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Cross polarisation/magic angle spinning C-13-NMR spectroscopic studies of cellulose structural changes in hardwood dissolving pulp process
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2007 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 61, no 6, 675-679 p.Article in journal (Refereed) Published
Abstract [en]

Cross polarisation/magic angle spinning C-13 NMR spectroscopy has been used to study structural changes in cellulose induced by the dissolving pulp process. The cellulose structure in several dissolving pulps was investigated for commercial and laboratory cooked Eucalyptus 92 alpha and 96 alpha. The average lateral dimension, or average thickness, of the cellulose fibril aggregates is related to the amount of surface area exposed and could be one controlling factor for the chemical reactivity of commercial dissolving pulps during modification reactions. The thickness of the cellulose fibril aggregates governs the amount of surface area present in the fibre wall, and cellulose surface material constitutes the part of the cellulose that is directly accessible to reagents. In all sample series investigated, the raw pulp was found to be less aggregated than the corresponding bleached final pulp. Furthermore, an irreversible increase in fibril aggregate width was observed on free drying for both laboratory cooked and commercial pulps. Upon rewetting with water, the freely dried 96 alpha pulp was found to be more aggregated than the freely dried 92 alpha pulp, although sugar analysis showed very similar carbohydrate compositions. As indicated by the molecular mass distribution, the commercial 92 alpha pulp contained larger amounts of degraded cellulose; this may be a plausible explanation for the different behaviour of the 92 alpha and 96 alpha pulps during free drying.

Place, publisher, year, edition, pages
2007. Vol. 61, no 6, 675-679 p.
Keyword [en]
92 alpha, 96 alpha, bleaching, cellulose fibril, cellulose fibril aggregate, cellulose supramolecular structure, CP/MAS C-13-NMR, dissolving pulp, eucalyptus, molecular mass distribution, sugar analysis
National Category
Paper, Pulp and Fiber Technology
URN: urn:nbn:se:kth:diva-25677DOI: 10.1515/HF2007.095ISI: 000251393500009OAI: diva2:359320

QC 20101027

Available from: 2010-10-27 Created: 2010-10-27 Last updated: 2015-05-26Bibliographically approved
In thesis
1. Suberin based polyesters
Open this publication in new window or tab >>Suberin based polyesters
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the wish to replace oil-based chemicals and materials with such based on biodegradable and renewable resources, this work has been performed. In a biorefinary concept, waste birch bark from paper pulp mills and timber production has been evaluated as a potential source for polyesters. 

In the present thesis investigations are made on synthesis of epoxy-functionalized polyesters from the birch outer bark aliphatic suberin ω-hydroxy fatty acid, cis-9,10-epoxy-18-hydroxyoctadecanoic acid. Studies of accessibility and reactivity of cellulose have been performed as a first step to enable covalent attachment or grafting of the epoxy-functionalized polyesters to cellulose. 

Candida antarctica lipase B (Novozym 435) is reported to be an efficient catalyst for condensation polymerization of cis-9,10-epoxy-18-hydroxyoctadecanoic acid to form poly(9,10-epoxy-18-hydroxyoctadecanoic acid) with high molecular weight (Mw). Performed in toluene in the presence of molecular sieves a Mw of 20000 (reaction time 68 h, Mw/Mn 2.2) was obtained. Performed in bulk without any drying agent a Mw of 15000  was obtained at a much shorter reaction time (reaction time 3h, Mw/Mn 2.2). Further the same lipase has been used for succesful co-polymerizations of cis-9,10-epoxy-18-hydroxyoctadecanoic acid with lactones. By combining condensation and ring-opening polymerization, epoxy-functionalized linear polyesters and cyclic oligomers have been synthesized. For example, co-polymerization of cis-9,10-epoxy-18-hydroxy-octadecanoic acid and ε-caprolactone performed in toluene in the presence of molecular sieves gave mainly cyclic oligomers, especially at shorter reaction times. Co-polymerization performed in bulk gave linear polyesters with a Mw of 35000 (reaction time 24 h, Mw/Mn 6), irrespective molecular sieves were added or not. 

The epoxy-functionalized polyesters could be used for surface modification of pulp fibres and cellulose fibrils, which further can be used for production of new valuable composite materials with improved features. Knowledge of how different processing conditions affect the structure of cellulose is an important tool in the work to achieve successful grafting of produced polyesters to cellulose fibres/fibrils. CP/MAS 13C-NMR spectroscopy has been used to study structural changes caused by the dissolving pulp process. An irreversible increase in average fibril aggregate width from raw pulp to final pulp during the process is shown. This increase in aggregate width could negatively influence the reactivity of the cellulose.



Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 37 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2009:21
National Category
Paper, Pulp and Fiber Technology
urn:nbn:se:kth:diva-10528 (URN)978-91-7415-311-8 (ISBN)
2009-05-15, K1, KTH, Teknikringen 56, Stockholm, 10:00 (English)
Available from: 2009-05-25 Created: 2009-05-25 Last updated: 2010-10-27Bibliographically approved

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