Javaid Athar

Graphene-iron oxide nanocomposite (GINC): an efficient catalyst for ammonium perchlorate (AP) decomposition and burn rate enhancer for AP based composite propellant

A facile and ecofriendly method for the synthesis of nano-sized iron oxide (Fe2O3) decorated graphene (GINC) hybrid by ultrasonication via microwave irradiation has been developed. During this process, nano-sized Fe2O3 particles with a size of approximately 20–30 nm were uniformly decorated over a graphene sheet. The nanohybrid was characterized by XRD, HRTEM, Raman spectroscopy and Raman mapping. To study the enhancement of catalytic activity of iron oxide by preparing GINC, several AP based compositions containing 1–5 weight% GINC were made and characterized through simultaneous thermal analysis (STA). Along with this, formulations with other catalysts with 1–5 weight% concentrations were also prepared and evaluated. Experimental results showed that GINC with 5 weight% concentration was considerably more effective as compared to other compositions. To further extend this application as a burn rate enhancer in composite propellants, several formulations of composite propellants containing 1 part of different burn rate enhancers, such as Fe2O3, nano-sized Fe2O3 and GINC, were prepared and evaluated using theoretical prediction, viscosity, ballistic properties, sensitivity parameter and thermophysical properties. To quantify the burn rate enhancement in the presence of GINC, burn rate measurement, STA, DSC and activation energy calculation were performed. The results show that the burn rate of propellant increases from micron-sized Fe2O3 (30% increases) to nano-sized Fe2O3 (37% increase). In the presence of GINC, a significant increase (52%) in burn rate is achieved. In GINC, effective iron content is about 50% as compared to nano- and micron-sized Fe2O3. Hence, GINC was found to be an excellent burn rate modifier for an advanced AP based propellant system.

Synthesis, Characterization, and Rheological Evaluation of 1,3-Diazido-2-ethyl-2-nitropropane as an Energetic Plasticizer

An energetic plasticizer, 1,3-diazido-2-ethyl-2-nitropropane (DAENP), was synthesized and characterized in good yield and high purity. DAENP is synthesized in three steps: 1) 1-nitropropane is condensed with formaldehyde to yield 2-ethyl-2-nitro-1,3-propane diol; 2) 2-ethyl-2-nitro-1,3-propane diol on tosylation gave 2-ethyl-2-nitro-1,3-bis(p-toluene sulfonyl) propyl ester; 3) azidation of the tosylated compound gives DAENP. The product was characterized by elemental analysis, Fourier transform infrared (FTIR) spectroscopy and 1H-NMR and purity was tested by high-performance liquid chromatography (HPLC). Thermal studies revealed that DAENP is thermally stable up to 196°C, has high energy output of the order 2,056 J/g, and a very low glass transition temperature (−96.76°C). DAENP is compatible with energetic binders like glycidyl azide polymer (GAP), 3,3-bis (azido methyl)oxetane–tetra hydroxyl furan (BAMO-THF) copolymer, and poly-3-nitrato methyl-3-methyl oxtetane (poly NIMMO or PLN). Rheological and thermal data showed that it can be used successfully with these binders.

Probing the compatibility of energetic binder poly-glycidyl nitrate with energetic plasticizers: thermal, rheological and DFT studies

The essential idea of developing energetic binders and plasticizers is to enhance the thermal stability and energy content, improve the oxygen balance and burning behaviour of moulds, reduce the glass transition temperature and improve other mechanical properties of propellant and explosives formulations. The compatibility of energetic binder poly-glycidyl nitrate (PGN) with some energetic plasticizers of solid propellants was studied using differential scanning calorimetry (DSC), rheology and DFT methods in relation to the effect of the addition of five different energetic plasticizers, i.e. bis(2,2-dinitro propyl) acetal (BDNPA), dinitro-diaza-alkanes (DNDA-57), 1,2,4-butanetriol trinitrate (BTTN), N-N-butyl-N′(2-nitroxy-ethyl) nitramine (BuNENA) and diethyleneglycol dinitrate (DEGDN), on the rheological and thermal properties of the energetic binder PGN. The results obtained for the mixture of plasticizer and binder with respect to decomposition temperature (Tmax) and the format of the peak are compared with the results obtained for the pure binder, indicating the compatibility of these plasticizers with PGN. The glass transition temperatures (Tg) of all these mixes were determined by low-temperature DSC, which showed a lowering of Tg with a single peak. Rheological evaluation revealed that the viscosity of the binder is sufficiently lowered with an increase in flow behaviour on addition of 20% (w/w) plasticizer. The addition of 20% DEGDN has the maximum effect on the lowering of the viscosity of PGN. Quantum chemically derived molecular electrostatic potential (MESP) shows the possible sites of interaction of plasticizers and binder with the estimated lowest Vmin values and their magnitudes provide an insight into their mutual interactions. The relative trend in interaction energies between plasticizer and binder, PGN, is well correlated with a corresponding trend in the ability of plasticizers towards reducing the viscosity of PGN. The information gathered in the present study would in general be valuable with respect to designing new plasticizers.

Calculation of enthalpies of formation and band gaps of polymeric binders

Enthalpies of formation and band gaps of polymeric binders are important parameters to consider when designing compositions of explosives and propellants. We have used computational methods to determine enthalpies of formation and band gaps of polymeric binders. Initially, we computed the enthalpy of formation of the known non-energetic binder hydroxy terminated polybutadiene (HTPB), and the value obtained is close to that of its experimentally determined enthalpy of formation. The applied computational methodology has also been validated by the calculation of enthalpies of formation for the known energetic binder glycidyl azide polymer GAP. Furthermore, enthalpy of formation of azido HTPB (AHTPB) was calculated, which indicates that the addition of the azido group helps produce an energetic, insensitive and compatible polymeric binder. In this study, enthalpy of formation of the polymer was determined by extrapolating the results of the calculations carried out on monomers and oligomers, whereas periodic boundary condition (PBC) computations were carried out on the dimers to obtain band gap values of polymers. Highly positive enthalpies of formation of oligomers of AHTPB compared to those of HTPB and GAP suggests that AHTPB can be a potentially energetic binder in explosive compositions. Analysis of periodic boundary condition (PBC) – frontier molecular orbital band gap studies suggests that stabilities or insensitivities of these polymeric binders are in the order: HTPB > GAP > AHTPB. A superior curable nature of AHTPB over HTPB is indicated by the calculation of interaction energies. These results are vital in the quest for molecular-based predictions of polymer properties in general, but they are in particular encouraging for the study of polymers with monomers of relatively large molecular weight.

Synthesis of bis(propargyl) aromatic esters and ethers: a potential replacement for isocyanate based curators

This study reports the synthesis and characterization of a novel class of non-isocyanate curing agents based on bis-propargyl aromatic esters 2a–e and ethers 4a–c. A total of eight non-isocyanate curators were prepared from the reaction of respective dicarboxy or dihydroxybenzene with propargyl bromide in the presence of potassium carbonate with good yields. The structure and purity of the synthesized compounds and the corresponding intermediates were confirmed by spectral (IR and NMR), thermal (DSC) and chromatographic techniques (HPLC & GC-MS). Furthermore, kinetics of the curing reaction between glycidyl azide polymer (GAP) and the synthesized alkynes (4b, 4c) were studied using time-resolved FT-IR spectroscopy as a function of time at 303, 323 and 333 K. It was found that the curing reaction was faster when the temperature was increased. Kinetic parameters of the curing reaction, such as the reaction order and activation energy, were calculated for the GAP–4a and GAP–4c systems. All the curing reactions followed first order kinetics and the corresponding activation energy of the curing reaction for the systems was found to be 15.56 and 13.22 kcal mol−1. For comparison, curing studies were performed for GAP with a conventional curator Desmodur N-100. GAP cured with non-isocyanate curators offered good mechanical properties compared to GAP cured with isocyanate (N-100). The advantage of these new curing systems is that they do not require catalyst and there is no need for specific environmental conditions. Based on these studies, 1,4-bis(2-propynyloxy)benzene (4b) has the most potential as a non-isocyanate curator for azide polymeric binders.