In a 2003 study, composites fabricated with halogenated resins performed quite differently from those employing ATH fillers in the NFPA 286 room corner burn test. ATH-filled systems with an ASTM E84 flame spread index of 20 easily passed the NFPA 286 test, whereas halogenated resins systems with the same ASTM E84 performance failed the NFPA 286 test. In vertical tests, such as the NFPA 286 room corner test, ATH-filled FR systems are thus more effective.
In the Single Burning Item (SBI) test, which is now being used to classify materials for buildings in the European Union and in China, there was no correlation between the results of the ASTM E84 test and the SBI test. The rating system used in both Europe and China has a letter rating for the flame spread of the system and an S number rating for the smoke index. A rating of Class B is the best rating that an FRP panel can obtain. A Class A rating is for noncombustible materials. The rating system utilized for smoke is S1 (low smoke), S2 (medium smoke) and S3 (high smoke).
Once again, halogenated resins do not perform as well in the SBI test as they do in ASTM E84. ATH-filled systems, however, easily deliver a Class B, S1 rating. Halogenated resin systems that achieve an ASTM E84 flame spread index of less than 25, however, only earned a Class D, S3 rating in the SBI test. The addition of ATH to brominated resin systems meets the Class B, S3 rating requirements.
The proper choice of fire-retardant technology depends not only on what fire tests must be passed, but also on the manufacturing process used to fabricate the FRP panels. The particle size and amount of ATH filler used will be limited if the fabrication process is RTM light or vacuum infusion. Suppliers have developed special resins with low enough viscosities to accept 100 phr (parts per hundred parts of resin) of 3-micron particle size ATH for vacuum infusion processes.
These highly-filled systems still deliver the low viscosities required for vacuum infusion. In addition, the type of flow media and the pitch configuration have a significant effect on the infusion process, particularly with larger, more complex parts.