Efficient Gas and Water Vapor Barrier Properties of
Thin Poly(lactic acid) Packaging Films: Functionalization with Moisture
Resistant Nafion and Clay Multilayers
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Abstract
Poly(lactic acid) (PLA) represents
one of the most promising and
attractive biobased polymer for the industrial development of environmentally
sustainable packaging. However, oxygen and water barrier properties
of PLA based films cannot compete with those of commercially available
composite multilayers. To fill this gap, we used the layer-by-layer
deposition technique on commercially used PLA thin films (30 μm
thick) in order to increase their barrier properties to oxygen and
water vapor. Nanometric films were grown by alternating branched poly(ethylene
imine) (BPEI), hydrophobic fluorinated polymer (Nafion), and montmorillonite
clay (MMT) layers with the aim of obtaining low gas permeability in
both dry and moist conditions as well as low water vapor permeability.
Two different kinds of architectures were designed and successfully
prepared, based on a 4 layer repeating unit (BPEI/MMT/BPEI/Nafion),
represented here as quadlayer (QL), and on a 6 layer repeating-unit
((BPEI/Nafion)<sub>2</sub>/BPEI/MMT), hexalayer (HL). Reduction in
oxygen and water permeabilities is observed for films based on both
types of repeat units. The reduction of the permeabilities increases
with the number of quad and hexalayers achieving reductions in terms
of oxygen permeability in both dry and humid conditions up to 98%
and 97% respectively for 10 HL and QL. Furthermore, a reduction of
78% of water vapor transmission rate through the functionalized film
was obtained for these films. As far as oxygen permeability is concerned,
HL films are more efficient than QL films for smaller numbers of deposition
units. These properties are shown to result from the complementarity
between the presence of BPEI/Nafion and MMT layers