Stress–strain curve of single pulp fibres and paper

Jarmo Kouko, Marina Jajcinovic, Wolfgang Fischer, Annika Ketola, Ulrich Hirn, Elias Retulainen

Research output: Chapter in Book/Report/Conference proceedingConference abstract in proceedingsScientific

Abstract

Fibre properties have a central role in the mechanical properties of paper. Fibre strength determines the strength potential of paper. Also the elongation potential of fibre network is strongly related to the behaviour of single fibres. When aiming at improved strength or elongation a better knowledge of the properties of single fibre and the effect of mechanical treatment is needed. The literature results typically suggest that the stress-strain curve of straight single fibre is practically linear or slightly concave downwards and the typical elongation is 2-5%. Refining has been shown to be an efficient way to improve the strength of paper, mainly due to improved bonding. High consistency refining has been shown to increase elongation of paper. This has been attributed to the deformations (curl, dislocations and micro-compressions) introduced by the treatment. But is that due to the improved fibre elongation of single fibres? The effect of mechanical treatment on the stress-strain behaviour of single fibres of bleached softwood kraft from a Nordic mill was investigated and compared also to the stress-strain curve of paper. The results showed that the individual fibres were strong and showed considerably higher elongation than expected. They also had a very wide variation in those properties. The measured strength and elongation ranged from 200 MPa to 1100 MPa, and from 8% to 32%, respectively. The refining did not improve the measured strength, nor did the HC refining increase the elongation of the single fibres. The effects of the refining seemed to correlate with the number of dislocations (measured using HCl cleavage test) in fibres. With increasing number of dislocations both the average breaking stress and strain decreased. High consistency refining introduced dislocations, but low consistency refining seemed to be able heal some of them. The shape of the stress strain-curves was rarely a linear, but often the slope increased with straining which behaviour could be related to the straightening of disordered regions in the fibre wall. Test also showed that fibres show a considerable plastic elongation and stress relaxation. Comparison of the single fibre tests with the paper test results, suggest that the main effect of refining on paper strength is not due to increased strength nor elongation of fibred but due to the increased bonding of the fibres, which is mainly responsible for the increased strength. Increased paper elongation caused by HC refining is not due to improved fibre elongation but due to reduced axial stiffness of the wet fibres that results in increased drying shrinkage of the paper.
Original languageEnglish
Title of host publicationProceedings of Paper and Biorefinery Conference 16-17 May 2018
Subtitle of host publicationAbstracts
PublisherAPV Graz - Akademischer Papieringenieurs Verein
Pages40-41
Number of pages2
Publication statusPublished - 16 May 2018
MoE publication typeNot Eligible
EventPaper and Biorefinery Conference - Graz, Austria
Duration: 16 May 201817 May 2018

Conference

ConferencePaper and Biorefinery Conference
CountryAustria
CityGraz
Period16/05/1817/05/18

Fingerprint

Pulp
Fibers
Elongation
Refining
Stress-strain curves
Straightening
Softwoods
Stress relaxation
Drying

Keywords

  • tensile strength
  • strain
  • fiber
  • paper

Cite this

Kouko, J., Jajcinovic, M., Fischer, W., Ketola, A., Hirn, U., & Retulainen, E. (2018). Stress–strain curve of single pulp fibres and paper. In Proceedings of Paper and Biorefinery Conference 16-17 May 2018: Abstracts (pp. 40-41). [TF3/11] APV Graz - Akademischer Papieringenieurs Verein.
Kouko, Jarmo ; Jajcinovic, Marina ; Fischer, Wolfgang ; Ketola, Annika ; Hirn, Ulrich ; Retulainen, Elias. / Stress–strain curve of single pulp fibres and paper. Proceedings of Paper and Biorefinery Conference 16-17 May 2018: Abstracts. APV Graz - Akademischer Papieringenieurs Verein, 2018. pp. 40-41
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Kouko, J, Jajcinovic, M, Fischer, W, Ketola, A, Hirn, U & Retulainen, E 2018, Stress–strain curve of single pulp fibres and paper. in Proceedings of Paper and Biorefinery Conference 16-17 May 2018: Abstracts., TF3/11, APV Graz - Akademischer Papieringenieurs Verein, pp. 40-41, Paper and Biorefinery Conference, Graz, Austria, 16/05/18.

Stress–strain curve of single pulp fibres and paper. / Kouko, Jarmo; Jajcinovic, Marina; Fischer, Wolfgang; Ketola, Annika; Hirn, Ulrich; Retulainen, Elias.

Proceedings of Paper and Biorefinery Conference 16-17 May 2018: Abstracts. APV Graz - Akademischer Papieringenieurs Verein, 2018. p. 40-41 TF3/11.

Research output: Chapter in Book/Report/Conference proceedingConference abstract in proceedingsScientific

TY - CHAP

T1 - Stress–strain curve of single pulp fibres and paper

AU - Kouko, Jarmo

AU - Jajcinovic, Marina

AU - Fischer, Wolfgang

AU - Ketola, Annika

AU - Hirn, Ulrich

AU - Retulainen, Elias

PY - 2018/5/16

Y1 - 2018/5/16

N2 - Fibre properties have a central role in the mechanical properties of paper. Fibre strength determines the strength potential of paper. Also the elongation potential of fibre network is strongly related to the behaviour of single fibres. When aiming at improved strength or elongation a better knowledge of the properties of single fibre and the effect of mechanical treatment is needed. The literature results typically suggest that the stress-strain curve of straight single fibre is practically linear or slightly concave downwards and the typical elongation is 2-5%. Refining has been shown to be an efficient way to improve the strength of paper, mainly due to improved bonding. High consistency refining has been shown to increase elongation of paper. This has been attributed to the deformations (curl, dislocations and micro-compressions) introduced by the treatment. But is that due to the improved fibre elongation of single fibres? The effect of mechanical treatment on the stress-strain behaviour of single fibres of bleached softwood kraft from a Nordic mill was investigated and compared also to the stress-strain curve of paper. The results showed that the individual fibres were strong and showed considerably higher elongation than expected. They also had a very wide variation in those properties. The measured strength and elongation ranged from 200 MPa to 1100 MPa, and from 8% to 32%, respectively. The refining did not improve the measured strength, nor did the HC refining increase the elongation of the single fibres. The effects of the refining seemed to correlate with the number of dislocations (measured using HCl cleavage test) in fibres. With increasing number of dislocations both the average breaking stress and strain decreased. High consistency refining introduced dislocations, but low consistency refining seemed to be able heal some of them. The shape of the stress strain-curves was rarely a linear, but often the slope increased with straining which behaviour could be related to the straightening of disordered regions in the fibre wall. Test also showed that fibres show a considerable plastic elongation and stress relaxation. Comparison of the single fibre tests with the paper test results, suggest that the main effect of refining on paper strength is not due to increased strength nor elongation of fibred but due to the increased bonding of the fibres, which is mainly responsible for the increased strength. Increased paper elongation caused by HC refining is not due to improved fibre elongation but due to reduced axial stiffness of the wet fibres that results in increased drying shrinkage of the paper.

AB - Fibre properties have a central role in the mechanical properties of paper. Fibre strength determines the strength potential of paper. Also the elongation potential of fibre network is strongly related to the behaviour of single fibres. When aiming at improved strength or elongation a better knowledge of the properties of single fibre and the effect of mechanical treatment is needed. The literature results typically suggest that the stress-strain curve of straight single fibre is practically linear or slightly concave downwards and the typical elongation is 2-5%. Refining has been shown to be an efficient way to improve the strength of paper, mainly due to improved bonding. High consistency refining has been shown to increase elongation of paper. This has been attributed to the deformations (curl, dislocations and micro-compressions) introduced by the treatment. But is that due to the improved fibre elongation of single fibres? The effect of mechanical treatment on the stress-strain behaviour of single fibres of bleached softwood kraft from a Nordic mill was investigated and compared also to the stress-strain curve of paper. The results showed that the individual fibres were strong and showed considerably higher elongation than expected. They also had a very wide variation in those properties. The measured strength and elongation ranged from 200 MPa to 1100 MPa, and from 8% to 32%, respectively. The refining did not improve the measured strength, nor did the HC refining increase the elongation of the single fibres. The effects of the refining seemed to correlate with the number of dislocations (measured using HCl cleavage test) in fibres. With increasing number of dislocations both the average breaking stress and strain decreased. High consistency refining introduced dislocations, but low consistency refining seemed to be able heal some of them. The shape of the stress strain-curves was rarely a linear, but often the slope increased with straining which behaviour could be related to the straightening of disordered regions in the fibre wall. Test also showed that fibres show a considerable plastic elongation and stress relaxation. Comparison of the single fibre tests with the paper test results, suggest that the main effect of refining on paper strength is not due to increased strength nor elongation of fibred but due to the increased bonding of the fibres, which is mainly responsible for the increased strength. Increased paper elongation caused by HC refining is not due to improved fibre elongation but due to reduced axial stiffness of the wet fibres that results in increased drying shrinkage of the paper.

KW - tensile strength

KW - strain

KW - fiber

KW - paper

M3 - Conference abstract in proceedings

SP - 40

EP - 41

BT - Proceedings of Paper and Biorefinery Conference 16-17 May 2018

PB - APV Graz - Akademischer Papieringenieurs Verein

ER -

Kouko J, Jajcinovic M, Fischer W, Ketola A, Hirn U, Retulainen E. Stress–strain curve of single pulp fibres and paper. In Proceedings of Paper and Biorefinery Conference 16-17 May 2018: Abstracts. APV Graz - Akademischer Papieringenieurs Verein. 2018. p. 40-41. TF3/11