polybutadiene is the most common polymeric binder for composite solid propellants. This polymer suffers from oxidative degradation reactions on storing with deterioration in mechanical properties. Certain anti-oxidant materials can retard such reaction offering enhanced aging characteristics. In this study, two different primary antioxidants including phenol-based (AO2246) and amine-based (Flexzone 6H) were employed to stabilize polybutadiene polymer. Oxidation induction time (OIT) was evaluated using isothermal DSC. High OIT value means high resistance to oxidative degradation. The impact of anti-oxidant on mechanical properties was evaluated using shore A. Flexzone 6H significantly improved binder oxidative stability with an increase in OIT value by 20 folds with significant decrease in oxidation enthalpy. Flexzone 6H can offer enhanced resistance toward oxidative reactions; as it can act as efficient H atom donor to break down chain degradation reaction. Additionally, the three stabilized aromatic rings can capture free radicals. AO2246 enhanced the binder mechanical characteristics during aging at 80 0C using Shore A test. In the meantime, AO2246 could enhance the mechanical properties due to its integration into the polymeric matrix due to –OH functional groups. The two anti-oxidants demonstrated controversy effects. Whereas Flexzone 6H offered enhanced resistance to oxidative degradation; AO2246 offered enhanced mechanical properties.

The burning rate of rocket propellants is one of the most important parameters having a direct influence on itsballistic characteristics, so accurate measurement of thisparameter is an active approach for achieving optimum design of the solid rocket motors. In this paper, acoustic emission technique was applied for measuring the burning rate of a composite propellant and tests were performed on a wide Pressure range(5 -9 MPa) at ambient temperature.3 % as a deviation co-efficient of acousticemission technique wasinvestigated by comparingthe burning rate results obtained by this technique and those obtained byactual burning of a small-scale test motors at 6.894MPa (1000 PSI) and curves obtained from previously mentioned techniques were analyzed.This paper reports that theacoustic emission technique is a simple, effective, economic, time-saving, reliable technique with a high accuracy nearly equivalent to the active field resultsand it is suitable for quality control of large-scale productions of composite propellant..

The addition of some advanced additives to improve the mechanical properties of polyurethane (PU) polymeric matrix, which acts as a binder system in composite solid rocket propellants (CSRPs), is a target for the energetic materials researchers. In this investigation, 45 compositions of different crosslinked PU matrices were produced to demonstrate the effect of adding crosslinking mixture (CM) on the mechanical capabilities of polyurethane gum stock. The crosslinking mixture (CM) is composed of a triol crosslinker, trimethylolpropane (TMP), and a chain extender, 1,4-butanediol (BD). For comparison, traditional PU samples without crosslinking additives were formulated. As a prepolymer, HTPB was used with a curing agent (HMDI). The research was carried out with different ratios of TMP to BD, different curing ratios (NCO/OH=0.7, 0.9, and 1.1), and crosslinking mixture contents in the range of 0-5 wt.%. The mechanical characteristics of all the cured formulations were measured. It was demonstrated that changing the ratio of TMP to BD has a significant impact on the mechanical performance causing a wide range of elongation and strength qualities. Increasing the wt.% of triol crosslinker in the sample enhanced the tensile strength, whereas the strain has been decreased. The addition of diol chain extender increased the strain rate of the samples. The mechanical parameters were adjusted simply by employing the crosslinking ingredients to get exceptional mechanical characteristics at each NCO/OH curing ratios. Also it was concluded that PU samples of curing ratio (NCO/OH= 0.7-0.9) with TMP:BD (1:1) showed a promising results and could be used according to the requirements of the rocket system designers.

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Polyurethanes are prepared by extending a prepolymer chains made from a macro diol and a diisocyanate and its mechanical properties could be improved by using special additives to enhance the crosslinking process. In this study, 15 hydroxyl terminated polybutadiene (HTPB) based poly urethanes were prepared using 1, 6- hexamethylene diisocyanate (HMDI) and crosslinking mixture (CM) consists of trimethylol propane (TMP) as a triol crosslinker and butane diol (BD) as a chain extender. Five different crosslinking mixtures were used through the combination between TMP: BD = 1:0, 0:1, 1:1, 2:1 and 1:2. The research investigated the impact occurred on the mechanical behaviour of PU formulations prepared by adding certain cross-linking additives with various content from 0 % to 5 % and the curing ratio NCO/OH maintained constant at 0.7. The strength-strain relationships of all the finished samples were determined by using a LLOYD testing machine. The mechanical properties have been plotted vs. crosslinking mixture content and TMP: BD percentage which could be utilized to choose an appropriate network forming agent formulation for a particular grain technology and implementation. It was concluded that both TMP and BD have a major influence on the mechanical behaviour which allow obtaining a wide range of strength and elongation capabilities. The tensile strength increased by the excess of triol addition while the strain had a lowering effect which was compensated by the existence of diol extender. Tailoring the mechanical characteristics was easy to make by using a suitable proportions of TMP and BD to obtain outstanding mechanical properties for fixed NCO/OH, especially elastic capabilities, compared to polyurethanes formulated without any crosslinking additives.