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A Review of the Polymer for Cryogenic Application: Methods, Mechanisms and Perspectives
Recently, the application of polymer-based composites at cryogenic conditions has become a hot topic, especially in aerospace fields. At cryogenic temperature, the polymer becomes more brittle, and the adverse effect of thermal stress induced by temperature is more remarkable. In this paper, the research development of thermoset and thermoplastic polymers for cryogenic applications are all reviewed. This review considers the literature concerning: (a) the cryogenic performance of modified thermoset polymers and the improving mechanisms of the reported modification methods; (b) the cryogenic application potential of some commercial thermoplastic polymers and the cryogenic performance of modified thermoplastic polymers; (c) the recent advance in the use of polymer for special cryogenic environment-liquid oxygen. This paper provides a comprehensive overview of the research development of the polymer for cryogenic application. Moreover, future research directions have been proposed to facilitate its practical applications in aerospace.
Journal Article
Cryogenic Mechanical Properties and Stability of Polymer Films for Liquid Oxygen Hoses
To select the appropriate polymer thin films for liquid oxygen composite hoses, the liquid oxygen compatibility and the cryogenic mechanical properties of four fluoropolymer films (PCTFE, ETFE, FEP and PFA) and two non-fluoropolymer films (PET and PI) before and after immersion in liquid oxygen for an extended time were investigated. The results indicated that the four fluoropolymers were compatible with liquid oxygen before and after immersion for 60 days, and the two non-fluoropolymers were not compatible with liquid oxygen. In addition, the cryogenic mechanical properties of these polymer films underwent changes with the immersion time, and the changes in the non-fluoropolymer films were more pronounced. The cryogenic mechanical properties of the two non-fluoropolymer films were always superior to those of the four fluoropolymer films during the immersion. Further analysis indicated that the fundamental reason for these changes in the cryogenic mechanical properties was the variation in the crystalline phase structure caused by the ultra-low temperature, which was not related to the strong oxidizing properties of the liquid oxygen. Analytical results can provide useful guidance on how to select the appropriate material combination to obtain a reasonable liquid oxygen composite hose structure.
Journal Article
Flame dynamics of an injection element operated with LOX/H2, LOX/CNG and LOX/LNG in a sub- and supercritical rocket combustor with large optical access
Hot fire tests were performed using a single-injector research combustor featuring a large optical access window (
255
×
38
mm) for flame visualisation. Three test campaigns were conducted with the propellant combination of liquid oxygen and hydrogen, liquid oxygen and compressed-natural-gas, as well as liquid oxygen and liquefied-natural-gas at conditions relevant for main- and upper-stage rocket engines. The large optical access enabled synchronised flame imaging using ultraviolet and blue radiation wavelengths covering a large portion of the combustion chamber for various sets of sub- and supercritical operating conditions. Combined with temperature, pressure and unsteady pressure measurements, this data provides a high-quality basis for the validation of numerical modelling. Flame width, length and opening angle as features describing the flame topology were extracted from the imaging. The suitability of flame imaging using ultraviolet and blue radiation wavelengths as qualitative markers of heat release was evaluated. Two-dimensional distributions of the Rayleigh Index were calculated for intervals with and without high-amplitude, self-excited oscillations of the longitudinal acoustic resonance modes. The calculated Rayleigh Index values properly reflect the thermoacoustic state of the chamber, indicating that both types of imaging may be used for qualitative study of thermoacoustic coupling of high-pressure cryogenic flames.
Journal Article
Preparation and Application of a Novel Liquid Oxygen-Compatible Epoxy Resin of Fluorinated Glycidyl Amine with Low Viscosity
A liquid oxygen-compatible epoxy resin of fluorinated glycidyl amine (TFEPA) with a low viscosity of 260 mPa·s in a wide range of temperatures, from room temperature to 150 °C, was synthesized and used to decrease the viscosity of phosphorus-containing bisphenol F epoxy resins. And the forming process and application performances of this resin system and its composite were investigated. The viscosity of the bisphenol F resin was decreased from 4925 to 749 mPa·s at 45 °C by mixing with 10 wt.% TFEPA, which was enough for the filament winding process. Moreover, the processing temperature and time windows were increased by 73% and 186%, respectively. After crosslinking, the liquid oxygen compatibility was preserved, and its tensile strength, elastic modulus, and breaking elongation at −196 °C were 133.31 MPa, 6.59 GPa, and 2.36%, respectively, which were similar to those without TFEPA. And the flexural strength and modulus were 276.14 MPa and 7.29 GPa, respectively, increasing by 21.73% in strain energy at flexural breaking, indicating an enhanced toughness derived from TFEPA. Based on this resin system, the flexural strength and toughness of its composite at −196 °C were 862.73 MPa and 6.88 MJ/m3, respectively, increasing by 4.46% and 10.79%, respectively.
Journal Article
Permeability and mechanical properties of nanoclay/epoxy liner used in type IV liquid oxygen vessel: experimental and numerical study
Consideration of the permeability and safety aspects of liquid oxygen (LOX) storage is of particular importance, because oxygen leaks can break down spacecraft missions. In this study, the effect of adding nanoclay to epoxy resin on the bending and tensile capacities of a clay/epoxy nanocomposite for using as a liner in type IV LOX was investigated experimentally and statistically. Consequently, samples were initially made with different nanoclay contents (0.5%, 1%, 3%, and 5% all by weights) using two distinct dispersion processes (HSS and ultrasonic), then evaluated using bending, tensile, and permeability testing methods, as well as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometry (XRD). In the optimal sample with 1% (weight) of nanoclay mixed with ultrasonic process, the permeability was reduced by 35%, the Young's modulus was improved by 3.5 times, and the toughness and fracture energy were increased by 3 times compared to the pure resin. However, all samples lost between 10 and 20% of their tensile strength due to the breakage of polymer chain links. Simulation findings revealed that at burst pressure, the tank with modified resin liner deforms four times less than PP and 50% more than PET without any rupture.
Graphical abstract
Journal Article
Liquid Oxygen Compatibility and Ultra-Low-Temperature Mechanical Properties of Modified epoxy Resin Containing Phosphorus and Nitrogen
Endowing epoxy resin (EP) with prospective liquid oxygen compatibility (LOC) as well as enhanced ultra-low-temperature mechanical properties is urgently required in order to broaden its applications in aerospace engineering. In this study, a reactive phosphorus/nitrogen-containing aromatic ethylenediamine (BSEA) was introduced as a reactive component to enhance the LOC and ultra-low-temperature mechanical properties of an EP/biscitraconimide resin (BCI) system. The resultant EP thermosets showed no sensitivity reactions in the 98J liquid oxygen impact test (LOT) when the BSEA content reached 4 wt% or 5 wt%, indicating that they were compatible with liquid oxygen. Moreover, the bending properties, fracture toughness and impact strength of BSEA-modified EP were greatly enhanced at RT and cryogenic temperatures (77 K) at an appropriate level of BSEA content. The bending strength (251.64 MPa) increased by 113.67%, the fracture toughness (2.97 MPa·m1/2) increased by 81.10%, and the impact strength (31.85 kJ·m−2) increased by 128.81% compared with that of pure EP at 77 K. All the above results demonstrate that the BSEA exhibits broad application potential in liquid oxygen tanks and in the cryogenic field.
Journal Article
The Influence of Rotating Speed on the Sealing Characteristics of a Liquid-Sealing Impeller for a Liquid Oxygen Turbopump
In order to explore the influence of rotating speed on the internal flow and sealing characteristics of the liquid-sealing impeller for a liquid oxygen turbopump of a rocket engine, unsteady numerical simulations of the flow characteristics and sealing performance of the first-stage liquid-sealing impeller for a liquid oxygen turbopump under liquid phase conditions were performed. The results show that the pressurization value increases with the increase in the rotating speed. The first-stage liquid-sealing impeller, whose structure is symmetrically distributed along the center of the rotation axis, tends to be an isobaric seal at a rotating speed of 12,000 rpm, and when the rotating speed is decreased or increased, it enters the leakage state or negative pressure sealing state, respectively. The matching relationship between the rotating speed and inlet pressure has a significant effect on the pressurization value, pressurization coefficient and leakage flow rate. Under the working condition with a good match between the rotating speed and inlet pressure, the pressurization value increases significantly and the leakage flow rate decreases significantly, and the pressurization coefficient is stable between 0.88 and 0.89. The empirical formulas proposed by Wood and the Shanghai Research Institute of Chemical Industry (1979) have high reference values for the design of the liquid-sealing impeller with a flow channel (groove) and retainer.
Journal Article
Study on epoxy resin modified by hyperbranched polysiloxane containing active amino group and its properties
A novel phosphorous/silicon hybrid containing active amino was synthesized by bisphenol F epoxy resin modified by 0-(2,5-Dihydroxyphenyl)−10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB) and hyperbranched polysiloxane (APTMS-HPSi). At first, APTMS-HPSi was synthesized by a simple reaction among aminoethylamino propyltrimethoxy silane (APTMS) and tripropylene glycol (TPG). ODOPB was used to modify bisphenol F epoxy resin. Then add different content of APTMS-HPSi to the phosphorus-containing modified epoxy resin (P-EP). Fourier Transform Infrared (FTIR) Spectroscopy was used to characterized the chemical structure of APTMS-HPSi. The effects of APTMS-HPSi content on key properties was systemically investigated. Results showed that the addition of APTMS-HPSi and ODOPB effectively improve the toughness and liquid oxygen compatibility. With the increase content of APTMS-HPSi, char yield and limited oxygen index (LOI) value of the cured resin increased, and the liquid oxygen sensitivity coefficient (IRS) decreased. The elongation at break was increased 45.32% by only 6wt% loading with APTMS-HPSi in epoxy resin, and at the same time the IRS of the modified resin was reduced from 7% to 0%. When the addition amount was 6wt%, the fracture elongation, impact strength and fracture toughness K
IC
were increased by 52.1%, 81.8% and 54.3% respectively. Therefore, adding phosphorus and hyperbranched polysiloxane to the resin can improve the liquid oxygen compatibility and toughness of the epoxy resin at the same time.
Journal Article
Enhanced cryogenic mechanical properties and liquid oxygen compatibility of DOPO-containing epoxy resin reinforced by epoxy-grafted polysiloxane
Excellent cryogenic mechanical properties are urgently requested for the materials used in liquid oxygen environment. However, a DOPO-modified epoxy resin (EP-P), which was compatible with liquid oxygen, had no improved cryogenic mechanical properties compared with the pure epoxy resin (EP). Besides, its mechanical properties at room temperature (RT) were obviously decreased compared with EP. Thus, a novel epoxy-grafted polysiloxane (EGP) was synthesized by dimethyldimethoxysilane, dimethoxydiphenylsilane and 3-glycidoxy-propyltrimethoxysilane through co-hydrolytic condensation reaction. EGP was introduced into EP-P to improve cryogenic mechanical properties, especially toughness of EP-P. Tensile properties and fracture toughness of the DOPO/EGP-modified epoxy resin (EP-P/Si) at RT and liquid oxygen temperature (90 K) were investigated. Compared with EP, at RT, failure strain and
K
IC
of EP-P/Si were increased by about 100% and 40%; at 90 K, the above two properties were increased by about 60% and 50%. Besides, EP-P/Si had almost same tensile strength with EP at both RT and 90 K. The results of the liquid oxygen mechanical impact test indicated that EP-P/Si was still compatible with liquid oxygen. XPS analysis showed that EP-P/Si had lower oxidation degree after the impact test compared with EP-P, indicating that liquid oxygen compatibility was enhanced.
Journal Article