Halogen-free flame retardancy for polyolefins and engineering resins

Magnesium hydroxide is the workhorse halogen-free flame retardant for polyolefins. It decomposes endothermically at 300–320 °C — high enough to survive PP, PE and PA processing, yet early enough to quench a fire. The result: water vapour, a ceramic MgO char, and no corrosive or toxic halogen gases.

01The problem with halogenated systems

Brominated flame retardants are efficient, but they release dense, corrosive smoke and halogenated dioxins when they burn — and they are increasingly restricted under RoHS, REACH and the WEEE directive. Cable, pipe and appliance makers who export to Europe are being pushed toward halogen-free alternatives, often by the customer's own specification rather than by law.

The obvious alternative, aluminium hydroxide (ATH), has its own limit: it starts to decompose around 200 °C, which is below the melt-processing window of polypropylene and polyamide. That gap is exactly where magnesium hydroxide belongs.

02How it works in the flame

Three things happen at once when the compound is exposed to fire:

• Endothermic cooling. Decomposition absorbs roughly 1.3 kJ/g, pulling heat out of the burning surface.

• Water release. About 31% of the mass leaves as water vapour, diluting the flammable gases around the flame.

• Ceramic char. The remaining MgO forms a coherent, refractory layer that shields the polymer underneath.

03Where it is used

LSZH cable compounds. The largest single application. EVA or PE-based jacketing and insulation loaded with surface-treated Mg(OH)₂ passes IEC 60332 and achieves low smoke, zero halogen, with no acid gas generation in a tunnel fire — the reason it is now standard in metros, tunnels, data centres and ships.

PP and PE articles. Injection-moulded junction boxes, appliance housings, pipes and sheets — anywhere the part must hold its shape at elevated temperature while still meeting UL 94 V-0 or a glow-wire requirement. Surface-treated, fine-ground grades keep impact strength and flow acceptable at high loading.

Engineering plastics. In PA and EVA, Mg(OH)₂ works synergistically with a charcoal-forming agent and a smoke suppressant: the intumescent char carries the flame-retardant effect, so V-0 can be reached at lower total filler loading and better mechanicals.

04Recommended grades