For most membrane filtration applications, cellulose acetate is the most frequently used cellulose ester, although cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) have been investigated.
Cellulose acetate is produced by the reaction of cellulose with acetic anhydride as shown in the following chart:
The level of substitution of hydroxyl groups by acetyl groups creates loosely defined classes referred to as cellulose mono-, di-, and tri-acetates. The amount of acetyl on the cellulose backbone can be expressed as degree of substitution (DS) or weight percent of acetyl. In theory the DS ranges from zero (0), which is just cellulose, to three (3) which is cellulose triacetate (CTA). All the levels of acetyl in between start as CTA in manufacturing and are then back hydrolyzed to the targeted levels. Actual DS=3 cannot be produced due to its high crystallinity and insolubility.
Products can be used neat or blended as required to achieve the desired performance.
An overview of the different nomenclatures is provided below:
|Cellulose monoacetate||Cellulose acetate 320||1.80||32.0|
|Cellulose diacetate||Membrane Material M203||2.45||39.8|
|Membrane Material M210|
|Membrane Material M230|
|Cellulose triacetate||Membrane Material M300||2.85||43.6|