# Study of the Preparation and Dielectric Property of PP/SMA/PVDF Blend Material
## 3 Result and Discussion
### Dielectric Properties  
The relationship of the dielectric constant (\(\epsilon\)) of PP/PVDF blends to frequency is shown in Figure 5a. It can be seen from the figure that \(\epsilon\) became greater with the increasing addition of PVDF, which can be explained by the influence of high dielectric properties of PVDF. There is an exception in PP/PVDF (60/40), due to the poorest interactions between two polymers according to our previous study [8; 9; 10]. A PVDF molecule contains two fluorine groups (-F) which show an intense polarity and have an orientation under the effect of external electric field, and the relaxation of the fluorine groups happens during the electric cycle. The orientation speed of fluorine groups (-F) is in line with the variations of the electric field at low frequency, and thus the \(\epsilon\) curve was flat at the beginning. However, as the frequency increases, those movements are prevented. The orientation speed of polarity groups of PVDF was less than the variations of electric field, which led to a steep fall of the \(\epsilon\) curve. Although the dielectric constant ranges of PP and PVDF are 2.2-3 and 8.4-13.5, respectively, PP/PVDF blends have poor dielectric properties, as their dielectric constant has a maximum value of 3, which is lower than that of pure PVDF [16; 17]. Figure 4: SEM micrographs of PP/SMA/PVDF blends in different magnification. (**a**) PP/PVDF (20:80); (**b**) PP/PVDF (50:50). Figure 3: Scanning electron microscope (SEM) micrographs of PP/PVDF blends in different magnification. (**a**) PP/PVDF (40:60); (**b**) PP/PVDF (80:20). Figure 5b shows the relationship of \(\varepsilon\) of PP/SMA/PVDF blends to frequency. It can be observed that the dielectric constant \(\varepsilon\) became greater with the increasing addition of PVDF, which is consistent with that of PP/PVDF blends. Besides, compared with PP/PVDF blends, the dielectric constant \(\varepsilon\) of PP/SMA/PVDF blends improved significantly, which proved that the polarization degree of PP was promoted through only a small amount of SMA addition in PP/PVDF blends, and thus the dielectric property improved and the dielectric constant \(\varepsilon\) increased as well. Figure 6a shows the relationship of the dielectric loss (tan\(\delta\)) of PP/PVDF blends to frequency. tan\(\delta\) of PP/PVDF blends increased gradually with frequency, and this tendency became more obvious with the increase of PVDF. An exception was seen in PP/PVDF (60/40), which can be explained by the reason discussed previously. The curve of dielectric loss is flat at low frequency, but it increased drastically starting at a frequency of \(10^{5}\) Hz and resulted in a significant inflection point in the graph. In addition, the inflection point appeared at approximately the same frequency for all compositions although the content of PVDF kept increasing, which suggested that the inflection point correlated to the basic property of the blends rather than PVDF. The relationship of the tan\(\delta\) of PP/SMA/PVDF blends to frequency is shown in Figure 6b. At small frequency, tan\(\delta\) showed the tendency to decrease with frequency. Meanwhile, with the decrease of PP amount, this tendency became more significant. In addition, with the increase of frequency, tan\(\delta\) of PP/SMA/PVDF blends remained almost constant, independent of frequency. Although there was a rising trend at large frequency, the tan\(\delta\) of PP/SMA/PVDF blends was relatively small, and it was below 0.03 with 3% SMA addition. Figure 5: Frequency dependence of \(\varepsilon\) for (**a**) PP/PVDF and (**b**) PP/SMA/PVDF. The dielectric constant of PP/PVDF blends and PP/SMA/PVDF blends with 3% SMA addition were tested at room temperature and at a frequency of 10\({}^{6}\) Hz. In Figure 7a, the dielectric constant \(\varepsilon\) of PP/SMA/PVDF blends decreased with the increase of PP content. In addition, it can also be seen from the figure that the dielectric constant of blends with added SMA was greater than that of PP/PVDF blends.