0.1% of the compound, and clear polycarbonate goes from V-2 drip risk to UL94 V-0. KSS is a catalyst, not a filler — the only additive that gets a machine guard or a light cover to V-0 without turning it cloudy. Halogen-free, supplied as fine powder for compounding into transparent PC.
Fig. K01 — KSS powder at incoming QCFine KSS powder measured in fractions of a percent, not phr.
KSS is short for potassium diphenylsulfone sulfonate — an aromatic sulfonate salt. It does not fill the resin or block light; it rides inside the PC matrix and steers how the polymer breaks down when it burns. That is the whole trick, and it only works because PC already wants to char on its own.
Mineral and phosphate systems need 8–25% to rate a resin. KSS does the same job in clear PC at 0.05–0.1% — a rounding error by comparison, and the reason it leaves no visible trace.
KSS is not a general-purpose flame retardant — it works by nudging a decomposition path unique to polycarbonate’s own molecular structure. It does not transfer to other resins the way phosphinates or minerals do.
Unlike its fluorinated cousin KPFBS (potassium perfluorobutane sulfonate), KSS carries no halogen atoms at all — the cleaner claim where a spec says zero halogen, not just RoHS.
KSS does not fight the flame directly. It changes what PC does when it starts to break down — three effects from one small dose.
The sulfonate shifts PC’s thermal breakdown toward crosslinking and char formation instead of chain scission into flammable fragments.
The resulting char layer insulates the material below and starves the flame of fresh fuel — PC’s own carbon becomes the barrier, no added mass required.
Because KSS dissolves at the molecular level rather than dispersing as particles, there is nothing present at a scale that scatters visible light — hence no haze.
Anywhere a part must be seen through and rated V-0 — the two requirements conventional flame retardants cannot satisfy together.
| Application | Wall Thickness | KSS Dose | Co-Additive | Related Page |
|---|---|---|---|---|
| Clear machine guards / safety glazing | 1.6–3.2 mm | 0.05–0.1% | Trace PTFE for drip control | FR polycarbonate sheet |
| LED lighting covers & diffusers | 1.5–2.5 mm | 0.05–0.1% | Minimal — optical clarity is the priority | FR polycarbonate |
| Electrical enclosure viewing windows | 2–3 mm | 0.1% | PTFE where V-0 drip rules apply | FR polycarbonate |
| Thermoformed clear sheet / canopies | Variable after forming | 0.05–0.1% pre-forming | Verify rating at the thinnest formed corner | FR polycarbonate sheet |
Both reach V-0 in PC. One question decides which: does the part need to be seen through?
Glazing, guards, light covers — anything where haze fails the part regardless of flame rating.
Housings, PC/ABS blends, anything colored or opaque — where the higher loading is not a visual problem.
The KSS dose barely moves. Everything else in the recipe is where a project actually gets tuned.
We supply KSS as fine powder for direct compounding into clear PC, with the PTFE anti-drip balance worked out for your wall thickness and haze spec — every ladder cast and burn-tested before we quote a number.
Fig. K02 — burn verification in our labClarity and V-0 checked together, not separately.
Fig. K03 — export packagingSmall-dose powder, precisely packed for accurate dosing.The four that come up on almost every clear-PC inquiry.
Potassium diphenylsulfone sulfonate — a sulfonate salt that takes clear polycarbonate to UL94 V-0 at just 0.05–0.1% loading. It works by redirecting PC’s own decomposition toward char formation, not by adding bulk filler.
The dose is a few hundred parts per million, and it dissolves into the PC matrix rather than sitting as filler particles. Conventional flame retardants need 8–25%; KSS needs about a hundredth of that, so there is nothing present at a scale that scatters light.
Usually a small amount of PTFE, yes. PTFE is the one ingredient in a KSS formulation that can add haze, so the anti-drip dose — not the KSS content — is what a formulator actually tunes to hit both V-0 and the optical spec.
Yes, fully. Its relative KPFBS (potassium perfluorobutane sulfonate) contains fluorine; KSS does not. Where a spec demands zero halogen rather than just RoHS compliance, KSS is the cleaner answer.
Tell us the wall thickness, whether the part is thermoformed, and your haze/clarity spec. We calibrate the KSS and PTFE dose together and prove V-0 at your actual thickness before you commit a trial.