104
The talc has a plate-like structure with magnesium-oxygen/hydroxyl octahedral
layers packed in two layers of tetrahedral silica (López et al. 2015). Highly lamellar
talc is associated with large single platelets, while microcrystalline talc has small
platelets. Talc has naturally poor interactions with nonpolar materials and has a high
surface energy (Gorrasi et al. 2018). Talc is mostly used to improve thermal resistance, mechanical properties and dimensional stability of the films (Sakthivel and
Pitchumani 2011).
Zeolites are aluminosilicates in the form of hydrated crystals with a highly
porous structure due to the system of three-dimensional channels. Zeolites have
univalent and divalent cations. Water molecules are the other components located in
the system of channels that give the exchange capacity and dehydration/rehydration
capacity to zeolites (Gascon et al. 2012). The underlying reason for the addition of
zeolites into the polymer is to form mixed-matrix membranes and improve the
mechanical and thermal properties.
6.3.2 Metallic Nanostructures
Ag NPs are one of the most used metals for the production of active biobased nanocomposites, due to their antimicrobial properties against a wide variety of microorganisms (Dallas et al. 2011). The widely recognized mechanisms of antimicrobial
activity are: (1) the interaction of Ag
+
ions with negatively charged nucleic acids
contributes to the disruption of metabolic processes, the disintegration of cell wall
causing the cell death (Kanmani and Rhim 2014), and (2) the membrane binding to
the surface causes morphological changes and then the structural integrity is lost
(Sondi and Salopek-Sondi 2004; Álvarez et al. 2018). Ag NPs are increasingly used
in the formation of nanocomposites for food packaging applications, since it provides slower release rates with lower acute antimicrobial responses due to the high
aspect ratio and, thus improving its surface reactivity (Egger et al. 2009).
Copper is another well-recognized nano-sized particle that exhibits a lower biocidal activity compared to Ag ions. However, the use of copper in nanocomposites
is restricted because it is considered as toxic when in contact with food and increases
the oxidation rate of the food product (Fernández et al. 2010).
Metal oxides (e.g. MgO, TiO 2 , and ZnO) also show antimicrobial activity against
various microorganisms, such as bacteria, yeasts and molds. Nanocomposites containing titanium dioxide (TiO 2 ) NPs show antimicrobial properties thanks to their
photocatalytic activity, related to their crystal structure. The antimicrobial effect of
TiO 2 NPs is associated with the generation of O 2 and hydroxyl radicals after irradiation at higher energies than the band gap. The organic molecules are then oxidized
by reactive oxygen species that lead to cell death (Llorens et al. 2012). In addition
to their antimicrobial activity, TiO 2 NPs protect food products against the oxidizing
effect of ultraviolet (UV) irradiation, as well as maintain optical clarity related to
their efficient short-wavelength light absorbing properties (Duncan 2011). Zinc
H. Cakmak and E. Sogut
The talc has a plate-like structure with magnesium-oxygen/hydroxyl octahedral
layers packed in two layers of tetrahedral silica (López et al. 2015). Highly lamellar
talc is associated with large single platelets, while microcrystalline talc has small
platelets. Talc has naturally poor interactions with nonpolar materials and has a high
surface energy (Gorrasi et al. 2018). Talc is mostly used to improve thermal resistance, mechanical properties and dimensional stability of the films (Sakthivel and
Pitchumani 2011).
Zeolites are aluminosilicates in the form of hydrated crystals with a highly
porous structure due to the system of three-dimensional channels. Zeolites have
univalent and divalent cations. Water molecules are the other components located in
the system of channels that give the exchange capacity and dehydration/rehydration
capacity to zeolites (Gascon et al. 2012). The underlying reason for the addition of
zeolites into the polymer is to form mixed-matrix membranes and improve the
mechanical and thermal properties.
6.3.2 Metallic Nanostructures
Ag NPs are one of the most used metals for the production of active biobased nanocomposites, due to their antimicrobial properties against a wide variety of microorganisms (Dallas et al. 2011). The widely recognized mechanisms of antimicrobial
activity are: (1) the interaction of Ag
+
ions with negatively charged nucleic acids
contributes to the disruption of metabolic processes, the disintegration of cell wall
causing the cell death (Kanmani and Rhim 2014), and (2) the membrane binding to
the surface causes morphological changes and then the structural integrity is lost
(Sondi and Salopek-Sondi 2004; Álvarez et al. 2018). Ag NPs are increasingly used
in the formation of nanocomposites for food packaging applications, since it provides slower release rates with lower acute antimicrobial responses due to the high
aspect ratio and, thus improving its surface reactivity (Egger et al. 2009).
Copper is another well-recognized nano-sized particle that exhibits a lower biocidal activity compared to Ag ions. However, the use of copper in nanocomposites
is restricted because it is considered as toxic when in contact with food and increases
the oxidation rate of the food product (Fernández et al. 2010).
Metal oxides (e.g. MgO, TiO 2 , and ZnO) also show antimicrobial activity against
various microorganisms, such as bacteria, yeasts and molds. Nanocomposites containing titanium dioxide (TiO 2 ) NPs show antimicrobial properties thanks to their
photocatalytic activity, related to their crystal structure. The antimicrobial effect of
TiO 2 NPs is associated with the generation of O 2 and hydroxyl radicals after irradiation at higher energies than the band gap. The organic molecules are then oxidized
by reactive oxygen species that lead to cell death (Llorens et al. 2012). In addition
to their antimicrobial activity, TiO 2 NPs protect food products against the oxidizing
effect of ultraviolet (UV) irradiation, as well as maintain optical clarity related to
their efficient short-wavelength light absorbing properties (Duncan 2011). Zinc
H. Cakmak and E. Sogut