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Vieillissement des propergols à matrice polybutadiène : modélisation cinétique de l'oxydation

Abstract : The goal of this thesis was the elaboration of a kinetic model for the lifetime prediction of polybutadiene matrix propellants. In the storage conditions, their ageing is dominated by radical chain oxidation of polybutadiene sequences. First, the thermooxidation of the linear prepolymer was studied. The classical physico-chemical determinations were made : double bond consumption, carbonyl, hydroxyl, epoxide and hydroperoxide build-up, but also molar mass determination using rheometry and global mass evolution using gravimetry. All these experimental data were used to build a mechanistic scheme from which a kinetic scheme was derived and solved numerically. It is used in inverse approach to determine certain elementary rate constants. Then, shear modulus measurements from dynamic torsion testing and gravimetry were realized on isocyanate crosslinked samples. The rubber elasticity theory was used to establish the relationship between modulus and number of chain scission or crosslinking events induced by oxidation. The modelling results allowed establishing that intramolecular radical additions to double bonds are considerably more frequent than intermolecular ones. Despite that, intermolecular additions are responsible for predominant crosslinking. The results of this part, integrated to the kinetic model (in which reaction-diffusion coupling was taken into account) allowed to predict the distribution of local modulus values in the sample thickness. Then, structure mechanics allowed calculating the overall mechanical response of a bulk part undergoing oxidative ageing. Finally, we studied the stabilization mechanisms and kinetics in the case of hindered phenol stabilizers. The experimental study showed that the phenol is mostly consumed by a direct reaction with oxygen. Polybutadiene differs, in this aspect, from polyolefins where this reaction plays a significant role only at high oxygen pressures (few MPa). It explains why polydienic rubbers need higher stabilizer concentrations than polyolefin for stabilizing performances of the same order or lower.
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Submitted on : Thursday, October 25, 2007 - 8:00:00 AM
Last modification on : Thursday, January 11, 2018 - 6:20:30 AM
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  • HAL Id : pastel-00002967, version 1



Marie Coquillat. Vieillissement des propergols à matrice polybutadiène : modélisation cinétique de l'oxydation. Sciences de l'ingénieur [physics]. Arts et Métiers ParisTech, 2007. Français. ⟨NNT : 2007ENAM0021⟩. ⟨pastel-00002967⟩



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