Hygroscopic Behavior of Paper and Books

2008

for sheets made from bleached kraft softwood pulps refined to different levels. We demonstrate the utility of the diffusion parameters by estimating moisture profiles through a stack of sheets using a mathematical model for transient moisture transport. The model predictions agreed with our measurements of the moisture profiles showing the usefulness of these diffusion parameters.

Nordic Pulp & Paper Research Journal, 2004

Experimental results for transient hygroexpansion of copy paper sheets subjected to step changes in RH were obtained. MD transient hygroexpansion strain rates (expressed in normalized forms) during adsorption were higher than the corresponding CD rates for every cycle tested. CD hygroexpansion strains were observed to be linear in the average moisture content of the sheets. MD strains however showed significantly non-linear behavior. A mathematical model for transient hygroexpansion of paper sheets was developed based on the twin mechanisms of moisture diffusion through the pore and fiber spaces. The model incorporates the effects of surface boundary layers also. Assuming the hygroexpansion to be "quasi-static" (i.e. local hygroexpansion coefficients are equivalent to the equilibrium values), traditional theory for linear thermal elasticity was applied to estimate hygroexpansion strains. The model describes different hygroexpansion strain rates in CD and MD.

The Science of …

The three dimensional structure of paper materials plays a critical role in the paper manufacturing process especially via its impact on the transport properties for fluids. Dewatering of the wet web, pressing and drying will benefit from knowledge of the relationships ...

2014

The three dimensional structure of paper materials plays a critical role in the paper manufacturing process especially via its impact on the transport properties for fluids. Dewatering of the wet web, pressing and drying will benefit from knowledge of the relationships between the web structure and its transport coefficients. Among transport, moisture diffusion in paper is central to the understand ing and optimal design of paper products for their performance in different environmental conditions. Our recent research of moisture sorption in paper has indicated that diffusion of water vapor through the pore space is an important mechanism for transport [Ramaswamy, 2001, Huang, 2002]. The effect of the three dimensional structure of the paper sheet on the diffusion of moisture is significant.

2004

The three dimensional structure of paper materials plays a critical role in the paper manufacturing process especially via its impact on the transport properties for fluids. Dewatering of the wet web, pressing and drying will benefit from knowledge of the relationships between the web structure and its transport coefficients. Among transport, moisture diffusion in paper is central to the understand ing and optimal design of paper products for their performance in different environmental conditions. Our recent research of moisture sorption in paper has indicated that diffusion of water vapor through the pore space is an important mechanism for transport [Ramaswamy, 2001, Huang, 2002]. The effect of the three dimensional structure of the paper sheet on the diffusion of moisture is significant.

Moisture adsorption and diffusion were examined in 17 samples of historical and modern papers and cardboards, differing in the time of production and the pulping process. The moisture adsorption data for paper materials made of rags, gelatin-sized were close to each other whereas wood-pulp papers showed higher intra-group variability due to varying contents of lignin and rosin sizing. The average adsorption curve for all specimens was close to that of pure cellulose. In-plane diffusivities along the paper sheets in a stack, primary direction of uptake and release moisture by library objects, were determined as a function of relative humidity and paper compression. Typically, the in-plane diffusivities fell within the range of 6·10-6 – 1.7·10-5 m 2 /s and were significantly affected by the paper fraction in the specimens which were combination of paper sheets and thin air layers or pockets between the sheets. The external mass transfer coefficient at the surface of the paper objects perpendicular to the paper sheets exceeded 2·10-3 m/s and significantly depended on the intensity of air motion in typical environments. Effective use of the adsorption and diffusion information obtained was demonstrated in modelling buffering capacities of books.

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2002

1985

This paper describes some studies of the effects of drying restraints and sheet density on the in-plane and out-of-plane hygroexParisivity of paper . It is shown that drying restraints in the RT E range, i .e . between 20°! and 0% moisture content, greatly influence hygroexpans :i_vity, with in-plane hygroexpansivity being 'Lower the lower the TH to

The conventional way to evaluate dimensional stability, regardless of end-use purpose, is to measure the change in dimensions when the moisture content is changed by changing the relative humidity. Sorption of moisture from moist air is a relatively slow process and for the evaluation of printing papers this may not be the most appropriate method. In the present work, data from conventional hygroexpansion measurements has been compared with data from hydroexpansion measurements, i.e. expansions caused by the sorption of liquid water, sprayed onto papers printed with a random speckle pattern, the expansion being monitored by electronic speckle photography. Sheets made from different pulps, with different fines contents and different modifications were studied at different grammages and water-transfer levels. The effect of drying-mode, i.e.

International Journal of Solids and Structures

This paper presents a method to predict the through-thickness moisture content distribution and associated induced deformations of paper and cardboard sheets as they are subjected to relative humidity changes. The transient moisture diffusion problem is solved using a “natural” analytic approach that has previously been applied for solving transient heat conduction in multi-layer solids. The deformation behaviour of the sheet during the moisture diffusion process is predicted using a semi-analytical approach based on a Rayleigh–Ritz minimization of the total potential energy. Geometrically nonlinear effects are taken into account. Curvatures of the originally flat sheet are predicted as a function of time, as are the shapes of the sheet for steady-state condition. As multiple solutions exist, stability is studied. The developed model was used to study the deformation behaviour of one paper and two cardboard sheets. Comparisons with finite-element results demonstrate that the develop...