LSZH polyolefin uses polyethylene as the base matrix, incorporating a large amount of magnesium hydroxide or aluminum hydroxide (activated by EVA - ethylene-vinyl acetate copolymer) into it. The flame retardancy primarily relies on these metal hydroxides. When subjected to heat from a fire, the hydroxides decompose into metal oxides and water.

1. Flame Retardant Principle
The flame retardant mechanism of LSZH polyolefin is as follows:

• Mechanism 1 (Endothermic Reaction): The decomposition of the hydroxide is an endothermic reaction, absorbing significant heat from the surrounding environment, thereby lowering the temperature at the fire site.

• Mechanism 2 (Cooling by Water Vapor): The released water molecules also absorb a substantial amount of heat.

• Mechanism 3 (Oxygen Barrier): The resulting metal oxide forms a protective char layer, preventing oxygen from contacting the underlying organic material again.
  Thus, LSZH polyolefin achieves flame retardancy primarily through this combination of heat absorption and oxygen barrier via metal oxide formation.

2. Application of Irradiation Cross-Linking Technology in LSZH Wires and Cables
The primary flame retardants used in LSZH polyolefins are hydroxides, which characteristically tend to absorb moisture from the air (hygroscopicity). This moisture absorption can drastically reduce the volume resistivity of the insulation layer, potentially dropping from an original value of 17 MΩ/km to as low as 0.1 MΩ/km.
To prevent this hygroscopicity, the molecular structure of the base polyolefin must be modified to create a dense layer that hinders water molecules in the air from combining with the hydroxide flame retardants. This process is called cross-linking.
Cross-linking methods fall into two main categories: chemical cross-linking and physical cross-linking. Chemical cross-linking is further divided into dry curing (e.g., silane steam) and warm water curing. Due to the specific requirements for cable materials, LSZH polyolefin materials for cables can only utilize irradiation cross-linking.

3. Characteristics of Irradiated Cross-Linked LSZH Wires and Cables
A. Higher Current-Carrying Capacity: After exposure to high-energy electron beam irradiation, the material's molecular structure changes from linear to a three-dimensional network. This raises the maximum service temperature from 70°C (for non-cross-linked) to 90°C, 105°C, 125°C, 135°C, or even 150°C, increasing the current-carrying capacity by 15-50% compared to cables of the same specification.
B. Higher Insulation Resistance: By avoiding the use of hydrides as flame retardants, irradiation cross-linked cables prevent issues like pre-cross-linking during the process and the decrease in insulation resistance caused by the insulation layer absorbing moisture. This ensures stable and high insulation resistance values.
C. Longer Service Life & Better Overload Capacity: The higher heat resistance and aging temperature of the irradiated cross-linked polyolefin material extend the cable's service life, especially under conditions involving cyclic heating loads.
D. Environmental & Safe: The cables use halogen-free, environmentally friendly materials, making their combustion characteristics compliant with environmental standards.
E. Stable Product Quality: The quality of traditional warm water-cross-linked cables can be unstable, influenced by factors like water temperature, extrusion process parameters, and cross-linking additives. In contrast, the quality of irradiated cross-linked cables depends on the electron beam irradiation dose, which is computer-controlled, minimizing human factors and ensuring consistent, stable quality.

4. Flame Retardant Ratings for Irradiated Cross-Linked LSZH Cables
According to the test conditions specified in GB/T 18380.3-2002, the flame retardant ratings for irradiated LSZH cables are classified into four grades: A, B, C, and D.