Overview
Antimony trioxide rarely does the job alone. Its main role is to boost the performance of halogenated flame retardants, letting a formulator use less of them for the same fire resistance. Beyond that it serves as a catalyst in PET production and turns up in some glass. It is a suspected carcinogen, which is why it draws regulatory attention.
Where it's restricted
Antimony trioxide is on the REACH Candidate List as a substance of very high concern. That status does not ban it. It does mean suppliers of articles must communicate its presence above 0.1 percent and, in some cases, notify the authorities.
The classification rests on suspected carcinogenicity by inhalation. Listing under REACH is the first formal step that can later lead to tighter measures.
Typical uses
The flame-retardant synergy is the largest use. Paired with brominated or chlorinated retardants in plastics, textiles and electronics housings, antimony trioxide multiplies their effect. As a polycondensation catalyst it helps produce PET for bottles and fibres, and small amounts decolourise or fine glass.
Because it is so often paired with halogenated flame retardants, finding antimony trioxide in a bill of materials is a hint that brominated or chlorinated retardants may be present too.
Note: this is general educational information, not legal advice. Verify against the official source before relying on it.