Abstract
The room-temperature dissolution of cellulose in aqueous tetraethylammonium hydroxide (TEAOH) in the presence of carbamides (ureas) was investigated. Without carbamide, 35 wt% TEAOH was able to dissolve cellulose (microcrystalline cellulose) up to 3 wt%, whereas carbamides—such as urea, N-methylurea, N-ethylurea, 1,3-dimethylurea, and imidazolidone—were able to improve the dissolution of cellulose. At 5 wt% cellulose concentration, the highest carbamide contents in the solvent still able to dissolve cellulose within 1 h were 56 and 55 wt% of 1,3-dimethylurea and N-methylurea, respectively. When using urea, up to 15% of cellulose could be dissolved in a solution containing 22 wt% of urea. To demonstrate the possibility of the use of a carbamide-based solvent in cellulose modification, cationic cellulose was produced using glycidyltrimethylammonium chloride (GTAC). At a molar ratio of 1:3 of cellulose and GTAC, all the studied TEAOH–carbamide solvents produce cationic cellulose with higher charge density compared to the reference NaOH–urea solvent.
Highlights
The replacement of oil-based materials, such as plastic, with the bioderived counterpart is highly desirable because of the disadvantageous properties of plastic (Shen et al 2010)
dimethyl sulfoxide (DMSO) was studied as a reference as it has been widely used as a solvent to dissolve cellulose together with various salts (Ostlund et al 2009; Chen et al 2018; Kostag and El Seoud 2019) and as a cosolvent to decrease the viscosity of cellulose solutions in ionic liquids (Rinaldi 2010; Ferreira et al 2019)
The dissolution efficiency depended on the structure of the carbamide, as, for example, two dimethylurea isomers had a completely different behavior: up to 56% 1,3DMU-containing solvent was able to dissolve 5% of cellulose, whereas no clear solvent could be produced when 1,1-DMU was mixed with tetraethylammonium hydroxide (TEAOH)
Summary
The replacement of oil-based materials, such as plastic, with the bioderived counterpart is highly desirable because of the disadvantageous properties of plastic (Shen et al 2010). The biodegradability of many oil-based materials is poor, leading to a severe environmental hazard because of the accumulation of solid waste in soil and water systems (Siracusa et al 2008). Several starting chemicals (i.e., monomers) for oil-based plastic are toxic. A vast variety of polymers already occurring in nature can serve as an important starting point for plastic replacement (Vieira et al 2011). Unlike many synthetic plastics, most natural polymers, such as carbohydrates, have poor formatibility; that is, they cannot be melted (Scandola et al 1991) and have poor solubility in common solvents (Guo et al 2017). Poor formatibility is severe with cellulose, which as such could be an ideal plastic replacement because of its wide availability; that is, cellulose is the most abundant natural polymer on Earth (Wang et al 2012).
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