Nanoclay modified silica phenolic composites: mechanical properties and thermal response under simulated atmospheric re-entry conditions

Ablative nanocomposites based on nanoclay-dispersed addition curable propargylated phenolic novolac (ACPR) resin, reinforced with chopped silica fiber, were investigated for their thermal response behavior under simulated heat flux conditions corresponding to typical atmospheric re-entry conditions. Organically modified nanoclay (Cloisite 30B) was incorporated to different extents (1-10%) in the ACPR resin matrix containing silica fiber to form the composite. The composites displayed optimum mechanical properties at around 3wt% of nanoclay loading. The resultant composites were evaluated for their ablative characteristics as well as mechanical, thermal and thermo-physical properties. The reinforcing effect of nanoclay was established and correlated to the composition. The mechanical properties of the composites and its pyrolysed product improved at moderate nanoclay incorporation. Plasma arc jet studies revealed that front wall temperature is lowered by 20 degrees C and that at backwall by 10-13 degrees C for the 3wt% nanoclay-incorporated composites due to impedance by nanoclay for the heat conduction. Nanoclay diminished the coefficient of thermal expansion by almost 50% and also reduced the flammability of the composites. The trend in mechanical properties was correlated to the microstructural morphology of the composites. The nanomodification conferred better strength to the pyrolysed composites. Copyright (c) 2014 John Wiley & Sons, Ltd.