The acid source at the heart of halogen-free intumescent systems: ammonium polyphosphate catalyzes a swelling char that insulates the polymer from the flame. Supplied as Phase II powder and coated (microencapsulated) grades for polypropylene, polyethylene compounds and intumescent coatings — alone or as a complete formulated system.
Fig. APP01 — APP powder at incoming QCWhite APP flame retardant powder checked before compounding.
Ammonium polyphosphate — (NH₄PO₃)ₙ, "APP" — is a halogen-free phosphorus-nitrogen flame retardant. In a fire it decomposes into polyphosphoric acid and ammonia: the acid drives the polymer surface to char instead of burn, and that char is the protection. Which grade you need depends on where it goes — the two crystal phases and the coated variants behave very differently in water and heat.
The plastics-compounding standard: long-chain crystalline APP, thermally stable above ~275 °C with low water solubility — it survives polyolefin extrusion and molding temperatures.
Silane, melamine-resin or polyurethane shells around each particle: sharply lower water uptake, better dispersion and stronger char — V-0 in PP from around 20% loading.
APP plus char former and blowing agent, pre-balanced and ready to dose — for compounders who want a one-pack system instead of sourcing three components and tuning ratios themselves.
Fig. APP02 — weighing an intumescent trial ladderRatio balance between acid source, char former and blowing agent.
Fig. APP03 — intumescent PP compound and burn barsThe swelling char is visible on tested specimens.Intumescent means "swelling": three components act in sequence to grow an insulating carbon foam over the burning surface. APP is the trigger — but it needs its two partners.
Heat decomposes APP into polyphosphoric acid, which dehydrates the surrounding material toward carbon instead of letting it volatilize as fuel.
A carbon donor — classically pentaerythritol — reacts with the acid to build the char skeleton. Some engineered systems build the char source into the APP coating itself.
Nitrogen gases released by melamine inflate the forming char into a thick, insulating foam — a physical barrier that cuts heat flux and starves the flame of fuel.
APP dominates wherever a halogen-free V-0 is required in polyolefins — resins that make no char of their own and cannot carry the mineral loads cable compounds tolerate.
| Application | System | Typical Loading | Key Targets | Notes | Related Page |
|---|---|---|---|---|---|
| PP compounds & molded parts | APP intumescent one-pack | 18–30% (coated: from ~20%) | UL94 V-0 · LOI 28+ · GWFI | The flagship APP application — halogen-free V-0 PP | FR polypropylene |
| PE film, sheet & thick parts | APP intumescent | 20–25% | UL94 · LOI 26+ | Halogen-free alternative where mineral loads are too stiff | FR polyethylene guide |
| Recycled polyolefins (rPP / rHDPE) | APP intumescent, re-validated per stream | 20–30% | UL94 · batch consistency | Growing PCR demand; contamination shifts burn behavior | rPE notes |
| Intumescent & fireproof coatings | APP (Phase I or II) + binder systems | Formulation-dependent | Fire-resistance time ratings | Steel-structure and wood coatings; water resistance decides grade | — |
| PU foam & thermosets | APP as co-flame-retardant | 10–25 phr | Application-specific | Partnered with liquid phosphates in flexible foam | — |
Halogen-free polyolefins have two main roads: an APP intumescent system or a mineral (MDH/ATH) load. They win in different places — and the deciding factors are loading tolerance and smoke.
The part cannot carry a 60% mineral load — which is most injection molded and thin-wall work.
Smoke numbers rule and the application tolerates high filler — the cable-compound world.
"APP" on a datasheet hides the choices that make or break the compound: phase, particle size, coating and the ratio of the full intumescent package.
We supply APP as Phase II and coated powders, and — where it saves the customer three sourcing headaches — as complete pre-balanced intumescent systems in powder or masterbatch form, burn-verified in-house before shipment.
Fig. APP04 — burn verification in our labEvery intumescent ratio is burn-tested before recommendation.
Fig. APP05 — export packagingBags, big bags and palletized supply for overseas buyers.Direct answers for engineers and procurement evaluating ammonium polyphosphate before sampling.
A halogen-free phosphorus-nitrogen flame retardant that decomposes in fire into polyphosphoric acid — the acid source of intumescent systems, driving the polymer surface to form an insulating swollen char instead of burning as fuel.
Phase I is short-chain: lower thermal stability, higher water solubility, used mainly in coatings. Phase II is long-chain crystalline — stable above ~275 °C with low water solubility — the standard for plastics compounding, where it must survive extrusion temperatures.
In polypropylene, complete APP-based intumescent systems typically reach UL94 V-0 at 18–30% total loading. Microencapsulated grades reach V-0 from around 20% while adding water resistance — loading depends on wall thickness and the exact system balance.
Plain APP is hygroscopic: in humid service it can migrate and leach, degrading both flame rating and surface quality. Silane, melamine-resin or PU coatings cut water uptake sharply, improve dispersion and typically strengthen the char — the default choice for outdoor and humid applications.
Send your resin, wall thickness, target standard and the service environment (humidity matters for grade choice). We will recommend the APP grade or complete intumescent system — and prove the loading in our burn lab before you commit a line trial.