## 2 Composite Laminates Toughened by Polymeric Nanofibers
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Ref.** & **Polymer** & **Composite Type** & **Impact Energy** & **Stacking Sequence** & **Curing Temperature** \\ \hline  & Carbon & Carbon/epoxy & & & [0\({}^{\circ}\)2/90\({}^{\circ}\)4/4\({}^{\circ}\)/0\({}^{\circ}\)2s] & - \\  & (10, 20, 30 g/m\({}^{2}\)) & Carbon/epoxy & 2.17, 4.34, 6.52 and 8.9 & & [0\({}^{\circ}\)2/90\({}^{\circ}\)2/0\({}^{\circ}\)2/90\({}^{\circ}\)2s] & - \\  & & & & [0\({}^{\circ}\)2/4\({}^{\circ}\)5/2\({}^{\circ}\)90\({}^{\circ}\)2/\({}^{\circ}\)4\({}^{\circ}\)2s] & - \\ \hline  & Carbon & Glass/Polyester & - & - & Room Temp. (12 h)+ \\  & Carbon & Glass/Polyester & - & 55 \({}^{\circ}\)C (1.5 h) +70 \({}^{\circ}\)C (1.5 h) \\ \hline  & Carbon & Carbon/epoxy & 10, 20 and 30 J & [0]\({}_{\rm He}\) & 80 \({}^{\circ}\)C (0.5 h) + 120 \({}^{\circ}\)C (2.5 h) \\ \hline  & TEOS & Glass/epoxy & & & \\  & (8 g/m\({}^{2}\)) & (Wovern) & 7, 15, 23, 31, 39 J & [0]\({}_{\rm He}\) & 120 \({}^{\circ}\)C (2 h) \\ \hline  & Epoxy 609 (E-03 609) & - & - & - & - \\  & and SiC & & & & \\ \hline  & Polyvinylidene fluoride & Glass/epoxy & & & \\  & (PVDF) & Glass/epoxy & & & \\  & 39 and 64 um & & & & \\ \hline  & Supreme Acryonitrile & & & & \\  & (SAM) & carbon fiber/epoxy & & & \\  & (1 g/m\({}^{2}\)) & carbon & & & \\ \hline  & polyvinyl alcohol (PVA) & carbon fiber/epoxy & & & \\  & (\(\bar{\Omega}\) 1 g/m\({}^{2}\)) & (unidirectional) & & & \\ \hline  & & & & \\ \hline  & & carbon fiber/epoxy & 1-Charyy test (2 1) & & \\  & (unidirectional and woven) & 2-drop-weight impact test (0.6 J) & & \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._PCL nanofibrous mat is another possible choice for toughening composite laminates and three papers were published in this field. [PERSON] et al. [32; 33] used PCL nanofibers and compared their effectiveness with PA6 and PA6.9. Their results showed that PCL could decrease the delaminated area of about 50% which is significantly better than the other two nanofibers. This was due to the low adhesion between the PA6 and PA6.9 nanofibers and the epoxy matrix causing debonding of the nanofibers. On the contrary, PCL nanofibers do have a good adhesion with the epoxy matrix resulting in much better load transfer to the nanofibers. A very important point regarding toughening by PCL is that the melting point of this polymer is about 60 \({}^{\circ}\)C. Therefore, if the curing process temperature is lower than this critical temperature, the nanofibers will be present between the composite layers and the toughening mechanisms will be similar to the one of NY, i.e., bridging between the layers. On the other hand, if the curing temperature is higher than the melting point, a heterogeneous morphology can be observed in which spherical particles of PCL are uniformly dispersed in the continuous matrix (phase separation) [49] (Figure 7). In [PERSON]'s study, the maximum curing temperature (80 \({}^{\circ}\)C) was higher than the melting point, but toughening mechanism was \"Bridging\". This was due to the fact that after the first curing stage, the epoxy resin had already reacted to such extent that complete dissolution of the PCL was prevented during the second curing stage. In the third study, [PERSON] et al. [50] cured the PCL-modified laminates at 150 \({}^{\circ}\)C. Therefore, phase separation was the toughening mechanism. Their results showed about 25% improvement, which is less than [PERSON]'s outcomes. Therefore, it can be concluded that the bridging mechanism is more powerful than the other mechanisms in toughening composite laminates. The effect of adding carbon nanofibers (CNF) on impact response of laminates was considered in eight papers [37; 38; 39; 40; 51; 52]. In almost all these studies, the vapor grown carbon fiber (VGCF) method was used for the production of the nanofibers. The diameter was between 20 to 150 nm and length of the nanofiber was 10-200 \(\upmu\)m and the nanofibers were mixed with the resin before manufacturing the composite sample.