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Strength Properties of Paper produced from Softwood Kraft Pulp: Pulp Mixture, Reinforcement and Sheet Stratification
Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. (Paper Technology)
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For paper producers, an understanding of the development of strength properties in the paper is of uttermost importance. Strong papers are important operators both in the traditional paper industry as well as in new fields of application, such as fibre-based packaging, furniture and light-weight building material. In the work reported in this thesis, three approaches to increasing paper strength were addressed: mixing different pulps, multilayering and reinforcement with man-made fibres. In specific:

The effects of mixing Swedish softwood kraft pulp with southern pine or with abaca (Musa Textilis) were investigated. Handsheets of a softwood kraft pulp with the addition of abaca fibres were made in a conventional sheet former. It was seen that the addition of abaca fibres increased the tearing resistance, fracture toughness, folding endurance and air permeance. Tensile strength, tensile stiffness and tensile energy absorption, however, decreased somewhat. Still it was possible to add up to about 60% abaca without any great loss in tensile strength. As an example, with the addition of 30% abaca, the tear index was increased by 36%, while the tensile index was decreased by 8%.

To study the effect of stratification, a handsheet former for the production of stratified sheets, the LB Multilayer Handsheet Former was evaluated. The advantage of this sheet former is that it forms a stratified sheet at low consistency giving a good ply bond. It was shown to produce sheets with good formation and the uniformity, evaluated as the variation of paper properties, is retained at a fairly constant level when the number of layers in the stratified sheets is increased. The uniformity of the sheets produced in the LB Multilayer Handsheet Former is generally at the same level as of those produced in conventional sheet formers.

The effects of placing southern pine and abaca in separate layers, rather than mixing them homogeneously with softwood pulp were studied. Homogeneous and stratified sheets composed of softwood and southern pine or softwood and abaca were produced in the LB Multilayer Handsheet Former. It was found that by stratifying a sheet, so that a pulp with a high tear index and a pulp with a high tensile index are placed in separate layers, it was possible to increase the tear index by approximately 25%, while the tensile index was decreased by 10-20%. Further, by mixing a pulp with less conformable fibres and no fines with a pulp with more flexible fibres and fines, a synergy in tensile strength (greater strength than that predicted by linear mass fraction additivity) was obtained.

The effects of stratifying sheets composed of softwood and abaca were compared to the effects of refining the softwood pulp. Homogeneous and stratified sheets composed of softwood with three different dewatering resistances and abaca were also produced in the LB Multilayer Handsheet Former. It was found that by stratifying the sheets the tear index was retained while the tensile index was increased by the refining.

The effects of reinforcing softwood pulp of different dewatering resistances with man-made fibres with low bonding ability were also investigated. Man-made fibres (i.e. regenerated cellulose, polyester and glass fibres) were added in the amounts 1, 3, or 5 wt% to softwood pulp of three different dewatering resistances. It was found that with refining of a softwood pulp and subsequent addition of long fibres with low bonding ability the tensile-tear relationship can be shifted towards higher strength values. The bonding ability of the man-made fibres was evaluated by pull-out tests and the results indicated that, in relation to the fibre strength, regenerated cellulose (lyocell) was most firmly attached to the softwood network while the glass fibres were most loosely attached.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet , 2010. , p. 96
Series
Karlstad University Studies, ISSN 1403-8099 ; 2010:15
Keywords [en]
paper strength, tensile strength, tearing resistance, folding endurance, fracture toughness, handsheet former, stratify, multilayer, multiply, reinforcement, refining, beating, abaca, glass fibre, polyester, lyocell, softwood, bond strength
National Category
Paper, Pulp and Fiber Technology
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-5612ISBN: 978-91-7063-302-7  (print)OAI: oai:DiVA.org:kau-5612DiVA, id: diva2:317178
Public defence
2010-06-17, Andersalen, 11D 121, Karlstads universitet, Karlstad, 09:00 (English)
Opponent
Supervisors
Available from: 2010-05-28 Created: 2010-05-03 Last updated: 2011-10-26Bibliographically approved
List of papers
1. Abaca as a reinforcement fibre for softwood pulp
Open this publication in new window or tab >>Abaca as a reinforcement fibre for softwood pulp
2007 (English)In: TAPPI Journal, ISSN 0734-1415, Vol. 6, no 10, p. 25-32Article in journal (Refereed) Published
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-1907 (URN)
Available from: 2007-10-08 Created: 2007-10-08 Last updated: 2019-03-12Bibliographically approved
2. Handsheet former for the production of stratified sheets
Open this publication in new window or tab >>Handsheet former for the production of stratified sheets
2009 (English)In: Appita journal, ISSN 1038-6807, Vol. 62, no 4, p. 272-278Article in journal (Refereed) Published
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-1908 (URN)
Available from: 2007-10-08 Created: 2007-10-08 Last updated: 2019-03-12Bibliographically approved
3. Paper strength of both stratified and homogeneous sheets with selected fibres: Part I: Effect of fibre properties.
Open this publication in new window or tab >>Paper strength of both stratified and homogeneous sheets with selected fibres: Part I: Effect of fibre properties.
2010 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The effect on paper strength of placing different types of fibres in separate layers instead of homogeneously mixing the fibres was examined. The aim was to displace the tensile‑tear relationship towards higher strength values. Two‑layer laboratory sheets were made in a multilayer handsheet former and compared to single‑layer sheets made from a homogeneous mixture of the two pulps. Fibres with high coarseness (southern pine) and fibres with a high fibre length (abaca, Musa textilis) were added to a Swedish softwood sulfate pulp. Placing the different fibres in separate layers was shown to give a higher tearing resistance but a lower tensile strength than mixing the fibres. The sheets containing southern pine showed results as expected, based on linear mass fraction additivity and the differences in density between the sheets, whereas the sheets containing abaca indicated a synergism for tensile strength in the mixed sheets. The results are discussed with respect to differences in load distribution in the sheets during the tensile and tear tests. It is suggested that the high tear index of the stratified sheets is because the degree of bonding is at a low level in the southern pine and abaca layers, while the high tensile index of the stratified sheets is a result of an increased activation of the additive fibres in the network together with the more flexible softwood fibres. Fibre length seems to be more important than fibre coarseness for achieving a positive effect on paper strength of stratification.

National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-5614 (URN)
Available from: 2010-05-03 Created: 2010-05-03 Last updated: 2019-05-02Bibliographically approved
4. Paper strength of both stratified and homogeneous sheets with selected fibres: Part II: Effect of refining.
Open this publication in new window or tab >>Paper strength of both stratified and homogeneous sheets with selected fibres: Part II: Effect of refining.
2010 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The effect on the tensile strength and tearing resistance of refining one of the pulps in mixed and stratified sheets composed of two pulps was examined. The aim was to see whether the stratification has a positive effect on the tensile-tear relationship, or whether the same effect can be reached by adjusting the degree of refining of the pulps. Moderately refined, fractionated abaca (Musa textilis) pulp with a high tearing resistance potential was added to a Swedish softwood sulfate pulp. The softwood pulp was refined to three different dewatering resistances. It was shown that by stratifying the sheets consisting of 50wt% abaca and 50wt% softwood, the tensile index can be increased by refining the softwood pulp while the tearing resistance is retained. The effect of stratification on the tensile-tear relationship thus differs from the effect of refining. However, for sheets composed of 17wt% abaca and 83wt% softwood, no effect of the stratification was observed. The effect of stratification with different amounts of abaca was also examined. In general, the tensile and tear indices of mixed as well as stratified sheets were close to the results predicted by linear mass fraction additivity. However the stratified sheets showed a slightly lower tensile index than predicted and the mixed sheets a slightly higher tensile index.

National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-5615 (URN)
Available from: 2010-05-03 Created: 2010-05-03 Last updated: 2019-05-02Bibliographically approved
5. The effect on paper strength of man-made fibres added to a softwood kraft pulp
Open this publication in new window or tab >>The effect on paper strength of man-made fibres added to a softwood kraft pulp
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-5616 (URN)
Available from: 2010-05-03 Created: 2010-05-03 Last updated: 2017-12-06Bibliographically approved

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