Study on dissolution of cellulose by [Emim]Ac-[Emim]OH-DMSO ternary system

doi:10.11949/0438-1157.20241123

Abstract

Abstract:

The ionic liquid 1-ethyl-3-methylimidazolium hydroxide ([Emim]OH) is a potential solvent for cellulose dissolution, however, its further application is limited by its unstable structure. To improve the stability of [Emim]OH, density functional theory (DFT) calculations and experimental analysis was used to select an appropriate polar aprotic solvent, dimethyl sulfoxide (DMSO). A ternary system consisting of 1-ethyl-3-methylimidazolium acetate ([Emim]Ac), [Emim]OH, and DMSO was proved to stabilize the hydroxide ionic liquid and enhance the cellulose-dissolving capability. The results indicated that the ternary solvent system including ionic liquid/DMSO with a molar ratio 1.25∶0.75 and the [Emim]Ac /[Emim]OH with a molar ratio 2∶1 can dissolve up to 9.9% bamboo pulp, representing a 23.8% improvement over that in pure [Emim]Ac. After dissolution and regeneration, the degree of polymerization of cellulose decreases from 523 to 466, and its crystal form transforms from Ⅰ to Ⅱ. The introduction of DMSO not only lowers the viscosity of the mixed ionic liquid system from 21.2 Pa∙s to 19.7 Pa∙s, but also accelerates the dissolution of cellulose.

Key words: ionic liquids, cellulose, DFT, polar aprotic solvent, dissolution

摘要：

离子液体1-乙基-3-甲基氢氧化咪唑（［Emim］OH）是一种极具潜力的纤维素溶剂，但是因其结构不稳定限制了进一步的应用。为了提高［Emim］OH的稳定性，通过密度泛函理论（DFT）计算以及实验选择合适的极性非质子溶剂二甲基亚砜（DMSO），构建1-乙基-3-甲基醋酸咪唑（［Emim］Ac）-［Emim］OH-DMSO三元体系稳定氢氧盐离子液体且提高其对纤维素的溶解能力。研究结果表明，离子液体与DMSO摩尔比为1.25∶0.75且［Emim］Ac与［Emim］OH摩尔比为2∶1时，竹浆在三元溶剂体系中的溶解度达9.9%，比在纯［Emim］Ac中的溶解度提高了23.8%。经三元溶剂体系溶解再生后，纤维素聚合度从523下降至466，纤维素的晶型由Ⅰ型变为Ⅱ型。DMSO的加入不仅降低了混合离子液体体系黏度，黏度从21.2 Pa∙s下降至19.7 Pa∙s，还加快了纤维素的溶解。

关键词: 离子液体, 纤维素, DFT, 极性非质子溶剂, 溶解

CLC Number:

TQ 352

Xiaoyu ZHANG, Jinxin LAN, Xin LI, Shilin CAO, Haili GAO, Xiaojuan MA. Study on dissolution of cellulose by [Emim]Ac-[Emim]OH-DMSO ternary system[J]. CIESC Journal, 2025, 76(7): 3226-3234.

张晓钰, 兰金鑫, 黎昕, 曹石林, 高海丽, 马晓娟. ［Emim］Ac-［Emim］OH-DMSO三元体系溶解纤维素的研究[J]. 化工学报, 2025, 76(7): 3226-3234.

Figures/Tables 10

Fig.1 Synthesis of ionic liquids [Emim]OH and [Emim]Ac

Fig.2 Electrostatic diagram of OH-, [Emim]+, DMSO, DMF and cellobiose

Fig.3 Structure diagram of [Emim]OH,DMSO, DMF and [Emim]OH interaction

Table 1 Binding energy of DMSO， DMF and ［Emim］OH， C2—H and canionic hydrogen bond length of cationic imidazole ring

比例

C2—H键长/Å

氢键键长/Å

结合能/

（kJ/mol）

Table 2 Hydrogen bond and binding energy between DMSO， DMF and cellobiose

DMSO/DMF-纤维二糖	编号	氢键	氢键键长/Å	平均键长/Å	结合能/（kJ/mol）
DMSO-纤维二糖	1	O1-H…O7	1.829	1.829	-63.11
	2	O4′-H…O7	1.835	2.280	-76.54
	2	C6′-H…O7	2.724	2.280	-76.54
	3	O3′-H…O7	1.787	1.787	-96.45
DMF-纤维二糖	1	O1-H…O8	1.726	1.726	-53.71
	2	O4′-H…O8	1.788	2.211	-64.46
	2	C6′-H…O8	2.633	2.211	-64.46
	3	O3′-H…O8	1.804	1.804	-61.10

Fig. 4 Solubility of cellulose in [Emim]Ac-DMSO and [Emim]Ac-[Emim]OH-DMSO mixed ionic liquids

Fig.5 Polarizing microscope image of cellulose in mixed ionic liquid

Fig.6 FTIR spectra (a) and XRD patterns (b) of cellulose and regenerated cellulose [a was protocellulose; b—e were dissolved and regenerated cellulose obtained by [Emim]Ac, [Emim]Ac/DMSO (1.25∶0.75), [Emim]Ac/[Emim]OH/DMSO (0.625∶0.625∶0.75), [Emim]Ac/[Emim]OH/DMSO (0.83∶0.42∶0.75), respectively)

Table 3 Crystallinity and polymerization of cellulose and regenerated cellulose

样品	结晶度/ %	聚合度（DP）
Raw	64.0	523
[Emim]Ac	19.3	423
[Emim]Ac/[Emim]OH/DMSO（0.625∶0.625∶0.75）	20.2	359
[Emim]Ac/[Emim]OH/DMSO（0.83∶0.42∶0.75）	28.8	466

Fig.7 Viscosity changes of ionic liquid and ionic liquid dissolved 2% cellulose with shear rate a—[Emim]Ac; b—[Emim]Ac/DMSO (1.25∶0.75); c—[Emim]Ac/[Emim]OH/DMSO (0.625∶0.625∶0.75); d—[Emim]Ac/[Emim]OH/DMSO (0.83∶0.42∶0.75)

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