## 3 Results
### Biochars Characterization
The spectral region between 1000 cm\({}^{-1}\) and 2000 cm\({}^{-1}\) provides more detailed information about the residual functionalities of the biochars. All spectra evidenced a broad weak band around 1690 cm\({}^{-1}\) (\(\
u_{\text{C-O}}\)) witnessing the presence of residual ketonic groups [25]. All spectra showed a medium intense \(\
u_{\text{C = C}}\) band around 1580 cm\({}^{-1}\) due to aromatic structures embedded in the carbonaceous matrix. The band around 1370 cm\({}^{-1}\) (\(\delta_{\text{O-H}}\)) was present in all samples but it was weaker in the RH spectrum (Figure 2e). A very intense envelop of bands can be observed between 1035 cm\({}^{-1}\) and 1070 cm\({}^{-1}\) due to several vibrational modes such as \(\delta_{\text{C-O}}\), \(\
u_{\text{C-O}}\). This region was particularly intense in the RH spectrum probably due to the massive presence of silica which presents an active IR mode (asymmetrical \(\
u_{\text{Si-O-Si}}\)) in the region 1020-1110 cm\({}^{-1}\)[26]. Silica is well-known component of rice husk derived biochar as reported by many authors [27; 28; 29; 30]. Furthermore, the great amount of silica could be imputable of low intense of RH \(\delta_{\text{O-H}}\) band. This was due to -OH reduced mobility induced by strong interactions with silica groups. In Figure 4, the Raman spectra of the biochars used in the range between 500 cm\({}^{-1}\) to 3500 cm\({}^{-1}\) are reported. Figure 3: FT-IR attenuated total reflectance (ATR) mode spectra of **(a)** RH, **(b)** MSP, **(c)** SWP, **(d)** OSR, and **(e)** WSP in the region between 500 cm\({}^{-1}\) to 3500 cm\({}^{-1}\). All the spectra showed two main peaks in the range 1000 to 2000 cm\({}^{-1}\) currently named as D (centered around 1360 cm\({}^{-1}\)) and G (centered around 1590 cm\({}^{-1}\)) [31]. Less intense peaks were observed in the range between 2400 to 3300 cm\({}^{-1}\) due to the overtones of the D and G peaks. According to [PERSON] et al. [32], the ratio between the area of I\({}_{\rm D}\) and I\({}_{\rm G}\) peak could be used to evaluate the order of carbonaceous structures. In all the observed spectra, I\({}_{\rm D}\)/I\({}_{\rm G}\) ratios were close to each other, ranging from 1.0 (SWP) to 1.1 (RH). This was strong proof that the carbonaceous materials are equally disordered after pyrolysis. Temperature and heating rate adopted in each case were the optimum to induce the same level of molecular order in the biochar produced. Before dispersion in polymeric matrix, biochars were mechanically grinded for 10 min and particle size distribution were analyzed. The results are reported in Figure 5.  
From these results, OSR showed a particle size distribution with a large distribution centered at well-around 10 \(\upmu\)m. RH, WSP, and MSP showed the same peak at 10 \(\upmu\)m together with a peak at a higher dimension ranging from around 50 \(\upmu\)m to more than 100 \(\upmu\)m. SWP showed great particle size with a tailored peak centered at 100 \(\upmu\)m. The different particle distributions were a consequence of grindability of the feedstock. Considering the residual group detected in Figure 4, such distributions were due to the different morphologies formed after pyrolytic treatments [33]. According to these observations, it is possible to assume that the SWP particles were hardly grindable because of their smooth surfaces. As highlighted in Figure 2e, f, SWP did not show a channeled and porous surface as all the other materials. Accordingly, it is reasonable to assume that pore and channel walls are more fragile than smooth surfaces and undergo a more relevant disruption during the grinding process. Figure 4: Raman spectra of biochars in the range between 500 cm\({}^{-1}\) to 3500 cm\({}^{-1}\).