Civil Engineering Reference
In-Depth Information
Biopolymer-based nanocomposites have also been the subject of recent reviews [35-
37]. It has been demonstrated that the incorporation of cellulose nanostructures in
dif erent kinds of polysaccharides and protein biopolymers results in enhanced mois-
ture resistance without reducing their huge advantages of biodegradability [38, 39].
Nevertheless, several factors have to be taken into account; for example, the processing
of starch-based materials with nanocellulose by traditional melt processing is always
critical because the agglomeration of i ber materials has to be controlled [40]. h ere
are very few research reports on the conventional melt processing of starch/cellulose
nanocomposites.
9.2.1
Bioplastics-Based Nanocellulosic Composites
9.2.1.1
h ermoplastic Starch (TPS)-Based Nanocomposites
h ermoplastic starch is a very attractive source for the development of biodegradable
plastics. It is one of the lowest cost biodegradable materials currently available on the
global market [41, 42]. It can be found in the form of discrete semicrystalline par-
ticles, whose size, shape, morphology and composition depend on the botanical origin
(corn, potato, maize, cassava, etc.). At er gelatinization (starch granules disruption),
TPS shows similar properties and processing conditions to those of polyolei ns. Starch
is composed mainly of two glucopyranose homopolymers: amylose and amylopectin.
While it is possible to produce plastics from native starch, they are not suitable for
use as packaging material due to their poor mechanical properties and high moisture
susceptibility [43]. Generally, the incorporation of nanoi llers such as cellulose nano-
crystals or clay platelets into thermoplastic starch produces a marked improvement in
the mechanical properties. h e characteristics of the interfacial bonding between the
starch molecules and the i ller nanoparticles are critical to the nanocomposite material
performance [44-47]. In this regard, the great chemical similarity and compatibility
between starch and cellulose molecules promises a good reinforcing ef ect. Starch and
cellulose molecules are almost identical. h e only dif erence in their structure is the
position of the molecular bond between D-glucose units: a-1,4 for starch and b-1,4 for
cellulose.
Dif erent types of starch have been used to prepare cellulose nanocomposites and
have been reported by several researches. Most of the literature refers to the prepa-
ration of TPS/CNW nanocomposite i lms by solvent casting. h is technique allows
the investigation of dif erent compositions and the inl uence of other variables to be
studied. Moran
et al.
[48] reported the incorporation of sisal i ber-derived nanocel-
lulose i bers into potato starch. h e incorporation of cellulose nanoi bers led to an
important improvement in the mechanical properties of starch i lms, even for i ber
contents as low as 5 wt%, increasing more than 100% the elastic modulus and 10%
the strength when compared to native starch. Savadekar and Mhaske [49] prepared
TPS/CNW composites by solvent casting. Nanocellulose was synthesized from cotton
i bers. h ey found improved mechanical properties at very low CNW concentrations
(< 0.5%), although they started to deteriorate easily at higher loads. h e most interest-
ing i nding was the improved water and oxygen barrier properties of the TPS matrix
[49] . Soykeabkaewa
et al.
[50] compared the reinforcing ef ect of dif erent contents of
