Novel cellulose esters for forward osmosis membranes

Syntheses and evaluation of novel cellulose esters consisting of a wide range of chemical compositions targeted for forward osmosis membrane fabrication have been carried out. Preliminary studies on the effects of the degree of substitution of hydroxyl, acetyl, and propionyl or butyryl functional groups on the membrane formation and permeation characteristics were conducted. Experiments results show that cellulose esters with high content of hydrophobic functional groups content exhibit great salt rejection, because of low water solubility and small hydrated free volume of hydrophobic cellulose esters. However, as the content of bulky hydrophobic functional groups increases, there is an accompanying increase in free volume due to poor chain packing, which causes a decrease in salt rejection. A high OH content in cellulose esters results in membranes with high salt and water permeation. Among the evaluated cellulose esters, those which have the highest hydrophobicity are unable to form membranes with defect-free selective layers via normal phase inversion casting conditions.