## 3 Experimental Results
The compression properties and the density of each sample are reported in Table 2.  
Figure 4: **(A)** Stress-strain curves of OF_P100N_C with and without coffee powder; **(B)** stress-strain curves of OF_P100N_C with a different amount of sawdust. Figure 3: Pictures of the urea formaldehyde (UF)/organic fraction of municipal solid waste (OFMSW) blends (**A**) before and (**B**) after the curing process. The density data reported in Table 2 show that, compared to the data reported in our previous work [1], the reduction of the curing temperature from 120 \({}^{\circ}\)C (used for unanalyzed blends) to 60 \({}^{\circ}\)C (used in this work for catalyzed blends) allows to completely eliminate the porosity of the produced samples, which in turn produces an increase of the density of the samples. This is better highlighted in Figure 5A, where a comparison between the density of the same blends obtained with and without the catalyst, and therefore cured at 60 \({}^{\circ}\)C or 120 \({}^{\circ}\)C, respectively, is shown. As better explained in a previous work, [1], the difference in the density is mainly due to the lower rate of water release during curing at lower temperatures; this allows a more efficient bubble removal during curing of the matrix. According to the results reported in Table 2, the addition of sawdust at relatively high amounts involves a decrease of the density, resulting from an incomplete wetting of the wood particles by the polymer matrix. The results for the mechanical properties, reported in Table 2, show that the addition of OFMSW to the UF matrix involves a decrease of the compressive strength, but also an increase of the compressive modulus. Furthermore, the results of Table 2 indicate that, within certain limits, the presence of the waste fillers does not significantly influence the mechanical properties of the OFMSW/UF blends. In particular, the compression properties (modulus, strength, and strain at break) of the blend containing up to 5% of sawdust are substantially equivalent to those of the neat resin. However, for higher contents, the mechanical properties show a substantial decrease. In contrast, the coffee does not significantly influence the mechanical properties of the OF_P100N_C composite up to an amount of 10%. Very relevantly, the void fraction decrease attained by a reduction of the curing temperature has a significant effect on the compression modulus of the samples, as highlighted by the results reported in \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Formulation** & **Density \(\rho\) (g/cm\({}^{3}\))** & \begin{tabular}{c} **Compressive** \\ **Strength \(\sigma_{\mathbf{R}}\) (MPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Strain at Break** \\ **(mm/mm)** \\ \end{tabular} &
\begin{tabular}{c} **Compressive** \\ **Modulus (MPa)** \\ \end{tabular} \\ \hline P100N\_C & 1.10 \(\pm\) 0.02 & 6.57 \(\pm\) 0.55 & 0.22 \(\pm\) 0.009 & 59.36 \(\pm\) 1.94 \\ OF\_P100N\_C & 1.15 \(\pm\) 0.023 & 4.60 \(\pm\) 0.09 & 0.12 \(\pm\) 0.002 & 65.57 \(\pm\) 1.31 \\ OF\_P100N\_C\_10c & 1.15 \(\pm\) 0.02 & 4.11 \(\pm\) 0.08 & 0.12 \(\pm\) 0.002 & 63.34 \(\pm\) 1.27 \\ OF\_P100N\_C\_5s & 1.12 \(\pm\) 0.022 & 4.15 \(\pm\) 0.08 & 0.13 \(\pm\) 0.003 & 60.87 \(\pm\) 0.22 \\ OF\_P100N\_C\_10s & 1.16 \(\pm\) 0.023 & 3.01 \(\pm\) 0.06 & 0.16 \(\pm\) 0.003 & 33.96 \(\pm\) 0.68 \\ OF\_P100N\_C\_15s & 1.09 \(\pm\) 0.021 & 3.11 \(\pm\) 0.06 & 0.15 \(\pm\) 0.003 & 36.93 \(\pm\) 0.74 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mechanical properties of the samples with and without additives. Figure 5: Density (**A**) and compressive modulus (**B**) of the catalyzed and uncatalysed UF/OFMSW blends. Figure 5B. For the unanalyzed blends cured at 120 \({}^{\circ}\)C according to the procedure reported in a previous work [1], the relatively high void fraction results in very low values of the modulus; a reduction of the curing temperature to 60 \({}^{\circ}\)C, attained by addition of the catalyst, involves a significant increase of the modulus.