We use the pulsed electroacoustic (PEA) method to quantify how moisture uptake alters space-charge formation and transport in low-density polyethylene (LDPE) films. Specimens were exposed to controlled water-vapor environments for up to 12 h, and space-charge density profiles were recorded every 50 s under applied fields reaching 80 kV mm. Moisture increases the density of deep traps, stabilizing negative charge at the electrode-polymer interface and enabling bulk space-charge through field-assisted ionization. Humidified films exhibit shorter charge-packet transit times, indicating higher effective carrier mobility. At elevated fields, the emergence of multiple packets evidences a nonlinear transport regime governed by trap saturation and dynamic retrapping. These effects erode LDPE dielectric stability, with implications for medium-voltage cable insulation. We interpret the observations using coupled models that combine Schottky-type injection, drift-dominated transport, and Poisson electrostatics, and emphasize the need for predictive multiphysics frameworks that integrate rigorous moisture quantification, polymer morphological evolution, and the nonlinear dynamics of charge migration.
