Modelling the degradation of acidic and alkaline printing paper

There has always been an interest in the professional communities of libraries, archives and conservation science to find ways of estimating the rate of degradation of paper under archival conservation conditions. Previously we reported a number of considerations for developing a kinetic degradation model based on Whatman no.1 paper. In the present research, this model was extended to 10 different papers and validated. Various physical and chemical properties of acidic, neutral, and alkaline papers were measured, such as the degree of polymerization (DP), tensile strength, equilibrium moisture content, and pH, as well as alkaline fillers content when applicable. The activation energy (E_a) based on DP of cellulose and zero-span tensile strength were determined. E_a and pH had the most significant influence on the simulated decay of paper. Papers with a high E_a (> 120 kJ mol⁻¹), alkaline such as those containing at least 2% CaCO₃, and acidic—but good printing quality papers made of bleached chemical pulp– were found the most durable in ambient conditions. Papers with a lower E_a (< 110 kJ mol⁻¹) such as lignocellulosic papers containing significant amount of mechanical pulp were much less stable over time. Whatman filter papers, used as models of pure cellulosic papers, were found to have low E_a despite the good quality cotton fibers. A generic isoperm equation based on E_a was developed to predict the changes in the state of papers under various climatic conditions, and was applicable independently of the pH of the paper. The model developed allows a better quantification of the deterioration rate of printing papers such as those that are currently, and will be in the future, found in our archival collections.