Phase separation and performance of polyethersulfone/cellulose nanocrystals membranes

We investigate the effect of cellulose nanocrystals (CNC) as a hydrophilic nanoparticle on the characteristics of polyethersulfone (PES) based membranes. The membranes are fabricated using typical nonsolvent induced phase separation (NIPS) method. We study the radius of gyration and aggregation of PES in dimethylformamide in the presence of CNC, the rheological behavior of dope dispersions, and the morphology, permeability, irreversible fouling, MWCO, zeta-potential, water contact angle and mechanical properties of final membranes. Small-angle X-ray scattering (SAXS) analysis show that high CNC and water concentrations lead a transition from mass fractal to surface fractal scattering. Addition of CNC into the PES solution induces the formation of an interconnected polymer network, yet excess CNC loading eventually results in a heterogeneous composite with diminished mechanical properties. Additionally, an increase in the viscosity and elasticity of the dope dispersions is observed in the presence of CNC, which changes the morphology of the final membranes. The CNC concentration up to 1.5 wt% increases the water permeability of membrane while retaining the same dye rejection and fouling resistance as the neat one. The enhanced performance of PES/CNC membrane is related to the rheological properties and phase separation behavior of the cast dispersion. The results of water contact angle analysis confirm the higher wettability of the CNC filled membranes. Incorporation of up the 2 wt% CNC leads to a higher strength but lower ductility in comparison to the neat PES membrane.