Viscoelastic behavior of hydroxyl terminated polybutadiene containing glycerin

Hydroxyl terminated polybutadiene (HTPB) is widely used as a propellant binder. A plasticizer is usually added to improve the processing properties, the mechanical properties, and the burning characteristics of the propellant. Glycerin was found to be an effective additive to improve these properties. The glycerin/HTPB blend was hard enough to act as a binder for the composite propellant when the glycerin/HTPB mole ratio was less than 10. Only a small quantity of glycerin was incorporated into the network structure of the cured HTPB. Most of the added glycerin physically entered the voids in the network of the cured HTPB. Addition of a small quantity of glycerin (mole ratio less than 0.1) significantly altered the network density and the viscoelastic properties of the blends. The properties were only slightly dependent on the amount of the added glycerin in the mole ratio range of 0.1–10. The dangling ends were formed in the HTPB network by the addition of glycerin and the network structure was loosened, thereby enhancing the mobility of the chain segment. The viscoelastic properties of the blends followed the time‐temperature superposition principle, and the properties were estimated accurately by the Williams‐Landel‐Ferry approach. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical Characteristics and Thermal Decomposition Behavior of Polytetrahydrofuran Binder using Glycerol Propoxylate (Mn=260) as Crosslinking Agent

Polytetrahydrofuran (PTHF) is an effective binder ingredient for improving propellant performance, even though it is not an energetic material. PTHF becomes sufficiently rubbery for use as a binder when a triol material such as glycerin is added as a crosslinking modifier. The cured PTHF/glycerin binder had unsatisfactory mechanical characteristics for use as a propellant binder, so a more appropriate crosslinking modifier than glycerin needs to be found. In this study, glycerol propoxylate (GPO), with a molecular weight of 260, was used as a crosslinking modifier, and the curing behavior, tensile properties, and thermal decomposition behaviors of the PTHF binder using GPO were investigated. The PTHF/GPO blend did not solidify when the PTHF/GPO mole ratio (ξ) was greater than a certain value. The PTHF (M_n=650)/GPO blend with ξ≤5 and the PTHF (M_n=1400)/GPO blend with ξ≤3 were used as propellant binders. From the curing behaviors and tensile properties, it was found that the PTHF/GPO binders ensured optimal mixing of the propellant ingredients and casting of the uncured propellant into the rocket motor case, and the tensile properties of the binders changed more drastically with the variation in ξ than did those of the PTHF/glycerin binders. The thermal decomposition behaviors of the PTHF/GPO binders were hardly dependent on ξ and were almost identical to those of the PTHF/glycerin binders.     

储氢合金/AP/HTPB推进剂的热分解性能

采用TG-DTG、DSC以及动力学分析方法研究了储氢合金/AP/HTPB推进剂的热分解性能。结果表明,相对于Al/AP/HTPB推进剂,储氢合金/AP/HTPB推进剂的热分解温度降低,放热量提高;A20/AP/HTPB推进剂的凝聚相反应程度提高2.44%,第二、三温区的热分解活化能(Kissinger法)分别降低4.06%和22.63%;A30/AP/HTPB推进剂的凝聚相反应程度提高10.61%,第二、三温区的热分解活化能(Kissinger法)分别降低30.89%和38.87%。储氢合金对AP/HTPB推进剂的热分解有催化作用,并且该催化作用随着储氢合金中Mg0.45Ni0.05B0.5Hx含量的增加而增强。     

Application of Amorphous Boron Granulated With Hydroxyl‐ Terminated Polybutadiene in Fuel‐Rich Solid Propellant

Amorphous boron powder granulated with HTPB, whose particle diameter could be controlled, was prepared by mechanical mill method. It was found that amorphous boron powder could be granulated with HTPB binder to form B‐HTPB particles, whose median particle diameter (d₅₀) and specific surface area are in the range of 125.0–431.0 µm and 0.02–0.1 m² g⁻¹, respectively. The B‐HTPB particles could be dispersed in the HTPB binder with relatively low viscosity compared with direct addition of amorphous boron powder to the HTPB binder. The experimental results showed that the content of boron particles in a fuel‐rich propellant could be increased by addition of B‐HTPB particles and the combustion characteristics of the fuel‐rich solid propellant could be improved.     

纳米级金属和金属复合物粉末对高氯酸铵和高氯酸铵/聚合丁二烯复合固体推进剂热分解特性的影响

Effects of metal (Ni, Cu, Al) and composite metal (NiB, NiCu, NiCuB) nanopowders on the thermal decomposition of ammonium perchlorate (AP) and composite solid propellant ammonium perchlorate/hydroxyterminated polybutadiene (AP/HTPB) were studied by thermal analysis (DTA). The results show that metal and composite metal nanopowders all have good catalytic effects on the thermal decomposition of AP and AP/HTPB composite solid propellant. The effects of metal nanopowders on the thermal decomposition of AP are less than those of the composite metal nanopowders. The effects of metal and composite metal nanopowders on the thermal decomposition of AP are different from those on the thermal decomposition of the AP/HTPB composite solid propellant.     

Burning‐rate enhancement of a high‐energy rocket composite solid propellant based on ferrocene‐grafted hydroxyl‐terminated polybutadiene binder

Four different samples of ferrocene‐grafted hydroxyl‐terminated polybutadiene (Fc‐HTPB), containing 0.20, 0.52, 0.90, and 1.50 wt % iron, were synthesized by the Friedel–Crafts alkylation of ferrocene with hydroxyl‐terminated polybutadiene (HTPB) in the presence of AlCl₃ as a (Lewis acid) catalyst. The effects of the reaction conditions on the extent of ferrocene substitution were investigated. The Fc‐HTPBs were characterized by IR, ultraviolet–visible, ¹H‐NMR, and ¹³C‐NMR spectra. The iron content and number of hydroxyl groups were estimated, and the properties, including thermal degradation, viscosity, and propellant burning rates (BRs), were also studied. The thermogravimetric data indicated two major weight loss stages around 395 and 500°C. These two weight losses were due to the depolymerization and decomposition of the cyclized product, respectively, with increasing temperature. The Fc‐HTPB was cured with toluene diisocyanate and isophorone diisocyanate separately with butanediol–trimethylolpropane crosslinker to study their mechanical properties. Better mechanical properties were obtained for the gumstock of Fc‐HTPB polyurethanes with higher NCO/OH ratios. The BRs of the ammonium perchlorate (AP)‐based propellant compositions having these Fc‐HTPBs (without dilution) as a binder were much higher (8.66 mm/s) than those achieved with the HTPB/AP propellant (5.4 mm/s). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Evaluation of Nano‐Co3O4 in HTPB‐Based Composite Propellant Formulations

Different propellant compositions were prepared by incorporating nano‐sized cobalt oxide from 0.25 % to 1 % in HTPB/AP/Al‐based composite propellant formulations with 86 % solid loading. The effects on viscosity build‐up, thermal, mechanical and ballistic properties were studied. The findings revealed that by increasing the percentage of nano‐Co₃O₄ in the composition, the end of mix viscosity, the modulus and the tensile strength increased, whereas the elongation decreased accordingly. The thermal property data envisaged a reduction in the decomposition temperature of ammonium perchlorate (AP) as well as formulations based on AP. The ballistic property data revealed an enhanced burning rate from 6.11 mm s⁻¹ (reference composition) to 8.99 mm s⁻¹ at 6.86 MPa and a marginal increase in pressure exponent from 0.35 (reference composition) to 0.42 with 1 % nano‐cobalt oxide.     

Burning Characteristics and Thermochemical Behavior of AP/HTPB Composite Propellant Using Coarse and Fine AP Particles

The burning rate of AP/HTPB composite propellant increases with increasing AP content and with decreasing AP size. In addition, the burning rate can be enhanced with the addition of Fe₂O₃. The burning characteristics and thermal decomposition behavior of AP/HTPB composite propellant using coarse and fine AP particles with and without Fe₂O₃ at various AP contents were investigated to obtain an exhaustive set of data. As the AP content decreased, the burning rate decreased and the propellants containing less than a certain AP content self‐quenched or did not ignite. The self‐quenched combustion began at both lower and higher pressures. The lower limit of AP content to burn the propellant with coarse AP was lower than that with fine AP. The lower limit of AP content to burn was decreased by the addition of Fe₂O₃. The thermal decomposition behavior of propellants prepared with 20–80 % AP was investigated. The decrease in the peak temperature of the exothermic decomposition suggested an increased burning rate. However, a quantitative relationship between the thermochemical behavior and the burning characteristics, such as the burning rate and the lower limit of AP content to burn, could not be determined.     

Evaluation of 4‐(Dimethylsilyl) Butyl Ferrocene Grafted HTPB as a Burning Rate Modifier in Composite Propellant Formulation using Bicurative System

High burning rate composite propellants are achieved by incorporation of fine particles of oxidizer, transition metal oxides, and liquid ballistic modifiers. However, they pose processing problems, inertness to the composition and migration related issues. To overcome such problems, an attempt was made to incorporate ferrocenyl grafted HTPB as a burning rate modifier by partly replacing HTPB from 10 % to 50 % using TDI/ IPDI bicurative system and to study their processability in terms of viscosity, mechanical, thermal, sensitivity, and ballistic properties. The data on viscosity reveal that there is a marginal enhancement in end of mix viscosity as percentage of ferrocenyl grafted HTPB increases. The mechanical data reveal that tensile strength and elastic modulus increases, whereas percentage elongation decreases compared to base composition. The results on thermal properties infer that, as the percentage of ferrocenyl grafted HTPB increases, onset decomposition temperature decreases. The impact and friction sensitivity data also envisage that sensitivity increases in comparison to base composition. The data on ballistic properties revealed that there is ca. 53 % increase in burning rate, while decrease in “n” value from 0.39 to 0.2 was obtained compared to base composition.     

Research on the Combustion Properties of Propellants with Low Content of Nano Metal Powders

A comparison of various experimental results for combustionrelated properties evaluation, including burning rates, deflagration heat, flame structures and thermal decomposition properties, of AP/RDX/Al/HTPB composite propellants containing nano metal powders is presented. The thermal behavior of n‐Al (nano grain size aluminum) and g‐Al (general grain size aluminum i.e., 10 μm) heated in air was also investigated by thermogravimetry. The burning rates results indicate that the usage of bimodal aluminum distribution with the ratio around 4 : 1 of n‐Al to g‐Al or the addition of 2% nano nickel powders (n‐Ni) will improve the burning behavior of the propellant, while the usage of grading aluminum powders with the ratio 1 : 1 of n‐Al to g‐Al will impair the combustion of the propellant. Results show that n‐Al and n‐Ni both have a lower heating capacity, lower ignition threshold and shorter combustion time than g‐Al. In addition n‐Al is inclined to burn in single particle form. And the thermal analysis results show that n‐Ni can catalyze the thermal decomposition of AP in the propellant. The results also confirm the high reactivity of n‐Al, which will lead to a lower reaction temperature and rather higher degree of reaction ratio as compared with g‐Al in air. All these factors will influence the combustion of propellants.     

Synthesis and Application of Borate Ester Bonding Agents for a Four‐Component Hydroxy‐Terminated Polybutadiene Propellant

Low molecular weight interconnection monomers including polyepichlorohydrin, poly(propylene oxide), poly(ethylene glycol adipate), and poly(butylene adipate) were synthesized to evaluate the effects of the molecular structure of interconnection monomers on the bonding efficiency of borate ester bonding agents (BEBA) applied in four‐component hydroxy‐terminated polybutadiene (HTPB) propellants. The monomers were characterized by IR spectroscopy, elemental analysis, and gel permeation chromatography. A series of new borate ester bonding agents were synthesized using the as‐synthesized interconnection monomers as well as poly(ethylene glycol) and applied in the preparation of four‐component HTPB propellants. The application results showed that BEBA‐4 prepared from poly(butylene adipate) could significantly improve the mechanical properties of the four‐component HTPB propellant, reduce the slurry viscosity leading to improvement of processing properties and aging resistant performance, while no significant effect on the burning characteristics of the propellant was observed.     

B/Fe_2O_3/NC复合物的制备及其对HTPB/AP推进剂性能的影响

为改善硼粉(B)的性能和纳米氧化铁(Fe_2O_3)在固体推进剂中的分散性,用静电喷雾法制备了B/Fe_2O_3/NC复合物,采用扫描电镜(SEM)表征了复合物的表面形貌,用TG-DSC分析了复合物的热性能及其对HTPB/AP推进剂热性能的影响,并用燃速测试和密闭爆发器实验研究了该复合物对HTPB/AP推进剂燃烧性能的影响。结果表明,所制备的B/Fe_2O_3/NC复合物均以团聚体的形式存在,复合物中B的活性提高,其氧化反应温度提前;团聚硼粉对HTPB/AP推进剂燃烧性能的改善效果明显优于原料硼粉;加入Fe_2O_3后,会进一步改善含硼推进剂的燃烧性能,而且随Fe_2O_3含量的增加,在密闭爆发器中HTPB/AP推进剂达到最高压力所需的时间逐渐减小。当Fe_2O_3的质量分数为8%时,推进剂在常压空气中的燃速最大,为不添加B/Fe_2O_3/NC复合物的HTPB/AP推进剂的2.77倍。B/Fe_2O_3/NC复合物对推进剂的热分解具有一定催化作用,且随Fe_2O_3含量的增加催化作用增强。     

Comparative study on phase and properties between rPET/PS and LCP/PS in situ microfibrillar-reinforced composites

Microfibrillar-reinforced composites based on two dispersed phases, liquid crystalline polymer (LCP) and recycled poly(ethylene terephthalate) (rPET), and polystyrene (PS) were prepared using extrusion process. The rheological behavior, morphology, and thermal stability of LCP/PS and rPET/PS blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into PS significantly improved the processability. The potential of rPET as a processing lubricant by bringing down the melt viscosity of the blend system was as good as LCP. The elongated LCP domains were clearly observed in as-extruded strand. Although the viscosity ratio of rPET/PS system was lower than that of LCP/PS system, most rPET domains appeared as small droplets. An addition of LCP and rPET into PS matrix improved the thermal resistance in air significantly. The obtained results suggested the high potential of rPET as a processing aid and thermally stable reinforcing-material similar to LCP. The mechanical properties of the LCP-containing blends were mostly higher than those of the corresponding rPET-containing blends when compared at the same blend composition.     

Preparation and characterization of LDPE/PVA blend films filled with glycerin‐plasticized polyvinyl alcohol

A series of LDPE/PVA blend films were prepared via a twin‐screw extruder, and their morphology, thermal property, oxygen and water vapor permeation, surface properties, and mechanical properties were investigated as a function of the PVA content. During the extrusion process of the blend films, glycerin improved the compatibility and processing conditions between LDPE and PVA. The melting temperature (T_m), melting enthalpy (ΔH_m), crystallinity (%), and thermal stability of the thermal decomposition temperature (T_5%) of the LDPE/PVA blend films decreased with increasing PVA content. The oxygen permeabilities of the blend films decreased from 24.0 to 11.4 cm³·cm (m²·day·atm)^?1 at 23°C. The WVTR increased from 7.8 to 15.0 g(m² day)^?1 and the water uptake increased from 0.13 to 9.31%, respectively. The mechanical properties of blend films were slightly enhanced up to 2% PVA and then decreased. The physical properties of the blend films strongly varied with the chemical structure and morphology depending on the PVA and glycerin. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41985.     

高强度、高燃速丁羟推进剂配方工艺研究

对高不挥发物质量分数、高强度、高燃速丁羟推进剂进行了配方研究。采用了HTPB(端羟基聚丁二烯)、TDI(甲苯二异氰酸酯)黏合剂体系及STR增强剂的固化网络,选用SX-1助剂以改善工艺性能,通过优化AP级配、调节混合工艺程序等方法,使推进剂具有不挥发物质量分数88%、密度1.82g/cm3、20℃抗拉强度σm3MPa、65℃抗拉强度σm≥2.3MPa,燃速35mm/s的良好性能,并具有药浆初始黏度低,工艺流动流平性好的特点。     

Effect of Coating of Ammonium Perchlorate with Fluorocarbon on Ballistic and Sensitivity Properties of AP/Al/HTPB Propellant

Fluorocarbon polymers are used to enhance thermal stability and electrostatic protection of composite propellant compositions. A precipitation technique has been developed to coat ammonium perchlorate (AP) using a copolymer of hexafluoropropylene and vinylidene fluoride (HFP‐VF) with the help of solvent‐counter solvent method. The coated AP has been used to prepare propellant compositions in different ratio based on hydroxyl terminated polybutadiene (HTPB), aluminium powder along with uncoated AP and studied for viscosity build‐up and visco‐elastic behaviour as well as mechanical, ballistic, thermal and sensitivity properties keeping 86% solid loading. The data on viscosity build‐up indicate that as the percentage of viton coated AP increases end of mix viscosity and viscosity build‐up increase accordingly. The mechanical properties data reveal that tensile strength and percentage elongation are found in increasing order. The burn rate of the composition also increases on higher percentage of HFP‐VF coated AP. The thermal stability of composition increases as the percentage of HFP‐VF coated AP increases. The data on sensitivity indicate that impact sensitivity decreases on increasing the percentage of HFP‐VF coated AP while no change is observed in friction sensitivity value.     

Mathematical modeling of rheological properties of hydroxyl‐terminated polybutadiene binder and dioctyl adipate plasticizer

Solid composite propellants contain 80–90% of a crystalline oxidizer like ammonium perchlorate and powdery metallic fuel like aluminum with 10 to 15% organic binders like HTPB or CTPB, to bind the solids together and maintain the shape under severe stress and strain environment. Also, the propellant must not crack or become brittle at subzero temperatures. Formulating and processing of the highly filled composite propellants are difficult tasks and need a thorough understanding of rheology, even apart from a knowledge of propellant chemistry, particulate technology, manufacturing methods, and safe handling of explosives and hazardous materials. The flow behavior or rheology of the propellant slurry determines the ingredients and some of the abnormalities of the motor during firing. The propellant viscosity and mechanical properties are determined by the binder system, and the unloading viscosity of the propellant slurry is dependent on the initial viscosity of the binder system, solid loading, particle size, and its distribution, shape, temperature, and pressure. In the present report an attempt is made to study the dependency of viscosity of the HTPB binder system on temperature, plasticizer level (composition), and torque (angular velocity of spindle). The viscosity measurements were made using a Brookfield viscometer model DV III at different plasticizer levels (10–50%), temperatures (30–65°C), and torques (50–100%). The data indicate that the viscosity of HTPB, DOA, and their mixture decreases with increasing temperature and is constant with torque. The Arrhenius equation gives the energy for viscous flow to be ?35 kcal/mol for HTPB. The variation of viscosity with temperature of HTPB/DOA and their mixture follows a mathematical model expressed as where T is the temperature and a₁, a₂, a₃, a₄, and a₅ are the constants. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1002–1007, 2002     

Mechanical Characteristics and Thermal Decomposition Behaviors of Polytetrahydrofuran Binder with Glycerol Propoxylate (Mn=1500) as a Crosslinking Agent

Polytetrahydrofuran (PTHF) is an effective binder ingredient for improving propellant performance, although it is not an energetic material. PTHF becomes sufficiently rubbery for use as a binder when a triol is added as a crosslinking modifier. In this study, glycerol propoxylate (GPO), with a molecular weight of 1500, was used as a crosslinking modifier, and the curing behavior, tensile properties, and thermal decomposition behaviors of the PTHF binder with GPO were investigated. A PTHF (M _n=650)/GPO blend with a PTHF/GPO mole ratio (ξ ) less than or equal to 4 and a PTHF (M _n=1400)/GPO blend with ξ ≤1 were used as propellant binders. The curing behaviors and mechanical properties of the PTHF/GPO blends were influenced by the molecular weight of PTHF and ξ , while the thermal decomposition behaviors were not affected. It was found that the PTHF/GPO blends had higher initial viscosity, longer pot life, and unique mechanical properties compared to those of the PTHF blends supplemented with GPO (M _n=260).     

Thermal Decomposition Behaviors and Burning Characteristics of Ammonium Nitrate/Polytetrahydrofuran/Glycerin–based Composite Propellants Supplemented with MnO2 and Fe2O3

Although a polytetrahydrofuran (PTHF) blend with added glycerin as a crosslinking modifier is an effective binder for improving the performance of a propellant, a burning catalyst is required for the combustion of the ammonium nitrate (AN)/PTHF/glycerin propellant. MnO₂ and Fe₂O₃ are useful burning catalysts for AN‐based propellants. The thermal decomposition behaviors of the AN/PTHF/glycerin propellant supplemented with MnO₂ and Fe₂O₃ catalysts, and the catalytic effect of these catalysts on the burning characteristics was investigated in this study. The thermal decomposition behaviors of these propellants depended on the kind of catalyst used. The propellants containing MnO₂ burned above 4 MPa, while those containing Fe₂O₃ burned above 0.5 MPa. The burning rate increased in the order, (AN/PTHF/Fe₂O₃)<(AN/PTHF/MnO₂)<(AN/PTHF/MnO₂/Fe₂O₃). The improvement in the ignitability and burning rate was dependent on the kind of catalyst used. The burning characteristics of the AN/PTHF/glycerin propellants were improved by the combined effect of multiple catalysts with differing catalytic mechanisms, as compared to the propellant supplemented with any single catalyst.     

Processing properties of polypropylene with a minor addition of silicone oil

Processing‐related properties of a polypropylene (PP)/silicone oil blend were investigated. It was found that an addition of a small amount (～2 wt%) of silicone oil, a low molecular weight linear poly(dimethyl siloxane) (PDMS), drastically changed the rheological properties of PP. The PDMS seemed to work both as an internal lubricant and an external lubricant in the blend system. In particular, the apparent viscosity of the blend in capillary rheometry was approximately 10 times lower than that of virgin PP. The local minima in the viscosity versus shear rate curve in capillary rheometry and the gap‐dependency of viscosity in parallel‐plate rheometry implied the existence of a slip wall condition, caused by the formation of a thin lubricant layer at die walls. Thermal analyses and mechanical tests showed that the thermal and mechanical properties of the blend were nearly unaffected by the minor addition of silicone oil. The blend was tested in a profile extrusion process, and a significant reduction in die swell and profile distortion was achieved. The jet stretchability or spinnability in fiber spinning was also greatly improved with the minor addition of silicone oil. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers