Nanocellulose’s inherent traits, like hygroscopicity, are attractive for water purification applications. They contribute to anti-fouling, permeance and facilitate efficient rejection performance of nanocellulose-enabled membranes [1, 2]. Nanocelluloses have a large modifiable surface area, which can be harnessed in filtration by using nanocellulose as an additive or as a thin coating. However, small dimensions of nanocellulose also govern the resulting membrane’s separation range and there is a tradeoff between membrane permeance and rejection [2]. We conducted a systematic study on the effects of nanocellulose blend, coating thickness and membrane pre-wetting on the nanocellulose-enabled membranes’ filtration performance.

Our objective was to identify the membrane’s tunability in its separation range and to chart the tradeoff between permeance and rejection. We utilized an approach demonstrated in pilot scale [1], where nanocellulose is cast-coated on a commercial polyethersulfone microfiltration membrane, resulting in a nanocellulose-enabled tight ultrafiltration membrane (Figure 1). Then, we studied the permeance, pore size distribution and surface charge of the membranes, and related these properties to the membranes’ electrostatic and steric rejection performance with Na₂SO₄ and polyethylene glycol, respectively.

With underlying statistical experimental design, we identified contributions of the nanocellulose blend, coating thickness and pre-wetting on the membrane performance. The nanocellulose-enabled membranes, at best, had molecular weight cut-offs below 10 kDa, pure water permeances over [...] L m^-2h^-1MPa^-1, pore size distributions around 5 nm and negatively charged surfaces. These properties contributed to dual steric and electrostatic rejection performance. The membranes could reject nearly [...]% of polyethylene glycol mixture simulating 5 nm particles and more than [...]% of Na₂SO₄. Overall, the nanocellulose-enabled membranes were tunable in ultrafiltration range and their performance either matched or improved the performance of reference commercial ultrafiltration membranes...