Characteristics of Different Systems for the Solar Drying of Crops

Solar dryers are used to enable the preservation of agricultural crops, food processing industries for dehydration of fruits and vegetables, fish and meat drying, dairy industries for production of milk powder, seasoning of wood and timber, textile industries for drying of textile materials. The fundamental concepts and contexts of their use to dry crops is discussed in the chapter. It is shown that solar drying is the outcome of complex interactions particular between the intensity and duration of solar energy, the prevailing ambient relative humidity and temperature, the characteristics of the particular crop and its pre-preparation and the design and operation of the solar dryer

The Effects of Acid Activation on the Thermal Properties of Polyvinylpyrrolidone and Organoclay Composites

The thermal stabilities of polyvinylpyrrolidone-organoclays or organo-acid-activated clay composites prepared by chemical exchange reactions were assessed. The raw clay mineral was acid-activated prior to expansion by cetyltrimethylammonium surfactants. The acid activation process affected the intercalated amount of cetyltrimethylammonium cations in the resulting organoclays and, thus, the amount of polyvinylpyrrolidone in the composite. The content of cetyltrimethylammonium cations decreased with the extent of acid activation. The organophilic modification of the clay mineral was an important step in the intercalation of the polyvinylpyrrolidone molecules and, thus, in the expansion of the silicate sheets from 3.80 nm to 4.20 nm. The composites exhibited better crystalline order with intense reflections at lower angles. The thermal stability of organoclays, acid-activated clays, and composites was studied using thermogravimetric analysis and in situ X-ray diffraction. The decomposition of intercalated surfactants occurred at lower temperatures relative to the neat surfactant salt, and the basal spacing of the organoclays (or acid-activated clays) shrunk to 2.0 nm at 215°C. However, the basal spacing of composites exhibited better stability and collapsed to 2.0 nm at 300°C. This type of material could offer an alternative stable product for engineering purposes in the design of new composites

Librational modes in layered double hydroxides and their calcined derivatives

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Effect of the acid activation levels of montmorillonite clay on the cetyltrimethylammonium cations adsorption

For the first time, the intercalation properties of acid-activated montmorillonites treated at different acid/clay (w/w) ratios with a cationic surfactant cetyltrimethylammonium (C16TMA) hydroxide are reported. The acid activation causes a reduction in the number of cation exchange sides and, hence improves the exfoliation of the silicate sheets at higher pH values. The basal spacing increases significantly from 1.54 to 3.80 nm, and is related to the acid activation extent. The acid activated clays with acid/clay ratios above 0.2 intercalated significant amounts of C16TMA cations with a basal spacing of 3.8 nm compared to the non acid activated montmorillonite with a basal spacing of 2.10 nm. The 13C CP/MAS NMR indicates that the intercalated surfactants exhibit a significant degree of gauche conformation in the acid-activated clays. According to in-situ powder XRD, an increase of the basal spacing to 4.08 nm is observed at intermediate temperatures of 50-150°C for organoclay with basal spacing of 3.80 nm, at higher temperatures above 300°C, the decomposition of the surfactant occurs and the basal spacing decreases to a value of about 1.4 nm, with the persistence of a reflection at 3.8 nm for clay at a higher acid/clay ratio of 0.5