Jialiang Li

The improvement in cryogenic mechanical properties of nano-ZrO2/epoxy composites via surface modification of nano-ZrO2

This study investigated the cryogenic mechanical properties of modified nano-ZrO2 reinforced epoxy composites. Nano-ZrO2 was surface modified by (3-aminopropyl)triethoxysilane (APTES) and results of Fourier transform infrared spectroscopy (FTIR) verified that APTES was successfully grafted onto the surface of nano-ZrO2. Transmission electron microscopy (TEM) observations indicated that APTES modification was favorable to the dispersion of nano-ZrO2 in an epoxy matrix. Glass transition temperatures of the modified nano-ZrO2/epoxy composites were also improved compared with those of the neat epoxy resin and the unmodified nano-ZrO2/epoxy composite. Results of the mechanical tests showed that the modified nano-ZrO2 could improve the mechanical properties of the epoxy composites more effectively than unmodified ones. Tensile strength and failure strain of the modified nano-ZrO2/epoxy composites were at most increased by 30.2% and 49.7% at room temperature (RT), while their highest enhancements at 90 K were 26.4% and 21.1%, respectively, compared with those of the neat epoxy resin. Besides, fracture toughness at RT and 90 K were at most increased by 53.3% and 39.4%, respectively. These enhancements were mainly attributed to the strong modified nano-ZrO2/epoxy interfacial bonding and the better dispersion of the modified nano-ZrO2 in the epoxy matrix. Summarily, it could be concluded that APTES modified nano-ZrO2 is a promising filler for enhancing cryogenic mechanical properties of epoxy resins.

Liquid oxygen compatibility and cryogenic mechanical properties of a novel phosphorous/silicon containing epoxy-based hybrid

A novel phosphorous/silicon containing epoxy-based hybrid was synthesized by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) containing epoxy resin and 3-glycidoxy-propyltrimethoxysilane (GLYMO). It was compatible with liquid oxygen according to the liquid oxygen impact test. Furthermore, the hybrid possessed significantly enhanced thermal stability compared with the neat and DOPO containing epoxy resin and the silicon containing epoxy hybrid due to the phosphorous/silicon synergetic mechanism. It could be inferred that enhanced thermal stability had a positive effect on liquid oxygen compatibility. After one week of the liquid oxygen immersion test, the surface roughness of the hybrid changed less compared with that of the neat epoxy resin, implying the hybrid owned a higher crack resistance under cryogenic temperatures. Surface elemental content analysis showed that the hybrid possessed the lowest oxidative degree after the liquid oxygen impact test, proving that the phosphorous/silicon synergetic mechanism has worked on enhancing liquid oxygen compatibility. Besides, the incorporation of the DOPO and GLYMO prepolymers endowed the epoxy resin with improved ductility at both room temperature and 90 K, consequently leading to an increased fracture toughness. The above results lead to the conclusion that the synthesized hybrid has potential as the matrix material of composite liquid oxygen tanks.

Investigating into the liquid oxygen compatibility of a modified epoxy resin containing silicon/phosphorus and its mechanical behavior at cryogenic temperature

A 9,10-dihydro–9–oxa–10–phosphaphenanthrene–10–oxide (DOPO) derivative (DOPO–TVS) was synthesized through a reaction between DOPO and triethoxyvinylsilane (TVS). To modify the common epoxy resin molecular without consuming the epoxy group, the general bisphenol F epoxy resin was first treated with isocyanate propyl triethoxysilane (IPTS). In the next step, the pretreated epoxy resin and DOPO–TVS were mixed to initiate the sol–gel process to generate the organic–inorganic hybrid Si–O–Si network within the epoxy matrix. The characterization of each reaction product was confirmed by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (1H NMR, 31P NMR) spectroscopy. The liquid oxygen compatibility of the cured epoxy resin was evaluated through mechanical impact in accordance with ASTM D2512-95. The surface elemental composition of the specimen before and after mechanical impact was investigated by X-ray photoelectron spectroscopy (XPS). The results of liquid oxygen mechanical impact showed that the liquid oxygen compatibility of the silicon/phosphorus containing epoxy resin was obviously enhanced. Moreover, the surface element composition also confirms the migration of the silicon to the surface of the cured epoxy resin and the generation of phosphoric oxyacid, which belongs to the condensed phase flame retardant mechanism. The tensile test and fracture toughness test under cryogenic conditions (77 K) were also carried out. The results showed that the modified epoxy resin possesses an elevated toughness property, which was attributed to the flexible Si–O–Si network in the cured modified epoxy resin.

Effect of hexabromocyclododecane and antimony trioxide on flame retardancy of bisphenol A epoxy resin

Abstract In the present work, the hexabromocyclododecane and the antimony trioxide were introduced into the bisphenol A epoxy resin to improve its flame retardancy. The effects of hexabromocyclododecane and antimony trioxide on flame retardancy of bisphenol A epoxy resin were estimated according to ASTM D2512-95 (2008). The specimen cured by T-31, with the addition of hexabromocyclododecane, did not show any flash and explosion during the 20 times of mechanical impact, whereas slightly empyreumatic scent was detected. The explosion was observed for the other specimens. The resin particles on the surface of the specimen after the mechanical impact were more than that before the mechanical impact, which was attributed presumably to the mechanical impact at the low temperature resulted in the crushing of the resin materials. It also indicated that bisphenol A epoxy resin cured by 593 with antimony trioxide at the low temperature had low flexibility. The XPS analysis confirmed that the surface of the specimen observed explosion was readily reacted with liquid oxygen. The O/C ratios of the specimen cured by T-31, with the addition of hexabromocyclododecane, before and after the mechanical impact were statistically approximate to 0.223 and 0.238, respectively, which revealed that the specimen was compatible with liquid oxygen.

Synthesis and characterization of a liquid oxygen-compatible epoxy resin

The bromine element was introduced into an epoxy resin to improve the liquid oxygen compatibility of the epoxy resin. After curing using 4,4′-diamino diphenylmethane, the liquid oxygen compatibility of all specimens was measured by the liquid oxygen mechanical impact test (ASTM D2512-95). The results suggested that the bromine-modified epoxy resin (BEP) was compatible with liquid oxygen, whereas the bisphenol F epoxy resin (EP) had poor liquid oxygen compatibility. The results of thermogravimetric analysis indicated that the incorporation of tetrabromobisphenol A into EP could accelerate the second-stage thermal degradation of BEP, leading to improvement of the liquid oxygen compatibility. X-ray photoelectron spectroscopy analysis indicated that the C–C/H groups on the surface of specimens could be oxidized to C–O–H/C and C=O groups during the impact process. The mechanism of bromine enhancement on the liquid oxygen compatibility of epoxy resin is proposed.

The effect of 10-(2,5-dihydroxyphenyl)-9, 10-dihydro-9-oxa-10-phosphaphenanthrene- 10-oxide on liquid oxygen compatibility and cryogenic mechanical properties of epoxy resins

In the present study, 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB) was chemically incorporated into bisphenol A epoxy resin (EP) to improve liquid oxygen compatibility of the EP. Fourier transform infrared (FTIR) spectroscopy verified that ODOPB was successfully introduced into the molecular chain of bisphenol A EP. Thermogravimetric analysis confirmed that the ODOPB-modified EPs exhibited much better thermal stability than the pristine ones during the whole decomposition process under oxygen atmosphere. The 4,4′-diaminodiphenyl sulfone (DDS)-cured resins showed higher initial degradation temperature, and the 4,4′-diaminodiphenyl methane (DDM)-cured resins demonstrated better thermal stability at high temperature. The results of limited oxygen index measurements indicated that the modified EPs also possessed much improved flame retardancy. Furthermore, the enhanced liquid oxygen compatibility of the modified EPs characterized by the liquid oxygen impact test implied that improving thermal stability and flame retardancy of EPs was beneficial to enhance their liquid oxygen compatibility. X-ray photoelectron spectroscopy results demonstrated that the DDS-cured modified EPs had much higher reactivity with liquid oxygen compared to the DDM-cured ones. Mechanical performance tests indicated that the introduction of ODOPB could simultaneously improve the tensile properties and fracture toughness of the EPs at cryogenic temperature. Summarily, it can be considered that the ODOPB-modified EPs have the application prospect in the fabrication of the composite liquid oxygen tanks.