Halogen-Free vs Halogenated Flame Retardants — Choosing on Evidence

Direct answer

Halogenated systems interrupt combustion chemically in the gas phase, which makes them extremely efficient: a brominated package with an antimony trioxide synergist reaches a UL 94 V-0 rating at loadings low enough to leave mechanical properties largely intact. Mineral halogen-free systems — aluminium trihydroxide and magnesium hydroxide — work physically by releasing water, cooling the flame front and diluting fuel gases, and they need 50 to 65 % loading to do it. That loading is the whole trade-off: halogen-free buys low smoke and no corrosive acid gas, and pays for it in stiffness, impact, density, melt flow and often cost per finished part.

The decision is usually made by the specification, not by chemistry

If the end use is a tunnel, a public building, rolling stock, a data centre or any confined space where smoke and acid gas kill before flame does, the specification will already require low smoke zero halogen. If the requirement is only a flammability rating on a component, halogenated remains technically and commercially viable in most jurisdictions. Ask which standard applies — UL 94, IEC 60332, EN 45545, CAN/ULC — before comparing additives, because those standards test different things and a V-0 result does not predict a cable vertical-tray result.

What mineral loading actually does to the compound

At 60 % ATH the compound is no longer the base polymer in any meaningful sense. Melt viscosity rises sharply, elongation at break falls, notched impact falls, and the part gets heavier. Two levers recover part of that: particle size and surface treatment of the mineral, and a coupling agent — typically a maleic anhydride grafted polyolefin — that bonds the polar filler surface to the non-polar matrix and restores a meaningful share of the lost mechanical performance. Skipping the coupling agent is the most common reason a halogen-free compound is written off as unworkable.

ATH decomposes from around 200 °C, so it cannot be used where processing runs above that. Magnesium hydroxide holds to roughly 300 °C and is the usual answer for polypropylene and engineering polymers, at higher cost.

Interactions to check before sampling

Halogenated retardants release acidic species that deactivate hindered amine light stabilizers — an outdoor flame-retarded part needs both, and the combination needs an acid scavenger or a low-basicity HALS. Mineral fillers adsorb antioxidants and slip agents. Antimony trioxide affects colour and opacity. None of these show up on a single-additive datasheet.

What we supply

Allzone supplies flame retardant masterbatch in halogenated and halogen-free configurations, LSZH cable compound, and aluminium trihydroxide as a halogen-free flame-retardant mineral filler. The applicable standard and test method must be stated at enquiry; ratings are confirmed by the supplier against the specific compound, never quoted generically.