(280b) Effect of Dehydration on RO Performance and Antifouling in Fully Aromatic Polyamide Membranes Containing Functionalized Cellulose Nanocrystals (CNCs)

Fully aromatic polyamide thin film composite membranes (TFCs), consisting of a thin selective layer and thick porous support, are commonly used materials for desalination by reverse osmosis (RO). Fully aromatic polyamide TFCs must be kept hydrated in order to maintain the pore structure needed for water transport. In real applications biofouling often occurs on the surface of TFCs as proteins accumulate on the surface inhibiting transport, and decreasing the efficiency of the membranes. Thin film nanocomposite membranes (TFNs) incorporate nanoparticles in the selective layer to improve upon traditional TFC performance. In this study we created TFNs by incorporating cellulose nanocrystals (CNCs) and studied the effects of CNC functionality, loading level, and dehydration on RO performance. CNCs are of interest due to their high aspect ratio, low cost, availability, sustainability, and for the possibility for future surface modifications allowing for functionalized derivatives affecting particle-polymer interactions. 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNs) or zwitterionic functionalized cellulose nanocrystals (zCNCs) were incorporated within fully aromatic polyamide TFNs synthesized via interfacial polymerization of m-phenylenediamine (MPD) and 1,3,5-benzenetricarbonyl trichloride (TMC).

The flux and salt rejection were investigated for TFNs prepared with various amounts of TOCNs or zCNCs. For membranes containing TOCNs these membranes were stored in deionized water or under vacuum prior to testing. zCNCs were only stored in water. The presence of nanoparticles in the final TFNs was confirmed using ATR-FTIR. Water transport increases as pathways for molecular transport develop at the interface between the polymer matrix and nanoparticle surface. Water transport is negatively impacted by membrane dehydration as the polymer pore structure collapse, but the impact is diminished by the presence CNC nanofillers in the membrane. Antifouling behavior was studied using a test solution containing bovine serum albumin (BSA) under conditions preferable for protein deposition on the membrane surfaces. The reduction in flux due to BSA fouling was examined over several hours. TFNs containing zCNCs exhibited slower decreases in performance relative to both TFNs containing TOCNs and TFCs without any nanoparticles.