SCG-OXFORD CENTRE OF EXCELLENCE

 

One of the major challenges in the circular economy relating to food packaging is the elimination of metallised film which is currently the industry standard approach to achieve the necessary gas barrier performance. Here, we report the synthesis of high aspect ratio 2D non-toxic layered double hydroxide (LDH) nanosheet dispersions using a non-toxic exfoliation method in aqueous amino acid solution. High O2 and water vapour barrier coating films can be prepared using food safe liquid dispersions through a bar coating process. The oxygen transmission rate (OTR) of 12 μm PET coated film can be reduced from 133.5 cc·m−2·day−1 to below the instrument detection limit (<0.005 cc·m−2·day−1). The water vapour transmission rate (WVTR) of the PET film can be reduced from 8.99 g·m−2·day−1 to 0.04 g·m−2·day−1 after coating. Most importantly, these coated films are also transparent and mechanically robust, making them suitable for flexible food packing while also offering new recycling opportunities.

 

We report a method to rationally control the aspect ratio of layered double hydroxide for use as 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. The 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 mL·m–2·day–1 is observed for a coating with thickness of 1175 ± 101 nm.

 

Recent publications:

Aspect Ratio Control of LDH Nanosheets and their Application for High Oxygen Barrier Coating in Flexible Food Packaging, J. Yu, J.-C. Buffet, D. O'Hare, ACS Appl. Mater. Interfaces.,  (2020), 12(9) 10973-10982.

High oxygen barrier coating using non-toxic nanosheet dispersions for flexible food packaging film, J. Yu, K. Ruengkajorn, D. Georgiana Crivoi, C. Chen, J-C. Buffet, D. O’Hare, Nature Communications, (2019), 10, Article number: 2398.