carbon_fiber (04/04/2014)

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Thanks a lot...


Dug out some of my old books so here goes.

Both polymers are related to Nylon but have aromatic backbones making them more rigid and durable. Nomex has good thermal and chemical properties hence its use in fire resistant clothing.
It is produced in both fibre and sheet form usually a paper formed by calendering. Honeycomb core is produced from the paper bound in resin. When I worked in the Aerospace industry we used far more Nomex than Kevlar honeycomb core but that may of changed now, not sure. The Airbus was really the first of our aircraft to use composites on a large scale. The A380 is even more composites based I believe.
FLD will hopefully be along soon to correct my mistakes as I think he is a chemist.

Warren

FLD (04/04/2014)

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Both fibres are remarkably similar.  Nomex is meta poly amide, kevlar is para.  This substitution pattern around the aromatic ring causes the different properties, kevlar has a greater elastic modulus making it tough whereas nomex changes its conformation with heat (ie it absorbs heat and changes chemically) hence its greater heat resistance.  If I were to speculate I'd expect a kevlar fibre to be quite straight whereas a nomex fibre would have a twist like DNA when viewed with a microscope (this is just speculation) the extra heat would be absorbed making that spiral straight.  I'd expect the fibre would be OK after exposure to heat but any matrix its in might suffer. 

There's a whole load of variants of polyamides, Nomex and Kevlar are just the dupont trade names.