A new method for predicting sorption isotherms at different temperatures using the BET model

A new methodology to predict sorption isotherms at different temperatures is proposed in this work. The classical BET model is used coupled with the Clausius–Clapeyron equation, and an Arrhenius temperature dependency is assumed for the BET energetic parameter C. When compared to the usual procedure based solely on the use of a model for the sorption isotherm, this methodology presents two main advantages: (i) a single set of parameters may be used to predict isotherms at different temperatures and (ii) fewer experimental data are required to estimate this set of parameters, using only one single sorption isotherm and one single value of differential enthalpy of sorption, at a specific and arbitrary humidity. The new methodology was tested with different food materials and the predicted results were in good agreement with experimental data, attesting the potential of this new approach.     

Production and characterization of oxidized cassava starch (Manihot esculenta Crantz) biodegradable films

Plastic is one of the most common pollutants in the environment. Therefore, the number of studies on the use of biodegradable packaging is increasing. Starch is the primary material used in the production of biodegradable plastics due to its natural abundance and high biodegradability. Yet, the strong hydrophilic character of starch presents a challenge. Therefore, the modification of its structure through oxidation may yield interesting results as the viscosity reduction. The objectives of this work were to obtain cassava (Manihot esculenta Crantz) starch oxidized with 0.8 and 2.0% active chlorine, to develop biodegradable films and characterize their mechanical properties, solubility in water, permeability to water vapor, degree of swelling, and sorption isotherms. Biodegradable films were produced with starch concentrations of 2, 3, 4, and 5% w/w and 25% glycerol (g/100 g starch) added as a plasticizer. Images of the films were obtained with an atomic force microscope and allow to observe a smooth surface and the absence of starch granules in the film produced with oxidized starches. The tensile strength of the biodegradable film produced with oxidized starch (0.8% active chlorine) was 80 MPa. The value of permeability to water vapor was 1.613 × 10⁻⁹ kg/day/m/Pa, and the average solubility was 41%. The sorption isotherms showed that biodegradable films made with oxidized starches cannot be used in environments with relative humidity below 35% or above 90%.