The antimony-free synergist: zinc stannate (ZS) and zinc hydroxystannate (ZHS) deliver halogen-system flame synergy and hard smoke suppression at 1–5 phr — the tin route for formulations that want antimony out entirely. Supplied as fine powder for PVC cable, brominated systems, LSZH compounds and engineering plastics.
Fig. ZS01 — fine white powder at incoming QCTin-based synergist powder checked for particle size before formulation.
Two closely related tin compounds share the name in practice: zinc hydroxystannate ZnSn(OH)₆ (ZHS), which carries bound water it releases from ~180 °C, and its dehydrated form zinc stannate ZnSnO₃ (ZS), stable well past 400 °C. Both do the same two jobs — halogen-system flame synergy and smoke suppression — without a milligram of antimony.
Where zinc borate typically caps out as a partial antimony substitute, tin synergy is strong enough that many flexible PVC and selected brominated systems can remove Sb₂O₃ completely and hold the rating.
Tin species catalyze char instead of soot. In smoke-limited cable and interior specs, ZS/ZHS routinely cut smoke density where antimony makes it worse.
ZHS adds an endothermic water-release bonus but must stay below ~180 °C processing — PVC territory. ZS gives up that bonus for thermal stability deep into engineering-plastic range.
Dual-phase action: tin and zinc species assist the halogen gas-phase chemistry the way antimony does, while simultaneously steering carbon into solid char instead of smoke.
In PVC and brominated systems, volatile tin and zinc halides shuttle halogen radicals into the flame — the same amplifying role antimony plays, from a tin platform with cleaner smoke behavior.
Tin oxides catalyze crosslinking and charring at the surface, locking fuel carbon into a protective layer — the root of the smoke suppression that distinguishes ZS/ZHS from antimony.
Below its ~180 °C ceiling, ZHS also releases bound water endothermically — a modest ATH-like cooling and dilution bonus stacked on top of the synergy.
Anywhere antimony trioxide sits in a formulation is a candidate — plus smoke-limited systems where antimony was never welcome.
| Application | Grade & Partner System | Typical Dose | What It Fixes | Related Page |
|---|---|---|---|---|
| Flexible PVC cable & sheet | ZHS in plasticized PVC | 1–5 phr | Full antimony removal; smoke density; LOI | PVC flame retardant |
| Brominated systems (PE, PP, ABS) | ZS with brominated FR | Partial-to-full Sb₂O₃ substitution | Antimony exposure; smoke; char strength | Brominated additives |
| LSZH / halogen-free compounds | ZS/ZHS with ATH or MDH | 2–5 phr, incl. coated-filler grades | Char sealing; smoke; peak heat release | Mineral FR (MDH & ATH) |
| Engineering plastics (PA, PBT) | ZS with brominated or phosphorus systems | 1–5 phr | Smoke; synergy without antimony declaration | FR PBT guide |
| Coatings, rubber & textiles backing | System-dependent | 2–10 phr | Smoke and afterglow in halogenated binders | — |
Three synergists, one seat at the formulation table. The honest ranking: antimony is still the strongest pure flame synergist per kilogram, zinc stannate is the strongest antimony-free one, and zinc borate is the cheapest partial fix.
Antimony has to go — entirely — or smoke is the binding clause.
Cost per rated part, not antimony removal, is the driver.
ZS or ZHS, dose, and whether to combine with borate or a reduced antimony core — each answer comes from the spec sheet, not the catalog.
As with every synergist we carry, the product is the ratio, not just the powder — substitution ladders are burn-tested in our lab before we put a number in a quote.
Fig. ZS02 — burn verification in our labEvery substitution ratio is burn-tested before we quote it.
Fig. ZS03 — export packagingBags, big bags and palletized supply for overseas buyers.Direct answers for formulators and procurement evaluating the tin route before sampling.
As an antimony-free synergist at 1–5 phr in PVC, brominated systems and LSZH compounds: it amplifies halogen flame chemistry the way antimony does, suppresses smoke strongly, and lets formulators reduce — or fully remove — antimony trioxide.
The processing temperature decides. ZHS keeps its bound water (and its extra cooling effect) only below ~180 °C — PVC and low-temperature elastomer territory. Above that, use ZS, which is thermally stable deep into engineering-plastic processing.
In many flexible PVC and selected brominated formulations, yes — full removal holds the rating with visibly better smoke. In demanding brominated polyolefins we recommend starting from partial substitution and laddering up with burn tests rather than assuming a 1:1 swap.
Per kilogram it is typically pricier than zinc borate and competes with antimony depending on the tin and antimony markets of the moment. The honest comparison is cost per rated part: at 1–5 phr effective doses, and with antimony’s price volatility, Sb-free tin packages frequently come out level or ahead — which is why we quote the whole package, not the powder.
Tell us the host system, your current antimony loading and the hardest clause in your spec — flame rating or smoke. We will design the ZS/ZHS package, ladder the substitution and prove it in our burn lab before you commit a trial.