## 3 Experimental Results
On the other hand, the potential application of the developed environmentally compatible products as insulating panels also suggests the possibility of generating in the bulk of the material a controlled amount of porosity, which was attained by the use of sodium bicarbonate as a blowing agent. Sodium bicarbonate slowly decomposes to form sodium carbonate above 50 \({}^{\circ}\)C, though the rate of decomposition is much higher at or above 200 \({}^{\circ}\)C [26]. \[2\ \text{NaHCO}_{3}\rightarrow\text{Na}_{2}\text{CO}_{3}+\text{H}_{2}\text{O} +\text{CO} \tag{1}\]  
As reported in Table 3, the addition of the foaming agent involves a decrease of the density of the UF/OFMSW blends. With an increasing amount of sodium bicarbonate, the density decreases. On the other hand, as the density decreases, the compressive modulus decreases as well. The specific modulus, defined as the ratio between the compression modulus and density, also decreases. The data reported in Figure 5 and Table 3 show that there are two different ways in order to obtain a porous material, which can be used for the production of insulating panels:  
1. [label=()]
2. Curing the samples at higher temperatures, which allows to foam the OFMSW/UF blends due to water evaporation/boiling [1];
3. The addition of the catalyst and foaming agent, which allows to cure and foam the sample at lower temperature. The difference in the porous structure obtained by the two methods is highlighted in the optical microscopy reported in Figure 6A,B, which show the images of the unanalyzed system without a blowing agent cured at a high temperature and the catalyzed system with a blowing agent cured at low temperatures, respectively. The unanalyzed samples were obtained in a previous work by a process defined as \"one step\", in which the sterilization and valorization process, were run simultaneously at 120 \({}^{\circ}\)C for 1 h (OF_P100N_one step) [1]. A comparison between Figure 6A,B clearly shows that the addition of sodium bicarbonate allowed to obtain a faster expansion process, which in turn resulted in the formation of pores with higher diameter. In particular, the results for the average pore size reported in Table 4 confirm the formation of bigger pores when the sodium bicarbonate is added as a blowing agent; on the other hand, the low standard deviation associated to the measurement (8% of the average value) highlights the formation of a controlled porosity. In contrast, the use of water as a foaming agent involves the formation of a dishomogeneous porous structure (the standard deviation is about 50% of the average). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Density\(\boldsymbol{\rho}\) (g/cm\({}^{3}\))** & **Compression Modulus E (Mpa)** & **Specific Modulus E\({}_{8}\) (10\({}^{3}\) m\({}^{2}\)s\({}^{-2}\))** \\ \hline OF\_P100N\_C & \(1.15\pm 0.023\) & \(65.57\pm 1.31\) & \(57.01\) \\ OF\_P100N\_C\_1 sb & \(1.05\pm 0.01\) & \(18.64\pm 0.9\) & \(17.75\) \\ OF\_P100N\_C\_2 sb & \(1.02\pm 0.02\) & \(12.20\pm 2.2\) & \(11.96\) \\ OF\_P100N\_C\_3 sb & \(0.97\pm 0.02\) & \(15.96\pm 0.9\) & \(16.45\) \\ OF\_P100N\_C\_5 sb & \(0.98\pm 0.01\) & \(15.63\pm 1.6\) & \(15.95\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Compression modulus, density, and specific modulus of the OF_P100N_C samples with different amounts of sodium bicarbonate. Figure 7 shows a comparison of the specific moduli of catalyzed samples obtained with the addition of sodium bicarbonate (OF_P100N_C_3 sb), which shows a significant decrease compared to the specific modulus of the blend without the foaming agent, OF_P100N_C. In addition, the specific modulus of the blend without the catalyst cured at 120 \({}^{\circ}\)C, OF_P100N, is reported. By comparing the two porous systems, it can be highlighted that the specific modulus for the porous samples obtained upon addition of the foaming agent is higher than that of the blend foamed by water evaporation/boiling.