Membrane fabrication using nanocrystalline cellulose

2020-10-13
Volkan, Ecem
Cellulose is a biopolymer which is resistant to many solvents due to inter- and intramolecular hydrogen bonds; also, it is hydrophilic and resistant to fouling, which makes cellulose attractive for membrane applications in aqueous and organic media. Nanocrystalline cellulose (NCC) is a promising material due to high surface area, rod-like structure, good dispersion abilities, biodegradability and nanoscale. It is produced by acid hydrolysis using mineral acids to digest amorphous regions of the cellulose chain, yielding crystalline regions as discrete crystalline nanofibers. In this study, the main aim is to fabricate membranes using nanocrystalline cellulose. The first procedure is to fabricate membranes via controlled precipitation of an NCC suspension on a support membrane to produce a selective membrane layer without using organic solvents, and these membranes’ stability, morphology, and separation performance were examined. In other procedure, the all-cellulose nanocomposite membranes with improved crystallinity with the ultimate goal of increasing solute rejection were produced by either adding NCC into membrane casting solution or partial dissolution of cellulose by investigation membranes’ crystallinity, morphology and separation performances. vi Using 50 % aqueous H2SO4 solution, 10 ml/g acid to cellulose ratio and 30 minutes reaction time (NCC50H2SO4-cotton-30/10) NCC with ~ 250 nm length and ~ 30 nm width was produced and used in membrane fabrication by deposition. For precipitating the stable colloids of NCC on the CA or PES support membrane, 200 mM AlCl3 and 1 M NaOH were used. Different NCC deposition amounts on the CA support membrane were used to see the deposition thickness effect on the NCC membrane. Deposition of NCC on CA support membrane decreased the pure water permeance, proportional to the deposition amount, and increased the rejection of Blue Dextran (5 kDa) from 52 % to ̴ 90 % for all deposition amounts. Besides, membranes with 0.24 mg/cm2 deposit were stable in water for up to 1 week. Membranes fabricated by alkali desulfation of deposited NCC, on the other hand, did not form defect-free continuous deposits, possibly due to the effect of the high alkalinity used on the support membrane pores. Membranes fabricated using polymer solutions containing NCC or partially dissolved cellulose did not show improved rejection due to aggregation, swelling or complete dissolution of crystalline regions of cellulose.

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Citation Formats
E. Volkan, “Membrane fabrication using nanocrystalline cellulose,” M.S. - Master of Science, Middle East Technical University, 2020.