Investigation of hydroxyl-terminated polybutadiene propellant breaking characteristics and mechanism impacted by submerged cavitation water jet

A submerged cavitation water jet(SCWJ)is an effective method to recycle solid propellant from obsolete solid engines by the breaking method.Solid propellant's breaking modes and mechanical process under SCWJ impact are unclear.This study aims to understand those impact breaking mechanisms.The hydroxyl-terminated polybutadiene(HTPB)propellant was chosen as the research material,and a self-designed test system was used to conduct impact tests at four different working pressures.The high-speed camera characterized crack propagation,and the DIC method calculated strain change during the impact process.Besides,micro and macro fracture morphologies were characterized by scanning electron microscope(SEM)and computed tomography(CT)scanning.The results reveal that the compressive strain concentration region locates right below the nozzle,and the shear strain region distributes symmetrically with the jet axis,which increases to 4% at first 16th ms,the compressive strain rises to 2% and 6% in the axial and transverse direction,respectively.The two tensile cracks formed first at the compression strain concentrate region,and there generate many shear cracks around the tensile cracks,and those shear cracks that develop and aggregate cause the cracks to become wider and cut through the tensile cracks,forming the tensile-shear cracks and the impact parts eventually fail.The HTPB propellant forms a breaking hole shaped conical after impact 10 s.The mass loss increases by 17 times at maximum,with the working pressure increasing by three times.Meanwhile,the damage value of the breaking hole remaining on the surface increases by 7.8 times while 2.9 times in the depth of the breaking hole.The breaking efficiency is closely affected by working pressures.The failure modes of HTPB impacted by SCWJ are classified as tensile crack-dominated and tensile-shear crack-dominated damage mechanisms.

Synthesis and Characterization of Hydroxyl-terminated Block Fluorinated Copolyether(FPO-PTHF-FPO)

We introduced fluorine into hydroxyl-terminated block copolyether so as to prepare polyurethane adhesive with better performance.Fluorine-containing epoxy compounds(FO)was synthesized by one-step method from 2,2,3,3-tetrafluoro-1-propanol(TFP)and epichlorohydrin(ECH).Then,a novel hydroxyl-terminated block fluorinated copolyether(FPO-PTHF-FPO)was prepared by cationic ring-opening polymerization of fluorinated epoxy compound(FO)with polytetrahydrofuran(PTHF)as the macromolecular initiator and boron trifluoride diethyl ether(BF_(3)·OEt_(2))as the catalyst.The structure and properties of hydroxyl-terminated block fluorinated copolyether were characterized by FTIR,^(1)HNMR,GPC,DSC,TGA,and viscosity-temperature curve analysis.In comparison with polytetrahydrofuran(PTHF),hydroxyl-terminated block fluorinated copolyether(FPO-PTHF-FPO)has lower viscosity and only one lower glass transition temperature(-66.6℃)on DSC curve.In addition,hydroxyl-terminated block fluorinated copolyether(FPO-PTHF-FPO)begins to decompose at 187.2℃and is completely decomposed until 431.6℃,which indicates that it has a good thermal stability.

SYNTHESIS OF HYDROXYL-TERMINATED POLYBUTADIENE POSSESSING HIGH CONTENT OF 1,4-UNITS VIA ANIONIC POLYMERIZATION

The hydroxyl-terminated polybutadiene （HTPB） possessing high content of 1,4-units was synthesized by anionic polymerization of butadiene, using alkyllithium containing silicon-protected hydroxyl group as initiator and cyclohexane as solvent. The polymers were characterized by GPC, IR and 1H-NMR. The mechanical properties of cured films were also evaluated. The results show that the content of 1,4-units for HTPBs made by anionic polymerization reaches up to 90%. The molecular weight distribution is very narrow （〈 1.05）. The functionality of hydroxyl groups approaches 2. Compared with free radical HTPB, the elongation at break of anionic HTPB films increased by 70%, while the tensile strength remained nearly unchanged. This new HTPB can be very useful in solid propellant.

A convenient,highly-efficient method for preparation of hydroxyl-terminated isotactic poly(propylene) and functional di-block copolymer

Both terminated functional isotactic polypropylene （iPP） and block copolymers containing iPP segment are desirable for commercial applications. This paper provides a convenient, highly-efficient method to prepare hydroxyl-terminated isotactic polypropylene （iPP-t-OH） and functional di-block copolymer containing the iPP segment through a combination of coordination polymerization and coupling reaction. The coordination polymerization was catalyzed by TiCI4/MgCI2/AIEt3 catalyst system using ZnEt2 as chain transfer agent. Further, the Zn-terminated iPP was oxidized and subsequently hydrolyzed to provide iPP-t-OH. Soxhlet extraction and 13C NMR were used to calculate the isotacticity of iPP-t-OH. The degree of polymerization and the number of hydroxyl groups at the chain end of iPP-t-OH were measured by GPC and 1H NMR. Despite the high molecular weight and heterogeneous reaction, iPP-t-OH is effectively linked with PEG-t-NCO to produce di-block copolymers. DSC analysis of the di-block copolymer shows an obvious decrease in Tm and To, which indicated that PEG was successfully linked to the terminal end of iPP.

Anti-corrosive, weatherproof and self-healing polyurethane developed from hydrogenated hydroxyl-terminated polybutadiene toward surface-protective applications

Self-healing polyurethane(PU)faces aging deterioration due to active dynamic bonds,which remain a challenging predicament for practical use.In this work,a novel strategy is developed to address this predicament by leveraging the hydrophobicity and gas barrier of hydrogenated hydroxyl-terminated polybutadiene(HHPB).The dynamic oxime-carbamate bonds derived from 2,4-pentanedione dioxime(PDO)enable the elastomer to exhibit surface self-repairability upon applied mild heat and achieve~99.5%mechanical self-healing efficiency.The mechanical properties remained nearly intact after 30-d exposure to thermal oxidation,xenon lamp,acids,bases,and salts.Gas permeability,positron annihilation lifetime spectroscopy(PALS),and contact angle measurements reveal the pivotal role of gas barrier,free volume,and hydrophobicity in blocking undesirable molecules and ions which effectively protects the elastomer from deterioration.HHPB-PU also exhibits excellent adhesion to steel substrate.The shear strength achieves(3.02±0.42)MPa after heating at 80°C for 4 h,and(3.06±0.2)MPa after heating at 130°C for 0.5 h.Regarding its outstanding anti-corrosive and weatherproof performances,this self-healable elastomer is a promising candidate in surface-protective applications.

Degradation of Disposal Hydroxyl-Terminated Polybutadiene Composite Solid Propellant

With the greatly increasing amount of discarded hydroxyl-terminated polybutadiene(HTPB)propellant year by year,it is of high significance to study the safe,efficient and environmental processing method of disposal HTPB propellant.In this paper,the decomposition agents are formulated for degrading the waste composite solid propellant.It is found that the following formulations of butanone 25%-55%,xylene 30%-75%,deionized water 40%-45%have effective influence on the degradation of the waste composite solid propellant.The proper degradation time is found to be about 7-8 h.With the help of infrared spectrum analysis,scanning electron microscope imaging,thermogravimetric analysis and solvent viscosity test,it was proved that after degradation reaction on the propellant sometimes,a large number of irregular fractures occurred in bulk resulting from effective degradation.The characterization of the propellant after degradation showed that the hardness of the propellant decreased,the viscosity increased,and a large number of holes and cracks appeared on the surface.The results showed that the formulated degradation agent and degradation condition perform good degradation effects on HTPB solid propellant.

Synthesis of multifunctional additives for solid propellants:Structure,properties and mechanism

To simplify the composite propellant formulation and address the current issue of the single-functionality present in existing additives,the multi-cyano,amine-based polybutadiene(AEHTPB-CN)was prepared based on AEHTPB by adopting appropriate synthesis strategies.By replacing 10% of HTPB binder in the propellant formulation,it can effectively enhance the interfacial bond strength between the propellant binder matrix and solid fillers(AP(ammonium perchlorate)and RDX(cyclotrimethylene-trinitramine)),the mechanical properties of the HTPB/AP/RDX/Al propellant were superior to blank control propellant with an improvement of 35.4% in tensile strength,62.0% enhancement in elongation at break,and reduce the propellant burn rate by 10.7% with any energy loss.The function mechanism of AEHTPB-CN was systematically elucidated through experiments and computer simulation techniques.The results show that the tertiary amine group in AEHTPB-CN can react with AP to form ammonium ionic bonds,and the hydroxyl and cyano groups can form hydrogen bonding interactions with AP,which enables AEHTPB-CN to be firmly adsorbed on the AP surface through chemical and physical interactions.For RDX,the interfacial bonding effect of AEHTPB-CN is attributed to their ability to form C-H···N≡C weak hydrogen bonding interaction between the cyano group and RDX methylene group.

Effect of TPB on curing reaction of HTPB-TDI

Catalysis effect of triphenyl bismuth （TPB） on kinetics of hydroxyl terminated polybutadiene-toluene diisocyanate （HTPB-TDI） curing reaction was studied by non-isothermal differential scanning calorimetry （DSC）. The characteristic temperature of curing system was measured for calculating kinetic parameters and establishing curing reaction kinetic equations. The results show that activation energy （Ea） of uncatalyzed HTPB-TDI curing system is 51.29 kJmol-1, and TPB decreases Ea to 46.43 kJ＇mol-1. Catalyst lowers reaction temperature and shortens curing time through decreasing ac- tivation energy of curing reaction and accelerating reaction rate. TPB can increase the reaction rate at 27 ℃ to the value of uncatalyzed system at 80 ℃. The catalytic activity reaches the maximum when concentration is 0.5 %.

Mechanical properties of thermal aged HTPB composite solid propellant under confining pressure

With the purpose of investigating the effects of confining pressure and aging on the mechanical properties of Hydroxyl-terminated polybutadiene(HTPB)based composite solid propellant,tensile tests of thermal accelerated aged propellant samples under room temperature and different confining pressure conditions were performed through the use of a self-made confining pressure device and conventional testing machine.Afterwards,the maximum tensile stressσmand the corresponding strainεm for the propellant under different test conditions were obtained and analyzed.The results indicate that confining pressure and aging can significantly affect the mechanical properties of HTPB propellant,and the coupled effects are very complex.On the one hand,the stressσmincreases as a whole when confining pressure becomes higher or thermal aging time rises.Besides,this stress is more sensitive to aging with increasing confining pressure.There are almost three regions in the stress increments(σm P-σm0)/σm0and thermal aging time curves for HTPB propellant.The maximum value of the stress increment(σm P-σm0)/σm0for the propellant is about 98%at 7.0 MPa and 170 d.On the other hand,the strainεm decreases with increasing thermal aging time under the whole confining pressure conditions.However,the variation of this strain with confining pressure is more complex at various thermal aging time,which is different from that of unaged solid propellant in previous researches.In addition,this strain is slightly less sensitive to aging as the confining pressure increases.Furthermore,there is also a critical confining pressure in this investigation,whose value is between 0.15 MPa and 4.0 MPa.Beyond this critical pressure,the trends of the stressσmand the corresponding strainεm all change.Moreover,there are some critical thermal aging time for the stress increment(σm P-σm0)/σm0and strain increment(εm P-εm0)/εm0of HTPB propellant in this investigation,which are about at 35,50 and 170 d.Finally,based on the twin-shear strength theory,a new modified nonlinear strength criterion of thermal aged HTPB propellant under confining pressure was proposed.And the whole errors of fitted results are lower than 6%.Therefore,the proposed strength criterion can be selected as a failure criterion for the analysis the failure properties of aged HTPB propellant under different confining pressures,the structural integrity of solid propellant grain and the safety of solid rocket motor during ignition operation after long periods of storage.

On-chip solid phase extraction coupled with electrophoresis using modified magnetic microspheres as stationary phase

A poly(dimethylsiloxane)(PDMS)/glass hybrid microchip for on-line solid phase extraction (SPE) and electrophoresis separation has been developed and evaluated. The SPE microchannel was crossed to the electrophoresis microchannel. All the microfluidic channels were etched on the glass substrate. The magnetic microspheres were coated with hydroxyl-terminated poly-dimethylsiloxane (PDMS-OH) serving as extraction phase,which could be conveniently immobilized into the sample pretreatment channel by magnetic field. The PDMS-OH microspheres were mobilized into and out of the pretreatment channel by injection flow. The 0.1 μmol/L solution of fluorescence isothiocyanate (FITC)-labeled phenylalanine (Phe) was electrically injected into the SPE channel and extracted onto the PDMS-OH microspheres bed. The enriched FITC-labeled Phe was electrically eluted by 9 mmol/L sodium acetate containing 10% acetonitrile and electrically driven into the electrophoresis channel and then separated. The preconcentration factor could reach 87.5 after sufficient extraction. A linear preconcentration curve was obtained with the initial FITC-labeled Phe concentration ranging from 6 nmol/L to 300 nmol/L (R2=0.9922) with 200 s loading time. The detection limit (S/N=3) for the FITC-labeled Phe was 3 nmol/L.

Radiation-induced pyrolysis of solid fuels for ramjet application

A wide variety of hydroxyl-terminated polybutadiene(HTPB)based fuels areexperimentally assessed in anaerobic reaction.In this study HTPB pyrolysis is investigatedusing a CO laser as the energy source.The formulation of the solid fuel samples issystematically changed to isolate the effects of carbon black,metal fuel additives,and smallamounts of oxidizer.In addition,chemical changes to the fuels including curative type andbase polymer are varied.Rates of pyrolysis reaction are reported for a wide range of solid fuelsapplicable to ramjet application.Processes involving the sintering together of metal particles,accumulation of carbon black,and formation of a melt layer are found to affect the reactionrate.It is determined that the surface composition is the most influential factor influencing theregression rate of HTPB based fuels.