# New Flame Retardant Systems Based on Expanded Graphite for Rigid Polyurethane Foams
## 2 Experimental
### Characterization Techniques  
The absolute viscosities of polyol and isocyanate were determined corresponding to ASTM D2930 (equivalent to ISO 2555) using a rotary viscometer DVII+ (Brookfield, Lorch, Germany). The torque of samples was measured as a range of shear rate from 0.5 to 100 s\({}^{-1}\) in ambient temperature. The structure and size distribution of the foam cells was examined on the basis of the images of the cell structure of the foam, made with the Leica MZ6 optical microscope at two magnifications: 50x and 250x and the JEOL JSM-5500 LV scanning electron microscopy (JEOL, Ltd., Peabody, MA, USA). All microscopic observations were made in high vacuum mode and with an accelerating voltage of 10 kV. The samples were scanned for free growth. Mean pore diameter, wall thickness and pore size distribution were calculated with ImageJ software (Media Cybernetics, Inc., Rockville, MD, USA). The apparent density of foams (5 specimens per sample were measured and averaged) was determined accordingly to ASTM D1622 (equivalent to ISO 845). The compressive strength (\(\sigma_{10\%}\)) of foams (averaged 5 measurements per each sample) was determined accordingly to the ASTM D1621 (equivalent to ISO 844) using Zwick Z100 Testing Machine (Zwick/Roell Group, Poland, Lodz). The compression strength was measured as a ratio of the load causing a 10% deformation of sample cross-section in the parallel and perpendicular direction to the square surface. A three-point bending test was carried out using Zwick Z100 Testing Machine (Zwick/Roell Group, Ulm, Germany) at room temperature, according to ASTM D7264 (equivalent to ISO 178). The obtained flexural stress at break (cf) results for each sample were expressed as a mean value. The average of 5 measurements per each type of composition was accepted. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample Codes**} & \multirow{2}{*}{**Comments**} & \multicolumn{5}{c}{**Mass Content (by Weight, wt\% )**} \\ \cline{3-6}  & & **Polyol** & **Isocyanate** & \begin{tabular}{c} **Expanded** \\ **Graphite** \\ \end{tabular} & \
\begin{tabular}{c} **Funded** \\ **Silica** \\ \end{tabular} &
\begin{tabular}{c} **Ionic Liquid** \\ **(emim) (BFx)** \\ \end{tabular} \\ \hline PU-0 & Reference foam (unfilled) & 100 & 160 & - & - & - \\ PU-EG & Foam with graphite & 100 & 160 & 5 & - & - \\ PU–EG+SiO\({}_{2}\) & Foam with graphite and silica & 100 & 160 & 5 & 1 & - \\ PU–EG+SiO\({}_{2}\)+IL & Foam with graphite, silica and & 100 & 160 & 5 & 1 & 0.33 \\  & ionic liquid & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Formulations of rigid polyurethane foams (RPUF) prepared in the study. Figure 1: Scheme for drawing-up the RPUF. The thermal conductivity of the foams obtained was determined based on the measurement of the thermal conductivity (\(\lambda\)). The test was carried out for \(200\times 200\times 50\) mm\({}^{3}\) samples using a FOX 200 apparatus (LaserComp, Inc., Saugus, MA, USA). Thermal conductivity was determined at 10 and 20 \({}^{\circ}\)C in the range from 20 to 100 mW/(m\({}^{*}\)K). The fire behavior was analyzed using a cone calorimeter apparatus according to ISO 5660 in S.Z.T.K. 'TAPS'--Maciej Kowalski Company (Saugus, Poland). Each specimen with dimensions of \(100\times 100\times 50\) mm\({}^{3}\) was wrapped with aluminum foil and burned at an external heat flux of 35 kW m\({}^{-2}\). The parameters were recorded during the time. The measurement for each specimen was repeated three times, and the error values of the typical cone calorimeter were reproducible within \(\pm 5\%\), and the reported results are the average of three measurements. The thermal stability testing of rigid polyurethane foams was performed using a Mettler Toledo thermogravimetric analyzer TGA/DSC1. Thermal decomposition was carried out in the range of 25-600 \({}^{\circ}\)C in an inert gas atmosphere with a flow of 50 mL/min and a heating rate of 10 \({}^{\circ}\)C/min.