brominated flame retardants (BFR)

Brominated flame retardants (BFRs) are a class of chemical additives containing bromine atoms, incorporated into plastics, printed circuit boards, foam and textile back-coatings to slow ignition and reduce flame spread. They suppress combustion by releasing bromine radicals that quench the gas-phase free-radical chain reaction sustaining a flame — a fundamentally different mechanism from halogen-free alternatives like phosphorus, aluminium hydroxide or magnesium hydroxide which work by char formation, dilution or endothermic decomposition. BFRs are highly effective at low loadings (5-15% of polymer mass), giving the lowest cost-per-unit-flame-retardant of any class.

The chemistry is diverse. Polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) were the dominant first-generation BFRs from the 1970s through 2010s, now globally restricted under the Stockholm Convention and RoHS. Tetrabromobisphenol A (TBBPA) is the workhorse BFR in printed circuit board epoxy resins, accounting for over 60% of global BFR consumption; it is chemically bonded to the epoxy matrix and considered less environmentally mobile than the older additive BFRs, but its degradation products under combustion still include polybrominated dioxins and furans. Hexabromocyclododecane (HBCD) was the principal BFR in polystyrene foam insulation, listed under Stockholm Convention Annex A in 2013 and progressively phased out. Decabromodiphenyl ethane (DBDPE) and other newer brominated polymers are commercial replacements with somewhat better environmental profiles but persistent and bioaccumulative concerns remain.

The recycling hazard is the formation of polybrominated dioxins and furans (PBDD/PBDF) during uncontrolled or low-temperature combustion of BFR-containing plastics. Open burning in informal e-waste yards at typical 400-700°C is the worst case — high yields of PBDD/PBDF, comparable in toxicity to the chlorinated dioxins from PVC combustion. Even controlled incineration at municipal-waste-incinerator temperatures (850°C) requires activated-carbon adsorbent injection and rapid quench of flue gas to suppress de novo dioxin formation in the 300-450°C cooling zone. Pyrolysis under inert atmosphere shifts the bromine to HBr (recoverable as ammonium bromide) and lighter pyrolysis oils, but Indian plastic pyrolysis units rarely operate with the gas-cleaning trains needed to capture HBr.

For Indian e-waste plastic recyclers, the operational discipline is XRF-based bromine screening at intake. Total bromine above 1,000 ppm triggers diversion of the affected plastic fraction to a hazardous-waste cement-kiln co-processing route (cement kilns operate at 1,400-1,800°C with several seconds residence time, destroying PBDD/PBDF and capturing HBr as calcium bromide in the cement matrix). Bromine-free plastics (below 1,000 ppm) can be safely regranulated into general-purpose ABS, HIPS or PS. The economic trade-off is that 15-35% of e-waste plastic by mass typically tests positive for bromine — a substantial fraction of potential revenue that becomes a disposal cost instead. This is the principal reason e-waste plastic regranulate from Indian plants sells at 40-60% discount to virgin polymer rather than commanding a premium.