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The cell wall ultrastructure of wood fibres: effects of the chemical pulp fibre line
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Knowledge of the ultrastructural arrangement within wood fibres is important for understanding the mechanical properties of the fibres themselves, as well as for understanding and controlling the

ultrastructural changes that occur during pulp processing.

The object of this work was to explore the use of atomic force microscopy (AFM) in studies of the cell wall ultrastructure and to see how this structure is affected in the kraft pulp fibre line. This is done in order to eventually improve fibre properties for use in paper and other applications, such as composites. On the ultrastructural level of native spruce fibres (tracheids), it was found that cellulose fibril aggregates exist as agglomerates of individual cellulose microfibrils (with a width

of 4 nm). Using AFM in combination with image processing, the average side length (assuming a square cross-section) for a cellulose fibril aggregate was found to be 15–16 nm although with a broad distribution. A concentric lamella structure (following the fibre curvature) within the

secondary cell wall layer of native spruce fibres was confirmed. These concentric lamellae were formed of aligned cellulose fibril aggregates with a width of about 15 nm, i.e. of the order of a single cellulose fibril aggregate. It was further found that the cellulose fibril aggregates had a

uniform size distribution across the fibre wall in the transverse direction.

During the chemical processing of wood chips into kraft pulp fibres, a 25 % increase in cellulose fibril aggregate dimension was found, but no such cellulose fibril aggregate enlargement occurred during the low temperature delignification of wood into holocellulose fibres. The high temperature in the pulping process, over 100 ºC, was the most important factor for the cellulose fibril aggregate enlargement. Neither refining nor drying of kraft or holocellulose pulp changed the cellulose fibril aggregate dimensions.

During kraft pulping, when lignin is removed, pores are formed in the fibre cell wall. These pores were uniformly distributed throughout the transverse direction of the wood cell wall. The lamellae consisting of both pores and matrix material (“pore and matrix lamella”) became wider and their numeral decreased after chemical pulping. In holocellulose pulp, no such changes were seen.

Refining of kraft pulp increased the width of the pore and matrix lamellae in the outer parts of the fibre wall, but this was not seen in holocellulose.

Upon drying of holocellulose, a small decrease in the width of the pore and matrix lamellae was seen, reflecting a probable hornification of the pulp. Refining of holocellulose pulp led to pore closure probably due to the enhanced mobility within the fibre wall. Enzymatic treatment using

hemicellulases on xylan and glucomannan revealed that, during the hydrolysis of one type of hemicellulose, some of the other type was also dissolved, indicating that the two hemicelluloses were to some extent linked to each other in the structure. The enzymatic treatment also decreased the pore volume throughout the fibre wall in the transverse direction, indicating enzymatic accessibility to the entire fibre wall.

The results presented in this thesis show that several changes in the fibre cell wall ultrastructure occur in the kraft pulp fibre line, although the effects of these ultrastructural changes on the fibre properties are not completely understood.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 70 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2005:2
Keyword [en]
Chemical engineering, atomic force microscopy, cellulose, cell wall, drying, fiber
Keyword [sv]
Kemiteknik
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-129OAI: oai:DiVA.org:kth-129DiVA: diva2:7109
Public defence
2005-02-18, STFI-salen, Drottning Kristinas väg 61, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101012Available from: 2005-02-14 Created: 2005-02-14 Last updated: 2010-10-12Bibliographically approved
List of papers
1. On the Lamellar Structure of the Tracheid Cell Wall
Open this publication in new window or tab >>On the Lamellar Structure of the Tracheid Cell Wall
2002 (English)In: Plant Biology, ISSN 1435-8603, E-ISSN 1438-8677, Vol. 4, no 3, 339-345 p.Article in journal (Refereed) Published
Abstract [en]

It is clear that cross sections of wood cells show a lamellar structure. This paper investigates the orientation of this lamellar structure of spruce (Picea abies) tracheids using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cross sections of spruce wood were produced through fracturing in longitudinal bending and tensile testing. When investigated with SEM, the fracture surfaces show a structure of mostly larger radial lamellae, in the order of 30-100 nm, i.e., agglomerations of a few cellulose aggregates. Thin transverse sections of the fracture zones investigated with atomic force microscopy show concentric lamellae with a width in the order of a single cellulose aggregate, i.e., 15-25 nm. No structural connection to the splinters in the radial direction can be seen. It is suggested that the radial lamellar structure is a consequence of the energy released during fracturing of the wood samples and that the undistorted wood has a concentric lamellar structure on a smaller structural level.

Keyword
atomic force microscopy, ultrastructure, Picea abies, Norway spruce, lamellar structure, scanning electron microscopy, fracture
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-4933 (URN)10.1055/s-2002-32341 (DOI)000176426800006 ()
Note
QC 20101012Available from: 2005-02-14 Created: 2005-02-14 Last updated: 2017-12-05Bibliographically approved
2. Cross-sectional structure of the secondary wall of wood fibers as affected by processing
Open this publication in new window or tab >>Cross-sectional structure of the secondary wall of wood fibers as affected by processing
2003 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 38, no 1, 119-126 p.Article in journal (Refereed) Published
Abstract [en]

Understanding the arrangement of wood polymers within the fiber wall is important for understanding the mechanical properties of the fibers themselves. Due to their high load bearing ability, the arrangement of cellulose fibrils within the cell wall are of special interest. In this work AFM-Atomic Force Microscopy-in combination with image processing has been used to obtain more information about the arrangement of cellulose aggregates (fibrils) in the secondary cell wall layer of spruce wood. The effects of chemical processing on the arrangement of these cellulose aggregates were also studied. Enlargement of cellulose aggregates was found in the initial phase of the kraft cook. This increase in cellulose aggregate dimensions depended mostly on temperature for treatment temperatures above 140degreesC, regardless of the amount of alkali present. Although hemicelluloses are lost to various degrees under alkaline conditions, the increase in cellulose aggregate size was mainly related to thermally induced rearrangement of the cellulose molecules. The mean side length of cellulose aggregates was found to be around 18 nm in unprocessed wood and 23 nm in processed wood. The cellulose aggregates were assumed to be square shaped in cross section in both cases.

Keyword
Atomic force microscopy, Cellulose, Image processing, Mechanical properties, Molecular structure, Natural fibers, Thermal effects, Cellulose aggregate, Cross-sectional structure
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-4934 (URN)10.1023/A:1021174118468 (DOI)000179246400016 ()
Note
QC 20101012Available from: 2005-02-14 Created: 2005-02-14 Last updated: 2017-12-05Bibliographically approved
3. Pore and Matrix Distribution in the Fiber Wall Revealed by Atomic Force Microscopy and Image Analysis
Open this publication in new window or tab >>Pore and Matrix Distribution in the Fiber Wall Revealed by Atomic Force Microscopy and Image Analysis
2005 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 1, 433-438 p.Article in journal (Refereed) Published
Abstract [en]

A method for the ultrastructural investigation of fiber cross-sections based on atomic force microscopy in combination with image analysis is presented. A uniform distribution of pores across the matrix material within the fiber wall was revealed by impregnation of pulp fibers with poly(ethylene glycol). The effects of chemical and mechanical processing on the pore and matrix structure and on the arrangement of the cellulose fibril aggregates were investigated. During chemical processing, changes in the fiber ultrastructure occur: a broadening of the pore and matrix lamella widths in combination with a reduction in their number and an enlargement of the cellulose fibril aggregates. It was found that pores formed during pulping are evenly distributed across the fiber wall in the transverse direction. In contrast, refining increases the pore and matrix lamella width in the fiber wall closest to the middle lamella an effect which gradually decrease in size toward the lumen side.

Keyword
Atomic force microscopy, Cellulose, Image analysis, Impregnation, Polyethylene glycols, Pore size, Fiber walls, Pore distribution, Pulp fibers
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-4935 (URN)10.1021/bm040068x (DOI)000226344300055 ()
Note
QC 20101012. Uppdaterad från in press till published (20101012).Available from: 2005-02-14 Created: 2005-02-14 Last updated: 2017-12-05Bibliographically approved
4. Ultrastructural changes in a holocellulose pulp revealed by enzymes, thermoporosimetry and atomic force microscopy
Open this publication in new window or tab >>Ultrastructural changes in a holocellulose pulp revealed by enzymes, thermoporosimetry and atomic force microscopy
2005 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 59, no 6, 589-597 p.Article in journal (Refereed) Published
Abstract [en]

To increase our knowledge of the ultrastructure within softwood fibres, enzymatic treatment, thermoporosimetry, light microscopy, and atomic force microscopy with image analysis were used to investigate the structure of holocellulose softwood pulp fibres. The size of the average cellulose fibril aggregates and the width of pore and matrix lamellae were found to be uniform across the secondary cell-wall layer in the transverse direction of the wood fibre wall. In holocellulose, these dimensions were very similar to those in the native wood, whereas in kraft pulp the cellulose fibril aggregates were larger and the pore and matrix lamellae broader. These differences between holocellulose and kraft pulp fibres suggest that a high temperature is needed for cellulose fibril aggregation to occur. Neither refining nor drying of the holocellulose pulp changed the cellulose fibril aggregate size. Upon drying and enzymatic treatment, a small decrease in the pore and matrix lamella width was evident throughout the fibre wall. This indicated not only uniform distribution of pores throughout the fibre wall, but also enzymatic accessibility to the entire fibre wall. The holocellulose pulp had a somewhat larger pore volume than the kraft pulp. Refining of the holocellulose pulp led to pore closure, probably due to increased mobility of the fibre wall. The enzymatic treatment revealed that during hydrolysis of one hemicellulose, part of the other was also dissolved, indicating that the two hemicelluloses are to some extent linked to each other in the structure.

Keyword
atomic force microscopy, cell wall, cellulose, drying, enzyme, fibril, hemicellulases, hemicellulose, holocellulose, Norwegian spruce, Picea abies, pores, pore size, pore volume, refining, ultrastructure
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-4936 (URN)10.1515/HF.2005.096 (DOI)000233697900001 ()
Note
QC 20101012. Uppdaterad från submitted till published (20101012). Tidigare titel: Ultrastructural changes in a holocellulose pulp revealed by enzymes, thermoporosimetry and atomic force microscopyAvailable from: 2005-02-14 Created: 2005-02-14 Last updated: 2017-12-05Bibliographically approved

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