1. School of Chemical Engineering, National Technical University of Athens, 9 Heroon Polytechniou Street, Zografou Campus, 15780 Athens, Greece and CNRS, Laboratoire des Composites ThermoStructuraux, CNRS—CEA—Snecma Propulsion Solide—Université Bordeaux 1, 3 allée de La Boëtie, 33600 Pessac, France