The PVC insulated wires we use in daily life can produce toxic gases in the event of a fire, which can be harmful to our health. However, flame-retardant wires offer advantages in this situation, featuring exceptional flame retardancy and toxic smoke suppression properties. They are relatively environmentally friendly, and these properties are partly due to the material they are made of.
Overview of Flame-Retardant Wires and Cables
Flame-retardant wires and cables possess exceptional flame retardancy, low smoke emission, and toxic smoke suppression properties, in addition to the required properties specified in IEC 694:1990. In the event of a fire, ordinary PVC insulated wires emit thick black smoke and toxic hydrochloric acid fumes, which can be fatal and hinder rescue operations.
Applications:
This product is suitable for fixed installation on AC 50Hz, 1kV and below transmission and distribution lines for power transmission.
It is primarily used in areas with high flame retardancy requirements, such as hotels, banks, hospitals, factories, and integrated wiring systems for commercial and residential buildings.
Materials for Flame-Retardant Wire and Cable
The higher the oxygen index of the material used in flame-retardant cable, the better its flame retardancy. However, as the oxygen index increases, some other properties are compromised. For example, the material's physical and process properties may decline, making handling more difficult while also increasing material costs. Therefore, it is important to choose an appropriate oxygen index. Generally, an oxygen index of 30 for insulating materials will pass the Class C test requirements of the standard. If both the sheath and filler are flame-retardant, the product can meet Class B and Class A requirements. Materials used in flame-retardant wire and cable are primarily categorized as halogen-containing and halogen-free flame retardant.
1. Halogen-Containing Flame-Retardant Materials
Hydrogen halides are released during combustion and heat. These hydrogen halides can capture active free radicals (HO) and thus delay or extinguish combustion, achieving flame retardancy. Commonly used materials include polyvinyl chloride, neoprene, chlorosulfonated polyethylene, and ethylene propylene rubber.
① Flame-retardant polyvinyl chloride (PVC): Due to its low price, excellent insulation properties, and flame retardancy, PVC is widely used in standard flame-retardant wire and cable. To improve the flame retardancy of PVC, halogen flame retardants (decabromodiphenyl ether), ② chlorinated paraffin, and synergistic flame retardants are often added to the formulation.
Ethylene propylene rubber (EPDM): A non-polar hydrocarbon with excellent electrical properties, high insulation resistance, and low dielectric loss. However, EPDM is flammable, and its flame retardancy must be improved by reducing its crosslinking level and reducing the low-molecular-weight substances produced by molecular chain breakage.
As the crosslinking degree of EPDM increases, the oxygen index increases. For example, adding crosslinking agent DC (P diisopropylbenzene peroxide), crosslinking aid TAIC (tripropylene cyanurate), and HVA-(2N, N-phenylene bismaleimide) to the formula can increase the oxygen index by 10 to 15. Another method is to add inorganic flame retardant fillers to EPDM rubber to increase the oxygen index. Commonly used fillers include A(lOH) (3). They can release crystal water at high temperatures and absorb a large amount of heat to achieve flame retardant effects; However, adding a large amount of fillers will reduce the mechanical and electrical properties of the material (such as tensile strength and elongation). Therefore, the filler cannot exceed 150 parts. In order to obtain better flame retardant properties and maintain high mechanical properties, it is necessary to appropriately reduce the flame retardant filler and appropriately increase other flame retardants; 2) Low smoke and low halogen flame retardant materials Mainly for polyvinyl chloride and chlorosulfonated polyethylene. Add CaCO3 and A(lOH)3 to the polyvinyl chloride formula. Zinc borate and MoO₃ can reduce HCl emissions and smoke generation in flame-retardant polyvinyl chloride, thereby improving the material's flame retardancy and reducing halogen, acid mist, and smoke emissions. However, this may slightly reduce the oxygen index. Larger amounts of these additives can also reduce the material's mechanical and electrical properties.
II. Halogen-Free Flame-Retardant Materials
Polyolefins are halogen-free materials composed of hydrocarbons. They decompose into carbon dioxide and water during combustion, producing no significant smoke or harmful gases. Polyolefins primarily include polyethylene (PE) and ethylene-vinyl acetate (EVA). These materials are not inherently flame-retardant and require the addition of inorganic and phosphorus-based flame retardants to produce practical halogen-free flame-retardant materials.
However, since non-polar substances lack polar groups in their molecular chains and are hydrophobic, they have poor affinity with inorganic flame retardants, making them difficult to securely bond with. To improve the surface activity of polyolefins, surfactants can be added to the formulation; alternatively, polymers containing polar groups can be blended into the polyolefin. This increases the amount of flame-retardant fillers, improves the mechanical and processing properties of the material, and achieves superior flame retardancy.
Overall, flame-retardant wires and cables offer significant advantages and are environmentally friendly. In fact, once you gain a deeper understanding of the different specifications and models of cables and wires, you'll discover their widespread use in our daily lives and their significant impact.
