Effect of restrained versus free drying on hygro-expansion of hardwood and softwood fibers and paper handsheet

Niels Vonk, Ron Peerlings, Marc Geers, Johan Hoefnagels (Corresponding author)

Onderzoeksoutput: Bijdrage aan tijdschriftTijdschriftartikelAcademicpeer review

3 Citaten (Scopus)
34 Downloads (Pure)


Earlier work on the hygro-expansion of paper states that the larger hygro-expansivity of freely compared to restrained dried handsheets is due to structural differences between the fibers inside the handsheet. To study this hypothesis, first, the hygro-expansion of freely and restrained dried, hardwood and softwood handsheets has been characterized. Subsequently, the transient full-field hygro-expansion (longitudinal, transverse, and shear strain) of fibers extracted from these handsheets was measured using global digital height correlation, from which the micro-fibril angle was deduced. The hygro-expansivity of each individual fiber was tested before and after a wetting period, during which the fiber’s moisture content is maximized, to analyze if a restrained dried fiber can “transform” into a freely dried fiber. It was found that the longitudinal hygro-expansion of the freely dried fibers is significantly larger than the restrained dried fibers, consistent with the sheet-scale differences. The difference in micro-fibril angle between the freely and restrained dried fibers is a possible explanation for this difference, but merely for the hardwood fibers, which are able to “transform” to freely dried fibers after being soaked in water. In contrast, this “transformation” does not happen in softwood fibers, even after full immersion in water for a day. Various mechanisms have been studied to explain the observations on freely and restrained dried hardwood and softwood, fiber and handsheets including analysis of the fibers’ lumen and cross-sectional shape. The presented results and discussion deepens the understanding of the differences between freely and restrained dried handsheets.

Originele taal-2Engels
Pagina's (van-tot)11135-11156
Aantal pagina's22
Nummer van het tijdschrift17
StatusGepubliceerd - nov. 2023


This work is part of an Industrial Partnership Programme (i43-FIP) of the Foundation for Fundamental Research on Matter (FOM), which is part of the Netherlands Organization for Scientific Research (NWO). This research programme is co-financed by Canon Production Printing, University of Twente, Eindhoven University of Technology.

Foundation for Fundamental Research on Matter
Nederlandse Organisatie voor Wetenschappelijk Onderzoek


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