## 7 Melt Electrospun Polymer Blends
While pure PLA was not spinnable at the temperature of 200 \({}^{\circ}\)C, PLA/PEG blends were easily spun, achieving the lowest fiber diameters of 3-6 \(\upmu\)m with 30 wt.% of PEG at an applied voltage of 70 kV. It was also found that viscoelastic parameters such as zero-shear viscosity and relaxation time as indicators of elasticity can give relevant information to optimize the processing. Addition of PEG into PLA resulted in enhanced polymer-chain mobility and disentanglement. To predict the miscibility at the melt-electrospinning temperature, interfacial tension between the two phases was calculated from rheological data, which predicted a good miscibility between both polymers. However, it was found that at the higher critical concentration of PEG (i.e., 30%), not enough elasticity existed causing the decrease of the melt electrospinning. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Polymer** & **Nanoparticle** & **Effects in the Process and/or Application** & **Ref.** \\ \hline PLLA & nHAP (3 wt.\%) & \begin{tabular}{c} Hydrophilic matrix. Biomedical applications due \\ to its biocompatibility and osteoconductivity. \\ \end{tabular} & [59] \\ \hline PLA & WO\({}_{3}\) (7 wt.\%) & \begin{tabular}{c} Efficient light-to-heat conversion, great NIR \\ absorption, high hydrophobicity. \\ \end{tabular} & [146] \\ \hline PP & TiO\({}_{2}\)/Sodium stearate nanoparticles & \begin{tabular}{c} Dyeing-wastewater decolourization, \\ photocatalytic applications. \\ \end{tabular} & [152] \\ \hline PET & SiO\({}_{2}\) nanoparticles & \begin{tabular}{c} Good thermal and chemical stability, excellent \\ mechanical properties, and well dye ability. \\ \end{tabular} & [153; 154] \\ \hline PCL & Fe\({}_{3}\)O\({}_{4}\) magnetic nanoparticles & \begin{tabular}{c} Magnetic hyperthermia treatments (cancer \\ treatment), wound dressing and haemostasis. \\ \end{tabular} & [160] \\ \cline{2-3}  & nHAp & \begin{tabular}{c} Increase roughness and diameter of the fibers. \\ Tissue engineering applications. \\ \end{tabular} & [163] \\ \hline PA6 & \
\begin{tabular}{c} MMT (montmorillonite) \\ (1–10 wt.\%) \\ \end{tabular} &
\begin{tabular}{c} Viscosity, Young’s modulus and electrical \\ conductivity increased. \\ \end{tabular} & [156; 165] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Nanoparticle additives in melt electrospinning. Figure 10: Schematic diagram of the 3D fibrous-composite scaffolds fabricated by the melt electrospinning writing process. Copyright 2020 Elsevier [163]. [PERSON] et al. [39] evaluated the effect of viscosity-reducing additives on the phenomenological properties of iPP in the melt electrospinningning process. Diameter of fibers could be reduced from 35 \(\upmu\)m to 840 nm. Ultrafine fibers of iPP/styrene-acrylonitrile (SAN) copolymer blends have been also obtained by melt electrospinningning [173]. Morphology and distribution of SAN in the blend logically varied with composition as well as its nucleating activity and the structure of the electrospun fibers. Even though the addition of SAN resulted in fiber diameters in the rage between 5 and 10 \(\upmu\)m and a narrow distribution, more spindle-shaped SAN particles were produced when SAN content was increased. Separated SAN particles joined at the highest concentrations and even formed filaments along the fiber axis (trends shown in Figure 11a-d). In the melt state, SAN particles were efficiently stretched and, as a result, the specific surface area changed. Regarding these observations, new morphologies of polymer blends can be favoured by melt electrospinning because of their faster stretching and cooling processes with respect to other techniques. It was also demonstrated that by using the dry mixing or melt blending prior to electrospinningning, it was possible to tune the morphology by modifying the process conditions and/or the material combinations. Recently, [PERSON] and [PERSON] [61] added polyvinyl butyl (PVB) into iPP and the prepared film was processed using laser melt electrospinningning.