MOISTURE-CONTENT ISOLINES OF GELATIN AND THE IMPLICATIONS FOR ACCELERATED AGING TESTS AND LONG-TERM STORAGE OF PHOTOGRAPHIC MATERIALS

The moisture-content isolines of a photographic gelatin were measured. Constant moisture content was established experimentally by sealing g elatin in a vapor-tight container with little free air volume compared with the volume of gelatin. The temperature was varied, and the relat ive humidity in the free space was measured after thermal and vapor ph ase equilibrium had been reached. A significant shift in the moisture vapor phase equilibrium over gelatin was found. Surprisingly, moisture -content isolines easily reveal the glass transition temperature of th e gelatin, and the glass transition's strong dependence on moisture co ntent was confirmed. Traditional moisture-absorption isotherms do not clearly indicate the glass transition temperature. The implications of these results are discussed with regard to interpretation of accelera ted aging tests, to storage in unregulated environments, and to low-te mperature storage of photographic materials.