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Shear strength development between couched papers during drying
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.ORCID iD: 0000-0001-8622-0386
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.ORCID iD: 0000-0001-8699-7910
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

The out-of-plane properties (e.g., out-of-plane shear strength) of paper materials are very important for their performance during converting and end use. There is, however, a lack of published data on how shear strength develops throughout the stages of paper manufacturing. The present study investigates how the shear strength developed between couched sheets during drying in a Rapid-Köthen laboratory sheet drier. The shear strength of sheets was measured, starting from sheets with a solids content of approximately 35% all the way to fully dry sheets. Shear strength development was examined between both never-dried and rewetted sheets made of unbeaten and beaten pulp. The results indicate that the shear strength increased with increasing solids content at all solids contents investigated. The shear strength was low (<120 kPa) up to a solids content of approximately 60–70%, after which it increased rapidly with increasing solids content, suggesting that interactions important for the shear strength of dry paper start to develop at this particular dry content.

National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-12317OAI: oai:DiVA.org:kth-12317DiVA: diva2:309613
Note

QC20100616

Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2016-06-08Bibliographically approved
In thesis
1. Influence of fibre modification on moisture sorption and the mechanical properties of paper
Open this publication in new window or tab >>Influence of fibre modification on moisture sorption and the mechanical properties of paper
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fibre modification might be a way to improve the performance of paper, to increase its cost competiveness and enable new paper-based products to be developed. Therefore, the influence of fibre modification (with polyelectrolytes or by fibre cross-linking) on the mechanical properties of special importance for packaging paper grades was studied.

Creep deformation under varying humidity conditions (i.e. mechano-sorptive creep) is of outmost importance for the stacking life of paper-based boxes. The influence on creep behaviour of adsorbing polyallylamine (a cationic polyelectrolyte) to fibre surfaces or throughout the fibre walls was studied. Adsorption to fibre surfaces reduced the creep at constant humidity. The mechano-sorptive creep was not however influenced. The use of polyelectrolytes did not thus appear to be a feasible strategy for reducing mechano-sorptive creep.

Polyelectrolytes can however be efficient in improving other mechanical properties. The use of multilayers consisting of polyallylamine (PAH) and polyacrylic acid (PAA) was for example shown to significantly increase the strength of paper with much less densification and build-up of residual stress than is obtained by beating.

Cross-linking by oxidation with periodate radically decreased the mechano-sorptive creep of sheets made from the oxidised fibres. The basic mechanism behind the reduction in mechano-sorptive with cross-linking was found to be that the cross-linking slowed down the moisture sorption kinetics. A lower sorption rate led to smaller moisture content variations during the mechano-sorptive creep testing, and thus less sorption-induced swelling and stress concentrations at fibre/fibre joints. However, for cross-linking to be a practical way to reduce creep, the large problem of embrittlement must be solved.

The shear strength of couched sheets was measured to study the interaction between the sheets at different solids content. The shear strength was low until a solids content of approximately 60−70% was reached, which suggests that interactions important for the strength at complete dryness start to develop at this solids content. The effect of different fibre modifications and additives on how the fibres interact during the consolidation process is not always well understood. The method of shear strength determination could in the future be applied to modified fibres to hopefully increase the understanding of how different modifications influence the fibre/fibre interactions. A deeper understanding might reduce the time for the development of new and improved fibre modifications.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 84 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2010:11
Identifiers
urn:nbn:se:kth:diva-12318 (URN)978-91-7415-606-5 (ISBN)
Public defence
2010-04-23, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC20100616Available from: 2010-04-09 Created: 2010-04-07 Last updated: 2010-06-16Bibliographically approved

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Wågberg, LarsÖstlund, Sören

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