How do plastic granules balance flexibility and structural strength in the inner and outer layers of electrical wires?
Publish Time: 2025-09-03
In modern power transmission and communication systems, electrical wires, as carriers of energy and signals, have a performance that is directly related to operational safety and service life. Electrical wires typically consist of an inner conductor (core) and an outer sheath. Plastic granules, as the core material for insulation and protection, play an irreplaceable role in both these layers. Especially in complex and changing outdoor environments, electrical wires must possess both excellent flexibility to accommodate bending and stretching, as well as sufficient structural strength to withstand external forces, abrasion, and environmental corrosion. Through a synergistic approach of material modification, formulation optimization, and processing technology, plastic granules successfully achieve this dual goal of flexibility and structural strength.
The inner core of an electrical wire, typically made of copper or aluminum, is responsible for conducting electricity. The inner insulation surrounding the core primarily prevents current leakage, short circuits, and the risk of electric shock. This layer requires extremely high material flexibility, as wires are frequently bent, threaded, and twisted during wiring. If the material is too hard, it will crack easily, while if it is too soft, it will deform easily. Plastic granules used for the inner insulation are often made of polyvinyl chloride (PVC), cross-linked polyethylene (XLPE), or low-density polyethylene (LDPE). These base resins inherently possess excellent ductility and processability. The addition of plasticizers (such as environmentally friendly phthalates or citrates) further enhances the material's flexibility and low-temperature bending properties, ensuring that the wire remains resistant to brittle cracking in cold environments. Furthermore, by controlling the degree of crosslinking or adding an appropriate amount of inorganic fillers, the insulation layer's heat resistance and mechanical stability can be enhanced without sacrificing flexibility, achieving the ideal "soft yet not weak" condition.
2. Outer Sheath: Strengthening the Structure to Protect Against External Challenges
The outer sheath of a wire is directly exposed to the elements and must withstand multiple challenges, including sun, rain, friction, compression, UV radiation, and chemical corrosion. Therefore, the outer sheath material places particular emphasis on structural strength, abrasion resistance, and aging resistance. Commonly used plastic granules include high-density polyethylene (HDPE), polypropylene (PP), low-smoke, halogen-free, flame-retardant polyolefin (LSZH), or modified nylon. These materials inherently possess high tensile strength and hardness. To enhance their overall performance, manufacturers employ blending and modification techniques, adding impact modifiers (such as EPR or POE) to the base resin. This introduces a slightly elastic phase while maintaining high rigidity, significantly enhancing the material's impact resistance and cracking resistance. Furthermore, additives such as carbon black, UV inhibitors, and antioxidants effectively resist UV degradation and extend outdoor service life. This "rigid yet tough" structural design enables the outer sheath to withstand the tension of overhead cable pulling while also resisting mechanical damage such as scrapes from branches and vehicle runover.
3. Material Synergy: Internal and External Layering for Complementary Functions
Modern electrical wires often utilize a two-layer or multi-layer co-extrusion process, with plastic granules of different formulations used in the inner and outer layers, achieving functional division and optimizing performance. For example, a soft inner layer of PVC or LDPE ensures reliable insulation, while a high-strength outer layer of HDPE or LSZH provides external protection. This structure avoids the conflict between a single material's difficulty in achieving both softness and hardness, while also ensuring overall structural integrity through interlayer bonding.
4. Precise Control of Formulation and Process
The ultimate performance of plastic granules depends not only on the resin type but also on precise formulation design and extrusion process control. During the granulation process, a twin-screw extruder thoroughly mixes and plasticizes the resin, plasticizer, stabilizer, flame retardant, filler, and other components to ensure uniform and stable material properties. During extrusion, precise adjustment of parameters such as temperature, pressure, and cooling rate directly influences the crystallinity, density, and surface quality of the wire sheath, ultimately determining its balance between flexibility and strength.
5. Targeted Optimization for Application Scenarios
The formulation ratio of plastic granules can be flexibly adjusted for different applications. For example, wires used for direct underground burial require enhanced compressive strength in their outer layers; wires used for overhead transmission lines prioritize tensile strength and weather resistance; and power cables for mobile devices demand high flexibility in both inner and outer layers. Through customized modification, plastic granules can precisely match the performance requirements of various types of wires.
Through scientific material selection, formulation modification, and advanced processing technology, plastic granules achieve the perfect balance of flexibility and structural strength in both inner and outer layers of wires. They are not only the guardian of safe power line operation but also the cornerstone of modern power system reliability.
