Abstract
In this study cellulose-rich membranes were fabricated from untreated and treated hardwood biomass solutions in 1-ethyl-3-methylimidazolium acetate ([Emim][OAc])—dimetylsulfoxide (DMSO) system via wet phase separation. Wood treatment methods aimed to get purified cellulose fraction of wood. Treatment sequence was as followed: deep eutectic solvent pretreatment, sodium chlorite bleaching, and alkaline treatment. Resulted biomass after each treatment step was characterized by chemical composition and crystalline fraction content. Flat-sheet membranes were produced from biomass samples after each treatment step. Characterization of membranes included measurements of pure water permeability and (poly)ethyleneglycol 35 kDa retention, Fourier-transform infrared and Raman spectroscopy, X-ray diffraction measurements and thermogravimetric analysis. The study revealed that it was possible to fabricate membrane from untreated wood as well as from wood biomass after each of treatment steps. The resulted membranes differed in chemical composition and filtration performance. Membrane prepared directly from untreated wood had the highest permeability, the lowest retention; and the most complex chemical composition among others. As treatment steps removed lignin and hemicelluloses from the wood biomass, the corresponding membranes became chemically more homogeneous and showed increased retention and decreased permeability values.
Highlights
Cellulose is considered an abundant renewable resource of great potential for bio-based materials and products
Solvents capable of cellulose dissolution can be divided into two groups: derivatizing solvents, which interact with hydroxyl groups and form a soluble intermediate that can be isolated later and non-derivatizing solvents, which do not alter the cellulose chemistry but break hydrogen bonds within the cellulose microfibrils during the dissolution process (e.g. cupro, NMMOÁH2O and lithium chloride/N,Ndimethylacetamide (LiCl/DMAc)) (Pinkert et al 2009; Khakalo et al 2019)
Fabrication of polymeric cellulose-rich membranes from hardwood biomass subjected to different pretreatments and dissolved in a mixture of [Emim][OAc]-DMSO via phase inversion method was performed
Summary
Cellulose is considered an abundant renewable resource of great potential for bio-based materials and products. The presence of many hydroxyl groups, which gives cellulose its remarkably high hydrophilicity, and the extensive network of inter- and intramolecular hydrogen bonds, which provides relatively high chemical and thermal stability, make cellulose an attractive material for filtration membranes (Woodings 2001; Slusarczyk and Fryczkowska 2019). Existing conventional cellulose dissolution and membrane fabrication (both derivatizing and non-derivatizing solvent-based processes) require expensive, hazardous chemicals and cause significant pollution, so there is a need for novel non-derivatizing solvents whose dissolution mechanism maintains the beneficial characteristics of cellulose as a membrane material (Zhang et al 2017; Khakalo et al 2019)
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