Hydroxyl-terminated Polybutadiene Research Articles

Experimental and theoretical studies on the compatibility of DNTF and typical hydrocarbon polymer binders.

3,4-bis(3-nitrofurazan-4-yl) furoxan (DNTF) is one of the third-generation energetic compounds with excellent comprehensive properties, which can be added to polymer bonded explosive (PBX) to improve energy levels and regulate sensitivity, so the compatibility of DNTF with other components in PBX, especially the binder, is the first question. Herein, two typical hydrocarbon polymers commonly used in PBX, which are hydroxyl-terminated polybutadiene (HTPB) and polyisobutylene (PIB), were selected as the binder, and the compatibility of HTPB and PIB with DNTF was investigated by differential scanning calorimetry (DSC), the vacuum stability test (VST), and in situ infrared spectroscopy (in situ IR). The results of compatibility experiments were verified by using the binding energy and solubility parameter criteria in molecular dynamics (MD). Experimental and MD simulation results showed that DNTF could be compatible with PIB but incompatible with HTPB. The frontier molecular orbital theory in quantum chemistry (QC) was adopted to explore the frontier orbital electron distribution and energy levels of DNTF/HTPB and DNTF/PIB composite systems to better understand the microscopic compatibility mechanism. The compatibility results of the two composite systems were explained from the perspective of electron transfer. All these can deduce that a hydrocarbon polymer binder with a saturated carbon-hydrogen bond at the end of the molecular chain has good compatibility with DNTF, compared with a hydroxyl group, which has bad compatibility with DNTF.

Analysis of thermomechanical coupled accelerated aging of HTPB propellants

AbstractThis study employed macroscopic uniaxial compression tests at low and medium strain rates, coupled with microscopic electron microscopy, to extensively analyse the impact of thermomechanical coupled aging on the accelerated aging of Hydroxyl‐terminated Polybutadiene (HTPB) propellants, contrasting it with the effects of isolated factors such as heat and dynamic reciprocating force. Results indicate that at various environmental temperatures (323 K, 343 K, and 363 K), thermomechanical coupled aging more significantly affects HTPB propellants than isolated factors. This effect is macroscopically evident in increased ease of deformation, permanent deformation during aging, continual increase in dissipated energy, and a decrease in average stress and ultimate strain post‐aging. Microscopically, the effect predominantly arises from the interplay between matrix thermal degradation and particle fragmentation, which rapidly accumulate and substantially impact the material's macroscopic mechanical properties. Furthermore, as the aging temperature rises, the alterations in both macroscopic mechanical properties and microscopic morphology of HTPB propellants become more pronounced. However, overly high temperatures may swiftly result in substantial material performance deterioration. Consequently, while elevating temperature effectively accelerates thermomechanical aging, the potential adverse effects on material performance must be judiciously considered. This underscores the necessity of balancing temperature regulation with aging efficiency enhancement in HTPB propellants to ensure effective control and quantitative assessment of the aging process, while minimizing material degradation.

Synthesis and characterization of new intrinsic self-healing hydroxyl-terminated polybutadiene (HTPB) functionalized with 2-ureido-4-pyrimidinone

Synthesis and characterization of new intrinsic self-healing hydroxyl-terminated polybutadiene (HTPB) functionalized with 2-ureido-4-pyrimidinone

Synthesis of Propellant Grade HHTPB by Hydrogenation of HTPB using Pd-activated charcoal as catalyst

To derive more performance from the conventional composite propellant based on Hydroxyl-terminated polybutadiene (HTPB) and ammonium perchlorate (AP), it is envisaged to hydrogenate HTPB, which increases the H/C (hydrogen to carbon ratio) of the base polymer. This paper attempts to describe the partial hydrogenation of HTPB using a catalytic method that uses palladium supported by activated charcoal as a catalyst and HTPB polymer as a precursor. HTPB has a hydroxyl value of 41.0 mg KOH/g with a number average molecular weight (Mn) of 6150, polydispersity (PD) of 2.25 was used as a precursor. Iso-propyl alcohol (IPA) and toluene were used as a solvent media to disperse the HTPB polymer during hydrogenation. The estimate revealed an increase in specific impulse (ISP) up to 1.2 sec with ∼37 % hydrogenated HTPB. Partial hydrogenation is only attempted to retain other process capabilities essential for realizing a defect-free solid propellant grain with good structural integrity. In contrast, others attempt to reach near saturation. A reactor capacity of 100 ml, operating at 60 bar pressure, was used to synthesize HHTPB, and the extent of hydrogenation was controlled based on the numerous experiments varying the reactor parameters like operating temperature, operating pressure, and solvent-to-polymer ratio for a given catalyst concentration. Detailed characterization of the end product by FTIR, 1H-NMR and 13C-NMR to reveal the degree of hydrogenation along with generic polymer characteristics. The measured hydroxyl value of HHTPB is comparable with HTPB; however, a marginal increase in molecular weight and polydispersity was noticed at 37 % conversion, wherein other researchers found a loss in -OH value. Thermogravimetry analysis revealed no significant change in the gasification rate. A slight increase in the H/C ratio and calorific value was observed for HHTPB compared to HTPB. Despite the increase in viscosity of HHTPB, the increase in the vinyl-type functional distribution of HHTPB aids for better process-ability during propellant processing. However, the propellant formulation should be optimized with the help of plasticizers, solid loading, etc., to achieve the required properties.

Transient numerical investigation on thermochemical erosion of C/C nozzles in hybrid rocket motors

Nozzle erosion is a vital important issue that impacts the performance of hybrid rocket motors. Serious nozzle erosion may significantly decrease the combustion chamber pressure and thrust, which increases the difficulty in designing flight control systems. This paper aims to reveal erosion mechanism systematically. In this paper, transient numerical simulations of thermochemical erosion in hybrid rocket motors are conducted, and combustion flow and thermochemical erosion are coupled calculated. The numerical computation of combustion flow is based on the chemical reactions of propellants and regression rate model, and that of thermochemical erosion is based on the surface reactions between oxidizing species and carbon. The movement of burning surface and nozzle inner surface is simulated through dynamic mesh method. The hybrid rocket motor adopts 90% hydrogen peroxide and hydroxyl-terminated polybutadiene. Distributions of flow field parameters and fuel regression rate are given. The spatial developing process of nozzle surface is presented, and it is found that the roughness of nozzle profile increases with time. The nozzle wall temperature and wall pressure decline with time. Erosion by different species is calculated. OH and H2O make a major contribution to the nozzle thermochemical erosion, while nozzle erosion contributed by CO2 and O2 are quite low. Time-varying characteristics of the erosion rate are unveiled. At the first 1.5 s, the total erosion rate remains almost constant, and then it reduces over time.

Effect of pressure, Mg content and AP size on the microscale flame structure of Mg-based propellant

The Mg-based propellant is considered to be a promising fuel for underwater propulsion, but the mechanism of the change of the burning rate is unclear. The Mg-based propellant was divided into two parts on the basis of the BDP multi-flame model: large-size oxidizer particle and pseudo-propellant consisting of fine oxidizer and other components, and the micro steady-state combustion model of Mg-based propellant was established. Quantitatively analysis on the gas-phase multi-flame structure was performed, which focused on the effect of pressure, Mg content, and oxidizer particle size on the burning rate. This model was verified by the results of combustion experiments on ammonium perchlorate (AP) /hydroxyl-terminated polybutadiene (HTPB) composite propellant and Mg-based propellant, and the mean absolute percentage error between the burning rate obtained from the simulation and the experimental measurements was less than 5%. Results indicated that the flame structure of Mg-based propellant exhibited typical BDP flame characteristic. As pressure increased from 1 MPa to 4 MPa, the premixed AP flame and the preliminary diffusion flame were closer to the burning surface, which enhanced the heat feedback. And accordingly, the burning rate raised from 5.93 mm/s to 9.79 mm/s. Mg content mainly affect the combustion process of the pseudo-propellant. The premixed flame above the pseudo-propellant gradually disappeared as the Mg content increased from 15% to 63%, which led the burning rate to decrease from 17.45 mm/s to 7.83 mm/s. AP particle size affected the effectiveness of the preliminary diffusion flame on the burning surface and resulted in a change in the burning rate. These findings can provide theoretical guidance for the design of Mg-based propellant formulations.

Shock-Tube Measurements of Carbon Monoxide During Combustion of Hydroxyl-Terminated Polybutadiene Products/Air

Hydroxyl-terminated polybutadiene (HTPB) is a fuel proposed for use in hypersonic rockets, specifically in solid fuel ramjets (SFRJs), where it combines with air and undergoes combustion processes that range from fuel pyrolysis to fuel lean- combustion. A better understanding and the improvement of SFRJ combustion can be accomplished through fundamental experiments and computational fluid dynamics modeling. The current chemical-kinetic models need data to capture the reaction kinetics at the conditions under which SFRJs operate. This work focuses on providing combustion data to assess the predictive capabilities of state-of-the-art mechanisms at conditions relevant to SFRJs. The University of Central Florida shock-tube facility was used to conduct experiments of various combinations of HTPB products in air near 5 atm for temperatures ranging from 1100 to 1800 K and Φ=0.5, 1.0, 4.76. Nonintrusive, time-resolved laser absorption spectroscopy was used to record carbon-monoxide-concentration time histories and compared against the predictions of AramcoMech3.0 and HyChem mechanisms. For each mixture, the mid- and high-temperature conditions matched the models well, whereas there was a significant discrepancy for the low-temperature condition. A sensitivity analysis was then conducted to determine which reactions warranted further investigation to address the discrepancy at low temperatures.

Preparation and Performance Study of HTPB-g-(PNIPAM/PEG) Thermoresponsive Polymer Brush.

In recent years, a great deal of work has been devoted to the development of thermoresponsive polymers that can be made into new types of smart materials. In this paper, a branched polymer, HTPB-g-(PNIPAM/PEG), with polyolefin chain segments as the backbone and having polyethylene glycol (PEG) and poly(N-isopropylacrylamide) (PNIPAM) as side chains was synthesized by ATRP and click reactions using N3-HTPB-Br as the macroinitiator. This initiator was designed and synthesized using hydroxyl-terminated polybutadiene (HTPB) as the substrate. The temperature-responsive behavior of the branched polymer was investigated. The lower critical solution temperature (LCST) of the branched polymer was determined by ultraviolet and visible spectrophotometry (UV-vis) and was found to be 35.2 °C. The relationship between the diameter size of micelles and temperature was determined by dynamic light scattering (DLS). It was found that the diameter size changed at 36 °C, which was nearly consistent with the result obtained by UV-vis. The results of the study indicate that HTPB-g-(PNIPAM/PEG) is a temperature-responsive polymer. At room temperature, the polymer can self-assemble into composite micelles, with the main chain as the core and the branched chain as the shell. When the temperature was increased beyond LCST, the polyolefin main chain along with the PNIPAM branched chain assembled to form the nucleus, and the PEG branched chain constituted the shell.

Investigation of aluminum particle ignition dynamics in various propellant environments

The ignition delay of aluminum particles can be profoundly influenced by the agglomeration and combustion characteristics of solid propellants. In this experimental study, the ignition of individual aluminum particles in nitrate ester plasticized polyether (NEPE) and hydroxyl‑terminated polybutadiene (HTPB) propellant atmospheres was examined using laser ignition tests and high-speed photography. Focus was directed at the effects of the atmospheric composition, pressure, and aluminum particle size (500, 800 and 1000 µm). It was observed that the non-homogeneous reaction heat generation and convective heat exchange rates during particle ignition could be increased by increasing the CO2 content or ambient temperature, resulting in a shorter ignition delay time. This explains why aluminum particles tended to burn more efficiently in nitrate ester plasticized polyether than in hydroxyl‑terminated polybutadiene. In addition, it was found that the ignition delay time decreased with increasing pressure and was inversely proportional to the particle size squared. An ignition model for aluminum particle ignition in a multi-component atmosphere was developed and validated to describe the temperature change and energy transfer during ignition. The calculated ignition delay times were found to be within 5% of the experimental values. The model also showed that increasing the ambient temperature was more effective than increasing the CO2 content at enhancing ignition, and that CO2 was more effective than O2, which was itself more effective than H2O. Overall, this study provides useful insight into the ignition characteristics of aluminum particles in different propellant environments. The results could be used to develop more effective propellant formulations, optimize combustion processes, and improve safety in the handling and use of aluminum-based propellants.

Exploring the synergistic effect of carboxymethyl cellulose and chitosan in enhancing thermal stability of polyurethanes through statistical mixture design approach

The thermal stability of polyurethanes, known for its limitations, was addressed in this research by seeking improvement through the introduction of carbohydrate-based chain extenders. In this research paper, we systematically sought to improve the thermal resistance of polyurethanes by incorporating carboxymethyl cellulose and chitosan, representing a pioneering application of the mixture design approach in their preparation. In this synthesis, hydroxyl-terminated polybutadiene and isophorone diisocyanate (IPDI) were reacted to prepare –NCO terminated prepolymer, which was subsequently reacted with varying mole ratios of CMC and CSN to develop a series of five PU samples. The prepared PU samples were characterized using the Fourier-transformed infrared spectroscopic technique. Thermal pyrolysis of PU samples was examined using thermal gravimetric analysis (TGA). It was observed that, among all the samples, PUS-3 showed remarkable thermal stability over a wide temperature range. A comprehensive statistical analysis was conducted to substantiate the experimental findings. It was estimated that CMC and CSN significantly enhance the thermal stability of the samples when involved in an interaction fashion. The ANOVA Table for the mixture design demonstrates that over 90 % of the total variation in thermal stability is explained by the mixture model across a wide temperature range. Moreover, PSU-3 exhibited 4 % more thermal stability over a wide range of temperatures on average, as compared to contemporary samples.

Transient plasma enhanced combustion of solid rocket propellants

We demonstrate the use of nanosecond pulse transient plasma (NPTP) to improve the control (and acceleration) of the combustion of solid rocket propellants. Here, we fabricate end-burning propellant samples (i.e., grains) with a co-axial center wire electrode using hydroxyl terminated polybutadiene (HTPB), isodecyl pelargonate (IDP), modified diphenyl diisocyanate (MDI), and ammonium perchlorate (AP) as the fuel, plasticizer, curative, and oxidizer, respectively. High voltage (20 kV) nanosecond pulses (20 nsec) produce a streamer discharge that provides electronic throttling of the solid rocket propellant. These studies are carried out over a wide range of oxidizer mass fractions, including those considered insensitive munitions (IM). In addition, real time imaging is performed characterizing the plasma-formation, evolution of the ignition process, and plasma enhanced flame-fuel coupling. We believe the plasma-based mechanisms of enhancement are 3-fold: 1.) The plasma provides highly energetic electrons that drive new chemical reaction pathways via highly reactive atomic species such as H, O, and Cl, 2.) The plasma sputters chunks of the solid fuel material up into the flame where it is combusted, producing an agitated flame profile. 3.) The plasma provides increased turbulence and multi-scale mixing due to hydrodynamic effects (i.e., ionic winds), which further improves the combustion process. Having electronic control of the burn rate introduces the ability to “throttle” solid rocket motors and introduce new flight profile options beyond a pre-selected profile such as the typical boost-sustain profile. While we are unable to quantify the burn rate or thrust from these relatively simple observations, we observe clear evidence of the effect of the plasma on the combustion of these solid rocket fuels even at high oxidizer content.

POSS/EHTPB synergistically toughened epoxy resin for cryogenic application

The high brittleness of epoxy resin at cryogenic temperature restricts their wide application in cryogenic engineering. In this study, polyhedral oligomeric silsesquioxane (POSS) with -Si-O-Si- molecular chains were synthesized, and the mechanical properties of diglycidyl ether of bisphenol A (E51 epoxy resin) were significantly enhanced at room temperature (RT) by incorporating a 4% POSS and curing agent 4,4′-diamino-diphenylmethane (DDM) as the E51/POSS/DDM resin system. Subsequently, by adding different contents of epoxidation hydroxyl-terminated polybutadiene (EHTPB) into the E51/POSS/DDM resin system, the EHTPB-E51/POSS/DDM resin system was prepared. The investigation into the impact of EHTPB content on the mechanical properties of EHTPB-E51/POSS/DDM resin system at room temperature (RT) revealed that EHTPB-E51/POSS/DDM resin system with 10% EHTPB exhibited the most favorable results. Specifically, the elongation at break, flexural strength, and critical stress intensity factor (KIC) were measured to be 6.82%, 143.75 MPa, and 1.83 MPa m1/2, respectively. These values demonstrated a notable improvement of 53.3%, 26.9%, and 86.7% compared to those for the E51/DDM resin system. Concurrently, at 77 K, the elongation at break and critical stress intensity factor (KIC) increased by 37.8% and 73.5%, respectively. The toughening mechanism of the prepared EHTPB-E51/POSS/DDM resin system was further explored through resin-curing cross-linking simulation networks and SEM images of the fracture surface of resin samples. The study of EHTPB and POSS synergistically toughened epoxy resin provided a new efficient method to prepare epoxy resins with high toughness at low temperatures.

Experimental and numerical investigation on thermochemical erosion and mechanical erosion of carbon-based nozzles in hybrid rocket motors

In order to enhance energy characteristics of propellants in hybrid rocket motors, aluminum particles are added into the solid fuel. However, these particles may lead to nozzle mechanical erosion, which significantly affects the motor performance. This paper intends to study thermochemical and mechanical erosion mechanism of carbon-based nozzles in hybrid rocket motors with aluminum metallized fuel. A firing test is performed, and 95 % hydrogen peroxide and hydroxyl‑terminated polybutadiene based fuel with aluminum particles are utilized. Experimental results show that many metal particles are ejected from the nozzle, and aluminum oxide deposits heavily on the nozzle inner surface. A method of numerical calculation coupled with two-phase flow, combustion of aluminum metallized fuel, thermochemical ablation reactions, and mechanical erosion is established. The errors of combustion chamber pressure and throat erosion rate between numerical calculation and test results are 0.53 % and 7.76 %, respectively. Simulation results indicate that with the increase of aluminum content, nozzle wall pressure gradually increases, while the mass fraction of H2O, CO2, OH, and O declines. The nozzle wall temperature and thermochemical erosion rate raise first and then reduce as aluminum content increases. The mechanical erosion is mainly distributed in the convergent section, and it raises with the increase of aluminum content. When aluminum content is up to 38 %, the maximum mechanical and thermochemical erosion rates are 0.09185 mm/s and 0.0976 mm/s, respectively. This reveals that effects of mechanical erosion on hybrid rocket nozzles should be carefully considered and evaluated under conditions of high aluminum content.

Investigating Thermal Decomposition Kinetics and Thermodynamic Parameters of Hydroxyl-Terminated Polybutadiene-based Energetic Composite

Background: Hydroxyl-Terminated Polybutadiene (HTPB)-based energetic compositions have been developed for enhanced blast energetic composite, composite rocket propellant formulations, metal cutting, demolition, welding and explosive reactive armour in civil and military applications. The types and choice of curing agents are crucial in enhancing the mechanical and structural integrity of the binder. To understand the stability and safety of energetic composites for potential applications, it is necessary to understand the thermal decomposition kinetics and thermodynamic parameters clearly. Objective: The main objective is to study the decomposition kinetic and thermodynamic parameters of energetic composites cured by different curing agents. Methods: A series of energetic composites based on HMX (1,3,5,7-tetranitro-1,3,5,7- tetrazocane) and HTPB-based binder system cured with various curing agents were prepared by the cast cured method. The curatives, namely MDI (4,4’-methylene diphenyl diisocyanate), IPDI (isophorone diisocyanate), TDI (toluene dissocyanate) and TMDI (2,2,4-trimethylhexamethylene diisocyanate) were used. The thermal analysis method was employed to investigate the thermal decomposition characteristics, which are closely associated with the thermal stability and safety considerations during handling, processing, and storage. The kinetic parameters for thermal decomposition reactions were studied by employing the Flynn-Wall-Ozawa method. The thermodynamic parameters of the activation enthalpy, activation Gibbs energy free and activation entropy of all energetic composites were also determined by the theory of activated complex. Results: The thermogravimetric results show that the thermal stability is almost similar for all composites cured with the different types of curing agents. The average activation energy of the energetic composites cured with IPDI, MDI, TMDI and TDI was 207.5, 237.3, 243.3 and 187.6 kJ/mol, respectively. The thermodynamic parameters for the thermal decomposition process show that they are generally thermodynamically stable and non-spontaneous. Scanning electron microscope (SEM) micrographs of all the samples clearly indicate that HMX crystals are well embedded in the polymer matrices. result: The thermogravimetric results show that the thermal stability and thermal decomposition behaviour do not change significantly by varying the type of the curing agent in the HTPB-based binder. The SEM micrographs of all the samples clearly indicate that HMX crystals are well embedded in the polymer matrices. The averaged activation energy for the HMX/HTPB/MDI, HMX/HTPB/IPDI, HMX/HTPB/TDI and HMX/HTPB/TMDI samples obtained from FO method was 237.3, 207.5, 187.6 and 243.3 kJ/mol, respectively. The thermodynamic parameters including the activation enthalpy, activation Gibbs free energy and activation entropy for the thermal decomposition process show that they are generally thermodynamically stable and non-spathaceous. Conclusion: The thermal stability of all energetic composites is almost constant. The activation energy of the prepared energetic composites is significantly varied with varying the type of curing agents in the HTPB-based binder system. The thermodynamic parameters indicate that composites possess superior stability and thermal safety. The SEM micrographs indicate that HMX crystals of prepared composites are embedded in the polymer matrix.

Molecular dynamics simulation of bonding role of cyclic borate ester in improving mechanical properties of the HTPB propellant

Excellent mechanical properties are the fundamental requirement for the practical application of solid propellants. However, solid oxidant fillers such as hexahydro-1,3,5-trinitros triazine (RDX) seriously weaken the mechanical strength of the propellant due to poor adhesion with the binder matrix. In this work, novel cyclic borate ester (CBE) bonding agents with long-chain alkyl moiety were designed by the molecular dynamics (MD) method to improve the unfavorable interfacial bonding effect. The interface models, which consist of RDX substrate and binder matrix where hydroxyl-terminated polybutadiene (HTPB) crosslinked with curing agents, were constructed to reveal the interface enhancement mechanism by CBE bonding agents. The results indicate that the designed CBE bonding agents with appropriate solubility parameters (SPs) can migrate from the binder matrix to the RDX surface. Besides, CBE bonding agents exhibit strong interaction with RDX compared to the binder matrix due to the formation of hydrogen bonds. Finally, the simulated tensile tests with two tensile modes showed that CBE bonding agents can enhance the interfacial strength and reduce stress softening rates by the calculation of debonding work. Moreover, this improvement can be controlled by adjusting the chain length of CBE bonding agents. The results obtained in this work deepen the understanding of the interfacial strengthening mechanism of bonding agents for solid propellants and provide a framework for designing high-performance bonding agents based on the MD method.

Effect of Fluoroalcohol Chain Extension Modified HTPB Binder on the Combustion Performance of Aluminized Propellants

To enhance both the mechanical properties of hydroxyl-terminated polybutadiene (HTPB) binder and the combustion efficiency of aluminized propellants, 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol (OFHD) was employed as a chain extender to impart mechanical regulation to the HTPB binder. Mechanical testing showed that the mechanical properties of fluoride-modified HTPB polyurethane (FPU) were significantly improved: the peak tensile strength of the optimized samples reached 1.99 MPa, and the elongation at break attained 486%. The structural characterization of the FPUs was conducted using Fourier transform infrared (FTIR) spectroscopy. Thermogravimetry-mass spectrometer (TG-MS) analysis revealed that the initial thermal decomposition temperature of the FPU shifted from 170 °C to 162 °C, accompanied by the release of fluorine-containing fragments during decomposition. Analysis of the combustion residue indicated that the addition of OFHD can reduce the agglomeration of aluminum (Al) powder in aluminized propellants. Dynamic pressure characteristics results showed an augmented pressurization rate under argon and oxygen atmospheres, increased by 18.67% and 37.29%, respectively. Heat release tests indicated that the aluminized propellants with the addition of OFHD had a higher combustion heat, being increased by 6.57%. The binder system is expected to be applied in aluminized propellants to improve the mechanical properties and combustion efficiency of Al powder.

High-nitrogen azotetrazole based pyrogen gas generating propellants: Aspects on synthesis, characterization, combustion characteristics and kinetics

Propellant formulations containing a novel high nitrogen azotetrazole salt viz., diammonium 5,5′-azotetrazolate (DAAzT) along with two different binders viz., hydroxyl terminated polybutadiene (HTPB) and glycidyl azide polymer (GAP) were realized as potential pyrogen-based gas generators for use in inflatable structures. The DAAzT-GAP and DAAzT-HTPB propellant systems were investigated for their gas generating capabilities and it was found that the GAP based system offers enhanced gas yield of ∼430 mL/g against ∼320 mL/g for the HTPB based propellant at standard operating pressure of 1 bar and temperature of 298 K. Combustion product analyses of the propellant were undertaken by pyro GC–MS and it was found that the combustion products are benign and constitutes 62% and 53% N2 (mass fraction) as major combustion products from GAP and HTPB propellant respectively. A detailed thermal analysis of DAAzT by isoconversional method of Vzayovkin was undertaken and the dependence of activation energy with conversion was evaluated. The activation energy was also determined using a classical Kissinger method. The impact and friction sensitivity of the promising GAP-DAAzT propellant was found to be 3 Nm and 360 N respectively and the auto ignition temperature is 177.0 °C. Functional evaluation and gas generating capability of DAAzT-GAP propellant were successfully demonstrated in a sub-scale inflation test in a stand-alone configuration.

Regulated synthesis of 3D nano-flower-like MnCo2O4.5 catalytic materials to enhance thermal decomposition of ammonium perchlorate

Morphological control enables precise modulation of the specific surface area, pore structure, and crystal structure of catalytic materials, thereby enhancing catalytic efficiency. In this study, morphology controlled synthesis of MnCo2O4.5 samples was achieved by solvent-hydrothermal method by varying the ethylene glycol to deionized water volume ratio. The 3D nano-flake-like MnCo2O4.5 material with a larger specific surface area was successfully prepared at a volume ethylene glycol to deionized water (6:40). The ammonium perchlorate (AP) is high temperature decomposition (HTD) peak temperature decreases from 473.48 °C of pure AP to 304.39 °C and the heat release increases from 888.26 J g−1 to 2094.50 J g−1 after the addition of 2.0 % 3D nano-flower-like MnCo2O4.5. The activation energy (Ea) goes down to 89.2 kJ mol−1 relative to pure AP (296.8 kJ mol−1). When applied to Hydroxy-terminated polybutadiene composite solid propellant (HTPB-CSP), the combustion process of HTPB-CSP containing 3D nano-flower-like MnCo2O4.5 is more intense compared with only containing pure AP. The time to achieve the maximal combustion effect is accelerated from 390 ms to 268 ms, and the ignition delay time is lowered from 35 ms to 23 ms. Based on its microstructural design and optimization, MnCo2O4.5 has a remarkable catalytic performance for AP thermal decomposition, according to the experimental results.

The flexoelectric properties of various polymers and energetic composites

Electroactivity of polymers used in energetic materials may result in charge separation that could result in safety concerns (unintentional ignition) or be exploited for multifunctional applications. We measured the flexoelectric properties of several polymers and energetic composites including poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)], nanosized aluminum (nAl)/P(VDF-TrFE), poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)], micron aluminum (μAl)/P(VDF-HFP), hydroxyl-terminated polybutadiene (HTPB), ammonium perchlorate (AP)/HTPB, μAl/AP/HTPB, polytetrafluoroethylene (PTFE), and polydimethylsiloxane (PDMS). The presence of flexoelectricity in PTFE (Teflon®) and the relatively high flexoelectric coefficient of P(VDF-HFP) (Viton®) measured in this work may help explain accidents involving the production and use of Magnesium-Teflon-Viton (MTV) that in many instances have been attributed to electro-static discharge. The addition of aluminum nanopowders to the P(VDF-TrFE) increased the flexoelectric coefficient by ∼30%. However, the addition of aluminum micrometer particles (10 wt. %) to P(VDF-HFP) decreased the effective flexoelectric coefficient, while an increase was observed when the aluminum loading was increased from 10 to 20 wt. %. The effective flexoelectric coefficient of HTPB and two propellant compositions (AP/HTPB and μAl/AP/HTPB) were measured to be in the same range as each other. The effect of particle addition (nAl, μAl, and AP) on flexoelectricity was different depending on the binder, further illustrating the complexity of flexoelectric properties in composite energetics. This may be somewhat explained by competing effects where particle additions (nAl, μAl, and AP) create additional strain gradients that contribute to flexoelectricity, but the particle additions also replace the mass of flexoelectric polymer binders (P(VDF-TrFE, P(VDF-HFP), and HTPB) with particles (nAl, μAl, and AP) that are less flexoelectric.

Enhanced gas and plasticizer barrier HTPB composite liner implanted with parallel orientation Fe3O4/RGO nanosheets by an ultrasound/magnet-coassisted method

It is of great significance to prepare liners with excellent inhibition of energetic plasticizer migration and gas barrier properties. Here, we have successfully prepared magnetic iron oxide decorated reduced-graphene-oxide nanosheets (MRGO) by using ultrasound-assisted method. The obtained MRGO nanosheet-fillers were filled into hydroxyl-terminated polybutadiene (HTPB) which was exposed to a magnetic field (200 mT) to achieve ordered orientation of MRGO in the HTPB matrix (Ordered MRGO/HTPB). The laser confocal microscopy demonstrates that MRGO exhibit ordered orientation structure in HTPB matrix with good dispersion, which renders the HTPB composite liners exhibiting high gas and plasticizer barrier capability, with a reduction of 18.9 % in water vapor permeability and a decrease of 14.1 % in dibutyl phthalate (DBP) migration equilibrium concentration as compared with those of random MRGO embedded HTPB composite liners (Random MRGO/HTPB). Moreover, a theoretical model accounting for such enhanced gas/plasticizer barrier performance of HTPB due to the implantation of order aligned MRGO was established, which shows that the effective diffusion pathways of plasticizer/gas for liner penetration would be significantly enhanced when the MRGO nanosheets are oriented within the HTPB matrix. This work provides an effective and facile strategy toward the design and development of composite liners with high plasticizer/gas barrier performance for industrial applications.