Carbohydrate Polymers 99 (2014) 438–446 Contents lists available at ScienceDirect Carbohydrate Polymers jo u r n al homep age: www.elsevier.com/locate/carbpol Influence of water on swelling and dissolution of cellulose in 1-ethyl-3-methylimidazolium acetate Carina Olsson a , Alexander Idström b , Lars Nordstierna b , Gunnar Westman a,∗ a Organic Chemistry, Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden b Applied Surface Chemistry, Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden a r t i c l e i n f o Article history: Received 28 March 2013 Received in revised form 17 July 2013 Accepted 18 August 2013 Available online 26 August 2013 Keywords: Ionic liquids EMIMAc Regenerated cellulose Rheology CP/MAS 13 C-NMR spectroscopy Cellulose allomorph a b s t r a c t In this study the effect of residual coagulation medium (water) on cellulose dissolution in an ionic liquid is discussed. Solubility of dissolving grade pulp; HWP and SWP, and microcrystalline cellulose in binary solvents, mixtures of 1-ethyl-3-methyl-imidazolium acetate and water, was investigated by turbidity measurements, light microscopy, rheometry, and CP/MAS 13 C-NMR spectroscopy. The viscoelastic prop- erties of the cellulose solutions imply that residual water affect the cellulose dissolution. However, it is not obvious that this always necessarily poses serious drawbacks for the solution properties or that the effects are as severe as previously believed. Turbidity measurements, viscosity data and crystallinity of the regenerated cellulose correlated well and an increased conversion to cellulose II was found at low water and cellulose contents with an apparent maximum of conversion at 2–5 wt% water. At high water content, above 10 wt%, dissolution and conversion was largely inhibited. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Native cellulose is an immensely important material for mankind, used in a variety of forms for everything from paper and clothes to building material (O‘Sullivan, 1997). With the ability to regenerate cellulose into other forms, new products with other properties could be developed. However, regeneration of cellulose has long been struggling with the use of inefficient or environmen- tally hazardous solvents (Kim, Kim, Kwak, Ko, & Kwon, 2006). With cellulose as the basis for large scale production of man-made tex- tile fibers, it is of growing interest to develop new, as well as to understand and improve existing, methods for its dissolution and coagulation to regenerated materials. Lately an increasing num- ber of studies have been presented in this field (Budtova et al., 2010; Hauru, Hummel, King, Kilpeläinen, & Sixta, 2012; Spinu, Dos Santos, Le Moigne, & Navard, 2011). Ionic liquids (ILs), organic salts with low melting points, can be used for direct dissolution of biomass, which is an important finding since most other sol- vents fail to dissolve biomass in general and cellulose in particular (Lindman, Karlström, & Stigsson, 2010; Sun et al., 2009; Swatloski, Spear, Holbrey, & Rogers, 2002). Despite a tendency to react with ∗ Corresponding author. Tel.: +46 317723072. E-mail addresses: carina.olsson@chalmers.se (C. Olsson), idstrom@chalmers.se (A. Idström), lars.nordstierna@chalmers.se (L. Nordstierna), westman@chalmers.se (G. Westman). cellulose (Ebner, Schiehser, Potthast, & Rosenau, 2008; Liebert, 2008), 1-ethyl-3-methyl-imidazolium acetate (EMIMAc) is still one of the most popular ionic liquids for cellulose dissolution. Regenerated cellulose can be produced from native cellulose by dissolution followed by precipitation. A conversion to regenerated cellulose means a change in the crystalline structure, from cellulose I  or I  in native cellulose to cellulose II in regenerated cellulose. This conversion can also be achieved by swelling or merceriza- tion. When producing regenerated cellulose via a direct dissolution route, native cellulose is dissolved and the solvent is thereafter sub- stituted with a coagulation medium, often water. The regenerated cellulose is removed and collected in a desired shape while the water/solvent-mixture is separated and recycled. A large part of water can be removed from the ionic liquid by e.g. partial phase separation using K 3 PO 4 to bind water before the enriched ionic liquid phase can be collected and further purified by energy con- suming evaporation of the water (Gutowski et al., 2003). Efficient recycling strategy is a key issue to minimize solvent consumption and environmental impact. However due to the hygroscopic nature of ionic liquids and the relatively high boiling point of water, this step would mean high energy costs in a large scale application. Understanding the effect of remaining water in the ionic liquid is therefore fundamental working with separation of water and ionic liquid. By changing solvent or solvent properties, the properties of the regenerated cellulose can be altered, ranging from a rigid and crys- talline state to a softer amorphous material (Cheng et al., 2012; 0144-8617/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbpol.2013.08.042