An innovative brominated polymeric flame retardant (FR) has been developed as an alternative to HBCD to provide effective flame retardant performance in polystyrene foams such as Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS).
These foams, commonly used in building and construction, ensure that homes, offices and public buildings are energy efficient and comfortable, whilst meeting fire safety requirements.
Reduced likehood of ignition
Slower fire growth
Reduced heat release
Lower % by mass of flame retardant
The new brominated polymer flame retardant is based on a co-polymer of styrene and butadiene where the polybutadiene portion is brominated on to the 1,2 and 1,4 isomer units to give a brominated polybutadiene. This flame retardant exhibits a superior environmental profile to that of HBCD – being stable, with a high molecular weight. It is also classified as a nonhazardous polymer and as a Polymer of Low Concern
(PLC) with officially recognised environment, health & safety characteristics (see figure 1). Polymeric flame retardants, generally speaking, are inherently sustainable substances. Their high molecular weight makes them unlikely to penetrate through the cell membranes of living tissues. They are therefore not likely to be bioavailable and to bioaccumulate in the food chain.
The table below is reproduced from the USEPA 2014 report:2
This table contains hazard information for each chemical; evaluation of risk considers both hazard and exposure. Variations in end-of-life processes or degradation and combustion by-products are discussed in the report but not addressed directly in the hazard profiles. The caveats listed below must be taken into account when interpreting the information in the table. VL= Very Low hazzard L=Low hazzard M=Moderate hazzard H=High hazzard VH=Very high hazzard – Endpoints in colored text (VL, L, M, H, and VH) were assigned based on empirical data. Endpoints in black italics (VL, L, M, H, and VH) were assigned using values from predictive models and/or professional judgment. d This hazard designation would be assigned MODERATE for a potential for lung overloading if >5% of the particles are in the respirable range as a result of dust forming operations § Based on analogy to experimental data for a structurally similar compound. ¥ Aquatic toxicity: EPA/DfE criteria are based in large part upon water column exposures which may not be adequate for poorly soluble substances such as many flame retardants that may partition to sediment and particulates.
As HBCD is being phased out globally, manufacturers of thermal insulation foams now have a more sustainable alternative flame retardant.
In response to the identification of HBCD as meeting the criteria for classification as a persistent, bioaccumulative and toxic (PBT) substance in the EU, industry embarked on a search for a feasible technical alternative. This alternative would not only need to meet requirements in terms of flame retardant efficacy, but would also need to be environmentally superior and more sustainable. The criteria for such an innovative technology are indicated in figure 1. After an intensive research and development exercise, the industry commercialized the new brominated polymeric flame retardant.
For polystyrene foam applications where HBCD was used, several conceptual elements were combined to meet existing fire safety and use requirements, including an improved environmental & health toxicity profile to comply with regulatory guidelines.
FLAME RETARDANT PERFORMANCE
4 Meet flammability requirements in foam globally (e.g. EU, JP, NA, CN, KR)
4 Acceptable cost, commercially available
In 2014, the US Environmental Protection Agency (USEPA) reviewed the environmental and hazard profile of the new polymeric alternative to HBCD and concluded:
3 EPA, 2014. Flame Retardant Alternatives to Hexabromocyclododecane (HBCD). USEPA Design for the Environment
Final Report June 12, 2014, http://www.epa.gov/sites/production/files/2014-06/documents/hbcd_report.pdf/
Not acutely toxic
Not sub-chronically toxic
Not developmentally toxic
Persistent by design
Not bio-accumulative – large molecule, not likely to be transported through cell membranes
Not toxic – below ecological toxicity concern levels