Fabrication and property modification of free-standing PSS/PDADMAC ultra- and microfiltration membranes by incorporating cellulosic additives

In classical membrane fabrication, water-soluble additives such as polyvinylpyrrolidone (PVP) have been pivotal in generating porosity and tuning surface properties. By contrast, comparable modifiers for membranes produced via all-aqueous processes — such as polyelectrolyte complex (PEC) membranes — remain largely unexplored. Here, we demonstrate that hydroxyethyl cellulose (HEC) and hydroxypropyl cellulose (HPC) act as effective pore formers and structural modifiers in PEC flat-sheet membranes prepared by salt-dilution-induced phase inversion. During fabrication, a fraction of the cellulosic additive is leached from the polymer solution, enhancing membrane porosity and permeability, while the residual fraction reinforces mechanical stability. Crosslinking with sodium trimetaphosphate (STMP) further strengthens the membranes. Membranes using HEC as the cellulosic additive exhibit a tunable increase in pure water permeability (from 43 ± 10 to 123 ± 47 LMH ⋅ bar −1 ) and molecular weight cut-off (from 117 ± 64 to 460 ± 360 kDa). In addition, additive pretreatment and crosslinking strategies enable surface charge modulation, shifting it from positive to neutral or negative, and tailoring salt retention profiles. These findings establish cellulosic additives as versatile design elements in the emerging class of aqueous PEC membrane systems. • Development of free-standing flat-sheet PEC membranes for UF/MF through incorporating cellulosic additives. • Fabrication via all-aqueous salt-dilution-induced phase separation. • Achieving tunable membrane surface charge through NaOH pretreatment of cellulosic additives. • Improved mechanical stability achieved through crosslinking with STMP.