Materials selection process for electrical insulation application was carried out using Cambridge Engineering Selector (CES) program. Melt mixing technique was applied to prepare polyvinyl-chloride- (PVC-) nanofumed silica and nanomontmorillonite clay composites. Surface analysis and particles dispersibility were examined using scanning electron microscope. Dielectrical properties were assessed using Hipot tester. An experimental work for dielectric loss of the nanocomposite materials has been investigated in a frequency range of 10 Hz–50 kHz. The initial results using CES program showed that microparticles of silica and clay can improve electrical insulation properties and modulus of elasticity of PVC. Nano-montmorillonite clay composites were synthesized and characterized. Experimental analyses displayed that trapping properties of matrix are highly modified by the presence of nanofillers. The nanofumed silica and nanoclay particles were dispersed homogenously in PVC up to 10% wt/wt. Dielectric loss tangent constant of PVC-nanoclay composites was decreased successfully from 0.57 to 0.5 at 100 Hz using fillers loading from 1% to 10% wt/wt, respectively. Nano-fumed silica showed a significant influence on the electrical resistivity of PVC by enhancing it up to 1 × 1011 Ohm·m.
Nanocomposites represent a very attractive route to upgrade and diversify properties of the polymers. Nanofiller-filled polymers might be differentiated from microfiller-filled polymers in three major aspects that the nanocomposites normally contain smaller amounts, are in range of nanometers in size, and have tremendously large specific surface area. All these characteristics are reflected in their material properties [
PVC is widely used in industrial applications. Chemically, PVC has a structure which is similar to that of PE but instead of several hydrogen atoms, it has chlorine atoms, which are attached to the molecular chains at the side in a random manner [
Effect of silica and clay particles on the performance of PVC can be governed by the mechanical and electrical properties. CES program (Granta Design Company) was initially used to predict the desired properties of PVC composites using different fillers (microscale)/matrix mixing ratio. Synthesis and manufacturing of PVC composites were carried out based on the obtained results using CES program.
Polyvinylchloride (PVC) was received from petrochemical company (Sabic, Saudi Arabia). Physical and mechanical properties of PVC are listed in Table
Physical and mechanical properties of polyvinyl chloride.
Physical and mechanical properties of polyvinyl chloride | |
---|---|
Young's modulus | 3.2 MPa |
Shear modulus | 1.2 MPa |
Bulk modulus | 1.8 GPa |
Poisson's ratio | 0.49 |
Yield strength (elastic limit) | 10 MPa |
Tensile strength | 10 MPa |
Compressive strength | 20 MPa |
Flexural strength (modulus of rupture) | 11 MPa |
Hardness—Shore D | 12 |
Heat deflection temperature at 455 KPa | −30°C |
Hipot Tester (HIOKI 3522-50 LCR Hi-tester) device is used to measure electrical parameters of nanocomposites at various frequencies: |Z|, |Y|,
Two sets of PVC composites were prepared. In the first set, PVC was composited with nano-fumed silica (1–10% wt/wt). Fumed silica was mixed and heated up to 200°C for 8 min using corotating twin-screw extruder (Berstorff ZE25A, Hannover, Germany) at 300 rpm. The compounded materials were ground and rolled at 185°C to obtain thin film (thickness of
Electrical and surface analysis of PVC-nanostructured material specimen were carried out. This was achieved by measuring dielectric properties losses, electrical resistivity, and SEM analysis. These tests are able to identify the best combination of polymers—nanofillers in addition to the optimum fillers loading, in terms of improved dielectric strength and smaller space charge accumulation.
Dielectric spectroscopy is a powerful experimental method to investigate the dynamical behavior of a sample through the analysis of its frequency-dependent dielectric response. This technique is based on the measurement of the dielectric loss constants as a function of frequency of a sample sandwiched between two electrodes. The tan
The morphology and dimensions of the PVC composites were tested using scanning electron microscopy. Specimens were cut in liquid nitrogen and then coated with nanogold layers using a sputter coater to make them conductive.
Figure
Electrical resistivity and mechanical properties of PVC-silica using CES program.
Figure
Electrical resistivity and mechanical properties of PVC-clay using CES program.
Figure
Measured loss tangent (a) and resistivity of PVC nano fumed silica.
Figure
Measured loss tangent (a) and resistivity of PVC-nano montmorillonite clay.
Microstructure studies were carried out in order to detect voids or agglomerates which can be formed through polymer composite processing. SEM images for PVC composites with nano-montmorillonite and nano-fumed silica fillers have been obtained as shown in Figures
SEM analysis of PVC nanocomposites (10% wt/wt): (a) nanoclay composites, (b) nanofumed silica.
As the electrical insulation of PVC composites contribute to its tan delta value, the variation of tan delta value in net PVC nanocomposites in lower frequency range may result in the electrical insulation of the nanocomposites having been affected by the presence of nanosize fillers. As this study was carried out under constant temperature, the influence of the relaxation time of the charge carriers on the electrical insulation of PVC nanocomposites can be ignored. Thus, the number of charge carriers and applied frequency become dominating factors of the electrical insulation of PVC nanocomposites. The presence of nanosize fillers inside PVC will restrict the chain mobility and result in increasing electric insulation as such restriction limited the generation of mobile charge and the movement of charge carriers in polymer dielectrics, especially at a lower frequency range where the insulation will play an important role. Thus, the variation of tan delta value at low frequency range may be due to the influence of inorganic fillers’ electrical insulation.
The present work was supported by the Deanship of Scientific Research, King Abdulaziz University, Saudi Arabia, Project ID: 1432/829/388.