Critical Role of Boundary Conditions in Sorption Kinetics Measurements

Area of Science:

• Materials Science
• Physical Chemistry
• Chemical Engineering

Background:

• Sorption-desorption dynamic tests are crucial for characterizing hygroscopic materials.
• Understanding water vapor interaction with cellulose is vital for applications like paper and textiles.
• Existing methods often simplify the complex interplay of factors governing moisture transport.

Purpose of the Study:

• To develop a theoretical framework for analyzing sorption-desorption kinetics in hygroscopic materials.
• To investigate the influence of air flux, material geometry, and surface properties on moisture transport.
• To validate the theoretical model using experimental data.

Main Methods:

• Developed a theoretical model based on vapor convection-diffusion.
• Introduced a multiplicative factor (δ) dependent on air flux and geometry.
• Utilized magnetic resonance imaging (MRI) for experimental validation on cellulose fiber stacks.

Main Results:

• Vapor mass flux is proportional to the difference in relative humidity (RH) and a factor (δ).
• Kinetics are governed by the competition between boundary conditions and internal transport.
• Moisture distribution within the material transitions from uniform to inhomogeneous based on air flux and thickness.

Conclusions:

• The theoretical model accurately describes sorption-desorption kinetics.
• Air flux intensity and sample thickness are critical parameters determining moisture distribution.
• This work provides a more nuanced understanding of moisture dynamics in porous materials.