7.3 Packaging Applications
161
The incorporation of nanofillers like nanoclays into biopolymers yields a remarkable improvement in barrier properties of bionanocomposites [1]. As a fundamental
principle, the transfer of molecules in polymer/clay nanocomposites requires a much
longer path rather than directly diffuse into neat polymers. As such, more tortuous
diffusive paths can be generated in a nanocomposite system resulting in a delay in the
transfer of molecules [18]. Because of good resistance to most organic compounds
and solvents, PVA and PVA bionanocomposites have been widely used in material
packaging industries so that packed products can be protected from the secondary
contamination by printing links [19]. Furthermore, the permeability is prone to the
reduction with increasing the nanofiller content. Aloui et al. [20] reported that the
addition of 3 wt% HNTs and 5 wt% cellulose nanocrystals (CNCs) within PVA
matrices in PVA bionanocomposites decreased both water and oxygen permeabilities. Similarly, Strawhecker and Manias [21] found that with the inclusion of 4–6
wt% nanofillers, water vapour permeability of PVA/Na
+ montmorillonite (MMT)
nanocomposite films was decreased by 40% when compared with that of neat PVA.
This result arises from a mix of exfoliated/intercalated clay structures, which generates a tortuous diffusion path through nanocomposite films. On the other hand, the
addition of graphene oxide (GO) particles within PVA matrices drastically reduced
the oxygen permeability owing to the exfoliation of GOs with a resulting tortuous
path again for oxygen molecules [22]. Kim et al. [23] revealed that the permeability of PVA/GO nanocomposite films was found to be decreased by 20% with
the inclusion of only 0.3 wt% GOs relative to that of pure PVA films. Polyhydroxyalkanoate (PHA) has impressive properties such as hydrophobic nature and water
vapour barrier properties, which are similar to those for polyethylene (PE) coating
applications. The drawback of PHA lies in its poor gas barrier properties and narrow
processing window, thus limiting its applications in food packaging. The addition
of nanoclays in PHA was found to result in much lower oxygen and water permeabilities [24]. On the other hand, starch as one of the most popular biopolymers
has high hydrophilicity, and thus limits its usage in material packaging applications.
The inclusion of nanofillers into thermoplastic starch (TPS) is regarded as a useful
method to overcome such a drawback with success. Park et al. [25] presented that
the water vapour transition rate of TPS/MMT nanocomposites was reduced by a
half, as opposed to that of pure TPS, owing to the tortuous pathway generated by
embedded MMTs. On the contrary, Change et al. [26] evaluated the effect of chitosan
nanoparticles (CNs) on the reduction in barrier properties of TPS because CN shape
could not induce a sufficient tortuous path with a certain limitation in contrast with
platelet-like MMTs. Overall, the applications of bionanocomposites may yield enormous applications in material packaging with sophisticated development, important
innovation and pronounced cost-effectiveness.
161
The incorporation of nanofillers like nanoclays into biopolymers yields a remarkable improvement in barrier properties of bionanocomposites [1]. As a fundamental
principle, the transfer of molecules in polymer/clay nanocomposites requires a much
longer path rather than directly diffuse into neat polymers. As such, more tortuous
diffusive paths can be generated in a nanocomposite system resulting in a delay in the
transfer of molecules [18]. Because of good resistance to most organic compounds
and solvents, PVA and PVA bionanocomposites have been widely used in material
packaging industries so that packed products can be protected from the secondary
contamination by printing links [19]. Furthermore, the permeability is prone to the
reduction with increasing the nanofiller content. Aloui et al. [20] reported that the
addition of 3 wt% HNTs and 5 wt% cellulose nanocrystals (CNCs) within PVA
matrices in PVA bionanocomposites decreased both water and oxygen permeabilities. Similarly, Strawhecker and Manias [21] found that with the inclusion of 4–6
wt% nanofillers, water vapour permeability of PVA/Na
+ montmorillonite (MMT)
nanocomposite films was decreased by 40% when compared with that of neat PVA.
This result arises from a mix of exfoliated/intercalated clay structures, which generates a tortuous diffusion path through nanocomposite films. On the other hand, the
addition of graphene oxide (GO) particles within PVA matrices drastically reduced
the oxygen permeability owing to the exfoliation of GOs with a resulting tortuous
path again for oxygen molecules [22]. Kim et al. [23] revealed that the permeability of PVA/GO nanocomposite films was found to be decreased by 20% with
the inclusion of only 0.3 wt% GOs relative to that of pure PVA films. Polyhydroxyalkanoate (PHA) has impressive properties such as hydrophobic nature and water
vapour barrier properties, which are similar to those for polyethylene (PE) coating
applications. The drawback of PHA lies in its poor gas barrier properties and narrow
processing window, thus limiting its applications in food packaging. The addition
of nanoclays in PHA was found to result in much lower oxygen and water permeabilities [24]. On the other hand, starch as one of the most popular biopolymers
has high hydrophilicity, and thus limits its usage in material packaging applications.
The inclusion of nanofillers into thermoplastic starch (TPS) is regarded as a useful
method to overcome such a drawback with success. Park et al. [25] presented that
the water vapour transition rate of TPS/MMT nanocomposites was reduced by a
half, as opposed to that of pure TPS, owing to the tortuous pathway generated by
embedded MMTs. On the contrary, Change et al. [26] evaluated the effect of chitosan
nanoparticles (CNs) on the reduction in barrier properties of TPS because CN shape
could not induce a sufficient tortuous path with a certain limitation in contrast with
platelet-like MMTs. Overall, the applications of bionanocomposites may yield enormous applications in material packaging with sophisticated development, important
innovation and pronounced cost-effectiveness.