Hydrolytic processes and condensation reactions in the cellulose solvent system N,N-dimethylacetamide/lithium chloride. Part 2: degradation of cellulose

Potthast, Antje; Rosenau, Thomas; Sartori, Jürgen; Sixta, Herbert; Kosma, Paul

doi:10.1016/s0032-3861(02)00751-6

Cited by 69 publications

(40 citation statements)

References 21 publications

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“…The aprotic polar solvent (N,N-dimethylacetamide) in combination with an inorganic salt, preferably lithium chloride (LiCl) [6] , is able to dissolve cellulose. The impetus behind investigating this solvent system for cellulose derivatization under homogeneous reaction has been extensively described in the literature [7][8][9][10][11][12][13] . The homogeneous reaction involves several steps, including cellulose activation, dissolution, and subsequent reaction with a derivatizing agent [10] .…”

Section: Introductionmentioning

confidence: 99%

Thermal decomposition of mercerized linter cellulose and its acetates obtained from a homogeneous reaction

Morgado

Frollini

2011

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Abstract:Cellulose acetates with different degrees of substitution (DS, from 0.6 to 1.9) were prepared from previously mercerized linter cellulose, in a homogeneous medium, using N,N-dimethylacetamide/lithium chloride as a solvent system. The influence of different degrees of substitution on the properties of cellulose acetates was investigated using thermogravimetric analyses (TGA). Quantitative methods were applied to the thermogravimetric curves in order to determine the apparent activation energy (Ea) related to the thermal decomposition of untreated and mercerized celluloses and cellulose acetates. Ea values were calculated using Broido's method and considering dynamic conditions. Ea values of 158 and 187 kJ mol -1 were obtained for untreated and mercerized cellulose, respectively. A previous study showed that C6OH is the most reactive site for acetylation, probably due to the steric hindrance of C2 and C3. The C6OH takes part in the first step of cellulose decomposition, leading to the formation of levoglucosan and, when it is changed to C6OCOCH 3 , the results indicate that the mechanism of thermal decomposition changes to one with a lower Ea. A linear correlation between Ea and the DS of the acetates prepared in the present work was identified. Keywords: Linter cellulose, cellulose acetates, thermal decomposition. Decomposição Térmica de Celulose de Linter Mercerizado e seus Acetatos Obtidos a partir de Reação HomogêneaResumo: Acetatos de celulose com graus de substituição, GS, variando entre 0,6 e 1,9, foram preparados previamente a partir de celulose de linter mercerizado, em meio homogêneo, usando N,N-dimetilacetamida/cloreto de lítio como sistema de solvente. A influência de diferentes graus de substituição nas propriedades dos acetatos de celulose foi investigada usando a análise termogravimétrica (TGA). Métodos quantitativos foram aplicados nas curvas termogravimétricas obtidas a fim de determinar a energia de ativação aparente (Ea) relacionado à decomposição térmica de celulose não-tratada e mercerizada e acetatos de celulose. Valores de Ea foram calculados usando o método de Broido e considerando condições dinâmicas. Valores de Ea de 158 e 187 kJ mol -1 foram obtidos para a celulose não-tratada e mercerizada, respectivamente. Em trabalho anterior verificou-se que o C6OH é o sítio mais reativo na acetilação, provavelmente devido ao impedimento estérico de C2 e C3. O C6OH participa da primeira etapa de decomposição da celulose, levando à formação de levoglucosana e, quando se tem a substituição para C6OCOCH 3 , o resultado indica que o mecanismo de decomposição térmica muda para um com Ea menor. Uma correlação linear entre Ea e o GS dos acetatos preparados no presente trabalho foi identificada. Palavras-chave: Celulose de linter, acetatos de celulose, decomposição térmica.

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Section: Introductionmentioning

confidence: 99%

Thermal decomposition of mercerized linter cellulose and its acetates obtained from a homogeneous reaction

Morgado

Frollini

2011

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“…of the latter leads to yellowing of the biopolymer, due to the formation of chromophors, including dehydroacetic acid, isodehydroacetic acid and dimethyl-gpyrone. 34 Using…”

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“…This cation is an extremely reactive electrophile, capable of random cleavage of the bonds present, e.g., between AGUs, or between an AGU and the acetate group. This results in rapid changes in the molecular weight distribution of cellulose, 34 and presumably a decrease in DS. We plan to investigate further the reason for the decrease in DS as a function of time.…”

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Some aspects of acetylation of untreated and mercerized sisal cellulose

Ciacco¹,

Morgado²,

Frollini³

et al. 2010

J. Braz. Chem. Soc.

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Este trabalho apresenta alguns aspectos da acetilação em LiCl/N,N-dimethylacetamida, DMAc de celulose de sisal nativa e mercerizada (sisal e M-sisal). A mercerização da fibra em solução de NaOH resulta nas seguintes alterações: decréscimo de 29.9 % no índice de cristalinidade; diminuição de 16.2% no grau de polimerização e aumento de 9.3% no conteúdo de a-celulose. Estudo com espalhamento de luz de soluções de sisal, M-sisal, celulose microcristalina e algodão mostrou que elas se apresentam na forma de agregados, com números médios de agregação de 5.2, 3.2, 9.8 e 35.3, respectivamente. A presença destes agregados afeta a acessibilidade à celulose durante sua funcionalização. Acompanhamento do grau de substituição, DS, de acetato de celulose em função do tempo, mostrou que o mesmo aumenta por um intervalo de tempo de 5 h, seguido por um decréscimo após 7 h. Possíveis razões para este decréscimo são discutidas. Como esperado, M-sisal apresenta um DS maior que a sisal nativa.We report here on some aspects of the acetylation in LiCl/N,N-dimethylacetamide, DMAc, of untreated and mercerized sisal cellulose, hereafter designated as sisal and M-sisal, respectively. Fiber mercerization by NaOH solution has resulted in the following changes: 29.9% decrease in the index of crystallinity; 16.2% decrease in the degree of polymerization and 9.3% increase in a-cellulose content. A light scattering study of solutions of sisal, M-sisal, microcrystalline and cotton celluloses in LiCl/DMAc has shown that they are present as aggregates, with (an apparent) average aggregation numbers of 5.2, 3.2, 9.8, and 35.3, respectively. The presence of these aggregates affects the accessibility of cellulose during its functionalization. A study of the evolution of the degree of substitution, DS, of cellulose acetate as a function of reaction time showed an increase up to 5 h, followed by a decrease at 7 h. Possible reasons for this decrease are discussed. As expected, M-sisal gave a higher DS that its untreated counterpart.

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“…While ''cellulose oxidation'' is, in principle, well-defined and can be related to precise chemical structures and structural changes (see below), it is only one single aspect of cellulose aging and not synonymous with it. ''Cellulose aging'' is a rather nebulous term, and the particular aspect of importance lies in the eye of the beholder: natural aging (Whitmore 2011), yellowing of freshly produced pulp upon transportation (Forsskahl 1994;Sevastyanova et al 2005), brittleness of historic papers (Luner 1988), changed surface properties of cellulosic materials (Kato and Cameron 1999;Sutý et al 2012), strength losses of cellulosic textiles (Uddin et al 2015;Block 1982), structural changes upon alkaline treatment of cellulosic fibers (Ö ztürk et al 2009;Eronen et al 2009), cellulose degradation during ripening of alkali cellulose in rayon production or upon alkali treatment in cellulose ether production (Freytag and Donze 1983;Lewin 1965), molecular weight losses upon cellulose dissolution (Rosenau et al 2005a, b;Potthast et al 2002)-all these facets are consequences of cellulose oxidation and can eventually be traced back to the same chemistry.…”

Section: Introductionmentioning

confidence: 99%

Insights into degradation pathways of oxidized anhydroglucose units in cellulose by β-alkoxy-elimination: a combined theoretical and experimental approach

et al. 2018

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Depolymerization of cellulose starting from an oxidized anhydroglucose unit through balkoxy-elimination, triggered by alkaline media, is one of the key reactions responsible for cellulose aging. This study investigates the detailed mechanisms for the chain cleavage by a combination of experimental and quantum chemical methods. Three model compounds for oxidized anhydroglucose units in cellulose were employed: C2-keto, C3-keto-, and C6-aldehyde 4-O-methyl methyl b-D-glucosides, representing anhydroglucose units of cellulose that have been oxidized at C2, C3, and C6, respectively. The alkali-induced b-alkoxy elimination from the model compounds started from the corresponding enolates and followed first order kinetics. While methanol is being released in the case of the model compounds, the analogous process effects chain cleavage in the case of the polymer cellulose. The kinetic rate constants for the C6-aldehyde compound 2, the 2-keto compound 3 and the 3-keto counterpart 4 had a ratio of 1:5:22, indicating the 3-keto compound to be the least stable one. Elimination from an oxidized 6-position (6-aldehyde) was thus more than 20 times slower than that from an oxidized C-3 (3-keto). A 6-carboxyl group is completely innocent with regard to belimination. MP4(SDQ)//DFT(M06-2X) calculations indicated that the degradation pathway starting from the 3-keto enolate had the smallest activation barrier because of stabilization of the transition state by charge transfer from O-5 to C-1. The 3-keto enolate path was consequently more favorable than the alternative ones involving the 2-keto and the 6-keto enolates, which do not exhibit this transition state stabilization. Experimental and computational data thus agreed very well. In polymeric cellulose, also leaving group effects of the O-4 and O-1 glucopyranosyl anions come into play. Calculations indicated the O-4 anion to be more stable, and hence the better leaving group. In actual cellulose, the degradation starting from 3-keto units will become even more dominant than in the model compound, suggesting that Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10570-018-1835-y) contains supplementary material, which is available to authorized users.

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Hydrolytic processes and condensation reactions in the cellulose solvent system N,N-dimethylacetamide/lithium chloride. Part 2: degradation of cellulose

Cited by 69 publications

References 21 publications

Thermal decomposition of mercerized linter cellulose and its acetates obtained from a homogeneous reaction

Thermal decomposition of mercerized linter cellulose and its acetates obtained from a homogeneous reaction

Some aspects of acetylation of untreated and mercerized sisal cellulose

Insights into degradation pathways of oxidized anhydroglucose units in cellulose by β-alkoxy-elimination: a combined theoretical and experimental approach

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