One of the most popular materials for the thermal insulation of buildings is expanded polystyrene. The example shows a quality control run on a commercially available expanded polystyrene material (EPS 040). Ten samples of the same batch were tested at 24°C and, according to DIN EN 13163, at 10°C. It can clearly be seen that the deviation between the different samples is less than 1%. The determined thermal conductivity λ 90/90 value according to DIN 13163 was 0.03808 W/(m*K). (measurement with HFM 436 Lambda)
PUR foam exhibits an insignificant level of anisotropic behavior which is shown by the dilatometer measurement. The CTE values are nearly the same in the y- and z-directions between -160°C and 100°C. An additional measurement was performed in each direction; the results also demonstrate the excellent reproducibility of the dilatometer DIL 402 C.
In addition to low thermal conductivity, PUR foams also offer high mechanical stability. This makes them useful as insulation material in roofs, cryotanks or even ships. The plot shows a comparison of a test with an HFM 436 Lambda at room temperature and a GHP 456 Titan® test down to -160°C. The two results are in perfect agreement. Additionally, the GHP result shows the impact of cell-gas condensation between -50°C and -125°C.
Extruded Polystyrene Foam (XPS): This material has air inclusions, which gives it moderate flexibility, a low density, and a low thermal conductivity. XPS has a well established reputation for longterm reliability and superior resistance to the elemental forces of nature. A 50 mm Styrodur® C board was measured between -150°C and 20°C with the GHP 456 Titan®. Good agreement with literature values was observed at RT.
The specific volume of polystyrene can be measured with a dilatometer using a special cylinder as a sample holder. Before the 1st heating, the sample was aged below glass transition temperature (Tg); the 2nd heating was conducted on the same sample after controlled cooling. The volume relaxation for the 1st heating is clearly visible at the Tg, as is the change in slope at the Tg for the 2nd heating. (measurement with DIL 402 C)
Glass Wool is often used for the insulation of houses and heating pipes. The STA measurement shows three mass-loss steps below approx. 600°C, which are due to the evaporation of humidity and the burn-up of organic binder. The latter can be seen from the strongly exothermic DSC signal in this temperature range. The step in the DSC signal at 728°C with an increase in the specific heat of 0.41 J/(g*K) is due to the glass transition. The exothermic DSC peak at 950°C with an enthalpy of -287 J/g is due to crystallization; the endothermic effects between approx. 1050°C and 1250°C with an entire enthalpy of 549 J/g show the melting. The slight mass changes above 700°C are most probably due to oxidation and evaporation of impurities.
How does a measurement in a heat flow meter compare to measurements with other standardized techniques such as guarded hot plate (GHP). As part of a Round Robin Test, a nanoporous insulation board was measured with different NETZSCH heat flow meters as well as with a guarded hot plate system (absolute measurement technique). The results obtained by the different instruments are in agreement within 2.5% in the overlapping temperature range. This clearly demonstrates the outstanding performance of the HFM 436 Series instruments.
Mineral wool is a widely employed material mainly used for the insulation of residential buildings. A mineral fiber insulation was investigated in a round robin test by means of the guarded hot plate apparatus (GHP 456 Titan) and heat flow meters (HFM 436 series) between 10°C and 30°C. As it is typical for most insulating materials, there is a linear increase in the thermal conductivity results around room temperature. The results obtained with the different measuring systems are in good agreement. This round robin test further confirms that by means of the absolute measurement method (GHP), an accuracy of <2% can be obtained.