Hydroxyl-terminated Polybutadiene Binder Research Articles

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

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

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.

High Calorific Values Boron Powder: Ignition and Combustion Mechanism, Surface Modification Strategies and Properties

Boron powder is a kind of metal fuel with high gravimetric and volumetric calorific values, which has been widely used in military fields such as solid propellants, high-energy explosives, and pyrotechnics. However, the easily formed liquid oxide layer can adhere to the surface of boron powder and react with the hydroxyl (-OH) group of hydroxyl-terminated polybutadiene (HTPB) binder to form a gel layer that is detrimental to propellant processing and restricts the complete oxidation of boron powder. Therefore, to improve the combustion efficiency of boron powder, the ignition and combustion mechanisms of boron powder have been studied, and surface coating modification strategies have been developed by researchers worldwide, aiming to optimize the surface properties, improve the reaction activity, and promote the energy release of boron powder. In this review, recent studies on the ignition and combustion mechanisms of boron powder are discussed. Moreover, the reported boron powder coating materials are classified according to the chemical structure and reaction mechanism. Additionally, the mechanisms and characteristics of different coating materials are summarized, and the mechanism diagrams of fluoride and metal oxide are provided. Furthermore, promising directions for modification methods and the potential application prospects of boron powder are also proposed.

Dynamic shearing resistance of a polymer-bonded energetic simulant: Composite of sucrose and hydroxyl-terminated polybutadiene (HTPB)

The mechanical behavior of polymer-bonded explosives (PBXs) and polymer-bonded simulants has been widely studied under normal impact. However, their shearing response under large pressures and shear strain-rates has not been explored, to the best of our knowledge. Such measurements are crucial in informing constitutive models that aim to predict hot-spot formation and ignition behavior of PBXs subject to multi-axial loading. Pressure-shear plate impact experiments have been conducted on a composite of hydroxyl-terminated polybutadiene (HTPB) binder and sucrose (an energetic simulant) under normal stresses of 3–10 GPa nominally and shear strain-rates of the order of 105 s−1. The shear strength of the composite shows a dramatic drop after reaching a critical shear strain. Such a drop could be due to fracture or localization in either of the two phases, further compounded by other mechanisms such as friction between the resulting interfaces or collapse of voids. It is also observed that the shear strength of the composite is highly pressure-sensitive, increasing from 176 to 453MPa as the normal stress increases nominally from 3 to 9.5 GPa. Comparison of the shearing behavior of the composite with that of a granular aggregate of sucrose grains at low normal stresses (∼3 GPa) indicates that the binder plays the role of a lubricant between the sucrose grains at those normal stresses. However, at normal stresses of ∼9–10 GPa, the shear strength of HTPB becomes similar to sucrose, and beyond these normal stresses, a transition in the failure mode and its location is expected.

Thermal decomposition mechanisms of LLM-105/HTPB plastic-bonded explosive: ReaxFF-lg molecular dynamics simulations

ABSTRACT Thermal decomposition is not only related to the explosive’s ignition and detonation performances but also to their sensitivity to the surrounding environment. Based on the molecular dynamics method, the interaction and the thermal decomposition mechanism of plastic-bonded explosives (PBXs) composed by 2,6-diamino-3,5-dinitropyrazine-1-oxidated (LLM-105) and hydroxyl-terminated polybutadiene (HTPB) were investigated using the reactive force field molecular dynamics (ReaxFF-lg MD) simulations at 2000 K-4000 K. The interaction between the explosive and the binder effectively stabilizes the explosive crystal and reduces its sensitivity. The predicted activation energy of LLM-105/HTPB is 39.86 kcal/mol, more than that of the pure LLM-105 (36.57 kcal/mol), which reduces the initial decomposition reaction rate of LLM-105 after adding HTPB binder. Products distribution in thermal decomposition shows that the main initial decomposition mechanisms of LLM-105 include the C-NO2, C-NH2 bonds breaking, nitroso rearranging, NH2 elimination and H atom transferring. The H ions from the HTPB dehydrogenation delay the chemical bond breaking to inhibit the decomposition of LLM-105, and the reversible H transfer reactions provide an energy buffering area to reduce sensitivity.

Microscale Analysis of Stress Wave Propagation Through Plastic Bonded Explosives Under Micro-Sphere Shock Impact

In this article, material stress during microscale shock wave propagation through hydroxyl-terminated polybutadiene (HTPB) binder and polycrystalline cyclotetramethylene-tetranitramine (HMX) based plastic bonded explosive is analyzed. An elliptical shock wave was created by 250 µm-size zirconia sphere impactors accelerated by a laser-based particle launch setup. Particle velocity and strain rate during shock wave stress rise were measured in the target using photon Doppler velocimetry. Viscous behavior of the HTPB binder was characterized through measurement of shock viscosity at strain rates higher than 106/s. Volumetric stress was measured at the interface region close to polycrystalline HMX particle and HTPB binder using in-situ time-gated Raman spectroscopy. Results show measured shock stress rise at the HTPB-HMX interface region is close to idealized simulation values. In-situ time-gated Raman spectroscopy predicts stress due to shock wave reflection from the HMX phase at the HTPB-HMX interface region. Predicted stress is higher than stress propagated through the binder because of impedance mismatch between HTPB and HMX.

Experimental study of rheological properties of solid propellant slurry at low‐shear rate and numerical simulation

AbstractThe steady state rheological properties of a three‐component hydroxyl‐terminated polybutadiene binder (HTPB) solid propellant slurry at low shear rate were investigated using a rotational rheometer. The data were analyzed and the rheological characteristics of the slurry were determined. The effect of shear rate on apparent viscosity and shear stress as well as the viscosity–time effect of the slurry were also analyzed. Herschel–Bulkley (H‐B) model was applied for the simulation of the flow process of a two‐dimensional container using CFD Ansys‐polyflow software. Experimental results showed that solid propellant slurry had yield pseudoplasticity. Yield characteristics were determined based on the fact that when shear stress was greater than yield stress, the slurry began to flow and the relationship between shear stress and shear rate obeyed power law function. Simulation results further verified the correctness of experimental results.

Molecular investigations on the adsorption and flow behavior of hydroxyl-terminated polybutadiene (HTPB) binders on Cu surfaces: The effects of surface nanostructure and perfluorosilylation

The flow behavior of highly viscous casting explosives in micro-channels and special shaped moulds are critical factors affecting the formations of solid propellants and explosives. In the present work, the spreading property and flow behavior of hydroxyl-terminated polybutadiene (HTPB) binders, a major component of casting explosives, on Cu surfaces with nanostructures and perfluorosilylation were investigated by classical molecular dynamics simulations. Our results suggest that the atomic steps, exposed on the pit-/terrace-structured Cu surfaces, seem able to restrict the spreading of HTPB molecules from crossing over the step edges. After surface perfluorosilylation, the adhesive strength between HTPB and Cu substrate has decreased by nearly two orders of magnitude, resulting a vigorous travel of single HTPB molecules. Moreover, the cohesive strength between two adjacent HTPB droplets (-343.2 kcal/mol) is found to be higher than the adhesive strength of HTPB droplets on the perfluorosilylated smooth Cu surface (−85.7 kcal/mol). Thus, HTPB droplets could spread slowly on the perfluorosilylated Cu surface with a semi-spherical shape, irrespective of the presence of surface diatomic terraces. The reduced adsorption strength could also result in a slower infiltration speed of HTPB into the perfluorosilylated grooves and an increased slip performance on the perfluorosilylated surfaces.

Investigating Dimensional Effects on Predicting Burning Rates of Heterogeneous Solid Propellants

The combustion of a randomly packed, heterogeneous propellant consisting of ammonium perchlorate and hydroxyl-terminated polybutadiene is investigated in a two-dimensional and three-dimensional numerical model to better understand the dimensional effects on the propellant burning rate. A ammonium perchlorate particle is set in a premixed hydroxyl-terminated polybutadiene binder and investigated using a two-dimensional model with finite-rate chemistry and detailed transport properties. The results from the detailed model are compared to two-dimensional and three-dimensional burning-rate codes with reduced chemistry. The gas-phase combustion chemistry is modeled using a reduced four-step mechanism developed from a detailed microscale model of ammonium perchlorate/hydroxyl-terminated polybutadiene combustion. Simple configurations of a single ammonium perchlorate particle and sandwich propellants at varying pressures are compared to determine leading-order effects of two-dimensional and three-dimensional approaches. The reduced chemistry models are then applied to real-world propellants for which a random packing algorithm is used to construct the ammonium perchlorate/hydroxyl-terminated polybutadiene propellant in a periodic cube for a given size distribution of spherical ammonium perchlorate particles and mass ratio of the oxidizer and binder. The decomposition of the ammonium perchlorate and hydroxyl-terminated polybutadiene on the surface is determined at discrete locations and is used to determine the average burning rate over a period of time. This approach combines a more detailed description of the gas-phase combustion processes, the condensed-phase morphology, and physics in a time-dependent simulation in hopes of developing a more predictive model of solid propellant combustion.

A Room Temperature Curing Agent for Hydroxyl-Terminated Polybutadiene: Synthesis of a Novel Nitrile N-Oxide and Curing Properties of the Polymer Network

2,5-Diethyl-1,4-benzenedinitrile N-oxide was designed and synthesized to achieve room temperature curing of hydroxyl-terminated polybutadiene binders. The structures and properties of the four cured elastomers having different content of curing agent were investigated. The results showed that the isoxazoline rings from the reaction of nitrile N-oxide with cis-alkene are observed in the four cured elastomers. The results also revealed that the hydroxyl-terminated polybutadiene with the lowest content of curing agent showed the lowest cross-linking density and stress at break. The proper activity and steric hindrance of 2,5‑diethyl-1,4-benzenedinitrile N-oxide gave better mechanical properties and hydrophobic properties of the cured elastomers than nitrile N-oxide prepared by our previous work.

Performance of advanced composite solid rocket propellants based on novel oxidizers

Three novel high energy dense oxidizers (HEDO), Bis(2,2,2-trinitroethyl)oxalate (BTNEOx), 2,2,2-Trinitroethyl-nitrocarbamate (TNENC), 2,2,2-Trinitroethyl-formate (TNEF) have been prepared and studied as oxidizers in composite solid rocket propellants (CSRPs). For comparison, traditional CSRP containing ammonium perchlorate (AP) bonded by hydroxyl-terminated polybutadiene (HTPB) binder system was studied. The optimum oxidizer percentage with respect to the specific impulse was determined using the thermodynamic code (EXPLO5_V6.03). In addition, the optimum oxidizer mixture based on the novel oxidizers with AP was studied. The combustion properties and gaseous products of the optimum propellant compositions were calculated. A selected composition was prepared in the lab. scale and the burning rate was measured by the strand burner method. It was concluded that TNEF based propellant possess the maximum specific impulse of all the studied compositions. In addition, TNEF based propellant has a higher burning rate than the traditional CSRP composition.

Molecular investigation of adsorption behaviors of hydroxyl-terminated polybutadiene (HTPB) binders onto copper surface: The effects of aluminum nanoparticles

The adherent behaviors of hydroxyl-terminated polybutadiene (HTPB), a typical high viscosity liquid widely used as a binder in rocket motor propellants, onto the copper (Cu) surfaces with/without the interference of Al nanoparticles were investigated by classical molecular dynamics (MD) simulations. The results indicate that HTPB molecules adsorbed directly onto Cu(001) surface exhibit the tendency to distribute parallel to the 〈110〉 crystal direction family as a result of tense atom arrangement along the close-packed crystal directions. The dynamic hydrogen-bonded network, formed by inter-/intra-molecular interactions among neighbouring hydroxyl groups, is also suggested to exert strong influence on the distribution of HTPB molecules. Moreover, Al nanoparticles have been proved to be readily enveloped by HTPB chains when placed close to the pure high viscosity liquid, which will in turn restrict the mobility of HTPB molecules, eventually resulting in the decrease of wettability of HTPB droplet on Cu surface. The flow slip behavior of HTPB liquid on Cu surface, regardless of the presence of Al nanoparticles, was tested and directly compared by confined shear simulations. The Al hemispheres, acting as convex obstacles on the flat surface, seem to be capable of suppressing the slippage of chain-like HTPB molecules, which will be easily entangled by local protrusions. Therefore, it can be inferred that the flow behavior and interfacial wettability of high viscosity liquid will be largely influenced by the discontinuous solid-phase particles dispersed in it.

Study on the Correlation of Crosslink Network Structure and Tensile Properties of HTPB Binder

To study the crosslink network structure and the correlation with tensile mechanical properties of hydroxyl-terminated polybutadiene (HTPB) binder, tensile test and nuclear magnetic resonance test were introduced, the crosslink data and tensile stress-strain curves were obtained at various temperatures. The results show that the temperature has a significant effect on the crosslink density. When heating the samples from 30°C to 90°C, the crosslink density decreases and the transverse relaxation time increases. From 90°C to 130°C, the crosslink density raises at first and then becomes lower, and the transverse relaxation time keeps increasing. When the temperature rises from 30°C to 90°C, the elastic modulus and tensile strength of the binder are reduced, the elongation at break gets greater, and the tensile strength and the crosslink density has a linear relationship, which can predict the tensile strength of the binder at different crosslink densities.

Improving the Mechanical Properties of Glycidyl Azide Polymeric Matrix Used in Composite Solid Rocket Propellant by Adding Advanced Cross‐Linker

Glycidyl azide polymer (GAP) based binders have poor mechanical characteristics in comparison with hydroxyl terminated polybutadiene (HTPB) binders. In this study, advanced cross‐linker was used to improve the mechanical properties of GAP binder. GAP was prepared and characterized in comparison with HTPB prepolymer. Density, characteristics groups, nitrogen content, humidity, viscosity, and milligram equivalent of (OH) per binders were determined. A cross‐linker consists of trimethylol propane (TMP) and curing catalyst, dibutyltin dilaurate (DBTDL), was used as an additive to GAP polymeric matrix to enhance its functionality. Polymeric matrices based on GAP and HTPB were prepared with different curing ratio (NCO/OH) ranging from 0.7 to 1.5. Different weight percentages of cross‐linker were added to study its effect on the mechanical properties of GAP matrix. Five samples based on HTPB polymer and twenty samples based on GAP polymer were prepared. A LLOYD testing machine was used to determine the stress‐strain curves of all the studied samples. It was concluded that the cross‐linker used has significant influence on the characteristics of GAP polymeric matrix. Also the addition of 5 wt % of cross‐linker to GAP matrix at curing ratio = 1 produced optimum mechanical characteristics very close to that of HTPB matrix used in composite solid rocket propellants (CSRP). The optimum GAP polymeric matrix is candidate to replace the traditional HTPB binder in advanced CSRP.

Effects of Dihydroxylammonium 5,5′‐Bistetrazole‐1,1′‐Diolate on the Properties of HTPB Based Composite Solid Propellant

AbstractSeveral industrial‐ and research‐type hydroxyl‐terminated polybutadiene (HTPB) composite solid rocket propellants, containing dihydroxylammonium 5,5′‐bistetrazole‐1,1′‐diolate (TKX‐50) particles and, featuring the same nominal composition, were prepared. The energetic properties of composite propellants containing different mass fractions of TKX‐50 particles were theoretically computed and experimentally evaluated. The effects of different mass fractions of TKX‐50 on the rheological properties of both TKX‐50/HTPB binder slurries and AP/HTPB/Al propellant slurries were investigated. The strand burning rates, the associated combustion flame structures, and the hazardous properties of the resulting propellants were experimentally analyzed. All of the properties mentioned above were also compared to those of the reference propellant without TKX‐50. The results show that the prepared TKX‐50 particles can sufficiently be dispersed in the HTPB binder plasticized by di‐2‐etylhexyl sebacate (DOS). The propellant compositions containing different mass fractions of TKX‐50 are insensitive to impact and friction, differentlyfrom the reference propellant without TKX‐50. Moreover, over the explored pressure range, TKX‐50 can affect the combustion behavior and decrease the burning rate as well as pressure exponent of composite solid propellants compared with the reference composition.

A novel form-stable paraffin-based hydroxyl-terminated polybutadiene binder containing microencapsulated paraffin wax

Leakage and incompatibility of paraffin wax (PW) in hydroxyl-terminated polybutadiene (HTPB) binders is a major obstacle to its application in polymer-bonded explosives (PBX). In order to solve this issue, we designed a microencapsulated PW (MePW)/PW/HTPB composite in this paper. Melamine–formaldehyde-shelled MePW (MF MePW)/PW/HTPB composites with different contents of MePW and PW were prepared by cast molding method. The chemical composition, crystallinity and microstructure of MePW/PW/HTPB composites were analyzed with Fourier transformed infrared spectroscopy, X-ray diffraction and scanning electron microscope, respectively. The results showed that PW and MF MePW have been uniformly dispersed in HTPB without any chemical interaction. Moreover, differential scanning calorimeter analysis, thermal gravimetric analyzer, thermal cycling test, leaking test, tensile and compressive test were used to investigate the thermal and mechanical properties of these composites. The composites have high latent heat and good thermal reliability. The thermal stability, tensile and compressive strength of MePW/PW/HTPB composites were dramatically increased with the increasing mass fraction of MePW. The introduction of MePW can obviously prevent the leakage of PW in both HTPB binders and PBX. Consequently, it is anticipated that MePW can be used in the next-generation of paraffin-based high-temperature PBX systems.

Hot Spot Interaction with Hydroxyl-Terminated Polybutadiene Binder in Energetic Composites

Binders play a pivotal role in solid propellants and polymer-bonded energetic composites by providing the means for safe transport, storage, and use. The fundamental role of binders is known qualitatively, but the exact role in the modification of chemistry and thermal transport is hard to quantify. Thermochemical response of a commonly used binder, hydroxyl-terminated polybutadiene (HTPB), in a model composite comprising of cyclotrimethylene trinitramine (RDX) in the presence of a thermal hot spot was studied using reactive molecular dynamics (RMD) simulations. The results from model interfaces between RDX and HTPB were analyzed to identify the unique role played by the binder phase. It was found that the binder phase provides a safety buffer by extending the time required for the hot spot to undergo ignition-to-deflagration transition. This delay is mainly due to the disparity in the heat capacities of HTPB and RDX. HTPB, which has a higher heat capacity than RDX, absorbs energy from the hot spot at a r...

Thermal and mechanical reinforcement of a novel paraffin-based hydroxyl-terminated polybutadiene (HTPB) binder containing a three-dimension (3D) diurea-paraffin wax (DU-PW) for prevention of PW leakage.

Leakage of paraffin wax (PW) is a major concern in the development of polymer bonded explosive (PBX) systems because it relates to the amount of PW that can be used as a desensitizer or a fuel, which, in turn, affects the mechanical performance and tolerance of PBX in high-temperature environments. Hydroxyl-terminated polybutadiene (HTPB) binders significantly contribute desirable polymer features to PBX. Thus, a three-dimension (3D) high-temperature non-flowing diurea–paraffin wax (DU–PW) composite was synthesized and creatively employed to a HTPB binder. DU–PW/PW/HTPB composites with different contents of the 3D DU–PW phase change material (PCM) were prepared through a cast molding process. The differential scanning calorimetry (DSC) results demonstrate that these composites can show high phase-change enthalpies and good thermal reliability. As observed from the scanning electron microscope (SEM) photographs, adding DU–PW can clearly reduce the number of holes caused by the leaked PW on the fracture surface of DU–PW/HTPB. Moreover, the addition of DU–PW can remarkably reduce the leakage of PW and improve the thermal stability as well as mechanical properties of the PW-based HTPB. These observations present the potential of utilizing form-stable PCM (FSPCM) to solve the problem of PW leakage in PBX systems.

Kinetic and thermodynamic analysis of the hydroxyl-terminated polybutadiene binder system by using microcalorimetry

The isothermal curing kinetics of hydroxyl-terminated polybutadiene (HTPB) binder system containing dioctyl sebacate (DOS) and polyaryl polyisocyanate (PAPI) was investigated by microcalorimetry. The curing was completed after 5.3×105, 4.2×105, 3.6×105, and 3.2×105s at 303.15, 313.15, 323.15, and 333.15K, respectively. Thus, a shorter time was required to complete curing at a higher temperature. The curing reaction was exothermic, and temperature had minimal effect on the values of the total reaction heat within the testing temperatures. The activation energy (Ea), activation free energy (ΔG≠), activation enthalpy (ΔH≠) and activation entropy (ΔS≠) were 29.37kJmol−1, 103.11kJmol−1, 26.35kJmol−1 and −241.28Jmol−1K−1 respectively. Therefore, the title reaction was non-spontaneous. The effect of plasticizer on curing kinetics has also been investigated. It was found that the reaction rate constants and total reaction heat decreased with the increase of DOS contents. The thermodynamic properties of the reaction were studied by varying the content of PAPI at 323.15K. The curing reaction of the HTPB-DOS-PAPI binder system at 323.15K followed a model function of dα/dt=10−3.68(1−α)2.18.

Performance and Kinetics Study of Self-Repairing Hydroxyl-Terminated Polybutadiene Binders Based on the Diels⁻Alder Reaction.

Based on the Diels–Alder reaction and hydroxyl-terminated polybutadiene (HTPB) binders of solid propellants, two novel compounds—furfuryl-terminated polybutadiene (FTPB) and trifurfuryl propane (TFP)—were designed and synthesized, and their structures were characterized. A new kind of reversible Diels–Alder reaction system was formed by FTPB as main resin, N,N′-1,3-phenylenedimaleimide (PDMI) as curing agent and TFP as chain extender. The results showed that this system had good mechanical properties with a tensile strength of 1.76 MPa and a tensile strain of 284% after curing, and the repair efficiency of the crack was 88%. Therefore, it could be used as a novel binder of energetic materials such as solid propellant and PBX explosives to provide them with self-repairing characteristics and improve the reliability for application.