## 2 Materials and Methods
### Coating Preparation and Characterization  
Sodium montmorillonite (MMT), with a typical dry particle size \(<\) 25 \(\upmu\)m and basal spacing of 1.17 nm (d\({}_{001}\) value), was obtained from Southern Clay Products, Inc., under the trade name of Cloisite(\({}^{\circledR}\)Na\({}^{+}\). A carboxylated and self-crosslinking styrene-butadiene latex (SB), with a solid content of 50%, was supplied by Lefatex Chemie GmbH (Bruggen-Bracht, Germany) along with the methylol melanin crosslinking agent (C, solid content 75%). Preliminary tests showed that no stable dispersion could be obtained by directly mixing the nano-clay in the polymeric latex. For this reason, a different protocol was developed in which the nano-clay particles were first dispersed in distilled water and successively mixed with the SB latex (Figure 2):  
1. First, 2.5 g of nano-clay particles were slowly added to 50 mL distilled water in a 100 mL round flask under vigorous stirring. The mixture was stirred for about 5 min and then was placed in an ultrasonic bath at 40 \({}^{\circ}\)C for 1 h.
2. The mixture was then refluxed for 3 h at 80 \({}^{\circ}\)C until a homogeneous dispersion was obtained. Once the dispersion was cooled down, it was filtered with a 14-19 \(\upmu\)m filter in order to remove possible agglomerated particles. In order to exclude the presence of agglomerates, the particles size distribution of the nanoclay in the aqueous dispersion was analyzed with Malvern Zetasizer Nano ZS Particle and ZetaPotential Analyzer. The distribution obtained was found equal to that reported in the technical sheet for Cloisite(\({}^{\circledR}\)Na\({}^{+}\), which indicates that the nanoclays were well dispersed;
3. The nanoclay dispersion was stirred for 15 min with the SB latex and distilled water. The proportion between nanoclay dispersion (MMTD), SB latex (SB), and distilled water (H\({}_{2}\)O) was calculated as follows: first, the amount of SB latex and MMTD dispersion were determined according to Equations (1) and (2), and then the obtained dispersion was diluted with distilled water in order to obtain a final solid content of 20% (Equation (3)). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Sizing** & **Coating** \\
**Name** & **(1 st Treatment Step)** & **(2 nd Treatment Step)** \\ \hline \multirow{2}{*}{PTMO} & 1\% N-propyltrimethoxysilane & \multirow{2}{*}{none} \\  & (PTMO) in distilled water & \\ \hline \multirow{2}{*}{SB} & 1\% 3-Aminopropyltriethoxysilane & self-crosslinking \\  & (AMEO) in distilled water & styrene-butadiene copolymer (SB) \\ \hline \multirow{2}{*}{CSB} & 1\% AMEO in distilled water & SB + 7\% crosslinking agent (C) \\ \hline \multirow{2}{*}{SB-MMT} & 1\% AMEO in distilled water & SB + 5\% montmorillonite (MMT) \\ \hline \multirow{2}{*}{CSB-MMT} & \multirow{2}{*}{1\% AMEO in distilled water} & \multirow{2}{*}{CSB + 5\% MMT} \\  & & \\ \end{tabular}
\end{table} 
Table 1: Surface modification of ARG fibers. \[m_{SB}[g]=\frac{x\cdot m_{SBMMT_{x}}[g]}{scSBC[\%]}\cdot 100\] \[with\quad x=\frac{0.2}{1.05},\] \[m_{MTTD}[g]=\frac{x\cdot m_{SBMMT_{x}}[g]\cdot 0.05}{scMMTD[\%]}\cdot 100, \tag{2}\] \[m_{H_{2}O}=m_{SBMMT_{x}}[g]-m_{SB}[g]-m_{MTTD}[g], \tag{3}\]  
where:  
* \(x\) is the polymer solid fraction in the SB-MMT coating;
* \(SBMMT_{x}\) is the desired amount of SB-MMT coating expressed in gram;
* \(scSBC\) is the SB latex solid content determined according to DIN EN ISO 3251;
* \(scMMTD\) is the solid content of the MMTD dispersion determined according to DIN EN ISO 3251. Coatings CSB and CSB-MMT were obtained adding the methylol melanin cross-linking agent respectively to the SB and the SB-MMT dispersion under stirring.