Abstract
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 m2/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.
Highlights
In the recent years, much attention has focused on managing indoor environments in museums, libraries and archives in a responsible manner, especially in terms of reducing energy use and carbon emissions (Hong et al 2012; Staniforth 2014)
Cellulose-based materials such as paper and cardboard contained in books, manuscripts, historical records, prints and drawings are vulnerable to temperature and relative humidity (RH) and scientific understanding of how storage conditions affect these materials is crucial to the development of rational guidelines for the long-term control of climate in the repositories
Research into climate-related issues of the preservation of paper materials has so far predominantly focused on hydrolysis and oxidation of cellulose (Strlic 2015), as well as risk of microbiological activity starting above 60% RH (Sedlbauer 2002)
Summary
Much attention has focused on managing indoor environments in museums, libraries and archives in a responsible manner, especially in terms of reducing energy use and carbon emissions (Hong et al 2012; Staniforth 2014). There are two further important consequences of paper’s capacity to gain moisture when the RH is high, or losing moisture when the surrounding air is dry. On one hand paper collections act as moisture buffers reducing RH fluctuations in the repositories, on the other paper objects experience dimensional response—they shrink as they lose moisture and swell when they gain moisture. Paper objects may experience uneven moisture distribution, and uneven dimensional change, in response to the RH variations as the moisture diffusion into or out of the object is not instantaneous. Paper may experience stress because of restraint on its dimensional response resulting from binding it into a book block or mounting into a rigid protective system
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