Dewatering of foam-laid and water-laid structures and the formed web properties

Jani Lehmonen*, Elias Retulainen, Jouni Paltakari, Karita Kinnunen-Raudaskoski, Antti Koponen

*Corresponding author for this work

Research output: Contribution to journalReview ArticleScientificpeer-review

3 Citations (Scopus)
11 Downloads (Pure)

Abstract

Abstract: The use of aqueous foams as a carrier fluid for pulp fibers instead of water has re-emerged in the paper and board industry in recent years. In foam forming, a surfactant is needed to reduce the surface tension of the carrier liquid and to create foam as a process fluid and flowing medium. This presents the following questions: (1) How do the water forming and foam forming processes differ? (2) How do the obtained wet/dry fibre sheets differ after forming and after wet pressing? (3) Which differences in the process behavior and sheet properties are due to the surfactant, and which are due to the presence of air bubbles in the flowing medium? The answers to these questions were sought by using an experimental academic approach and by applying a special dynamic vacuum assisted sheet former. Although foams are much more viscous than water, dewatering times were found to be approximately equal in water and foam forming at higher vacuum levels. The hydrodynamic resistance of sheet was approximately constant during water forming, while in foam forming resistance was initially even smaller than in water forming but it increased with time, being substantially higher at the end of the forming process. In certain cases, surfactant alone was found to have a similar, albeit often lower, effect on the sheet properties of foam. Surfactant improved sheet dryness (both after forming and wet pressing), lowered density, and lowered strength properties also in water forming. Foam, on the other hand, had a crucial effect particularly on certain structural properties such as formation and porosity. The difference between water and foam-laid sheets typically reduced in line with higher wet pressing pressure. This suggests that the role of surface tension and foam bubbles in controlling interfiber contact is overridden by wet pressing pressure. Thus applying foam as a carrier fluid has characteristic effects both on the papermaking process and the end product properties. The main features of foam forming can be explained by the chemical effects caused by the surfactant, and the structural effects caused by the foam bubbles. Graphic abstract: [Figure not available: see fulltext.]

Original languageEnglish
Pages (from-to)1127–1146
JournalCellulose
Volume27
Issue number3
DOIs
Publication statusPublished - 2020
MoE publication typeA2 Review article in a scientific journal

Keywords

  • Dewatering
  • Foam forming
  • In-plane strength properties
  • Interfiber contact
  • Structural properties
  • Water forming
  • z-strength

Fingerprint Dive into the research topics of 'Dewatering of foam-laid and water-laid structures and the formed web properties'. Together they form a unique fingerprint.

  • Cite this

    Lehmonen, J., Retulainen, E., Paltakari, J., Kinnunen-Raudaskoski, K., & Koponen, A. (2020). Dewatering of foam-laid and water-laid structures and the formed web properties. Cellulose, 27(3), 1127–1146. https://doi.org/10.1007/s10570-019-02842-x