Size-Dependent Diffusive Transport in Alkali-Insolubilized Konjac Glucomannan Free-Standing Membranes

As the demand for sustainable and bio-based alternatives to petroleum-derived membranes grows, polysaccharides have emerged as promising candidates. In this study, we fabricated free-standing membranes from konjac glucomannan (KGM), a neutral polysaccharide, using a simple base-induced insolubilization process. Fourier transform infrared spectroscopy revealed that the deacetylation of KGM chains promotes extensive intermolecular hydrogen bonding, creating a robust and stable three-dimensional network without the need for chemical cross-linkers. The resulting KGM free-standing membranes exhibited excellent mechanical properties, characterized by high tensile strength in the dry state and remarkable flexibility when hydrated. Furthermore, the membranes demonstrated superior chemical resistance to organic solvents such as acetone and n-hexane. Transport studies showed that the membranes possess a highly dense structure with no detectable pressure-driven pure-water permeation up to 0.25 MPa. Solute permeation experiments using eight model molecules (molecular weight = 144–14,600 Da) indicated that transport behavior is consistent with diffusion through a hydrated polymer network. The effective diffusion coefficient Deff showed a strong correlation with molecular weight M, following the relationship Deff ∝ M−1.7. Furthermore, the permeation behavior remained stable across a wide pH range (2–12), and, within the investigated range of monovalent solutes, Deff was insensitive to solute charge, indicating that mass transport is dominated by size-based diffusion rather than electrostatic interactions. These findings suggest that KGM free-standing membranes enable reliable molecular fractionation based on size-dependent diffusion within a stable, neutral matrix, offering significant potential for sustainable separation technologies and biomedical applications.