HTPB Binder Research Articles

Computational Determination of the Specific Impulse of Solid Rocket Propellant Compositions of closo-Dodecaborate ([B12H12]2‒) Salts with HTPB Binder and Ammonium Perchlorate as an Oxidizer

Computational Determination of the Specific Impulse of Solid Rocket Propellant Compositions of closo-Dodecaborate ([B12H12]2‒) Salts with HTPB Binder and Ammonium Perchlorate as an Oxidizer

Evolution of structural damage of solid composite propellants under slow heating and effect on combustion characteristics

Composite propellants are used to fabricate solid motors for space vehicles. The fundamental factor that affects motor safety is the structural damage in the propellant owing to slow heating in an abnormal storage or service environment. Hence, their thermal damage and combustion characteristics should be studied comprehensively. In this study, we investigated the combustion behaviours of hydroxyl-terminated polybutadiene/ammonium perchlorate/aluminium powder (HTPB/AP/Al) and hydroxyl-terminated block copolyether/AP/Al (HTPE/AP/AI) propellants under slow heating conditions. The pore structure was observed using scanning electron microscopy and micro-computerised tomography. Their weight loss behaviour, gaseous products, and pore structure evolution were analysed using thermogravimetric analysis, mass spectrometry, and Fourier-transform infrared spectroscopy. The influence of the pore structure on the combustion behaviour was studied by establishing the relationship between combustion and energy release rates. The weight loss rates of HTPB/AP/Al and HTPE/AP/Al before ignition were 34.5% and 16.1%, respectively. Upon heating, the HTPB binder decomposed to form pore channels, through which the gaseous products produced from the decomposition of AP were released, which increased the structural damage in this propellant. In contrast, upon heating, the HTPE binder liquefied and formed a coating on the AP particles, which slowed the structural damage in this propellant. Moreover, the calculated reaction intensity of HTPB/AP/Al was 4.16 times that of HTPE/AP/Al, indicating that larger pore channels increase the burning surface for combustion.

Synthesis of multifunctional additives for solid propellants: Structure, properties and mechanism

To simplify the composite propellant formulation and address the current issue of the single-functionality present in existing additives, the multi-cyano, amine-based polybutadiene (AEHTPB-CN) was prepared based on AEHTPB by adopting appropriate synthesis strategies. By replacing 10% of HTPB binder in the propellant formulation, it can effectively enhance the interfacial bond strength between the propellant binder matrix and solid fillers (AP (ammonium perchlorate) and RDX (cyclotrimethylene-trinitramine)), the mechanical properties of the HTPB/AP/RDX/Al propellant were superior to blank control propellant with an improvement of 35.4% in tensile strength, 62.0% enhancement in elongation at break, and reduce the propellant burn rate by 10.7% with any energy loss. The function mechanism of AEHTPB-CN was systematically elucidated through experiments and computer simulation techniques. The results show that the tertiary amine group in AEHTPB-CN can react with AP to form ammonium ionic bonds, and the hydroxyl and cyano groups can form hydrogen bonding interactions with AP, which enables AEHTPB-CN to be firmly adsorbed on the AP surface through chemical and physical interactions. For RDX, the interfacial bonding effect of AEHTPB-CN is attributed to their ability to form C–H⋅⋅⋅NC weak hydrogen bonding interaction between the cyano group and RDX methylene group.

Interaction Mechanism of Composite Propellant Components under Heating Conditions.

To examine the interactions between two binder systems-hydroxyl-terminated polybutadiene (HTPB) and hydroxyl-terminated block copolyether prepolymer (HTPE)-as well as between these binders and ammonium perchlorate (AP) at various temperatures for their susceptibility to varying degrees of thermal damage treatment, the thermal characteristics and combustion interactions of the HTPB and HTPE binder systems, HTPB/AP and HTPE/AP mixtures, and HTPB/AP/Al and HTPE/AP/Al propellants were studied. The results showed that the first and second weight loss decomposition peak temperatures of the HTPB binder were, respectively, 85.34 and 55.74 °C higher than the HTPE binder. The HTPE binder decomposed more easily than the HTPB binder. The microstructure showed that the HTPB binder became brittle and cracked when heated, while the HTPE binder liquefied when heated. The combustion characteristic index, S, and the difference between calculated and experimental mass damage, ΔW, indicated that the components interacted. The original S index of the HTPB/AP mixture was 3.34 × 10-8; S first decreased and then increased to 4.24 × 10-8 with the sampling temperature. Its combustion was initially mild, then intensified. The original S index of the HTPE/AP mixture was 3.78 × 10-8; S increased and then decreased to 2.78 × 10-8 with the increasing sampling temperature. Its combustion was initially rapid, then slowed. Under high-temperature conditions, the HTPB/AP/Al propellants combusted more intensely than the HTPE/AP/Al propellants, and its components interacted more strongly. A heated HTPE/AP mixture acted as a barrier, reducing the responsiveness of solid propellants.

Numerical study on the effect of pressure on transient micro-combustion and heat release characteristics of AP/HTPB/Al composite propellant fuel

The effect of pressure on transient micro-combustion and heat release characteristics of AP/HTPB/Al composite propellant is investigated in the present study. Detailed combustion mechanism with 42 species and 136 reactions and segmented regression rate model are established and validated for the propellant fuel. The results show that temporal evolution of regression rate is not synchronous with temperature due to the heterogeneous properties of the burning surface. With combustion time increasing from t = 0.6 ms to t = 6.0 ms, the standard deviation of temperature of the burning surface increases by 65.08% while the standard deviation of regression rate decreases by 18.80%. Although raising pressure increases both the temperature and regression rate of the burning surface, the distribution uniformity of temperature and regression rate exhibits distinct response characteristics to pressure. With pressure increasing from 2 MPa to 10 MPa, the standard deviation of temperature of burning surface decreases by as much as 36.50% due to enhanced heat transfer to the burning surface. However, the standard deviation of regression rate increases by as much as 66.68% with pressure. Both the gas-phase temperature and solid-phase temperature increase and become more uniform with pressure. With progress of combustion, total heat transfer coefficient decreases slightly due to the reduced combustion heat release rate. Although the contribution of heat radiation increases significantly during the combustion process, heat convection is dominant heat transfer. With the increase of pressure, the combustion heat release rate increases significantly due to the enhanced oxidation reactions in diffusion flame. With consumption of the propellant, the combustion heat release rate decreases and squeezes to a smaller region. The experimental results of extinguished burnt surface show that AP particles become higher than the surface of HTPB binder as pressure increases. The non-uniformity of morphology of the burning surface of the AP/HTPB/Al composite propellant increases with pressure.

INCREASING THE ENERGY OF alpha, omega - DIHYDROXYPOLIBUTADIENE (HTPB) USED IN SOLID HETEROGENEOUS ROCKET PROPELLANT

Solid heterogeneous rocket propellants (SHRP), which are very popular and widely used in the armaments industry (guided missile propulsion engines and long-range, short-range and medium-range anti-aircraft rockets) have inert binders that significantly affect the final performance parameters of propulsion charges. In this study, the popular HTPB binder was modified by introducing azide groups into the polymer chain during three different syntheses. Compounds with different content of explosive groups were obtained and tested for compatibility with the essential SHRP components: ammonium chlorate(VII) and dioctyl adipate. Then, preliminary application tests of the obtained HTPB derivative were carried out, showing the potential of the obtained energetic polymer and the possibility of its use as a binder in solid heterogeneous rocket fuels. HTPB, energetic binder, azide groups

High Performance Sheet of PBX based on NTO

3-nitro-1,2,4-triazol-5-one (NTO) is a low sensitive high explosive which has been used in the formation of low sensitive ammunitions. In this study, the preparation method of NTO explosive was discussed. A sheet of PBX on the basis of NTO bonded by HTPB binder matrix was prepared (NTO-PBX). The formulation is investigated for explosive properties to understand the influence of NTO on the performance of the PBX sheet. Impact and friction sensitivities of NTO-PBX, heat of Combustion and Detonation velocity were specified. EXPLO5 code, version 5.04, was utilized to calculate the theoretical detonation characteristics of NTO-PBX. For comparison, Data-sheetC, EPX-1, Semtex 1A and Formex P1, were also studied. By comparing the obtained results, confirmation of some relationships was investigated. The detonation velocity of the NTO sheet explosive was the highest of all the studied samples. The experimental and calculated results of NTO-PBX and the other compositions are in a good agreement.

Rheokinetic studies on the curing process of energetic systems containing RDX, HTPB with high content of 1,2-vinyl groups and hydantoin-based bonding agent

Series of rheokinetic studies involving pure HTPB with high content of 1,2-vinyl groups, binder systems with HTPB, IPDI and DBTDL, and energetic systems containing RDX, HTPB binder system and hydantoin-based bonding agent were conducted. Using the viscosity-temperature dependency of pure HTPB the VFT parameters were calculated. Next, pot-life and curing rate constants of HTPB/IPDI binder systems and kinetic parameters of Arrhenius and Eyring equations were determined. The influence of RDX and bonding agent on curing process of energetic systems was examined.

Anisotropic Reaction Properties for Different HMX/HTPB Composites: A Theoretical Study of Shock Decomposition.

Plastic-bonded explosives (PBXs) consisting of explosive grains and a polymer binder are commonly synthesized to improve mechanical properties and reduce sensitivity, but their intrinsic chemical behaviors while subjected to stress are not sufficiently understood yet. Here, we construct three composites of β-HMX bonded with the HTPB binder to investigate the reaction characteristics under shock loading using the quantum-based molecular dynamics method. Six typical interactions between HMX and HTPB molecules are detected when the system is subjected to pressure. Although the initial electron structure is modified by the impurity states from HTPB, the metallization process for HMX does not significantly change. The shock decompositions of HMX/HTPB along the (100) and (010) surface are initiated by molecular ring dissociation and hydrogen transfer. The initial oxidations of C and H within HTPB possess advantages. As for the (001) surface, the dissociation is started with alkyl dehydrogenation oxidation, and a stronger hydrogen transfer from HTPB to HMX is detected during the following process. Furthermore, considerable fragment aggregation is observed, which mainly derives from the formation of new C−C and C−N bonds under high pressure. The effect of cluster evolution on the progression of the following reaction is further studied by analyzing the bonded structure and displacement rate.

Research on Detonation Growth Characteristics of the Cast CL-20

In order to study the detonation growth characteristics of the cast CL-20, shock initiation experiments were carried out. The ∅50mm samples content of 84wt% CL-20, 5wt% mental fuel and 11wt% HTPB binder were prepared. The one-dimension Lagrangian gauge measuring method was used to obtain the pressure histories of the cast CL-20. The results showed that when the loading pressure decreased, the growth of the leading shock wave speed and the front pressure of the explosive slowed down and the time to form a stable detonation was longer. The binder elastomer network effectively reduced the shock wave sensitivity of the cast CL-20 and the critical initiation pressure is 1.40GPa∼2.17GPa. A two-dimension axisymmetric shock initiation numerical model was established. The adaptive genetic algorithm compiled by MatLab was used to call the nonlinear finite element fluid dynamics software (LS-DYNA) to calculate the reaction rate equation parameters of the ignition growth model of the cast CL-20 combined with the results of shock initiation experiments.

Enhancing the propulsion characteristics of rockets by adding the energetic Nitro-hydroxyl-terminated polybutadiene (NHTPB) in the propellant compositions

Replacing the inert binder by an energetic one could increase the specific impulse of the propellants and enhance the propulsion characteristics of rockets. In this study, Nitro-bhydroxyl-terminated polybutadiene (NHTPB) was prepared by a simple method. The prepared NHTPB in addition to HTPB binder were characterized. FTIR spectra of both HTBP and NHTPB was determined and compared. The thermal behavior of the prepared NHTPB was studied using DSC technique at heating rate 5 degree/min. A composite propellant based on AP/NHTPB was prepared and the specific impulse was measured for AP/NHTPB using two inch motor. It was concluded that the energetic nitro-hydroxyl-terminated polybutadiene has a clear max. exothermic peak at 203 °C with heat release of 323 J/g. By comparing the results, the prepared propellant AP/NHTPB has specific impulse higher than the traditional AP/HTPB propellant. NHTPB is a promising binder for the application of rocket propellants and needs more tests for its approval.

Mechanical Properties and Thermal Decomposition Behaviors of Hydroxyl‐Terminated Polybutadiene/Glycerol Propoxylate Blend and Its Application to Ammonium Nitrate‐Based Propellants

AbstractHydroxyl‐terminated polybutadiene (HTPB) is commonly used as a binder ingredient in composite propellants. In this study, a plasticizer was added to the binder to promote its plasticity and flexibility. Glycerol propoxylate (GPO) is a triol material with a zigzag structure, and it has one oxygen atom in a repeating unit. GPO would be a good plasticizer for HTPB binder to obtain good elasticity; furthermore, it would be suitable for improving the burning characteristics of the HTPB propellant. The addition of GPO to the HTPB binder was effective in extending the pot life and improving the mechanical properties of the propellant. The thermal decomposition behaviors of the HTPB/GPO blends were almost the same as that of the HTPB binder, except that the beginning consumption temperature of the blends was lower than that of HTPB. The ignitability at low pressure for the ammonium nitrate‐based propellant was improved by using the HTPB/GPO binder, whereas GPO did not enhance the burning rate of the propellant.

Cohesive finite element modeling of the delamination of HTPB binder and HMX crystals under tensile loading

Accurately modeling the mechanical behavior of the polymer binders and the degradation of interfaces between binder and crystal is important to science-based understanding of the macro-scale response of polymer bonded explosives. The paper presents a description of relatively a simple bi-crystal HMX-HTPB specimen and associated tensile loading experiment including computed tomography imaging, the pertinent constitutive theory, and details of numerical simulations used to infer the behavior of the material during the delamination process. Within this work, mechanical testing and direct numerical simulation of this relatively simple bi-crystal system enabled reasonable isolation of binder-crystal interface delamination, in which the effects of the complicated thermomechanical response of explosive crystals were minimized. Cohesive finite element modeling of the degradation and delamination of the interface between a modified HTPB binder and HMX crystals was used to reproduce observed results from tensile loading experiments on bi-crystal specimens. Several comparisons are made with experimental measurements in order to identify appropriate constitutive behavior of the binder and appropriate parameters for the cohesive traction-separation behavior of the crystal-binder interface.This research demonstrates the utility of directly modeling the delamination between binder and crystal within crystal-binder-crystal tensile specimen towards characterizing the behavior of these interfaces in a manner amenable to larger scale simulation of polycrystalline PBX materials. One critical aspect of this approach is micro computed tomography imaging conducted during the experiments, which enabled comparison of delamination patterns between the direct numerical simulation and actual specimen. In addition to optimizing the cohesive interface parameters, one important finding from this investigation is that understanding and representing the strain-hardening plasticity of HTPB binder is important within the context of using a cohesive traction-separation model for the delamination of a crystal-binder system.

Characterization of Aging Behavior of Butacene® Based Composite Propellants by Loss Factor Curves

AbstractButacene® is a polymeric binder with ferrocenyl groups chemically bonded to HTPB backbone. Through incorporation in the AP−Al composite propellant formulation, it leads to high burning rates (BR) >20 mm/s at 7 MPa, and low pressure exponents n<0.5, allowing more flexibility to the rocket design, keeping the characteristics (process, mechanical properties, pot‐life) of HTPB binder formulations together with a lower vulnerability (IM) contribution by Butacene®. The key molecular level characteristic of such HTPB based elastomeric binder systems of solid composite rocket propellants (SCRP) is the glass‐rubber transition region, which is mainly defined by the molecular mobility of the components in the polymeric network during the transition from energy to entropy elasticity with respect to temperature. The molecular rearrangement regions or binder mobility fractions related to the glass‐rubber transition of such composite propellants during storage are important in terms of in‐service time estimations. They are detectable by dynamic mechanical analysis (DMA). Formulations with and without Butacene® were prepared and analyzed using the loss factor curves obtained by torsion DMA. A special modelling with so named Exponentially Modified Gaussian (EMG) distribution was used to define and quantify sub‐transition regions in the loss factor curve. SEM images revealed the network formation connected with AP bonding, which correlate to the tensile results. DMA loss factors revealed a strong oxidation with Butacene® containing formulations during aging. Burning rates of the formulations show slight increases with aging.

HTPB 바인더의 화학적 구조에 따른 추진제의 유변학적, 기계적 특성 연구

HTPB 바인더의 화학적 구조에 따른 추진제의 유변학적, 기계적 특성 연구

Effects of Nano-Sized Al on the Combustion Performance of Fuel Rich Solid Rocket Propellants

Several industrial- and research – type fuel rich solid rocket propellants containing nano-metric aluminum metal particles, featuring the same nominal composition, were prepared and experimentally analyzed. The effects of nano-sized aluminum (nAl) on the rheological properties of metal/HTPB slurries and fuel rich solid propellant slurries were investigated. The energetic properties (heat of combustion and density) and the hazardous properties (impact sensitivity and friction sensitivity) of propellants prepared were analyzed and the properties mentioned above compared to those of a conventional aluminized (micro-Al, mAl) propellant. The strand burning rate and the associated combustion fl ame structure of propellants were also determined. The results show that nAl powder is nearly “round” or “ellipse” shaped, which is different from the tested micrometric Al used as a reference metal fuel. Two kinds of Al (nAl and mAl) powder can be dispersed in HTPB binder suffi ciently. The density of propellant decreases with increasing mass fraction of nAl powder; the measured heat of combustion, friction sensitivity, and impact sensitivity of propellants increase with increasing mass fraction of nAl powder in the formulation. The burning rates of fuel rich propellant increase with increasing pressure, and the burning rate of the propellant loaded with 20% mass fraction of nAl powder increases 77.2% at 1 MPa, the pressure exponent of propellant increase a little with increasing mass fraction of nAl powder in the explored pressure ranges.

Synthesis, Characterization and Properties of Nitropolybutadiene as Energetic Plasticizer for NHTPB Binder

The nitration of low molecular weight polybutadiene (PB) by a convenient and inexpensive procedure was investigated. To retain the unique physico-chemical properties of the plasticizer, it was nitrated to an extent of 10 % double bonds. The product nitropolybutadiene (NPB) was characterized by FT-IR and 1H NMR spectroscopy as well as GPC, DSC, and TGA methods. The kinetic parameters for the decomposition of NPB from room temperature to 400 °C were obtained from non-isothermal DSC. The changes in glass transition temperature (Tg) and inert uncured binder systems were used for determination of its efficiency as plasticizer. NPB was used in cured and unfilled nitro-hydroxyl terminated polybutadiene (NHTPB) binder. Isothermal thermogravimetric analysis (Iso-TGA) was employed to determine the migration rate in cured and unfilled HTPB binder systems compared to the dioctyladiphate (DOA) plasticizer. It was found that the exudation of the NPB plasticizer is slower than that of the DOA plasticizer. Thus, the NHTPB/NPB binder system (binder/plasticizer) presents more convenient mechanical properties than HTPB/DOA and is a promising new energetic binder system for polymer bonded explosives.

Thermal Decomposition Mechanism For Azidopolyester Based HTPB Binder By Using Pyrolysis-GC/MS

Thermal Decomposition Mechanism For Azidopolyester Based HTPB Binder By Using Pyrolysis-GC/MS

Study on catalysis effect of TEPB on the curing reaction of HTPB binder system

The catalysis effect of tri (exhoxyphenyl) bismuthine (TEPB) on the curing reaction of HTPB binder system was studied by using DSC method. The curing peak temperatures of the catalyst systems were measured to calculate kinetic parameters by using Kissinger and Crane methods, respectively. Two curing reaction kinetic equations were established. The results show that TEPB has high catalytic activity and can decrease the curing temperature of HTPB binder system, down to 35 °C, in which the optimum volume of TEPB is 0.5% of HTPB binder system.

Synthesis of Hydroxyl Terminated Epoxidized Natural Rubber as a Binder for Solid Rocket Propellant

Hydroxyl terminated epoxidized natural rubber (HTENR) was prepared by oxidative degradation of epoxidized natural rubber (ENR) with cobalt (II) acetylacetonate (co (II) aa) as a chemical agent in toluene as a solvent. Different of cobalt amount and reaction time used to study the effect on molecular weight. It was found that the number average molecular weight (Mn) and weight average molecular weight (Mw) depended on the reaction time and cobalt amount. Burning rate of solid propellant based on HTENR binder is 2.93mm/s which is approximately same with HTPB binder with 3.0mm/s. As a conclusion, HTENR binder is suitable to be used as a binder for solid rocket propellant.