Moisture sorption and diffusion in historical cellulose-based materials

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.