# Sustainable Materials from Waste Paper: Thermal and Acoustical Characterization
## 5 Conclusions  
The present study has shown the results achieved by developing different mixes using pulp paper waste. The effect of the addition of three different aggregates (fava bean residue, sawdust powder, coffee grains) was investigated in a laboratory by performing physical, thermal and acoustic tests. As shown by SEM analysis, the presence of a more porous and fibrous structure of the pure aggregate, as in sawdust, allows a more porous final matrix and a consequent higher porosity of the final specimens. Conversely, the presence of a more compacted fava bean residue, also in the form of grains, provokes a lower bulk porosity and a higher bulk density in the final specimens. Overall, the thermal conductivity of the tested samples ranged from 0.071 to 0.093 W\(\cdot\)m\({}^{-1}\).K\({}^{-1}\), allowing us to include the tested materials in the category of thermal insulators. As expected from the physical tests, the best insulator was the SP mix. Moreover, the CG and FB mix had a bulk density and thermal conductivity comparable to plywood. In terms of acoustic behavior, generally, the measurement of the normal incidence sound absorption coefficient found that the upper and the lower faces of all the specimens were not uniform, due to the manufacturing process and to the different shrinkage provoked by the aggregates used. Additionally, the use of different sized samples based on the frequency range contributed to an increase in dissimilar acoustic behavior. The comparison between the measured average sound absorption curves for each mix and the variation \begin{table}
\begin{tabular}{l c c c c c c} \hline  & \multicolumn{2}{c}{**FB**} & \multicolumn{2}{c}{**CG**} & \multicolumn{2}{c}{**SP**} \\ \hline
\begin{tabular}{c} **Non-Acoustic** \\ **Properties** \\ \end{tabular} & **Min abs** & **Max abs** & **Min abs** & **Max abs** & **Min abs** & **Max abs** \\ \hline \(\sigma^{*}\) (kN\(\cdot\)s\(/\)m\({}^{4}\)) & \(37\times 10^{4}\) & \(22\times 10^{4}\) & \(160\times 10^{4}\) & \(48\times 10^{4}\) & \(68\times 10^{4}\) & \(32\times 10^{4}\) \\ \(\varepsilon^{*}\) (-) & 0.6664 & 0.6864 & 0.7683 & 0.7983 & 0.8506 & 0.8806 \\ \(\tau^{*}\) (-) & 14.8 & 6.6 & 4.9 & 4.3 & 2.2 & 4.9 \\ s\({}^{*}\) & 2.9 & 1.85 & 0.5 & 0.95 & 0.5 & 2.9 \\ A\({}^{*}\) & 5.1433 \(\times 10^{-5}\) & 2.5901 \(\times 10^{-5}\) & 4.80 \(\times 10^{-5}\) & 4.24 \(\times 10^{-5}\) & 4.61 \(\times 10^{-5}\) & 1.73 \(\times 10^{-5}\) \\ \(\Lambda^{\prime*}\) & 5.1433 \(\times 10^{-5}\) & 6.475 \(\times 10^{-5}\) & 1.20 \(\times 10^{-4}\) & 4.24 \(\times 10^{-4}\) & 1.153 \(\times 10^{-4}\) & 4.325 \(\times 10^{-5}\) \\ \hline \end{tabular} Note: \(\sigma^{*}\), \(\varepsilon^{*}\), \(\tau^{*}\), \(\sigma^{*}\), \(\Lambda^{*}\), \(\Lambda^{*}\) are air flow resistivity, porosity, tortuosity, shape factor, viscous and thermal characteristic lengths determined with the inverse method.  
\end{table} 
Table 5: Non-acoustic properties of experimental samples resulting from numerical estimation. range of the predicted normal sound absorption coefficient obtained from the inverse method allows us to observe that high frequency values range in the estimated area, except for the FB mix. Furthermore, for this latter mix, an increased absorption in the low frequency range and a reduced absorption in the high frequencies was observed. Conclusively, the experimental results achieved and described in this paper demonstrate that the materials are suitable to be proposed as insulation panels due to the low thermal conductivity values. Moreover, taking into account the acoustic properties, it can be asserted that they might be used either for wall paneling or false ceilings. Further detailed investigations are underway to evaluate the bond of the experimented materials with existing supports, mechanical performances and hygric properties. Moreover, an LCA (Life Cycle Analysis) will be carried out to support future potential commercial applications. Conceptualization, S.L. ; Methodology, S.L., F.M., C.R. and P.S. ; Investigation, S.L. and C.R.