Polyethylene/clay flame retardant

Fire retardants used in polystyrene (PS) include montmorillonite clay, polytetrafluoro-ethylene (PTFE) [8], bromine-based flame retardants such as brominated bisphenol A [9], brominated phenyl oxide or tetrabromophthalic anhydride, or magnesium hydroxide [10,11]. Sanchez-Olivares and co-workers [12], in their study of the effect of montmorillonite clay on the burning rate of PS and PS-polyethylene terephthalate blends, showed that increased combustion rate accompanied the incorporation of montmorillonite particles in high-impact polystyrene (FlIPS) formulations. 

Flame retardant performance can be enhanced in some magnesium hydroxide protected systems by the incorporation of clay or talc. In a polyethylene formulation the addition of 60% magnesium hydroxide and 5% tale instead of 65% magnesium hydroxide, improved the V-0 rating from 3.2 mm to the thinner 1.6 mm level. More tale at the expense of further magnesium hydroxide dropped the V-0 rating baek to 3.2 mm. 

A Japanese patent issued to Sekisui Chemical Co. Ltd." describes cone calorimeter data for polyethylene (PE)-derived nanocomposites in which organically modified layered silicates (OMTs) were combined with a variety of conventional flame retardant additives. The ammonium salt-modified silicate (SBAN-400) was incorporated into the PE compositions at 10 phr (Table 8.10). The PHRR results for the PE nanocomposite materials are 50% lower than the PHRRs for pure PE and PE with 10 phr pristine clay (MMT). These results suggest that without suitable organic treatment of the clay, the addition of MMT has little effect on flame retardant properties. Due to the favorable interactions arising from the organic surface treatment of the clay, the OMT forms a nano-dispersed structure in the PE matrix, while the PE-pristine MMT material is an immiscible or conventional composite. At 10-phr loading levels, where the OMT reduces the PHRR substantially for PE nanocomposite, DB-AO has little effect and APP alone has only a weak effect on PHRR of PE, respectively. Addition of either 15 phr of DB-AO or 15 phr of APP to pure PE decreases the PHRR values by only 10 to 20% from that of pure PE. However, addition of 5 phr of APP to a PE-SBAN N-400 nanocomposite with 10 phr of SB AN N-400 causes a 63% reduction in the PHRR. The addition of 5 phr of phenylphosphate and 10 phr of SB AN N-400 also reduces the PHRR by 60% (Table 8.10). 

Lee, Y. H., T. Kuboki, C. B. Park, M. Sain, and M. Kontopoulou. 2010. The effects of clay dispersion on the mechanical, physical and flame-retarding properties of wood fiber/ polyethylene/clay nanocomposites. JAppl Polym Sci 118 452-61. 

---