102
pathway within the film, and the resulting film has excellent barrier properties
(Adame and Beall 2009). The mechanical strength of biopolymer films is also
improved, thus increasing the glass transition temperature (T g ) and thermal degradation temperature, while some studies have reported a decrease in transparency as
minor disadvantages of fillers on polymer (Yu et al. 2003; Petersson and Oksman
2006; Weiss et al. 2006; Cyras et al. 2008). In this section, the use of inorganic fillers (e.g. clay minerals) and natural fillers (e.g. cellulose based nanostructures) in the
nanocomposite films will be discussed.
6.3.1 Clays and Silicate-Based Fillers
Clay minerals contain tetrahedral and octahedral sheets which are negatively
charged or neutral layers of hydrated aluminum phyllosilicates (Murray 2000;
Unalan et al. 2014; Gutiérrez et al. 2017b). The superimposition of tetrahedral and
octahedral sheets creates layered structures, which then form a layer called platelet.
The isomorphic replacement of aluminum and/or silicon with a lower-valence atom
causes a negative surface charge for minerals. In some clay groups, the negative
surface charge is balanced with positive inorganic ions found in the interlayer
(Unalan et al. 2014). The cations have an important effect on the swelling behavior
of clay when in contact with water molecules. In general, two arrangements of main
sheets are observed, namely 1:1 and 2:1, in nanoclays (Unalan et al. 2014). The
nanoclays are grouped as smectite, kaolinite, halloysite, etc., according to their morphology and chemical structure (Fig. 6.2).
Mt is the most commonly used filler in the formation of nanocomposites. The
surface of Mt is negatively charged because the trivalent Al-cation is partially
replaced with the Mg divalent cation. Sodium and calcium ions, which are hydrated
between the layers, balance the charge (Manias et al. 2001). The weak forces that
hold layers together allow water and other polar molecules to penetrate between the
layers that expand the matrix (Chin et al. 2001). In addition to improving the tensile
strength and gas barrier properties of composite films, modified Mt particles also
show an antibacterial effect that increases the potential use for food packaging
applications (Sothornvit et al. 2009; Souza et al. 2012; Kanmani and Rhim 2014).
However, the migration of the metal from packaging film to the food due to the
addition of clay should be observed.
Kaolinite is a the crucial mineral among the group of kaolin clays, and is a layered silicate consisting of a tetrahedral sheet with dioctahedral sheet layers (Murray
2000). The structure of kaolinite provides great cohesive energy regarding hydrogen
bonds between adjacent layers (Sanchez-Garcia et al. 2008a). In addition to its
lower aspect ratio, kaolinite has a low absorption capacity, associated with the low
surface area and the minimal layer loading (Krishnamachari et al. 2009). Although
it is inexpensive, abundant and environmentally friendly, kaolinite is rarely used for
the preparation of nanocomposites due to the difficulties faced by intercalation of
polymers. Within the kaolin group, halloysites represent a dominant form of hollow
H. Cakmak and E. Sogut
pathway within the film, and the resulting film has excellent barrier properties
(Adame and Beall 2009). The mechanical strength of biopolymer films is also
improved, thus increasing the glass transition temperature (T g ) and thermal degradation temperature, while some studies have reported a decrease in transparency as
minor disadvantages of fillers on polymer (Yu et al. 2003; Petersson and Oksman
2006; Weiss et al. 2006; Cyras et al. 2008). In this section, the use of inorganic fillers (e.g. clay minerals) and natural fillers (e.g. cellulose based nanostructures) in the
nanocomposite films will be discussed.
6.3.1 Clays and Silicate-Based Fillers
Clay minerals contain tetrahedral and octahedral sheets which are negatively
charged or neutral layers of hydrated aluminum phyllosilicates (Murray 2000;
Unalan et al. 2014; Gutiérrez et al. 2017b). The superimposition of tetrahedral and
octahedral sheets creates layered structures, which then form a layer called platelet.
The isomorphic replacement of aluminum and/or silicon with a lower-valence atom
causes a negative surface charge for minerals. In some clay groups, the negative
surface charge is balanced with positive inorganic ions found in the interlayer
(Unalan et al. 2014). The cations have an important effect on the swelling behavior
of clay when in contact with water molecules. In general, two arrangements of main
sheets are observed, namely 1:1 and 2:1, in nanoclays (Unalan et al. 2014). The
nanoclays are grouped as smectite, kaolinite, halloysite, etc., according to their morphology and chemical structure (Fig. 6.2).
Mt is the most commonly used filler in the formation of nanocomposites. The
surface of Mt is negatively charged because the trivalent Al-cation is partially
replaced with the Mg divalent cation. Sodium and calcium ions, which are hydrated
between the layers, balance the charge (Manias et al. 2001). The weak forces that
hold layers together allow water and other polar molecules to penetrate between the
layers that expand the matrix (Chin et al. 2001). In addition to improving the tensile
strength and gas barrier properties of composite films, modified Mt particles also
show an antibacterial effect that increases the potential use for food packaging
applications (Sothornvit et al. 2009; Souza et al. 2012; Kanmani and Rhim 2014).
However, the migration of the metal from packaging film to the food due to the
addition of clay should be observed.
Kaolinite is a the crucial mineral among the group of kaolin clays, and is a layered silicate consisting of a tetrahedral sheet with dioctahedral sheet layers (Murray
2000). The structure of kaolinite provides great cohesive energy regarding hydrogen
bonds between adjacent layers (Sanchez-Garcia et al. 2008a). In addition to its
lower aspect ratio, kaolinite has a low absorption capacity, associated with the low
surface area and the minimal layer loading (Krishnamachari et al. 2009). Although
it is inexpensive, abundant and environmentally friendly, kaolinite is rarely used for
the preparation of nanocomposites due to the difficulties faced by intercalation of
polymers. Within the kaolin group, halloysites represent a dominant form of hollow
H. Cakmak and E. Sogut