Abstract
Pervaporation is a membrane-separation technique which uses polymeric and/or ceramic membranes. In the case of pervaporation processes applied to dehydration, the membrane should transport water molecules preferentially. Reactive ionic liquid (RIL) (3-(1,3-diethoxy-1,3-dioxopropan-2-yl)-1-methyl-1H-imidazol-3-ium) was used to prepare novel dense cellulose acetate propionate (CAP) based membranes, applying the phase-inversion method. The designed polymer-ionic liquid system contained ionic liquid partially linked to the polymeric structure via the transesterification reaction. The various physicochemical, mechanical, equilibrium and transport properties of CAP-RIL membranes were determined and compared with the properties of CAP membranes modified with plasticizers, i.e., tributyl citrate (TBC) and acetyl tributyl citrate (ATBC). Thermogravimetric analysis (TGA) testified that CAP-RIL membranes as well as CAP membranes modified with TBC and ATBC are thermally stable up to at least 120 °C. Tensile tests of the membranes revealed improved mechanical properties reflected by reduced brittleness and increased elongation at break achieved for CAP-RIL membranes in contrast to pristine CAP membranes. RIL plasticizes the CAP matrix, and CAP-RIL membranes possess preferable mechanical properties in comparison to membranes with other plasticizers investigated. The incorporation of RIL into CAP membranes tuned the surface properties of the membranes, enhancing their hydrophilic character. Moreover, the addition of RIL into CAP resulted in an excellent improvement of the separation factor, in comparison to pristine CAP membranes, in pervaporation dehydration of propan-2-ol. The separation factor β increased from ca. 10 for pristine CAP membrane to ca. 380 for CAP-16.7-RIL membranes contacting an azeotropic composition of water-propan-2-ol mixture (i.e., 12 wt % water).
Highlights
Cellulose-based polymers are commonly utilized as sustainable and green materials because of their eco-friendly nature in the production of food packaging, coating and wrapping [1,2,3,4,5]
The average values of Young’s modulus (YM) and εmax as a function of reactive ionic liquid (RIL) content is plotted in Figure 4 for cellulose acetate propionate (CAP)-RIL membranes
Afterwards, the results obtained for CAP membranes with RIL were compared to those for membranes modified with tributyl citrate citrate (TBC) and acetyl tributyl citrate (ATBC) as well as to data in the literature (Table 2)
Summary
Cellulose-based polymers are commonly utilized as sustainable and green materials because of their eco-friendly nature in the production of food packaging, coating and wrapping [1,2,3,4,5]. The properties of cellulose esters depend on the number of acyl groups and their chain length, as well as on the degree of polymerization, which explains the enhanced properties of cellulose triesters compared to cellulose monoesters. Such polymers possess drawbacks related to weak mechanical properties and poor thermal processability [17]. The use of plasticizers alters cellulose ester polymers by diminishing intermolecular forces between polymer chains, enhancing flexibility [15] and provoking polymer material softening due to reduced glass transition temperature (Tg ) and elastic modulus [17]. The effectiveness of plasticization refers to the amount of plasticizer necessary to obtain the required mechanical performance of the elaborated membrane materials
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