Tailoring the Structure and Morphology of Low-Molecular-Weight Cellulose Produced during Supercritical Water Hydrolysis

Abstract

This paper discusses the influence of reactor design and initial consistency when partially hydrolyzing microcrystalline cellulose (MCC) in supercritical water. Experiments conducted on two pilot reactors located in Finland and in Spain showed that stopping the reaction using depressurization instead of quenching, combined with a sufficiently high MCC consistency, led to significant change in reaction kinetics. A complete particle size reduction was achieved after 50 ms only due to additional shearinduced degradation, with a low-molecular-weight product yield above 50 wt % and an average DP of 25. In addition, gradually increasing the MCC consistency triggered precipitation under higher apparent temperature, which affected both the morphology and structure of the product. A range of particles from ribbon-like cellulose II to shish-kebab structures to lamellar cellulose IV II crystals was obtained. Furthermore, heat requirements as low as 66 kJ•g −1 of product confirm the high potential and versatility of this process for refining MCC into colloidal low-molecular-weight cellulose with different particle shapes and structural properties.

Biocatalytic oligomerization-induced self-assembly of crystalline cellulose oligomers into nanoribbon networks assisted by organic solvents

“…The images revealed a well-grown network structure composed of nanoribbon-shaped fibers (Fig. 9), which were similar in shape to lamellar crystals of cellulose oligomers [42,52–54]. According to our examination, the cross-linking of the nanoribbons was apparently based on their physical contact, possibly through the hydrophobic effect and hydrogen bonding.…”

Solvent-Assisted Fractionation of Oligomeric Cellulose and Reversible Transformation of Cellulose II and IV

“…24 Others reported the formation of cellulose IV 2 via deacetylation of low-DP cellulose triacetate and water-precipitation, treating DP18 with methylamine and DMSO mixtures, 25 and supercritical or compressed water hydrolysis. 26,27 The examples shows that cellulose IV is a high-temperature phase obtained from relatively loose or activated high-energy structures. Similarly in this study, solution precipitation in acetone, although at room temperature, is a kinetic-controlled process resulting in fine structures of high-energy states.…”

“…21,22 Cellulose IV 2 has also been produced by regenerating cellulose xanthate at 100 °C in the fiber form 23 and heating DP21 cellulose II in water at 190 °C for 2 h. 24 Others reported the formation of cellulose IV 2 via deacetylation of low-DP cellulose triacetate and water precipitation, treating DP18 with methylamine and DMSO mixtures, 25 and supercritical or compressed water hydrolysis. 26,27 The examples show that cellulose IV is a hightemperature phase obtained from relatively loose or activated high-energy structures. Similarly, in this study, solution precipitation in acetone, although at room temperature, is a kinetic-controlled process resulting in fine structures of highenergy states, while DMSO vapor annealing at the elevated temperature offers the advantage of high molecular mobility to equilibrate the system with well-defined surface energetics.…”

pH‐Triggered Self‐Assembly of Cellulose Oligomers with Gelatin into a Double‐Network Hydrogel

“…Even if the faster selfassembly kinetics makes the resultant assembled structure less uniform, appropriate strategies (e.g., DN strategy) help to elicit excellent functionalities from the assemblies. Importantly, the pH-triggered method can accept naturally derived cellulose oligomers [54][55][56] as the raw materials. Taken together, this study prompts us to use cellulose oligomers as a building block for the development of the next generation of self-assembled materials.…”