Failure Mechanism of Iodine-Doped Poly(vinyl alcohol) Polarizer under High Temperature and High Humidity Conditions

This study investigates the long-term failure mechanism of an iodine-doped poly(vinyl alcohol) (PVA) polarizer film under accelerated aging conditions of 85 °C and 85% relative humidity. The polarizer consists of seven layers: iodine-doped PVA sandwiched by triacetate cellulose (TAC) films as protective layers, poly(ethylene terephthalate) (PET) films as release layers, and pressure-sensitive adhesive (PSA) layers between TAC and PET. Optical microscopy and scanning electron microscope (SEM) reveal that failure initiates with air bubble growth at the film edges, propagating inward and causing PSA delamination. Optical measurements show a marked decrease in polarizing efficiency and color shifts linked to iodine species degradation, with Raman and UV–vis spectroscopy confirming a 2.8% reduction in I5– species. Structural changes were characterized by two-dimensional (2D) wide-angle X-ray scattering (WAXS), showing a decrease in PVA crystallinity from 25% to 18% and a slight increase in the lamellar orientation factor. Low-field NMR indicates no significant change in chain mobility, while high-resolution solid-state NMR detects PSA hydrolysis through the appearance of methylene carbon. These findings emphasize the critical role of PSA degradation in polarizer failure and provide insight into the interplay among crystallinity, iodine stability, and adhesive integrity under harsh environmental aging.