Polypropylene Materials

Polypropylene (PP) is a thermoplastic and commodity polymer used in a wide variety of applications. Its properties are similar to polyethylene, but it is slightly harder, stronger and more heat resistant. PP is produced via chain-growth polymerization from high purity propylene monomer that is obtained from the cracking of the petroleum hydrocarbons. Upon polymerization, PP can form three basic chain structures depending on the relative orientation of the methyl groups, namely isotactic PP (methyl groups are positioned at the same side with respect to the backbone of the polymer chain), syndiotactic (alternating methyl group arrangement) and atactic (irregular methyl group arrangement). The stereoregularity of these polymers is determined by the catalyst used to prepare it. In 1950s, Natta showed that the Ziegler organometallic type catalyst could be used to produce stereoregular PP with high crystallinity. Isotatic PP was synthesized by using heterogeneous Ziegler-Natta catalyst of a violet crystalline modified titanium (III) chloride with a co-catalyst or activator, usually organometallic compounds such as diethylaluminium chloride. However, this polymerization reaction simultaneously produces syndiotactic PP and atactic PP as minor products because these Ziegler-Natta based catalysts are multi-sites. Syndiotactic PP can be produced selectively using different catalysts such as homogenous Ziegler-Natta based catalyst and metallocene based catalyst. These different catalysts produce different microstructures of syndiotactic PP with different crystallization behavior and properties through different polymerization mechanisms. Atactic polypropylene can also be produced selectively using metallocene catalysts, atactic polypropylene produced this way has a considerably higher molecular weight [62,63].

For electrical applications, PP is commonly used as insulators due to their excellent electrical, mechanical, chemical and thermal properties. For high-voltage insulation, PP with average molecular of 250,000 g/mol, a density of 0.9 g/cm<sup>3</sup> and melt flow index of 12 g/10 min has been reported to have average dielectric strength of 55 kV/mm which is lower than the average values of 70 and 79 kV/mm for pure HDPE and LDPE respectively. However, the electric strength of PP was improved when blended with LDPE and HDPE

samples in different ratios. A maximum values of 63 kV/mm for PP/LDPE blend and 67 kV/mm for PP/HDPE blend were reported [59].

Similarly, different ethylene ratios (9, 12, 15 mol%) blended with a polymer having various percentage weight and formed copolymer systems of propylene-ethylene (namely, VERSIFY ™ 2200, 2300, and 2400; series no) for high voltage application. The Dow H358- 02 was used as the isotactic polypropylene throughout the studies [64]. Some of the components need to be dissolved during the blending, and xylene was the best solvent. The blending process can be summarized in the below points:


The desired properties of the material with polypropylene achieved with the presence of space-filling morphologies. PEC blends' molecular structure was an essential parameter for its behavior, and LDPE used in polyethylene was a secondary choice. Materials were formed with various ratios and cooled with different rates, behave like an XLPE system. All materials are compatible with low temperatures. Considering the material's thickness, the cable performance with PP blend is the excellent and average thickness for E2200 (3.39 mm) and XLPE (4.34 mm) for mini cable insulation. The PE blended materials can be used for mini cables and XLPE based materials as references for mini wires.

## Carbon Nanotube–Polyurethane Nanocomposite

The composite material produced with thermoplastic and carbon nanotubes (CNTs) can be used with a high voltage system. For this purpose, extruder temperature and screw speed were maintained at 215 ◦C and 300 rpm, respectively, for mixing CNTs (3 wt%) and polyurethane. The composites are in the form of granules. The thermoplastic polyurethane (TPU) materials are dried for 3 h, at 90 ◦C, followed by injection molding. Molding and melt temperature (40 and 220 ◦C) were controlled with a plate thickness of about 2 mm, but for extrusion, melt temperature was 185 ◦C and plate thickness 1.5 mm [12].

The acceptance criteria for any material for the industrial application have a large-scale melting range. The developed TPU can work with high temperature and confirmed by transmission electron microscopy (TEM) with injection molding, and extrusion samples gave across 10 m. It is homogeneous as well as elongation breaks about 560%. The size of dispersed particles of powder sample was obtained with the scanning electron microscope (SEM). It also confirmed the attachment of CNTs into the moiety of composite and not emerged through tubular protrusions by anchoring junctions with structural size about 20 μm after accumulation fragments with 100 mm plane surface level in the powder sample. The weathering was investigated by keeping composite test material and reference with latitude northern at 50◦ for 9 to 18 months and found that the filler will not degrade, only the matrix [65,66]. Analytical ultracentrifugation (AUC) and photoelectron spectroscopy (XPS) studies gave a strong indication of carbon nanotubes' presence in the nanocomposite materials. The internal diameter of pure material means the matrix of polyurethane and CNTs is smaller than the composite. Similar behavior can be seen in a composite having polyamide (PA) and silicon dioxide as well as with carbon nanotubes mixed polyoxymethylene (POM) and cement [66]. TGA recorded the decomposition of CNTs in the range of 500–650 ◦C [67]. Therefore, the composite material with CNTs has importance in electrical equipment, mainly in rollers and electromagnetic shielding.

2.2.3. Epoxy Resin of 9,9-bis-(3,5-dibromo-4-hydroxyphenyl)anthrone-10 and Jute Composite

Thanki et al. [68] synthesized an epoxy resin from 9,9-bis-(3,5-dibromo-4-hydroxyphenyl) anthrone-10 and epichlorohydrin by diluting them in isopropyl alcohol, and adding sodium hydroxide solution dropwise as a catalyst. After refluxing at 70 ◦C, they obtain a brown resin that was purified by extraction with chloroform [68].

At room temperature, synthesized EANBr was dissolved in tetrahydrofuran, and the curing agen<sup>t</sup> was added (EPK 3251). The fabric jute was mixed with the resultant solution, and the remaining solvent evaporated. The mylar film was introduced in duplicate between developed sheets, and temperature and pressure were controlled, also silicon lubricant was used as mold release spray. The product was known as J–EANBr composite [68].

The Fourier transform infrared spectroscopy (FTIR) confirmed the presence of alkane (C–H, 1450 cm<sup>−</sup>1), stretching (–OH, =C–H, –C=O, Ar C==C, Ar–O–R, C–O–H, C–Br) at 3532.56, 3070.21, 1664.48, 1592.61, 1254.19, 1071.1 and 631.2 cm<sup>−</sup><sup>1</sup> absorption frequencies respectively with EANBr sample. The nuclear magnetic resonance (NMR) studies indicated the formation of EANBr. The differential scanning calorimetry (D.S.C.) thermograms of EANBr and EANBrC are compared and found the broad endothermic transition of EANBrC (291.4 ◦C) and EANBr (265.3 ◦C) are expected due to tangible change and confirmed by no weight loss in the corresponding thermogravimetric analysis (TGA) thermogram. EANBr has a single step degradation reaction compared with J–EANBr, transition (291.4 ◦C) and two-step degradation and stable up to 310 ◦C [69]. EANBr and EANBrC are thermally steady up to 340 and 310 ◦C, respectively. As related to EPK 3251 cured EAN (360 ◦C), EPK 3251 cured EANBr (310 ◦C) has shown lower thermal stability. As well, the maximum weight loss (*T*max) value for EANBrC (416.5 ◦C) is significantly more than EPK 3251 cured EAN (394.4 ◦C) but EANBrC (416.5 ◦C) has exhibited a higher value of *T*max than EANBr (407.1 ◦C).

The mechanical and electrical properties of J-EANBr is better than J-EAN. In terms of tensile strength, almost similar with J-EAN with lower flexural strength. The electric strength is 40% lower in case of J-EANBr but volume resistivity is 29 times better than J-EAN, primarily expected to distinct degrees of cross linking and polarity, which impacts interfacial bond, due to annulment of partial charges because of OH groups of jute. The jute and EANBr have a better option as polymeric materials for electrical components due to their excellent properties with harsh environment, better hydrolytic activity, and thermal stability for low load bearing housing, electrical and electronic applications.

#### **3. Properties of Polymers**
