Nicolas Quiévy

Electromagnetic Absorption Properties of Carbon Nanotube Nanocomposite Foam Filling Honeycomb Waveguide Structures

Carbon nanotube reinforced polymer foams filling a metallic honeycomb were processed and characterized for the production of hybrid materials with high electromagnetic absorption potential. Electromagnetic modeling and experimental characterization of the hybrids proved that the honeycomb, acting as a hexagonal waveguide, improves the absorption properties in the gigahertz range above the cutoff frequency. The electromagnetic absorption can be tuned by changing the hybrid material properties. The required levels of electrical conductivity are attained owing to the dispersion of low amounts (1-2 wt%) of carbon nanotubes inside the polymer matrix. The combination of the foam and honeycomb architecture contributes to decrease the real part of the relative effective permittivity Re{εr,eff }. Varying the cell shape of the honeycomb changes the frequency range for high absorption. An analytical model for the absorption has been developed, showing good agreement with the experimental results.

Influence of steam explosion on physicochemical properties and hydrolysis rate of pure cellulose fibers

The aim of this study is to compare the effect of different steam explosion treatments on the physicochemical properties and the hydrolysis rate of a pure bleached cellulose. The results showed that moderate steam explosion treatments (severity factor below 5.2) did not appear to improve the enzymatic hydrolysis rate of the cellulose fibers. However, characterization of the samples showed a modification of the physicochemical properties of the cellulose, resulting in an increase of the water retention values (WRV) coupled to an increase of the overall crystallinity. For higher treatment intensities, an important thermal degradation of the cellulose was highlighted. This thermal degradation caused an important modification of the cellulose composition which leads to a decrease of the hydrolysis rate.

Characterization of sugar beet pectic-derived oligosaccharides obtained by enzymatic hydrolysis.

Three pectic oligosaccharides (POS) obtained by enzymatic hydrolysis of sugar beet pectin by combining endopolygalacturonase and pectinmethylesterase, were characterized using high performance liquid chromatography, thermogravimetric analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry and X-ray diffraction. According to chromatographic analyses, POS are composed of mixture of polymers with different molecular weights and different galacturonic acid contents. The thermal analysis showed no major variation in thermal behavior regarding POS composition but showed that POS were more sensitive to thermal degradation than the parent pectin as well as the deesterified pectin. No change in composition of the gaseous products was obtained through TGA-FTIR analysis. The X-ray pattern of POS clearly indicated a considerable decrease in crystallinity when compared to the native pectin. Thus, thermal characterization of POS may have practical repercussions if the formulation in which POS is incorporated is submitted to a high temperature treatment.