Speciality Chemicals Magazine SEP / OCT 2025 | Page 80

CONTRACT RESEARCH & TOXICOLOGY

IGNITION SOURCE

olymer

Battery Coalition commented recently that the current shortage is a“ national emergency”. 9 Export restrictions have led to significant market tightening, driving the price of antimony metal outside of China from $ 12 / kg in early 2024 to over $ 50 / kg in 2025( Figure 2).

In contrast, prices within China have seen more moderate increases, recently easing due to domestic oversupply. However, a market correction is now underway as antimony ore suppliers begin withholding stock. As of June, approximately 66 % of Chinese antimony smelters were offline, and antimony metal price has started to stabilise at $ 25 / kg. 10

Outside China, efforts are underway to secure localised antimony supply chains. The US Department of Defense has recently committed $ 75 million funding to Perpetua Resources’ stibnite mine project in Idaho, and the Hillgrove project in Australia is to commence production in 2026.11 As with many mining projects, there is no certainty on time to production, ore quality and resultant output.

An increased demand for military applications as antimony-containing

Flamtard

Figure 3-FR mechanism of zinc hydroxystannate in a chlorinated polymer

Zn 2 +

ammunition is replaced during the Ukraine-Russia war, 12 and an increase in demand from the solar market for sodium pyroantimonate could put further stresses on antimony availability.

Antimony-free solutions

The term‘ antimony-free’ has become increasingly prevalent among polymer compounders as companies search for FR solutions that can meet performance, cost and availability requirements.

There are few direct replacements for ATO, which is predominantly employed in PVC and other halogencontaining polymer systems. During combustion, ATO reacts with halogen halides to form antimony halides and oxyhalides. The halides are volatilised in the gas phase and act as radical scavengers, whilst a small proportion of oxyhalides operate in the condensed phase to promote polymer dissociation. 13

One compound with similar FR mechanisms is zinc stannate. Upon burning, the tin and zinc in zinc stannate or zinc hydroxystannate react with the halide ions, just as

antimony does, to form metal halide andoxyhalide compounds, which can act as radical scavengers in the gas phase and promote polymer crosslinking in the condensed phase( Figure 3). 14 William Blythe has supplied zinc stannate and zinc hydroxystannate FR synergists under the Flamtard product family since the 1990s.

Other routes can be employed to fully or partially replace antimony, such as including or increasing ATH loading in the system, using phosphate-based plasticisers instead of the incumbent phthalate-based plasticisers, or using borate-based FRs. Whilst the FR performance can be met via these routes, new additives will often influence other polymer properties, such as mechanical, colouration, electronic resistivity and weatherability, all of which will require polymer reformulation to meet the application needs.

Outlook

The FR industry stands at a critical juncture, shaped by the dual forces of regulatory scrutiny and geopolitical tension. ATO, once a cornerstone of halogenated FR systems, now faces significant supply chain volatility and regulatory headwinds. While alternative chemistries such as zinc stannate and phosphorus-based systems offer promising pathways, they often require reformulation to meet the complex property requirements of polymer compounds.

As the industry moves toward more sustainable and circular solutions, the development of biobased and low-carbon FRs will be essential. Navigating this evolving landscape will require innovation, collaboration, and a proactive approach to regulatory compliance and material sourcing. ●

80 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981