process continues, and these fluids move to small gaps to fill up. Polyurethane only achieves the most homogeneous foaming process with homogeneous sections. After completion of the foaming reactions, millions of small, closed cells are created. Each cell is filled with blowing gas-originated gas. The underlying reason for polyurethane foam provides the perfect thermal insulation is intracellular gases with low thermal conductivity and polyurethane material with relatively low thermal conductivity. Identifying itself as “Eco-Friendly”, Assan Panel uses HC Pentane (n) gas, which is not harmful to ozone, as a blowing gas in its products.

Thanks to the closed cell form of polyurethane, it does not absorb water due to capillary effect. Water intake is only possible due to diffusion effect based on application. Moisture balance is affected by the ambient temperature and relative humidity. Even under ambient conditions of 100% Relative Humidity (RH), polyurethane is not affected more than 5% in weight and more than 0.15% in volume as these are the maximum limits. In this case, the fact that metal surfaces of sandwich panels create closed surfaces particularly reduce the practical importance of moisture activity. When the high heat transmission of water (i.e., 0.60 W/mK) is considered, such surfaces would also contribute to the thermal insulation properties of polyurethane which does not allow moisture intake. Water vapor permeability is highly crucial for comfort in buildings. Water vapor diffusion resistance (μ) and diffusion equivalent thickness (Sd) are two key characteristic values. Water vapor diffusion resistance (μ) value is specific to the material and determined by comparing it to the air diffusion resistance, which is considered to be 1. Water vapor permeability in sandwich panel systems is dependent on the density of polyurethane, manufacturing process, and the type of metal surface.