Lignin interdiffusion - a mechanism behind improved wet strength

Tove Joelsson, Amanda Mattsson, J A Ketoja, Gunilla Pettersson, Per Engstrand

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review

Abstract

We have studied ways of improving strength properties of paper made from high yield pulps and lignin-rich chemical pulps by utilizing the thermoplastic properties of the lignin present in the fibre walls. Both dry and wet strength can be improved by hot pressing of sheets made from lignin-rich pulps. In this paper, we focus on aspects of the wet-strength development as a function of lignin content and temperature. Here we apply an activation energy evaluation approach to study lignin intermixing or interdiffusion. By means of hot pressing, it is possible to reach wet strength levels up to 50% of the dry strength level, provided that we use pulps with high enough lignin content. Our study included hot pressing of high yield pulps such as thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), high-temperature chemithermomechanicalpulps (HTCTMP), unbleached northern softwood kraft (NSK) and northern bleached softwood kraft (NBSK). The sheet pressing trials were performed for varied temperatures from room temperature up to 270°C. As the activation energy for the high yield pulps and the lignin-rich NSK were all in the range of 20-32 kJ/mol, we suggest that the wet strength development as function of temperature has a similar mechanism as long as the pulp fibres contain enough lignin. We also suggest that the phenomenon involves intermixing and/or interdiffusion of wood polymers between adjacent fibres when they are in a close contact. Most probably both the amorphous wood polymers, i.e. the linear hemicelluloses and the cross-linked lignin, mix with each other across the fibre-fibre or even more probable over the fibril-fibril contact surface. While the hemicellulose can intermix already at room temperature under moist conditions, the lignin intermixes more easily at the higher temperature we use. We do not know how far the hemicellulose or lignin could move within the fibre walls, but it seems that the amount of lignin present on the fibre surfaces plays an important role.
Original languageEnglish
Title of host publicationAdvances in Pulp and Paper Research, Cambridge 2022
Subtitle of host publicationTransactions of the 17th Fundamental Research Symposium
EditorsDouglas W. Coffin, Warren J. Batchelor
PublisherPulp & Paper Fundamental Research Society
Pages105-118
Volume1
ISBN (Print)978-0-9926163-6-6
Publication statusPublished - 29 Aug 2022
MoE publication typeA4 Article in a conference publication
Event17th Fundamental Research Symposium - Cambridge, United Kingdom
Duration: 29 Aug 20221 Sep 2022

Conference

Conference17th Fundamental Research Symposium
Country/TerritoryUnited Kingdom
CityCambridge
Period29/08/221/09/22

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