## 3 Results and Discussion  
### Characterization of Cork Waste  
The FTIR and the STA analyses confirmed the chemical composition of the cork waste resulting in cork, polyurethane glue, and paraffin (Figure 1). Precisely, in the FTIR spectrum of Figure 1a, the characteristic peaks of cork can be identified at 3400 cm \({}^{1}\) (-OH bond), 2920, 2850 cm \({}^{1}\) (stretching) and 1737 cm \({}^{1}\) (bending) [24]. Paraffin can be detected  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Cork** & **Cork** & **Cork** & **Isocyanate** & **Polyol** \\
**(wt\%)** & **(vol\%)** & **(g)** & **(g)** & **(g)** \\ \hline
0 & 0.00 & 0.00 & 94.99 & 67.85 \\
5 & 34.99 & 8.14 & 94.99 & 67.85 \\
10 & 51.84 & 16.28 & 94.99 & 67.85 \\
15 & 61.75 & 24.43 & 94.99 & 67.85 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Mix design of polyurethanes containing increasing content of cork waste (from 0 wt% to 15 wt%).  
On the other hand, the presence of cork, paraffin, and polyurethane glue was confirmed by thermal analysis. Considering DTGA (Figure 1b, black dashed line), the complete degradation of cork can be observed at around 371 C and 410 C [24]. The other exothermic peaks (between 600 C and 800 C) can be attributed to the degradation of paraffin [27] and polyurethane glue [26]. Moreover, the TGA curve (continuous green line) showed a mass loss of around 76.22% related to cork degradation [28] and a mass loss of 22.73% attributable to the degradation of paraffin and polyurethane glue [26, 29]. Contrary to expectations, a greater content of glue and paraffin (>21 wt%) was observed. This is attributable to the fact that, during the production of agglomerated cork caps, the glue and paraffin tend to concentrate on the cap surface, which is the part subject to smoothing and from which the cork waste is generated. So, the cork waste under investigation displayed a slight difference in composition compared to the original agglomerated cork cap.  
As reported in Figure 2, the cork waste displayed a bimodal particle size distribution with main peaks at 150 \(\upmu\)m and 600 \(\upmu\)m. A fine particle size of cork waste can also be observed (0.063 mm \(<\) d \(<\) 1 mm).  
Figure 3 shows the morphology of cork waste at different magnifications, namely 8 and 35 magnification. The powder particles own the peculiar cork color, have an angular shape, and are different in size. Particle agglomerations and a high porosity rate between them can be observed.  
Figure 1: Composition of cork waste through ATR FT-IR analysis (**a**) and STA analysis (**b**). In Figure 1b are displayed the following curves: TGA (green line), first derivative of TGA (DTGA, black dashed line) and DSC (blue line).  
Figure 2: Particle size distribution of cork waste.  
Remarkably, a water absorption of 177% was detected for cork waste, which is a consistent value considering the low particle size of the cork powder [27; 30]. Moreover, an apparent density of 340 kg/m\({}^{3}\) and a real density of 1110 kg/m\({}^{3}\) were registered. These values are slightly higher than those about virgin cork from the literature [27] but are consistent considering the presence of polyurethane glue and paraffin.