MAGNESIUM HYDROXIDE- ▸ Flame retardant: Halogen-free flame retardant and smoke suppressant for polymers.
- ▸ Acid neutralization: Neutralizing agent for acids in the chemical industry.
- ▸ Wastewater treatment: pH adjustment and treatment in wastewater.
- ▸ Chemical intermediate: Raw material for magnesium metal and magnesium compounds.
- ▸ Process additive: Additive in residual fuel oil and sulfite pulp processing.
A grade-specific Safety Data Sheet (SDS) — with the complete hazard classification, handling precautions, and transport information — is supplied with every shipment and available on request. Confirm all safety and regulatory details against the SDS for your specific grade.
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Magnesium hydroxide (MDH) is the higher-temperature endothermic mineral flame retardant — like ATH but stable to a higher processing temperature, so it suits engineering plastics processed above ATH’s decomposition point. Identity: CAS 1309-42-8.
What it is
Magnesium hydroxide (CAS 1309-42-8, Mg(OH)2) is a white mineral powder. It is halogen-free, acts as a functional filler and smoke suppressant, and decomposes at a higher temperature than ATH.
How it performs in fire
It decomposes endothermically at roughly 300–340°C, absorbing heat and releasing water that cools and dilutes, with the residual magnesia forming a protective layer and suppressing smoke. The higher decomposition temperature lets it survive the compounding of higher-temperature polymers. Like ATH it is used at high loadings.
Applications
MDH is used in halogen-free flame-retardant polypropylene and polyamide compounds, wire and cable, and other higher-temperature polyolefin and engineering-plastic applications. For lower-temperature polymers compare aluminum hydroxide (ATH).
Forms, grades and handling
MDH is supplied as a white powder in a range of particle sizes and surface treatments in bags and bulk. Properties are typical reference values; the Certificate of Analysis (CoA) for the lot you buy governs. Handle per the current Safety Data Sheet (SDS), and confirm regulatory status and restrictions for your market and end use. Each lot ships with CoA, TDS and SDS.
Bulk supply and RFQ
RawSource sources Magnesium Hydroxide direct from producers in bulk, with CoA, TDS and SDS per lot. Tell us your polymer or system, the fire test you must pass, your maximum loading, and any particle-size or grade requirement, and we will quote the right grade. See the full range and selection logic in the flame retardants guide.
Typical Properties
Typical reference values, not a specification; the Certificate of Analysis (CoA) for the lot governs.
| Property | Typical Value |
|---|---|
| Chemical / class | Flame retardant / smoke suppressant (mineral hydroxide) |
| Flame-retardant type | Mineral hydroxide (endothermic) |
| Role in fire performance | Endothermic; higher-temp; smoke suppressant |
| CAS Number | 1309-42-8 |
| Molecular Formula | Mg(OH)2 |
| Molecular Weight | 58.3 g/mol |
| Handling | Refer to the current SDS |
Regulatory & registration requirements
- TSCA (US):
- REACH (EU):
- EC number: 215-170-3
Source: EPA TSCA Inventory (July 2025 release) · ECHA CHEM — retrieved 2026-07-12
Solutions Using This Product
Process-solution guides on this site that specify this chemistry:
- Heavy Metal Removal & Precipitation (Water Treatment)
- Flame Retardants for Plastics & Polymers (Plastics & Polymers)
- Flame Retardants for Textiles: APP, Mineral & N-P Systems (Textiles)
Frequently Asked Questions
What is magnesium hydroxide (MDH) used for?
Magnesium hydroxide (MDH, CAS 1309-42-8) is a halogen-free endothermic flame retardant for higher-temperature polymers such as flame-retardant polypropylene and polyamide compounds and wire and cable, where its ~300–340°C decomposition temperature lets it survive compounding.
Why choose MDH over ATH?
MDH decomposes at a higher temperature (~300–340°C vs ~180–200°C for ATH), so it is used for polymers processed hot enough that ATH would decompose during compounding, such as polypropylene and polyamides.
How is bulk magnesium hydroxide supplied and quoted?
RawSource supplies magnesium hydroxide in bulk with CoA, TDS and SDS per lot. Pricing is quote-based on grade, particle size and volume; submit an RFQ with your polymer/system and the fire test you must pass.
What is the REACH and TSCA regulatory status of Magnesium Hydroxide (MDH)?
Magnesium Hydroxide (MDH) (CAS 1309-42-8) is subject to U.S. TSCA Inventory requirements; supplying it into the EU requires valid REACH registration ((EC) No 1907/2006). RawSource cannot verify a third-party supplier's registrations — buyers should require documented TSCA and REACH compliance for their jurisdiction and volume (EC 215-170-3).