A Novel Method for Determination of the Concentration of Active Antioxidant in Stored HTPB-Based Composite Propellants

Abstract

The aim of this work has been to ®nd a simple, non-destructive method for determination of the concentration of active antioxidant in HTPByAP composite propellants. Differential Scanning Calorimetry (DSC) was used for determination of Oxidation Induction Time (isothermal OIT) and Oxidation Induction Temperature (dynamic OIT) at different antioxidant concentrations. The ammonium perchlorate content in the propellants were 80% by weight. The antioxidant was BKF with concentration up to 2.5% by weight of the polymer. Iron oxide was added to some of the samples, and to one of these samples aluminium was also added.The results show that the dynamic OIT depends on the active antioxidant concentration, and useful calibration curves were obtained for the propellants with and without iron oxide. Concentrations of active BKF up to 1.5% by weight of polymer could be determined using this method. Aluminium content in the propellant had no effect on the results. The results also indicate that the isothermal OIT cannot be used for determination of the active antioxidant concentration.

Chemical Bond Between Stabilizers and HTPB Binders in Propellants

“…For DTBHQ he also reported (21) an ef®cient protection against oxidation but, as we now know at a NCO=OH ratio of 0.85, DTBHQ is not attached to the binder. As shown in literature (15) , it is obvious that the OH functions of the phenolic antioxidant (DTBHQ or AO-2246) have to be free in the binder to participate to the stabilizing effect. Thus, the DTBHQ attached to the network will never be very effective.…”

“…For composite motors, we found in some cases that the stabilizers (antioxidants) were not extractable by any common organic solvents. In these situations the determination of antioxidant concentration in the rocket motor would need other innovative methods as recently suggested by Sande Ân et al (15) . Nevertheless, it is important to understand the chemical phenomenon leading to the problem of the nonsoluble antioxidants.…”

NMR Analysis of Thermally‐Oxidized Hydroxyl‐Terminated Polybutadiene (HTPB)

“…Notably, 2,2‐methylene‐bis‐(4‐methyl‐6‐tert‐butylphenol) (AO2246) stands out as the preferred choice owing to its exceptional antioxidant properties [11] . This preference stems from the ability of AO2246 to act as a primary H‐atom donor, effectively quenching free radicals and hindering the propagation of the degradation chain reaction [12] . The efficacy of AO2246 as an antioxidant in HTPB is not solely dependent on its free radical scavenging ability.…”

“…[11] This preference stems from the ability of AO2246 to act as a primary H-atom donor, effectively quenching free radicals and hindering the propagation of the degradation chain reaction. [12] The efficacy of AO2246 as an antioxidant in HTPB is not solely dependent on its free radical scavenging ability. Temperature, the concentration of AO2246 itself, and the reactivity of peroxy radicals (POO°) all exert critical influences on the overall effectiveness of this additive.…”

“…AO possess the ability to scavenge free radicals before their rapid proliferation, they convert peroxides and hydroperoxides into alcohols and stabilize the polymer binder againt these oxidative reactions [11] . The most common AO, 2,2‐methylene‐bis‐(4‐methyl‐6‐tert‐butylphenol) (AO2246), is highly effective and thus extensively used for HTPB [12,13] . However, it has been established that AO evaporates or depletes with prolonged ageing processes.…”