FL-ZS, FL-ZHS, and FL-ZB—proven zinc synergists for ATO reduction and replacement in halogenated PVC, polyolefins, and engineering plastics.
FL-ZS, FL-ZHS, and FL-ZB are established commercial synergists with existing industrial application data. They are not experimental alternatives—they are commercially proven, TSCA-listed materials used in PVC, polyolefin, rubber, and engineering plastic compounds worldwide.
Unlike antimony trioxide, zinc-based synergists offer additional performance benefits: superior smoke suppression, reduced CO evolution in flexible PVC, no IARC classification, and in the case of FL-ZB, afterglow suppression and char promotion in a single additive.
| Property | ATO | Zinc-Based |
|---|---|---|
| FR Mechanism | Gas-phase only | Gas + solid phase |
| Smoke Suppression | Limited | Strong |
| CO Reduction | Minimal | Meaningful |
| IARC Classification | Group 2B | None |
| Supply Status | Constrained | Available |
| Afterglow Suppression | No | FL-ZB: Yes |
| Halogen-Free Compatible | No | FL-ZB: Yes |
Performance varies by system. Substitution requires formulation testing.
Zinc stannate (ZnSnO₃)—inorganic FR synergist and smoke suppressant for PVC, polyolefin masterbatch, engineering thermoplastics, thermosets, rubber, coatings, and adhesives. Partially replaces ATO in brominated and chlorinated systems. Both gas-phase and solid-phase FR activity. TSCA listed.
| Property | Value |
|---|---|
| CAS Number | 12036-37-2 |
| Appearance | White powder |
| Decomposition temperature | >932°F (>500°C) |
| Function | FR synergist + smoke suppressant |
| TSCA Status | Listed |
| ATO replacement | Partial—formulation dependent |
| Substrate | FL-ZS |
|---|---|
| Rigid PVC | Primary |
| Flexible PVC | Primary |
| Polyolefin masterbatch | Primary |
| Halogenated rubber | Suitable |
| Engineering thermoplastics | Suitable |
| Thermosets & epoxies | Suitable |
| Coatings & adhesives | Suitable |
Zinc hydroxystannate (ZnSn(OH)₆)—hydrated zinc stannate with enhanced smoke suppression vs. FL-ZS and ATO. Particularly effective in flexible PVC wire and cable insulation where NBS smoke density or IEC 61034 smoke emission limits apply. The endothermic dehydration at ~356°F (~180°C) further reduces flame spread. TSCA listed.
| Property | Value |
|---|---|
| CAS Number | 12027-96-2 |
| Appearance | White powder |
| Decomposition | ~356°F (~180°C) (endothermic—beneficial) |
| Key advantage vs. ATO | Superior smoke suppression + lower CO |
| Primary sector | Wire & cable, flexible PVC |
| TSCA Status | Listed |
| Substrate | FL-ZHS |
|---|---|
| Flexible PVC (W&C) | Primary—recommended |
| Rigid PVC | Suitable |
| Polyolefin masterbatch | Suitable |
| Halogenated rubber | Suitable |
| Engineering thermoplastics | Suitable |
| Thermosets | Suitable |
Zinc borate (2ZnO·3B₂O₃·3.5H₂O)—provides FR synergy, smoke suppression, afterglow suppression, and char promotion in a single additive. Works in both halogenated and halogen-free systems. The boric acid melt forms a protective glassy char layer; ZnO promotes crosslinking; water of crystallisation provides endothermic cooling. TSCA listed.
| Property | Value |
|---|---|
| CAS Number | 138265-88-0 |
| Formula | 2ZnO·3B₂O₃·3.5H₂O |
| Appearance | White free-flowing powder |
| Dehydration temperature | >554°F (>290°C) |
| Functions | FR + Smoke + Afterglow + Char |
| Halogen-free compatible | Yes—unique vs. FL-ZS and FL-ZHS |
| TSCA Status | Listed |
| Substrate | FL-ZB | Key Function |
|---|---|---|
| Rigid PVC | Primary | FR + smoke + afterglow |
| Flexible PVC | Primary | FR + smoke + afterglow |
| Polyolefins | Primary | FR + char promotion |
| Engineering plastics | Suitable | FR synergy |
| Thermosets | Suitable | FR + char |
| Halogen-free systems | Compatible | Unique advantage |
| Product | Chemistry | Best Substrate | Smoke Suppression | Afterglow | HF Compatible |
|---|---|---|---|---|---|
| FL-ZS | Zinc stannate | Rigid/flex PVC, polyolefins | Good | No | No |
| FL-ZHS | Zinc hydroxystannate | Flexible PVC, wire & cable | Excellent | No | No |
| FL-ZB | Zinc borate | Universal—incl. HF | Good | Yes | Yes |
| ATO-65⁄85 | Antimony trioxide | Masterbatch, plastics | Limited | No | No |
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