Agriculture Reference
In-Depth Information
Some of the problems of bio-based plastics, such as hydrophilicity, poor barrier,
conductivity and inferior biocompatibility, narrow processing window, or low heat
deflection temperatures, can be overcome by the use of bio-nanocomposites (Reddy
et al.
2013
). The rheological, thermal, mechanical, and barrier properties of the base
biopolymers are improved due to the high surface area and high aspect ratio of the
nanoparticles, as happened with the conventional polymers.
Nanocomposites for food packaging applications have to resist the stress of food
processing (sometimes at high temperatures), storage, and transportation (Sinha
Ray and Okamoto
2003
; Thostenson et al.
2005
). Recently, some biodegradable
polymer nanocomposites with good properties for a wide range of applications have
been prepared and characterized (Sinha Ray and Bousmina
2005
). Layered silicate
has been used as filler in biodegradable natural and synthetic polymers; this has
increased their desirable properties (barrier and mechanical properties) while
retaining their biodegradability in a comparatively economic way. Typical biode-
gradable polymers are those based on polylactic acid (PLA), polycaprolactone
(PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), poly(butylene
succinate) (PBS), starch or thermoplastic starch (TPS), and chemically modified
cellulose. And the nanomaterials used to prepare the nanocomposites are different
kinds of clays or organically modified nanoclays, natural biopolymers like chitosan,
and different metals and metal oxides.
Biodegradability is one of the most controversial and interesting issues in the
bio-nanocomposite materials. Biodegradation of biodegradable polymers may
comprise many different processes like loss of mechanical properties, fragmenta-
tion, or at times degradation through the action of microorganisms such as algae,
bacteria, and fungi. The degradation can be due to oxidation or to hydrolysis
catalyzed by enzymes. The main advantage in the use of biopolymers is their
biodegradability, so it
is expected that
the bio-nanocomposites retain the
biodegradability rate.
Many authors have studied the degradability of different bio-nanocomposites
with contradictory results. The first studies were made by Tetto et al. (
1999
), and
they showed that PCL/clay nanocomposites showed improved biodegradability
compared to pure PCL. Different posterior studies (Zhou and Xanthos
2008
;
Sinha Ray et al.
2003a
) with a series of biodegradation tests for PLA/clay
nanocomposites (using soil compost tests at 58
C, respirometric test by measuring
CO
2
evolution during biodegradation, and the molecular weight and residual weight
with time) concluded that the biodegradability of PLA nanocomposite was signif-
icantly enhanced compared to neat PLA. Nieddu et al. (
2009
) also reported similar
results of enhanced biodegradation (up to 10 times when measuring the lactic acid
release or 22 times when measuring the weight change) of PLA-based
nanocomposites using five different types of nanoclays and different concentrations
of nanoclay using a melt intercalation method; it was found that the degradation rate
depended on both variables. Paul et al. (
2005
) used phosphate buffer solution of
PLA and PLA/organoclay nanocomposite films using three different types of
organoclays, and they also found an improvement in biodegradability of the
nanocomposites compared to the neat PLA. They also found that as the nanoclay
