Clariant’s Exolit™ OP phosphinates: halogen-free and ATO-free alternatives to brominated flame retardants for engineering plastics
Exolit™ OP is Clariant’s halogen-free flame-retardant range for engineering plastics, based on DEPAL (aluminum diethylphosphinate), a phosphinate chemistry developed and patented by Clariant. It offers an alternative to brominated flame-retardant systems that rely on antimony trioxide (ATO), which has experienced price volatility and supply chain instability in recent years due to its concentrated production base. What sets Exolit™ OP apart is its ability to maintain performance properties throughout the product lifecycle and after recycling. The portfolio combines excellent fire safety performance with high mechanical strength, outstanding comparative tracking index (CTI) of 600 V and above, and proven recyclability, while being halogen-free. Exolit™ OP can be used in all kinds of polyamides (e.g. PA6, PA66, high-temperature PA), polyesters, like polybutylene terephthalate (PBT), and polyethylene terephthalate (PET) for end applications such as consumer electronics, household appliances, electrical installations (connectors, circuit breakers), data center and AI infrastructure, energy storage as well as transport applications like E-mobility, trains and aviation. Exolit™ OP is supplied as a specialty ingredient to compounders and engineering plastics producers.
The benefits of Exolit™ OP halogen-free flame retardants for engineering plastics
- Exolit™ OP contains no bromine, chlorine, or antimony. The EU-funded ENFIRO project (Life Cycle Assessment of Environment-Compatible Flame Retardants, Prototypical case study), which evaluated 15 commercially available non-halogenated flame retardants across 12 research institutions, confirmed that halogen-free options like Exolit™ OP "offer similar fire performance and technical application capabilities as brominated flame retardants while producing less smoke and less undesirable components in smoke."
- UL 94 V-0 performance: Exolit™ OP achieves UL 94 V-0 classification in reinforced PA and PBT systems. The newest grades – Exolit™ OP 1260 and Exolit™ OP 1266 (TP) – reach V-0 classification at a sample thickness of 0.4 mm at dosing levels of 15–20% in PBT, specifically developed for e-mobility applications.
- Maintained mechanical properties: Phosphinate-based flame retardants have a lower specific gravity than brominated/ATO-containing systems. This contributes to lighter parts without reducing flame protection. Mechanical properties of the base polymer are almost maintained after compounding with Exolit™ OP and are in the same range as with brominated solutions.
- Recyclability: Exolit™ OP retains its flame-retardant properties after multiple mechanical recycling cycles (Fraunhofer LBF/pinfa study V-O classification maintained over several recycling cycles). This makes it compatible with circular economy requirements in electronics and automotive, where recycled content targets are increasing.
- Reduced smoke during combustion: Phosphorus-based flame retardants produce less smoke during combustion compared to halogenated alternatives (PINFA Crepim study The impact of halogen free phosphorus, inorganic and nitrogen flame retardants on the toxicity and density of smoke from 10 common polymers).
- Carbon Footprint: A February 2024 life cycle assessment published by researchers at the Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT confirmed measurable environmental advantages for phosphinate-based flame retardants vs. brominated alternatives across the product lifecycle (Life Cycle Assessment of Phosphinate-Based and Brominated Flame Retardants in E-Mobility and Electronic Devices) .
- ATO-free and PTFE-free: Exolit™ OP does not require antimony trioxide or fluorinated polymers to achieve its flame-retardant performance. This removes two supply-sensitive and regulation-relevant materials from the compound formulation.
- Independently validated environmental profile: Exolit™ OP grades have received GreenScreen® Assessment (benchmark 3 for DEPAL), TCO certification (TCO Certified Accepted Substance List), and validation through the US EPA Design for Environment program (Design for the Environment Alternatives Assessments). The ENFIRO project (Life Cycle Assessment of Environment-Compatible Flame Retardants, Prototypical case study), funded by the European Commission, independently confirmed the environmental profile of phosphinate-based flame retardants.
Halogen-free vs. brominated flame retardants for engineering plastics (polyamides): performance and regulatory comparison
Sources:
Criterion Brominated + ATO Organophosphinate (Exolit™ OP) Melamine-based (MPP / MC) Mineral (MDH) Red phosphorus Halogen-free No Yes Yes Yes Yes ATO-free No Yes Yes Yes Yes Mechanism Gas phase – radical quenching [S3] Gas phase + solid phase (char formation) [S3] Gas phase / inert gas dilution [S3] Endothermic – water release [S3] Solid phase – char formation [S3] UL 94 V-0 thin wall (< 1 mm) Yes Yes MC: unfilled PA only No Yes (GF PA) CTI in GF PA / PBT Lower than phosphinate 600 V [S1] [S2] MC: 600 V (unfilled PA) [S2] Moderate 600 V [S2] GWIT in GF PA — 775 °C (all thicknesses) [S1] MC: ~775 °C unfilled PA [S2] — 775 °C [S2] Typical loading for V-0 ~25% ~20% [S2] MPP: ~25%; MC: 10–15% (unfilled) [S2] 45–50% [S2] 5–8% (GF PA) [S2] Smoke – corrosive gases in fire Generates HBr in fire [S4] No halogen gas release; smoke toxicity comparable to neat polymer [S4] [S6] No halogen gas release; note: melamine can contribute HCN emissions in fire [S6] No halogen gas release No halogen gas release Smoke density Higher vs. PIN FRs (tested across 10 polymers per EN 45545-2) [S4] Low [S4] Low – moderate Low Moderate Carbon footprint vs. Br+ATO Baseline Slightly lower (LCA, PA 66) [S8] — — — Impact on mechanical properties Low – moderate Low (low dosage) [S1] Moderate High (high loading) Low (very low dosage) [S2] Density impact High (--> heavier) Low Low – moderate High Low Color restriction None None None None Red / black only [S2] Recyclability Waste stream can be separated, but are generally not recycled; WEEE restricts PBB / PBDE composites [S5] Compatible with mechanical recycling; validated in PA GF (Fraunhofer LBF / pinfa) and PET [S1] [S7]; difficult sorting of post-consumer waste Compatible depending on formulation [S7] Compatible depending on formulation — Regulatory status ECHA (Dec 2024) recommends group restriction of non-polymeric additive BFRs; >40 of 60 ABFRs identified as PBT / likely PBT; PBBs and PBDEs banned under RoHS [S5] Compliant; not subject to EcoDesign halogen restrictions [S1]; identified as low concern (ENFIRO) [S2] SHVC status for melamine has only indirect impact on derivatives MPP, MC (free melamine) Compliant; ATH identified as low concern (ENFIRO) [S2] Compliant [S2] Environmental assessment Multiple aromatic brominated FRs classified PBT / vPvB [S5] GreenScreen® Benchmark 3 (pure phosphinate) [S1]; self-classified by Clariant as very persistent and very mobile, pending ECHA confirmation MPP and MC compliant (melamine proposal for harmonized classification as vPvM / PMT) Compliant Compliant; risk of PH3 emissions Renewable feedstock option No Yes (Exolit™ OP Terra), using mass balanced renewable carbon [S1] — — —
[S1] Clariant, "Exolit Flame Retardants for Thermoplastics", 2026
[S2] pinfa, "Flame Retardants in Electric and Electronic Applications", 3rd ed., 2017
[S3] pinfa / A. Beard, C. Thornton, "Flame Retardants: An introduction to chemistry and technology", Edition 1/2025
[S4] H. Feuchter, F. Poutch, A. Beard, "The impact of halogen free PIN FRs on the toxicity and density of smoke from 10 common polymers", Fire and Materials, 2023
[S5] ECHA, "Investigation report on Aromatic Brominated Flame Retardants", December 2024
[S6] pinfa, "Summary of FRPM Conference 2025", incl. Clariant case study (A. Beard)
[S7] PNO for pinfa, "A study of the state-of-the-art and potential impact of PIN FRs on plastic recycling", February 2023
[S8] Maga et al., "LCA of Clariant aluminium diphosphinate vs. brominated FR + ATO in PA 66", ACS Sustainable Chemistry and Engineering, 2024
Engineering plastics applications for Exolit™ OP
Select an application to learn more.
Electrical and electronic applications
- Electrical connectors, circuit breakers, and housing components made from engineering plastics must meet UL 94 V-0 flame retardancy in most applications while maintaining dimensional stability and mechanical strength. Brominated systems with ATO have been widely used in these applications but face increasing scrutiny from OEMs because of environmental requirements and supply chain exposure to ATO volatility.
- Exolit™ OP in polyamide connector applications: Exolit™ OP 1400 is a non-halogenated flame retardant for reinforced PA6, PA66, and high-temperature polyamides. It achieves UL 94 V-0 while maintaining the mechanical properties of the glass-fiber-reinforced matrix. It is used in switches, plugs, and structural housing components in industrial and consumer electrical installations.
E-mobility
- E-mobility applications, including high-voltage connectors, charging systems, and battery housing, place demanding requirements on flame retardant materials. Systems operating at 800 V and above require both superior electrical insulation and long-term stability under thermal and moisture stress.
- Exolit™ OP 1266 (TP) for high-voltage connectors: Exolit™ OP 1266 (TP) provides a stable comparative tracking index (CTI) of 600 V even after extended storage periods in PBT systems. It achieves UL 94 V-0 at a sample thickness of 0.4 mm at dosing levels of 15–20%. This combination of thin-wall V-0 performance and stable CTI makes it suitable for high-voltage connector applications in 800 V+ e-mobility platforms.
- Exolit™ OP 1242 (TP) addresses hydrolysis in e-mobility: Exolit™ OP 1242 (TP) is formulated for PBT applications where hydrolysis resistance is critical – relevant for components exposed to humidity, condensation, or cleaning fluids in under-hood or charging system environments. It maintains flame retardant performance and mechanical properties under hydrolytic stress conditions.
- Exolit™ OP 1400: Exolit™ OP 1400 is the preferred flame retardant for reinforced polyamides due to its excellent thermal and hydrolytic stability.
Consumer electronics and household appliances
- Consumer electronics and household appliances require flame retardant materials that maintain appearance, dimensional stability, and electrical insulation under repeated thermal cycling. OEM sustainability requirements and ecodesign regulations increasingly specify halogen-free materials for these product categories.
- The phosphinate chemistry in Exolit™ OP is compatible with thin-wall injection molding in PA and PBT. UL 94 V-0 is achievable at low wall thickness, supporting component miniaturization in smartphones, laptops, and small appliances. The non-hygroscopic nature of DEPAL contributes to dimensional stability in humid environments.
- Newly developed Exolit™ OP grades address the glow wire requirements for reinforced polyamides in unattended household appliances (glow wire flammability index GWFI and glow wire ignition temperature GWIT)
- Does Exolit™ OP affect the color or surface quality of molded parts? Exolit™ OP does not adversely affect the color development of PA or PBT compounds. The halogen-free chemistry can be combined with typical UV and light stabilizers, supporting consistent color quality in visible consumer-facing components.
Transportation – trains and aviation
- Rail and aviation applications require materials that meet rigorous fire, smoke, and toxicity (FST) standards. Engineering plastics used in seating components, cable management systems, and interior panels must comply with sector-specific fire regulations while being processable at scale.
- What fire safety standards does Exolit™ OP support in transport applications? Exolit™ OP-based compounds have been validated in PA and PBT systems for transport applications requiring low smoke emission and reduced toxicity during combustion. The ENFIRO project (Life Cycle Assessment of Environment-Compatible Flame Retardants, Prototypical case study) confirmed that phosphinate-based systems produce less smoke and fewer undesirable combustion products compared to brominated alternatives – relevant for enclosed transport environments where evacuation safety is a design criterion..
- How does the environmental profile of Exolit™ OP support transport OEM requirements? Exolit™ OP grades hold GreenScreen Assessment (benchmark 3 for DEPAL) and TCO certification (TCO Certified Accepted Substance List), and have been evaluated under the US EPA Design for Environment program (Design for the Environment Alternatives Assessments). These third-party assessments support OEM and Tier 1 documentation requirements for substances of concern and environmental compliance. In 2025, Clariant self-classified DEPAL as very persistent and very mobile (vPvM) in Europe, according to the Classification & Labelling Regulation. However, this classification is still subject to final experimental tests based on a request from ECHA (European Chemicals Agency).
Data center and AI infrastructure
Data center & AI infrastructure is driving strong demand for flame-retardant engineering plastics across critical components, including power distribution units (PDUs), circuit breakers, terminal blocks, power connectors, memory sockets (DDR5/DDR6), and thermal management parts such as liquid-cooling manifolds and facility-loop connectors. These applications demand UL 94 V-0 rated materials with stable electrical insulation properties under continuous thermal load. With data centers rapidly adopting 800V DC (HVDC) power architectures, halogen-free flame retardants are increasingly specified by OEMs. Exolit™ OP achieves UL 94 V-0 performance in reinforced PA6, PA66, high-temperature PA, and PBT – without halogen chemistry or antimony trioxide (ATO). Manufactured at two production sites in Germany and China, and validated in established OEM-grade specifications, it is a proven option for data center component manufacturers.
Which Exolit™ OP grade is right for your application?
Exolit™ grade Polymer End applications (examples) Key performance data Exolit OP 1230 HPPA DDR RAM / memory sockets (DDR4–DDR6) for consumer electronics and data center & AI infrastructure, PCB / SMT components UL 94 V-0 (0.4–3.2 mm) at low loading (< 15%); its thermal stability of up to 350°C in air makes it suitable for processing of all kinds of high temperature polyamides; high CTI; no blistering in reflow soldering; passed JEDEC-J-STD 020C (MSL 2); reflow soldering up to 260 °C; GreenScreen® Benchmark 3 Exolit OP 1240 PBT; PET (injection molding, not fiber melt spinning) Automotive, E&E, appliances, data center wind cooling and electrical equipment CTI up to 600 V; lower density vs. brominated alternatives; combinable with melamine polyphosphate and/or melamine cyanurate Exolit OP 1242 PBT; PET (injection molding, not fiber melt spinning) High-voltage connectors (e-vehicles) UL 94 V-0 (0.4–3.2 mm); CTI up to 600 V; improved hydrolysis resistance (85 °C / 85% rh, 1,000 h); no blooming; no mold deposit; no copper contact corrosion Exolit OP 1248 PBT; PET (injection molding, not fiber melt spinning) Automotive, E&E, data center wind cooling and electrical equipment Compared to Exolit OP 1240, Exolit OP 1248 shows an improved efficiency in UL 94 V-0 Exolit OP 1260 PBT; PET (injection molding, not fiber melt spinning) E&E, automotive UL 94 V-0 (0.4-3.2mm) at 18 wt% loading; enhanced melt flow and mechanical properties; potential drop-in solution for Br/Ato containing compounds due to mechanical properties and flowability similar to brominated solution plus ATO Exolit OP 1266 (TP) PBT; PET (injection molding, not fiber melt spinning) High-voltage connectors (e-vehicles) UL 94 V-0 (0.4 mm); improved CTI (600 V) vs. Exolit OP 1260; 15–20% loading Exolit OP 1312 PA 6; PA 66 E&E, data center power distribution (MCB/MCCB, terminal blocks), automotive circuit breakers UL 94 V-0 (0.4–3.2 mm); CTI 600 V; GWFI 960 °C; GWIT 775 °C (≥ 2 mm); most efficient grade for UL 94 and GWIT performance; suitable for all colors Exolit OP 1314 PA 6; PA 66 E&E, data center power distribution (MCB/MCCB, terminal blocks), automotive circuit breakers UL 94 V-0 (0.4 mm); GWFI 960 °C; enhanced thermal stability vs. OP 1312; suited for high processing temperatures and complex cavities Exolit OP 1380 PA 6; PA 66 Appliances, e.g. RAST connectors UL 94 V-0 (0.4–3.2 mm); GWFI 960 °C; GWIT 775 °C (all thicknesses 0.75–3.0 mm); GreenScreen® Benchmark 3 Exolit OP 1400 PA 6; PA 66; HPPA E&E, data center & AI infrastructure (power connectors, high-voltage components, liquid-cooling connectors), automotive circuit breakers, high voltage connectors (e-vehicles) UL 94 V-0 (0.4–3.2 mm); GWFI 960 °C; CTI 600 V; its thermal stability of up to 350°C in air makes it suitable for processing of all kinds of high temperature polyamides; suited for complex cavities; hot/humid environment stability; suitable for all colors; GreenScreen® Benchmark 3; UL 94 V-0 retained after multiple recycle cycles; FR properties stable after 1,000 h at 120 °C; elongation at break preserved; no severe color shifts Exolit OP 1466 PA 6; HPPA Appliances, e.g. RAST connectors UL 94 V-0 (0.4–3.2 mm); GWFI 960 °C; GWIT 775 °C (all thicknesses 0.75–3.0 mm); GreenScreen® Benchmark 3 Exolit OP 1480 PA 66 Appliances, e.g. RAST connectors UL 94 V-0 (0.4–3.2 mm); GWFI 960 °C; GWIT 775 °C (all thicknesses 0.75–3.0 mm); GreenScreen® Benchmark 3
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Frequently asked questions
How does Exolit™ OP work as a flame retardant in engineering plastics?
Exolit™ OP is based on DEPAL – aluminum diethylphosphinate – the pure form of which is sold as Exolit™ OP 1230. All Exolit™ OP grades for polyamides are built on this phosphinate chemistry. DEPAL works through a dual mechanism. In the gas phase, volatile diethylphosphinic acid interrupts the chemical reactions in the flame zone. In the condensed phase, an aluminium phosphate residue forms a protective char layer on the polymer surface, acting as a barrier against heat and oxygen. This combined action achieves UL 94 V-0 flame retardancy in reinforced polyamide and polyester systems. Unlike brominated flame retardants, this mechanism does not require antimony trioxide as a synergist and does not rely on fluorinated polymers such as PTFE as anti-drip agents.
What is Exolit™ OP used for?
Exolit™ OP is a halogen-free flame retardant range used in engineering plastics including PA6, PA66, high-temperature PA, PBT, and PET as well as in some elastomers like TPU and TPEE (based on polyurethane or polyester). It is used in electrical connectors, circuit breakers, consumer electronics housing, household appliances, e-mobility components, and transport applications requiring UL 94 V-0 flame retardancy and some cable insulations.
What is DEPAL and what role does it play in Exolit™ OP?
DEPAL (aluminum diethylphosphinate) is the core active substance in all Exolit™ OP grades for polyamides. It is a phosphinate salt that works through a combined gas-phase and condensed-phase flame retardant mechanism. Clariant invented and commercialized DEPAL in 2004 and holds patents covering the substance, its formulations, and its application in engineering thermoplastics.
How does Exolit™ OP compare to brominated flame retardants with antimony trioxide?
Exolit™ OP achieves equivalent UL 94 V-0 performance without bromine, chlorine, or antimony trioxide. It does not require PTFE as a co-additive. Compared to brominated/ATO systems, Exolit™ OP-based compounds have lower density, produce less smoke during combustion, and retain flame retardant performance through mechanical recycling cycles. The EU ENFIRO project (Life Cycle Assessment of Environment-Compatible Flame Retardants, Prototypical case study) confirmed that halogen-free phosphinate systems offer similar fire performance while producing less smoke and fewer undesirable combustion products.
Why are manufacturers reconsidering brominated flame retardants with antimony trioxide?
Manufacturers are switching away from brominated flame-retardant systems for two main reasons. The first is supply chain risk. Approximately 75–80% of global antimony trioxide production is concentrated in China. Export controls on antimony, introduced citing national security concerns, combined with environmental restrictions in key production regions, have contributed to price volatility and availability uncertainty in recent years. Manufacturers relying on ATO as a flame-retardant synergist have faced production planning challenges as a result. The second is the push for halogen-free materials. Demand for halogen-free solutions in electrical, electronic, and automotive applications is growing, driven by sustainability commitments, environmental certifications, and material specifications from OEMs. Exolit™ OP addresses both factors with a commercially proven chemistry that has been in use since 2004 and validated by independent research.
Can Exolit™ OP-containing compounds be mechanically recycled?
Yes. Exolit™ OP retains its flame-retardant properties after multiple mechanical recycling cycles. This is confirmed through testing (Fraunhofer LBF/pinfa study V-O classification maintained over several recycling cycles) and is increasingly relevant for electronics and automotive applications where recycled content requirements are growing.
What grades of Exolit™ OP are available for PBT in e-mobility?
Two grades are specifically developed for PBT in e-mobility: Exolit™ OP 1242 (TP) for hydrolysis-resistant applications, and Exolit™ OP 1266 (TP) for high-voltage applications requiring a stable CTI of 600 V. Both achieve UL 94 V-0 at 0.4 mm wall thickness at 15–20% dosing levels. Exolit™ OP 1260 combines flame retardancy with good mechanical properties.
Where is Exolit™ OP manufactured?
Exolit™ OP is produced at two manufacturing sites. The Knapsack facility in Germany is a world-scale plant that has supplied Exolit™ OP since its commercial introduction in 2004. The Daya Bay facility in Huizhou, Guangdong Province, China, represents Clariant's CHF 100 million investment in halogen-free flame-retardant capacity. Its two production lines support growing demand in Asia and globally, particularly in e-mobility and E&E applications. Local technical expertise at Daya Bay supports customers in the Asia Pacific region with application development and qualification support.
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