378058 Ultrafiltration Membranes Composed of Cellulose Acetate and N-Isopropylacrylamide (NIPAAm)
Ultrafiltration Membranes Composed of Cellulose Acetate and N-Isopropylacrylamide (NIPAAm)
Membrane fouling occurs when there is reversible or irreversible attachment of macrosolutes present in the water to the membrane surface. Membrane replacements due to fouling can add to the operating costs of membrane systems. Reversible fouling can be minimized by crossflow operation, backflushing and/or by chemical pretreatment. On the other hand, irreversible fouling cannot be corrected by backflushing or crossflow filtration, and it results in permanent flux decline. Among irreversible foulants, natural organic matter (NOM) is considered to be a major contributor. NOM is composed of a wide range of hydrophilic and hydrophobic components; hence, any static hydrophobic or hydrophilic membrane can get fouled. Therefore, a dynamic membrane able to alternate between being hydrophobic and hydrophilic is hypothesized to decrease fouling. Stimuli-sensitive polymers can change their conformation from a coiled and hydrophobic state to an uncoiled (or globular) and hydrophilic state in the presence of a stimulus. By using such polymers to make a membrane and then alternating between the phases, the membrane surface can be made dynamic.
The purpose of this study was to develop stimuli responsive membranes to control fouling using membrane casting dopes made of cellulose acetate with N-isopropylacrylamide (NIPAAm). NIPAAm is a stimuli-responsive polymer, which offers the potential to reversibly collapse or expand the membrane as a function of changes in temperature. As a response to a temperature decrease, NIPAAm expands into a hydrophilic state, while a temperature increase causes it collapse into a less hydrophilic state. The phase change arises from the existence of a lower critical solution temperature (LCST) such that the polymer precipitates from aqueous solution as the temperature is increased. By continuously activating the film, it is hypothesized that a dynamic stimuli-responsive surface can prevent foulants from attaching to the membrane surface.
Membranes were cast using phase inversion, and then were characterized chemically, morphologically, and were used in filtration experiments using bovine serum albumin (BSA) and Lipase. Flux studies were conducted at alternating cold and hot temperature cycles, which confirmed the temperature activation of CA-NIPAAm membranes as compared to pure cellulose acetate membranes. Protein rejection was higher in case of CA-NIPAAm membranes. CA-NIPAAm membranes offered an average higher flux during operation and lower protein accumulation on the membrane surface as compared to regular CA membranes. CA-NIPAAm membranes showed higher flux recovery than CA membranes.