Ionic liquids for the textile industry – part 1
In the last 20 years ionic liquids, a new class of solvents, have gained increasing awareness in the scientific community. Numerous potential applications are described in the literature and a couple have already reached commercial stage. These include solvents in analytical applications, sensors and supercapacitors in electrochemical applications, and in chemical synthesis and catalysis, nano particle synthesis and as solvents for organic reactions. For textile applications, ionic liquids are still in laboratory stage, and in some cases they have reached pilot stage.
There is abundant literature available on the topic of ionic liquids in textile applications. Potentially they are considered as „green“ solvents. In this short article, only selected examples are cited. For readers who are interested in a comprehensive summary, the author refers to the excellent review article on the published literature of ionic liquids for textile application, recently published by Meksi & Moussa1.
The chemistry of ionic liquids
The first ionic liquids were reported in the literature in the late 19th century were alkylammonium nitrates2,3. Since the 1970s ionic liquids based on alkyl-substituted imidazolium and pyridinium cations, have been explored as potential electrolytes in batteries4.
In many publications dealing with potential textile applications, derivatives of imidazolium salts are used as ionic liquids (examples for ionic liquids see Figure 1), due to their properties and commercial availability. 1-Ethyl- or 1-Butyl- 3-methyl-imidazolium salts (Figure 2) were frequently used, and as counter ion, various anions have been tested.
General properties of ionic liquids
Ionic liquids are considered as potentially „green solvents“ due to certain environmentally favourable properties, allowing safe and versatile applications. These properties include
- extremely low vapour pressures
- non flammability
- high temperature and mechanical stability
- broad liquid range
- electric conductivity
- high electrochemical stability
- potential for recycling
A ionic liquid is a salt in the liquid state which typically has a melting point below 100 °C, therefore being liquids at moderate processing temperatures. While ordinary solvents are predominantly made of electrically neutral molecules, ionic liquids are made of electrically charged ions.
The physical properties of selected ionic liquids are available as a comprehensive database5. Melting point, viscosity, chemical and thermal stability and water or organic solvent miscibility is determined by the cation as well as choice of the anion.
Certain ionic liquids have even low melting points below room temperature (RTILs – room temperature ionic liquids). They consist of bulky and asymmetric organic cations that inhibit crystallisation, while lowering the melting points. Due to their thermostability, some ionic liquids are distillable even at high temperatures, thus allowing recycling in pure form for future reuse.
Availability of ionic Liquids
A supplier of ionic liquids is the German chemical giant BASF, under the brand name Basionics(™)6. For example, popular ionic liquids are available from BASF on bulk scale. Iolitec, a German startup company founded in 2002, offers 300 ionic liquids from catalogue7. This has provided a toolbox for research into the applications of ionic liquids in various processing industries.
Applications of ionic liquids
In the industry, various applications are explored.
The applications include
- chemical processing in chemical reactions and separation processes
- metal processing: ionic liquids in metal deposition processes
- Separation processing
- polymer processing: issolving and processing cellulose fibres, antistatic polymer additives
- electroytes in electronic devices
- functional fluids: hydraulic fluid and lubricants
Ionic liquids in textile applications
The potential applications for the textile industry are
- fibre manufacturing: dissolving macromolecules in ionic liquids and spinning
- electrospinning for nanofibres
- fibre modifications
- recycling of textiles: dissolving used textiles in ionic liquids
- coloration: dyeing from ionic liquids, or use ionic liquids as dyebath additives
- wastewater treatment
- functional finishing effects
Certain ionic liquids are capable of dissolving textiles fibers (figure 3). Therefore, ionic liquids are potentially suitable for fibre manufacturing and recycling.
Part 2 will look deeper into some of these applications of ionic liquids for the textile industry.
A compressed version of this article (all parts) was published in the journal International Dyer & Textile Finisher 5/2018, 21-25.
1 Meksi, N., Moussa,A., „A review in the progresss in the ecological application of ionic liquids in textile processes“, J. Clean. Prod. 161 (2017), 105-126
2 Gabriel, S., Weiner, J. (1888), “Ueber einige Abkömmlinge des Propylamins”. Chemische Berichte 21 / 2 (1888), 2669–2679
3 Walden,P., Bull. Acad. Sci. St. Petersburg, 1914, 405-422.
4 Wilkes, J.S. et al. (1982). “Dialkylimidazolium chloroaluminate melts: a new class of room-temperature ionic liquids for electrochemistry, spectroscopy and synthesis”. Inorg. Chem. 21/3 (1982), 1263–1264
5Zhang,S. et al., „Physical Properties of Ionic Liquids: Database and Evaluation“, J. Phys. Chem. Ref. Data 35 (2006), 1475-1517