Abstract
Nitrocellulose/glycidyl azide polymer/2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane nanocomposites, in which 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane nanoparticles uniformly embedded in nitrocellulose/glycidyl azide polymer matrix, were synthesized using a sol–gel supercritical method. The micron morphology, crystal phase, molecular structure, specific surface area, and surface elements were characterized using scanning electron microscopy, X-ray diffractometry, infrared, Brunauer–Emmett–Teller, and X-ray photoelectron spectroscopy analyses, respectively. Thermal analyses were performed, and the kinetic and thermodynamic parameters, such as activation energy, per-exponent factor, rate constant, activation heat, activation free energy, and activation entropy, were calculated. The decomposition products of the nitrocellulose/glycidyl azide polymer matrix and nitrocellulose/glycidyl azide polymer/2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane were also investigated by differential scanning calorimetry–infrared analysis. The result indicated that the main decomposition product of nitrocellulose/glycidyl azide polymer is carbon dioxide and the –N3 group in glycidyl azide polymer decomposed to nitrogen without being detected by infrared spectrometer; the main decomposition products of nitrocellulose/glycidyl azide polymer/2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane are carbon dioxide, nitrous oxide, and water, and few carbon monoxide, methane, and nitrogen oxide are also detected. Energy performances of nitrocellulose/glycidyl azide polymer matrix and nitrocellulose/glycidyl azide polymer/2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane nanocomposites were evaluated, that is, the parameters such as standard specific impulse, characteristic speed, combustion chamber temperature, average molecular weight of combustion products, and explosion heat were calculated. The results illustrated that as the weight percentage of nitrocellulose increases, the values of standard specific impulse, characteristic speed, average molecular weight of combustion products, combustion chamber temperature, and explosion heat increase. This was ascribed to that the oxygen balance of glycidyl azide polymer is substantially lower than that of nitrocellulose, which results in that the chemical energy of glycidyl azide polymer does not release sufficiently. Additionally, as weight percentage of glycidyl azide polymer increases, the impact and friction sensitivity of the composites decrease obviously. This means that glycidyl azide polymer is much more insensitive than nitrocellulose.
Highlights
The development of high-energy, low-sensitivity, low-cost explosives has long been the goal in the field of energetic materials
NC/glycidyl azide polymer (GAP)/CL-20 nanocomposites are prepared by sol–gel supercritical method, in which CL-20 nanoparticles are embedded in the NC/GAP matrix
IR spectrum shows that NC/GAP/CL-20 nanocomposite contains the molecular structure of NC, GAP, and CL-20
Summary
The development of high-energy, low-sensitivity, low-cost explosives has long been the goal in the field of energetic materials. It is because that the sol–gel method has many advantages, such as the convenience of low-temperature preparation, easy control over the stoichiometry and homogeneity of composites, and environment-friendly.[24,25] the existence of the gel matrix effectively prevents the agglomeration of nanoparticles, controls the particle size at nanometer level, reduces the sensitivity of energetic materials, and enhances the energy and combustion performances. As a new type of energetic polymer binder, GAP has the advantages of high nitrogen content, low mechanical sensitivity, good thermal stability, and very low Tg. GAP is an ideal alternative for NC to fabricate nanocomposites. Tertiary amines undergo complex reaction with –NCO radicals to form complexes with high reactivity This complex can quickly react with alcohol to produce carbamate and TED. Each lot was tested three times to obtain a mean value and a standard deviation
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