Formulation and Characterization of a New Nitroglycerin‐Free Double Base Propellant

Double base propellants composed of nitrocellulose (NC) and nitroglycerine (NG) are widely used. However, the inclusion of liquid NG presents both stability and performance problems: the NG may migrate from the propellant in storage, and it softens the propellant at high inclusion levels. In this work, the novel nitrate ester 1,4‐dinitrato‐2,3‐dinitro‐2,3bis(nitratomethylene) butane (SMX) is considered as a replacement for NG in a double base propellant. Thermochemical calculations indicate improved performance when compared with the common double base propellant JA2 at SMX loadings above 40 wt‐%. Also, since SMX is a room temperature solid, migration may be mitigated. Both unplasticized and plasticized propellants were formulated to enable the study of the interaction of SMX with nitrocellulose. Thermal analysis of unplasticized propellant showed a distinct melt‐recrystallization curve, which indicates that a solid phase solution is being formed between SMX and NC, and that SMX would not act as plasticizer. Analysis of propellant prepared with diethyleneglycol dinitrate (DEGDN) plasticizer indicates that the SMX is likely dissolved in the DEGDN. The plasticized material also showed similar hardness and modulus to JA2. Safety characterization showed that sensitivity is similar to JA2. In short, replacing NG with SMX results in a new family of propellants with acceptable safety characteristics and which may also offer improved theoretical performance.     

热塑性聚氨酯弹性体在改性双基推进剂中的应用

为了改善力学性能,合成了与硝化甘油(NG)、硝化纤维素(NC)具有良好相溶性的新型热塑性聚氨酯弹性体(TPUE),并应用于改性双基推进剂研究中。研究了热塑性聚氨酯弹性体对硝胺改性双基推进剂的能量性能、力学性能、燃烧性能以及工艺性能的影响。结果表明,在改性双基推进剂中引入TPUE,推进剂的工艺性能、力学性能,尤其是低温力学性能明显提高,燃速和爆热会稍有降低。     

Preparation and Characteristics of Foamed NC‐Based Propellants

Foaming properties of the three NC‐based (nitrocellulose‐based) propellants, namely, single‐base propellant, NG (nitroglycerine) propellant and TEGDN (triethylene glycol dinitrate) propellant were investigated in the batch foaming process by using supercritical CO₂ as the physical foaming agent. Burning characteristics of the foamed NC‐based propellants were also investigated in this work. For this study, the CO₂ desorption of the three NC‐based propellants were plotted by the gravimetric method. The morphology and burning characteristics of these foamed NC‐based propellants were characterized by scanning electron microscope (SEM) and closed vessel experiment. The test data revealed that the energetic plasticizer has a considerable effect on the pore formation in the NC matrix although it has little effect on the CO₂ solubility in the NC‐based propellants. Moreover, the SEM images showed the foaming temperature also plays an important role in the pore parameters of foamed propellants. Furthermore, the data of closed vessel experiment indicated that the burning characteristics of foamed NC‐based propellants largely depend on the pore parameters, and the porous structure of foamed propellants would considerably increase the mass conversion rate.     

以NC和TMETN为基的微烟推进剂机械感度研究

研究了以硝化棉（ Ｎ Ｃ）和三羟甲基乙烷三硝酸酯（ Ｔ Ｍ Ｅ Ｔ Ｎ）为基的微烟推进剂的感度性能。结果发现：用 Ｔ Ｍ Ｅ Ｔ Ｎ 取代 Ｎ Ｇ,是实现双基推进剂低感性能的重要途径。 Ｎ Ｇ 被 Ｔ Ｍ Ｅ Ｔ Ｎ 取代后,推进剂的撞击感度和摩擦感度明显降低。也讨论了所用复合催化剂、消焰剂和低感度的含能添加剂对机械感度的影响。     

Smokeless GAP‐RDX Composite Rocket Propellants Containing Diaminodinitroethylene (FOX‐7)

Composite rocket propellants prepared from nitramine fillers (RDX or HMX), glycidyl azide polymer (GAP) binder and energetic plasticizers are potential substitutes for smokeless double‐base propellants in some rocket motors. In this work, we report GAP‐RDX propellants, wherein the nitramine filler has been partly or wholly replaced by 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7). These smokeless propellants, containing 60% energetic solids and 15% N‐butyl‐2‐nitratoethylnitramine (BuNENA) energetic plasticizer, exhibited markedly reduced shock sensitivity with increasing content of FOX‐7. Conversely, addition of FOX‐7 reduced the thermochemical performance of the propellants, and samples without nitramine underwent unsteady combustion at lower pressures (no burn rate catalyst was added). The mechanical characteristics were quite modest for all propellant samples, and binder‐filler interactions improved slightly with increasing content of FOX‐7. Overall, FOX‐7 remains an attractive, but less than ideal, substitute for nitramines in smokeless GAP propellants.     

CL-20基高能低特征信号推进剂性能初探

开展了CL－20含量对推进剂能量性能、安全性能、燃烧性能的影响研究,研究结果表明：随着CL－20含量增加,推进剂理论比冲、密度、爆热增加,推进剂药浆、药块机械感度（冲击感度和摩擦感度综合考虑）增加,推进剂的燃速增加,含CL－20的推进剂配方的静态压强指数均低于不含CL－20的推进剂配方的压强指数。CL－20含量相同时,以NG／TEGDN为增塑剂的推进剂压强指数与以NG／BTTN的相当。     

Development of Composite Solid Propellant Based on Nitro Functionalized Hydroxyl‐Terminated Polybutadiene

This paper presents an overview of a modified composite propellant formulation to meet future requirements. The composite propellant mixtures were prepared using nitro functionalized Hydroxyl‐Terminated Polybutadiene (Nitro‐HTPB) as a novel energetic binder and addition of energetic plasticizer. The new propellant formulation was characterized and tested. It was found that the Nitro‐HTPB propellant with and without energetic plasticizer exhibited high solid loading, high density, and reasonable mechanical properties over a wide range of temperatures. It was shown that the burning rate of Nitro‐HTPB propellant is up to 40% faster than that of the HTPB propellant. These results are encouraging and suggest that it should be possible to improve the ballistic performance of popular HTPB propellants through use of the studied Nitro‐HTPB binder.     

Optimization of Propellant Binders – Part Two: Macroscopic Investgation of the Mechanical Properties of Polymers

The development of new propellant binder systems requires the thermodynamic calculation of physico‐chemical data as well as the adaption of the mechanical properties in order to achieve a reliable innerballistic profile of the resulting propellant. Therefore, this study focuses on the mechanical properties of a binder system comprising GAP, NC as well as the energetic plasticizer DNDA and the curing agent Desmodur N100. By applying statistical methods, the mechanical properties of the binder can be predicted as a function of its composition. A macroscopic analysis of the interrelations between the E‐modulus, the ultimate tensile strength as well as the elongation at break and the specific deformation energy lead to the creation of failure master curves, which can be used as a rule of thumb criterion for the formulation of propellant binders.     

叠氮硝酸酯对硝胺改性双基推进剂燃烧性能的影响

研究了一种叠氮硝酸酯PDADN对硝胺改性双基推进剂燃烧性能的影响。结果表明添加叠氨酸酯是一种提高硝胺改性双基推进剂燃速与能量的切实可行途径。     

P(E-CO-T)-N100预聚物的合成、表征及其在改性双基推进剂粘合剂体系中的应用

用本体聚合法合成了含—NCO端基的P(E-CO-T)-N100预聚物体系,并对其在交联改性双基推进剂粘合剂体系中的应用进行了研究。红外数据确定P(E-CO-T)-N100体系的预聚反应时间是180 min,X-ray结果显示P(E-CO-T)-N100预聚物没有结晶峰,是无定形的。预聚物与推进剂的主要组分硝化甘油(NG)、一缩二乙二醇二硝酸酯(DEGDN)和硝化纤维素(NC)的溶度参数差均小于4×10-3J0.5m-1.5,具有良好的相溶性。P(E-CO-T)-N100预聚物的加入使粘合剂体系的交联密度由1.03×10-5mol.cm-3提高到了2.17×10-5mol.cm-3,并且随着溶棉质量比{(NG+DEGDN)与〔NC+P(E-CO-T)-N100〕的质量比}的提高,粘合剂体系的交联密度(XLD)、凝胶分数(V2)、压缩模量Ep均急剧下降,而平均相对分子质量增大,说明网络结构逐渐松散,力学性能下降。常温力学性能数据显示,P(E-CO-T)-N100预聚物上的活性—NCO与NC上的—OH进行了交联,使粘合剂体系的延伸率达到191.70%,提高了73.48%。     

Neutral Polymeric Bonding Agents (NPBA) and Their Use in Smokeless Composite Rocket Propellants Based on HMX‐GAP‐BuNENA

Very few efficient bonding agents for use in solid rocket propellants with nitramine filler materials and energetic binder systems are currently available. In this work, we report the synthesis, detailed characterization, and use of neutral polymeric bonding agents (NPBA) in isocyanate‐cured and smokeless composite rocket propellants based on the nitramine octogen (HMX), the energetic binder glycidyl azide polymer (GAP), and the energetic plasticizer N‐butyl‐2‐nitratoethylnitramine (BuNENA). These polymeric bonding agents clearly influenced the viscosity of the uncured propellant mixtures and provided significantly enhanced mechanical properties to the cured propellants, even at low NPBA concentrations (down to 0.001 wt‐% of propellant). A modified NPBA more or less free of hydroxyl functionalities for interactions with isocyanate curing agent provided the same level of mechanical improvement as regular NPBA containing a substantial number of reactive hydroxyl groups. However, some degree of reactivity towards isocyanate is essential for function.     

BuNENA含能增塑剂的性能及应用

BuNENA(N–丁基硝氧乙基硝胺)是一种性能优良的新型含能增塑剂,在枪炮发射药和火箭推进剂应用中均受到研究者的广泛关注,并被进行系统研究。在发射药中,BuNENA具有塑化能力强、工艺性能好、感度低、能量高等优点,能进一步提高配方力学性能,其应用前景广阔。而在HTPE(端羟基聚环氧乙烷–四氢呋喃嵌段共聚醚)火箭推进剂中,BuNENA已被证明是一种对提高能量、降低感度和提高推进剂力学性能等具有明显作用的新型含能增塑剂,使用HTPE/BuNENA黏合剂体系的钝感固体推进剂的综合性能优于HTPB/AP(端羟基聚丁二烯/高氯酸铵)推进剂,并可满足钝感弹药(IM)要求,已在各种战术发动机中获得了实际应用。     

Studies on n‐Butyl Nitroxyethylnitramine (n‐BuNENA): Synthesis,Characterization and Propellant Evaluations

The laboratory synthesis of the energetic plasticizer n‐buNENA was scaled up to one kg batch size and the compound was fully characterized by spectral data and elemental analysis. N‐buNENA was formulated with CMDB and EDB propellant compositions. The results showed an improvement in mechanical properties and burning rate over a wide range of pressure along with acceptable limits of hazard and thermal stability as compared to DEP based propellant systems.     

Effect of nitrocellulose (NC) on morphology,rheological and mechanical properties of glycidyl azide polymer based energetic thermoplastic elastomer/NC blends

As a new kind of propellant binder, energetic thermoplastic elastomer (ETPE ) can improve propellant recyclability and environmentally friendly disposal. The rheological behavior of the ETPE binder can be beneficial to identify suitable and safe conditions for processing ETPE propellants. In this paper, ETPE /nitrocellulose (NC ) blends with different mass ratios of NC to ETPE were prepared by the physical mixing method. The heat of explosion and the morphological, thermal, mechanical and rheological properties of the resulting blends were studied systematically. It was found that the heat of explosion of ETPE /NC blends increased with increasing NC content. SEM images showed that the NC domains in the blends changed from tiny pieces to fibers with increasing NC mass ratio, which indicates phase separation in the blends. The tensile mechanical properties of the blends had a peak value when the NC content was 10 wt%, and then increased with the increasing addition of NC . The thermal behavior made clear that the ETPE and NC were partially miscible. Rheological studies on dynamic strain sweep and frequency sweep demonstrated that the content of NC in the blends had a monotonic effect on their rheological properties at 130 °C. Rheological studies also showed that the rheology of the blends is dependent on temperature. The Cole ? Cole and Han plots confirmed phase separation in the blends. © 2016 Society of Chemical Industry     

含CL-20、DNTF和FOX-12的CMDB推进剂的热分解

用PDSC研究了添加CL-20（或DNTF或FOX-12）的改性双基推进剂的热分解行为.发现PDSC曲线中CL-20、DNTF推进剂有两个放热峰,第一个为双基黏结剂的分解峰,第二个为CL-20或DNTF的分解峰.FOX-12改性双基推进剂只有一个分解峰,表明FOX-12和双基黏结剂（NC、NG等组分）一起分解.     

Viscoelastic behavior of hydroxyl terminated polybutadiene containing glycerin

Hydroxyl terminated polybutadiene (HTPB) is widely used as a propellant binder. A plasticizer is usually added to improve the processing properties, the mechanical properties, and the burning characteristics of the propellant. Glycerin was found to be an effective additive to improve these properties. The glycerin/HTPB blend was hard enough to act as a binder for the composite propellant when the glycerin/HTPB mole ratio was less than 10. Only a small quantity of glycerin was incorporated into the network structure of the cured HTPB. Most of the added glycerin physically entered the voids in the network of the cured HTPB. Addition of a small quantity of glycerin (mole ratio less than 0.1) significantly altered the network density and the viscoelastic properties of the blends. The properties were only slightly dependent on the amount of the added glycerin in the mole ratio range of 0.1–10. The dangling ends were formed in the HTPB network by the addition of glycerin and the network structure was loosened, thereby enhancing the mobility of the chain segment. The viscoelastic properties of the blends followed the time‐temperature superposition principle, and the properties were estimated accurately by the Williams‐Landel‐Ferry approach. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Experimental Research on Cohesion and Internal Friction Angle of the Double‐base Propellant

A conventional triaxial confining pressure test was designed to suit the working environment of propellant grain. The mechanical properties of the double‐base propellant under varied confining pressure conditions were studied and analyzed. The results show that confining pressures have a pronounced influence on the mechanical properties of propellant materials. The yield value and compressive strength of propellant material increase as the confining pressure increases. The propellant material shows great ductility before it is destroyed, the ductility of propellant material increases with an increase in the confining pressure. The yield values and failure values of the propellant materials show linear relationships with the confining pressures. According to the Mohr‐Coulomb theory, the cohesion and internal friction angle of the double‐base propellant material were obtained. The influence factors of cohesion and internal friction angle of the double‐base propellant material are analyzed. The failure process and mechanism of propellant materials under varying confining pressures were studied. These projects have contributed to the understanding of the innate character of propellant materials and explain the damage and destruction of the structures and components. With this information, measures can be taken to improve the quality and structural performance of propellant grain. The information collected herein may lay the foundation for yield criteria and viscoelastic‐plastic constitutive model of propellant materials.     

Synthesis of GAP-PB-GAP Triblock Copolymer and Application as Modifier in AP/HTPB Composite Propellant

A new triblock copolymer polyglycidylazide-block-polybutadiene-block-polyglycidylazide (GAP-PB-GAP) has been synthesized. The synthesis was done by cationic ring opening polymerization of epichlorohydrin (ECH) with HTPB as the alcohol and boron trifluoride etherate as the catalyst followed by the conversion of the -CH₂Cl group into -CH₂N₃ group. The presence of the azido groups in the GAP polymer chain makes it more energetic and the triblock copolymer can be used as an energetic binder/additive for propellant energy modification. Since the triblock copolymer has polybutadiene (PB) as the central block, which is from HTPB itself, it can be used as an additive in HTPB based polymeric formulations to improve their properties. In the present work, a part of HTPB, the propellant binder in ammonium perchlorate (AP)/HTPB propellant was removed and replaced with the GAP-PB-GAP copolymer. Burn rate, mechanical properties, and heat of combustion properties of these propellants were measured and compared with the unmodified HTPB/AP propellant. The results show that the burn rate of the HTPB/AP solid propellant could be enhanced by the addition of the triblock copolymer.     

Volatility of NENA and Other Energetic Plasticizers determined by thermogravimetric analysis

Thermogravimetric analysis (TGA) at constant temperature was used to measure weight loss of plasticized nitrocellulose (NC) propellants due to vaporization of plasticizer. Plasticizers consisted of three 2-nitroxyethylnitramine (NENA) compounds, diethylene glycol dinitrate (DEGDN), and nitroglycerin (NG). Initial concentration of plasticizer and degree of nitration of NC were also varied. Each propellant was tested at three temperatures. Plasticizer diffusivities (D) and their activation energies were calculated. Observed trends were generally consistent with calculated plasticizer solubility parameters, expected increases in molecular mobility for more highly plasticized materials, and the more polar and more disordered structure of NC with a lower degree of nitration. Some unexpected effects could be explained by changes in entropy of activation due to variation in plasticizer or NC structure. In general, the NENA plasticizers had lower vaporization rates than DEGDN or NG, suggesting that plasticizer losses during manufacturing or storage of practical formulations should not be a problem.     

Analysis for Decomposition Characteristics and Piecewise Thermokinetics of Nitramine Modified Double‐base Propellant with High Solid Content

The thermal stability and decomposition characteristic of nitramine modified double‐base propellant (RDX‐CMDB propellant) with high solid content and its components were investigated under dynamic and isothermal conditions by differential scanning calorimetry (DSC). It was found that the mixture of nitrocellulose (NC) and nitroglycerin (NG) had a promote effect on the decomposition of RDX. The activation energy (E ) and the pre‐exponential factor (A ) of two obviously exothermic processes were obtained by Friedman iso‐conversional method. The screening method suggested by ICTAC was used to determine the most probable mechanism functions and kinetic parameters of the two processes which are corresponding to the deceleration model and the autocatalytic model. The theoretical value was consistent with the experiment result.