(342c) Cellulose-Cellulose Composite Membranes for Ultrafiltration

Membranes made from cellulose were in history and are also currently important for the development of membrane technologies. Alternative fabrication methods for completely biopolymer-based separation membranes are of high interest with view on improved sustainability [1].

This project explores a new kind of composite membrane, with a thin selective cellulose layer on filter paper as porous support. Suited ionic liquids (IL) in combination with dimethylsulfoxide (DMSO) can be used to dissolve cellulose under mild conditions and subsequently to cast regenerated cellulose materials via shaping and phase separation [2]. The novel fabrication method of completely renewable and biodegradable cellulose-cellulose composite membranes for ultrafiltration (UF) is therefore based on film casting of a solution of cellulose in an IL/DMSO mixture on filter paper as support and subsequent phase separation in water. Typical composite membranes have a cellulose film thickness of a few µm on filter paper with a pore size in the range of several µm. The separation performance of the obtained membranes can be specifically adjusted by fabrication parameters such as cellulose concentration, structure of IL and DMSO co-solvent content in the casting solution as well as coagulation bath conditions. When using the dry support, it is partially penetrated by the cellulose solution during the film casting, leading to too low permeance. The separation performance can be improved by pre-wetting the support with various liquids to prevent pore penetration, but that can also weaken the lamination between cellulose barrier layer and paper support, as shown by adhesion tests. It was found that prewetting of the filter paper with DMSO can solve the problem, leading to composite membranes with a strongly attached cellulose film on the paper support and superior, tunable UF properties for aqueous feeds. Such membranes have also been evaluated in terms of their UF separation performance in a wide range of organic solvents.

[1] S. P. Nunes, P. Z. Culfaz-Emecen, G. Z. Ramon, T. Visser, G. H. Koops, W. Jin, M. Ulbricht, Thinking the future of membranes: Perspectives for advanced and new membrane materials and manufacturing processes, Journal of Membrane Science 598 (2020) 117761.

[2] A. S. M. Wittmar, D. Koch, O. Prymak, M. Ulbricht, Factors affecting the non-solvent induced phase separation of cellulose from ionic liquid-based solutions, ACS Omega 5 (2020) 27314-27322.