Bismuth Trioxide Doped Polyamide 6.6 Nanocomposites for Electrically Insulating Materials

Polymer-based insulators have attracted much attention amongst researchers due to their various advantages such as light weightness, lower cost and ease of production. In this study, it is aimed to manufacture lightweight and thin insulator by electrospun composite bers and to observe the effect of bismuth oxide (Bi 2 O 3 ) on insulating property of polymer-based composite structure. For that purpose, polyamide 6.6 polymer (PA6.6) with high dielectric constant was doped with bismuth trioxide micro particles and it was used for coating polyester spunbonds by electrospinning technique. Morphological properties, thermal behaviours and electrical resistance of coated spunbonds were investigated. Scanning electron microscopy (SEM) and electron dispersive X-ray spectroscopy (EDX) showed that Bi 2 O 3 was succesfully adapted into ber structure and nano-scale PA6.6/Bi 2 O 3 composite bers were obtained. Thermal behaviours of coated samples were developed by increasing Bi 2 O 3 loading according to differential scanning calorimetry (DSC) and thermogravimetic analysis (TGA) results. Addition of Bi 2 O 3 caused remarkable increase on electrical resistance of PA6.6 electrospun surfaces. Bi 2 O 3 /PA6.6. nanocomposite bers are promising and good candidates for thin electrically insulating polymer-based structures for micro- or nanodimensional devices. of Bi 2 O 3 loadings in PA 6.6 nanocomposite bers. According to DSC and TGA thermograms, thermal characteristics of samples developed and Bi 2 O 3 loading decreased mass loss percentages for studied samples. Electrical conductivity of Bi 2 O 3 /PA6.6 coated PES spunbonds have been signicantly declined by increasing Bi 2 O 3 loading and increase in Bi 2 O 3 loading lead to crucial increase in electrical resistivity. Results demonstrate that Bi 2 O 3 /PA6.6 nanocomposite structures are promising canditates for being used as insulating materials in miniaturized electronic devices with advantages of their light weightness and neness. Further studies should be performed on different concentration values of various polymers.


Introduction
Usage of polymers and polymer based materials has been tremendously increased in speci c elds for last many decades. Especially for electrical applications, polymer insulators have been increasingly used in both distribution and transmission of various voltage ranges by considering their medium or high dielectric constants. Polymers having high and low dielectric constants have satis ed demands for manufacturing of capacitors and developed dielectric materials, respectively. Besides their wide ranges of dielectric constants, polymeric materials offer many attractive advantages such as; high elastic surface, low surface energy, good thermal stability, good hydrophobic characteristics and compatibility with organic and inorganic llers for electrical applications [1].
Bismuth oxide (Bi 2 O 3 ) is a semi-conductive metal oxide [2]. It is generally used in various elds such as gas sensors, microwave entegrated circuits, optical devices and photovoltaic applications. Due to the high conductivity of oxygen ions, it has been taken in consideration for solid electrolite applications [3]. In manufacturing of functional materials with Bi 2 O 3 , electro-deposition, synthesis with microwave method and chemical vapor deposition method are generally used and various composite structures or semiconductive nano brillates can be succesfully produced in form of nanoparticles, nano lms or nano bers [4][5][6]. Some studies are available in production of Bi  Electrospinning is an alternative method to produce functional composite structures. In this technique, solvent is an actor from which is utilized to electrospin polymer or its blends under electrostatic eld and deposition of randomly aligned micro or nano bers is observed on collector [10]. The mostly known advantage of this manufacturing method is the ability of processing with different types of polymers [11][12][13][14][15][16][17][18][19][20][21][22][23]. Many researchers focused on electrospun nanostructure manufacturing due to unique and/or superior characteristics of nanostructures by means of electronic, magnetic, optical, mechanical, physical and chemical properties [24][25][26][27][28][29][30]. For changing electrical behaviours of materials, many methods have been studied such as; blending polymers with a conductive polymer or material, addition of co-solvent into polymer solution and using different solvents for dissolving polymer [31][32][33][34][35]. Electrical characteristics of electrospun structures have been studied by few researchers but most of these studies focus on improving electrical conductivity of end product [36][37][38][39][40] produced electrically insulating nano brillated cellulose lms with Al 2 O 3 and graphene llers and they claimed that these lms were super insulators in next generation electrical packing eld [42]. Zhang et al.
In the present study, it is investigated whether electrospinning technique can be used for production of a thin composite insulator. For that purpose, PA 6.6. polymer having high dielectric constants was doped with Bi 2 O 3 micro particules and nanocomposite bers were deposited on PES spunbond. The objective of current study was to produce light weight polymer-based insulator using electrospinning technique with preparation of well dispersed Bi 2 O 3 in polymer ber mats and examine the effect of Bi 2 O 3 doping on electrical conductivity, morphological properties and thermal characteristics of PA 6.6. electrospun surfaces.

2.2.2.
Electrospinning conditions: Polymer solutions were transferred to a 10 ml syringe with 11.99 mm inside diameter. The applied voltage and ow rate was ~ 37-38 kV and 1 ml/h, respectively. Distance between needle tip and target was 8 cm. The resulting randomly-oriented Bi 2 O 3 /PA 6.6. bers were deposited on at collector covered with PES spunbond for 45 minutes.

Fourier Transform Infrared Spectroscopy (FT-IR)
FT-IR spectra of samples were examined by considering EDX test results to detect possible bond occurence in nanocomposite bers. In Figure 2,  process was not applied to surfaces, such as drying in a oven for awhile. Therefore, no crystallization would occur during electrospinning. Besides, randomly aligned electrospun bers were manufactured and perfect alignment of nano bers were not observed which was a factor triggering crystallization [50]. Tm and Tg values of samples are given in Table 2. TGA thermograms and percentage weight loss of samples are given in Figure 4. TGA analysis was used to determine the thermal stability of neat PA6.6 and Bi 2 O 3 /PA6.6 nanocomposites with different percentages. For neat PA6.6 (PA6.6-0), small weight loss was observed above 200 o C due to evoluation of traces of moisture or unreacted monomers and decomposition was available above 350 o C due to decomposition of base polymer to leave residual carbon from polymer back bone. [51].

Electrical analysis by dielectric spectroscopy:
Electrical insulating property of a solid material can be characterized by considering dielectic constant of corresponding material. Dielectric constants (ε) of PA 6.6 polymer was reported as 3.4-3.6 at 1 MHz and PA 6.6 was considered as an insulating polymer amongst other commercial polymers [52][53][54]. Electrical resistance of Bi 2 O 3 /PA6.6 nanocomposite ber coated PES spunbonds are shown in Figure 6. 5% Bi 2 O 3 loading increased electrical resistance of PA6.6-0 from 592.287 kΩ.cm to 949.398 kΩ.cm. Coated PES spunbonds showed more insulating property than uncoated PES spunbond. This can be correlated with tortuosity effect of nano bers collected on PES spunbond and slow discharge of electrical energy in nano ber layers [55]. On the other hand, there is reciprocal proportion between electrical resistance and conductivity. Electrical conductivity of uncoated PES spunbond was obtained as 5,864E-06 S/cm. Bi 2 O 3 loading lead to more insulating material production. This case could be explained that decrease in electrical conductivity was related with polymer type and nano ber production utilized both Bi 2 O 3 propogation and decisive characteristics' exhibition in composite structures [52][53][54][55].

Conclusion
In summary, we develop thin nanocomposite surfaces with electrically insulating property by electrospinning technique. In particular, Bi 2 O 3 microparticules were adapted to PA 6.6 nanocomposite bers. By means of ber neness, addition of Bi 2 O 3 microparticules did not result to a considerable increase in ber diameter of PA 6.6 composite bers and this was result of easy electrospinnability of PA6.6 polymer. FT-IR spectra showed that structural formations were preserved and negligible shifts were observed due to concentration changes of Bi 2 O 3 loadings in PA 6.6 nanocomposite bers. Declarations