Effect of clay type on WVP
The WVP values, along with actual RH conditions at the
undersides of films during testing, of the agar and agar-based
nanocomposite films are shown in Table 5.
The WVP values of
neat agar film were 2.22±0.19×10−9 g·m/m2·s·Pa.
The WVP of
nanocomposite films changed significantly (P < 0.05) depending
on the type of nanoclays used.
The WVP of nanocomposite films
compounded with natural MMT, that is, Cloisite Na+ decreased,
while those of films composited with organically modified nanoclays,
that is, Cloisite 30B and Cloisite 20A, increased slightly.
This result is mainly attributed to the surface hydrophilicity or
hydrophobicity of the clay types used.
Expectedly, hydrophilic
Cloisite Na+ is more compatible with hydrophilic agar polymer
matrix than the other organoclays resulting in well dispersed in
the polymer matrix and indicating lower WVP with agar/Cloisite
Na+ nanocomposite films. Between the organically modified nanoclays,
Cloisite 30B was more effective in reducing WVP than
Cloisite 20A, since the former is more hydrophilic than the latter.
This result also indicates that Cloisite Na+ is more compatible with agar polymer matrix than the other clays.
Lim and others
also found the WVP of G. corneum films decreased significantly
after compositing with nanoclays, which was dependent on the
nanoclay types used. They reported the WVP of the G. corneum
films decreased from 1.59 × 10−9 to 1.19 × 10−9 and 1.43 ×
10−9 g·m/m2·s·Pa for the Cloisite Na+ and Cloisite 30B
nanocomposite films, respectively.
Sothornvit and others (2009)
also found the same trend of decrease in WVP of WPI/clay nanocomposite films, in which WPI/Cloisite Na+ showed the
most decrease in WVP followed by WPI/Cloisite 30B, while
WPI/Cloisite 20A did not show significant change in WVP compared
to the neat WPI films.
Their results are coincided with those
of the present study.
The increase in water vapor barrier property
of polymer/clay nanocomposite films is mainly attributed to
the tortuous path for water vapor diffusion due to the impermeable
clay layers distributed in the polymer matrix consequently