## 2 Methods for Adhesion Improvement
### Fiber Treatment and Matrix Modifications
The final anchorage on the surface, previous to the propylene polymerization reaction, is AlO\({}_{3}\), with one of the O of the AlO\({}_{3}\) linked to an alkyl group and the other two to Si or Al. The addition of a hydroxy-\(\alpha\)-olefin to supply the necessary vinyl-bonds to initiate the propylene polymerization is performed. It was demonstrated that short hydroxy-\(\alpha\)-olefins (5-hexen-1-ol) [39] tend to act as Lewis bases; however the use of long-chain hydroxy-\(\alpha\)-olefins (9-decen-1-ol,10-undecen-1-ol) is preferred to assure a low level of poisoning [40]. * _Reaction of the glass surface with hydroxy-\(\alpha\)-olefin_. After the MAO reaction to the glass surface, hydroxy-\(\alpha\)-olefin is added. The hydroxy-\(\alpha\)-olefin reacts with the MAO-CH\({}_{3}\) groups with evolution of methane and the setting of terminal vinyl groups to the glass. Then, a copolymerization reaction can be initiated from these macrocomonomers. The propylene (CH\({}_{3}\)-CH=CH\({}_{2}\)) molecules are attached via catalytic polymerization using EtInd\({}_{2}\)ZrCl\({}_{2}\) (metallocene)/MAO. The MAO is included in the metallocenic catalyst to alkylate the metallocene, and to generate and stabilize the cationic active zirconocene. As a result, PP chains grow by copolymerization of propylene with the vinyl group of the Al-O(CH\({}_{2}\))n-C=CH\({}_{2}\), remaining chemically bonded to the glass. Finally, the polymer precipitates by acidified ethanol aggregate. Details of the experimental procedure are described in previous works [36,38]. This reaction scheme (Figure 1) was further proved by consistent evidence obtained by combining scanning electron microscopy techniques (SEM) with X-ray energy dispersive analysis (EDX). The hydroxy-\(\alpha\)-olefin concentration used in each case was calculated in order to ensure the activity of the metallocene catalyst. The metallocene concentration remained constant. Therefore, the reaction variables were selected aimed to obtain a high level of PP coverage on the glass surface by chemical bonding between them. Table 1 summarizes the nomenclature of all reactions performed, where the concentrations in percentage were calculated following the calculations explained in reference [37]. The experimental methodology, as well as the techniques used for characterization, are schematically described in Figure 2. \begin{table}
\begin{tabular}{l c c} \hline
**Name** & **Hydroxy-\(a\)-olefin [\(\mu\)L]** & **Total MAO [mL]** \\ \hline F0 &..... &..... \\ F0.5\% & 50 & 10 \\ F1\% & 100 & 10 \\ F1.5\% & 150 & 12 \\ F2\% & 200 & 12 \\ \hline \end{tabular}
\end{table} 
Table 1: Nomenclature of all reactions performed. In order to determine the reaction occurrence, a comparative study was performed on fiber surfaces after strong PP extraction. In a previous work, screening experiments were performed using extremely low and high hydroxy-\(\alpha\)-olefin concentrations, 0.4 and 4%, respectively. In these studies, it was demonstrated that propylene effectively copolymerizes onto fiber surfaces and the final morphology depends on the hydroxy-\(\alpha\)-olefin amount used during the reaction [36, 41].