CONTRACT RESEARCH & TOXICOLOGY products. This layer acts as a barrier between the flame and the flammable material, limiting heat transfer and oxygen contact, thereby removing two key elements necessary for further ignition.
There are five core classes of FRs: halogenated, phosphorus-based, inorganic, nitrogen-based and carbon-based. These have different modes of FR action and are often used in combination to realise the most effective condensed and gas phase mechanisms.
For example, halogenated FRs release halogen radicals( Br · and Cl ·), which neutralise the energy rich OH · and H · radicals and prevents chain radical propagation in the gas phase. Often these are combined with inorganic antimony trioxide( ATO) or zinc stannate chemistries, which can provide catalytic cross-linking mechanisms in the condensed phase to promote char formation.
Phosphorus-based additives promote charring in the condensed phase and provide intumescent properties, with some gas-phase effects via phosphorus radicals. Nitrogen-based additives can also provide intumescent properties and release nitrogen, diluting the fire gases. Mineral hydrates such as aluminium trihydrate( ATH) release water that also dilutes the fire gases and leads to cooling of the combustion zone.
Regulatory pressures
Additional to FR performance, these products also have to remain stable for the lifespan of the plastic, which
Figure 2- Antimony metal prices
Source: Fast Market in many construction and transport applications is at least 20 years. This long-term durability poses concerns of environmental persistence when it comes to end-of-life, particularly when these additives are toxic and have the potential to bioaccumulate.
Regulatory bodies across the globe now restrict the use of certain FRs that pose human and environmental hazards, with outright bans on select chemistries and many others being placed on lists for further investigation. Halogenated FRs have been the primary focus of regulation.
In the early 2000s, the Stockholm Convention on Persistent Organic Pollutants( POPs) highlighted a number of halogenated FRs, such as decabromodiphenyl ether( decaBDE) and short-chain chlorinated paraffins( SCCPs). 4 Penta- and octaBDE were restricted in the EU in 2003 and decaBDE in 2017. China and Japan also have restrictions on some brominated and chlorinated FRs, including decaBDE.
REACH also has a candidate list of Substances of Very High Concern( SVHCs). Included in this are nonhalogenated FRs such as triphenyl phosphate and melamine, one of the most common nitrogen-based FRs, citing environmental hazards and suspected carcinogenic properties, respectively. 5
In the US there are now stateby-state restrictions for FRs in certain applications. Historically this includes some of the brominated additives listed, but in 2020 California added tris( chloropropyl) phosphate and ATO to Proposition 65, restricting use in certain furniture and children’ s products to < 0.1 %.
Massachusetts followed suit in 2021 with a similar ban on multiple brominated, chlorinated and ATO FRs. Delaware signed a similar restriction into law in 2023 and Georgia introduced a bill at the start of 2025 addressing halogenated and antimony FRs for the same applications.
US, China & antimony
ATO is one of the key FRs used globally. In 2023 the price of ATO was around $ 11 / kg, but in recent months plastic compounders are paying up to $ 70 / kg, if they can access the material. A combination of supply concentration, mine depletion and geopolitics are responsible for this spike.
The hike in the ATO price began in August 2024 when China, accounting for 70 % of global production in 2022- 3, announced export controls on antimony products. The decision was made following a year-on-year decline in Chinese antimony ore production as a result of falling ore grades and stringent environmental requirements.
As a result, any exporters would require licences for certain military and civilian applications. By October 2024, total export of antimony products from China dropped by 97 %. 6 Imports of antimony products into the Netherlands dropped from 3,012 tonnes in 2023 to 1,016 tonnes in 2024, with no shipments arriving after October. 7
Then, in December 2024, the US announced a fresh round of export restrictions on China for semiconductor-related technologies. In retaliation, China’ s Ministry of Commerce imposed an export ban on gallium, germanium and antimony to the US. 8
This presents a significant challenge and not just the FR market. Another key application for antimony is leadacid batteries and the executive director of the US-based Responsible
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