119
Rhim, 2016b; Deng et al. 2017; Kwak et al. 2018; Niu et al. 2018). One option to
solve this is the incorporation of plasticizers or stabilizers into composite films or
the modification of nanocellulose to promote the dispersion and reduce the agglomeration, so the mechanical and optical properties can also be improved in this way
(Bilbao-Sainz et al. 2011; Vigneshwaran et al. 2011; Song et al. 2014).
Mt stands out among the most commonly used nanoreinforcements among biodegradable composites (Avella et al. 2005; Azeredo 2009; Sothornvit et al. 2009;
Arora and Padua 2010; Rhim et al. 2013; Kanmani and Rhim 2014; Azevedo et al.
2015). However, other types of clays such as laponite or hectorite have also been
used as nanocomposites (Doblhofer et al. 2016; Valencia et al. 2018). The processing capacity, the low cost and the availability make the Mt a good candidate as a
nanoreinforcing agent (Azeredo 2009; Souza et al. 2012; Kanmani and Rhim 2014).
However, exfoliated structure is necessary for the formation of improved barrier
properties, and as explained in Nielsen’s theory, homogeneously distributed clay
sheets create a longer and more tortuous pathway which makes gas transfer difficult
(Azeredo 2009; Arora and Padua 2010). As shown in Table 6.2, the gas and water
vapor barrier properties of nanocomposite films are improved with the increasing
amounts of Mt. Although above a critical limit, the homogeneity of the clay within
the matrix is destroyed and no further improvement in the barrier properties is
observed (Tunc et al. 2007; Luecha et al. 2010; Alboofetileh et al. 2013). In some
cases, the amount of clay is kept constant and the effect of other ingredients such as
plasticizers and metal/metal oxide NPs are evaluated, or nanocomposites are compared with the pure matrices or commercial polymers (Sothornvit et al. 2009; Souza
et al. 2012; Heydari et al. 2013; Kanmani and Rhim 2014; Doblhofer et al. 2016).
Doblhofer et al. (2016) found that bionanocomposites composed of silk spidroin
and Na-hectorite had better water vapor and oxygen barrier properties compared to
the commercial PET and EVOH films, respectively (Doblhofer et al. 2016). In contrast to other protein-based nanocomposites, the spidroin-hectorite nanocomposites
were not sensitive to the relative humidity variations. López et al. (2015) incorporated talc NPs into TPS-based thermo-sealed packages, resulting in materials with
better water vapor and oxygen barrier properties.
These authors also tested the packaging performance during the storage of cherry
tomatoes and observed that the sealing of the packages with talc NPs was better than
pure TPS.
In order to improve the σ max and ε b values, glycerol can be added as a plasticizer
into the nanocomposites containing clay NPs (Souza et al. 2012; Heydari et al.
2013). However, the improvement in mechanical properties is insignificant, since
the water vapor and oxygen vapor barrier properties are destroyed with the increase
in the glycerol content (Souza et al. 2012).
The transparency of nanocomposite films due to the incorporation of clay NPs
remains constant or decreased significantly (Luecha et al. 2010; Abdollahi et al. 2013;
Heydari et al. 2013; Kanmani and Rhim, 2014; Rhim and Wang, 2014; Zolfi et al.
2014; Doblhofer et al. 2016). The reduction in transparency is attributed to the blocking
of light transmission by NPs (Kanmani and Rhim 2014; Rhim and Wang 2014).
Nonetheless, the addition of plasticizers such as glycerol can improve the transparency
of the nanocomposites containing clay NPs (Heydari et al. 2013).
6 Functional Biobased Composite Polymers for Food Packaging Applications
Rhim, 2016b; Deng et al. 2017; Kwak et al. 2018; Niu et al. 2018). One option to
solve this is the incorporation of plasticizers or stabilizers into composite films or
the modification of nanocellulose to promote the dispersion and reduce the agglomeration, so the mechanical and optical properties can also be improved in this way
(Bilbao-Sainz et al. 2011; Vigneshwaran et al. 2011; Song et al. 2014).
Mt stands out among the most commonly used nanoreinforcements among biodegradable composites (Avella et al. 2005; Azeredo 2009; Sothornvit et al. 2009;
Arora and Padua 2010; Rhim et al. 2013; Kanmani and Rhim 2014; Azevedo et al.
2015). However, other types of clays such as laponite or hectorite have also been
used as nanocomposites (Doblhofer et al. 2016; Valencia et al. 2018). The processing capacity, the low cost and the availability make the Mt a good candidate as a
nanoreinforcing agent (Azeredo 2009; Souza et al. 2012; Kanmani and Rhim 2014).
However, exfoliated structure is necessary for the formation of improved barrier
properties, and as explained in Nielsen’s theory, homogeneously distributed clay
sheets create a longer and more tortuous pathway which makes gas transfer difficult
(Azeredo 2009; Arora and Padua 2010). As shown in Table 6.2, the gas and water
vapor barrier properties of nanocomposite films are improved with the increasing
amounts of Mt. Although above a critical limit, the homogeneity of the clay within
the matrix is destroyed and no further improvement in the barrier properties is
observed (Tunc et al. 2007; Luecha et al. 2010; Alboofetileh et al. 2013). In some
cases, the amount of clay is kept constant and the effect of other ingredients such as
plasticizers and metal/metal oxide NPs are evaluated, or nanocomposites are compared with the pure matrices or commercial polymers (Sothornvit et al. 2009; Souza
et al. 2012; Heydari et al. 2013; Kanmani and Rhim 2014; Doblhofer et al. 2016).
Doblhofer et al. (2016) found that bionanocomposites composed of silk spidroin
and Na-hectorite had better water vapor and oxygen barrier properties compared to
the commercial PET and EVOH films, respectively (Doblhofer et al. 2016). In contrast to other protein-based nanocomposites, the spidroin-hectorite nanocomposites
were not sensitive to the relative humidity variations. López et al. (2015) incorporated talc NPs into TPS-based thermo-sealed packages, resulting in materials with
better water vapor and oxygen barrier properties.
These authors also tested the packaging performance during the storage of cherry
tomatoes and observed that the sealing of the packages with talc NPs was better than
pure TPS.
In order to improve the σ max and ε b values, glycerol can be added as a plasticizer
into the nanocomposites containing clay NPs (Souza et al. 2012; Heydari et al.
2013). However, the improvement in mechanical properties is insignificant, since
the water vapor and oxygen vapor barrier properties are destroyed with the increase
in the glycerol content (Souza et al. 2012).
The transparency of nanocomposite films due to the incorporation of clay NPs
remains constant or decreased significantly (Luecha et al. 2010; Abdollahi et al. 2013;
Heydari et al. 2013; Kanmani and Rhim, 2014; Rhim and Wang, 2014; Zolfi et al.
2014; Doblhofer et al. 2016). The reduction in transparency is attributed to the blocking
of light transmission by NPs (Kanmani and Rhim 2014; Rhim and Wang 2014).
Nonetheless, the addition of plasticizers such as glycerol can improve the transparency
of the nanocomposites containing clay NPs (Heydari et al. 2013).
6 Functional Biobased Composite Polymers for Food Packaging Applications