Highly reactive wood pulps for cellulose acetate production

Sears, Karl D.; Hinck, J. F.; Sewell, C. G.

doi:10.1002/app.1982.070271207

Cited by 13 publications

(9 citation statements)

References 5 publications

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“…It is well known that the treatment with cold alkali is a physical phenomenon characterized by penetration and solubilisation, and therefore, mainly influenced by the morphology of the fiber wall. The cellulose I is partly converted to Na-cellulose I and after neutralisation to cellulose II which leads to a lower reactivity towards acetylation (Sears et al 1982). Furthermore, a lower reactivity of cellulose towards xanthation was also reported for NaOH treated pulps (Krässig 1984).…”

Section: Introductionmentioning

confidence: 90%

Sulfur-free dissolving pulps and their application for viscose and lyocell

Schild

Sixta

2011

Cellulose

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In this study, the concept of multifunctional alkaline pulping has been approved to produce high-purity and high-yield dissolving pulps. The selective removal of hemicelluloses was achieved by either water autohydrolysis (PH) or alkaline extraction (E) both applied as pre-treatments prior to cooking. Alternatively, hemicelluloses were isolated after oxygen delignification in a process step denoted as cold caustic extraction (CCE). Eucalyptus globulus wood chips were used as the raw material for kraft and soda-AQ pulping. In all process modifications sulfur was successfully replaced by anthraquinone. By these modifications purified dissolving pulps were subjected to TCF bleaching and comprehensive viscose and lyocell application tests. All pulps met the specifications for dissolving pulps. Further more, CCE-pulps showed a significantly higher yield after final bleaching. Morphological changes such as ultrastructure of the preserved outer cell wall layers, specific surface area and lateral fibril aggregate dimension correlated with the reduced reactivity towards regular viscose processing. The residual xylan after alkali purification depicted a lower content of functional groups and a higher molecular weight and was obviously entrapped in the cellulose fibril aggregates which render the hemicelluloses more resistant to steeping in the standard viscose process. Simultaneously, the supramolecular structure of the cellulose is partly converted from cellulose I to cellulose II by the alkaline purification step which did not influence the pulps reactivity significantly. Nevertheless, these differences in pulp parameters did not affect the lyocell process due to the outstanding solubility of the pulps in NMMO. Laboratory spinning revealed good fiber strength for both, regular viscose and lyocell fibers. The high molecular weight xylan of the CCE-treated pulps even took part in fiber forming.

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Section: Introductionmentioning

confidence: 90%

Sulfur-free dissolving pulps and their application for viscose and lyocell

Schild

Sixta

2011

Cellulose

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“…The cellulose II modification is characterized by an increased number of inter-and intra-planar hydrogen bonds compared to cellulose I. As a consequence, mercerized pulps become relatively inert towards derivatization when they are dried because of the collapse of interfibrillar spaces (Kleinert 1975;Krässig 1984;Kyrklund and Sihtola 1963;Oksanen et al 1997;Sears et al 1982). The resulting fiber aggregates of a mercerized dried pulp show decreased surface area and pore volume, which is called hornification, and are thus less accessible and less reactive to esterification agents (El-Din and ElMegeid 1994;Jayme and Schenck 1949).…”

Section: Introductionmentioning

confidence: 98%

“…Alkaline treatment at elevated alkali concentration induces the conversion of the cellulose modification from cellulose I (native cellulose) to cellulose II (Na-cellulose I and regenerated cellulose after acidification) (Krässig 1984). Mercerized cellulose is less crystalline and more accessible to reagents (Sears et al 1982), and thus, is known to show enhanced reactivity over native cellulose. The cellulose II modification is characterized by an increased number of inter-and intra-planar hydrogen bonds compared to cellulose I.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, detailed characterization of the fiber surface in terms of hemicellulose residues and fibrillation as well as fibril structure in terms of hornification, accessible inner surface and pore volume is required to fully understand the term of reactivity (Krässig 1993a). Many treatments such as swelling, solvent exchange, degradation procedures (Krässig 1993b) and chemical modification (Sears et al 1982) were investigated for increasing the reactivity of a pulp.…”

Section: Introductionmentioning

confidence: 99%

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A precise study on the feasibility of enzyme treatments of a kraft pulp for viscose application

2010

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The development of efficient process steps to convert paper-grade to dissolving pulps was investigated as part of the work programme to improve the process economics. The challenge of pulp refinement comprises the selective removal of hemicelluloses and the precise adjustment of the pulp viscosity, while maintaining the reactivity of the pulp as required for viscose application. The purpose of this study was to investigate the effects of various enzyme treatments on a commercial oxygen-delignified Eucalyptus globulus paper-grade kraft pulp in the course of a total chlorine free bleaching sequence in combination with refining techniques following the principle of Modified Kraft Cooking (Sixta et al. 2007). The objectives were to assess its applicability as viscose pulp besides the reduction of chemical consumption in alkaline and ozone bleaching steps by means of xylanase pretreatment and the controlled adjustment of final pulp viscosity utilizing endoglucanase post-treatment. Xylanase pre-treatment combined with cold caustic extraction at reduced alkalinity efficiently removed the hemicelluloses from the pulp and clearly increased the pulp brightness by extensive removal of hexenuronic acid side chains. The xylanase pre-treated pulp showed increased reactivity towards xanthation and high viscose dope quality in terms of particle content. The dependence of cellulose chain scission on the applied endoglucanase concentration was analyzed in detail, and this allowed precise viscosity reduction as well as reactivity increase. The differently treated pulps, with and without xylanase pre-treatment, were of very narrow molecular weight distribution and the quality of the spun fibers were very similar to those viscose fibers from commercial dissolving pulps.

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“…Several physical and chemical activation methods have been developed to increase the accessibility of solvents or reagents to the whole cellulosic structures in pulps. These treatments aim at disrupting aggregated cellulosic microstructures and comprise treatments such as swelling, solvent exchange, degradation procedures (Krässig 1993b), chemical modification (Sears et al 1982), the activation of the dissolving pulp prior to steeping by e-beaming, liquid ammonia or steam explosion treatments (Weightman et al 2009), and enzymatic treatment with cellulase, as first reported by Rahkamo et al (1996). Another approach deals with the introduction of spacers, such as polyethylene glycol of specified molar mass.…”

Section: Introductionmentioning

confidence: 98%

Reactivity of dissolving pulps modified by TEMPO-mediated oxidation

2012

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The reactivity of dissolving pulps towards derivatization or dissolution is a crucial quality parameter and is mainly determined by the accessibility of the hydroxyl groups. When dissolving pulps are produced from paper-grade pulps by cold caustic extraction (CCE), their reactivity is often inferior as compared to commercial prehydrolysis kraft dissolving pulps. It was hypothesized that pulp reactivity can be enhanced by the introduction of small amounts of substituents to facilitate interchain accessibility. In this study, CCE-treated Eucalyptus globulus kraft paper pulp was subjected to TEMPO-mediated oxidation to initiate partial oxidation of the C 6 -hydroxyl groups to carboxyl groups. The effect of this pulp modification on the reactivity towards xanthation and the subsequent dissolution in diluted aqueous alkali solution (viscose process) as well as the dissolution in complexing and non-complexing solvents, respectively, was thoroughly examined. The results revealed that the oxidized pulps rich in C 6 -carboxylate groups impeded the xanthation reaction obviously because of the reduced availability of hydroxyl groups. When Nmethylmorpholine-N-oxide monohydrate was used as a direct solvent, a very high content of C 6 -carboxylate groups was found to reduce the solubility of the pulp fibers as less hydrogen bonds can be formed with NMMOÁH 2 O. In the case of dissolution in the complexing solvent cupriethylenediamine, the dissolution mechanism of cellulose was not deteriorated by the high content of C 6 -carboxylate groups. Instead, the oxidation procedure increased the hydrophilic character and the swelling capacity of the outer cell wall layers allowed homogeneous dissolution.

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Highly reactive wood pulps for cellulose acetate production

Cited by 13 publications

References 5 publications

Sulfur-free dissolving pulps and their application for viscose and lyocell

Sulfur-free dissolving pulps and their application for viscose and lyocell

A precise study on the feasibility of enzyme treatments of a kraft pulp for viscose application

Reactivity of dissolving pulps modified by TEMPO-mediated oxidation

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