## 3 Results and Discussion
### Fiber Surface Morphology  
The presence of agglomerates in the CSB-MMT polymer results in the formation of a non-homogeneous coating on the fiber surface, as can be observed in the SEM images reported in Figure 6. Although all the fibers were coated with the same polymeric dispersion, using the same procedure, it can be seen that they deeply differ one from the other.  
The fiber in Figure 6a presents on its surface some agglomerates of dimensions varying from some tens of nanometers to almost one micrometer. The agglomerates differ for dimension and distribution on the fibers surface. These agglomerates cannot be seen on the other fiber (Figure 6b), which shows a much more homogeneous surface. On the contrary, Figure 7 shows that all the other coatings form a homogeneous film on the fiber surface.  
Figure 8 displays AFM surface topography imaging and mean roughness values of the fibers modified with the four different coatings previously described. The average roughness R\({}_{a}\), square roughness R\({}_{q}\), and maximum roughness R\({}_{max}\) are reported in Table 2.  
Figure 6: SEM images of two fibers coated with CSB-MMT. Magification 2.00 K\(\times\).  
Figure 7: IPF fibers sized with AMEO (**a**) and coated with: SB (**b**), SB-MMT (**c**), and CSB (**d**). Magification 2.00 K\(\times\).  
The surface of AR-glass fibers coated with the self-crosslinked styrene-butadiene copolymer SB exhibits a quite smooth coating (Figure 8a), showing a rather homogeneous material distribution in accordance with Figure 7b. The same coating with 5 wt% MMT (Figure 8b) exhibits a marked increase of the surface roughness. A similar change in the surface morphology can be observed when the methylol melanin cross-linker is added to the carboxylated-styren butadiene coating (Figure 8c). It can be observed that, by adding both 5 wt% MMT and the methylol melanin cross-linking agent, no significant enhancement of the surface roughness is observed (Figure 8d). On the contrary, a pronounced increase in the surface roughness was observed by adding a 5 wt% of MMT in the SB polymer. Indeed, the highest average roughness, square roughness, and maximum roughness are obtained for fibers SB-MMT, and they are three to four times higher than those obtained for the same polymer without nanoclay particles. An increase in the maximum roughness is also observed for CSB-MMT. However, the square roughness is similar to that obtained for fibers CSB and the R\({}_{a}\) parameter is the lowest obtained. This confirms the presence of nanoclay agglomerate in the CSB-MMT coating, rather than a uniform distribution of the MMT particles in the polymeric matrix.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Fiber Type** & **R\({}_{a}\) [nm]** & **R\({}_{q}\) [nm]** & **R\({}_{max}\) [nm]** \\ \hline SB & 2.27 \(\pm\) 0.29 & 3.33 \(\pm\) 0.4 & 38.88 \(\pm\) 32.34 \\ SB-MMT & 11.90 \(\pm\) 1.17 & 16.91 \(\pm\) 1.61 & 160 \(\pm\) 19.65 \\ CSB & 2.46 \(\pm\) 1.03 & 3.66 \(\pm\) 1.91 & 46.05 \(\pm\) 30.96 \\ CSB-MMT & 1.92 \(\pm\) 0.5 & 3.70 \(\pm\) 1.22 & 107.20 \(\pm\) 26.93 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Average roughness R\({}_{a}\), square roughness R\({}_{q}\), and maximum roughness R\({}_{max}\) values of fibers with SB, SB-MMT, CSB, and CSB-MMT coating, determined by AFM.  
Figure 8: AFM images of IPF fibers coated with (**a**) SB, (**b**) CSB (**c**) SB-MMT, and (**d**) CSB-MMT.