Hydroxyl-terminated Polybutadiene Research Articles

Hydrobromination of hydroxyl-terminated polybutadiene (HTPB) resin under optimal conditions with aqueous hydrobromic acid using response surface methodology (RSM)

Hydrobromination of hydroxyl-terminated polybutadiene (HTPB) resin under optimal conditions with aqueous hydrobromic acid using response surface methodology (RSM)

Acoustically transparent polybutadiene-based polyurethane encapsulants for deep-sea and transducers

Copolyether polyurethane (PUR), as a typical encapsulation material, is widely used for underwater acoustic transducers. Two novel types of polybutadiene-based PURs were prepared using a one-step method and compared with copolyether PURs. The polybutadiene-based PUR exhibited excellent mechanical properties. Epoxidized hydroxyl-terminated polybutadiene (EHTPB)–based PUR exhibited tensile strength and hardness of up to 17.3 MPa and Shore A95, respectively, which were 76.5% and 13.3% higher than those of copolyether PURs. The molecular chain of hydroxyl-terminated polybutadiene (HTPB)-based PUR exhibited good flexibility, a soft segment glass transition temperature (Tg) (approximately -52 °C), and complete microphase separation. Compared with HTPB-based PUR, EHTPB-based PUR exhibited a higher molecular chain rigidity and a lower degree of microphase separation. The insertion losses of HTPB-based PUR at 350 and 700 kHz were 69.8 dB/m and 204.6 dB/m, respectively, which were 57.4% and 47.1% lower than those of copolymer PUR. The water absorption and water vapor transmission coefficient of HTPB-based PUR were an order of magnitude lower than those of copolymer PUR. EHTPB-based and copolymer PURs exhibited similar insertion losses at 350 kHz. EHTPB-based PUR exhibited the lowest water vapor transmission coefficient of 7.2 × 10−14 g·cm/cm2·s·Pa, which was approximately 1/15th of that of copolyether PUR.

Microstructure and mechanical property analysis of HTPB adhesive under thermal aging based on molecular dynamic simulations

The solidified network structure formed by the addition reaction of hydroxyl-terminated polybutadiene and toluene diisocyanate, under the action of long-term internal and external factors, changes over time in its system structure. The resulting mechanical properties have a great impact on the reliability and structural integrity of solid propellants. In this study, an all-atom molecular dynamics method was used to study the sensitivity of the adhesive to temperature and loading rate at different aging stages, as well as the differences in the damage and fracture process under large deformation. The simulation results showed that degradation chain scission weakened the system modulus and strengthened the deformation ability, making nonbonded energy the main storage form of strain energy. Oxidative crosslinking produced an opposite modulus and deformation effects, with the storage form of strain energy changed from nonbonded energy to bond and angular energy during the loading process. In addition, increased temperature increased the distance between molecules and intensified molecular motion, causing the system strain to expand globally, reducing the stress peak, and enhancing deformation ability. The increase in loading rate increased local strain, causing some covalent bonds to break, while viscosity replaced elasticity as the main mechanical property, causing the stress-strain curve to shift to the upper left.

Evaluating Catalyst Performance in Synthesizing Hydroxyl-Terminated Polybutadiene by Ring-Opening-Metathesis Polymerization

AbstractHydroxyl-terminated polybutadiene (HTPB) can be synthesized by ring-opening metathesis polymerization (ROMP) in a one-step process using cyclooctadiene in the presence of a hydroxyl-functionalized chain-transfer agent (CTA). However, previous studies have shown that the presence of primary alcohols can lead to the degradation of some ruthenium catalysts and that the hydroxyl end groups may be converted into aldehydes. Here we compare the performance of five ruthenium-based catalysts — Grubbs first-, second-, and third-generation catalysts (G1, G2, and G3, respectively), Hoveyda–Grubbs Z-selective catalyst (HGZ), and Hoveyda–Grubbs second-generation catalyst (HG2) — in ROMP with a CTA containing primary alcohols. We found that HTPB can be rapidly synthesized in a single step using G3 while avoiding end-group isomerization (2.2% aldehyde formation after full conversion is reached in 5 min). This result suggests that G3 may enable a more effective approach to synthesizing HTPB that avoids protecting groups but still maintains high end-group fidelity.

Study on Rheological Properties and Pouring Process of Hydroxyl-Terminated Polybutadiene (HTPB) Propellants.

The process of solid propellant production, which is the most widely used high-energy material, has garnered significant attention from researchers. However, there have been relatively few studies on its processing, due to the unique nature of the casting process. This paper aims to further analyze the pouring process of the propellant slurry. Initially, we obtained a sample of the propellant slurry and measured its rheological parameters using a rotary rheometer. From the analysis of the experimental results, we derived the viscosity parameters and the yield values of the propellant slurry. Subsequently, we simulated the pouring process, setting the slurry parameters based on the data obtained from the rheological measurement experiment. The simulation results demonstrated that the flower plate significantly impacts upon the cutting and separating effect on the slurry during pouring. Upon leaving the flower plate, the slurry descends onto the core mold platform under the influence of gravity, gradually flowing along the edge of the core mold. Although there may be some small voids in the pouring process, the voids will disappear completely at the end of pouring. A comparison with the actual pouring situation revealed a higher consistency between the simulation results and reality, thus establishing the reliability of the simulation method as a reference for analyzing the pouring process.

Study on the dynamic numerical simulation of flow and combustion in hybrid rocket motors based on a discrete phase model

Numerical simulation based on the discrete phase model and dynamic mesh model can more accurately simulate the working process for hybrid rockets, including the motion and evaporation process of particles and regression process of the fuel grain. The dynamic numerical simulation of combustion and flow in hybrid rocket motors based on a discrete phase model is carried out. Aluminum and aluminum hydride are added to the internal flow field as discrete droplets. Then, a hybrid rocket is designed with 95 % hydrogen peroxide as oxidizer and 38 % aluminum hydride+20 % aluminum+42 % hydroxyl-terminated polybutadiene as the fuel and used to verify the model by firing test. A high degree of agreement between experiment and simulation findings is found. The average deviations for thrust and pressure are 3.6 % and 5.9 %, respectively. It offers the required backing for using the simulation method to investigate the flow and combustion process for the hybrid rockets. The results also demonstrate the transient characteristics of the inner flow field, including the separation and merging of vortexes in the pre-chamber. It is found that a peak of the regression rate appears at the front of the grain and moves backward. This is mainly because the vortex appears here and enhances its heat transfer. Through the discrete phase model, it is worth noting that the aluminum droplet content gradually decreases at the nozzle over time, which is consistent with the firing test. Further research on the impact of aluminum hydride content on the performance of the hybrid rockets has been carried out. The results show that the higher aluminum hydride content can lead to better performance for the hybrid rockets. The thrust, pressure, specific impulse, and characteristic velocity enhance with the increase of aluminum hydride content. An interesting discovery is that the average regression rate is maximum at 48 % aluminum hydride content. This research innovatively couples dynamic mesh and discrete phase models, which can help better understand the working process for hybrid rockets and provide important guidance for the selection of fuel formula.

Uniaxial tensile mechanical behavior research of HTPB propellant under wide temperature and confining pressure

To investigate the effects of confining pressure, strain rates, and temperatures on the mechanical properties of the Hydroxyl-terminated Polybutadiene (HTPB) propellant, uniaxial tensile tests were performed utilizing wide-temperature-confining pressure systems. The resulting damage was subsequently analyzed and characterized through scanning electron microscopy and mirco-ct. The results indicate that the stress–strain curves of HTPB at 20 and 70 °C are comparable, and the propellant damage is primarily attributed to de-wetting at 20 and 70 °C with respect to the mechanism. At −50 °C, the maximum tensile strength and ultimate tensile strain at 8 MPa surpass those at 0 and 2 MPa to a significant degree and the damage shifts from de-wetting and ductile fracture of particles to severe particle breakage with the elevated confining pressure. Ultimately, the primary curve of the HTPB propellant's maximum tensile strength was constructed by the curve fitting analysis based on the time–temperature equivalent superposition principle (TTSP) and time–pressure equivalent superposition principle (TPSP). Comparing to the properties of TPSP, TTSP exhibits a wider range of applicability and greater fitting precision in relation to the HTPB propellant. This study mainly serves to establish a fundamental theory and furnish data support for the enhancement of mechanical properties and structural integrity of solid rocket motors.

HTPB propellant binder supplemented with nitro potato starch: Formulation, characterization, and thermal decomposition behavior

This study conducted a detailed examination of the characteristics of hydroxyl‑terminated polybutadiene (HTPB) doped with potato starch nitrate (NPS) as a high-energy-density binder. The investigation specifically focused on evaluating the impact of NPS doping on the chemical structure, energetic attributes, and thermokinetic behavior of HTPB-NC binder systems. The findings demonstrated advantageous features, including favorable chemical compatibility, improved material density accompanied by remarkable thermal stability, substantial energy release, and high chemical reactivity. These findings contribute to the understanding of HTPB-NPS composite and offer evidence for its remarkable features, indicating promising prospects for its utilization in the development of advanced formulations for high-energy-density propellants in future applications.

Exploring the potential of boron carbide in enhancing energy output of solid fuels for SFRJ and hybrid rocket propulsion systems

AbstractBoron carbide (B4C) is known for its exceptional hardness and high energy release during combustion, despite its ignition processes presents considerable challenges. This study focuses on exploring the potential of B4C as an enhancer for the energy output of solid fuels designed for hybrid rocket engines (HRE) or solid fuel ramjets (SFRJ). This study presents the successful incorporation of B4C and fluorinated PTFE (polytetrafluoroethylene) polymer into the HTPB (hydroxyl‐terminated polybutadiene) fuel matrix, aiming to enhance the ignition, combustion, and regression rate performance of solid fuel. Five different fuel compositions were formulated with varying mass ratios of B4C, and their post‐combustion products were characterized using XRD (X‐ray diffraction), HRSEM (high‐resolution scanning electron microscopy), and EDS (energy‐dispersive X‐ray spectroscopy) techniques. The HRSEM‐EDS analysis confirmed a uniform dispersion of B4C/PTFE additives throughout the HTPB matrix. To evaluate the combustion behavior of the B4C/PTFE additives, an opposite flow burner was employed with a gaseous oxygen oxidizer. The F4 fuel sample, loaded with B4C/PTFE (10/20), exhibited an average regression rate increase ranging from 0.61 to 1.15 mm/s when evaluated within the oxidizer flux range of 36–77 kg/m2s, in comparison to that of pure HTPB (0.4 mm/s to 0.76 mm/s). The ignition delay time was investigated as a key parameter affected by the B4C concentration in the solid fuel formulations. Furthermore, a comprehensive combustion mechanism is proposed and discussed for B4C/PTFE loaded in the HTPB matrix under an oxygen environment.

Enhancing the performance of HTPB‐IPDI‐based polyurethane composite liner through effective carbon black dispersion**

AbstractThis study aims to improve the dispersion of Carbon Black (CB) filled Hydroxyl‐Terminated Polybutadiene (HTPB)‐Isophorone Diisocyanate (IPDI) based polyurethane liner by both adding a dispersant and developing a production process to obtain improved mechanical, rheological, thermal, and adhesion properties. Printex‐U (CB1) and Thermax N‐991 (CB2) carbon blacks were used as fillers. Three different dispersants, which are BYK 9076 (D1), BYK 9077 (D2), and BYK Silclean 3700 (D3) were added to the liner formulation at various amounts. BYK 9076 (D1) was found as the most effective dispersant due to its bifunctional chemical structure. By adding 2 wt.% of BYK 9076 (D1) dispersant to the polyurethane liner comprising 10 wt.% CB1, viscosity was reduced by 45 %, and tensile strength and elongation at break were improved from 1.77 MPa to 1.88 MPa and from 375 % to 385 % respectively. The dispersion of the CB in the polyurethane liner was further improved by the ultrasonication process and tensile strength and elongation at break were increased to 2.03 MPa and 425 %, respectively. This process also contributed to an improved Limiting oxygen index (LOI), elevating it from 20 % to 22 % initially and further by 25 % through ultrasonication. Scanning Electron Microscopy (SEM) verified that the addition of D1 dispersant and ultrasonication effectively reduced CB particle agglomeration. The migration of plasticizer was also assessed over 12 months through bonding testing, TGA, and FTIR analysis. It was noticed that the effective dispersion of CB particles made the liner more resistant to the plasticizer migration.

Tailoring the mechanical and combustion performance of B/HTPB composite solid fuel with covalent interfaces

The development of high-performing solid fuels with desired mechanical and combustion properties is critical to future air-breathing propulsion systems for space exploration and hypersonic navigation. Boron (B)/hydroxyl-terminated polybutadiene (HTPB) composite has been studied for this purpose due to the high energy density (heat of combustion) of B and the appropriate processability and mechanical properties of HTPB. However, the weak interface between B and HTPB results in weakened mechanical properties, agglomerated B particles, and slow and inefficient combustion, especially for composites with high B loading (30 wt% and above). In this study, the effect of interface between B and HTPB on the combustion and mechanical performance of high-loading B/HTPB composites was investigated by surface functionalization of B particles. Three interfacial characteristics were compared: polar (pristine B)/nonpolar (HTPB), nonpolar (hydrocarbon-functionalized B)/nonpolar (HTPB), and covalently bonded (amine-functionalized B/HTPB) interfaces. It was found that both covalently bonded and nonpolar/nonpolar interfaces effectively reduced the aggregation of B particles in the HTPB matrix, even with up to 45 wt% B loading, thus promoting the combustion efficiency and burning rate. Moreover, covalently bonded interfaces in B/HTPB composites led to strain-hardening behaviors, resulting in enhanced strength, ductility, and toughness. This work highlights the significance of interface engineering in B/HTPB composites for the efficacy and safety of future air-breathing solid-fueled propulsion devices.

Dynamic layer-by-layer surface self-assembly on aluminum fuel for improving the comprehensive performance of propellants

Aluminum-based fuels generally suffer from poor compatibility with the polymer matrix, low combustion heat and severe agglomeration after combustion, which seriously restrict the overall effectiveness of solid propellants. Herein, due to the synergy of borate ester bonding and unsaturated boron-nitrogen coordination, the highly incompatible fluoride and glycidyl azide polymer (GAP) were orderly aligned on Al to construct novel dynamically layer-by-layer coated aluminum fuel (Al@PFND-B-GAP). The thermal reaction performance of Al@PFND-B-GAP with oxygen was significantly improved, and its heat release was 2.42 times that of Al. In the ignition tests, Al@PFND-B-GAP released multiple bright flames to induce microexplosion with the mushroom cloud morphology, which greatly improved the detonation performance of aluminum powder. When Al@PFND-B-GAP was used for building up the hydroxyl-terminated polybutadiene (HTPB)-based propellants, the agglomeration of the aluminum powder was significantly inhibited after combustion. Even with a solid loading of up to 86%, the dynamic interface via layer-by-layer assembly on Al could simultaneously improve the mechanical properties, combustion performance, and anti-agglomeration of the solid propellant. Our proposed Al@PFND-B-GAP could improve the comprehensive performance of solid propellants. And it was an inspiration for the future construction of multistage dynamic coatings and micro/nano ordered interfaces.

Mapping oft the optimal mechanical responses in commercial‐grade HTPB‐based binders

AbstractAlternative binders for composite solid propellants (CSP) have always been a concern. One of the closest alternative to the broadly used military‐grade hydroxyl‐terminated polybutadiene (HTPB) would be its commercial‐grade. Factorial design of experiments (DoE) was applied to optimize the mechanical properties of the binder. Commercial‐grade HTPB was used, in addition to 1,4‐butanediol (BDO) as chain extender, and either isophorone diisocyanate (IPDI) or 4,4’‐methylenedicyclohexyl diisocyanate (H12MDI) as curing agents. The effect of simultaneously varying two factors: [NCO]/[OH] molar ratio, and BDO:HTPB mass fraction on the mechanical properties of the binder was evaluated. DoE gave the optimal conditions at 0.68 molar ratio, and 0.71 % BDO:HTPB mass fraction for IPDI; and at 0.66 and 0.57 %, respectively, for H12MDI. Higher strength was observed for binders formulated with H12MDI. At the optimal conditions, CSP formulated with commercial HTPB showed higher strength than CSP formulated with military HTPB. Moreover, with H12MDI higher elongation was observed (28±4 %) when compared to IPDI (19±1%). Thus, the former is a promising diisocyanate for tailoring CSP formulations with commercial‐grade HTPB.

Experimental measurement and simulation of the biaxial mechanical properties of solid propellant HTPB

AbstractHydroxyl‐terminated polybutadiene (HTPB) solid propellant was widely used in carrier rocket and guided missiles, owing to its excellent mechanical properties. The material of HTPB subjected to complex load such as in the process of manufacturing, storage and transportation. Therefore, the mechanical properties of HTPB had important implications for the safety of structure and service life. The purpose of this work is to study the effects of different loading ratios and loading speeds on the biaxial tension of hydroxyl‐terminated polybutadiene (HTPB) solid propellant with a proper kind of biaxial tensile specimen and a high volume fraction three dimensional particle filling model of the material. The proper kind of biaxial tensile specimen with which the stresses in its central part could be obtained with the loads acted on each loading direction was designed and used in the study, and the strains in its central parts were obtained with digital image correlation (DIC) method. The stress‐strain relationship at each direction could be obtained by experiments. Experimental results indicated that the loading speed remarkably influenced the biaxial tensile behaviors of HTPB propellant at room temperature and at different loading ratios. The finite element simulation results demonstrated the accuracy of the biaxial experiment. Based on the experimental results, the particle debonding in biaxial experiments were analyzed and an equivalent Poisson's ratio parameter was proposed to evaluate the degree of debonding. The highly volume fraction three dimensional particle filling model provides a good simulation with experimental results and the equivalent Poisson's ratio parameter can conveniently and accurately determine the debonding of particles which is meaningful to the structure integrity assessment of HTPB solid propellant.

A facile strategy for the preparation of carbon nanotubes/polybutadiene crosslinked composite membrane and its application in osmotic energy harvesting

The osmotic energy between riverine water and seawater can be converted into electricity by reverse electrodialysis (RED). However, the facile fabrication of advanced RED membranes with high energy conversion efficiencies, large areas, and excellent mechanical properties remains a challenge. Carbon nanotubes (CNTs) exhibit excellent conductivity and provide suitable channels for ion transport but cannot form membranes independently, which limits the related applications in osmotic energy conversion. Herein, a new organic–inorganic composite membrane is prepared by combining hydroxyl-terminated polybutadiene as a matrix and carbon nanotubes as transport nanochannels. The nanotubes are pre-subjected to plasma treatment to increase the surface charge density and transport capacity of the nanochannels, improving the ion selectivity and energy conversion efficiency. Under actual seawater/river water conditions, the developed membrane delivers a power density of ∼5.1 W/m2 and shows good mechanical strength (219 MPa). Our work provides a facile solution to the problem posed by the inability of ideal nanochannels to form membranes independently and paves the way for the application of RED membranes in osmotic energy conversion.

Experimental and Numerical Investigation into the Mechanical Behavior of Composite Solid Propellants Subject to Uniaxial Tension.

To further explore the quasi-static mechanical characteristics of composite solid propellants at low strain rates, an investigation was conducted on the mechanical behavior and damage mechanisms of a four-component hydroxy-terminated polybutadiene (HTPB) propellant by means of experiments and numerical simulation. A uniaxial tensile test and scanning electron microscope (SEM) characterization experiment were carried out. A microstructural model, which accurately represents the mesoscopic structure, was developed via the integration of micro-CT scanning and image-processing techniques. The constructed microstructural model was utilized to conduct a numerical simulation of the mechanical behavior. The experimental results demonstrated that the maximum tensile strength increases with increasing strain rate, and the primary cause of propellant failure at low strain rates is the dewetting phenomenon occurring at the interface between the larger particles and the matrix. The maximum tensile strength is 0.48 MPa when the strain rate is 0.00119 s-1, and the maximum tensile strength is 0.37 MPa when the strain rate is 0.000119 s-1. The simulation results indicated a consistent trend in variation when comparing the simulation and experimental curves. This suggested that the established model exhibits a high level of reliability, and provides a promising approach for carrying out microstructural simulations of heterogeneous propellants in future. The mechanical behavior of the propellant can be effectively described by utilizing a mesoscopic finite element model that incorporates the superelastic constitutive model of the matrix and the bilinear cohesive model. This framework facilitates the representation of mesoscopic damage evolution, which consequently provides insights into the damage mechanism. Additionally, the utilization of such models assists in compensating for the limitations of damage evolution characterization experiments.

Impact Velocity and Temperature Effects on the Shock Wave Propagation and Spallation of Hydroxyl-Terminated Polybutadiene: A Molecular Dynamics Study

Impact Velocity and Temperature Effects on the Shock Wave Propagation and Spallation of Hydroxyl-Terminated Polybutadiene: A Molecular Dynamics Study

Biaxial Tensile Mechanical Properties of HTPB Solid Propellant

The purpose of this work is to study the effects of different loading rate ratios and loading speeds on the biaxial tension of hydroxyl-terminated polybutadiene (HTPB) solid propellant. A proper kind of biaxial tensile specimen with which the stresses in its central part can be obtained with the loads acted on each loading direction is designed and used in the study, and the strains in its central parts are obtained with the digital image correlation (DIC) method. The stress and strain relationship at each direction can be obtained by experiments. The uniaxial stress vs. strain curves and the biaxial stress vs. strain curves were obtained, and it was found that the loading speed remarkably influenced the biaxial tensile behaviors of HTPB propellant. The Mises equivalent stress and strain could be used to describe the biaxial tension stress and strain state, and the exponential constitutive model obtained in the study could be used to predict the stress vs. strain curve under different test conditions.

Doping HTPB binder with cellulose nitrate: A promising strategy for advanced energetic material applications

This study explored the characteristics of hydroxyl-terminated polybutadiene (HTPB) supplemented with cellulose nitrate (NC), as a high-energy density binder. The effect of NC doping and its content on the chemical structure, morphology, energetic, and thermokinetic behavior of HTPB–NC binder highlighted attractive features such as good compatibility, improved density, homogeneity, and fiber dispersion. Additionally, HTPB–NC exhibited excellent thermal stability with significant energy release and notable chemical reactivity. These interesting properties of the HTPB–NC binder, provide evidence for the excellent synergistic effect between HTPB and NC, which could promote its application in the next generation of energetic propellant formulations.

Data science assisted cohesive finite element modelling of impact behaviour of AP‐HTPB crystal binder composite

AbstractIn this work, the response of an ammonium perchlorate (AP)‐hydroxyl‐terminated polybutadiene (HTPB) composite material under impact loading is presented, utilizing computational cohesive finite element method (CFEM) simulations that are validated with drop hammer experiments. This study examined the impact behaviour of AP crystal sizes between 200 and 400 μm by varying impact velocities between 3 and 10 m/s. Based on the outcome of CFEM simulations, analysis of variance (ANOVA) tests and a response surface method (RSM) were utilized to construct a mathematical model approximating the relationships between simulation inputs and outcomes. Both computational and experimental results show that the local strain rate has a considerable positive correlation with crystal size, and the rate of temperature change has positive correlations with both crystal size and impact velocity. Further, it was observed that stiffness and compression energy are the primary factors to variances in local strain rate and rate of change of temperature. RSM has been found to be an effective tool for modelling impact responses of materials under varying experimental conditions.