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2 Central European Journal of Energetic Materials

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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.

Improvements in the Structural Integrity of Resin Based Combustible Cartridge Cases (CCC) at Elevated Temperatures

Dey A., Athar J., Gogoi S., Navle P. B., Sikder A. K.

Central European Journal of Energetic Materials

2015

Vol. 12, no. 1

117--127

An advanced, solvent-less resin based Combustible Cartridge Case (CCC), designed to resolve the inherent problems of shrinkage and limited mechanical strength associated with the gelatinisation of nitrocellulose, has already been developed. The felt-moulded components contain thermoplastic polyvinyl acetate (PVAc) resin as the binder and the enhanced mechanical strength is achieved by carrying out hot compaction of dry felts at an elevated temperature (105 ± 2 °C). Presently, resin based technology is adopted for tank gun ammunition and also for the developed modular CCCs, i.e. the Modular Combustible Case (MCC) for different types of artillery gun ammunition. However, during exhaustive trials conducted with the resin based CCCs in 120 mm tank gun ammunition at three temperatures, i.e. -10, 27 and 55 °C, severe geometrical deformation was noticed when the rounds were conditioned at 55 °C for 24 h., adversely affecting the loading of rounds into the gun chamber. This was attributed to the combined effects of softening of the resin at that temperature and the load of the projectile/ shell (14.4 kg) experienced by the CCC region during conditioning of the round in the horizontal mode. In order to resolve this problem of deformation, PVAc resin was required to be modified. The PVAc resin was modified to the form of a nanocomposite. PVAc nano composite was prepared by dispersing organically modified nano clay, i.e. Cloisite 30B, into the resin before making the CCCs. The nanocomposite of PVAc resin was characterized by FTIR, DMA, softening point measurement etc. The results showed a remarkable improvement in the glass transition temperature (Tg) and in the softening temperature of the modified PVAc resin. This modified PVAc resin was used to prepare CCCs. Furthermore, these CCCs were coated with hexamethylene diisocyanate (HMDI) on the inner and the outer surfaces. The isocyanate coating becomes crosslinked in the matrix, thereby improving the softening point as well as the mechanical properties of the CCCs. These modified CCCs were repeatedly tested at 55 and 60 °C for 24 h. After testing, it was found that no deformation had taken place and the assembled rounds were easily loaded into the gun chamber. The use of the PVAc nanocomposite in the preparation of resin based CCCs, followed by isocyanate coating, is an effective means of achieving the required improvement in structural integrity of the resin CCCs at elevated temperatures.