Agriculture Reference
In-Depth Information
et al.
2012
), clay nanoplatelets (Ku et al.
2004
; Schuetz et al.
2011
), organoclay
(Ham et al.
2013
; Gokkurt et al.
2013
), graphene (Lee et al.
2013
; Yousefi
et al.
2013
), polysaccharide nanocrystals (Lin et al.
2012
), carbon nanotubes
(Swain et al.
2013
; Prashantha et al.
2009
), cellulose-based nanomaterials (Floros
et al.
2012
; Sandquist
2013
), chitosan nanoparticles (Chang et al.
2010
), and other
metal nanoparticles like ZnO
2
(Esthappan et al.
2013
), colloidal Cu (C
ยด
rdenas
et al.
2009
), or Ti (Li et al.
2011
).
The inclusion of nanofillers in the polymer matrix affects the barrier properties
in two ways: by creating a tortuous path for gas diffusion and by causing changes to
the polymer matrix itself at the interfacial regions (Choudalakis and Gotsis
2009
).
In the first way, due to the impermeability of the inorganic nanofillers, gas mole-
cules can
t follow a straight-line path (perpendicular to the film surface) but must
diffuse around the nanoparticles. The result is a longer mean path for gas diffusion
through the film in the presence of the nanofillers. It allows the manufacturer to
accomplish larger effective film thickness with lower amounts of polymer.
In the second way, if the interactions between nanoparticles and polymer are
favorable, the polymer strands close to each nanoparticle would be partially
immobilized. As a result, the gas molecules have attenuated hopping rates between
free volume holes or altered density and/or size of holes in the interfacial zones.
This has been directly observed using positron annihilation lifetime spectroscopy
(PALS) (Wang et al.
2007
). Also, the presence of surfactants and other additives
used to incorporate the nanofiller efficiently into the matrix can also modify the
solubility or diffusivity of the gases. These effects in the interfacial regions are
particularly important in polyolefins (Picard et al.
2007
), which are polymer
matrices that possess very high native gas permeability.
These mechanisms are the reasons why nanomaterials have been more success-
ful than micromaterials as fillers for polymer composites. They have much higher
aspect ratios, and the interfacial volume element is significantly greater in a
polymer nanocomposite than in a polymer microcomposite from the same
materials.
'
7.2.2 Active Packaging Materials
Active packaging relates to the incorporation of additives to the packaging systems
with the purpose of maintaining or extending the shelf life and product quality. The
active additives can be incorporated directly into the packaging matrix, attached to
the interior of the packaging material, or introduced inside the package in separate
containers such as sachets (Restuccia et al.
2010
).
It provides dynamic, rather than the conventional passive, protection to the food
inside and has an active role in food preservation, different from just providing an
inert barrier from external conditions (Lim
2011
). The additives release or absorb
substances into or from the food and the surrounding environment (Brody
2001
),
thus promoting food preservation. Most used active packaging materials include
