Rocket Propellants Research Articles

Understanding the reactivity of magnesium powder subjected to various aging conditions

Metal fuels are emerging as one of the promising alternatives to fossil fuels by providing considerable heat energy without CO2 generation. In particular, magnesium (Mg) is utilized in rocket propellants, fuel cells, and energy storage systems by virtue of its high reactivity, great energy density, and low cost. While its performance degradation when exposed to both short-term and prolonged storage conditions is expected, the clear aging characteristics have not been explained in the past. Two products of hygrothermal aging process of Mg are identified as Mg(OH)2 and MgO, where Mg(OH)2 decomposes at a relatively low temperature for accelerating the oxidation process while MgO tends to desensitize the reactivity of Mg by the surface oxidation of particles. Here, a decreased on-set reaction temperature or enhanced reactivity is observed on relatively short-term aged samples, which is attributed to the formation of Mg(OH)2. For accelerated aging conditions beyond 25 weeks, the oxide film covers the entire particle surface, and thus only the core oxidation could occur, which results in an increase of activation energy. This observation is contrary to the decreased reactivity of metal fuels subjected to aging in general. Moreover, the reactivity based on the stoichiometry is examined by varying the amount of oxygen supplied. The activation energy for long-term aging periods tended to increase under oxygen-rich condition, which can be ascribed to the reaction between Mg(OH)2 and O2. Also, the effects of the generation or the decomposition of various intermediates of the oxidation process can be included. Thus, the present study identified the peculiar enhancement of reactivity of Mg subjected to hygrothermal aging and further clarified the roles of surface and core oxidations as they both affect the reactivity under the oxygen enrichment conditions.

Comprehensive ignition characterization of a non-toxic hypergolic hybrid rocket propellant

This paper describes a comprehensive characterization of ignition properties of a metal-hydride based non-toxic hypergolic hybrid rocket propellant. The propellant consists of Rocket Grade Hydrogen Peroxide (RGHP) as oxidizer, high-density Polyethylene (HDPE) as fuel and sodium borohydride (NaBH4) as the additive, embedded in the HDPE matrix. Ignition quality was characterized as ignition delay, ignition probability and flame spread. In a drop-test setup, ignition characteristics were determined as a function of seven parameters: RGHP concentration, additive loading, oxidizer droplet impact velocity, oxidizer droplet volume, pressure, diluent gas, and environmental exposure. The parameters encompass thermo-chemical, fluid/droplet dynamics and environmental factors affecting ignition. Ignition delays as low as 3 ms were observed, one of the lowest using non-toxic hypergolic hybrid propellants in open-air. An overwhelming majority of conditions tested yielded <10 ms ignition delays and 100% ignition success. All conditions tested affected ignition to varying degrees with RGHP concentration, NaBH4 loading and drop impact velocity significantly affecting ignition. Further, contrary to expectations, exposing sanded fuel samples to humidity for a few h enhanced ignition instead of hampering it and exposure for 24 h did not lead to ignition degradation. Tests with diluent gases other than air (at atmospheric and elevated pressures) revealed that atmospheric oxygen played a negligible role in the reaction process. This proved that oxygen for the initial ignition event was obtained from RGHP decomposition, with atmospheric oxygen playing no role in ignition performance. Aside from demonstrating excellent ignition characteristics, our results further show a need to go beyond thermo-chemical properties and to consider aspects of ignition other than ignition delay in hypergolic propellant research to enable a complete understanding of the ignition processes. The comprehensive ignition characterization demonstrates the chosen propellant's ability to overcome ignition challenges in hybrid rockets and serves as a proof of concept for its further development.

Numerical investigation of pyrolysis and surface coking of hydrocarbon fuel in the regenerative cooling channel

Fuel pyrolysis is a common phenomenon in regenerative cooling channels. However, the alkenes and aromatic hydrocarbons produced by thermal cracking tend to deposit on the channel surface, leading to local heat transfer deterioration, corrosion resistance reduction, or blockage. This study establishes a numerical investigation at a supercritical pressure to evaluate the fuel flow effects on thermal cracking and surface coking. The results indicate a threshold of fuel flow rate or conversion rate that can improve the utilization of chemical heat sink. The threshold of the conversion rate for RP-3 fuel (Rocket Propellant No. 3 jet fuel) is around 80%, exceeding which will reduce the benefits of fuel endothermic pyrolysis. Moreover, a critical criterion of buoyancy parameter has been proposed for the severe pyrolysis of RP-3 fuel. In addition, the variation of fuel flow significantly influences the distribution of wall temperature and coking precursors, which further affects the coke layer thickness.

Understanding the pyroelectric combustion behaviour of metallized electrically controlled solid propellants

Solid rocket propellants that demonstrate variable burning rates are highly desirable in various propulsion applications. Electrically controlled solid propellants (ECSPs) are one such kind that ignite and combust only when external electric power is applied, which enables to adjust/control their combustion rates. However, the knowledge on their combustion mechanisms is scant in the limited literature. In this study, pyroelectric combustion behaviour of metallized ECSPs, based on lithium perchlorate (LP) and poly vinyl alcohol (PVA), containing 5%, 10%, and 15% tungsten (W) are investigated, in comparison to the non-metallized baseline propellant. Theoretical performance parameters, heat release and mass loss from decomposition process, and combustion rates are obtained. Pyroelectric combustion of ECSPs involves electrolytic decomposition of LP producing oxidizer species, which react with fuel species from PVA and/or W in thermochemical reactions, to generate heat and products including LiCl, HCl, LiOH, WO3, etc. Results indicate that addition of W reduces the theoretical adiabatic combustion temperature and overall heat release from exothermic decomposition by 19% and 36% respectively, in ECSP-M15 containing 15% W, compared to the baseline case. However, relatively low voltage response time for metallized ECSPs implies that their ionic conductivity is higher than the baseline ECSP. More importantly, combustion rates of all ECSPs increase exponentially with increase in applied initial voltage in the 100–500 V range. Inclusion of W enhances the combustion rates significantly by 4.9 times at 100 V and by 1.7 times at 500 V for ECSP-M15 relative to the baseline propellant. This signifies that electrochemical mechanisms become the rate controlling step at high electric power, in governing the pyroelectric combustion behaviour of ECSPs. Further, these propellants were successfully tested for multiple burn/no-burn conditions under the application/removal of the external electric power, which is highly desirable for various propulsion systems.

Enhanced performance of barium and cobalt doped spinel CuCr2O4 as decomposition catalyst for ammonium perchlorate

The spinel oxide, CuCr2O4 is well known for its catalytic applications. In this study an attempt was made to explore the catalytic effects of CuCr2O4 and Barium and Cobalt doped CuCr2O4 on the thermal decomposition of ammonium perchlorate (AP), a widely used rocket propellant oxidizer. The nano catalysts were prepared by hydrothermal method and characterized by Powder XRD, SEM, TEM and BET. The nano catalyst embedded AP samples were prepared and thermogravimetric analysis was carried out to evaluate the effect of prepared nano catalysts on the AP thermal decomposition process. The prepared nano catalysts were efficient in lowering the decomposition temperature, among which highest efficiency was shown by cobalt doped CuCr2O4. Pure AP showed decomposition at 356 ​°C whereas catalyzed samples showed decomposition below 309 ​°C. Further, an attempt was made to elucidate the possible decomposition mechanism by Coats-Redfern method.

Aziridine type bonding agents for composite solid rocket propellant

Bonding agents, as a paramount component in the composite solid rocket propellant, effectively enhance the interactions between polybutadiene matrix and oxidizer. It mainly affects the processing ability, mechanical behavior, and aging. Bonding agent plays the role of an anonymous soldier to defeat stresses produced by loading conditions, changes in the environmental condition, and transportation of composite propellant. The role and the mechanism of aziridine type bonding agents are discussed focusing on a novel MST aziridine bonding agent (Tris-(2-methyl-1-aziridinyl) phosphine oxide (MAPO) plus Stearic acid plus Tartaric acid) (poly (isopropylamine N(2-methyl-1-aziridinyl) phosphine oxide octadecanoic)-co-(isopropylamine tartrate)). Preparation of composite solid propellant samples containing the same weight percentage of different bonding agents is conducted. Mechanical properties and aging behavior for the prepared samples were monitored to extract the impact of bonding agent type. Mechanical properties of the bonding agents were recorded at three different temperatures in order to simulate various environmental conditions. Results of stress-strain responses during uniaxial tensile tests showed that MST bonding agent has the strongest interaction with solid particles reaches a value of 50.4 % strain and 8.052 Kg/cm2 stress at normal conditions. Compared to MT-4 (produced from the reaction of 2 moles MAPO plus 0.7-mole Adipic acid and 0.3-mole Tartaric acid) and MAPO, MST improved the aging behavior.

Study of Elastomeric Heat Shielding Materials for Solid Rocket Motor Insulation

Thermal insulation of solid rocket motor casing is necessary to overcome the catastrophic breakdown during the rocket propellant combustion. In our study, a comprehensive review on different types elastomeric heat shielding materials (EHSMs) such as polyurethane, silicon rubber, ethylene propylene diene monomer (EPDM) and nitrile rubber was conducted. Various types of fillers are added to the EHSMs to enhance their thermal, mechanical and ablative performances. The charring phenomenon, which offers a means of protection to the virgin polymer layer from direct flame, as well as the synergetic effect, that may occur between fillers and polymer matrices, were studied. All different methods and machines used for manufacturing EHSMs are described in detail. Moreover, the different techniques used to characterize the EHSMs are discussed. Last but not least, the empirical models that relate the thermal insulation performance to the filler concentration are presented.

Thermal decomposition and kinetic modeling of HNTO/AN-based composite solid propellant in the presence of GO-based nanocatalyst

The present study has been conducted to investigate the characteristics of composite solid propellant (CSP) based on hydrazinium 3-nitro-1,2,4-triazol-5-one and ammonium nitrate (HNTO/AN) cocrystal as an oxidizer and hydroxyl-terminated polybutadiene (HTPB) as a binder, supplemented with or without nanocatalyst (triaminoguanidine-transition iron, containing graphene oxide). NASA Lewis Code, Chemical Equilibrium with Application (CEA), has been used to select the optimal formulation through the evaluation of the theoretical performance. Compared to the AP/HTPB baseline formulation, the developed one presents promising properties since it may deliver an interesting specific impulse value (231 s−1). On the other hand, based on the DSC data, the kinetic triplet of the studied samples was determined using four model-free integral methods, namely, it-KAS, it-FWO, VYA, and TAS. It was observed that the decomposition peak temperature (Tp) and the activation energy (Ea) decreased obviously after the addition of the nanocatalyst. This study will certainly motivate further researches in the field of energetic cocrystals and graphene-based materials expected to be used in solid rocket propellant formulations.

Reductive transformation of the insensitive munitions compound nitroguanidine by different iron-based reactive minerals

Nitroguanidine (NQ) is an emerging contaminant being used by the military as a constituent of new insensitive munitions. NQ is also used in rocket propellants, smokeless pyrotechnics, and vehicle restraint systems. Its uncontrolled transformation in the environment can generate toxic and potentially mutagenic products, posing hazards that need to be remediated. NQ transformation has only been investigated to a limited extent. Thus, it is crucial to expand the narrow spectrum of NQ remediation strategies and understand its transformation pathways and end products. Iron-based reactive minerals should be investigated for NQ treatment because they are successfully used in existing technologies, such as permeable reactive barriers, for treating a wide range of organic pollutants. This study tested the ability of micron-sized zero-valent iron (m-ZVI), mackinawite, and commercial FeS, to transform NQ under anoxic conditions. NQ transformation followed pseudo-first-order kinetics. The reaction rate constants decreased as follows: commercial FeS > mackinawite > m-ZVI. For the assessed minerals, the NQ transformation started with the reduction of the nitro group forming nitrosoguanidine (NsoQ). Then, aminoguanidine (AQ) was accumulated during the reaction of NQ with m-ZVI, accounting for 86% of the nitrogen mass recovery. When NQ was reacted with commercial FeS, 45% and 20% of nitrogen were recovered as AQ and guanidine, respectively, after 24 h. Nonetheless, NsoQ persisted, contributing to the N-balance. When mackinawite was present, NsoQ disappeared, but AQ was not detected, and guanidine accounted for 11% of the nitrogen recovery. AQ was ultimately transformed into cyanamide, whose dimerization triggered the formation of cyanoguanidine. Alternatively, NsoQ was transformed into guanidine, which reacted with cyanamide to form biguanide. This is the first report systematically investigating the NQ transformation by different iron-based reactive minerals. The evidence indicates that these minerals are attractive alternatives for developing NQ remediation strategies.

Hydrogenation reactions of kerosene on nickel-based catalysts

The hydrotreating of kerosene was studied to develop a crude kerosene distillate to produce products with specifications suitable for marketing as kerosene and rocket grade fuel. To saturate the aromatic structures from kerosene, hydrogenation experiments were carried out in a batch steel reactor with different amounts (20 ml and 40 ml) of crude kerosene, using silica-supported nickel and kieselguhr supported nickel-sulfur catalysts. The catalysts were analyzed with Brunauer, Emmett ve Teller (BET), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and x-ray diffraction analysis (XRD). The aromatic fractions and paraffin structures content of the obtained samples were examined. The experiments were carried out at 200–220 °C temperature with 5 bar hydrogen initial pressure for 2 h. The obtained products were analyzed by performing a 1H NMR analysis. According to proton NMR result, the ratio of paraffinic methylene, beta methyl, epsilon methylene groups of 20 ml crude kerosene with kieselguhr supported nickel-sulfur is more than 4.5 times compared to crude kerosene, and % the percentage of aromatic hydrogen structures of it is two times lower. As a result of hydrogenation experiments with both nickel-based catalysts, aromatic hydrogen structures in crude kerosene were reduced. The total H/C ratio of rocket grade hydrocarbon fuels increased after hydrogenation experiments. For this reason, the scope of ongoing research can be extended to hybrid rocket propellants (SP-1) used in hybrid rocket engines.

Intelligent and Robust Controller Tuned with WOA: Applied for the Inverted Pendulum

Inverted pendulum is a well-known problem in the control theory because several systems such as robot balancing, Segway, hover board riding and operation of a rocket propeller are inherently based on Inverted Pendulum, furthermore it possesses a height non-linear and unstable dynamics. The main objective of our study is to introduce a comparative analysis of fuzzy logic (FLC), radial basis function neural network (RBF) and integral sliding mode control (ISMC) tuned with whale optimizer algorithm (WOA) for the control of the angle position and velocity of the inverted pendulum system. The implemented controller schemas can adequately reflect and approximate a certain type of uncertainties, nevertheless their parameters should be fine-tuned in order to get height and efficient performance, therefore all the antecedents and consequences of those controllers were tuned with WOA. This later provide height accuracy and fast convergence with height dimensional cost function. Comparative results shows that ISMC-WOA outperforms other techniques in term of settling time and overshoot.

Working Fluid modeling Based on Air Turbine Rocket Engine and Propellant Comparative Analysis

The propellant of the Air Turbo Rocket (ATR) engine is burned in the gas generator to produce primary gas. This paper uses the established ATR engine working fluid calculation model to calculate the physical parameters and components of the primary gas produced by the combustion of four propellants at a given pressure and temperature, and compares and analyzes them according to the propellant selection requirements, Choose the appropriate propellant for the ATR engine.

HYBRID ROCKET PROPULSION DEVELOPMENT AND APPLICATION.

Satellite technology is advancing. Satellite propulsion requires several desired rocket properties. This is necessary for 1 kg of payload. Launch vehicles no longer need rocket engines. Application includes satellite movement, orbit transfer, and probe and lander propulsion. Space travel is inventive and exciting. Research, production, and use costs must be decreased to make space transportation systems generally available. Security shouldn't be affected. Rocket propellants must be high-performing, non-toxic, and safe. Rocket engines have other parts. Restarting and throttling are crucial. These are inaccessible to solid rocket motors. Developing a liquid rocket engine is hard and expensive, but it can be restarted and throttled. It's being studied for use in hybrid rocket propulsion and other space applications. Space tourist vehicles, lunar and planetary landers, suborbital launch vehicles, satellite maneuvering systems, etc. are potential applications for microsatellites (including orbit transfer). More of these applications are pending approval. Hybrid propulsion is straightforward, safe, and permits regenerative braking, throttling, and restarting. Hybrid propellants are mostly non-toxic and storable. Separate oxidizer and fuel storage enhance safety. This study examines the history, development, current applications, and future of hybrid rocket propulsion. We'll discuss popular fuels and oxidizers. Explains hybrid rocket motor's low regression rate. The article includes the author research.

Bimetallic ruthenium compound derived from 6,12-dihydroindeno[1,2-b]fluorene ligand as burning rate catalyst for solid rocket motor propellant

We reported the synthesis of a novel bimetallic compound with the formula [(Cp*Ru)2-IF] derived from 6,12-dihydroindeno[1,2-b]fluorene ligand (IFH2). This compound was characterized by 1H and 13C NMR, elemental analysis, FT-IR, and UV-vis.The bimetallic compound was tested as a burning rate catalyst on the thermal decomposition of ammonium perchlorate. It was assessed by differential scanning calorimetry technique (DSC) analysis to understand its catalytic behavior further. [(Cp*Ru)2-IF] shows a decrease in the decomposition temperature of AP to 381°C, increasing the energy release to 1271 J•g−1. In addition, this compound leads to the lowest activation energy (20.7 kJ•mol−1), suggesting a suitable and competitive alternative to be used as a modifier for composite solid propellants.

Wavelength-modulation spectroscopy in the mid-infrared for temperature and HCl measurements in aluminum-lithium composite-propellant flames

This work presents the design, development, and application of a laser-absorption-spectroscopy diagnostic capable of providing quantitative, time-resolved measurements of gas temperature and HCl concentration in flames of metallized composite propellants containing ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene (HTPB). This diagnostic utilizes a quantum-well distributed-feedback diode laser emitting near 3.27 μm to measure the absorbance spectra of HCl using a scanned-wavelength-modulation-spectroscopy technique that is insensitive to non-absorbing transmission losses caused by metal particulates in the flame. This diagnostic was applied to characterize the spatial and temporal evolution of temperature and HCl mole fraction in small-scale flames of AP-HTPB composite propellants containing either an aluminum-lithium alloy or micron-scale aluminum. Experiments were conducted at 1 and 10 atm. At both pressures, the flame temperature of the aluminum-lithium propellant, on a time-averaged basis, was 80 to 200 K higher than that of the aluminum propellant (depending on location in the flame) indicating more complete combustion. In addition, the mole fraction of HCl in the aluminum-lithium propellant flame reached values 65–70% lower than the conventional aluminum-propellant flame at the highest measurement location in the flame. The measurements at both pressures showed similar trends in the reduction of HCl in the aluminum-lithium propellant flame but at elevated pressures this occurred on a length scale nearly an order of magnitude smaller than the flame at atmospheric pressure. The results presented further support that the use of an aluminum-lithium alloy is effective at reducing HCl produced by the propellant flame without compromising performance, thereby making it an attractive additive for solid rocket propellants.

On the Use of Fluorine‐Containing Nano‐Aluminum Composite Particles to Tailor Composite Solid Rocket Propellants

AbstractThe burning rate of solid propellants is an important factor for optimizing rocket motors and improving performance. The enhanced burning rate can increase thrust and reduce a propulsion system‘s overall size and weight. In this study, a novel nano‐aluminum/THV composite additive was prepared and introduced into a solid ammonium perchlorate/polybutadiene composite solid rocket propellant to enhance its burning rate. The morphology of the composite particle additive and its effects on combustion were characterized. The use of small quantities (&lt;15 wt.%) of the additive resulted in a burning rate enhancement of up to 2.1 times that of the conventional coarse aluminized propellant with a specific impulse loss of only 3 seconds, and as much as 4.7 times enhancement with a predicted loss of 22 seconds in theoretical specific impulse. Some of this loss may be recovered by the improved combustion efficiency in smaller rocket motors because the additive was shown to significantly reduce the aluminum agglomeration at the propellant burning surface and reduce the size of reaction products which may reduce two‐phase flow losses. The additive also provides wide burning rate tailorability, favorable for motor, grain, and thrust curve design. The burning rate enhancement mechanism is thought to be a physical cratering mechanism governed by the burning rate disparity between the binder/oxidizer system and the nano‐aluminum/fluoropolymer additive and not a chemical catalytic effect.

Combustion and Thermal Decomposition Research on 1,2‐Dicyclopropyl‐1‐Methyl Cyclopropane (DMCP) as High Energy Fuel for Liquid Rocket Propellants

Abstract1,2‐Dicyclopropyl‐1‐methyl cyclopropane (DMCP) was found a high‐energy liquid hydrocarbon propellant. A model combustion chamber was designed and manufactured to investigate the combustion performance of DMCP and Chinese rocket kerosene (RK) in comparison. Due to the higher density of DMCP, its orifice flow coefficient was 3.4 % larger than that of RK. The chamber pressure fluctuation amplitude of DMCP was within 10 % of the average pressure value. Under typical conditions, the flame intensity of DMCP combustion flame was more intense than that of RK. When the mixture ratios varied from 2.0–2.8, the characteristic velocity changes of DMCP were between 1626 m/s and 1636 m/s. It was not apparent that the characteristic velocity of DMCP was affected by the change of mixture ratio. The combustion efficiency of DMCP increased with the rise of its mixture ratio (varying between 0.902 and 0.921), higher than that of RK in a low mixture ratio. The apparent activation energy values (E) of DMCP were 202.0 kJ ⋅ mol−1 and 202.9 kJ ⋅ mol−1, respectively, according to Kissinger and Flynn‐Wall‐Ozawa (FWO) equations.

4‐Amino‐1‐Butyl‐1,2,4‐Triazolium Dinitramide – Synthesis, Characterization and Combustion of a Low‐Temperature Dinitramide‐Based Energetic Ionic Liquid (EIL)

AbstractSalts being liquid below 100 °C are defined as ionic liquids. Due to their unique properties, they are attracting increasing interest and are also being investigated in the field of energetic materials. Combining nitrogen‐rich cations and oxygen‐rich anions, it is possible to obtain energetic ionic liquids (EILs). Potential applications are plasticizers, high explosives, gun and rocket propellants. However, only few works have been done in the field of EILs which show a glass transition temperature less than −40 °C, the so called low‐temperature EILs (LT‐EILs). LT‐EILs with dinitramide as an anion are an almost unknown group with interesting properties and potential. In this paper we present synthesis, characterization and combustion properties of 4‐amino‐1‐butyl‐1,2,4‐triazolium dinitramide (C4 DN) as a low temperature dinitramide‐based EIL in its entirety for the first time. A classic synthesis route and a metal‐free route are presented. The physical properties were measured and compared to conventional non‐ionic energetic plasticizers like BDNPA/F, TMETN/BTTN, Bu‐NENA and DNDA‐57. The combustion behaviour was studied using an optical window bomb and compared to non‐ionic energetic liquids in use. To evaluate the performance as an energetic plasticizer or additive, the interaction with the energetic binder GAP is investigated by manufacturing of dog bone‐shaped test specimen and comparing their mechanical properties and their glass transition temperatures with conventional energetic plasticizers, based on non‐ionic energetic compounds. As one result, C4 DN showed an intense softening effect. Based on the result, propellant samples were prepared and characterized.

RRx-001 and the “Right stuff”: Protection and treatment in outer space

From antibiotics to aspirin to antimalarials and to anticancer agents, about half of the world's best-selling drugs are derived from nature. However, accelerating climatic disruption, habitat destruction, pollution, and biodiversity loss all negatively impact the potential of natural sources to continue to serve as repositories of novel pharmaceuticals. On that basis, the final frontier for drug development is perhaps not the rainforests, coral reefs, and other natural habitats but rather the aerospace industry with its virtually unlimited and inexhaustible man-made ‘library’ of potentially bioactive compounds. The first aerospace-sourced therapeutic to reach the clinic is RRx-001, an inhibitor of the NOD-like receptor - Nucleotide-binding oligomerization domain with Leucine rich Repeat and Pyrin domain (NLRP3) inflammasome in a Phase 3 trial for the treatment of small cell lung cancer (SCLC) and in a soon-to-start Phase 3 trial for protection against chemoradiotherapy-induced severe oral mucositis in first line head and neck cancer. As manned missions to the Moon, Mars, and asteroids as well as space tourism beckon, it is perhaps fitting that a compound like RRx-001, which is derived from 1,3,3-Trinitroazetidine (TNAZ), an explosive propellant for rockets, is a potential "all purpose" option to mitigate the major biomedical effects of space radiation exposures including cancer development and other tissue degenerations both within mission and after mission. This article highlights the promise of RRx-001 to attenuate the acute and late effects of radiation exposure on astronauts including the development of cancer.

Investigation of the Gum Stock Behavior of Polyurethane Crosslinking Matrix by Adding Triol Diol Mixtures for the Application of Composite Solid Rocket Propellants

The addition of some advanced additives to improve the mechanical properties of polyurethane (PU) polymeric matrix, which acts as a binder system in composite solid rocket propellants (CSRPs), is a target for the energetic materials researchers. In this investigation, 45 compositions of different crosslinked PU matrices were produced to demonstrate the effect of adding crosslinking mixture (CM) on the mechanical capabilities of polyurethane gum stock. The crosslinking mixture (CM) is composed of a triol crosslinker, trimethylolpropane (TMP), and a chain extender, 1,4-butanediol&#x0D; (BD). For comparison, traditional PU samples without crosslinking additives were formulated. As a prepolymer, HTPB was used with a curing agent (HMDI). The research was carried out with different ratios of TMP to BD, different curing ratios (NCO/OH=0.7, 0.9, and 1.1), and crosslinking mixture contents in the range of 0-5 wt.%. The mechanical characteristics of all the cured formulations were measured. It was demonstrated that changing the ratio of TMP to BD has a significant impact on the mechanical performance causing a wide range of elongation and strength qualities. Increasing the wt.% of triol crosslinker in the sample enhanced the tensile strength, whereas the strain has been decreased. The addition of diol chain extender increased the strain rate of the samples. The mechanical parameters were adjusted simply by employing the crosslinking ingredients to get exceptional mechanical characteristics at each NCO/OH curing ratios. Also it was concluded that PU samples of curing ratio (NCO/OH= 0.7-0.9) with TMP:BD (1:1) showed a promising results and could be used according to the requirements of the rocket system designers.