Thermal Experimental Dielectric Characterization of Cost-Fewer Low-Density Polyethylene Nanocomposites

Polymer properties can be experimentally tailored by adding small amounts of different fillers, but they are expensive with respect to the classical polymer materials. This paper has been studied the enhancement and controlling of electric and dielectric properties of low-density polyethylene (LDPE) polymer materials by cost-fewer nanoparticles. Certain percentages of clay and fumed silica nanoparticles have been enhanced electric and dielectric properties of low-density polyethylene nanocomposite. Dielectric spectroscopy has been measured the electric and dielectric properties of low-density polyethylene with and without nanofillers at various frequencies (10 Hz–100 kHz) and temperatures (20 ◦C, 40 ◦C and 60 ◦C). Also, it has been investigated the optimum percentages of nanofillers with respect to nanofillers type, filler concentration and temperature for enhancing electric and dielectric characterization of low-density polyethylene. Experimental measurements have been carried out on dielectric breakdown strength of new polyethylene nanocomposites materials under variant electric fields (uniform, and nonuniform) and variant temperatures. It has been specified the effective nanofillers factors on dielectric breakdown strength of polyethylene nanocomposites materials.


Introduction
Polymer nanocomposites have attracted wide interest with regard to enhancing polymer properties and ex-tending their utility in recent years.The nanocomposite material which the nanofillers are evenly distributed in the polymer material attracts attention as an insulating material because the properties of the original material can be drastically improved by adding a few percent of nanofillers.Low-density polyethylene (LDPE) is widely used as an insulating material for power cables.Electrical insulating polymers are usually modified with inorganic fillers to improve electrical, mechanical, thermal properties.Generally, inorganic fillers are dispersed non-uniformly in the polymer matrix, and the irregular interfaces are usually electrically weak spots.It is well known that electrical properties of insulating polymer composites depend strongly on their microstructures.In particular, the size and shape of the fillers, the dispersion of the fillers, the filler-filler, filler-matrix interactions including interfacial strain, directly affect the electrical properties of composites [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11].
Nanoparticles/polymer composites are now of considerable interest for their specific electrical properties.It is recognized that the interfaces between the host dielectric and the nanometric particles can strongly influence the dielectric properties of the composite material as a whole.Since interfaces dominate dielectric situations at this level, nanodielectrics and interfaces become inextricable.Low frequency polarization is a type of polarization concerning to interface polarization, and it strongly relates to the space charge storage and transportation in dielectric materials [12], [13], [14], [15], [16].Also, it has been extend for studying dielectric characterization of cenosphere filled lowdensity polyethylene composites, the effect of filler distribution on the dielectric constant is examined and the observed differences are attributed to the differences in two kinds of interfaces present: one formed between the touching cenosphere particles and the other formed between LDPE and cenosphere [17].Electrical and elec-tronic properties of thin films of variant nanocomposites were characterized with respect to their thermal properties and so, the fabrication procedures [18], [19], [20], [21].
As of now, work is underway to examine the physical properties of nanocomposite materials composed of nanoparticles of metals and their compounds stabilized within a polymeric dielectric matrix .In recent years polymer nanocomposites have attracted wide interest with regard to enhancing polymer properties and extending their utility.It has been found that the dielectric properties have a close relationship with the interfacial behavior between the nanofillers and the polymer matrix in such nanocomposites [22], [23], [24], [25], [26], [27], [28], [29].The electric and optic properties of these materials have been demonstrated to be highly dependent on the size, structure, and concentration of the nanoparticles, as well as on the type of polymeric matrix [30], [31], [32], [33], [34], [35].Great expectations have focused on costless nanofillers.However, it has been concerned in this paper about the effect of types of cost-fewer nanofillers on electrical properties of polymeric nanocomposite.With a continual progress in polymer nanocomposites, this research depicts the effects of types and concentration of cost-fewer nanoparticles in electrical properties of industrial polymer material.Experimental results have been discussed the effects of Clay and Fumed silica nanofillers with various volume fractions and temperatures on electric and dielectric properties of Lowdensity Polyethylene (LDPE).

Nanofillers
Clay is nanometer, and its spherical particle shape (Dia.: 10 nm) is the most important characteristic for polymer applications.The reason of selection clay nanofillers is due to having a greater effect on properties such as viscosity, stiffness and strength, using clay as nanofillers give high levels of flame retardancy to the produced composite.Cost-fewer clay nanoparticles are catalyst to be the best filler among nanofillers industrial materials.On the other wise, fumed silica is a fluffy white powder with an extremely low-density.Also, fumed silica powder is used in paints and coatings, silicone rubber and silicone sealants, adhesives, cable compounds and gels, printing inks and toner, and plant protection.Thus, industrial materials studied here is low-density polyethylene that has been formulated utilizing variant percentages of nanoparticles of clay and fumed silica.Pure and fabricated nanocomposites (variant percentages of mass-weight (wt.) of nanoparticles mixed and penetrated inside polymer matrix) have been measured their electric and dielectric properties after manufacturing and detailed as shown in Tab. 1.

LDPE Nanocomposites
It has been prepared and fabricated by using recent nanotechnology procedures and devices for melting low-density polyethylene, mixing and penetrating nanoparticles inside the base matrix (LDPE) by modern ultrasonic devices.The distribution of nanoparticles within the polymer matrix has been detected by using scanning electron microscope (SEM) as shown in Fig. 1, that illustrates Clay/LDPE nanocomposites and Fumed silica/LDPE nanocomposites illustrate penetration of nanoparticles inside low-density polyethylene.

Measurement Devices
Figure 2 shows HIOKI 3522-50 LCR Hi-tester device that measured characterization of nanocomposite insulation industrial materials, it has been used for measuring electrical parameters of nanometric solid dielectric insulation specimens at various frequencies.Specification of LCR is Power supply: 100 V, 120 V, 220 V or 240 V (±10 %) AC (selectable), 50/60 Hz, and Frequency: DC, 1 MHz to 100 kHz, Display Screen: LCD with backlight / 99999 (full 5 digits), Basic Accuracy:

Results and Discussion
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 capacitance as a function of frequency of a sample sandwiched between two electrodes.The tan δ, and capacitance [C] were measured as a function of frequency in the range of 10 Hz to 10 kHz at variant temperatures for all the test samples. of clay nanofillers in the nanocomposite up to 5 %wt but the measured capacitance of Low-density polyethylene nanocomposites increases with increasing the clay percentage of nanofillers up to percentage of 10 %wt.Whatever, Fig. 6 shows that the measured capacitance are closed with increasing the percentage of fumed silica nanofillers in the nanocomposite especially at high frequencies.
It is cleared that nanoparticles have been changed electric and dielectric polymer properties.The dielectric properties of insulating polymer nanocomposites have been investigated in the frequency domain from 0.1 Hz to 1 kHz.Also, it has been found that the dielectric properties have a close relationship with the interfacial behavior between the fillers and the polymer matrix in such composites.

Dielectric Characterization of LDPE Nanocomposites at Temperature (40 • C)
There are effects of rising temperatures on nanoparticles inside the suggested nanocomposites, it is cleared that, rising temperature of nanocomposite materials changes nanofillers temperatures that changing dielectric behavior over the normal conditions.
Figure 7 gives the loss tangent as a function of frequency for Clay/ LDPE nanocomposites samples under testing at temperature (40 • C).It is noticed that the loss tangent of Clay/ LDPE nanocomposites increases with increasing percentage of clay nanofillers in the nanocomposite up to 1 %wt, after that the loss tangent of Clay/ LDPE nanocomposites decreases with increasing percentage of clay nanofillers in the nanocomposite up to 10 %wt.    as similar as increasing percentage of fumed silica nanofillers in the low-density polyethylene nanocomposite up to 10 %wt.
On the otherwise, Fig. 9 shows the tested samples capacitance as a function of frequency for Clay/LDPE nanocomposites at temperature (40 • C); the measured capacitance increases with increasing clay nanofillers percentage up to 1 %wt but it decreases with increasing clay nanofillers percentage up 10 %wt.Noting that, Fig. 10 shows the measured capacitance of Fumed silica/LDPE nanocomposites follow the same behavior of Clay/LDPE nanocomposites.voltage frequency for Clay/LDPE nanocomposites at a given temperature (60 • C).The measured loss tangent of Low-density polyethylene nanocomposite increases with increasing clay percentage nanofillers up to 5 %wt, especially, at low frequencies.After that, the loss tangent of Clay/LDPE nanocomposite decreases with increasing clay percentage nanofillers up to 10 %wt, specially, at high frequencies.Also, Fig. 12 shows that the measured loss tangent of Fumed silica/LDPE increases with increasing fumed silica nanoparticles percentage up to 5 %wt, especially, at low frequencies.But, it decreases with increasing fumed silica nanoparticles percentage up to 10 %wt.
Figure 13 depicts capacitance versus the applied voltage frequency for Clay/ LDPE nanocomposites at temperature (60 • C); The measured capacitance decreases with increasing clay nanofillers percentage up to 1 %wt, then, the measured capacitance increases with increasing clay percentage nanofillers up to 10 %wt.Although, Fig. 14 shows that the mea-sured capacitance increases with increasing fumed silica percentage nanofillers up to 5 %wt, after that, the capacitance of Fumed silica/LDPE nanocomposites decreases with increasing fumed silica nanofillers percentage (5 %wt-10 %wt).This is obvious that, rising temperature of nanocomposite materials raises nanofillers temperatures that changing dielectric behavior with respect to normal conditions.

Comparative Study for Thermal Characterization of LDPE Nanocomposite Materials
With respect to results of the effect of temperature and types of nanofillers on the electric characterization, in the beginning, adding fumed silica increased permittivity of the new nanocomposite materials whatever, adding clay has decreased permittivity of the new Nanocomposite materials as tabulated in Tab. 1.
With comparing results for depicting the effect of raising concentration of clay and fumed silica nanofillers are pointed out in Fig. 3, Fig. 4, Fig. 5, Fig. 6 at room temperature (20 • C), the measured loss tangent depends on increasing the certain percentages of nanoparticles, specially, the measured loss tangent characteristics varies between low and high frequencies.On the otherwise, the measured capacitance varies with increasing percentage of clay nanofillers inside the nanocomposite, whatever, the measured capacitance are closed with increasing the percentage of fumed silica nanofillers in the nanocomposite especially at high frequencies.
For high thermal conditions, at temperature 40 • C as shown in Fig. 7, Fig. 8, Fig. 9, Fig. 10, the loss tangent of Clay/ LDPE nanocomposites increases with increasing percentage of clay nanofillers in the nanocomposite up to 1 %wt, after that the loss tangent of Clay/ LDPE nanocomposites decreases with increasing percentage of clay nanofillers in the nanocomposite up to 10 %wt.And so, fumed silica nanofillers follow the same behavior of clay nanoparticles inside low-density polyethylene up to 10 %wt.With rising samples temperature up to 60 • C, it can be noticed that the effects high temperature values on nanoparticles inside the nanocomposites and so, the effect of raising concentration of nanofillers is pointed out in Fig. 11, Fig. 12, Fig. 13, Fig. 14 i.e the measured capacitance decreases and increases at a certain values of clay or fumed silica nanofillers percentage up to 10 %wt, This is obvious that, rising temperature of nanocomposite materials effects on nanofillers heating temperatures which changing dielectric behavior over the normal conditions.Finally, the importance of adding nanofillers of clay or fumed silica can be concluded in controlling in increasing or decreasing the dielectric strength of pure LDPE by using nanotechnology techniques.Also, increasing environment temperature of nanocomposite materials causes nanofillers heating temperatures that changing dielectric behavior over the normal conditions.

Conclusion
Adding the clay is decreasing the permittivity of new nanocomposite materials and the effects of adding small amount of clay nanoparticles percentage to Lowdensity polyethylene decreases capacitance and loss tangent depending on thermal nanoparticles temperatures, on the otherwise, adding fumed silica is increasing the permittivity of new nanocomposite materials and the effects of small amount of fumed silica nanoparticles percentage to Low-density polyethylene increases capacitance and loss tangent with respect to thermal nanoparticles temperatures.
Thermal stability of new nanocomposites occurs at small amounts clay or fumed silica nanoparticles but adding large amounts these nanoparticles to Lowdensity polyethylene will be reverse dielectric behavior characteristics gradually.This is obvious that rising temperature of nanocomposites materials effects on nanoparticles temperatures which changing dielectric behavior over the normal conditions.Italy, and USA etc.On 2009, he had been a Principle Investigator of a funded project from Science and Technology development Fund STDF for developing industrial materials of ac and dc applications by nano-technology techniques.He has been established first Nano-Technology Research Centre in the Upper Egypt http://www.aswan.svu.edu.eg/nano/index.htm.

3. 1 .Fig. 3 :
Figure3shows loss tangent (tan δ) of the tested samples as a function of frequency for Clay/ Lowdensity polyethylene nanocomposites at room temperature (20 • C).The measured loss tangent contrasts on increasing the loss tangent with increasing the percentage of clay nanoparticles up to 1 %wt, specially, at low frequencies but it is decreasing with increasing clay nanoparticles percentage up to 10 %wt, specially, at high frequencies.Whatever, Fig.4contrasts on the measured loss tangent that increases with increasing percentage of fumed silica nanofillers in the nanocomposite up to 10 %wt especially at high frequencies.On the otherwise, Fig.5contrasts on capacitance of Clay/LDPE nanocomposites samples versus frequency at room temperature (20 • C), the measured capacitance decreases with increasing percentage

3. 3 .
Dielectric Characterization of LDPE Nanocomposites at Temperature (60 • C) Awarded to the effects of high-temperature values on nanoparticles inside the nanocomposites, Fig. 11 shows the relation between loss tangent versus the applied