Posted by Paul Fletcher
3 Comments
Select your polymer type, desired UL rating, and particle size to get the recommended loading percentage for aluminium hydroxide.
- wt %
When you hear the name Aluminium Hydroxide is a white, inorganic powder that has been used for decades in pharmaceuticals, water treatment and, increasingly, as a flame retardant, you might wonder how a simple mineral can stop a fire. The secret lies in its chemistry: when heated, it undergoes an endothermic reaction that absorbs a lot of heat and releases water vapor, both of which choke the flame.
Many manufacturers still reach for traditional brominated or antimony‑based retardants because they’re proven fire‑stoppers. However, those chemicals can generate corrosive gases, pose health risks, and often run afoul of stricter environmental regulations like REACH or RoHS. Aluminium hydroxide flame retardant offers a clean alternative that’s inexpensive, abundant, and fully halogen‑free.
Key benefits include:
At temperatures around 200°C, the compound begins to decompose:
2 Al(OH)₃ → Al₂O₃ + 3 H₂O (g)
The reaction absorbs roughly 1kJ/g of heat (an endothermic process) while delivering a burst of water vapor. The water does two things: it cools the surrounding polymer matrix and displaces oxygen, starving the flame. The remaining aluminium oxide (Al₂O₃) forms a thin, insulating layer on the material’s surface, slowing heat transfer even further.
Because the decomposition temperature is relatively low, aluminium hydroxide is best paired with polymers that melt below 180°C, such as Polyethylene or Polypropylene. For high‑temperature plastics like polycarbonate, you’d need a higher‑temperature retardant or a hybrid system.
| Retardant | Mechanism | Decomposition Temp (°C) | Smoke Production | Environmental Rating | Typical Use |
|---|---|---|---|---|---|
| Aluminium Hydroxide | Endothermic water release | 200‑220 | Low | Halogen‑free, REACH compliant | Polyethylene, PP, cable sheathing |
| Magnesium Hydroxide | Endothermic water release, higher temp | 340‑380 | Very Low | Halogen‑free, REACH compliant | High‑temp plastics, rubber |
| Antimony Trioxide + Halogen | Gas phase radical quenching | 150‑200 (halogen component) | Medium‑High | Potentially toxic, REACH restricted | Thermosets, electronics |
| Brominated Flame Retardants | Gas phase radical capture | 150‑180 | Medium | Persistent, bio‑accumulative | Foams, textiles |
| Phosphate‑Based (e.g., APP) | Char formation | 250‑300 | Low‑Medium | Generally REACH compliant | Wood composites, intumescent paints |
From the table it’s clear why many manufacturers lean toward aluminium hydroxide when they need a cheap, safe solution for low‑to‑moderate temperature polymers.
The performance of aluminium hydroxide hinges on two practical factors: particle size and surface treatment.
Typical loading levels:
This workflow keeps equipment wear low and helps maintain mechanical properties while hitting fire safety goals.
Even though aluminium hydroxide is non‑toxic, handling fine powders can generate dust. Workers should wear standard respirators and use dust extraction systems. Inhalation of large quantities can irritate the respiratory tract, but no chronic effects have been reported.
Regulatory highlights:
End‑of‑life disposal is straightforward: the material can be incinerated without releasing toxic gases, and the resulting aluminium oxide can be recycled into raw material streams.
Because of its low cost and environmental profile, aluminium hydroxide shows up in many everyday products.
In each case, the key is matching the polymer’s melt temperature with the retardant’s decomposition range.
For low‑melting polymers like polyethylene, about 30‑45wt% will typically achieve a V‑0 rating, provided the particles are fine (<10µm) and well‑dispensed.
Yes. Because it is GRAS‑listed by the FDA, aluminium hydroxide can be used in food‑contact applications up to the limits set by regulatory bodies, though typical flame‑retardant loadings are higher than needed for food safety, so a barrier coating is often added.
Magnesium hydroxide decomposes at a much higher temperature (340‑380°C), making it suitable for high‑temperature polymers. However, it is more expensive and often requires higher loadings to reach the same fire performance as aluminium hydroxide.
Absolutely. Hybrid systems that blend aluminium hydroxide with a small amount of halogen‑free phosphates or nanoclays can improve char formation and reduce the required loading, preserving mechanical properties.
It’s non‑persistent, non‑bioaccumulative, and produces only water and aluminium oxide when it burns. This means lower smoke toxicity and easier recycling compared with brominated alternatives.
With these basics under your belt, you can decide whether aluminium hydroxide fits your next product’s fire‑safety plan.
Comments
Miriam Rahel
While the exposition is comprehensive, the practical implications for low‑temperature polymers remain understated.
October 16, 2025 at 21:07
Frank Diaz
One cannot help but notice that the allure of halogen‑free retardants is wrapped in a veneer of progress, yet the underlying chemistry betrays a simplicity that many overlook. The author extols aluminium hydroxide’s virtues without confronting the trade‑offs inherent to high‑load formulations. In the grand theatre of material science, such omissions amount to a disservice to engineers seeking balanced solutions. It is therefore incumbent upon the discerning reader to probe beyond the glossy metrics presented.
October 19, 2025 at 02:45
Mary Davies
Imagine a world where each polymer, once innocent, transforms into a silent guardian against fire, thanks to a humble white powder-such is the poetry of aluminium hydroxide! Yet, beneath this lyrical veneer lies a pragmatic dance of particles, temperature thresholds, and mechanical compromises that demand our sober attention.
October 21, 2025 at 08:23