Aerogel preparation from short cellulose nanofiber of the Eucalyptus species

Abstract

Wood is the main industrial source for obtaining cellulose. It is a natural composite, constituted by cellulose, polyoses, lignin, small amounts of extracts and mineral salts, wherein cellulose is the most abundant component. Many studies are being developed for obtaining materials based on natural fibers, which combine interesting properties such as renewability, biodegradability, low density and low cost. Aerogels are solid, lightweight materials with high porosity and high internal surface area. These features combined in one single material make the aerogels a differentiated product with potential for use as an adsorbent. In this context, aerogels made of cellulose nanofibers obtained from short-fiber cellulose of Eucalyptus sp. were made. The cellulose suspension was first disintegrated by a mechanical grinder, and the aerogels were undergone to freeze-drying. The characterization of the samples was performed by apparent density, porosity, scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analyses. According to the micrographs obtained by scanning electron microscopy and field emission gun scanning electron microscopy, it was observed the formation of pores formed by the interconnection of cellulose fibers. The apparent density of the starting cellulose fibers (pressed plates) was 0.6998 g.cm−3 and the aerogel density decreased to 0.0240 g.cm−3. The values for aerogel porosity were about 97%, which benefits the passage of liquids and gases from the external environment to the internal structure of the material. Fourier transform infrared spectroscopy and thermogravimetric analyses showed no change in the chemical composition or in the thermal stability of the obtained aerogels in comparison to their starting materials.

Cellulose/biochar aerogels with excellent mechanical and thermal insulation properties

“…A difference is noted in T onset (temperature at which sample degradation starts) and T max (temperature at which the rate of degradation is maximal), as shown in Table 2. These temperatures of the cellulose aerogels decreased in relation to the Pinus elliottii cellulose fiber, probably due to the increase of the specific surface area obtained after the mechanical process, which facilitates the degradation process when compared to the original material, and contributes to thermal stability decrease (Zanini et al 2017). The residual mass of the aerogels had a slight decrease compared to the original cellulose.…”

Tobacco stalk lignocellulosic nanofibers characterization for pharmaceutical applications

“…For FD samples, the lignocellulosic suspensions were dried in a Lio Top, model L-101 Liobrás (Brazil) freeze-dryer equipment at a freezing temperature of -50˚C for 24 hours. After that, the samples were transferred separately to a vacuum chamber (Lio Top, model L-101 Liobrás, Brazil) for ice sublimation, using initial vacuum of 500 µHg and final vacuum of 100 µHg (Zanini et al, 2017).…”

Drying of cellulose nanocrystal gel beads using supercritical carbon dioxide

“…One major challenge for the preparation of aerogels is to eliminate the liquid solvent from the wet gel whilst avoiding the collapse of the already existing nanoporous structure due to the subsequent shrinkage of the dried gel. Aerogels from cellulosic materials have been prepared through freeze‐drying of solutions or gels . However, aerogels produced by freeze‐drying showed significant damage with respect to the original pore structure of the gel, and the formation of cracks due to the expansion of crystals in the gel could not be avoided .…”

“…Aerogels from cellulosic materials have been prepared through freeze-drying of solutions or gels. 7,8 However, aerogels produced by freeze-drying showed significant damage with respect to the original pore structure of the gel, and the formation of cracks due to the expansion of crystals in the gel could not be avoided. 9 In addition, the microstructure of aerogels obtained by freeze-drying is plate-shaped because of the edging of ice crystals and the aggregation of nanoparticles during the freezing.…”