Controlling morphological transition and transport trade-offs in NMMO-regenerated cellulose membranes via feedstock engineering

The industrial maturity of N-methylmorpholine-N-oxide (NMMO) as a cellulose solvent enables direct fabrication of regenerated cellulose membranes (RCMs). This study systematically examines how the intrinsic feedstock properties, beyond the solvent, govern membrane formation and transport performance using a range of industrial pulps. Results showed that reducing the degree of polymerization (DP) decreased dope viscosity and accelerated phase inversion, driving a structural transition from dense lamellar architectures to highly interconnected porous networks. This transition significantly enhanced permeability but at the expense of solute rejection, revealing an inherent trade-off between transport and selectivity. Residual xylan in the pulp was further identified as an intrinsic pore-forming component that promotes pore connectivity. To overcome the limited processability of high-DP feedstocks, a synergistic blending strategy with low-DP microcrystalline cellulose (MCC) was introduced. By exploiting viscosity contrasts between components, the accessible polymer concentration window was expanded without compromising spinnability, enabling finer control over membrane structure. In addition, regulating coagulation bath temperature was found to be more effective than increasing casting temperature in enhancing permeability in high-viscosity systems. Under optimized conditions (3 wt% pulp and 7 wt% MCC, coagulation at 35 °C), the membrane achieved a pure water permeability of 63.3 L m −2  h −1 bar −1 , along with a bovine serum albumin permeability of 62.0 L m −2  h −1 bar −1 and a rejection of 95.3%. This work establishes a feedstock engineering framework for controlling morphological transition and transport trade-offs in NMMO-based RCMs, offering new insights into the efficient utilization of biomass-derived cellulose for high-performance membrane fabrication.