Water interactions, barrier properties, and biodegradation of cellulose acetate butyrate and cellulose acetate propionate films

Biobased food packaging barrier materials have not yet achieved broad adoption because they often fail to meet key requirements such as water vapor resistance, flexibility, and cost. Petroleum based plastics therefore remain dominant despite their environmental impact, driving the search for renewable and biodegradable alternatives. Cellulose esters have emerged as promising candidates, yet links between ester composition, molecular water interactions, and macroscopic barrier performance remain limited. Films of six commercially available cellulose acetate butyrates (CABs) and one cellulose acetate propionate (CAP) were investigated regarding water interactions, barrier performance, biodegradability, and thermal behavior. Composition dependent differences in hydration were observed, with CAP showing higher humidity and liquid water uptake than CAB. In contrast, macroscopic barrier properties, including water vapor permeability and water absorption, were weakly influenced by ester composition and instead governed by film morphology and processing history. Thermal analysis indicated that calorimetric features observed during first heating reflect the hydrated state of the films rather than crystalline melting. Biodegradation experiments showed limited but measurable soil degradation dependent on substitution chemistry. Overall, substitution chemistry controls molecular water interactions, while morphology and processing dominate macroscopic barrier performance, supporting cellulose esters as candidates for next generation food packaging.