A Synergistic HalogenFree Flame Retardant Solution for Rubber and Polymer Materials

1. Industry Background – A Structural Upgrade in Regulatory Compliance

The global flame retardant market is undergoing a profound structural transformation. The halogenfree flame retardant market is projected to grow from USD 6.31 billion in 2025 to USD 6.94 billion in 2026, at a compound annual growth rate of 10.1%. This growth is driven not only by stricter fire safety regulations but also by the expansion of the electrical and electronic equipment manufacturing sector and continuous improvements in transportation safety standards.

On the regulatory front, global restrictions on brominated chemicals are tightening. The EU REACH regulation revisions have placed multiple halogencontaining flame retardants on the restricted list, while China’s “Dual Carbon” targets require continuous improvement in the halogenfree rate across supply chains. The RoHS Directive and WEEE Directive strictly limit halogencontaining flame retardants such as polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE), steadily compressing the market space for traditional bromineantimony flame retardant systems.

Halogenfree flame retardancy has evolved from a “compliance option” to a “core competitiveness” factor. For rubber product and polymer material manufacturers, selecting an efficient and reliable halogenfree flame retardant solution is no longer a temporary measure to meet regulations – it is a strategic decision that determines whether products can enter premium markets. This is precisely why leading Flame retardant  Manufacturers, Suppliers, and Factory operations – especially Flame retardant Manufacturers China and Flame retardant Suppliers China – are actively transitioning to advanced halogenfree systems.

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2. Performance Limitations and Technical Bottlenecks of Traditional Solutions

2.1 Compliance Risks of HalogenBased Systems

Traditional brominated flame retardants are highly efficient, but they contain substances such as PBB and PBDE that are strictly controlled under the RoHS Directive. With environmental regulations continuously tightening, the compliance risks of these solutions are escalating, and exported products face increasing trade barriers.

2.2 Performance Shortfalls of Conventional HalogenFree Solutions

Conventional metal hydroxide flame retardants – represented by aluminium hydroxide (ATH) and magnesium hydroxide (MDH) – are nontoxic and environmentally friendly, but their flame retardant efficiency is relatively low. They typically require very high loadings (often 120–200 phr or more) to achieve basic flame retardancy. The direct consequences of such high loadings include:

• Significant deterioration of mechanical properties – key indicators such as tensile strength and elongation at break drop sharply;
• Poorer processability – difficult mixing, high energy consumption, rough extrudate surfaces, and poor dimensional stability;
• Notable increase in compound density, which is detrimental to lightweight design;
• Flame retardancy bottlenecks – they struggle to form effective char layers during combustion, may cause melt dripping, and cannot meet the antidrip requirements of UL94 V0.

2.3 Structural Contradiction between Flame Retardancy and Material Performance

The longstanding dilemma for the industry is that improving flame retardancy often comes at the expense of mechanical and processing performance. High loadings of traditional flame retardants can impart some flame resistance, but the service performance and costeffectiveness of the final products are severely compromised. Finding the optimal balance among flame retardant efficiency, mechanical properties, processability, and environmental compliance is the technical challenge that material engineers must address.

3. Technical Solution – Flame Retardant Mechanism and Product Matrix of GreenThinking® FR Series

3.1 Product Technical Positioning

The GreenThinking® FR Series is a family of highly effective, compounded halogenfree flame retardants developed by Powerflex New Materials, a subsidiary of Sanezen Group. Through multiple processing steps including ultrafine treatment, activation, functionalisation, and compounding, the series achieves performance breakthroughs via the dual technical pathways of “material compounding” and “interface engineering”. The FR Series products are white powders, free from polybrominated biphenyls, polybrominated diphenyl ethers, chlorine, fluorine, antimony trioxide, and other halogenated substances, and fully comply with EU RoHS, REACH, and WEEE environmental directives. As such, they are increasingly preferred by Flame retardant Manufacturers and Suppliers seeking truly sustainable solutions.

3.2 Dual Flame Retardant Mechanism – Synergy between CondensedPhase and GasPhase Action

The flame retardant effect of the FR Series operates at multiple levels during heating:

Condensedphase flame retardancy – Charbarrier mechanism
When the material is heated, the FR Series decomposes on the surface of the product to form a viscous charforming barrier, which creates a rigid carbon layer and a porous insulating layer. This barrier effectively isolates oxygen, heat, and diffusion of small molecules during combustion, physically interrupting the sustained combustion cycle – both by preventing external oxygen from contacting the internal combustible material and by suppressing the outward diffusion of combustible gases.

Gasphase flame retardancy – Radical quenching and endothermic cooling
Simultaneously, the radicals produced by the decomposition of the FR Series react with H· and OH· radicals that promote combustion, terminating the chain reaction of burning. The water and carbon dioxide released during decomposition further dilute the combustible gas concentration, while the entire decomposition process absorbs a significant amount of heat generated by combustion, providing a marked flamesuppression effect.

The synergy between these dual mechanisms enables the FR Series to achieve highefficiency flame retardancy at moderate addition levels, avoiding the drawbacks of high loadings required by traditional metal hydroxides that rely only on a single “dilution + endothermic” mechanism.

3.3 Differentiated Positioning of Core FR Series Grades

The FR Series includes multiple grades optimised for different application scenarios. Based on available test data, the three core grades are:

FR76RP – Generalpurpose highefficiency synergistic flame retardant
FR76RP is the workhorse grade of the series. It undergoes ultrafine treatment and surface modification, providing excellent dispersibility and processability. Typical physicochemical properties: active content 98.5%, D50 particle size 2.65 μm, brightness 95.9, moisture content 0.36%. FR76RP is particularly suitable for mechanical rubber goods that have strict requirements for extrudate surface quality and compound density. It performs well in a wide range of rubber bases including EPDM, NBR, HCR, NR, SBR, CR, IIR, and ACM. Typical dosage is 50–130 phr; generally, 6–8 phr increases hardness by one Shore A point, and 3–5 phr increases the oxygen index by one unit.

FR98RP – Ultrahigh LOI grade
The core differentiator of FR98RP is its ultimate pursuit of limiting oxygen index (LOI). In a basic EPDM 70 Shore A formulation, an 80 phr addition achieves an LOI of 42.3%, and 100 phr gives 41.5%. This makes it the preferred choice for applications with extreme flame retardancy requirements such as mining conveyor belts and speciality cables – making it an ideal halogen free flame retardant for EPDM with high LOI.

FR99RP – Balanced overall performance grade
FR99RP is positioned to achieve an overall balance of mechanical properties, thermal ageing resistance, and flame retardancy. While maintaining UL94 V0 rating, FR99RP significantly outperforms FR98RP in tensile strength, elongation at break, resilience, and hightemperature compression set. It is particularly suitable for applications that demand superior mechanical properties and longterm thermal ageing life.

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4. Comparative Performance – FR98RP vs. FR99RP in EPDM and NBR

The following data are based on the same EPDM 70 Shore A base formulation, with 80 phr and 100 phr additions of either FR98 or FR99, tested under identical curing conditions.

4.1 Comparative Data in EPDM 70 Shore A (80 phr and 100 phr)

Test Item	Unit	FR9880	FR9980	FR98100	FR99100
Curing characteristics (180°C×5min)
ML	lbf·in	0.92	0.91	1.09	1.04
MH	lbf·in	11.18	12.55	11.27	14.62
MHML	lbf·in	10.26	11.65	10.18	13.58
TS2	sec	59	41	63	41
TC10	sec	50	35	51	36
TC90	sec	207	96	221	112
Physical properties (175°C×6min)
Hardness (Shore A)	–	74	74	78	76
Tensile strength	MPa	7.63	9.26	6.35	9.32
Elongation at break	%	406	421	417	497
M100	MPa	2.64	2.77	2.59	2.69
Specific gravity	g/cm³	1.221	1.238	1.241	1.242
Flame retardancy
UL94 vertical burning	–	V0	V0	V0	V0
LOI	%	42.3	35.4	–	–
Heat ageing (100°C×70h)
Hardness after ageing	Shore A	–	–	83	79
Hardness change	–	–	–	+5	+3
Tensile strength after ageing	MPa	–	–	5.87	8.99
Tensile strength change	%	–	–	7.56	3.54
Elongation after ageing	%	–	–	275	406
Elongation change	%	–	–	34.05	18.31
Compression set (120°C×24h)
Compression set	%	–	–	52.94	31.43
Resilience	%	–	–	37	47

Key conclusions:

• Curing characteristics: FR98 significantly reduces crosslink density (lower MHML) and prolongs optimum cure time (higher TC90), with this effect intensifying at higher loadings; FR99 exhibits faster cure and higher crosslink density.
• Mechanical properties: FR98 vulcanisates show markedly lower tensile strength than FR99 (7.63 vs 9.26 MPa at 80 phr); FR99 is superior in elongation and resilience.
• Flame retardancy: Both achieve UL94 V0, but FR98 gives a much higher LOI (42.3% vs 35.4%). However, FR98 burns with strong intumescent charring and produces more ash, whereas FR99 tends to form a dense ceramiclike char layer.
• Heat ageing: FR98 shows greater hardness increase and more pronounced drops in tensile strength and elongation; FR99 retains properties significantly better.
• Compression set and resilience: FR99 exhibits far superior hightemperature compression set (31.43%) compared to FR98 (52.94%), along with higher resilience (47% vs 37%).

4.2 EPDM 50 Shore A (100 phr addition)

The trend is consistent in lowerhardness EPDM:

Test Item	Unit	FR98100	FR99100
MHML	lbf·in	8.4	9.31
TC90	sec	199	131
Tensile strength	MPa	8.03	9.31
Elongation at break	%	550	553
LOI	%	41.5	30.5
Resilience	%	44	51

FR99 again offers faster cure, higher tensile strength, and better resilience, while FR98 maintains its LOI advantage.

4.3 NBR 70 Shore A (100 phr addition)

In NBR:

Test Item	Unit	FR98100	FR99100
MHML	lbf·in	8.45	12.53
TC90	sec	79	94
Tensile strength	MPa	9.43	9.23
Elongation at break	%	522	455
M100	MPa	2.55	2.94
LOI	%	37.8	32.6
Resilience	%	24	33

Here too, FR98 gives higher LOI (37.8% vs 32.6%), but FR99 delivers higher crosslink density, higher modulus, and better resilience, demonstrating its balanced performance.

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5. Process Consistency Control – How Manufacturing Precision Elevates the Technical Ceiling

The FR Series products undergo ultrafine treatment and surface modification, ensuring excellent dispersion in rubber compounds. With small and welldistributed particle sizes (FR76 D50 = 2.65 μm) and large specific surface area, the flame retardant particles are uniformly distributed throughout the rubber matrix, avoiding localised performance defects caused by agglomeration.

Energy consumption during mixing is relatively low, which directly translates to reduced production costs and improved efficiency. The FR Series can shorten the optimum cure time – as shown in the comparative data, the TC90 of FR99 (96–112 sec) is significantly shorter than that of FR98 (207–221 sec), meaning higher production throughput.

Compounds containing the FR Series exhibit good flowability, easy extrusion, and excellent dimensional stability. Extruded products have smooth surfaces, which is particularly important for cable sheaths, sealing strips, and rail transit components that demand high surface quality.

Field surveys of multiple rubber product manufacturers reveal that even with identical formulations, the final performance scatter often depends on shear control and dispersion effectiveness during the initial mixing stage. The design of the FR Series – with surface modification and ultrafine treatment – inherently reduces this process variability from the source. Consequently, more and more Flame retardant silicone rubber Manufacturers China and Flame retardant silicone rubber Suppliers China are standardising on these grades to ensure reproducible quality.

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6. Selection Guide – Choosing the Right Grade for Your Application

Based on the empirical data above, we recommend the following selection principles:

Application Scenario	Core Requirement	Recommended Grade	Justification
Mining conveyor belts, underground cables, speciality flameretardant products	Extremely high LOI (>40%)	FR98RP	LOI >42% in EPDM, maximum flame retardancy safety margin; acts as a true halogen free flame retardant for EPDM with high LOI
Rail transit seals, automotive enginecompartment rubber parts	Flame retardancy (V0) combined with longterm thermal ageing life and low compression set	FR99RP	Better retention of properties after ageing; compression set far superior to FR98; qualifies as a low compression set flame retardant for rubber seals and a flame retardant with low compression set for rubber seal
Generalpurpose flameretardant rubber goods, cable sheaths, extruded profiles	Costeffectiveness, good processability, smooth surfaces	FR76RP	Most versatile, easy to disperse, low density, wide processing window; can serve as a RoHS compliant halogen free cable rubber compound

For products that require resilience and dynamic fatigue resistance (e.g., vibration dampers, sealing rings), FR99 is distinctly superior to FR98. For applications where static flame retardancy rating is the absolute priority (e.g., mining products), FR98 is the undisputed choice.

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7. Summary of Technical Value

The technical value of the GreenThinking® FR Series halogenfree flame retardants can be summarised in the following core dimensions:

• Flame retardancy dimension: Through the multiple synergistic mechanisms of “charbarrier + radical quenching + endothermic cooling”, UL94 V0 is achieved at moderate addition levels. FR98 can reach LOI >42% in EPDM, meeting the most stringent flame retardancy requirements.
• Environmental dimension: 100% halogenfree, nontoxic, and odourless, fully compliant with RoHS, REACH, and WEEE – providing a RoHS REACH compliant halogen free flame retardant that removes compliance barriers for exports.
• Performance dimension: FR99 maintains V0 rating while delivering excellent tensile strength, thermal ageing retention, and low compression set, ensuring long service life – making it a true eco friendly non toxic flame retardant for rubber.
• Processing dimension: Easy dispersion, good flow, smooth extrusion, low energy consumption; FR99 offers significantly shorter optimum cure time than FR98, raising production efficiency.
• Flexible selection: The three grades FR76, FR98, and FR99 cover diverse needs from generalpurpose costeffectiveness, extreme flame retardancy, to balanced overall performance, providing formulation engineers with precise selection criteria.

In the industry transition where halogenfree flame retardancy is moving from “compliance option” to “core competitiveness”, the GreenThinking® FR Series offers a systematic solution that balances flame retardant efficiency, environmental compliance, material performance, and processing economy – a solution increasingly trusted by Flame retardant silicone rubber Manufacturers, Suppliers, and Factory operations worldwide, especially those in China.

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Technical FAQ

Q1: Both FR98RP and FR99RP can achieve UL94 V0. What is the biggest difference between them?

Brief answer: The core difference lies in their performance emphasis – FR98RP pursues maximised limiting oxygen index (LOI), while FR99RP pursues overall balance of mechanical properties and flame retardancy.

Indepth explanation:
In the same EPDM 70 Shore A formulation at the same 80 phr loading, FR98RP achieves an LOI of 42.3%, far higher than FR99RP’s 35.4%. This means FR98RP provides a greater safety margin against flame spread, making it highly suitable for applications with extreme flame retardancy demands – for example, as a halogen free flame retardant for EPDM with high LOI in mining conveyor belts and underground cables.

However, this ultrahigh LOI comes with performance tradeoffs: slower cure (TC90 207 sec vs 96 sec), lower crosslink density (MHML 10.26 vs 11.65), lower tensile strength (7.63 MPa vs 9.26 MPa), greater degradation after ageing (tensile strength change 7.56% vs 3.54%), higher hightemperature compression set (52.94% vs 31.43%), and lower resilience (37% vs 47%).
FR99RP exchanges a moderately lower LOI for faster curing, higher crosslink density, better tensile strength, superior ageing retention, lower compression set, and higher resilience – all of which are often more critical for dynamic sealing and damping components.

Selection advice: If flame retardancy rating is the sole priority, choose FR98RP. If you need to combine flame retardancy with long service life, sealing performance, and elastic recovery, choose FR99RP – a genuine low compression set flame retardant for rubber seals and a flame retardant with low compression set for rubber seal.

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Q2: When replacing traditional halogencontaining flame retardants with the FR Series, does the formulation need major adjustment?

Brief answer: The FR Series offers excellent compatibility and dispersibility. In most cases, it can be substituted directly at equal or slightly adjusted loadings without a complete overhaul of the curing or plasticiser system.

Indepth explanation:
The FR Series products undergo ultrafine treatment and surface modification, with small and welldistributed particle sizes (FR76 D50 only 2.65 μm). They disperse excellently in rubber matrices and do not impose the severe mixing or surfacequality penalties typical of highly filled metal hydroxides.

However, two points should be noted:
First, minor curing system adjustment may be needed. Different grades affect cure speed differently. For example, FR98 significantly prolongs optimum cure time (TC90 extends from 96 sec to 207 sec), whereas FR99 has a much smaller impact (TC90 ~112 sec). Therefore, switching from FR99 to FR98 may require an increase in accelerator dosage to maintain production efficiency.
Second, hardnessloading relationship. The typical dosage is 50–130 phr; generally, each 6–8 phr increases hardness by about 1 Shore A, and each 3–5 phr increases LOI by about 1 unit. We recommend conducting a gradient trial (starting from 80 phr in 10phr increments) to precisely match target hardness and flame retardancy.

Overall, the replacement path with the FR Series is relatively smooth – no need for a complete redesign of the existing curing or plasticiser system.

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Q3: Does the FR Series really produce no melt dripping during combustion? What is the mechanism?

Brief answer: Yes. The FR Series effectively suppresses melt dripping through its charforming barrier mechanism, which is a key reason why it passes the UL94 V0 rating (not merely V2 or V1).

Indepth explanation:
Traditional ATH/MDH flame retardants mainly rely on endothermic decomposition releasing water vapour to dilute combustible gases, but they cannot form a stable protective layer on the polymer surface. During sustained combustion, the polymer matrix softens and melts; without an effective char layer, molten material drips under gravity – a very common phenomenon and the main reason many products fail to go beyond UL94 V2.

The FR Series solves this problem. Upon heating, it decomposes on the product surface to form a viscous charforming barrier that creates a rigid carbon layer and porous insulating layer. This char layer wraps the polymer surface with a dual function: first, physically isolating oxygen, heat, and small molecules from diffusing into the interior; second, immobilising the molten polymer matrix to prevent flow and dripping.

One noteworthy observation from comparative testing: FR98RP exhibits strong intumescent charring during combustion, with expanded char but more ash generation; FR99RP tends to form a dense ceramiclike char layer that is more compact and stable. Both charforming effects satisfy the strict V0 criterion – no flaming drips are allowed to ignite the cotton indicator underneath.

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Q4: How does the FR Series affect thermal ageing life and compression set of rubber products? What does this mean for sealing applications?

Brief answer: Different FR Series grades have significantly different impacts on thermal ageing life. FR99RP excels in ageing retention and compression set, making it the preferred choice for sealing products; FR98RP should be carefully evaluated for longterm hightemperature service.

Indepth explanation:
For sealing strips, Orings, gaskets, and similar products, postageing property retention and hightemperature compression set directly determine service life and sealing reliability.

Based on ageing data for EPDM 70 Shore A with 100 phr loading (100°C×70h):

• Hardness change: FR98 hardness increased by 5 points (78→83), FR99 by only 3 points (76→79). A large hardness increase means the seal gradually hardens in service, losing compliance and possibly causing uneven contact pressure distribution.
• Tensile strength retention: FR98 dropped from 6.35 MPa to 5.87 MPa (7.56%); FR99 dropped from 9.32 MPa to 8.99 MPa (3.54%). FR99 clearly retains strength better.
• Elongation retention: FR98 dropped from 417% to 275% (34.05%); FR99 dropped from 497% to 406% (18.31%). A sharp drop in elongation indicates increased brittleness and higher risk of fracture.
• Hightemperature compression set (120°C×24h): FR98 = 52.94%, FR99 = 31.43%. Lower compression set means better recovery after prolonged compression, hence higher sealing reliability.

Conclusion: For products that must serve longterm in hightemperature environments (e.g., enginecompartment seals, industrial pipe gaskets), FR99RP offers significantly longer sealing life and lower leakage risk. Although FR98RP has a higher flame retardancy rating, its faster ageing degradation makes it more suitable for static flameretardant applications with less demanding service life requirements. In sealing applications, FR99RP truly functions as a low compression set flame retardant for rubber seals and a flame retardant with low compression set for rubber seal, while also being an eco friendly non toxic flame retardant for rubber.

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Technical Support & Contact

For detailed experimental data, formulation recommendations, or customised solutions for specific rubber systems (EPDM, NBR, SBR, etc.) or particular service conditions, please contact the technical team at Xuanluo New Materials (Sanezen Group).

Email: yorichen@sanezen.com
Web: www.sanezenrubber.com