Polyethylene Materials

High-density polyethylene (HDPE) and low-density polyethylene (LDPE) are commodity polymers that are widely used for varieties of applications that include electrical insulations, packaging, household items and automotive parts. Some of the interesting properties of these polymers include chemical resistance, rigidity, stiffness and thermal stability. For electrical applications, these polymers are commonly used as insulators due to their exceptional electrical, mechanical, chemical and thermal properties. Polymer-based electric insulators exhibit high dielectric strength, high resistivity, low dielectric loss, and adequate mechanical properties. HDPE (density of 0.947 g/cm<sup>3</sup> and melt flow index of 42 g/10 min) and LDPE (density of 0.92 g/cm<sup>3</sup> and melt flow index of 25 g/10 min) are reported to have average dielectric strength of 70 and 79 kV/mm respectively. Though, LDPE exhibit relatively high electric strength, but its weak mechanical properties, thermal resistance and melt flow viscosity restricted its application in certain areas. However, these properties can be improved by mixing the LDPE with other polymers (polymer blend) or other materials (polymer composites) to produce material with optimum desirable properties [59].

The Dow material acting as the base resin was a non–commercial low-density polyethylene (LDPE) blended with high-density polyethylene (HDPE, Dow 40055E) to prepare new polymeric material that has the capacity to work with high temperature that can be applied as an insulation product with different types of cable. Small-scale material was synthesized by utilizing HDPE and LDPE (20:80) with the help of an extruder (Haake PTW 16/40D) [60]. However, for large scale, cross-linked low-density polyethylene (XLPE) and LDPE were produced as a reference for mini cables by incorporating the LDPE as a base material Berstorff ZE40UT extruder for blending [61]. The samples were prepared for mechanical (1.7 mm thickness) and breakdown (thickness 85 μm) testing using compression molding. The behavior of materials with temperature was studied with Mettler Toledo FP82 hot stage. The sample's thickness required for the mini cable material will be 4 mm and blended on the Troester extruder.

The crystallization temperature (Tc) isothermal for the LDPE/HDPE blended material in the range of 113–119 ◦C indicating the formation of lamellar crystals due to the presence of HDPE [61]. It also suggests that polymeric material's cooling temperature must be within the range of 0.5–10 ◦C/min, enhancing the breakdown strength and regenerating electrical effects [60]. When blended materials are cooled slowly, it would be challenging to retain mechanical properties that require high operating temperatures. Generally, stiff materials were formed than XLPE, which help to construct cable due to their operating condition, usually 30 ◦C higher than XLPE. The XLPE cable and mini cable breakdown data were studied and suggested maximum voltage below 400 kV; conversely, none of the extruded thermoplastic systems failed and shown both systems were extremely good electric materials for cable. The PE blended materials can be used for mini cables and XLPE based materials as reference for mini cables.
