Gelatin has remarkable ability to form thin films which are characterized by random molecular arrangements in a glassy state. However, when stored below the glass transition temperature, the molecular chains form helical structures (microcrystals), leading to physical aging as they shift toward a more stable state. Despite microcrystal formation, this aging negatively affects the film’s strength and flexibility. To address this, we explored delaying microcrystal formation by stacking gelatin films with different isoionic points: Type A (acidic) and Type B (alkaline), creating two to five-layer structures. Each film was prepared as a 7.5% (w/v) solution with 20% glycerin added relative to gelatin weight. The films were dried at 37°C, alternately stacked, and heat-pressed to form multilayer samples. These were stored at 30°C and 50% relative humidity for 50 days, with periodic monitoring.

Physical aging was assessed through enthalpy recovery measurements using differential scanning calorimetry (DSC) and tensile tests to evaluate mechanical strength changes due to lamination.

DSC results showed that both Type A and Type B monolayers experienced gradual enthalpy recovery from day 0 to 20, a sharp increase from day 20 to 30, and deceleration approaching saturation by day 50. Type A exhibited higher recovery than Type B. In laminated films, enthalpy recovery did not follow a simple linear average of Type A and B. Instead, it declined depending on layer configuration and sequence. This irregularity is attributed to electrostatic interactions at the Type A–B interface, altering free volume distribution and helix formation, and leading to hydrogen bond reorganization and water redistribution.

Tensile tests on films with four or more layers revealed embrittlement initially, followed by ductility recovery over time. This dual-stage behavior likely results from initial free volume reduction and heterogeneous helix nucleation near interfaces, followed by the formation of a tougher, more homogeneous network through helix reorganization, interface restructuring, and water redistribution.

To better understand these thermal and mechanical changes, dynamic analyses such as dielectric relaxation measurements are needed to monitor the gelatin molecular chains’ motion.