Preparation of κ-Al2O3/resin composite coating on polyethylene terephthalate foil for gas-permeation barrier

Surface of κ-alumina (κ-Al2O3) nanoplatelets was grafted by 3-(trimethoxysilyl)propyl methacrylate (MPS) molecules over a broad MPS/κ-Al2O3 weight ratio from 0 to 0.9 in water/ethanol mixtures. The organic grafting resulted in a hydrophobic alumina surface with a contact angle greater than 90° from an initially hydrophilic surface with a contact angle of about 25°. The MPS-grafted nanoplatelets were dispersed in organic, ultraviolet (UV) curable resin with solids concentrations ranging from 0.01 to 0.15 weight fraction to form a coating layer of 50 μm on polyethylene terephthalate (PET) foil of 100 μm in thickness initially. The coated foil showed a maximum of 20% reduction on both water-vapor and oxygen-gas permeations when compared to that of the bare PET foil. The coated foil also showed a reduced transmission of visible light at wavelengths <500 nm. This became particularly pronounced as the κ-Al2O3 fraction in resin was increased. A high transmission (>80%) yet remained for the visible light with wavelengths greater than ~550 nm over the κ-Al2O3 fraction examined (up to 15 wt%).