In‐Situ Tensile Testing of Propellants in SEM: Influence of Temperature

A tensile module system placed within a Scanning Electron Microscope (SEM) was utilized to conduct in‐situ tensile testing of propellant samples. The tensile module system allows for real‐time in‐situ SEM analysis of the samples to determine the failure mechanism of the propellant material under tensile force. The focus of this study was to vary the experimental parameters of the tensile module system and analyze how they affect the failure mechanism of the samples. The experimental parameters varied included strain rate and sample temperature (−54, +25 and +40 °C). Stress‐strain diagrams were recorded during the in‐situ tensile tests, and these results were coupled with the in‐situ images and videos of the samples captured with SEM analysis. The experiments conducted at −54 °C showed a different failure behavior of the propellant sample due to its rigidity at this low temperature, while experiments conducted at +25 and +40 °C displayed a similar failure mechanism. For future testing using this tensile tester, special attention should be given to improved temperature control of the specimen, especially at low temperatures.     

In–situ Characterization and Cure Kinetics in NEPE Propellant/ HTPB Liner Interface by Microscopic FT‐IR

The content distribution of chemical groups and the kinetics of curing process in the micro‐region interfaces of nitrate ester plasticized polyether (NEPE) based propellant/hydroxyl‐terminated polybutadiene (HTPB) based liner were studied by in‐situ diffuse reflection FT‐IR spectroscopy. During the curing process, the content of –NCO groups showed little increase in the liner region toward the interface. It rises quickly through the interface layer and is then stable in the region of the propellant layer, while the content of –NH groups gradually increases from liner to propellant. In the micro‐region between liner and propellant, the –C=O decreases rapidly through interface and then has a slight increase in the propellant region. Migration of nitrate esters appears at the interface of the NEPE propellant/liner at early period of curing, and –O–NO₂ decreases from propellant to liner in the bonding interface micro‐region. A study of curing kinetics indicates that the second‐order reaction model can describe the curing reaction in the bonding interface at the early stage of curing process. The order of apparent curing reaction rate constant (k ) of liner (L point), intermediate point (I point) and propellant (P point) in the interface micron‐region is k L > k I > k P at the same curing temperature. The apparent reaction activation energy (E _a) at L, I, and P points are 39.96, 81.49, and 62.51 kJ mol^–1, respectively, based on the Arrhenius equation.     

Effect of Bonding Agent on the Mechanical Properties of GAP High‐Energy Propellant

Three kinds of bonding agent were chosen to improve the mechanical properties of GAP high‐energy composite propellant based on GAP, BuNENA, HMX, AP, and Al. These bonding agents are N,N ′‐bis(2‐hydroxyethyl) dimethylhydantoin and 1,3,5‐trisubstituted isocyanurates (BA1), cyano‐hydroxylated amines (BA2), and hyperbranched polyether with terminal groups substituted by hydroxyl, cyano and ester functional groups (BA3). To study the interaction between bonding agents and oxidizers, the effect of coating by bonding agents on the characteristic absorption peaks of AP and HMX were first studied by infrared spectroscopy. Then the effect of bonding agents on the adhesion work between oxidizers and binder system were determined. The results showed that BA2 has the strongest interaction with AP, whereas BA1 and BA3 have relatively strong interaction with HMX. The AP grain coated by BA2 has the strongest adhesion work to the binder system, and there is not much difference in the values of adhesion work towards binder system of three coated HMX grains. At last the three bonding agents were added to GAP propellant, which has a theoretical specific impulse of 276.03 s. When the three kinds of bonding agent was used alone, the sense of “dewetting” in propellant was relieved but still existed. The combination of BA2 to BA1 or BA3 improved the adhesions between oxidizers and binder system effectively, and the mechanical properties of GAP propellant reached to δ _m=0.69 MPa, ϵ _b=32.7 %.     

Multi‐Parameter Study of Nanoscale TiO2 and CeO2 Additives in Composite AP/HTPB Solid Propellants

A statistical Taguchi L8 matrix was used to conduct a multi‐parameter study of the use of nanoscale additives in composite solid propellants. The additives studied were TiO₂ (titania) and CeO₂ (ceria). The other parameters involved in the experiment were the oxidizer loading and distribution, additive percentage and size, additive size (nano‐scale or μm‐scale), and the mixing method. Four baseline propellants without additives were also produced for comparison. The propellants were tested from 3.45 to 13.78 MPa in a strand bomb, and burning rate curves were determined for all formulas. By analyzing the Taguchi matrix, the sensitivity of each parameter according to the pressure sensitivity and burning rate of the propellant was calculated. The dominant factors depend on whether the additive is needed for modifying the pressure index or the absolute value of the burning rate. In general, the effectiveness of the additives was most influenced by oxidizer percentage, oxidizer size distribution, and additive type. The amount of additive, mixing method, and additive size all had relatively minor impacts on the effectiveness of the additives.     

Comparison of Commercially Available and Synthesized Titania Nano‐Additives in Composite HTPB/AP Propellant

This study presents a comparison of commercially available titania nano‐particles produced using electric wire explosion with nano‐particles manufactured by the authors using a sol‐gel synthesis process. For the present study, 20‐nm titania was purchased off‐the‐shelf. It was determined to be rough spheres of 20 nm forming large, micron‐sized agglomerates, whereas particles synthesized using the sol‐gel process were found to be fundamentally 10 nm but with sub‐micron agglomerations thereof. The nano‐titania was added to 80% AP monomodal propellants at 0.3% and 1.0% by mass. Additional, 85% bimodal‐AP mixtures were made, comparing commercial titania to the laboratory‐synthesized particles at 1.0% by mass. Another set of samples compared a method of pre‐mixing the synthesized additives directly into the binder material at 0.3% by mass of laboratory titania; two additional pre‐mixed titania batches at 0.5% by mass were doped with either Fe or Cu into the nanocrystals. All propellants were tested up to 13.8 MPa at 3.8 MPa increments. Dry powder laboratory additives show a 60‐to‐100% increase in burning rate over the baseline samples with no catalyst and a 20‐to‐30% increase over the commercial nano‐particles. Pre‐mixed additives were found to produce similar burning rate increases but with lower concentrations required. This latest generation of particle synthesis techniques was further demonstrated in this study to have great potential for future propellant catalyst development.     

The role of a novel p‐phenylen‐bis‐maleamic acid grafted atactic polypropylene interfacial modifier in polypropylene/mica composites as evidenced by tensile properties

Present work is devoted to the study of the tensile behavior of polypropylene (PP)/mica composites with improved interfacial interactions from the matrix side caused by the presence of a p‐phenylen‐bis‐maleamic acid grafted atactic polypropylene (aPP‐pPBM) as an interfacial agent. Hence, aPP‐pPBM was previously obtained, in our laboratories, by reactive processing in the melt of a by‐product (atactic PP) from industrial polymerization reactors. Present article is two‐fold, on one hand it has been planned to evidence the so called interfacial effects caused by this novel interfacial agent (aPP‐pPBM) yielding better final properties of the heterogeneous system as a whole as revealed by tensile mechanical properties, and on the other to obtain models to forecast the overall behavior of the system. For such purpose, a Box‐Wilson experimental design considering the amount of mica particles and of interfacial agent as independent variables was used to obtain polynomials to forecast the behavior of the PP/Mica system in the experimental space scanned. The existence of a critical amount of aPP‐pPBM to optimize mechanical properties appears to emerge. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis,microstructure and mechanical properties of Cr2AlC/Al2O3 in situ composites by reactive hot pressing

Al₂O₃ particle-reinforced Cr₂AlC in situ composites were successfully fabricated from powder mixtures of Cr₃C₂, Cr, Al, and Cr₂O₃ by a reactive hot-pressing method at 1400 °C. A possible synthesis mechanism was proposed to explain the formation of the composites in which Al₂O₃ was formed by the aluminothermic reaction between Al and Cr₂O₃, meanwhile, Cr₃C₂, Al, together with Cr reacted to form Cr₂AlC in a shortened reaction route. The effect of Al₂O₃ addition on the microstructure and mechanical properties of Cr₂AlC/Al₂O₃ composites was investigated. The results indicated that the as-sintered products consisted of Cr₂AlC matrix and Al₂O₃ reinforcement, and the in situ formed fine Al₂O₃ particles dispersed at the matrix grain boundaries. The flexural strength and Vickers hardness of the composites increased gradually with increasing Al₂O₃ content. But the fracture toughness peaked at 6.0 MPa m^1/2 when the Al₂O₃ content reached 11 vol.%. The strengthening and toughening mechanism was also discussed.     

Application of the BAMO‐AMMO Alternative Block Energetic Thermoplastic Elastomer in Composite Propellant

A BAMO‐AMMO alternative block (BAAB)‐based thermoplastic composite propellant with 80 % solid content was prepared using BAAB energetic thermoplastic elastomer (ETPE) as the binder, and the formulation was optimized through energy calculation. The densities, heats of explosion, glass‐transition temperatures, and mechanical properties of the samples were determined by surface tension measurements, oxygen bomb calorimetry, differential scanning calorimetry and static tensile tests, respectively. The results showed that this composite propellant can reach a standard theoretical specific impulse of 275.45 s (10 MPa), a density of 1.8102 g cm⁻³, a heat of explosion of 6256 kJ kg⁻¹, a T_g of −50.46 °C, a tensile strength of 1.56 MPa and an elongation at break of 20 %, thus presenting a superior comprehensive property to BAMO‐AMMO random block (BARB)‐based thermoplastic composite propellant.     

Mechanical properties up to 1900 K of Al2O3/Er3Al5O12/ZrO2 eutectic ceramics grown by the laser floating zone method

Directionally solidified Al₂O₃–Er₃Al₅O₁₂–ZrO₂ eutectic rods were processed using the laser floating zone method at growth rates of 25, 350 and 750 mm/h to obtain microstructures with different domain size. The mechanical properties were investigated as a function of the processing rate. The hardness, ∼15.6 GPa, and the fracture toughness, ∼4 MPa m^1/2, obtained from Vickers indentation at room temperature were practically independent of the size of the eutectic phases. However, the flexural strength increased as the domain size decreased, reaching outstanding strength values close to 3 GPa in the samples grown at 750 mm/h. A high retention of the flexural strength was observed up to 1500 K in the materials processed at 25 and 350 mm/h, while superplastic behaviour was observed at 1700 K in the eutectic rods solidified at the highest rate of 750 mm/h.     

Investigation of the structural and mechanical properties of micro-/nano-sized Al2O3 and cBN composites prepared by spark plasma sintering

Alumina-cubic boron nitride (cBN) composites were prepared using the spark plasma sintering (SPS) technique. Alpha-alumina powders with particle sizes of ∼15 µm and ∼150 nm were used as the matrix while cBN particles with and without nickel coating were used as reinforcement agents. The amount of both coated and uncoated cBN reinforcements for each type of matrix was varied between 10 to 30 wt%. The powder materials were sintered at a temperature of 1400 °C under a constant uniaxial pressure of 50 MPa. We studied the effect of the size of the starting alumina powder particles, as well as the effect of the nickel coating, on the phase transformation from cBN to hBN (hexagonal boron nitride) and on the thermo-mechanical properties of the composites. In contrast to micro-sized alumina, utilization of nano-sized alumina as the starting powder was observed to have played a pivotal role in preventing the cBN-to-hBN transformation. The composites prepared using nano-sized alumina reinforced with nickel-coated 30 wt% cBN showed the highest relative density of 99% along with the highest Vickers hardness (H_v2) value of 29 GPa. Because the compositions made with micro-sized alumina underwent the phase transformation from cBN to hBN, their relative densification as well as hardness values were relatively low (20.9–22.8 GPa). However, the nickel coating on the cBN reinforcement particles hindered the cBN-to-hBN transformation in the micro-sized alumina matrix, resulting in improved hardness values of up to 24.64 GPa.     

Densification and mechanical properties of pulsed electric current sintered B4C with in situ synthesized Al3BC obtained by the molten-salt method

The in situ generated ternary compound Al₃BC shows good dispersion on the surfaces of B₄C particles (10 ± 0.6 μm), obtained using the molten-salt method rather than the ball-milling method, which can form a conductive network in the pulse electric current sintering process to improve the sinterability of B₄C. The sintering behaviour, microstructure and mechanical properties of compacts were investigated at different sintering temperatures and Al₃BC contents. The study found that the relative density, elastic modulus, Vickers hardness, and fracture toughness of samples reached as high as 100%, 495 GPa, 37.0 GPa, and 6.32 MPa m^1/2 at 1700 °C, respectively, when the content of Al₃BC was 18 wt.%. The crack propagation mode can provide an explanation for the higher toughness than that of pure B₄C (3.19 MPa m^0.5). Additionally, the good dispersion of Al₃BC in B₄C was found to change the fracture mode from the single transgranular mode to a mixture of intergranular and transgranular modes. The compositions of the compacts were almost pure B₄C.     

Synthesis and mechanical properties of high impact polystyrene with in situ bulk polymerization toughened by one‐pot Nd‐based styrene–isoprene–butadiene terpolymer rubber

High impact polystyrene (HIPS) resins were obtained with in situ bulk polymerization toughened by styrene–isoprene–butadiene terpolymer rubber (SIBR). SIBR prepolymer was prepared through selective polymerization of styrene (St), isoprene (Ip), and butadiene (Bd) in St with [Nd]/[Al]/[Cl] catalyst. Nd‐based catalyst exhibited more favorable activity toward conjugated diene other than St, resulting in St solution of random SIBR with high cis‐1,4 stereoregularity and low St content, which was directly exposed to the free radical polymerization of St to generate HIPS. Effect of toughened rubber and the initiators [difunctional (D2) and trifunctional (T3)] were examined to attain HIPS possessing mechanical properties as follow: impact strength, 0.9–24.8 kJ/m²; tensile strength, 16.0–27.5 MPa; and elongation at break, 7.4–107.0%. Increasing SIBR matrix in HIPS improved the impact strength and decreased tensile strength. The fracture surface morphologies of HIPS specimens were studied by notched impact tests and scanning electron microscopy (SEM), illustrating that the incremental SIBR matrix presented synergistic toughening effect of crazing to enhance the ductile fracture behavior. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43979.     

In‐depth characterization of granular starch‐graft‐polyester compositions as obtained by in situ polymerization of lactones from the starch surface

The synthesis of poly(ε‐caprolactone) (PCL)‐grafted granular starch was carried out either in bulk (without solvent) or in toluene suspension by a two‐step procedure. First step relied upon the activation of the hydroxyl groups available at the starch surface by alkylaluminum derivatives like AlEt₃ and removal of non‐surface‐grafted organo‐aluminum active species. The latter species were made free in solution by reaction with the remaining water molecules still contaminating the polymerization medium despite intensive drying of the starch granules. In the second step, ε‐caprolactone was polymerized via a coordination‐insertion ring‐opening polymerization as initiated by the surface‐grafted aluminum alkoxide species. The present contribution aims at investigating various parameters such as nature of the alkyl aluminum activator and monomer (δ‐valerolactone was studied as well), temperature, concentration, and addition of a solvent (polymerization in toluene suspension), reaction time, and also the experimental procedure used to recover the polyester chains and measure the grafting efficiency. It turns out that, under the studied conditions, dialkylaluminum alkoxides surface‐grafted onto the starch granules were more likely generated and promote a fast polymerization reaction with the formation of grafted PCL chains with a molecular weight that can be as high as 225 000 (M_n value) for polymerization carried out in toluene suspension. Copyright © 2004 Society of Chemical Industry     

The improvement of mechanical properties of SiC/SiC composites by in situ introducing vertically aligned carbon nanotubes on the PyC interface

In order to improve the mechanical properties, vertically aligned carbon nanotubes (VACNTs) were in situ introduced on the pyrocarbon (PyC) interfaces of the multilayer preform via chemical vapor deposition (CVD) process under tailored parameters. Chemical vapor infiltration (CVI) process was then employed to densify the multilayer preform to acquire SiC/SiC composites. The results show that the growth of VACNTs on PyC interface is highly dependent to the deposition temperature, time and constituent of gas during CVD process. The preferred orientation and high graphitization of VACNTs were obtained when temperature is 800?℃ and C₂H₄/H₂ ratio is 1:3. The bending strength and fracture toughness of SiC/SiC composites with PyC and PyC-VACNTs interfaces were compared. Compared to the SiC/SiC composite with PyC interface, the bending strength and fracture toughness increase 1.298 and 1.359 times, respectively after the introduction of PyC-VACNTs interface to the SiC/SiC composites. It is also demonstrated that the modification of PyC interface with VACNTs enhances the mechanical properties of SiC/SiC composites due to the occurrence of more fiber pull-outs, interfacial debonding, crack branching and deflection     

Towards transparent PMMA/SiO2 nanocomposites with promising scratch‐resistance by manipulation of SiO2 aggregation followed by in situ polymerization

Poly(methyl methacrylate) grafted silica (SiO₂‐g‐PMMA) was synthesized via in situ suspension polymerization. To achieve better uniform dispersion, hexadecyltrimethylammonium bromide (CTAB) was introduced into xylene to manipulate SiO₂ aggregation. SiO₂‐g‐PMMA or SiO₂ was incorporated into PMMA matrix by in situ polymerization to prepare PMMA‐based nanocomposites. The effect of CTAB amount, in the range 0–35 wt %, on the modification was evaluated by DLS, TGA, and FTIR. Furthermore, morphology, optical, mechanical, and thermal properties of PMMA nanocomposites was characterized by SEM, UV–vis, DMA, and TGA. Owing to surface functionalization, SiO₂‐g‐PMMA exhibited far more excellent compatibility and dispersion in matrix compared with SiO₂. Surface hardness and thermal properties of nanocomposites were enhanced significantly under the premise in high transparency. It is expected that transparent nanocomposites with promising scratch‐resistance could have wide applications, such as airplane shielding window and daily furniture. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44612.     

Investigation on the melt spinning fibers of PP/organoclay nanocomposites prepared by in‐situ polymerization

Fibers prepared by melt spinning process from the PP (polypropylene)/organoclay nanocomposite were characterized in details with the aid of SEM, FTIR, XRD, DSC, and mechanical measurements. The results suggested that the lower content of organoclay (0.1%) added to the PP matrix increased the crystallinity and mechanical property (tensile strength) of the PP/organoclay nanocomposite fiber. With increasing the content of organoclay (≥ 0.3%), the crystallinity and the tensile strength both a little decreased, and the fiber containing organoclay exhibited multi‐peaks at the same draw ratio during the heating process. Furthermore, the degree of orientation of the fiber increased a little with lower content of organoclay (0.1%) introduction to PP during the infrared dichroism measurement. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Investigation of the extraction process in gel‐spinning technology for ultrahigh‐molecular‐weight polyethylene fibers by low‐field nuclear magnetic resonance

A portable, low‐field nuclear magnetic resonance scanner, the nuclear magnetic resonance mobile universal surface explorer, is introduced as a tool for investigating the extraction process of mineral oil in the gel‐spinning technology of ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers. Factors affecting the extraction process were studied systematically; these included the UHMWPE type, extraction agent type, and concentration and ultrasound. We found that the extraction process could be described by a replacement–dilution dual‐effect model. The extraction agent not only replaced and extracted the mineral oil but also considerably decreased the viscosity of mineral oil and thus enhanced the molecular motion and diffusion of mineral oil. Although chloroform had a smaller molecular size and lower boiling point, benzene and cyclohexane were found to exhibit more efficient extraction and dilution effects on mineral oil. The extraction efficiency could be characterized by the diffusion of mineral oil in the mineral oil/UHMWPE gel/deuterated extraction agent multicomponent systems during the extraction. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42018.     

The majority of minerals present in natural rubber are associated with the macrogel: An ICP‐MS and SEM/EDX investigation

The mineral composition of the insoluble (macrogel) and soluble fractions of two natural rubber (NR) samples made from the latex of two different clones (RRIM600 from Thailand and GT1 from Côte d'Ivoire) was determined using inductively coupled plasma mass spectrometry (ICP‐MS). The ICP‐MS results showed that mineral elements were concentrated in the macrogel. The major mineral elements found in macrogel were phosphorus, magnesium, potassium, and sulfur. Some mineral elements were mostly concentrated in micron‐sized mineral aggregates, visible at the surface of the samples using scanning electron microscopy coupled with an energy dispersive X‐ray microanalyzer (SEM/EDX). The nature of these mineral aggregates was found to be highly variable. Their inhomogeneous distribution in the macrogel indicates that these aggregates do not have a major influence on macrogel structure. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43062.     

Physical and mechanical properties of Al(OH)3/polypropylene composites modified by in situ‐functionalized polypropylene

Al(OH)₃/polypropylene (PP) composites modified by in situ‐functionalized polypropylene (FPP) were prepared by a one‐step melt‐extrusion process. The effect of in situ FPP on the crystallization and melting behavior, melt‐flow index, limiting oxygen index, thermal degradation, mechanical properties, and fracture morphology of Al(OH)₃/PP composites was studied. Formation of in situ FPP resulted in a decreased crystallization temperature and melting point of PP in the composites, an increased melt‐flow index, and improved tensile and flexural strengths of Al(OH)₃/PP composites, whereas the thermal degradation behavior and limiting oxygen index was not been influenced. The impact strength of the Al(OH)₃/PP composites modified by in situ FPP depended upon the content of the initiator, dicumyl peroxide, and the monomer, acrylic acid. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2850–2857, 2002; DOI 10.1002/app.10269     

An Investigation of Structure–Property Relationships in Silicone‐Based Dielectric Electroactive Elastomers by Varying Stoichiometric Imbalance of the Network

Silicone‐based elastomers are promising materials for future dielectric elastomer actuators. To ensure optimum performance and the long‐term reliability of the actuators, it is essential to gain a fundamental understanding of the correlation between the elastomer's network structure and the mechanical and electrical responses of the material. For this purpose, mechanical and electrical tests are performed on a series of silicone elastomer films with different crosslinking densities, which are prepared by changing the stoichiometric imbalance of the network. It is determined that higher cross‐linking density leads to a higher elastic modulus and a longer fatigue lifetime, whereas reduced permittivity is observed because of lower chain mobility. Dielectric breakdown strength is also observed to increase in line with increasing cross‐linking density, and the variations in relation to the measured elastic modulus and permittivity agree well with the Stark–Garton model based on electromechanical instability.