Eastman cellulose esters are available with a range of substituents and molecular weights that determine their solubility, compatibility, viscosity, film formation, and hardness. The size of the acyl group—acetyl, propionyl, or butyryl—on the cellulose backbone affects the packing density and the polarity of the cellulose chains. The cellulose backbone provides three hydroxyls per anhydroglucose unit, which are replaced during esterification with acyl groups. The extent of this replacement of the hydroxyl group can be expressed as degree of substitution with a range of 0 (cellulose) to 3 (tri-ester) or in weight percent of acyl and hydroxyl.
The following table provides guidance about the impact of butyryl content, hydroxyl content, or viscosity on film properties.
For a cellulose ester with greater:||
Choose a cellulose ester with:|
|Compatibility||Higher butyryl content|
|Solubility||Higher butyryl content or higher hydroxyl content if the solvent blend is high in alcohol|
|Reactivity||Higher hydroxyl content|
|Hardness||Lower butyryl content or higher hydroxyl content |
|Chemical resistance||Lower butyryl content|
|Flexibility||Higher butyryl content|
|Higher solids at fixed viscosity||Lower viscosity|
|Moisture resistance||Lower hydroxyl content|
|Adhesion||Higher butyryl and hydroxyl content|