Cellulose Dissolution, Modification, and the Derived Hydrogel: A Review

The cellulose-based hydrogel has occupied a pivotal position in almost all walks of life. However, the native cellulose can not be directly used for preparing hydrogel due to the complex non-covalent interactions. Some literature has discussed the dissolution and modification of cellulose but has yet to address the influence of the pretreatment on the as-prepared hydrogels. Firstly, the "touching" of cellulose by derived and non-derived solvents was introduced, namely, the dissolution of cellulose. Secondly, the "conversion" of functional groups on the cellulose surface by special routes, which is the modification of cellulose. The above-mentioned two parts were intended to explain the changes in physicochemical properties of cellulose by these routes and their influences on the subsequent hydrogel preparation. Finally, the "reinforcement" of cellulose-based hydrogels by physical and chemical techniques was summarized, viz., improving the mechanical properties of cellulose-based hydrogels and the changes in the multi-level structure of the interior of cellulose-based hydrogels.

Progress on chemical modification of cellulose in “green” solvents

Chemical modification of cellulose in "green" solvents.

Cationic hydrophobicity promotes dissolution of cellulose in aqueous basic solution by freezing–thawing

Hydrophobic cations accumulate at the cellulose interface, favouring the physical dissolution of cellulose in aqueous quaternary ammonium hydroxides.

On the dissolution state of cellulose in aqueous tetrabutylammonium hydroxide solutions

We have characterized the dissolution state of microcrystalline cellulose (MCC) in aqueous 40 wt% tetrabutylammonium hydroxide (TBAH) using a combination of light and small angle X-ray scattering, up to 0.1 g cm⁻³.

Facile, room-temperature pre-treatment of rice husks with tetrabutylphosphonium hydroxide: Enhanced enzymatic and acid hydrolysis yields

Aqueous solutions of tetrabutylphosphonium hydroxide have been evaluated as pretreatment media for rice husks, prior to sulphuric acid hydrolysis or cellulase enzymatic hydrolysis. Varying the water:tetrabutylphosphonium hydroxide ratio varied the rate of delignification, as well as silica, lignin and cellulose solubility. Pre-treatment with 60wt% hydroxide dissolved the rice husk and the regenerated material was thus heavily disrupted. Sulphuric acid hydrolysis of 60wt%-treated samples yielded the highest amount of glucose per gram of rice husk. Solutions with good lignin and silica solubility but only moderate to negligible cellulose solubility (10-40wt% hydroxide) were equally effective as pre-treatment media for both acid and enzymatic hydrolysis. However, pre-treatment with 60wt% hydroxide solutions was incompatible with downstream enzymatic hydrolysis. This was due to significant incorporation of phosphonium species in the regenerated biomass, which significantly inhibited the activity of the cellulase enzymes.