Aspect Ratio Control of Layered Double Hydroxide Nanosheets and their Application for High Oxygen Barrier Coating in Flexible Food Packaging

We report a method to rationally control the aspect ratio of a layered double hydroxide for use in a barrier coating for food packaging films. The reconstruction of a Mg2Al-layered double oxide (LDO) in concentrated aqueous glycine solutions produces dispersions of Mg2Al-LDH nanosheets. Mg2Al-LDH nanosheet samples with different aspect ratios can be prepared by fine-tuning the Mg2Al-LDH calcination temperature and LDO reconstruction time in aqueous glycine. We find that nanosheet thickness decreases and diameter increases with increasing reconstruction time from 16 to 96 h. We observe a limiting nanosheet aspect ratio of ca. 336 ± 170. These Mg2Al-LDH nanosheets can be dispersed in PVA to give a water-based dispersion that can be used to coat flexible polymeric films. Oxygen transmission rate (OTR) of a PET film decreases when the thickness of the dried coated layer increases, an OTR of <0.005 cc·m–2·day–1 is observed for a coating with thickness of 1175 ± 101 nm.