Analysis of the application prospects of magnesium hydroxide flame retardant cable materials in the field of rail transit
With the rapid expansion and intelligent upgrading of the global rail transit network, the requirements for the safety, environmental protection and durability of cable materials are increasing. Among them, magnesium hydroxide flame retardant cable materials have become a new type of material that has attracted much attention in the field of rail transit due to their unique performance advantages. This article will explore its development prospects in depth from multiple dimensions such as technical characteristics, application scenarios, market trends and challenges.
1. The core demand of rail transit for cable materials
The cables of rail transit systems (including subways, light rails, high-speed rails, etc.) must meet the following key requirements:
1. High flame retardancy: In confined spaces such as tunnels and carriages, cables must meet strict fire protection standards (such as EN 45545, GB/T 18380, etc.) to prevent the spread of fire.
2. Low smoke and low toxicity: The release of toxic gases (such as hydrogen chloride, carbon monoxide) and smoke must be reduced during combustion to ensure the safety of personnel escape.
3. High temperature resistance and weather resistance: Materials need to maintain stability when exposed to complex environments such as vibration, humidity, and temperature changes for a long time.
4. Environmental compliance: Comply with regulations such as RoHS and REACH, and avoid the use of halogen-containing flame retardants (such as traditional chlorinated paraffin).
Traditional halogen flame retardants are gradually being eliminated due to environmental and toxicity issues. Magnesium hydroxide (Mg(OH)₂), as a representative of halogen-free flame retardants, has become a core option for alternatives.
2. Advantages and characteristics of magnesium hydroxide flame retardant cable materials
1. Flame retardant mechanism and performance advantages
Magnesium hydroxide decomposes into magnesium oxide and water vapor at high temperatures (above 340°C):
Mg(OH)₂ → MgO + H₂O↑
This reaction can absorb a lot of heat and reduce the surface temperature of the material. At the same time, the released water vapor dilutes the concentration of combustible gases, forming a physical barrier to isolate oxygen and achieve efficient flame retardancy. Its advantages include:
- Halogen-free and environmentally friendly: no corrosive or toxic gases are produced, which is in line with the trend of green materials.
- Significant smoke suppression effect: smoke density is reduced by more than 50%, improving visibility during fire.
- High filling compatibility: the addition amount can reach 40%-60%, without affecting the mechanical properties of the cable.
2. Comparison with other flame retardants
| Flame retardant type | Flame retardant efficiency | Environmental protection | Cost | Applicable scenarios |
|------------------|----------|--------|--------|------------------------|
| Magnesium hydroxide | Medium | Excellent | Low | Medium and high temperature environment, high environmental protection requirements |
| Aluminum hydroxide (ATH) | Medium | Excellent | Low | Low temperature environment |
| Phosphorus flame retardant | High | Medium | High | Precision electronic equipment |
| Halogen flame retardant | High | Poor | Medium | Phased out |
Magnesium hydroxide has outstanding performance in cost and environmental protection, especially suitable for scenarios such as rail transit that require large-scale laying and extremely high safety requirements.
3. Typical applications of magnesium hydroxide cable materials in rail transit
1. Subway tunnel cables
The subway tunnel environment is closed, and the cables need to pass strict flame retardant tests such as BS 6853 or EN 50266. Magnesium hydroxide flame retardant cable materials are widely used in power transmission lines, signal control lines, etc., for example:
- London Elizabeth Line: Halogen-free flame retardant cables are used to reduce the risk of tunnel fires.
- Shanghai Metro Line 18: Magnesium hydroxide composite cables are used and passed the "low smoke and halogen-free" certification.
2. High-speed rail carriage wiring harness
High-speed rail carriage cables need to withstand long-term vibration and high temperature, while meeting the fire protection standards of EN 45545-2. Composite materials of magnesium hydroxide and polyolefins (such as EVA, PE) are both flexible and flame retardant, and are suitable for scenarios such as in-vehicle lighting and communication systems.
3. Charging piles and energy storage systems
With the development of rail transit electrification, the demand for cables for charging facilities and energy storage equipment along the line has surged. Magnesium hydroxide cables can effectively prevent chain reactions caused by battery thermal runaway and improve system safety.
IV. Technical Challenges and Solutions
1. Surface modification to improve dispersibility
Magnesium hydroxide particles are prone to agglomeration, resulting in a decrease in the mechanical properties of the material. Modification with silane coupling agents or nano-treatment can enhance its compatibility with the polymer matrix. For example, the use of nano magnesium hydroxide (particle size <1μm) can increase the tensile strength by more than 20%.
2. Optimization of composite flame retardant system
The flame retardant efficiency of single magnesium hydroxide is limited, and it needs to be compounded with synergists such as red phosphorus and zinc borate. For example, adding 5% red phosphorus can increase the limiting oxygen index (LOI) from 28% to 35%.
3. Processing technology improvement
High-filling magnesium hydroxide can easily lead to poor melt fluidity, and it is necessary to optimize the mixing uniformity through a twin-screw extrusion process, or introduce lubricants (such as zinc stearate) to improve processing performance.
V. Market prospects and policy drivers
1. Global rail transit investment growth
According to Research and Markets, the global rail transit cable market will grow at an average annual rate of 6.2% from 2023 to 2030, with the Asia-Pacific region (especially China and India) accounting for more than 50%. China's "14th Five-Year Plan" clearly states that the mileage of urban rail transit will be increased by 3,000 kilometers, which will directly drive the demand for flame-retardant cables.
2. Environmental regulations force technology upgrades
The Europeanｕｎｉｏｎhas completely banned the use of halogen flame retardants in electronic equipment, and China's GB/T 19666-2019 standard also requires public facility cables to be "halogen-free". As a mainstream substitute, magnesium hydroxide will continue to expand its market share.