A study of stress development in aqueous gelatin coatings

A cantilever deflection technique was used to monitor stress during the drying of aqueous gelatin coatings. Photographic-grade gelatin was dissolved in deionized water and coated, chilled, and dried. The final average in-plane tensile stress ranged from 0 to 50 MPa. Measured stresses were independent of the coating thickness and initial solution concentration. At low relative humidity (0%) and low drying temperature (∼ 20°C), the stress grew with time, reaching a constant average magnitude of 46 MPa. Raising the relative humidity above 0% or raising the temperature above 50°C changed the manner in which stress evolved. Stress rose to a peak value and then relaxed to a lower final value. Humidity affected stress evolution more than did temperature, within the limits of this work.