Real time monitoring of the through thickness moisture profile of thin sheets using NMR

Julie Bossu,Carina Waldner,Jean-Christophe Perrin,Ulrich Hirn,Aninda Chatterjee

doi:10.1016/j.ces.2022.117464

Abstract

The through-thickness distribution of liquids and liquid migration over time in thin, porous media is highly relevant for the production and product properties of materials such as textiles, membranes, paper, barrier materials, and thin films. We present a 1D NMR profiling method for the analysis of through-thickness liquid distribution during liquid absorption, migration, and drying of thin sheets. The good temporal resolution (1.3 s) and high spatial resolution (10 μm) make it possible to study changes of liquid distribution in sheets of about 100 μm thickness. A key aspect of our method is the simultaneous scanning of a liquid saturated reference sheet. Using a reference, local liquid saturation and absolute amount of liquid present over time can be evaluated. We studied the drying of water-based inkjet ink on paper substrates with differing water absorption behaviors. Differences in z-directional liquid distribution, penetration depth, and drying kinetics over time could be observed.

Highlights

On the production side, knowing the moisture profile in thickness direction can help to get a better understanding of the drying process and its kinetics
For the weakly absorbing (92 mm) and the almost non-absorbing (105 mm) paper, on the other hand, the moisture profiles did not extend over the whole thickness of the sheets
We have introduced an nuclear magnetic resonance (NMR) based setup for comprehensive zdirectional analysis of liquid distribution and migration in thin sheets

Summary

Introduction

The z-directional distribution of liquids in thin porous media and liquid migration over time is of interest in many fields such as textiles (Bencsik et al, 2008; Varga et al, 2009; Weder et al, 2006), membranes (Klein et al, 2013), production and printing of paper (Batchelor et al, 2004; Harding et al, 2001; Katugampola et al, 2006; Keränen et al, 2009; Tåg et al, 2010b), and barrier materials, coatings, and thin films (Bennett et al, 2003; Ciampi and McDonald, 2003; Erich et al, 2006, 2005; Hughes et al, 1996; Voogt et al, 2018; Wallin et al, 2000). Temporal changes in moisture distribution are relevant when studying processes like liquid absorption, migration, diffusion, and drying. On the production side, knowing the moisture profile in thickness direction can help to get a better understanding of the drying process and its kinetics. Time resolved moisture profiles in thickness direction can be used to distinguish different stages during a drying process (e.g. stages in which evaporation is limited by the evaporation from the surface or by the mass transport from the substrate’s core to the surface (Tåg et al, 2010a)). Temporally and spatially resolved moisture profiles enable the determination of mass transport coefficients that are needed for modelling.

Methods

Results

Conclusion