Gelatin Size as a PH and Moisture Content Buffer in Paper

Two experiments were conducted to investigate the role of gelatin sizes in paper permanence. In the first experiment, the acid-base chemistry of paper extracts was studied using titrations to determine gelatin's potential role as a pH buffer. Gelatin was observed throughout this experiment to behave as a pH buffer in the strict sense via the common ion effect. This buffering is expected to take place during long-term natural aging. In the second experiment, when gelatin-sized papers and unsized controls were subjected to controlled humidity cycling, the gelatin-sized papers gained and retained slightly more moisture compared to the controls and exhibited the same rates of moisture pickup and loss. Therefore, gelatin does not appear to protect fibers against harmful stresses caused by RH cycling by simply slowing or limiting the overall moisture pickup and loss. Future studies on the specific location of moisture pickup, which was not monitored in this experiment, may yet reveal that gelatin does limit the stresses of humidity cycling on cellulose polymers. Interestingly, two historical leaves with known gelatin content showed diminished adsoption/desorption in humidity cycling similar to that for the modern unsized controls.