Flame retardant SBS-clay nanocomposites

MAURO COMES-FRANCHINI, MASSIMO MESSORI, GUIDO ORI, AND CRISTINA SILIGARDi  

A new class of materials, called nanocomposites, can avoid the disadvantages of traditional flame retardant systems. Generally, the term nanocomposite describes a two-phase material with a suitable nanofiller (organoclay, nanoparticles, carbon nanotubes, etc.) dispersed in the polymer matrix at the nanometric scale [3,4]. 

Among all the potential nanocomposite precursors, clay and layered silicates have been most widely investigated, probably because starting clay materials are easily available and because their intercalation chemistry has been studied for a long time [5, 6]. 

Layered silicates used in the synthesis of nanocomposites are natural or synthetic minerals, consisting of very thin layers that are usually bound together with counterions. 

Among layered silicates, 2 1 phyllosilicates (smectites) have received the most attention in regard to nanocomposite applications. The main reasons are their potentially high aspect ratio and unique intercalation/exfoliation characteristics. Furthermore, smectites have been used extensively to prepare nanocomposites because of properties such as 

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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). 

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