110
waves. This is achieved due to the cavitation effect, which is the formation, growth,
and the collapse of bubbles in a liquid (Hielscher 2005; Gutiérrez and Álvarez
2017a). After the collapse of the bubbles, several important local events accelerate
deagglomeration of dispersed micro-sized particles. The acoustic cavitation helps
form unique materials at room-temperature liquid in contrast to the extreme conditions such as high pressures and temperatures, or a longer reaction period than that
required in the conventional methods. The ultrasonication was first adopted to manufacture polymer nanocomposites based on petroleum-derived polymer/inorganic
clay systems, and was then gradually extended to biobased nanocomposites (e.g.
polysaccharides, proteins and lipids) (Feng et al. 2014; Soheilmoghaddam
et al. 2014).
As another processing method, the sol-gel process is a synthesis process that
contains in the preparation of a sol, successive gelation and solvent removal. In
these systems, the sol (colloidal solution) acts as a precursor and the gel (threedimensional polymeric network) is formed from hydrolysis, followed by polycondensation (Vartiainen et al. 2014).
6.5 Properties of Polymer Nanocomposites
The mechanical, barrier, optical, thermal and functional (i.e. antimicrobial, antioxidant) performance of nanocomposites are the most important parameters for food
packaging applications. The properties of biobased nanocomposites depend on their
microstructure related to their high aspect ratio. Substantial improvements in these
properties are associated with the degree of crystallinity, presence of amorphous
phase, polar or apolar groups into the polymer, degree of crosslinking, T g and pretreatments (Galić and Ciković 2003). This section presents the main properties that
can be improved by incorporating fillers.
6.5.1 Barrier Properties
The quality of a food product is exposed to continuous change due to the transfer of
water vapor and oxygen through the wall of the polymer package (Gagnard et al.
2004). The type and size of the nano-fillers and the structure of the nanocomposites
influence the degree of improvement in the barrier performance of nanocomposites
(Shankar and Rhim 2016a). The reason for such improvement is the presence of
highly dispersed nano-fillers that form an impermeable structure to the molecules in
the polymer matrix due to the their high aspect ratio (Xu et al. 2006; Choudalakis
and Gotsis 2009). The permeant molecules are forced to travel through a tortuous
pathway within the polymer composite, thus increasing the length of the diffusion
path (Gutiérrez and Álvarez 2017b; Tapia-Blácido et al. 2018). The barrier properties are also influenced by the size, shape, and polarity of the penetrating molecule
H. Cakmak and E. Sogut
waves. This is achieved due to the cavitation effect, which is the formation, growth,
and the collapse of bubbles in a liquid (Hielscher 2005; Gutiérrez and Álvarez
2017a). After the collapse of the bubbles, several important local events accelerate
deagglomeration of dispersed micro-sized particles. The acoustic cavitation helps
form unique materials at room-temperature liquid in contrast to the extreme conditions such as high pressures and temperatures, or a longer reaction period than that
required in the conventional methods. The ultrasonication was first adopted to manufacture polymer nanocomposites based on petroleum-derived polymer/inorganic
clay systems, and was then gradually extended to biobased nanocomposites (e.g.
polysaccharides, proteins and lipids) (Feng et al. 2014; Soheilmoghaddam
et al. 2014).
As another processing method, the sol-gel process is a synthesis process that
contains in the preparation of a sol, successive gelation and solvent removal. In
these systems, the sol (colloidal solution) acts as a precursor and the gel (threedimensional polymeric network) is formed from hydrolysis, followed by polycondensation (Vartiainen et al. 2014).
6.5 Properties of Polymer Nanocomposites
The mechanical, barrier, optical, thermal and functional (i.e. antimicrobial, antioxidant) performance of nanocomposites are the most important parameters for food
packaging applications. The properties of biobased nanocomposites depend on their
microstructure related to their high aspect ratio. Substantial improvements in these
properties are associated with the degree of crystallinity, presence of amorphous
phase, polar or apolar groups into the polymer, degree of crosslinking, T g and pretreatments (Galić and Ciković 2003). This section presents the main properties that
can be improved by incorporating fillers.
6.5.1 Barrier Properties
The quality of a food product is exposed to continuous change due to the transfer of
water vapor and oxygen through the wall of the polymer package (Gagnard et al.
2004). The type and size of the nano-fillers and the structure of the nanocomposites
influence the degree of improvement in the barrier performance of nanocomposites
(Shankar and Rhim 2016a). The reason for such improvement is the presence of
highly dispersed nano-fillers that form an impermeable structure to the molecules in
the polymer matrix due to the their high aspect ratio (Xu et al. 2006; Choudalakis
and Gotsis 2009). The permeant molecules are forced to travel through a tortuous
pathway within the polymer composite, thus increasing the length of the diffusion
path (Gutiérrez and Álvarez 2017b; Tapia-Blácido et al. 2018). The barrier properties are also influenced by the size, shape, and polarity of the penetrating molecule
H. Cakmak and E. Sogut