Homogeneous methylation of wood pulp cellulose dissolved in LiOH/urea/H2O

Nagel, Matilde C. V.; Koschella, Andreas; Voiges, Kristin; Mischnick, Petra; Heinze, Thomas

doi:10.1016/j.eurpolymj.2010.05.009

Cited by 27 publications

(18 citation statements)

References 25 publications

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“…It has been found that the distribution of methyl group on the AGUs and along the chains plays a role in the sol-gel transition. Commercial MC with non-uniform distribution of methyl groups (prepared from heterogeneous reaction) normally shows thermoreversible sol-gel transition at 30-60°C, but MC with uniform distribution (prepared from homogeneous solution such as LiCl/dimethylacetamide (DMAc)) displays thermoreversible sol-precipitation (Nagel et al 2010;Sakakibara et al 2011). To tune the sol-gel transition of HPMC, Hu et al (2004) prepared some water soluble azo-HPMCs with hydrophobic azobenzene moieties through esterification reaction.…”

Section: Introductionmentioning

confidence: 99%

Thermal inverse phase transition of azobenzene hydroxypropylcellulose in aqueous solutions

Zhang

Liu

2016

Cellulose

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Water soluble 2-azobenzenoxy-ethoxyhydroxpropylcelluloses (azo-EHPC) were synthesized by etherification reaction of bromoethoxy-azobenzene (BEA) with hydroxypropylcellulose (HPC) to study their phase transition behavior in aq. solution. The degree of substitution (DS) of the water soluble azoEHPCs was less than 0.066. Their chemical structure and thermal property were characterized by proton nuclear magnetic resonance ( 1 H-NMR), fourier transform infrared spectroscopy (FT-IR), and differential scanning calorimetry. The azo-EHPC showed a reversible sol-gel transition behavior in its aq. solution, i.e. a clear azo-EHPC aq. solution became turbid when the solution temperature surpassed a lower critical solution temperature (LCST). The sol-gel transition phenomenon was investigated by optical microscopy and turbidimetric measurement. It was found that the LCST was related to the cis-/transconformation of the azobenzene side group, the type of cyclodextrin (CD), concentration of azo-EHPC, and NaCl concentration. The LCST of azo-EHPC was lower than that of HPC (36.6°C) by at most 13.6°C, and the LCST of trans-azo-EHPC was less than that of cis-azo-EHPC by ca. 3°C. Additionally, the presence of CD in solutions displayed a positive effect on the LCST, i.e. increasing the LCST by 3-5°C. And this impact was more profound on the azo-EHPC with higher DS values. The thermoreversible phase transition mechanism was discussed. We proposed that the effect of DS, conformation of azobenzene group, azo-EHPC concentration, salt concentration, and CD on the LCST of azo-EHPCs was a rearrangement of the hydrophilic/hydrophobic interaction between side azobenzene groups and water molecules.

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Section: Introductionmentioning

confidence: 99%

Thermal inverse phase transition of azobenzene hydroxypropylcellulose in aqueous solutions

Zhang

Liu

2016

Cellulose

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“…The alditol acetate method (AAM), introduced for the analysis of monosaccharide mixtures by Gunner et al (1961), is a well-established procedure to determine substituent distribution in monomer units of polysaccharides by gas liquid chromatography (GLC) (Mischnick and Kühn 1996;Nagel et al 2010;Theander 1991). Oades (1967) first applied this procedure to the analysis of sugars in complex hydrolysates.…”

Section: Introductionmentioning

confidence: 99%

Critical re-investigation of the alditol acetate method for analysis of substituent distribution in methyl cellulose

Voiges

Adden

Rinken³

et al. 2012

Cellulose

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The alditol acetate method is a common procedure for sugar analysis, also applied to determine the substituent distribution in monomer units of polysaccharide ethers like methyl cellulose by gas liquid chromatography. Consisting of several preparation and work-up steps this procedure is both time consuming and prone to side reactions that promote discrimination of single constituents, especially when no peralkylation step is performed prior to hydrolysis. As a consequence results scatter in dependence on individual treatment and conditions. In the context of this work these critical points were overcome by strict but simplified work-up procedures and using acid instead of alkaline catalyzed acetylation. Under the acidic conditions the tedious removal of borate is no longer necessary and a reduced time requirement was achieved as well as good reproducibility. Comparison with independent reference methods excluded a systematic error of the method and confirmed the results obtained. Without peralkylation, i.e. in the presence of free hydroxyl groups, another fast modification of the method using DMSO as solvent, no removal of borate, and 1-methylimidazole as catalyst for acetylation was found to produce a systematic error.

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“…Several methods are described in the literature to synthesize cellulose aerogels. These aerogels can be synthesized by dissolving cellulose in suitable media, such as sodium hydroxide [3][4][5], an aqueous alkali hydroxide/urea solution [6][7][8], salt hydrate melts [9][10][11][12], NMMO (N-Methylmorpholin-N-oxide) [3,[13][14][15] or other ionic liquids [16][17][18]. Synthesis followed by washing, coagulation and finally drying by using special techniques, like supercritical or freeze drying in order to preserve their solid nano-porous network structure.…”

Section: Introductionmentioning

confidence: 99%