Crystallinity reduction and enhancement in the chemical reactivity of cellulose by non-dissolving pre-treatment with tetrabutylphosphonium acetate

Abstract

Herein, we demonstrate the activation of commercial chemical cellulose pulps towards chemical modification by a pre-treatment step with tetrabutylphosphonium acetate ([P 4444 ][OAc]). A heterogeneous (non-dissolving) pre-treatment was applied allowing for a significant reduction in crystallinity, without concomitant formation of the thermodynamically stable cellulose II. An increase in chemical reactivity was demonstrated using two model reactions; (1) acetylation (organic swelling conditions), where high degrees of substitution (DS) were obtained without the need for a catalyst, and (2) 4-acetamido-TEMPO oxidation (aqueous swelling conditions), where significant degrees of oxidation (DO) were obtained, beyond those for the untreated pulps. In both tests a notable improvement in cellulose reactivity was observed. Regioselectivity of acetylation was assessed using 2D NMR for one low and one high DS sample. The low DS showed a small degree of acetylation of the 6-OH, whereas, the high DS from the pre-treated sample showed mainly mixtures of triacetate and diacetates. Important mechanistic information is attained for future development of aqueous and organic-based reactions involving this ionic liquid pre-treatment.

Phase-Separation of Cellulose from Ionic Liquid upon Cooling: Preparation of Microsized Particles

“…Figure 10 shows the result obtained from WAXS (orange line), which is typical the Cellulose II 1D diffraction pattern (French 2014;Langan et al 2001). The diffraction pattern also contains a signi cant amorphous contribution The crystallinity of cellulose II is 37.2%, which has been calculated based on the method of Rico del Cerro, D., et al (Rico del Cerro et al 2020). The peak tting is shown in Figure S12 (SI).…”

“…On the opposite of the stability scale, tetraalkylphosphonium-based ILs are among the most stable ILs, both thermally and chemically. They are known to dissolve cellulose as the OESs (Holding 2016;Holding et al 2017) and are even applied as solvents for solution-state NMR analysis of crystalline celluloses (King et al 2018;Koso et al 2020) at high dilution in DMSO-d 6 .…”

“…Aside from their high cost, tetraalkylphosphonium ILs offer interesting potential for cellulose processing, over the different phase-compositions of IL and co-solvent (Rico del Cerro et al 2020). Pure tetraalkylphosphonium acetates do not dissolve cellulose, as such, but become excellent solvents if mixed with a polar aprotic co-solvent, e.g.…”

Ionic liquids in the pretreatment of lignocellulosic biomass

“…The result of such interaction may be for example a reduction in crystallinity of the cellulose fraction, which will facilitate the reaction and transformation of this biopolymer in subsequent stages [43,44]. After that, the other biopolymers originally composing the lignocellulosic matrix will be likely more accessible.…”

Irregular solution thermodynamics of wood pulp in the superbase ionic liquid [m-TBDH][AcO]

“…[2][3][4][5][6][7][8] To date, focus in the literature has largely been bounded by efforts to identify liquid salts with qualitative dissolution utility for biomass components, among various contributions detailing new developments in synthetic carbohydrate derivatisation chemistry. 9,10 Much less attention has been given towards gaining a detailed understanding of the energetics governing solventsolute contact-encounters in such mixtures, using robust thermodynamic methods. 11 Knowledge gained from such approaches reveal available composition-and temperature-dependent solvation character of both solvent-j and solute-i, which in turn provides the fundamental basis upon which the solvent selection process may be anchored, and furthermore, the means to identify a given solvent's utility in terms of true task specicity.…”