Hydroxyl Terminated Poly Ether Research Articles

Synthesis of α,ω-Primary Hydroxyl-Terminated Polyether Polyols Using Prussian Blue Analogs as Catalysts

Synthesis of α,ω-Primary Hydroxyl-Terminated Polyether Polyols Using Prussian Blue Analogs as Catalysts

A study on the decomposition pathways of HTPB and HTPE pyrolysis by mass spectrometric analysis

Hydroxyl-terminated polybutadiene (HTPB) and hydroxyl-terminated polyether (HTPE) are used as binders for rocket propellants, while the mechanisms for their pyrolysis processes are still not clear. In this work, the slow and fast pyrolysis behavior of HTPB and HTPE were studied with a combination of single photoionization mass spectrometry (SPI-MS) and GC-MS, respectively. SPI-MS allowed on-line studying the dynamics of volatile formation as a function of the pyrolysis process, and GC-MS was utilized to characterize the condensed products. Furthermore, the heavy products (m/z > 300) in the condensed liquids were also characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS). Based on the experimental results, a full picture of the product distributions from the HTPB and HTPE pyrolysis was described. Meanwhile, the decomposition pathways were proposed and discussed in detail. The results showed that the radical-addition reaction dominated the decomposition pathways of HTPB, in which the six-membered ring products were readily formed. HTPE was mainly transformed into ethers or aldehydes during the pyrolysis process, and the cyclic products were mainly composed of tetrahydrofuran and its derivatives.

A polyurethane binder with excellent mechanical properties based on copolymerization and dynamic bond crosslinking

Hydroxyl-terminated polybutadiene (HTPB) based polymer binder is expected to possess exceptional mechanical performances, as the matrix of composite solid propellant. In this study, HTPB and hydroxyl-terminated polyether (HTPE) were copolymerized by isocyanate (IPDI) to form HTPB-HTPE, and then ZnCl2 was added to prepare a polyurethane binder (HTPB-HTPE-Zn) with excellent mechanical performances. The thermal properties and dynamic mechanical characteristics of the synthesized polyurethane were characterized by a differential scanning calorimeter, dynamic thermomechanical analyser, and Instron universal testing machine. The experimental results show that HTPB-HTPE-Zn exhibits significantly enhanced elongation at break (1122.52%) and basically unchanged tensile strength (0.37 MPa), compared with pure HTPB (503.42%/0.38 MPa). This work provides a method for preparing binders with high mechanical properties and broadens the application field of HTPB-based polyurethane.

Comparative Study on Thermal Response Mechanism of Two Binders during Slow Cook-Off.

The HTPE (hydroxyl-terminated polyether) propellant had a lower ignition temperature (150 °C vs. 240 °C) than the HTPB (hydroxy-terminated polybutadiene) propellant in the slow cook-off test. The reactions of the two propellants were combustion and explosion, respectively. A series of experiments including the changes of colors and the intensity of infrared characteristic peaks were designed to characterize the differences in the thermal response mechanisms of the HTPB and HTPE binder systems. As a solid phase filler to accidental ignition, the weight loss and microscopic morphology of AP (30~230 °C) were observed by TG and SEM. The defects of the propellant caused by the cook-off were quantitatively analyzed by the box counting method. Above 120 °C, the HTPE propellant began to melt and disperse in the holes, filling the cracks, which generated during the decomposition of AP at a low temperature. Melting products were called the “high-temperature self-repair body”. A series of analyses proved that the different thermal responses of the two binders were the main cause of the slow cook-off results, which were likewise verified in the propellant mechanical properties and gel fraction test. From the microscopic point of view, the mechanism of HTPE’s slow cook-off performance superior to HTPB was revealed in this article.

Investigations on the thermal response of a solid rocket motor with complex charge structure using CL-20/GAP propellant

The thermal safety of a solid rocket motor with a complex charge structure using CL-20 (Hexanitrohexaazaisowurtzitane)/GAP (Glycidyl Azide Polymer) propellant was evaluated. The morphology and thermal decomposition properties of the propellant were first studied by differential thermal analysis, thermogravimetric analysis and scanning electron microscopy experiments. A numerical model of cook-off for a solid rocket motor using GAP/CL-20 propellant was developed. This model takes into account the entire process of cooking off, i.e., the thermal decomposition before ignition and the combustion reaction after ignition. The model is verified, and the kinetic parameters are determined by bomb cook-off experiments. Comparisons between experiments and simulations show that the developed model can accurately predict the thermal response of the propellant. The cook-off processes of a 3D-solid rocket motor with complex charge structures are then simulated with different heating rates. It shows that the charge structure and the annular area of the motor casing play an import role in the ignition location of the propellant. Meanwhile, the heating rate has a dramatic effect on the ignition time. The reaction intensity after the ignition of the solid rocket motor using the GAP/CL-20 propellant is more intense than those using HTPE (hydroxyl-terminated polyether)/HTPB (Hydroxyl-terminated polybutadiene) propellant.

Development of novel urea burning rate suppressants in AP/HTPE propellants with superior efficiency and desirable mechanical performance

ABSTRACT The liquid burning rate suppressants (BRSs) at room temperature were first prepared by combining urea with adsorption group from AP-bonding agents. The novel urea BRSs were applied in triethylene glycol dinitrate (TEDGN) plasticized hydroxyl-terminated polyether (HTPE) propellants. The results show that only 0.5% of them can reduce the burning rate and pressure index of the propellants at the same time. Owing to the adsorption group from AP bonding agents, the novel urea BRSs can adsorb onto the surface of AP during mixing by themselves, which are more suitable for industrial application than nano-sized or encapsulated BRSs. In addition, the desirable mechanical performance can be obtained and the BRSs have little influence on the hazardous properties of propellants.

Oxidizability Enhancement of Hydroxyl Terminated Polyether Polyurethane Elastomers via Fluoroalcohols Grafting

AbstractA series of fluoroalcohol grafted hydroxyl‐terminated polyether (HTPE) polyurethanes (PU) elastomers were synthesized by a two‐step method. The reaction progress was investigated by chemical titration and Fourier transform infrared spectroscopy (FTIR). The glass transition temperature (Tg), mechanical properties, morphology, and thermal decomposition behavior were determined for the preliminary analysis of PUs; the oxidizability property was tested by the decomposition of PU/Al composites. The results of mechanical and morphology properties demonstrated that the mechanical strength of modified PU elastomers was effectively improved for microphase separation of the hard segment. The PU film with the optimized fluoroalcohol content shows excellent performance of 17.7 MPa (tensile strength) and 547 % (elongation at break) at room temperature. Analysis of the thermal behaviors suggests that the oxidation ability of the modified PU is enhanced by the strong electronegativity of fluorine. The oxidizing gas HF, CFx, released during fluoroalcohol decomposition reacts with the alumina shell, releasing internal reactive Al, which improves the activity of the aluminum. This study might provide a new idea for utilizing high‐performance polymer binders in composite solid propellants and casting explosives.

Influence of Fluorinated Polyurethane Binder on the Agglomeration Behaviors of Aluminized Propellants.

In this study, fluorinated polyurethane (FPU) was prepared from dialcohol-terminated perfluoropolyether as a soft segment; isophorone diisocyanate (IPDI) as a curing agent; 1,2,4-butanetriol (BT) as a crosslinker; and 1,4-butanediol (BDO) as a chain extender. Fourier transform infrared spectroscopy (FTIR) and 1H NMR were used to characterize the structure of the FPU. The mechanical properties of the FPUs with different BDO and BT contents were also measured. The tensile strength and breaking elongation of the optimized FPU formula were 3.7 MPa and 412%, respectively. To find out the action mechanism of FPU on Al, FPU/Al was prepared by adding Al directly to FPU. The thermal decomposition of the FPU and FPU/Al was studied and compared by simultaneous differential scanning calorimetry-thermogravimetry-mass spectrometry (DSC-TG-MS). It was found that FPU can enhance the oxidation of Al by altering the oxide-shell properties. The combustion performance of the FPU propellant, compared with the corresponding hydroxyl-terminated polyether (HTPE)-based polyurethane (HPU) propellant, was recorded by a high-speed video camera. The FPU propellants were found to produce smaller agglomerates due to the generation of AlF3 in the combustion process. These findings show that FPU may be a useful binder for tuning the agglomeration and reducing two-phase flow losses of aluminized propellants.

Experimental and simulative thermal stability study of HTPE solid propellants in different scales

The hydroxyl-terminated polyether (HTPE) solid propellants are widely recognized as promising alternatives for hydroxyl-terminated polybutadiene (HTPB) propellants due to their compliance with insensitive munition characteristics of composite solid propellant. This study reports thermal stability investigation of HTPE solid propellants in different scales with the help of differential scanning calorimetry (DSC, 0.9 mg), accelerating rate calorimetry (ARC, 0.219 g), and slow cook-off (112 g) tests by taking HTPE/A3/Al/AP/PSAN composite solid propellant as an example. More importantly, for the first time, thermal decomposition kinetic parameters of HTPE solid propellant were calculated by employing iso-conversional Friedman method and using DSC experimental data at different heating rates. The simulation results of adiabatic combustion and slow cook-off of the HTPE propellant were obtained by applying the kinetic parameters in Advanced Kinetics and Technology Solutions software, which exhibited satisfied consistency with the experimental results, with less than 2% average deviation. Finally, the validated kinetic parameters were further employed to describe the large-scale thermal hazards of HTPE propellant and the predicted self-accelerating decomposition temperature of HTPE propellant in 50 kg-scale was 94.2 °C. Our simulative study provided a cogent and convenient strategy to understand thermal hazard of HTPE solid propellant in different scales during usage, storage, and transportation.

Effect of Plasticizer on Mechanical and Thermal Properties of In Situ-Prepared Block Hydroxyl-Terminated Polyether Applied in Propellants

The relationship between the mechanical properties of in situ-prepared hydroxyl-terminated polyether (HTPE)/N-butyl-N-(2-nitroxyethyl)nitramine (Bu-NENA) binders and the plasticization ratio (pl/po), ranging from 0.4 to 1.2, was studied. The thermal properties and the very early stage of evaporation of Bu-NENA from an HTPE/Bu-NENA binder with a pl/po of 1.0 were also investigated. The results revealed that the pl/po ratio has a strong influence on the mechanical properties. When the pl/po ratio was 1.0, the mechanical properties of the in situ-prepared HTPE/Bu-NENA binder were satisfactory. The results showed that the Tg values of the in situ-prepared and traditional HTPE/Bu-NENA binder decreased as the plasticization ratio increased, and finally stabilized at approximately −75 and −78°C, respectively; moreover, the degree of phase mixing of the two soft segments of the in situ-prepared HTPE/Bu-NENA binder was greater than that of the traditional HTPE/Bu-NENA binder. The activation energy of the Bu-NENA evaporation from the in situ-prepared HTPE/Bu-NENA binder was close to that for the traditional HTPE/Bu-NENA binder, but the pre-exponential factor differed by an order of magnitude. Compared with the traditional HTPE propellant, the mechanical properties of the in situ-prepared HTPE propellant were greatly improved.

High-strain-rate mechanical response of HTPE propellant under SHPB impact loading

The high-strain-rate dynamic response of a hydroxyl-terminated polyether (HTPE) propellant during impact loading is essential for assessing the structural reliability and impact safety of HTPE propellant. In this study, a modified split Hopkinson pressure bar (SHPB) apparatus has been developed to research the stress–strain behavior of the HTPE propellant over strain rates ranging from 470 to 5910 s−1 at room temperature, and the validity of the SHPB test is analyzed in detail. Meanwhile, the evolution of deformation to failure of the HTPE propellant was recorded by a high-speed digital camera synchronized with the SHPB test, which revealed the correlation between mechanical response and failure mode. Scanning electron microscopy was applied to investigate the microscopic failure mechanism of the post-test HTPE propellant, which indicated two characteristic failure modes: cracking propagates along the (1) debonding surface and (2) transgranular damage path. Finally, based on the stress–strain plots derived from the SHPB tests, the ultimate stress, strain energy density, and adiabatic temperature-rise effect of the HTPE propellant were seen to show strong strain rate dependence by following an empirical power law function.

Investigation of Hydroxyl‐Terminated Polyether Cured with Different Isocyanates: Curing Process and Mechanical Property

AbstractIn order to study the curing process of hydroxyl‐terminated polyether (HTPE) with different curing agents, aliphatic triisocyanate (N100) and toluene diisocyanate (TDI), the crosslink density (XLD) and chemical processes of the curing reactions have been investigated by low‐field NMR spectroscopy and FTIR spectroscopy, respectively, while the mechanical properties of those two cure systems were studied as well. The results show that, for either HTPE/N100 or HTPE/TDI, the higher curing temperature leads to the shorter curing time to reach stability of XLD, while the final XLD decreases by increasing the temperature. The XLD and tensile strength of HTPE/TDI are both lower than those of HTPE/N100, although curing reaction of the HTPE/TDI system is faster and more complete, as seen from FTIR spectra. Besides, the tensile strength of HTPE/N100 based propellant attains the maximum value of 0.64 MPa at NCO/OH ratio of 1.4, while the maximum XLD value of 6.5 10−5 mol⋅cm−3 was obtained at the same time. The XLD is well correlated in tensile strength with the variation of NCO/OH, that suggests regulation of XLD value may be an effective way to optimize the curing conditions for improving mechanical properties of HTPE/isocyanate‐based propellants.

Enhancing the Performance of an HTPE Binder by Adding a Novel Hyperbranched Multi‐Arm Azide Copolyether

AbstractModern composite solid propellants must exhibit excellent mechanical properties together with high energy outputs, and the binder system plays a vital role in establishing these characteristics. In the present work, varying proportions of a novel hyperbranched multi‐arm azide copolyether (POG) were combined with a hydroxyl‐terminated polyether (HTPE) to prepare crosslinked elastomeric binders. The compatibility of the POG and HTPE was demonstrated before a series of HTPE/POG blend binders were prepared based on a urethane reaction using hexamethylene diisocyanate (HMDI) as the curing agent. The mechanical properties of HTPE/POG/HMDI elastomers were found to be superior to those of traditional HTPE/N100 crosslinked binders as a result of the formation of a hyperbranched crosslink structure. Evaluations of the local motions of polymers chains and parameters related to the cured network structure demonstrated the advantages of introducing the hyperbranched POG. Hydrogen bonding in the HTPE/POG/HMDI binder was investigated and the results confirmed that these elastomers also benefited from hydrogen bonding, as well as the entanglement and interpenetration of molecular chains. Decomposition behavior was studied by thermogravimetric analysis, differential thermogravimetry and differential scanning calorimetry, and the new binders exhibited good thermal stability and superior energetic performance that could potentially meet the requirements for military applications.

Preparation of Bi2O3/Al Core-Shell Energetic Composite by Two-Step Ball Milling Method and Its Application in Solid Propellant.

In this article, Bi2O3/Al high-density energetic composites with a core-shell structure were prepared by a two-step ball milling method using a common planetary ball milling instrument, and their morphology, structure, and properties were characterized in detail. Through a reasonable ratio design and optimization of the ball milling conditions, the density of the Bi2O3/Al core-shell energetic composite is increased by about 11.3% compared to that of the physical mixed sample under the same conditions. The DSC (Differential Scanning Calorimetry) test also showed that the exothermic quantity of the thermite reaction of the energetic composite reached 2112.21 J/g, which is very close to the theoretical exothermic quantity. The effect of Bi2O3/Al core-shell energetic composite on the energy performance of insensitive HTPE propellant was further studied. The theoretical calculation results showed that replacing the partial Al with Bi2O3/Al core-shell energetic composite can make the density of propellant reach 2.056 g/cm3, and the density specific impulse reach 502.3 s·g/cm3, which is significantly higher than the density and density specific impulse of the conventional composite solid propellant. The thermal test showed that the explosive heat of the HTPE (Hydroxyl terminated polyether) propellant also increased with the increase of the content of Bi2O3/Al core-shell energetic composite.

Investigation on the thermal decomposition of hydroxyl terminated polyether based polyurethanes with inert and energetic plasticizers by DSC-TG-MS-FTIR

Thermal decomposition behavior of hydroxyl terminated polyether (HTPE) based polyurethanes (PUs) containing glycerol triacetate (TA), bis(2,2-dinitropropyl)-acetal/formal (BDNPA/F, also known as A3) and N-butyl-N-(2-nitroxyethyl)nitramine (NENA) respectively as plasticizers were investigated by the combination of differential scanning calorimetry-thermogravimetry-mass spectrometry-Fourier transform infrared spectroscopy (DSC-TG-MS-FTIR) techniques. Instead of DSC, DTG curves were applied to evaluate the compatibility since no intense exothermic effect appears in decomposition of HTPE based PU. Three plasticizers, especially the inert TA, were absolutely compatible with HTPE in perspective of engineering application according to the evaluated standard of compatibility. Decomposition of HTPE based PU after endothermic melting is a two-step process including, exothermic depolymerization succeed by intense decomposition. Influence mechanisms of energetic and inert plasticizers on decomposition of HTPE based PU are different. NO· free radical generated by the pyrolysis of NENA and A3 is the major incentive of chain scission resulting in depolymerization of HTPE based PU, and chain scission temperature are shifted forward with the increasing concentration of NO· as the NENA-PU is more vulnerable. While carbanion and electrophile intermediate resembling CO2 generated by decarboxylation reaction of carboxylic acid are the major reactive products in TA. Furthermore, micro defect caused by migration of TA in TA-PU accelerates the degradation of HTPE based PU under acidic condition.

Thermal and mechanical properties of two kinds of hydroxyl-terminated polyether prepolymers and the corresponding polyurethane elastomers

In order to analyze the differences in performance between two kinds of hydroxyl-terminated polyether (HTPE) binders, the curing reaction kinetics of the prepolymers and polyfunctional isocyanate (N-100) molecules and the thermal properties of the prepolymers and the corresponding polyurethane (PU) elastomers were studied by non-isothermal differential scanning calorimetry. The mechanical properties of PU elastomers were also studied by uniaxial tensile tests. With these data, the binder type could be chosen more appropriately for its application in rocket propellant formulations. The results showed that the reactivity of hydroxyl-terminated block copolyether (TPEG) with an isocyanate group is higher than that of hydroxyl-terminated random copolyether (PET). The chain flexibility of TPEG was less than that of PET, but the stereoregularity and crystallization ability of the former were superior. Compared to the prepolymers, the chain flexibility of the corresponding PU elastomers was reduced, and the crystallization ability became weaker such that their onset of crystallization was delayed. After the prepolymers were reacted with N-100, the thermal properties of PU elastomers remained consistent with their respective prepolymers. In summary, it was concluded that the mechanical properties of TPEG/N-100 PU elastomer films were found to be superior to the PET/N-100 films.

Curing reaction kinetics of HTPE polymer studied by simultaneous rheometry and FTIR measurements

In order to study the curing reactions of hydroxyl-terminated polyether (HTPE) with a curing agent hexamethylene diisocyanate biuret (HDIB), the rheology and chemical processes of the curing reactions have been studied by simultaneous rheometry and FTIR spectroscopy. It was shown that the gel point was a key parameter in the curing reaction of HTPE with HDIB. The gel point was at the intersection of G′ and G″ curves. The gel point was when gelation occurred. After gelation, the polymer could not flow and the viscosity and real modulus increased rapidly. The curing reaction of the HTPE/HDIB kinetics system, monitored by an FTIR technique, showed a characteristic intensity peak at 2270 cm−1, corresponding to the –N=C=O stretching vibration which decreased as a function of time and the curing reaction of the HTPE/HDIB system and obeyed a three-dimensional (spherical symmetric) diffusion model.

Gas Permeation Properties of Organic-Inorganic Hybrid Membranes Prepared from Hydroxyl-Terminated Polyether and 3-isocyanatopropyltriethoxysilane

Organic-inorganic hybrid materials were prepared by reacting 3-isocyanatopropyltriethoxysilane (IPTS) with hydroxyl terminated poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG) and poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) (PEPG), followed by hydrolysis and condensation with acid catalysis. Composite membranes have been obtained by casting hybrid sol on the microporous polysulfone substrate. The membranes were characterized by Fourier transform infrared (FT-IR), 13C NMR and 29Si NMR. The permeability coefficients of N2, O2, CH4 and CO2 were measured by variable volume method. The gas permeability coefficients increase with increasing molecular weight of the polyethers. For the membranes containing PEG and PEPG, the higher values of CO2 permeability coefficients and CO2/N2 separation factors are due to the presence of ethylene oxide segments. In case of PEPG membranes, molecular weight has more influence on CO2 permeability than the effect of facilitation by ethylene oxide. The addition of TEOS into hybrid sol results in the decrease of all the gas permeability and does not affect the gas selectivity. PEG2000 membrane display the most performance among the hybrid membranes investigated here. The best values observed are CO2 permeability of 94.2 Barrer with selectivity of 38.3 for CO2/N2 and 15.6 for CO2/CH4.

INSENSITIVE MUNITIONS PROPULSION PROGRESS

Increasing interest in the application of thrust-managed, solid-propellant rocket motors for future missiles has prompted a desire to learn how these motors might react to the stimuli involved in the MIL-STD 2105B1 insensitive munitions (IM) hazards tests. An opportunity became available for the Insensitive Munitions Advanced Development (IMAD) Propulsion Project to obtain four experimental, dual-pulse (two chamber) rocket motors; these motors were subjected to the fast cookoff, slow cookoff, bullet impact, and fragment impact IM hazards tests. These motors had steel cases with a bulkhead separating one pulse from the other. The propellant for each pulse grain was a nitrate-ester-plasticized, reduced-smoke, hydroxyl-terminated polyether (HTPE) propellant. Reactions in the IM hazards tests were classified as follows: fast cookoff, deflagration (fail); slow cookoff, explosion (fail); bullet impact, burn (pass); and fragment impact, explosion (fail). In the cookoff tests, the aft pulse (pulse 1) reacted first followed by the forward pulse (pulse 2). Delay times between the reaction of pulse 1 and pulse 2 were 5 seconds for the fast cookoff and 45 seconds for the slow cookoff tests. It was unexpected when pulse 1 reacted first, because this pulse's chamber consisted of thicker insulation. In the impact tests, the projectiles and fragments were aimed at the pulse 2 chamber resulting in the reaction of this pulse with no accompanying reaction from pulse 1. The implication of these results is that separate chamber, pulsed motors containing a relatively insensitive propellant such as the HTPE propellant will probably provide less collateral damage than motors in which an equivalent amount of propellant is contained in one chamber.