Variation of Methods in Small‐Scale Safety and Thermal Testing of Improvised Explosives

One of the first steps in establishing safe handling procedures for explosives is small‐scale safety and thermal (SSST) testing. To better understand the response of homemade or improvised explosives (HMEs) to SSST testing, 16 HME materials were compared to three standard military explosives in a proficiency‐type round robin study among five laboratories, two U.S. Department of Defense and three U.S. Department of Energy, sponsored by the Department of Homeland Security, Science & Technology Directorate, Explosives Division. The testing included impact, friction, electrostatic discharge (ESD) and thermal. The testing matrix was designed to address problems encountered with improvised materials: powder mixtures, liquid suspensions, partially wetted solids, immiscible liquids, and reactive materials. All testing materials and/or precursors came from the same batch distributed to each of the participants and were handled, pretreated, and mixed by standardized procedures. For this proficiency test, the participants had similar equipment, usually differing by vintage. This allowed for a direct comparison of the results from each participant to the average of the results from all the participants. Some general trends observed for each series of tests were: (1) Drop hammer – LLNL usually found the materials less sensitive than the average with materials that have high sensitivity to impact and LANL usually found the materials less sensitive than the average with materials that have high sensitivity to impact; (2) friction – LLNL found the materials less sensitive than the average; (3) and ESD – IHD usually found the materials less sensitive than the average. In this report, the proficiency test data from all the participants is compared and contrasted for impact, selected friction, and ESD testing. Other friction and thermal data will be addressed elsewhere as well as the statistical analysis of several repeated measurements on the proficiency test standards.     

Characterisation of the Major Synthetic Products of the Reactions Between Butanone and Hydrogen Peroxide

The reactions between butanone and hydrogen peroxide, both catalysed and un‐catalysed, were investigated and spectral and sensitiveness data reported. The major product of the un‐catalysed reaction, 2‐hydroxy,2‐hydroperoxybutane, displayed a Figure of Insensitiveness (F of I) of 10, Temperature of Ignition (T of I) of 132 °C, and initiated when 128 N of frictional force or an electrostatic discharge (ESD) of 4.5 J was applied. Differential scanning calorimetric analyses revealed an onset of decomposition at 128 °C, peak maximum of 140 °C, and decomposition energy of 203 J g⁻¹. The major product of the cooled (5 °C) acid catalysed reaction between butanone and hydrogen peroxide, 2,2′‐dihydroperoxy‐2,2′‐dibutyl peroxide, displayed a F of I of<10, T of I of 110 °C and initiated upon application of 5 N of friction or a 0.45 J ESD. Calorimetry showed a melt at 38.3 °C, an onset of exothermic decomposition at 127 °C and the evolution of 1292 J g⁻¹. The major product of the raised temperature (20 °C) acid catalysed synthesis, 1,4,7‐trimethyl‐1,4,7‐triethyl‐1,4,7‐cyclononatriperoxane, displayed F of I of<10 and initiated upon application of 5 N of friction or a 0.45 J ESD. Calorimetry revealed an onset to melting at 28.9 °C, an onset to thermal decomposition at 128 °C, and decomposition energy of 1438 J g⁻¹.     

Optical characterization of porous silicon monolayers decorated with hydrogel microspheres

The optical response of porous silicon (pSi) films, covered with a quasi-hexagonal array of hydrogel microspheres, to immersion in ethanol/water mixtures was investigated. For this study, pSi monolayers were fabricated by electrochemical etching, stabilized by thermal oxidation, and decorated with hydrogel microspheres using spin coating. Reflectance spectra of pSi samples with and without deposited hydrogel microspheres were taken at normal incidence. The employed hydrogel microspheres, composed of poly-N-isopropylacrylamide (polyNIPAM), are stimuli-responsive and change their size as well as their refractive index upon exposure to alcohol/water mixtures. Hence, distinct differences in the interference pattern of bare pSi films and pSi layers covered with polyNIPAM spheres could be observed upon their immersion in the respective solutions using reflective interferometric Fourier transform spectroscopy (RIFTS). Here, the amount of reflected light (fast Fourier transform (FFT) amplitude), which corresponds to the refractive index contrast and light scattering at the pSi film interfaces, showed distinct differences for the two fabricated samples. Whereas the FFT amplitude of the bare porous silicon film followed the changes in the refractive index of the surrounding medium, the FFT amplitude of the pSi/polyNIPAM structure depended on the swelling/shrinking of the attached hydrogel spheres and exhibited a minimum in ethanol-water mixtures with 20 wt% ethanol. At this value, the polyNIPAM microgel is collapsed to its minimum size. In contrast, the effective optical thickness, which reflects the effective refractive index of the porous layer, was not influenced by the attached hydrogel spheres.

PACS

81.05.Rm; 81.16.Dn; 83.80Kn; 42.79.Pw     

Polyurethanes based on 2,2‐Dinitropropane‐1,3‐diol and 2,2‐bis(azidomethyl)propane‐1,3‐diol as potential energetic binders

On the base of 2,2‐bis(azidomethyl)propane‐1,3‐diol (BAMP) and 2,2‐dinitropropane‐1,3‐diol (DNPD) four different polyurethanes were synthesized in a polyaddition reaction using hexamethylene diisocyanate (HMDI) and diisocyanato ethane (DIE). The obtained prepolymers were mainly characterized using vibrational spectroscopy (IR) and elemental analysis. For determination of low and high temperature behavior, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used. Investigations concerning friction and impact sensitivities were carried out using a BAM drop hammer and friction tester. The energetic properties of the polymers were determined using bomb calorimetric measurements and calculated with the EXPLO5 V6.02 computer code. The obtained values were compared with the glycidyl azide polymer (GAP). The compounds turned out to be insensitive toward friction (>360 N) and less sensitive toward impact (40 J). The good physical stabilities, along with their sufficient thermal stability (170–210 °C) and moderate energetic properties renders these polymers into potential compounds for applications as binders in energetic formul;ations. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43991.     

Compression‐molded,lubricant‐treated UHMWPE composites

Lubricant‐treated ultra high molecular weight polyethylene (UHMWPE) composites were prepared by compression molding. Composites were made from mixtures containing up to 5.0 wt % of lubricant. Two solid lubricants, molybdenum disulfide (MoS₂), and carbon black (CB), and one liquid lubricant, perfluoropolyether (PFPE), were used in the study. UHMWPE and the lubricants formed 3D networks, where the lubricant was evenly spread over the UHMWPE particles. The amounts of MoS₂ and CB were determined by thermogravimetric analyses, and the amounts of PFPE by ATR‐IR spectroscopy. All the lubricant treated composites showed better friction properties than pure UHMWPE. The addition of PFPE to UHMWPE improved the hydrophobicity of the surface, whereas the addition of solid lubricant had little effect. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1762–1768, 2007     

Superlow friction and diffusion behaviors of a steel-related system in the presence of nano lubricant additive in PFPE oil

The lubrication performances of diamond like carbon (DLC) films were investigated by a ball-on-disc tribometer under perfluoropolyether (PFPE) oil lubrications. The influence of nano lubricant additives in PFPE oil on the tribological properties of DLC films was evaluated. The experimental results show that the solid-liquid synergy lubrication is beneficial to improve the tribological properties of the steel-related friction system and the tribological properties of the friction pair are significantly influenced by lubrication modes and the types and contents of nano lubricant additives under PFPE oil lubrication. The friction system exhibits super low friction behaviors under PFPE oil with nano MoS₂ lubricant additive lubrication due to the excellent compatibility of nano MoS₂ additives with PFPE oil. Coefficient of friction (CoF) of the friction system is as super low as 0.02 under PFPE oil with 0.2?wt.% nano MoS₂ additive lubrication. Superlow friction mechanism is attributed to the pointlike contact of nano MoS₂ additive as soft phase and the excellent diffusion behaviors of nano MoS₂ additives in PFPE oil. The potential usefulness of nano MoS₂ particles as the lubricant additives in PFPE oil for the steel/DLC films has been demonstrated.     

Synthesis of ultraviolet‐curable modified polysiloxane and its surface properties

A novel ultraviolet (UV)‐curable monomer α,ω‐dichloropolysiloxane was synthesized by the telomerization of dichlorodimethylsilane and octamethylcyclotetrasiloxane (D₄). The products with very low peel strength (<0.332 N/cm) could be used as release agents in pressure‐sensitive adhesives. Moreover, the values of the dispersion component of surface energy (γ) from the films of UV‐curable prepolymers (26.40–33.75 mJ/m²) were determined and the effects of γ on the reduction of adhesion were investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2135–2139, 2002     

The tribological characteristics of phosphorylated 3‐aminopropyltriethoxysilane nanometer film

Thin films deposited on the phosphonate 3‐aminopropyltriethoxysilane (APTES) self‐assembled monolayer (SAM) were prepared on the hydroxylated silicon substrate by a self‐assembling process from specially formulated solution. Chemical compositions of the films and chemical state of the elements were detected by X‐ray photoelectron spectrometry. The thickness of the films was determined with an ellipsometer, whereas the morphologies and nanotribological properties of the samples were analyzed by means of atomic force microscopy. As the results, the target film was obtained and reaction may have taken place between the thin films and the silicon substrate. It was also found that the thin films showed the lowest friction and adhesion followed by APTES‐SAM and phosphorylated APTES‐SAM, whereas silicon substrate showed high friction and adhesion. Microscale scratch/wear studies clearly showed that thin films were much more scratch/wear resistant than the other samples. The superior friction reduction and scratch/wear resistance of thin films may be attributed to low work of adhesion of nonpolar terminal groups and the strong bonding strength between the films and the substrate. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

5‐Amino‐3,4‐dinitropyrazole as a Promising Energetic Material

The nitrogen‐rich energetic compound 5‐amino‐3,4‐dinitropyrazole (5‐ADP) was investigated using complementary experimental techniques. X‐ray diffraction indicates the strong intermolecular hydrogen bonding in 5‐ADP crystals. Compound exhibits low impact sensitivity (23 J) and insensitivity to friction. The activation energy of thermolysis determined to be 230±5 kJ mol⁻¹ from DSC measurements. Accelerating rate calorimetry indicates the lower thermal stability (173 °C) of 5‐ADP than that of RDX, which is probably the main concern about using this compound. 5‐ADP also exhibits good compatibility with common energetic materials (viz. TNT, RDX, ammonium perchlorate), including an active binder. The burning rate of 5‐ADP monopropellant is higher than that of benchmark HMX, while the pressure exponent 0.51±0.04 is surprisingly low. Addition of ammonium perchlorate does not affect the pressure exponent of 5‐ADP, while the burning rate increases. The 5‐amino‐3,4‐dinitropyrazole exhibits a notable combination of combustion performance, low sensitivity, and good compatibility, which renders it as a promising energetic material.     

Surface structure of conductive polypyrrole‐containing composites

The surface structures of polypyrrole/silicon crosslinked poly( styrene/butyl acrylate/hydroxyethyl acrylate) (PSBH) conductive composite films were investigated by X‐ray photoelectron spectroscopy and scanning electron microscopy. It was found that the conductive composite films were of a “sandwich” structure, and the surfaces greatly differ in chemical compositions and phase morphologies from the bulk. The Si and N contents exhibit opposite gradient change with the measured depth of the two surface layers in the composite films, namely, the decrease in Si content and the increase in N content with increase in the depth of the surface layers. However, the N^δ+/N ratios in polypyrrole decreased with the measured depth of the conductive composite film. It was also found that the conductive composite film based on silicon crosslinked matrix exhibits more environmental stable than that based on linear matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 95–101, 1999     

Development of polymer‐molding‐releasing metal mold surfaces with perfluorinated‐group‐containing polymer plating

The polymer‐molding‐releasing properties of metal molds were found to be related to the following factors: (1) interfacial chemical bonding between the surfaces of polymers and metal molds and (2) a friction force or friction coefficient between polar substances and/or low‐molecular‐weight components in the polymers and physical factors on mold surfaces. We theoretically and experimentally confirmed that metal molds with good polymer‐molding‐releasing properties had very small surface free energies. We also proved that the surface free energies in the resulting polymer moldings were lower than before shaping. The molding releasing properties improved with decreasing friction force and friction coefficient between the surface of polymers and metal molds and with decreasing surface free energy. To obtain metal molds with lower surface free energies, we developed a polymer plating method with perfluorinated‐group‐containing triazine dithiol. The Metal mold treated by polymer plating had lower critical surface tension (7.5 mJ/m²) than Teflon (18 mJ/m²), indicating that the surface consisted of CF₃ ? groups. The treated mold showed excellent durability in its releasing properties, which was better than that of the untreated mold. This technique was developed for the production of molds for the Fθ lens and the naturally bright focusing screen. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2549–2556, 2003     

Improvement of the water selectivity of ULTEM poly(ether imide) pervaporation films by an allylamine‐plasma‐polymerized layer

The wettability and surface energy of extruded ULTEM poly(ether imide) films strongly increased (the water contact angle varied from 75 to 38° and the surface energy varied from 45.3 to 59.5 mJ m^?2, respectively) with the deposition of an allylamine‐plasma‐polymerized layer and were characterized with X‐ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy according to the experimental parameters. Pervaporation tests for dehydrating the water/ethanol azeotropic mixture were performed at 40°C with nontreated and plasma‐treated ULTEM films for 15, 30, 60, and 120 min. No significant difference was noticed in the total flow (ca. 2.5 g/m² h) among the various films. However, for the 30‐min duration, a great increase in the water selectivity from 850 to 10,850 was measured, and it was related to the higher N/C ratio and the presence of amide groups on the surface. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2088–2096, 2005     

Explosives Based on Diaminourea

Diaminourea (DAU, 1 ) is synthesized by the reaction of dimethylcarbonate with hydrazine hydrate. DAU was protonated using nitric as well as perchloric acid yielding diaminouronium nitrate ( 2 ), diaminouronium dinitrate monohydrate ( 3 ) and diaminouronium perchlorate ( 4 ). The bis‐perchlorate salt could not be isolated due to its high hygroscopicity. Explosives 2 – 4 were fully characterized using X‐ray diffraction, NMR and vibrational spectroscopy, mass spectrometry and elemental analysis. The thermal properties were determined by differential scanning calorimetry (DSC). The sensitivities towards impact ( 2 : 9 J, 3 : >40 J, 4 : 2 J), friction ( 2 : 288 N, 3 : >360 N, 4 : 5 N) and electrical discharge ( 2 : 0.60 J, 3 : 0.50 J, 4 : 0.30 J) were investigated using Bundesanstalt für Materialforschung (BAM) methods and a small scale electrostatic discharge device. The detonation parameters of 2 and 3 were computed using the EXPLO5.04 code with the X‐ray densities as well as calculated (CBS‐4 M) energies of formation as input values.     

New fluoro‐modified thermoplastic polyurethanes

New fluoro‐modified thermoplastic polyurethanes containing perfluoropolyether (PFPE) blocks were synthesized by the reaction of a fluorinated macrodiol with a hydrogenated prepolymer based on poly(tetramethylene glycol) and 4,4′‐methylene‐bis‐phenylisocyanate, followed by subsequent chain extension with 1,4‐n‐butanediol. This multistep bulk process opened the way for a new family of polymeric materials whose tensile properties appear to be excellent and unchanged in comparison with the corresponding unmodified hydrogenated polymers. Dynamic mechanical analysis and differential scanning calorimetry revealed peculiar characteristics. These polymers showed an unusual multiphase structure in which not only the hard and the hydrogenated soft segments were self‐organized, but also a second soft phase, constituted by the PFPE segments, was present. Moreover, an easier hard‐phase segregation and self‐organization were observed, as was evidenced by the higher melting temperatures of the semicrystalline phase. This unique characteristic combined with a selective enrichment of PFPE segments to the surface, as indicated by the unusually low coefficient of friction data and superior chemical resistance. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2279–2294, 2003     

Synthesis and Characterization of 1‐Azido‐2‐Nitro‐2‐Azapropane and 1‐Nitrotetrazolato‐2‐Nitro‐2‐Azapropane

1‐Azido‐2‐nitro‐2‐azapropane ( 1 ) was synthesized in high yield from 1‐chloro‐2‐nitro‐2‐azapropane and sodium azide. 1‐Nitrotetrazolato‐2‐nitro‐2‐azapropane ( 2 ) was synthesized in high yield from 1‐chloro‐2‐nitro‐2‐azapropane and silver nitrotetrazolate. The highly energetic new compounds ( 1 and 2 ) were characterized using vibrational (IR and Raman) and multinuclear NMR spectroscopy (¹H, ¹³C, ¹⁴N), elemental analysis and low‐temperature single crystal X‐ray diffraction. 1‐Azido‐2‐nitro‐2‐azapropane ( 1 ) represents a covalently bound liquid energetic material which contains both a nitramine unit and an azide group in the molecule. 1‐Nitrotetrazolato‐2‐nitro‐2‐azapropane ( 2 ) is a covalently bound room‐temperature stable solid which contains a nitramine group and a nitrotetrazolate ring unit in the molecule. Compounds 1 and 2 are hydrolytically stable at ambient conditions. The impact sensitivity of compound 1 is very high (<1 J) whereas compound 2 is less sensitive (<6 J).     

Nanostructuring of Pure and Composite‐Based K6 Formulations with Low Sensitivities

The aim of this work was to desensitize keto‐RDX, respectively 2‐oxo‐1,3,5‐trinitro‐1,3,5‐triazacyclohexane (K6). For this purpose, two different methods were employed. First, nano‐K6 was produced by means of the Spray Flash Evaporation process. Particles with a median size of 74 nm were obtained. Sensitivity to friction and electrostatic discharge were reduced by downscaling particle size of K6. Second, due to their molecular analogy, the mixing of K6 and RDX was studied. For that reason, a physical nanometric mixture of K6 and RDX was produced by the same technique. In the latter case, an inter‐particular synergy between both compounds was noticed but without forming a cocrystal. The median particle size of the mixture is about 82 nm, and its sensitivity is between the ones of raw nano‐materials concerning friction and electrostatic discharge. Moreover, the mixture is less sensitive to impact (3.03 J) than nano‐K6 (<1.56 J) and nano‐RDX (threshold is 2.0 J).     

The effect of nonionic monomer HAM on properties of cationic surfactant‐free acrylic/alkyd hybrid emulsion

A series of cationic acrylic/alkyd resin (CPAAR) hybrid emulsions was successfully prepared through surfactant‐free emulsion polymerization, using methacryloxyethyltrimethyl ammonium chloride, methyl methacrylate, butyl acrylate and alkyd resin as reaction monomers. And nonionic N‐hydroxymethyl acrylamide (HAM) of different content was simultaneously incorporated into the CPAAR backbone. The structure of CPAAR copolymer was characterized by Fourier transform infared spectrometer, and then the effect of HAM content on properties of CPAAR emulsions was studied by particle size analyzer, transmission electron microscopy and rheometer. In addition, thermal properties, water absorption and contact angle of CPAAR latex films were also investigated. The results showed that the CPAAR emulsions prepared with 4.9 wt % HAM displayed smallest average particle size of 92.2 nm. As HAM content increased from 0 to 19.6 wt %, the initial viscosity of the emulsions increased from 22.48 to 53 mPa.s. At the same time, the emulsions transferred from Newtonian fluid to pseudoplastic fluid, and a transition from viscous liquid to elastic liquid was also detected. Meanwhile, the degradation temperature at 5% weight loss increased by 30.59°C. In addition, with increasing HAM content from 0 to 4.9 wt %, the water absorption and surface free energy of films increased by 4.42% and 5.02 mJ m^?2, respectively. However, the water absorption and surface free energy kept almost invariable with further increase in HAM content. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41406.     

Efficient Sensitivity Reducing and Hygroscopicity Preventing of Ultra‐Fine Ammonium Perchlorate for High Burning‐Rate Propellants

In this research, several inert materials, including some functional carbon materials, paraffin wax and the well‐known insensitive energetic material 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) were selected to reduce the undesirable high sensitivity and hygroscopicity of ultra‐fine ammonium perchlorate (UF‐AP) via polymer modified coating. Structure, sensitivity, thermal and hygroscopicity performances of the UF‐AP based composites were systematically studied by scanning electron microscopy, sensitivity tests, thermal experiments, contact angle, and hygroscopicity analysis. The results showed that both the impact and friction sensitivity of UF‐AP can be remarkably reduced, respectively, with only a small amount of 2 % (in mass) desensitization agents. Meanwhile, improved thermal decomposition was gained, and the hygroscopicity can also be reduced to a large extent. Propellants containing 10 % coated UF‐AP in mass were processed and tested, the burning rate reached 45.7 mm s⁻¹, 50 % higher compared with that of normal AP, with remarkably reduced impact sensitivity from 11.5 J to 29.6 J and friction sensitivity from 76 % to 28 %.     

Ibuprofen‐imprinted ultrathin poly[N‐(2‐hydroxypropyl) methacrylamide] films

Surface molecularly imprinted (MIP) poly[N‐(2‐hydroxypropyl) methacrylamide] [poly(HPMA)] films were prepared via interface‐mediated reversible addition‐fragmentation chain transfer (RAFT) polymerization from 4‐cyano‐4‐(propylsulfanylthiocarbonyl) sulfanyl pentanoic acid immobilized silicon substrate using N‐(2‐hydroxypropyl) methacrylamide as the functional monomer, N,N′‐methylene(bis)acrylamide as the crosslinking agent, and ibuprofen as the template molecule. The highly crosslinked MIP layer (～12 nm) was homogeneously grafted onto the silicon surface, which favors fast mass transfer and rapid binding kinetics. Binding capacities and adsorption parameters of the MIP poly(HPMA) films were calculated from the root‐mean‐square roughness data obtained by atomic force microscopy measurements using the Luzinov and Langmuir equations adopted for this study. The target binding assays demonstrate the desirable binding capacity and imprinting efficiency of the MIP poly(HPMA) films. Meanwhile, the computational optimization and energy calculations showed the formation of the self‐assembly of monomer and template molecule via noncovalent interactions that leads to a 1:4 molecular complex between ibuprofen and N‐(2‐hydroxypropyl) methacrylamide. This study provides a versatile approach to the quantitative determination of low‐molecular‐weight biomolecules on surface‐imprinted polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45707.     

Synthesis,characterization and surface properties of poly(lactic acid)–perfluoropolyether block copolymers

Laboratory‐scale synthesis and morphological and surface energy characterization of triblock A–B–A copolymers based on poly(lactic acid) (PLA; A segment) containing various block lengths of perfluoropolyether (PFPE; B segment) at 5 wt% PFPE content are reported. Incorporation of PFPE segments in PLA lowers significantly both the polar and dispersive components of total surface energy. Total surface energy is lowered from ca 35 to ca 17 mN m^?1 on copolymerization of PLA with 5 wt% PFPE. Thermal analysis data reveal that lower molecular weight PFPE segments lower significantly the glass transition, crystallization and melting temperatures of the PLA matrix. Although block length variation of the PFPE segment does not affect surface energies of copolymer films, smaller PFPE segments increase significantly the low‐temperature modulus as observed from dynamic mechanical analysis. Copyright © 2010 Society of Chemical Industry