Nanocelluloses fine-tuned polyvinylidene fluoride (PVDF) membrane for enhanced separation and antifouling

Abstract

To mitigate membrane fouling and address the trade-off between permeability and selectivity, we fabricated nanocellulose (NC) fine-tuned polyvinylidene fluoride (PVDF) porous membranes (NC-PVDFs) using phase inversion method through blending NCs with varied aspect ratios, surface charges and grafted functional groups. NC-PVDF presented rougher surface (increased by at least 18.3 %), higher porosity and crystallinity compared to PVDF membrane. Moreover, cellulose nanocrystals incorporated PVDF (CNC-PVDF) elevated membrane surface charge and hydrophilicity (from 74.3° to 71.7°), while 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized cellulose nanofibers modified PVDF (TCNF-PVDF) enhanced the porosity (from 25.0 % to 40.3 %) and tensile strength (63.6 % higher than PVDF). For separation performance, NC improved flux, rejection and fouling resistance due to facilitation of phase transition thermokinetics as pore-forming agent and increased hydrophilicity at both interface and pore wall. For water flux, NC-PVDFs (139–228 L·m−2·h−1) resulted in increased permeability compared to bare PVDF. CNC-PVDF membrane exhibited the highest water flux because of improved porosity, roughness and hydrophilicity. For bovine serum albumin (BSA) rejection, the removal rates of all NC-PVDFs were all above 90 %. Notably, TCNF-PVDF exhibited the most remarkable elevation of BSA rejection (95.1 %) owing to size exclusion and charge repulsion in comparison with PVDF.