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Abstract  

The dehydration of an opal specimen was investigated by thermogravimetric analysis (TG) in powder and bulk forms. The change in geometry resulted in a significant difference in the temperature range in which dehydration occurred with peak temperatures in the differential TG (DTG) curve for the hand ground opal at 203°C and for the bulk opal at 340°C. This difference was attributed to time taken for diffusion of free water in the bulk opal to the specimen surface prior to evolution as a registered mass loss. A model was proposed to account for the diffusion of water and was used to estimate the diffusion coefficient.

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medium comprises three porosity levels, the maximum value of 10 is assumed in this model. At 613 °C, the Fickian diffusion coefficient is 1.1 × 10 −5 m 2 s −1 . This value is roughly 1.6 times the diffusion coefficient obtained from

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Abstract  

A model developed for the estimation of the diffusion coefficient based on Fickian diffusion is applied to the dehydration of a Coober Pedy white play of colour (precious) opal using thermogravimetric analysis (TG). The model was originally applied to bulk and powdered opal (opal with no bulk). In this paper the opal was graded prior to TG analysis. The diffusion coefficient was calculated and is reported up to the critical point of water.

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In this study, limonene was encapsulated by using gelatine, Na-alginate, polyvinyl alcohol, lactalbumin or xanthan gum with the uniaxial electrospinning process. The highest encapsulation efficiency was obtained for the sample containing polyvinyl alcohol. The release kinetic studies of nanofibre encapsulated limonene were carried out at 5.5, 20, and 38.5 °C. The Peppas equation expressed the release behavior of limonene for all systems very well, indicating quasi-Fickian diffusion. The modelling data suggested that maybe more than one mechanism was involved for the release at 20 °C. The activation energy for releasing limonene from the electrospun polyvinyl alcohol-alginate encapsulation system was found to be 6.2 kJ mol–1 from the Arrhenius equation.

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Acta Alimentaria
Authors: M. Włodarczyk-Stasiak, A. Mazurek, J. Jamroz, U. Pankiewicz, and R. Kowalski

pineapple: considering Fickian diffusion in cubical configuration . LWT — Food Sci. Technol. , 37 ( 1 ), 43 – 47 . Rutkowski , A. & Kozłowska , H

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obtained. Therefore, the higher R 2 value of model that is Peppas suggested that drug-release formulation (ONbp) followed “ Non-Fickian Diffusion Transport ” mechanism. The resulted mechanism support prolongs drug-release behavior through diffusion and

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