Impact of Instant Controlled Pressure Drop Treatment on Moisture Adsorption Isotherm of Cork Granules

Abstract

Some special thermal and mechanical treatments may completely modify the composition, and the structure of organic material changes its interaction with water. In the case of the instant controlled pressure drop (DIC) technique, the main modification, which is structure expansion and high porosity, allows the product to generally reduce moisture activity. In the special case of cork granules, the impact of DIC in terms of porosity is completely absent and expansion is linked to a tear effect obtained from only the large size granules. In order to characterize this type of treatment, we considered natural and DIC-treated cork granules and determined moisture adsorption isotherms at three different temperatures (25, 40, and 60 C) and different water activity levels ranging from 0.05 to 0.9 using the static gravimetric method. We used three samples of the same cork variety with 0.5-1 mm, 2-4 mm, and 4-6 mm as granule diameter. The adsorption isotherms of both natural untreated and DIC-treated cork whatever granules display a sigmoid form type II isotherm, with equilibrium moisture contents at constant water activity decreasing when temperature increases. The impact of DIC treatment depends of cork shape; the larger the shape, the lower the water activity for the same water content. Such a result is linked to the modification of structure. Thus, for the smallest shape, DIC implying only low thermal effect without any structure modification allows cork to lightly increase its water activity compared to the untreated samples. With higher shape cork granules, as DIC treatment induces a tear effect and some expansion, activity of water is lower for the same water content. For describing the experimental data of adsorption isotherms, we used GAB, BET, and Henderson models. We found the GAB to be the most suitable model with predicted values higher than those obtained using the BET model. We note that monolayer moisture content values increase in the case of big shape cork granules after having been treated by DIC.

Sorption et propriétés thermodynamiques du liège pour les isothermes 35ºC et 50ºC

“…Based on earlier studies, it can be stated that the water sorption mechanism in cork appears to be similar to this mechanism in wood, and is divided into three phases: monolayer sorption, multilayer sorption and capillary condensation (Abdulla et al, 2009). However, some authors (Lequin et al, 2010) have questioned the monolayer sorption phase.…”

“…As in wood, the physical properties of cork are closely associated with water content (Lequin et al, 2010). Although many studies have been made of the hygroscopic behaviour of wood through its isotherms (e.g., Kollmann, 1951;Skaar, 1988;Siau, 1995;Wang, Cho, 1993;Esteban et al, 2004;2005), cork-water relations have been little studied, particularly through the sorption-desorption isotherms (González-Adrados, Haro, 1994;Gil, Cortiço, 1998;González-Adrados et al, 2008;Abdulla et al, 2009;Lequin et al, 2010;De Palacios et al, 2011).…”

Some Recent Advances in Drying Technologies to Produce Particulate Solids

“…By texturing by Instant controlled pressure drop DIC, raw materials (plants, medicinal herbs) could get higher porosity. Dehydration by successive decompression (DDS; de shydratation par de tentes successives) is a process particularly suited to thermo-sensitive products, in which the product undergoes a series of cycles, during which it is placed under pressure (<10 bar) for a defined time and is then subjected to an instantaneous decompression to a vacuum (5-90 kPa) [63][64][65][66][67][68] The product is maintained under a vacuum for a defined time before the following cycle begins. Each decompression step results in partial water removal by autovaporization.…”

“…A variation of operating pressure by controlled instantaneous means or in cyclic way can be used to achieve high quality of dried products 63,64) . In a controlled instanta-neous pressure drop (commonly referred to as DIC) method, the product is subjected to vacuum in a processing chamber and then exposed to steam pressure followed by an instantaneous drop in pressure toward a vacuum and finally a return to atmospheric pressure 65,66) . By texturing by Instant controlled pressure drop DIC, raw materials (plants, medicinal herbs) could get higher porosity.…”

Dehydration, Water Vapor Adsorption and Desorption Behavior of Zn[B3O3(OH)5] · H2O and Zn[B3O4(OH)3]

“…[31,32] The samples kept in atmospheres with different water activities were weighed against time until their mass was unchanged. However, the mass of samples that were taken out of the controlled atmospheres to ambient air for weighing could change during this transfer process.…”