Don't Just Keep Adding More Primary FR – A Charring Agent Saves You Money and Improves Performance

Here's a real story.

A cable factory kept failing the bundle flame test. Their formulation used 17% brominated flame retardant – expensive, yet the flame spread still exceeded the limit. The engineers tried everything: adding dispersants, adjusting extrusion temperature – a whole month of trial and error, with little improvement.

Then we suggested: stop focusing only on the bromine level, try a charring agent.

He was skeptical, but gave it a try. He replaced part of the bromine with 3% nano organic charring agent, and the total additive load dropped to 15%. The overall flame retardant cost decreased by 40%, and the bundle test passed immediately. The cable also retained better flexibility and aging performance.

This is not an isolated case.

Why can a charring agent replace up to 50% of halogenated FR?

Halogenated FRs (brominated, chlorinated) work in the gas phase – they release hydrogen halides, scavenge free radicals, and interrupt the combustion chain. They are efficient, but have two drawbacks: high cost, and they tend to reduce impact strength and elongation.

Charring agents (especially triazine-based and organic nano types) take a different route: condensed phase action. When burning, they promote the formation of a dense char layer on the material surface. This char acts like a wall – insulating heat, blocking oxygen, and preventing flammable gases from escaping.

When halogenated FR and charring agent are combined, you get a dual barrier: gas phase + condensed phase. The charring agent shares the flame retardant workload, so you can use less halogen. Many tests confirm that 10-15% of a high‑efficiency charring agent can replace 30-50% of halogenated FR while maintaining or even improving the V-0 rating.

This is especially important for bundle flame tests on cables. Flame spreads quickly and heat flux is high – halogen alone often fails. Adding a nano organic charring agent creates a char layer that rapidly covers the cable surface, blocking flame propagation along the cable. Pass rates improve dramatically.

What other “tough problems” can a charring agent solve?

Beyond cost reduction, charring agents bring several underappreciated benefits:

1. Improved mechanical properties
High loadings of traditional FR often make materials brittle and reduce elongation. But nano organic charring agents, with their small particle size (hundreds of nanometers), disperse uniformly and can even act as a nano‑reinforcement. In PA6, adding 8% charring agent increased impact strength by 30-40% compared to the same FR system without it.

2. Melt drip suppression
Many FR systems (especially halogen‑free) easily drip, igniting the cotton underneath. A charring agent quickly solidifies the material surface, and the melt is trapped by the char layer – drip is significantly reduced.

3. Lower smoke density
Halogenated FRs produce dense smoke, a major problem in enclosed spaces (subways, ships). The char layer itself generates little smoke and also blocks decomposition products from the bulk material – smoke density can drop by more than 50%.

Which materials benefit most from a charring agent?

• PA, PP, ABS – thin‑wall parts, electronic housings requiring good impact and surface finish

• Cables (especially bundle flame test scenarios) – PVC, PE, TPU jackets needing low smoke and no drip

• PBT, PET – connectors, relays requiring high CTI and thermal stability

Blending recommendations:

• With halogen‑antimony systems: charring agent : bromine‑antimony FR = 1:2 ~ 1:4, total loading 12‑18%

• With halogen‑free phosphorus systems: charring agent : phosphorus FR = 1:3 ~ 1:5 – synergistic char formation, better mechanicals

Two real cases

Case 1 – ABS electrical housing
Original formulation: 20% total bromine‑antimony, high cost. We suggested replacing part of it with 5% charring agent. New formulation: 14% bromine‑antimony + 6% charring agent (same total loading). Bromine‑antimony content dropped by 6%, cost decreased by 30%. V-0 passed, impact strength unaffected.

Case 2 – Bundle flame test (Class C) for cables
Original: 15% bromine + antimony trioxide – expensive, flame spread 1.8 m (failure). We added 4% nano organic charring agent K100 and reduced bromine‑antimony total to 10% (lower total loading than original). Re‑test: flame spread only 0.5 m, drip significantly reduced – easy pass. The customer said: “We didn't expect such a big improvement from just a little charring agent.”

YINSU Flame Retardant's charring agent product line

We know that a charring agent is not a “supporting role” – it is a core component for cost reduction and performance improvement. YINSU Flame Retardant offers several grades for different materials and processes:

• CFA series (triazine‑based charring agents) – general purpose, stable performance when blended with halogen or halogen‑free FRs for PP, ABS, PA. Cost‑effective.

• K100 (nano organic charring agent) – ultra‑fine particle size (D50 ≤4 μm), excellent dispersion. Particularly suitable for cable bundle flame tests and thin‑wall injection moulded parts. Can replace 30-50% of halogenated FR while significantly improving impact strength and surface smoothness.

We do not push “just add more”. Instead, we recommend testing small batches based on your specific formulation and cost targets. A charring agent is not a magic cure‑all, but in most FR systems it can help you save unnecessary expense and pass more stringent tests.

Selecting flame retardants is like cooking. Too much salt ruins the dish; too little makes it bland. The charring agent is that spoonful of broth – you don't need to pile on seasonings, yet the flavour becomes richer.