Cellulose-cellulose composite membranes for ultrafiltration

Research and development towards sustainable chemistry includes also the development of new materials and the exploration of new ways to fabricate them. In this work, composite membranes were fabricated from fully biodegradable materials (cellulose) through a simple and scalable process, i.e., a combination of film casting, nonsolvent-induced phase separation and lamination, in which only environmentally friendly solvents are used. Filter paper was utilized as support material. Cellulose was dissolved in a mixture of an ionic liquid (1-ethyl or 1-butyl-3-methylimidazolium acetate) with a co-solvent (dimethylsulfoxide, DMSO) and used for casting the barrier layer. The influence of pre-wetting the filter paper with different liquids (water, glycerine, DMSO) was investigated. It was found that using DMSO as impregnation liquid improved both, the membrane separation performance and the strength of the lamination between the cellulose barrier layer and the filter paper as demonstrated by adhesion tests. Barrier layer thickness could be reduced to a few μm by appropriate cast film thickness. Membrane separation performance in terms of permeance and solute rejection could also be adjusted by the choice of cellulose concentration and co-solvent fraction in the casting solution. The applicability of the cellulose-cellulose composite membranes in ultrafiltration (UF) of aqueous or organic solvent-based mixtures was evaluated with dextran or polyethylene glycol and polyethylene oxide, respectively, as test solutes. Molecular weight cut-off data for one specific UF membrane type were ∼100 kDa, ∼170 kDa, or ∼390 kDa in water, dimethylformamide or DMSO. All results obtained in this study indicate that the novel membranes have potential as a more sustainable alternative material for various relevant separations.