118
(around 50 g/m
2
/day). In this amount of cellulose, WVTR was similar to the film
containing pristine PLA.
The type of cellulose nanomaterial also affects the WVTR values of composite
films. Bilbao-Sainz et al. (2011) studied HPMC based films containing nanofibrillated cellulose (NFC), modified nanofibrilated cellulose (NFCt) and cellulose
nanowhiskers produced from eucalyptus sulphite wood pulp. No significant difference between the control film and the composite films containing NFC, NFCt and
nanowhiskers were observed at a level of 2.66% (of HPMC), but the lowest WVTR
value was obtained for the composite films containing NFCt and nanowhiskers at a
level of 13.33% nanocellulose (of HPMC) (Bilbao-Sainz et al. 2011). When the
thicknesses of these films were considered, the lowest WVP belonged to the films
containing 2.66% and 13.33% nanocellulose whisker added samples due to
increased tortuosity.
Qazanfarzadeh and Kadivar (2016) also observed that the amount of nanocellulose in whey protein isolate (WPI)-based nanocomposite films had a significant
reduction effect on the level of incorporation of WVP up to 5%, but no further
improvement on water vapor barrier properties was observed at 7.5% nanocellulose
content. These authors stated that the WVP values remained constant at a level
greater than 5% of the nano-fillers. This is due to the agglomeration and non-homogeneous distribution of nanocellulose within the WPI based film, which was also
confirmed by SEM images (Qazanfarzadeh and Kadivar 2016). A similar behavior
was observed by Reddy and Rhim (2014) for agar-based nanocomposites. The WVP
values of the composites decreased significantly containing up to 3% of the content
of cellulose nanocrystals. The WVP improvement was lost above this content, and
increased to 1.86 × 10
−9
gm/m
2
Pa.s for composite film containing 10% nanocrystals. The agglomeration behavior was also confirmed by SEM images for 5% and
10% cellulose-containing films. Savadekar et al. (2012) also reported that the
WVTR for kappa-carrageenan films decreased from 0.0042 g/m
2
h to 0.0001 g/m
2
h
when the amount of nanocellulose filler increased from 0 to 0.5%. However, it had
increased to 0.0021 g/m
2
h for a nanocellulose content of 1%.
The WVP of composite films are also quite dependent on the different components of the matrix and the nano-fillers. For example, Pereda et al. (2014) incorporated olive oil into nanocellulose-reinforced Cs-based films, which had a
comparatively lower WVP than the nanocellulose-reinforced Cs-based films without olive oil. The addition of nanocellulose improved the water vapor barrier properties of Cs composite films, and their combination with 10% olive oil resulted in a
further improvement of the barrier properties (Pereda et al. 2014).
The homogeneous dispersion of nanocellulose can be followed by means of
SEM images, which also provide information about the surface roughness of the
film. Nanocellulosic materials begin to agglomerate above a certain content, which
increases the roughness and has a detrimental effect on the film integrity (Khan
et al. 2010; Abdollahi et al. 2013; Celebi and Kurt 2015; Shankar and Rhim 2016b).
The agglomerated particles can decrease the transparency, and σ max and strain values
of the films, while there is an increase in water vapor transmission and oxygen
transmission rates (Savadekar et al. 2012; Reddy and Rhim, 2014; Shankar and
H. Cakmak and E. Sogut
(around 50 g/m
2
/day). In this amount of cellulose, WVTR was similar to the film
containing pristine PLA.
The type of cellulose nanomaterial also affects the WVTR values of composite
films. Bilbao-Sainz et al. (2011) studied HPMC based films containing nanofibrillated cellulose (NFC), modified nanofibrilated cellulose (NFCt) and cellulose
nanowhiskers produced from eucalyptus sulphite wood pulp. No significant difference between the control film and the composite films containing NFC, NFCt and
nanowhiskers were observed at a level of 2.66% (of HPMC), but the lowest WVTR
value was obtained for the composite films containing NFCt and nanowhiskers at a
level of 13.33% nanocellulose (of HPMC) (Bilbao-Sainz et al. 2011). When the
thicknesses of these films were considered, the lowest WVP belonged to the films
containing 2.66% and 13.33% nanocellulose whisker added samples due to
increased tortuosity.
Qazanfarzadeh and Kadivar (2016) also observed that the amount of nanocellulose in whey protein isolate (WPI)-based nanocomposite films had a significant
reduction effect on the level of incorporation of WVP up to 5%, but no further
improvement on water vapor barrier properties was observed at 7.5% nanocellulose
content. These authors stated that the WVP values remained constant at a level
greater than 5% of the nano-fillers. This is due to the agglomeration and non-homogeneous distribution of nanocellulose within the WPI based film, which was also
confirmed by SEM images (Qazanfarzadeh and Kadivar 2016). A similar behavior
was observed by Reddy and Rhim (2014) for agar-based nanocomposites. The WVP
values of the composites decreased significantly containing up to 3% of the content
of cellulose nanocrystals. The WVP improvement was lost above this content, and
increased to 1.86 × 10
−9
gm/m
2
Pa.s for composite film containing 10% nanocrystals. The agglomeration behavior was also confirmed by SEM images for 5% and
10% cellulose-containing films. Savadekar et al. (2012) also reported that the
WVTR for kappa-carrageenan films decreased from 0.0042 g/m
2
h to 0.0001 g/m
2
h
when the amount of nanocellulose filler increased from 0 to 0.5%. However, it had
increased to 0.0021 g/m
2
h for a nanocellulose content of 1%.
The WVP of composite films are also quite dependent on the different components of the matrix and the nano-fillers. For example, Pereda et al. (2014) incorporated olive oil into nanocellulose-reinforced Cs-based films, which had a
comparatively lower WVP than the nanocellulose-reinforced Cs-based films without olive oil. The addition of nanocellulose improved the water vapor barrier properties of Cs composite films, and their combination with 10% olive oil resulted in a
further improvement of the barrier properties (Pereda et al. 2014).
The homogeneous dispersion of nanocellulose can be followed by means of
SEM images, which also provide information about the surface roughness of the
film. Nanocellulosic materials begin to agglomerate above a certain content, which
increases the roughness and has a detrimental effect on the film integrity (Khan
et al. 2010; Abdollahi et al. 2013; Celebi and Kurt 2015; Shankar and Rhim 2016b).
The agglomerated particles can decrease the transparency, and σ max and strain values
of the films, while there is an increase in water vapor transmission and oxygen
transmission rates (Savadekar et al. 2012; Reddy and Rhim, 2014; Shankar and
H. Cakmak and E. Sogut