Fiber Modification

Kraft-TMP Bonding

Fiber Modification: Fiber Bond Enhancement

Background: What is unknown • Why tensile strength of TMP-made paper is weaker than

KP-made paper? Weaker bonding or something else?

• Structure of interfiber bonding has focused on chemical pulp sheets. However, there are no comprehensive models for describing the structure of mechanical pulp bonds.

• Mechanism of bond enhancement by bonding agents was studied for chemical pulp. Same study should be prosecuted to understand the mechanical pulp bonding for the development of bond enhancement strategy.

Fiber Modification: Fiber Bond Enhancement

Background: What needs to be understood

• Structure of mechanical pulp bond– Surface of long fibers and fines (layer separation by

pulping)– Contact between fines and long fibers– Chemical contamination on the surface (extractives)– TMP/TMP bond– TMP/KP bond– KP/KP bond

• Effect of bonding agent on the mode of bond breakage

Fiber Modification: Fiber Bond Enhancement

• How to approach to the mechanical pulp sheet bonding

Fiber Modification: Fiber Bond Enhancement

Fiber Modification: Fiber Bond Enhancement

Fiber Modification: Fiber Bond Enhancement

Fiber Modification: Fiber Bond Enhancement

Fiber Modification: Fiber Bond Enhancement

Fiber Modification: Fiber Bond Enhancement

Fiber Modification: Fiber Bond Enhancement

Fiber Modification: Fiber Bond Enhancement

Fiber Modification: Fiber Bond Enhancement

Fiber Modification: Fiber Bond Enhancement

Fiber Modification: Fiber Bond Enhancement

Effect of bonding agent dosage on the mode of bond breakage

• Significance– It is believed that improvement of tensile

strength of paper by addition of bonding agents is due to the increase of specific bond strength (bond strength/bonded area) not by the increase of the bonded area.

– Observation of broken bond will provide insight into how bonding agents improve bond strength.

Visualization of broken bonds by vapor phase osmium coating of paper

Coating of internal surface of paper by osmium

Sheet splitting

Handsheet used for sheet splitting

Cationic Potato Starch

505560657075

0 0.5 1 1.5 2

Dosage, %

Tens

ile, N

m/g

Pulp: Southern Pine Bleached Kraft

Freeness: 500 ml CSF

Starch: cationic potato starch

Dosage: 0.3, 0.5, 1.0, 2.0%

Bond breakage mode: type AVery smooth surface with no fibrils rising from it

Bond breakage mode: type BRelatively smooth surface with some fibrils rising from it

Bond breakage mode: type CThe S1 layer is broken and partially peeled off from the S2

Bond breakage mode: type DThe S1 is peeled off and the S2 is exposed

Effect of C-starch dosage on the bond breakage mode

Dosage: 0%

32

58

6 40

20

40

60

80

A B C D

Dosage: 0.3%

4

3854

40

20

40

60

80

A B C D

Dosage: 0.5%

0

3344

23

0

20

40

60

80

A B C D

Dosage: 1.0%

011

70

19

0

20

40

60

80

A B C D

Dosage: 2.0%

0 3

60

37

0

20

40

60

80

A B C D

Mechanism of Fiber-Fiber BondingConclusions

• The improvement of paper tensile strength is not simply due to the increase of specific bond strength.

• The position of the bond breakage shifts from the bonded surface to the S1, and to the S1/S2 border with the increase of dosage of the bonding agent.