# Multifunctional Modifying Systems Based on Ionic Liquids for Epoxy Resin Systems and Composites
## 4 Conclusions  
This study presented multifunctional modifying systems based on ionic liquids for epoxy resin. The proposed modifying systems introduced into the epoxy composite in an amount of 10% by weight: (i) increase the degree of crosslinking of the polymer matrix, (ii) increase the glass transition temperature, and (iii) improve the fire resistance of the material. Moreover, the produced systems showed a significant effect on the value of storage modulus, allowing for control of this parameter depending on the modifying system used. The studied systems showed an effect on increasing the flexibility of the fabricated structures. The paper pointed out the determining effect of the structure of the ionic liquids included in the modifying system, and in particular, the influence of long  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Sample**} & **LOI** & **UL-94** \\  & **[V/V\%]** & **UL-94** \\ \hline R & 25 & HB \\ A & 26 & HB \\ B & 29 & HB \\ C & 27 & HB \\ D & 27 & HB \\ E & 30 & HB \\ \hline \hline \end{tabular}
\end{table}
Table 7: Limiting oxygen index and UL-94 results of the reference and samples modified with ionic liquids.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **TTI** & **pHRR** & **Time of pHRR** & **THR** & **Residue** \\  & **[s]** & **[kW/m\({}^{2}\)]** & **[s]** & **[M]/m\({}^{2}\)]** & **[Mass\%]** \\ \hline R & 17 & 107 & 32 & 5.7 & 68\% \\ \hline A & 15 & 133 & 28 & 7.4 & 66\% \\ \hline B & 20 & 100 & 33 & 4.8 & 69\% \\ \hline C & 15 & 127 & 28 & 6.5 & 65\% \\ \hline D & 16 & 104 & 30 & 5.4 & 67\% \\ \hline E & 21 & 143 & 36 & 7.2 & 64\% \\ \hline \hline \end{tabular}
\end{table}
Table 8: Mass loss calorimetry results of the reference and samples modified with ionic liquids.  
alkyl chains on individual material parameters such as crosslinking density. In addition, all modifying systems contained silicon and phosphorus atoms in various ratios, but due to the limiting content of the modifying system in the resin, it was not possible to thoroughly investigate the effect of the presence of these elements on individual parameters, in particular, on fire resistance. This aspect will be more thoroughly studied in future work. To summarize, the most important result of the present work is the confirmation, that ionic liquids can simultaneously modify many parameters both in the epoxy resin itself and in the composite, and each time the use of these substances and their effect on the final material should be studied in a multifaceted manner. Properly selected ionic liquids can be great alternatives as functional additives in composite materials with more than one functionality, but sometimes the wrong liquid can result in improving some values at the expense of worsening others.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13910661/s1](https://www.mdpi.com/article/10.3390/app13910661/s1)]([https://www.mdpi.com/article/10.3390/app13910661/s1](https://www.mdpi.com/article/10.3390/app13910661/s1)), 1. NMR spectrum, 2. DSC curves, 3. TGA curves, 4. DMA curves and 5. MLC curve.  
Conceptualization, D.Z., A.T. and A.S.; Formal analysis, D.Z.; Funding acquisition, M.S.; Investigation, D.Z., A.S., A.P., Z.K., B.P. and B.S.; Methodology, D.Z., A.T. and M.S.; Software, D.Z., B.S., B.P. and A.S.; Supervision, A.T. and M.S.; Validation, D.Z., A.T. and M.S.; Visualization, D.Z.; Writing--original draft, D.Z.; Writing--review & editing, D.Z., A.T., A.P., A.S. and M.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Science Centre, grant number 2017/26/E/ST8/01059 and grant number 2019/35/B/ST8/03736. This research was funded by the National Research, Development and Innovation Office (NKFIH K142517).  
Not applicable.  
The authors declare no conflict of interest.