Impact of carbon fibre/epoxy corrugated cores

The dynamic compressive response of corrugated carbon-fibre reinforced epoxy sandwich cores has been investigated using a Kolsky-bar set-up. Compression at quasi-static rates up to v 0=200ms -1 have been tested on three different slenderness ratios of strut. High speed photography was used to capture the failure mechanisms and relate these to the measured axial compressive stress. Experiments show significant strength enhancement as the loading rate increases. Although material rate sensitivity accounts for some of this, it has been shown that the majority of the strength enhancement is due to inertial stabilisation of the core members. Inertial strength enhancement rises non-linearly with impact velocity. The largest gains are associated with a shift to buckle modes composed of 2-3 half sine waves. The loading rates tested within this study are similar to those that are expected when a sandwich core is compressed due to a blast event. © 2012 Elsevier Ltd.

Water, salt water, and alkaline solution uptake in epoxy thin films

As a means of characterizing the diffusion parameters of fiber reinforced polymer (FRP) composites within a relatively short time frame, the potential use of short term tests on epoxy films to predict the long-term behavior is investigated. Reference is made to the literature to assess the effectiveness of Fickian and anomalous diffusion models to describe solution uptake in epoxies. The influence of differing exposure conditions on the diffusion in epoxies, in particular the effect of solution type and temperature, are explored. Experimental results, where the solution uptake in desiccated (D) or undesiccated (U) thin films of a commercially available epoxy matrix subjected to water (W), salt water (SW), or alkali concrete pore solution (CPS) at either 20 or 60°C, are also presented. It was found that the type of solution did not significantly influence the diffusion behavior at 20°C and that the mass uptake profile was anomalous. Exposure to 60°C accelerated the initial diffusion behavior and appeared to raise the level of saturation. In spite of the accelerated approach, conclusive values of uptake at saturation remained elusive even at an exposure period of 5 years. This finding questions the viability of using short-term thin film results to predict the long-term mechanical performance of FRP materials. © 2013 Wiley Periodicals, Inc.

Physical properties of a hybrid and a nanohybrid dental light-cured resin composite.

This work was aimed at the study of some physical properties of two current light-cured dental resin composites, Rok (hybrid) and Ice (nanohydrid). As filler they both contain strontium aluminosilicate particles, however, with different size distribution, 40 nm-2.5 mum for Rok and 10 nm-1 mum for Ice. The resin matrix of Rok consists of UDMA, that of Ice of UDMA, Bis-EMA and TEGDMA. Degree of conversion was determined by FT-IR analysis. The flexural strength and modulus were measured using a three-point bending set-up according to the ISO-4049 specification. Sorption, solubility and volumetric change were measured after storage of composites in water or ethanol/water (75 vol%) for 1 day, 7 or 30 days. Thermogravimetric analysis was performed in air and nitrogen atmosphere from 30 to 700 degrees C. Surface roughness and morphology of the composites was studied by atomic force microscopy (AFM). The degree of conversion was found to be 56.9% for Rok and 61.0% for Ice. The flexural strength of Rok does not significantly differ from that of Ice, while the flexural modulus of Rok is higher than that of Ice. The flexural strengths of Rok and Ice did not show any significant change after immersion in water or ethanol solution for 30 days. The flexural modulus of Rok and Ice did not show any significant change either after immersion in water for 30 days, while it decreased significantly, even after 1 day immersion, in ethanol solution. Ice sorbed a higher amount of water and ethanol solution than Rok and showed a higher volume increase. Thermogravimetric analysis showed that Rok contains about 80 wt% inorganic filler and Ice about 75 wt%.

The effect of carbon nanotube orientation on erosive wear resistance of CNT-epoxy based composites

Aligned carbon nanotube (CNT) polymer composites are envisioned as the next-generation composite materials for a wide range of applications. In this work, we investigate the erosive wear behavior of epoxy matrix composites reinforced with both randomly dispersed and aligned carbon nanotube (CNT) arrays. The aligned CNT composites are prepared in two different configurations, where the sidewalls and ends of nanotubes are exposed to the composite surface. Results have shown that the composite with vertically aligned CNT-arrays exhibits superior erosive wear resistance compared to any of the other types of composites, and the erosion rate reaches a similar performance level to that of carbon steel at 20° impingement angle. The erosive wear mechanism of this type of composite, at various impingement angles, is studied by Scanning Electron Microscopy (SEM). We report that the erosive wear performance shows strong dependence on the alignment geometries of CNTs within the epoxy matrix under identical nanotube loading fractions. Correlations between the eroded surface roughness and the erosion rates of the CNT composites are studied by surface profilometry. This work demonstrates methods to fabricate CNT based polymer composites with high loading fractions of the filler, alignment control of nanotubes and optimized erosive wear properties. © 2014 Elsevier Ltd. All rights reserved.

Hydrodynamics in an expanded bed of large size ion-exchange resin, and natural product adsorption

Successful applications of expanded bed adsorption (EBA) technology have been widely reported in the literature for protein purification. Little has been reported on the recovery of natural products and active components of Chinese herbal preparations using EBA technology. In this study, the hydrodynamic behavior in an expanded bed of cation resin, 001 x 7 Styrene-DVB, was investigated. Ephedrine hydrochloride (EH) was used as a model natural product to test the dynamic binding capacity (DBC) in the expanded bed. EBA of EH directly from a feedstock containing powdered herbs has also been investigated. These particles are different from commercially available expanded bed adsorbents by virtue of their large size (20S to 1030 gm). When the adsorbent bed is expanded to approximately 1.3 to 1.5 times its settled bed height, the axial liquid-phase dispersion coefficient was found to be of the order 10(-5) m(2) s(-1), which falls into the range 1.0 x 10(-6) to 1.0 X 10(-5) m(2) s(-1) observed previously in protein purification. Because of the favorable column efficiency (low axial dispersion coefficient), the recovery yield and purification factor values of EH directly from a feedstock reached 86.5% and 18, respectively. The results suggest that EBA technology holds promise for the recovery of natural products and active components of Chinese herbal preparations.

Links between energy dissipation and wear mechanisms in solid epoxy/epoxy sliding contact

This paper covers wear and energy dissipation of solid epoxy induced by the alternative rubbing between two samples of identical thermosetting polymer. Varying normal load, sliding velocity and sliding distance, the authors were able to define and discuss wear and friction laws and associated energy dissipation. Moreover, traces of several wear mechanisms were distinguished on the worn surfaces and associated with applied conditions. Observed under higher velocity, polymer softening and local state transition were explained by surface temperature estimate and confirmed by infra-red spectroscopy measurements. To conclude this study, all observed phenomena are classified into two wear scenarios according to sliding velocity. © 2014 Elsevier Ltd.

Transparent and Light-Emitting Epoxy Super-Nanocomposites Containing ZnO-QDs/SiO2 Nanocomposite Particles as Encapsulating Materials for Solid-State Lighting

In this article, the ZnO quantum dots-SiO2 (Z-S) nanocomposite particles were first synthesized. Transparent Z-S/epoxy super-nanocomposites were then prepared by introducing calcined Z-S nanocomposite particles with a proper ratio of ZnO to SiO2 into a transparent epoxy matrix in terms of the filler-matrix refractive index matching principle. It was shown that the epoxy super-nanocomposites displayed intense luminescence with broad emission spectra. Moreover, the epoxy super-nanocomposites showed the interesting afterglow phenomenon with a long phosphorescence lifetime that was not observed for ZnO-QDs/epoxy nanocomposites. Finally, the transparent and light-emitting Z-S/epoxy super-nanocomposites were successfully employed as encapsulating materials for synthesis of highly bright LED lamps.

Production of biodiesel from soapstock using an ion-exchange resin catalyst

The feasibility of biodiesel production from soapstock containing high water content and fatty matters by a solid acid catalyst was investigated. Soapstock was converted to high-acid acid oil (HAAO) by the hydrolysis by KOH and the acidulation by sulfuric acid. The acid value of soapstock-HAAO increased to 199.1 mg KOH/g but a large amount of potassium sulfate was produced. To resolve the formation of potassium sulfate, acid oil was extracted from soapstock and was converted to HAAO by using sodium dodecyl benzene sulfonate (SDBS). The maximum acid value of acid oil-HAAO was 194.2 mg KOH/g when the mass ratio of acid oil, sulfuric acid, and water was 10:4:10 at 2% of SDBS. In the esterification of HAAO using Amberylst-15, fatty acid methyl ester (FAME) concentration was 91.7 and 81.3% for soapstock and acid oil, respectively. After the distillation, FAME concentration became 98.1% and 96.7% for soapstock and acid oil. The distillation process decreased the total glycerin and the acid value of FAME produced a little.