Hydroxyl-terminated Polybutadiene Research Articles

Effect of Dual Curing Agent (TDI:DDI) on the Mechanical Properties and Burning Rate of HTPB-Based Solid Propellant

ABSTRACT In this study, the effect of dual curing agent (toluene diisocyanate:dimeryl diisocyanate (TDI:DDI)) on the properties of hydroxyl-terminated polybutadiene (HTPB)-based solid propellant (such as mechanical strength, elongation percentage, elastic modulus, hardness, burning rate and pressure exponent (n)) has been investigated. Thus, five solid propellant formulations with different proportional amounts of TDI and DDI, with same loading rate and constant R value, were prepared, and the mechanical properties and burning rate of the prepared samples were evaluated. Tensile test conducted on the solid propellant cured for 7 days showed that increasing the proportional amount of DDI compared to TDI in the solid propellant formulation increases the elongation percentage and decreases the tensile strength, modulus, burning rate and pressure exponent (n). Considering that DDI also plays the role of a softening agent in the solid propellant formulation, increasing its amount in the solid propellant formulation will decrease the viscosity, causing a higher pot life.

Novel Glycidyl Carbamate Functional Epoxy Resin Using Hydroxyl-Terminated Polybutadiene

Herein, a novel glycidyl carbamate functional epoxy resin (GCE) is synthesized by the additional reaction of the isocyanate group of tolylene diisocyanate (TDI) with the hydroxyl group of hydroxyl-terminated polybutadiene (HTPB) and glycidol. The successful synthesis of the GCE is confirmed by FT-IR and 1H NMR spectroscopy. Furthermore, a dual-curing adhesive system is developed using acrylic acid and trimethylolpropane triacrylate with varying GCE contents, and its adhesive performance is assessed by testing adhesive strength, pencil hardness, and surface energy. As a result, the dual-cure adhesive containing 0.2 mol of GCE demonstrates an impressive adhesive strength of 11.1 MPa, a pencil hardness of B, and surface energy comparable to that of standard polycarbonate film.

Bonding of rubber to steel: Effects of hydroxyl-terminated polybutadiene on the adhesion of waterborne polyurethane adhesives

Rubber as a substrate exhibits very different surface physical and chemical characteristics from steel. It still remains challenging to achieve a complete interface stripping of steel while maintaining double-sided adhesion between rubber and steel. Hydroxyl-terminated polybutadiene (HTPB) possesses remarkable low-temperature flexibility that contributes to migration and orientation of molecular chains, and contains abundant C=C bonds that facilitate cross-linking reaction. In this work, the hydroxyethyl acrylate (HEA)-terminated waterborne polyurethane (WPUH) adhesive was prepared by introducing HTPB into polyurethane backbone. The impact of HTPB on the properties of WPUH adhesive was investigated by changing HTPB/poly(tetramethylene ether) glycol (PTMG) molar ratio. The reasons for such change were studied focusing on the structure and bonding mechanism of WPUH adhesive. When rubber and steel were bonded together by WPUH adhesive, the rubber would induce non-polar HTPB segments to approach the bonding interface while the steel would attract the polar carbamate groups to its surface. The adhesion was strengthened by the interfacial interaction once WPUH adhesive wetted two substrates. In addition, the 1,2-isomer C=C bonds of HTPB could undergo free radical polymerization with HEA to form a cross-linked network, which improved the cohesion. This study provides a feasible strategy for achieving the goal of effectively bonding rubber-to-steel without residual adhesive stripping.

Surface Wetting Behaviors of Hydroxyl-Terminated Polybutadiene: Molecular Mechanism and Modulation.

The surface wetting or coating of materials by polymers is crucial for designing functional interfaces and various industrial applications. However, the underlying mechanisms remain elusive. In this study, the wetting behavior of hydroxyl-terminated polybutadiene (HTPB) on a quartz surface was systematically investigated using computer simulation methods. A notable tip-dominant surface adsorption mode of HTPB was identified, where the hydroxyl group at the end of the polymer chain binds to the surface to initiate the wetting process. Moreover, it was found that with the increase in the degree of polymerization (e.g., from DP = 10 to 30), spontaneous adsorption of HTPB becomes increasingly difficult, with a three-fold increase in the adsorption time. These results suggest a competition mechanism between enthalpy (e.g., adhesion between the polymer and the surface) and entropy (e.g., conformational changes in polymer chains) that underlies the wetting behavior of HTPB. Based on this mechanism, two strategies were employed: altering the degree of polymerization of HTPB and/or regulating the amount of interfacial water molecules (e.g., above or below the threshold amount of 350 on a 10 × 10 nm2 surface). These strategies effectively modulate HTPB's surface wetting process. This study provides valuable insights into the mechanisms underlying the surface adsorption behavior of HTPB and offers guidance for manipulating polymer wetting processes at interfaces.

Functionalization of Titania Nanoparticles with Carboxyl Groups for Improved Mechanical Performance of Hydroxyl Terminated Polybutadiene (HTPB) Composites

Functionalization of Titania Nanoparticles with Carboxyl Groups for Improved Mechanical Performance of Hydroxyl Terminated Polybutadiene (HTPB) Composites

Thermosetting boron-nitride-filled polybutadiene composites with enhanced thermal conductivity and good dielectric properties

Low dielectric materials with high heat dissipation, low dielectric constant (Dk), and dielectric loss (Df) are urgently needed to address the issues of signal cross-talk and heat accumulation arising from the rapid development of modern communication technology and the integration of microelectronics. Polyolefins, as hydrocarbon polymers, have shown significant potential due to their excellent low dielectric properties. However, their low polarity and flexible structures limit their thermal conductivity and thermomechanical properties. In this study, we developed a method to prepare thermosetting polybutadiene composites with enhanced thermal conductivity and good dielectric performance by modifying hexagonal boron nitride (h-BN) and hydroxyl-terminated polybutadiene (HTPB) with thermally cross-linkable benzocyclobutene (BCB) groups. The properties of the resulting composites were tailored by varying the filler content. With 30 wt% of the BCB-modified filler, the composite (HB-30) displayed excellent dielectric properties (Dk = 2.70; Df = 1.67 × 10−3 @10 GHz). Meanwhile, it exhibited a thermal conductivity of 0.615 W/mK at 35 °C, which was 7.1 times that of pristine HTPB. It also showed significantly enhanced mechanical properties and thermal stability with a storage modulus of 2.7 GPa and a glass transition temperature (Tg) of 208.5 °C. This method proved effective for preparing polymer composites with enhanced thermal conductivity, heat resistance, mechanical properties and good dielectric properties, making them suitable for high-frequency communication applications.

Research on microscopic structure–activity relationship of AP particle–matrix interface in HTPB propellant

Abstract The matrix and particle interface of hydroxyl-terminated polybutadiene (HTPB) propellant is the weakest part of its mechanical properties, making it prone to dewetting damage and destroying the structural integrity of the propellant. This article uses nano-indentation, gas cluster ion beam etching, and X-ray photoelectron spectroscopy experimental analyses to study the physicochemical properties of the interface and subsequently construct a microscopic model for the HTPB matrix and ammonium perchlorate particle interface. The model fully considers the existing forms of curing agent toluene diisocyanate, bonding agent Tris (2-methyl-aziridine) phosphine oxide (MAPO), and the aging products of the propellant in the interface structure. Meanwhile, the physicochemical properties, mechanical properties, and adhesive properties of the interface under different tensile loading conditions were analyzed. The results indicate that the bonding agent MAPO significantly enhances the mechanical and adhesive properties of the interface. The interface is sensitive to changes in temperature and tensile rate, and the aged interface is more fragile.

Manufacture of Solid Propellants Based on Renewable Succinic Acid Polyols

AbstractModern energy policies encourage the replacement of fossil fuels with a more sustainable type. Succinic acid is a promising renewable material that can react with ethylene glycol and 1,4‐butanediol in a two‐step polycondensation reaction to form hydroxylated polyesters. Copolymerization reactions were investigated to produce novel green binders for manufacture of solid propellants. The ester of the first step of polycondensation was used as a plasticizer in the propellant formulation. These products can be an alternative to binders of fossil sources, such as hydroxyl‐terminated polybutadiene (HTPB), frequently used as fuel of commercial propellants. Initially, analyses of Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography indicated the formation of polymeric products and adequate chain growth at reaction conditions. Then, the obtained copolymers were characterized by rheological analyses, which revealed that the processability of the copolymer materials was similar to that of the HTPB samples. Additionally, thermogravimetric analyses indicated that the copolymers presented good thermal stability below 200°C. Furthermore, differential scanning calorimetric (DSC) analyses indicated that the glass transition temperatures of the obtained copolymer samples ranged from −20 to −60°C, a suitable range for the intended use. Solid propellants were then prepared with solid loadings above 70 wt %, heat of combustion above 11,300 J g−1 and heat of explosion above 4,980 J g−1, which are compatible with values expected for solid propellants. Finally, oxygen balance calculations showed that the intrinsic oxygen content of the polyesters can allow the reduction of amounts of oxidizers in the final propellants.

Thermal Degradation Behavior of Thermally‐Oxidized Hydroxyl‐Terminated Polybutadiene (HTPB): An Assessment of Thermal Stability

AbstractThermal analysis was performed on different thermally oxidized hydroxyl‐terminated polybutadiene (HTPB) samples, varying in molecular weights, polydispersities, and viscosities. The HTPB sample was subjected to thermal ageing at 65 °C for 10 weeks and periodically withdrawn for thermal analysis. During thermal ageing, HTPB undergoes chain rearrangements that may include scission and subsequent crosslinking, leading to a higher average molecular weight and viscosity. Differential scanning calorimeter (DSC) and thermogravimetric analyses were performed on thermally oxidized HTPB samples under inert heating conditions to investigate their degradation behavior. The DSC results revealed no significant correlations between the glass transition (Tg) and the samples' molecular weight, viscosity, and polydispersity. In TGA, all HTPB samples showed a two‐step thermal decomposition process characterized by two distinct mass loss stages. Notably, the first stage exhibited a lower total mass loss and a considerably lower peak rate of mass loss than the second stage. The thermal stability of HTPB is significantly compromised by thermal‐oxidative degradation, leading to a pronounced decrease in the initial degradation temperature (TIDT) values, from 372 °C (pristine or 0 week) to 228 °C (10 weeks). Furthermore, we measured the energy of activation (Ea) and the pre‐exponential factor (A) from TGA data using the Coats–Redfern integral equation. Notably, we observed a slight but systematic increase in both Ea and A as the molecular weight of the aged samples increased.

Synthesis and optimization of molecular weight of chitosan and carboxymethyl cellulose based polyurethanes

For the first time in this research, using a mixture design approach, polyurethanes (PUs) based on chitosan (CSN) and carboxymethyl cellulose (CMC) were synthesized to develop a high molecular weight polymer. In the synthesis process, a reaction between isophorone diisocyanate (IPDI) and hydroxyl-terminated polybutadiene was carried out to synthesize a prepolymer containing free NCO groups at the corners. This prepolymer was further reacted with changing moles ratio of CSN and CMC following the principles of statistical mixture design. The structural confirmation of the developed PUs was carried out through spectroscopic techniques (FTIR and NMR). The molecular weights of the PU specimens were characterized using gel permeation chromatography. The findings demonstrated that the interaction between CMC and CSN led to a notable increase in the molecular weights of the samples, supported by a significant p-value of 0.006. Additionally, the analysis of variance (ANOVA) disclosed that the employed mixture design and the resulting interaction model effectively account for 98 % of the total variation observed in the molecular weights. The sample labeled as PUS-3 (CMC0.50:CSN0.50) emerged as the most significant formulation, exhibiting a noteworthy 27.9 % improvement in the polymer molecular weight compared to the base sample, denoted as PUS-1 (CMC1.00:CSN0.00).

First applications of ultrasound technology in solid rocket propellant combustion promotion

The regulation of propellant combustion using ultrasonic waves is proposed. Under ultrasonic frequencies of 25–40 kHz, we systematically examined the combustion characteristics of Al particles, ammonium perchlorate (AP)/hydroxyl-terminated polybutadiene (HTPB) propellants, and Al-containing Al/AP/HTPB propellants. Ultrasonic treatment increased the ignition delay time of the Al particles by 48.3 %. However, it increased the burning rate of the AP/HTPB propellants by up to 26.1 % and decreased their ignition delay by 39.3 %. As the ultrasonic frequency increased, the burning rate of the solid Al/AP/HTPB propellants increased by 22.5 %, and the degree of Al agglomeration decreased, resulting in a 24 % decrease in the size of the condensed-phase combustion products. The action mechanism was analyzed in terms of the effects of ultrasonic waves on Al droplets and combustion flames. The introduction of ultrasonic waves split the Al droplets near the burning surface into smaller particles, which affected combustion efficiency. Bringing the diffusion flame closer to the burning surface affected the burning rate. These findings demonstrate that the combustion and agglomeration characteristics of solid propellants can be modified using ultrasonic techniques, providing a new method for controlling the thrust of solid rocket motors.

Poly (lactic acid)/Poly (butylene adipate-co-terephthalate) Films with Simultaneous High Oxygen Barrier and Fast Degradation Properties

Although poly (lactic acid) (PLA) is a good environmentally-friendly bio-degradable polymer which is used to substitute traditional petrochemical-based polymer packaging films, the barrier properties of PLA films are still insufficient for high-barrier packaging applications. In this study, oxygen scavenger hydroxyl-terminated polybutadiene (HTPB) and cobalt salt catalyst were incorporated into the PLA/poly (butylene adipate-co-terephthalate) (PLA/PBAT), followed by melting extrusion and three-layer co-extrusion blown film process to prepare the composite films. The oxygen permeability coefficient of the composite film combined with 6 wt% oxygen scavenger and 0.4 wt% catalyst was decreased significantly from 377.00 cc∙mil∙m-2∙day-1∙0.1MPa-1 to 0.98 cc∙mil∙m-2∙day-1∙0.1MPa-1, showing a remarkable enhancement of 384.69 times compared with the PLA/PBAT composite film. Meanwhile, the degradation behavior of the composite film was also accelerated, exhibiting a mass loss of nearly 60% of the original mass after seven days of degradation in an alkaline environment, whereas PLA/PBAT composite film only showed a mass loss of 32%. This work has successfully prepared PLA/PBAT composite films with simultaneously improved oxygen barrier property and degradation behavior, which has great potential for high-demanding green chemistry packaging industries, including food, agricultural, and military packaging.

Insight into HTPB pyrolysis mechanism under high-temperature: A reactive molecular dynamics study

Hydroxyl-terminated polybutadiene (HTPB) is widely utilized in solid and hybrid rocket propellants due to its mechanical properties and combustion performance. Insight into its pyrolysis process is key to enhancing combustion efficiency in rocket engines. This study employs ReaxFF molecular dynamics (MD) simulations to explore the pyrolysis mechanism of HTPB under extreme conditions, with temperatures ranging from 1000 K to 2000 K. The results identify the primary degradation products and elucidate their formation mechanisms. The simulation reveals that C-C bond cleavage at polymerization sites is the initial step, followed by the formation of linear oligomers and butadiene. Subsequent reactions, including hydrogenation and dehydrogenation, lead to the generation of smaller molecular species. The kinetic analysis confirms that HTPB pyrolysis follows first-order reaction kinetics, with an activation energy of 8.12 kcal/mol. The findings are compared with existing experimental data, highlighting the influence of thermal environments on pyrolysis mechanisms and product distributions.

Combustion and mechanical properties enhancement strategy based on stearic acid surface activated boron powders

Boric acid and other impurities on the surface of boron (B) particles can interact with hydroxyl-terminated polybutadiene (HTPB), weakening the mechanical properties and energy release efficiency of boron-based solid rocket propellants. SA@B composite particles were created by coating stearic acid (SA) on the surface of B particles through solvent evaporation-induced self-assembly. The study investigated the impact of SA coating on the combustion performance of B particles and the mechanical properties of HTPB matrix composites. The results showed that the SA coating enhanced the oxidation efficiency of B particles in air. The combustion heat of SA@B composite particles is 30.29 MJ/g, about 50% higher than that of B particles. During the combustion of SA@B composite particles, fewer molten solid particles surround the flame, which enhances the stability of the combustion process of the B particles. Furthermore, the SA coating effectively enhanced the dispersion of B particles in HTPB. At a stretching speed of 100 mm/min, the tensile strength of the SA@B/HTPB composite materials is higher than that of the B/HTPB composite materials. Moreover, when the mass loading of the SA@B composite particles reaches 50 wt%, the tensile strength of SA@B/HTPB composite materials is 2.46 MPa. Activating the surface of boron particles with SA can significantly improve their compatibility with HTPB, which is crucial for the stable storage of boron-based solid rocket propellants.

Preparation of protective coatings for the leading edge of wind turbine blades and investigation of their water droplet erosion behavior

The damage caused by rain droplet erosion to the leading edge of wind turbine blades is extremely severe. To reduce this issue, in this study, hydroxyl-terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI) were used as the polyurethane (PU) polyol and curing agent, respectively, to prepare a PU coating with a high resistance to water droplet erosion (WDE) for the protection of the leading edge of wind turbine blades. The effect of n (–NCO):n (–OH) (R-value, n is the molar ratio) on the mechanical properties and WDE resistance of PU coatings, the relationship between the two performances, and the influence of the erosion conditions on the WDE behavior were investigated for the first time. The results show the existence of a correlation between the mechanical properties (hardness, impact, flexibility, and tensile strength) and WDE resistance of the coating. While, a better abrasion resistance is found not to result in a better WDE resistance. The PU coating with an R-value of 1.2 shows an optimal WDE resistance in both atomization and jet erosion experiments. In atomized droplet erosion (ADE) experiments, the change in erosion velocity accelerates the incubation period of coating erosion damage and increases the erosion rate. In jet droplet erosion (JDE) experiments, the damage to the coating is closely related to the erosion angle, reaching a maximum at an impact angle of 60°. Furthermore, in the ADE experiments, various erosion morphologies, such as pits, grooves, cracks, and stepped texture, are observed on the damaged coating surface. While, regarding the JDE experiments, holes, grooves, and cracks are observed. Such damage is caused by the combined effects of water hammer pressure, lateral jets, and local permeation.

Catalytic effects of transition metal oxides on HTPB-based fuel polymer matrices

Low regression rate due to difficult pyrolysis is a major challenge in the practical application of terminated hydroxyl‑terminated polybutadiene (HTPB)-based fuels in hybrid rocket propulsion. Accelerating the decomposition of the polymer matrix is an effective method to improve the regression rate of HTPB fuels. To determine the difference in combustion performance between different transition metal oxides loaded HTPB-based fuels, nickel oxide (NiO), ferric oxide (Fe2O3), copper oxide (CuO) and manganese dioxide (MnO2) were introduced into the HTPB matrix at 5% mass fraction. The experimental results showed that the metal oxides could significantly catalyze the pyrolysis of HTPB-based fuels and enhance the fuel regression rate, and the catalytic effect was mainly concentrated in the middle and late stages of the thermal decomposition process of polybutadiene components. Among the four transition metal oxides, CuO and MnO2 showed better catalytic effects on the combustion performance of HTPB-based fuels in the high oxygen mass flux region, while NiO showed better catalytic effects in the low oxygen mass flux region. The present study compares the regression rate of fuel grains modified with different transition metal oxides, which provides a basis for the selection of future catalysts, verifies the catalytic effect of the transition metal oxides on the combustion of HTPB-based fuels and further analyzes the combustion reaction mechanism of the fuels.

EVALUATION OF SOLID ROCKET PROPELLANTS FOR LOW EARTH ORBIT

In contemporary aerospace technology, solid rocket propellants are commonly employed in the thriller and boost of space cargoes to LEO. These are reliable, uncomplicated, and high in thrust; and thus, can be used in both military as well as civil space ventures. This paper provides a comprehensive evaluation of five prominent solid rocket propellants: Five categories namely Ammonium Perchlorate Composite Propellant (APCP), Double-Base Propellant, Composite Modified Double Base (CMDB) Propellant, Hydroxyl-terminated polybutadiene (HTPB)-Based Propellant, and Ammonium Nitrate Composite Propellant (ANCP) have been identified. This also falls under the evaluation and includes aspects such as historical bases to see how the formulation of the propellant has changed over time regarding the development of propellant technology. In the case of each propellant, the chemical properties of the mix and reactions that its fundamental are analyzed. It also shares details regarding the changes and advancements made in the little while to enhance capability, safety, and environmental compatibility of these fuels, such as synthesizing fuels for liquid bipropellants. Some of the modern applications of technologies within the active spectrum of aerospace operations are explained in more detail to provide clients with the most versatile and essential information. Among the essentials of this work, the complex calculation of thrusts developed by the specific propellant with corresponding graphics has significant importance. These estimations afford chances of comparing the efficiency of the propellant in terms of producing thrusts as well as achieving the indicated optimal performance. Thus, the main objective of this study is to identify which of the solid rocket propellants to use in LEO missions and if any, what modifications could be made to improve them. Thus, the purpose of this paper is to contribute to the development of the constantly evolving branch of rocket propulsion by discussing the benefits and shortcomings of each propellant. These findings and recommendations could be useful in perfecting the recipes for the propellants and improving the efficiency of the subsequent missions to planets. Keywords: Aerospace, Solid rocket propellants, Thrust, Low earth orbit.

Study of Aging Characteristics for Metalized HTPB Based Composite Solid Propellants Stored in Ambient Conditions

The aging of any propellant is defined as the change in the physical, chemical, and performance parameters of solid rocket propellants. The propellant’s service life and aging properties are important parameters of the study, especially for missiles and other defense applications. Hydroxyl-terminated polybutadiene (HTPB) based composite solid propellants with ammonium perchlorate (AP) are the most prominently used propellants in the operations of solid rocket motors in the defense and space sectors. Thus, studying this composite solid propellant is of essential when determining ambient service life. Performance parameters studied in this research are burn rate under high-pressure conditions in Crawford bomb setup, Thermogravimetric Analysis, and Fourier Transform Infrared Spectroscopy (FTIR). SEM and X-ray diffraction (XRD) analysis of the aged sample were also conducted to ascertain the chemical composition and morphological changes in the samples. Naturally aged propellant strands manufactured in different years have been compared with freshly prepared ones to establish a trend for deriving conclusions. The results from different analysis techniques, FTIR, XRD, and FESEM, depicted that oxidation of metals happens while aging of propellant due to atmospheric moisture, and the metal oxides prominently affect the propellant chemical composition and decomposition process of the propellant samples. The ballistic properties of the aluminium added samples showed an increment in burn rate. In contrast, the bimetal addition of aluminium and magnesium combined as an additive decreased the ballistic burn rate.

Noncovalent Interactions Define Global Properties of HTPB Isomers.

Commercially available hydroxyl-terminated polybutadiene (HTPB) variants [containing various percentages of its isomers (cis, trans, and vinyl) and utilized in numerous applications ranging from rocket propellant binders to automobile tires] exhibit differences in their thermomechanical properties. Observed thermomechanical response variation between two isomers of HTPB (based upon simulation work at the molecular dynamic level) has been shown to be associated with noncovalent interaction between the isomers. Even though the study has been presented for a specific polymeric system, it could be of interest to the broader polymer chemistry community concerned with the reasons behind the property variation of different isomers of a specific molecule.

Study of curing kinetics of 4‐ (dimethylsilyl) butyl ferrocene grafted HTPB and effect of catalysts by differential scanning calorimetry

AbstractThe cure kinetics of 4‐ (dimethylsilyl) butyl ferrocene grafted hydroxyl terminated polybutadiene (HTPB) with Isophorone diisocyante (IPDI) was investigated using differential scanning calorimeter (DSC). Furthermore, the catalytic effect of Iron (III) acetylacetonate (Fe(AA)3) and Dibutyltin dilaurate (DBTDL) on the curing reaction was studied. The experimental data was fitted to Kissinger and Ozawa models, and the kinetic parameters were expressed as Arrhenius activation energy (E), pre‐exponential factor (A) and rate constants. The Crane model was explored to determine the reaction order of the curing reaction. The study categorically showed that the activation energy of the curing reaction with 4‐ (dimethylsilyl) butyl ferrocene grafted HTPB is higher as compared to the pure hydroxyl terminated polybutadiene (HTPB) based system. However, the rate of curing reaction is higher with 4‐ (dimethylsilyl) butyl ferrocene grafted HTPB as compared to HTPB, and the viscosity build‐up data is too aligned with the DSC kinetic study. In addition, both catalysts increased the rate of the curing reaction but Fe(AA)3 displayed a superior catalytic effect.