Thermal annealing effect on cellulose acetate reverse osmosis membrane structure

The structure variation of cellulose acetate (CA) reverse osmosis (RO) membranes due to thermal annealing was investigated by using gas adsorption. When the CA membranes were dehydrated by freeze-drying, the morphology of the unannealed membrane was similar to that of the annealed membrane. On the contrary, with air-drying which induced structure collapse of the CA membranes, gas adsorption behavior of the unannealed membrane showed a significant difference from that of the annealed membrane. The CA RO membrane in an unannealed state totally collapsed during air-drying, but the membrane that was annealed for 10 min at 90°C showed significantly reduced collapsing compared to the unannealed one. However, even though the CA membranes were annealed, use of methanol as the wetting agent caused complete collapsing during air-drying.