Free Volume and Water Sorption by Cellulose Esters

Area of Science:

• Polymer Science
• Materials Chemistry
• Physical Chemistry

Background:

• Cellulose acetate (CA) is a versatile polymer with applications influenced by its sorption properties.
• Understanding water vapor sorption is crucial for predicting CA material behavior in various environments.

Purpose of the Study:

• To investigate the sorption properties of cellulose acetate (CA) with varying degrees of substitution (SD).
• To analyze the relationship between acetate group content and water vapor sorption capacity.
• To elucidate the underlying mechanisms governing water sorption in CA.

Main Methods:

• Experimental determination of water vapor sorption isotherms for CA samples with different SD.
• Analysis of sorption isotherms using the double sorption model.
• Calculation of hydrate numbers for hydroxyl and acetate groups.
• Determination of Flory-Huggins interaction parameters.

Main Results:

• Sorption capacity for water vapor in CA decreases with increasing degree of substitution (acetate group content).
• The Langmuir sorption component diminishes due to the replacement of hydroxyl groups with ester groups, which exhibit lower local sorption capacity.
• At high humidity, plasticization of the sorbent leads to an increase in vacancy sizes.

Conclusions:

• The degree of substitution in cellulose acetate significantly influences its water vapor sorption behavior.
• The findings provide insights into the molecular interactions governing water sorption in cellulose derivatives.
• This research contributes to the understanding of cellulose acetate as a sorbent material.