The dielectric constant (DC) is one of the key properties for detection of threat materials such as Improvised Explosive Devices (IEDs).In the present paper,the density functional theory (DFT) as well as ab-initio approaches are used to explore effective methods to predict dielectric constants of a series of 12 energetic materials (EMs) for which experimental data needed to experimentally determine the dielectric constant (refractive indices) are available.These include military grades energetic materials,nitro and peroxide compounds,and the widely used nitroglycerin.Ab-initio and DFT calculations are conducted.In order to calculate dielectric constant values of materials,potential DFT functional com-bined with basis sets are considered for testing.Accuracy of the calculations are compared to experi-mental data listed in the scientific literature,and time required for calculations are both evaluated and discussed.The best functional/basis set combinations among those tested are CAM-B3LYP and AUG-cc-pVDZm,which provide great results,with accuracy deviations below 5％ when calculated results are compared to experimental data.

In this work, a thiol-ene click reaction was used to graft polystyrene (PS) chains onto the surface of ethylene propylene diene monomer-based ground tire rubber (GTR). A thiol-terminated PS (11 kg mol−1) was selected, due to its commercial availability, to modify a postconsumer GTR. The resulting PS-grafted GTR (GTR- g-PS) particles were analyzed via Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) to detect surface changes on treated samples. An increase in aliphatic and aromatic carbon atoms was observed by FTIR and XPS, while grafted material was observed by SEM on the GTR surface, confirming that grafting took place. Then, composites were prepared from these GTR- g-PS particles and from PS by solution evaporation, at 50 wt%. A significant increase in tensile (20%) and storage moduli (from 80% at 65°C to 510% at 95°C) was observed by dynamic mechanical thermal analysis when compared to composites prepared with untreated GTR. In addition, GTR samples showed improved thermal resistance, as attested by the shift in degradation temperature for 10% mass loss (from 400°C for GTR to 450°C for GTR- g-PS). This increases the possible range of processing temperature and service temperature (applications) for introduction of GTR in other polymer matrices.

The present article reports the synthesis of soluble, propyl-substituted aromatic ring telechelic polycondensation blocks having molecular weights ranging from 1800 to 6500 g mol(-1) and polymolecularities of 1.3 to 1.7. Chain-growth polycondensation is performed, and the initiator is selected through reactivity studies, using F-19 nuclear magnetic resonance (NMR) measurements. Gel permeation chromatography, NMR spectroscopy, and matrix-assisted laser desorption/ionization time of flight mass spectrometry show that blocks are terminated by a methoxy group at one end and a fluorine atom at the other. Polymers are crystalline as synthesized, as shown by X-ray diffraction and differential scanning calorimetry, do not recrystallize once melted, and undergo solvent-induced crystallization. Crystalline peak positions and relative intensities are different from those observed for other poly(ether ketones). The difference in crystal form is proposed to stem from packing disruption related to the presence of propyl substituents. Thermogravimetry shows a good thermal resistance up to 450 degrees C.

Sensitive energetic materials are an issue for military and civilian applications. To prevent undesired explosions, sensitive energetic materials are embedded in a protective polymer, resulting in polymer-bonded explosives (PBX). The appropriate polymer will absorb part of the energy caused by stimuli such as shock, impact, friction, and heat, thus decreasing sensitivity. To investigate how an appropriate polymer absorbs energy, three PBX models were simulated using molecular dynamics. The COMPASS force field implemented in the Materials Studio software was used. Molecular dynamics simulations were performed for three RDX-based formulations in which a single polymer chain (HTPB, Estane, or EVA) was placed at the boundary surface of an RDX crystal. Simulations were carried out at high temperature (700 K) and high pressure (15 GPa). The resulting models were analyzed in terms of potential energy increase, energy distribution, and values of the different potential energy contributions for RDX/HTPB, RDX/Estane, and RDX/EVA. The polymer binders HTPB, Estane, and EVA in such PBX formulations absorbed between 24% and 31% of internal energy, respectively, thereby making less sensitive PBXs formulations than pure RDX. This percentage is proposed as an indicator key for experimentalists to determine the most efficient polymer that can be used, for a given explosive, to minimize munition sensitivity. A clear correlation is established between the calculated absorption of internal energy by polymers and experimental sensitivity values for the three formulations studied under extreme experimental conditions. This approach may be applied to other new formulations prior to testing them in laboratories.

Polyetherethersulfones with double bonds inserted along the main polymer chain are synthesized by polycondensation. The glass transition is modulated by increasing the size of aromatic etherethersulfone rigid blocks and decreasing the ratio of flexible allyl segments which contain a double bond. Resulting copolymers have a M-n of up to 60 000 g mol(-1), moderate polydispersity indices ( D or I-p) of 1.70 to 2.11, and are shown, by the presence of a single glass transition temperature in differential scanning calorimetry and by matrix-assisted laser desorption/ionization time-offlight ( MALDI-TOF) mass spectrometry, to be random. The glass transition of copolymers follows the Gordon-Taylor relationship. The thermal resistance of copolymers increases when decreasing the amount of the flexible segment and increasing the length of the rigid block. Chemical aging of films is investigated by immersion in bleach, which is commonly used to clean membranes. Films show high resistance to bleach, therefore making this approach relevant to membrane fabrication.

ABSTRACTAppraisal of the main rubber characterization techniques for styrene butadiene rubber (SBR) was performed on standard SBR samples as well as recycled ground tire rubber (GTR) from an industrial tire recycling facility, containing a blend of SBR and natural rubber. The aim of the work was to provide additional information relevant to quality control in the field of rubber recycling. Benchmark characterization of industrial samples by inductively coupled plasma optical emission spectrometry, atomic absorption spectrometry, solid‐state proton nuclear magnetic resonance, and elemental (CHNS) analysis are reported. X‐ray fluorescence spectrometry is shown to be rapid and quantitative for determining the zinc content in an industrial context. Thermogravimetric analysis, already used to determine carbon black and inorganic material content in rubbers and GTR, is recommended for determination of monomer weight ratios of SBR sources not containing other rubbers, but not for GTR. Differential scanning calorimetry (DSC) measurements of the glass‐transition show that changes in monomer ratio affect glass‐transition temperature values, and therefore, DSC can be used to detect changes in rubber composition from batch to batch. These results show that DSC and X‐ray fluorescence spectroscopy characterization techniques can be used for GTR and may lead to more thorough and rapid quality control procedures of these complex samples. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42692.

This paper proposes a novel approach to predict Hugoniot properties to characterize explosives materials. The originality and uniqueness of the approach consists in using together quantum mechanics, molecular dynamics calculations combined with known analytical methods. Indeed, four highly experimentally characterized energetic materials, cyclotrimethylenetrinitramine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), pentaerythritol tetranitrate (PETN) and triaminotrinitrobenzene (TATB), were investigated using quantum mechanics calculations and analytical methods. Using the pressure p and the ratio of specific densities v/v(0), the p-v Hugoniot diagrams were obtained. Detonation velocities D were determined and used to define the Raleigh line. For the four compounds, the ratio of specific heats gamma, a value between 2 and 3, was obtained. The gamma effect, in terms of sensitivity and importance, was demonstrated. At the Chapman-Jouguet (CJ) state, the parameters (shock, particle and detonation velocities, CJ pressure and density, ratio of specific heats, and Hugoniot diagrams) were predicted and all compared quite well with the published experimental data. Moreover, molecular dynamics simulations were carried out to obtain the compression p-v diagrams. Using the isothermal-isobaric ensemble (NPT), molecular dynamics simulations were conducted at various pressures ranging from 2 to 40 GPa with progressive increments of 2 GPa. The Rankine-Hugoniot jump conditions were considered, and the associated shock speed U-s and particle velocity u(p) for each pressure p and relative volumetric change v/v(0) were calculated. The simulations showed that a linear behavior exists between U-s and u(p) for the four explosives investigated.

Acyclic diene metathesis (ADMET) polymerisation and nucleophilic aromatic substitution polycondensation are used to synthesize alternating copolymers based on polyetherethersulfone (PEES) blocks. ADMET results in incorporation of trans-allyl groups with more than 94 to 98% selectivity. The resulting polymers have a Mw of up to 13600 g mol−1 and low dispersity (Đ = 1.1 to 1.4). Polycondensation, on the other hand, allows incorporation of either cis- or trans-allyl groups depending on the starting monomers. Molecular weights in the same range are obtained, but with much larger dispersity (up to 2.3), as expected. Characterization by differential scanning calorimetry and wide angle X-ray diffraction shows that incorporation of the cis group completely suppresses crystallization, whereas that of the trans group results in semi-crystalline polymers. Crystallinity is lost post-melting, but can be restored using appropriate solvent treatments. The crystal form changes with the length of the etherethersulfone (EES) group indicating that, when the repeat unit is small (containing a 4-ring etherethersulfone (EES) block), the allyl function is incorporated into the crystallographic repeat, whereas when the EES segment increases to eight rings, the allyl group is excluded from the crystal phase. Post-functionalization of the allyl group is demonstrated by using hydrogenation. The resulting polymer adopts a different crystal form for the 4-ring block, but the same crystal form for the 8-ring block, confirming the dependence on the block length for incorporation into the crystallographic repeat unit.

The properties of recycled styrene-butadiene rubber (SBR) powder with polystyrene (PS) have been studied as a function of compounding conditions in an internal batch mixer. In particular, the effect of temperature (160–220°C), rotor speed (30–120 rpm), homogenization time (3–9 min), components introduction order, surface treatment of SBR powder with a PS/tetrahydrofuran (THF) solution, and addition of a coupling agent (styrene-ethylene-butylene-styrene, SEBS) were studied. The compounds were then compression moulded and samples were prepared to measure their hardness, tensile properties (modulus, strength and elongation at break) and impact strength. Morphological analysis via scanning electronic microscopy (SEM) on selected samples was also performed to determine the interfacial state between the components. From all the results obtained, an optimisation procedure is proposed allowing the best compound to be determined as a function of final application.

ABSTRACT Investigations on ethylene–propylene–diene rubber (EPDM) with varying cross-link densities and carbon black contents, as well as commercial EPDM waste ground rubber (WGR), have been performed to improve characterization. The aim is to provide additional quality-control methods in the field of rubber recycling, as WGR is transformed and reused in the form of rubber mats mainly for playground, agricultural, sport, and automobile applications. Inductively coupled plasma optical emission spectrometry, atomic absorption spectrometry, and elemental (CHNS) analyses were used to determine the content of various chemical elements. Thermogravimetric analysis (TGA) was used to determine the amount of carbon black and inorganic material in the sample. Mass loss at 400 °C was related to cross-link density. TGA coupled with mass spectrometry showed that this mass loss corresponds to the loss of SO2 as cross-links are destroyed during heating. Melt point and glass transition temperatures determined by differential scanning calorimetry are mainly proportional to the ethylene/propylene weight ratio.

Gas–liquid membrane contactors are promising alternatives to conventional absorption technologies. However, in spite of their important advantages, such systems suffer from gradual wetting of porous membranes with liquid absorbents. This review focuses on the wetting phenomenon, which is the main concern for long-term operation of CO2 absorption in membrane contactors and has therefore an important impact on industrial applications. The impact of membrane wetting on mass transfer resistance and absorption efficiency, the effect of influencing parameters including absorbent (operational conditions, type and concentration) and membrane (hydrophobicity, pore size and porosity) properties on wetting phenomenon, as well as different methods to prevent membrane wetting, along with their advantages and drawbacks are discussed in detail.

The synthesis of four amphiphilic thieno[3,4-c]pyrrole-4,6-dione (TPD)-based alternating copolymers and their behavior at the air-water interface are reported. Homogeneous and stable monolayers of TPD-based copolymers were prepared. Brewster angle microscopy (BAM) was utilized to characterize the morphology and topography of these Langmuir films, UV-vis absorption spectroscopy as well as atomic force microscopy has revealed a regular transfer of some copolymers on glass substrates. It was possible to obtain homogeneous Langmuir-Blodgett films of up to 30 layers. Infrared dichroic measurements revealed an edge-on orientation. These Langmuir-Blodgett films made of conjugated polymers are therefore good candidates for organic field-effect transistors (OFETs).

Models of plastic-bonded explosives were created with the aim of studying the mechanical properties and sensitivity because the latter is one of the most important problems in relation to energetic materials. Previous models proposed in the literature used short plastic chains, which are appropriate for interaction modeling. In the present work, a model with a single, long chain was built, which is more appropriate for modeling mechanical properties. The representative hydroxyl-terminated polybutadiene (HTPB)/dioctyladipate (DOA)/cyclotrimethylenetrinitramine (RDX) system was used (81.4 w/w% of RDX and 18.6 w/w% of the amorphous HTPB/DOA phase, with a 60/40 ratio between the polymer and plasticizer). The HTPB chain was composed of 48 trans groups, 16 cis groups, and 16 vinyl groups. Due to the length of the chain, superposing the crystalline RDX cell [cleaved at the crystalline (2 0 0), (0 2 0), and (2 1 0) planes] to the amorphous HTPB/DOA cell introduced considerable void, and therefore resulted in low density-much more so than when using models with shorter chains. A compression/minimization iterative procedure was used to converge to the optimal density. Pair distributions were calculated to verify that the procedure did not lead to abnormal changes in the RDX crystal model. Comparable energies were obtained for models built with each cleavage plane, contrary to previous work with small molecules. Long chains have lower entropy and are less able to change conformations and maximize interactions with the crystal surface. Models with densities higher than the minimum value were shown to have energy stored in two main components; i.e., the internal energy was stored mainly in the bond and torsion contributions, whereas the external energy storage was performed by van der Waals interactions. These preliminary models show the potential for studying the sensitivity of explosives through molecular modeling.

Syntheses of symmetrical etherketone rigid blocks containing from four to ten aromatic rings were performed by a succession of Williamson synthesis steps, followed by deprotection by BBr3. Solubility decreased upon an increase in number of aromatic rings. Bis-(p-oxy-(p-hydroxyphenyl))benzophenone, a four-ring block, was soluble in the usual solvents (dichloromethane and chloroform), while 6 and 8-ring blocks were only soluble in dichloromethane to which trifluoroacetic acid was added. Rigid-flexible copolyetherketones with very short flexible segments were synthesized by reacting the 8-ring block with dibromo-terminated short alkane chains of 4 to 10 CH2 units in the presence of sodium hydride. Molar masses were estimated by MALDI-TOF, which was also used to verify the incorporation of the flexible spacers in a regular way. Copolymers are of moderate molecular weights (Mw values from 1240 to 2610 g mol−1), and of low polydispersity (from 1.02 to 1.17). Rigid blocks and rigid-flexible copolymers show high crystallinity and low solubility, in spite of the presence of the aliphatic spacers along the chain backbone, showing that incorporation of regularly spaced flexible segments does not decrease crystallization significantly. These flexible chains however decrease thermal stability of the copolymers.

Microporous and highly hydrophobic low‐density polyethylene (LDPE) hollow fiber membranes were successfully prepared via a solvent‐free method, combining melt‐extrusion, and salt‐leaching techniques. NaCl particles with particle size of 5–10 µm were mixed with LDPE pellets to produce a blend of 35, 40, 50, 60, 65 and 68 wt% of salt. A microporous structure was produced by leaching the salt particles from the hollow fiber matrix via immersion in water at 60°C. The fabricated membranes were then characterized in terms of morphology, porosity and pore size distribution, surface roughness, and hydrophobicity, as well as mechanical properties. The remarkable increase in the water contact angles from 98° for LDPE hollow fibers fabricated without the addition of salt (blank sample) to 130° for membranes fabricated with initial salt content of 68 wt% is mainly attributed to the rough surface structure, comprising a large number of micropapillas produced by removing the imbedded salt crystals. The increase in surface roughness and porosity of hollow fiber membranes with increasing initial salt content was confirmed by scanning electron microscope and atomic force microscopy. Copyright © 2013 John Wiley & Sons, Ltd.

The synthesis of telechelic poly(ether sulfone)s with methoxy end groups is reported. Molecular weights ranging from 1600 to 2800 g mol−1 and polydispersities of 1.1–1.2 are synthesized by chain‐growth condensation polymerization. The initiator is chosen by using semiempirical calculations and 19F NMR spectroscopy measurements. The polymers are characterized by NMR spectroscopy and matrix‐assisted laser desorption/ionization time of flight (MALDI‐TOF) mass spectrometry (MS), and are terminated by a methoxy group at one end and a fluorine at the other, and up to approximately 20% polymer of similar mass but slightly higher polydispersity, methoxy terminated at both ends, is present, along with less than 5% of polymer terminated at both ends by fluorine atoms. These do not need to be separated, and can be converted to methoxy‐ending telechelic blocks, yielding polyvalent, reactive rigid building blocks for copolymer synthesis. image

Crystal forms of polyethersulfones (PES) were investigated by using a model compound and a low molecular weight oligomer. These are amorphous as-synthesized, and can undergo solvent-induced crystallization under the appropriate conditions. The model compound, 4,4′-bis(p-methoxyphenoxy)diphenyl sulfone, yielded monocrystals, and its structure was solved using X-ray diffraction. Conformational disorder is present, two conformers cohabiting in 55:45 proportions. This model compound, combined to previous structural studies published in the literature, served as a basis for conformational studies of polyethersulfone. Low molecular weight polymers submitted to solvent-induced crystallization resulted in a PES crystal form different from that previously published in the literature, as shown by powder X-ray diffraction.

Uniaxial deformation of amorphous L-polylactic acid films was performed at two different temperatures at which thermal degradation was minimal, 70 degrees C or Tg + 10 and 90 degrees C or Tg + 30. Samples were annealed postdeformation for long times (either 15 or 45 min) to approach equilibrium conditions. Samples deformed and annealed at 70 degrees C showed low crystallinity and poor crystalline order or crystal size, as determined by wide-angle X-ray diffraction. At 90 degrees C, high crystallinity and order parameters were observed. In addition, once the oriented chains had crystallized at this temperature, nonoriented chains also underwent crystallization, and a small fraction of nonordered crystal phase was therefore observed after long annealing times. These observations are explained on the basis of different morphologies in samples drawn at the two temperatures. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Soluble organic nanorods were prepared from phenylacetylene macrocycles using the topochemical polymerization of butadiyne moieties placed both inside and outside the macrocycles' skeletons. Macrocycles containing amide groups were self-assembled in a columnar fashion through the formation of an organogel in ethyl acetate. Upon irradiation with UV light, the Raman signals associated with butadiyne units completely vanished, indicating the creation of covalently linked nanorods.

The gradual deterioration in the morphological and chemical stability of membranes in membrane contactors can extensively influence the membrane wettability, leading to reduction of CO2 absorption efficiency. In the present work, morphological, chemical and thermal stability of microporous low density polyethylene (LDPE) hollow fiber membranes, intended to be used in membrane contactors, was studied in contact with primary amine (monoethanolamine, MEA) and sterically hindered amine (2-amino-2-hydroxymethyl-1,3-propanediol, AHPD) solutions. The effect on membrane stabilization of a diamine (piperazine, PZ) having the operational advantages of fast CO2 absorption rate and capacity was also investigated.The surface properties of neat (before contact) and used (after contact with amine solutions) membranes were analyzed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and contact angle measurements. For membranes immersed in amine solutions of commonly used concentrations (30 wt.% MEA and 11 wt.% AHPD), the results show morphological degradation of membranes, caused by the intrusion of the solution into the pores, as well as chemical degradation caused by the LDPE auto-oxidation. However, a less significant effect was found by the addition of PZ. A two-step mechanism was proposed to explain the stabilizing effect of PZ. PZ containing amine solutions are suggested as strong candidates for CO2 absorption in membrane contactors due to their efficient dual-function properties (high CO2 absorption efficiency and polyolefin membrane stabilization). (C) 2012 Elsevier B.V. All rights reserved.