Water vapor sorption determination of starch based porous packaging materials

Starch-based packaging materials of different compositions were manufacture d in a thermopressing solidification process. These porous materials were u sed for investigations on their water vapor sorption behavior. The adsorpti on isotherms at 20 degrees C and the water vapor adsorption during storage of samples in conditioned air with a relative humidity of 93% at 23 degrees C were determined. The sigmoidal type isotherms obtained were modeled usin g the BET and GAB equations and linear regression analysis. The GAB model s howed a good fit to experimental data for water activities of up to about 0 .9. A prediction of water vapor adsorption in dependence on temperature up to 50 degrees C was obtained with good accuracy by using the GAB equation. It was shown that the two methods of describing the water vapor sorption be havior of starch-based products correlate with each other. In order to obta in quick results about the sorption behavior of materials for practical app lications, the method of determination of moisture uptake between two relat ive humidities is suggested. Furthermore, it is possible to simulate the wh ole sorption isotherm of a starch-based product with the: help of the GAB e quation by determining the mass of dry matter and the water vapor adsorptio n between 50% and 93% RH only.