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Nano composites, a new class of polymer systems,
are essentially, modified layered silicates or clays dispersed at
nanometer levels in a polymer matrix. These nanocomposites provide
extraordinary properties; particularly in the areas of thermal stability
and flame retardancy.
The layered silicates enhance formation of char. This is achieved
because the aspect ratio of nano filler is particularly very high
(>1000). The nano composite structure enhances the barrier properties
of char as well as reinforces the char. Infact the multilayered
structure acts as an excellent insulator as well as barrier; slowing
the escape of volatile products arising from combustion of polymer.
Both these actions reduce the amount of volatile products available
for burning.
These nano composites provide excellent flame retardancy at fairly
low levels. In order to achieve good flame retardancy of non halogen
cables a very high level, Aluminium Trihydrate (ATH) is required.
At this level of ATH, the mechanical properties of cables are apprecially
dropped. The addition of nanoclay at 5% level could help in reducing
the level of ATH almost by 30%, thereby reducing the total filler
dosage by 25%. The mechanical properties of the modified system
certainly improve significantly without adversely affecting the
flame retardancy of the cable system. The processing of the modified
system also improves because of overall reduction of fillers. Combining
nanoclay with ATH therefore offers a better option for flame retardant
cables.
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