Maximizing Interlaminar Fracture Toughness in Bidirectional GFRP through Controlled CNT Heterogeneous Toughening.

"Interleaving" is widely used for interlaminar toughening of fiber-reinforced composites, and the structure of interleaving is one of the important factors affecting the toughening efficiency of laminates. Several experiments have demonstrated that compared to continuous and dense structures, toughening layers with structural heterogeneity can trigger multiple toughening mechanisms and have better toughening effects. On this basis, this work further investigates the application of heterogeneous toughening phases in interlaminar toughening of bidirectional GFRP. CNT was selected to construct toughening phases, which was introduced into the interlaminar of composites through efficient spraying methods. By controlling the amount of CNT, various structures of CNT toughening layers were obtained. The fracture toughness of modified laminates was tested, and their toughening mechanism was analyzed based on fracture surface observation. The results indicate that the optimal CNT usage (0.5 gsm) can increase the initial and extended values of interlayer fracture toughness by 136.0% and 82.0%, respectively. The solvent acetone sprayed with CNT can dissolve and re-precipitate a portion of the sizing agent on the surface of the fibers, which improves the bonding of the fibers to the resin. More importantly, larger discrete particles are formed between the layers, guiding the cracks to deflect in the orientation of the toughened layer. This generates additional energy dissipation and ultimately presents an optimal toughening effect.

Free-Standing CNT Film for Interlaminar Toughening: Insight into Infiltration and Thickness Effects.

Carbon fiber reinforced polymer composites have the advantages of being lightweight, having high strength and designability, and having been extensively used. However, the interlaminar toughness and delamination resistance of these composites are relatively poor due to their laminated structure and intrinsic brittleness of resin matrix. In this paper, commercialized free-standing carbon nanotube (CNT) films, drawn from CNT forests, were used to toughen the interlaminar interfaces of the composites. The effects of resin infiltration state and thickness of CNT films on the interlaminar toughening effect were systematically investigated. The results show that the pre-infiltration treatment of CNT films with acetone diluted epoxy resin solution can effectively improve the degree of resin infiltration. Compared with the samples containing untreated CNT film, the Mode I and Mode II interlaminar fracture toughness of the treated samples were significantly improved. The GIC reached a maximum of 1412.42 J/m2 at a CNT film thickness of 5 µm, which was about 61.38% higher than that of the baseline. At a CNT film thickness of 15 µm, the GIIC reached a maximum value of 983.73 J/m2, approximately 67.58% higher than that of the baseline. The corresponding toughening mechanisms were also systematically analyzed.

A dual-response ratiometric fluorescent probe for hypochlorite and hydrazine detection and its imaging in living cells.

In this work, a dual-response ratiometric fluorescent probe (E)-3-(5-(2-nitrovinyl)thiophen-2-yl)-9-phenyl-9H-carbazole (NTPC) for high selectivity and sensitivity detection of ClO- and N2H4 was successfully developed. This probe NTPC showed ratiometric fluorescent response to ClO- and N2H4, which induces obvious naked-eye color changes, respectively. In addition, the NTPC for ClO- and N2H4 detection displayed low detection limits of 71.4 nM and 0.6 µM, respectively. And the sensing mechanism of NTPC with ClO- and N2H4 was well confirmed by 1H NMR and HR-MS spectra. Moreover, this novel probe was applied to monitoring and differentiating ClO- and N2H4 in living cells, and exhibits good biocompatibility and low cytotoxicity.

Energy storage in structural composites by introducing CNT fiber/polymer electrolyte interleaves.

This work presents a method to produce structural composites capable of energy storage. They are produced by integrating thin sandwich structures of CNT fiber veils and an ionic liquid-based polymer electrolyte between carbon fiber plies, followed by infusion and curing of an epoxy resin. The resulting structure behaves simultaneously as an electric double-layer capacitor and a structural composite, with flexural modulus of 60 GPa and flexural strength of 153 MPa, combined with 88 mF/g of specific capacitance and the highest power (30 W/kg) and energy (37.5 mWh/kg) densities reported so far for structural supercapacitors. In-situ electrochemical measurements during 4-point bending show that electrochemical performance is retained up to fracture, with minor changes in equivalent series resistance for interleaves under compressive stress. En route to improving interlaminar properties we produce grid-shaped interleaves that enable mechanical interconnection of plies by the stiff epoxy. Synchrotron 3D X-ray tomography analysis of the resulting hierarchical structure confirms the formation of interlaminar epoxy joints. The manuscript discusses encapsulation role of epoxy, demonstrated by charge-discharge measurements of composites immersed in water, a deleterious agent for ionic liquids. Finally, we show different architectures free of current collector and electrical insulators, in which both CNT fiber and CF act as active electrodes.

Mechanical Characterization of the Tensile Properties of Glass Fiber and Its Reinforced Polymer (GFRP) Composite under Varying Strain Rates and Temperatures.

Unidirectional glass fiber reinforced polymer (GFRP) is tested at four initial strain rates (25, 50, 100 and 200 s-1) and six temperatures (-25, 0, 25, 50, 75 and 100 °C) on a servo-hydraulic high-rate testing system to investigate any possible effects on their mechanical properties and failure patterns. Meanwhile, for the sake of illuminating strain rate and temperature effect mechanisms, glass yarn samples were complementally tested at four different strain rates (40, 80, 120 and 160 s-1) and varying temperatures (25, 50, 75 and 100 °C) utilizing an Instron drop-weight impact system. In addition, quasi-static properties of GFRP and glass yarn are supplemented as references. The stress⁻strain responses at varying strain rates and elevated temperatures are discussed. A Weibull statistics model is used to quantify the degree of variability in tensile strength and to obtain Weibull parameters for engineering applications.

NMR spectral assignments of two sterols from a soft coral Sinularia brassica.

Two new steroids, named 4α,22-dimethyl-Cholest-22-en-3ß-ol (1) and 4α-methyl-Cholest-7,22-dien-3ß-ol (2), along with two known steroids, were isolated from the soft coral Sinularia brassica. The structures of the new compounds were determined on the basis of extensive spectroscopic data (MS, (1)H and (13)C NMR, (1)H-(1)H COSY, (13)C-(1)H COSY, HMBC and NOESY) analysis.

[Determination of monosaccharides in Sargassum hemiphyllum (Turner) C. Ag. polysaccharides by ion chromatography].

Sargassum hemiphyllum polysaccharides (SHP) was extracted from dry Sargassum hemiphyllum (Turner) C. Ag. powder using 60 - 80 degrees C purified water and then hydrolyzed with 4.0 g/L trifluoroacetic acid at 80 degrees C. Without any derivatization reaction, the determination of monosaccharides in SHP was developed by anion-exchange chromatography with pulsed amperometric detection with an Au working electrode and an Ag/AgCl reference electrode. Monosaccharides were separated on a CarboPac PA10 anion-column (2 mm i. d. x 250 mm) by using isocratic elution consisting of 14 mmol/L sodium hydroxide at a flow rate of 0.20 mL/min. Six monosaccharides, xylose, galactose, arabinose, glucose, rhamnose and fructose, contained in SHP were separated and determined. Their contents in SHP were 2 200, 820, 98, 4 560, 358 and 740 mg/kg, respectively. The recoveries of the six monosaccharides were in the range 86.0% - 108.0%. The detection limits for these monosaccharides ranged from 5.6 to 89.6 microg/kg. The experimental results showed that SHP mainly consisted of xylose and glucose with smaller quantities of galactose, arabinose, rhamnose and fructose. This method is suitable for the determination of monosaccharides without any derivatization reaction at the level of microg/kg in dry algae with high sensitivity and good precision.