In Situ Formation of Cellulose Acetate Carbamate Dry-RO (Trade Name) Membranes

摘要

The in situ formation of cellulose acetate (CA) carbamates was investigated to increase the performance of Dry-RO membranes of CA. The CA casting solutions were charged with reversibly blocked isocyanate monomers, which when heated, formed CA carbamates. This approach is economical since it uses a small amount of inexpensive blocked isocyanate monomer for a large amount of preformed polymer, CA carbamate. The performance of modified CA membranes was tested on several levels (neutral, neutral in situ, sulfonated, sulfonated in situ, quarternized in situ) to establish a basis for comparison. The modification of the CA membranes with neutral carbamate groups decreased the permeability but not the permselectivity. Monofunctional isocyanate monomers were not as efficient as diisocyanate monomers in carbamate formation and the later technique appears to be the most promising. Sulfonated CA carbamates gave poor RO efficiency and solubility and their formation was not efficient. CA carbamates formed in situ with quaternary ammonium groups appeared quite promising and a nonswelling QCAC Dry-RO membrane from a commercial polyurethane prepolymer containing two isocyanate groups and a single quaternay ammonium group was prepared.