• Ahmad, M. Al-Qararah
• Ketoja, Jukka A.
• Lappalainen, Timo
• Paananen, Arja
• Hjelt, Tuomo
• Laine, Christiane
• Koponen, Antti Ilmari
• Pajari, Heikki

Abstract

Use of foam as a material carrier in the manufacturing ofnovel paper-like structures has recently been studiedintensively [1]. Tailoring the microporous structurerequires control over various physical and chemical foamproperties including air content, bubble size,interfacial rheology and foam stability. The relativeimportance of these factors has been studied in mixingexperiments and in laboratory forming of sheet structuresusing foam-fibre mixtures.In axial mixing [2], the bubble size is affected byseveral physical factors such as rotational speed, aircontent and surface tension. At high shear rates, thebubble size becomes small and the importance of surfaceinteractions increases affecting the rheologicalbehaviour described by the Herschel-Bulkley equation.The inclusion of natural fibres (like wood fibres) to themixing environment reduces the mean bubble size. However,the inclusion of the regenerated fibres (e.g. viscosefibres) does not affect the mean bubble size in the sameway. The likely reason behind this behaviour is the roughsurfaces of the natural fibres (and their fine particlefraction) that lead to high contact forces between thefibres and the foam bubbles [2,3].The bubble size is inherited in the formed microstructureas a characteristic mean pore size after the foam carrieris removed from the foam-fibre system. With the samesurfactant, bigger bubbles increase the mean pore size.Besides the above physical parameters, we have studiedthe effect of different surfactant types on the bubblesize, interfacial rheology and the microstructure. Theeffects of the chemically different surfactants canexceed that of the varying bubble size leading to adecrease in the mean pore size even though the averagebubble size increases. This provides an additional handleto the tailoring of the microstructure of the endproduct.1) A. M. Al-Qararah, A. Ekman, T. Hjelt, J. A. Ketoja, H.Kiiskinen, A. Koponen, J. Timonen, A uniquemicrostructure of the fiber networks deposited fromfoam-fiber suspensions. Colloids and Surfaces A:Physicochem. Eng. Aspects 482, 544-553 (2015).2) A. M. Al-Qararah, T. Hjelt, A. Koponen, A. Harlin, J.A. Ketoja, Response of wet foam to fibre mixing. Colloidsand Surfaces A: Physicochem. Eng. Aspects 467, 97-106(2015).3) A. Jäsberg, P. Selenius, A. Koponen, Flow rheology offibre-laden aqueous foams. Proceedings of Papercon 2015,19.4 - 22.5.2015, Atlanta, Georgia.

Topics

• impedance spectroscopy
• microstructure
• pore
• surface
• inclusion
• forming
• wood
• surfactant