Page 14 - PERIODIC Magazine Issue 7

Re
Transparent, cyclable,
low-energy food
packaging
Researchers in the O’Hare group
have developed a nanosheet-based
barrier coating that provides an
environmentally friendlier alternative
to the metallised films used in food
packaging. They explain how their
new coating formulation is recyclable,
low-energy, non-toxic and highly
efficient at preventing oxygen and
water vapour from getting to your
snacks.
Supermarket shelves displaying snacks in traditional non-recyclable packaging
14
Periodic The Magazine of the Department of Chemistry
Open a packet of crisps or a bag of candy, and there it is:
the shiny metallised film that keeps our snacks pleasantly
crisp and fresh. Structurally, it is a polymer (often PET,
polyethylene terephthalate) film coated with a thin layer
of a metal, usually aluminium. The glossy looks of such
metallised films are a comforting reassurance that our
crisps and popcorn are protected from the oxygen and
moisture in the environment, thus extending their shelf
life.
But these metallised films have a less shiny side to them;
their inability to be easily recycled and the high carbon
footprint used in their production. Metallised films are
also non-transparent, which is a distinct disadvantage
when you want to show off the product inside your food
packaging and attract unsuspecting and hungry shoppers
on their way to check out.
So we decided to turn our attention to these current
environmental and practical concerns over non-
degradable plastics.
Our low-energy alternative barrier coating eliminates
the metallic layer from the polymer packaging film. It is
therefore much easier to recycle, completely non-toxic
and mechanically stronger than metallised film. It is also
transparent and has a lower carbon footprint. It is even
microwavable.
Our barrier properties arise from a synthetic inorganic
material, a layered double hydroxide (LDH), which
is prepared by a reconstruction method that allows
the formation of high aspect ratio nanosheets. When
embedded in a PVA (polyvinyl alcohol) matrix and coated
onto a PET film, these nanosheets form what is essentially
a complex labyrinth that oxygen or water molecules need
to traverse in order to reach the food contained within
the packaging (a mechanism known as the “tortuous
pathway”). And much like the average person when
they encounter a labyrinth: most of the molecules do
not enter or eventually just go back the way they came,
never reaching the crisps or popcorn we are protecting in
the middle of the LDH labyrinth.