Comparison Between Water Vapor Sorption Isotherms Obtained Using The New Dynamic Dewpoint Isotherm Method and those Obtained Using The Standard Saturated Salt Slurry Method

Abstract

The Dynamic Dewpoint isotherm method directly determines sample aw using chilled-mirror technology, while changes in sample weight are tracked gravimetrically. The objective of this research was to compare the Dynamic Dewpoint isotherms to saturated salt slurry isotherms for five materials: dent corn starch, isolated soy protein, microcrystalline cellulose, crystalline sucrose, and corn flakes. The Dynamic Dewpoint isotherms were obtained using the AquaSorp Isotherm Generator between 0.10 and 0.95 aw at 25°C. Comparison working isotherms were obtained using 12 saturated salt slurries, between 0.064 and 0.973 aw in desiccators and proximity equilibration cells at 25°C. The Dynamic Dewpoint isotherms exhibited similar sorption behavior to the saturated salt slurry isotherms, except for corn flakes, where there was a marked decrease in moisture content compared to the saturated salt slurry isotherms between 0.40 and 0.70 aw. This difference was attributed to the slow diffusion of water into the very dense laminated corn flake matrix, highlighting the rate of sorption (time) dependency of the Dynamic Dewpoint isotherm method. The Dynamic Dewpoint isotherm method offers the opportunity for real-time investigation of water sorption-related material properties, such as the glass to rubbery transition, recrystallization, hydrate formation, and deliquescence.