Magnesium hydroxide vs aluminum hydroxide: Flame game of white twins
When the fire licks the bones of polymer materials, two white minerals go from the laboratory to the battlefield - magnesium hydroxide and aluminum hydroxide, the "inorganic twins" of the flame retardant world are reshaping the boundaries of fire safety with completely different tactics. A contest between fire resistance limit and smoke suppression wisdom is quietly staged between the temperature difference of 340℃ and 200℃.
1. Fire-resistant battlefield: the life and death line of decomposition temperature
1. Calm warrior at 340℃
Magnesium hydroxide shows amazing temperature resistance in the flames. When the temperature breaks through the 340℃ mark, it starts the crystal water release program, like a precise fire commander, opening the high-pressure water valve at the most vulnerable moment of the polymer. This calmness allows engineers to handle high-temperature engineering plastics (such as nylon and polycarbonate) with ease - when the screw of the injection molding machine rotates at 210℃, magnesium hydroxide still holds its ground, while the opponent has already been defeated. More importantly, each gram of magnesium hydroxide absorbs up to 1,300 joules of heat, instantly lowering the surface temperature of the material by 80°C, opening a golden window for escape.
2. 200°C low-temperature guard
Aluminum hydroxide is the pioneer in the low-temperature battlefield. As early as 180-200°C, it releases crystal water rapidly, which is good news for materials such as PVC and rubber with lower processing temperatures. When the hot pressing mold operates at 160°C, aluminum hydroxide has activated the protection mechanism. But this "impatient" is also a double-edged sword: in the processing of engineering plastics, premature dehydration can easily cause blistering on the surface of the product, just like chiseling a secret loophole in the fireproof clothing.
2. Smoke suppression battlefield: chemical game in poisonous fog
1. Scavenger of alkaline shields
Magnesium hydroxide shows dominant performance in the smoke suppression battlefield. The residual magnesium oxide decomposed by it forms a highly active alkaline barrier, which accurately strangles the acidic poison gas. Laboratory data show that when PVC burns, the amount of hydrogen chloride released is reduced by more than 75%, turning the "poisonous gas chamber" into an escape route. More subtly, the magnesium oxide debris promotes the carbonization of the polymer surface, forming a honeycomb-shaped oxygen-free layer, which causes the smoke density to drop by 60%. In a subway tunnel test, the cable sheath with magnesium hydroxide added increased visibility by 3 times.
2. Gentle neutralization watchman
Although aluminum hydroxide also has the ability to neutralize acidic gases, it is more gentle. Its decomposition product aluminum oxide has weaker alkalinity, and the neutralization speed is only 60% of that of magnesium hydroxide. In the EPDM rubber fire simulation, the smoke density of aluminum hydroxide alone is 1.8 times that of the magnesium hydroxide system. However, this mild property makes it more popular in sensitive fields such as medical catheters-after all, excessive alkalinity may corrode precision instruments.
3. Application battlefield: Temperature determines battlefield boundaries
1. Magnesium armor for high-temperature materials
Magnesium hydroxide has established fortresses in four major areas with its temperature resistance advantage:
High-temperature cables: withstand arc shocks above 300°C during short circuits
New energy battery packs: magnesium oxide debris builds a fireproof isolation wall for battery cores
Automobile hood: maintains protective activity under continuous working conditions at 180°C
Special engineering plastics: standard flame retardants for high-temperature resins such as PEEK and PPS
2. Aluminum shields in the low-temperature world
Aluminum hydroxide dominates another territory:
Soft PVC flooring: a stable guardian in the 160°C calendering process
Epoxy resin encapsulation: avoids the risk of foaming during the processing of precision electronic components
Flame retardant coatings: a cost-effective choice at a curing temperature of 200°C
Paper processing: an environmentally friendly solution in the low-temperature impregnation process
4. Evolutionary path: genetic recombination in the nano era
1. Molecular marriage of surface modification
The common shortcoming of both is compatibility with polymers. Silane coupling agent is becoming the key to breaking the deadlock:
Modified magnesium hydroxide forms a molecular handshake in the PP matrix, and the impact strength is increased by 18% against the trend
The dispersion of aluminum hydroxide coated with titanate in epoxy resin is increased by 40%, and the "white spot" defect is completely bid farewell
The practice of a factory in Zhejiang Province has proved that the amount of modified flame retardant added can be reduced by 30%, and the mechanical properties are reversed to the pure resin substrate.
2. The combat power of nanometer scale is doubled
When the particle size exceeds the threshold of 100nm, the flame retardant performance changes qualitatively:
The specific surface area of nano magnesium hydroxide increases sharply to 450m²/g, just like upgrading a fire hose to a high-pressure water cannon
50nm aluminum hydroxide reduces the foaming rate of flame-retardant EVA by 35%, and the surface finish is improved by 2 levels
The production line data of Shanghai Cable Factory shows that the extrusion speed of nano flame-retardant sheath has soared from 20 meters/minute to 45 meters/minute
3. The ultimate form of composite concerto
The most advanced tactic is to let the twins work together:
The compound system of 75% magnesium hydroxide + 25% aluminum hydroxide reduces the smoke density of EPDM rubber to 55% of that of a single system
Magnesium-aluminum layered double hydroxide (LDH) embeds flame retardant factors between nanolayers, increasing heat absorption efficiency by 200%