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2 Central European Journal of Energetic Materials

2 2018

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Optimization of Curing Agents for Linear Difunctional Glycidyl Azide Polymer (GAP), with and without Isocyanate, for Binder Applications

Agawane N. T., Soman R. R., Wagh R. M., Athar J., Talawar M.

Central European Journal of Energetic Materials

2018

Vol. 15, no. 1

206--222

Glycidyl Azide Polymer (GAP) is one of the most potential energetic binders for rocket propellants and gas generator compositions. In the present paper GAP of molecular weight (Mn) ~2000 was cured with a mixture of di- and tri-isocyanates without a cross linker. The curing profile and time of curing was recorded using a rheometer. The minimum curing time was observed for samples cured with Desmodour N-100 alone, whereas the maximum curing time was observed for samples cured with a mixture of Desmodour N-100 and Isophorone Diisocyanate (IPDI) (1:1 w/w). It was observed that all of the samples cured well and were void or bubble free. The mechanical properties data showed that the tensile strength (TS) of GAP cured with Desmodour N-100 alone was 1.19 kgf/cm2, which is a minimum, while the maximum TS (3.66 kgf/cm2) was achieved with a mixture of N-100 and 4,4’methylenebis(phenylisocynate) (MDI). The percent elongation for a sample cured with Desmodour N-100 was 160, and was reduced to 64.27 when a mixture of MDI and N-100 was used. In order to study the curing of GAP without an isocyanate, GAP diol was cured with hexanediol di-acrylate. GAP was also cured with an alkyne-based curing agent i.e. bis-propargyl succinate (BPS), which showed improved curing. Comparative thermal studies of GAP cured with isocyanate and acrylate was carried out. Differential Scanning Calorimetry (DSC) and Simultaneous Thermal Analysis (STA) curves for all of the cured samples were recorded in order to study and compare the thermal decomposition behaviour of the cured GAP. Isocyanate cured GAP exhibited a single stage decomposition, with larger heat output. Acrylate cured GAP exhibited a two stage decomposition. Finally, a mixture of IPDI and Desmodour N-100 was selected for curing of GAP. Accordingly, curing was carried out and was tested in a small ballistic evaluation motor (BEM) to observe the combustion behaviour and burn rate. From the pressure-time profile it was found that this composition gave smooth burning with a pressure of ~3 kg/sec2 for 7 seconds of burn.

Influence of Guanylurea Dinitramide (GUDN) on the Thermal Behaviour, Sensitivity and Ballistic Properties of the B-KNO3-PEC Ignition System

Badgujar D. M., Phatak S., Wagh R. M., Bhingarakar V., Talawar M. B., Kakade S. D.

Central European Journal of Energetic Materials

2018

Vol. 15, no. 2

315--326

Boron and potassium nitrate are the key components for the ignition system of the igniter composition for rocket propellants. Boron-potassium nitrate-ethyl cellulose (B:KNO3:PEC) in proportions of 30:70:10 is a well established igniter composition. The composition delivers a maximum pressure in the range 4.0-4.6 MPa in closed vessel firing at a loading density of 0.01 g/cm3. For the effective ignition of a large booster stage propellant (length more than 4 m), an enhancement in the maximum pressure, without affecting safety, is a prime requirement. The use of guanylurea dinitramide (GUDN) in an igniter composition has not been reported in the literature. Hence, the present study on the effect of GUDN on the combustion behaviour and sensitivity of the B/KNO3 composition (30/70) has been carried out. Several compositions containing different weight percents of GUDN were prepared. Their thermal behaviour was determined by thermal analysis DSC-TGA. Their sensitivities to external stimuli such as impact, friction and spark were evaluated. The results of closed vessel firings indicated that GUDN-based igniter compositions produced higher peak pressures (up to 4.5 MPa to 5.8 MPa), with invariably lower burning times, compared to the control composition. The REAL computer programme indicated an increase in the flame temperature of the composition from 2238 K to 2425 K on addition of GUDN. All of the compositions were insensitive towards friction up to 36 kg, and towards spark up to 5 J energy.