Nanocomposites of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 100

manipulation has to be made. 19 This is generally achieved by ion-exchange
reactions using cationic surfactants such as primary, secondary, tertiary, and
quaternary alkylammonium or alkylphosphonium. 9 The presence of these
cations in the organosilicates is suggested to have a reducing effect on the
inorganic host's surface energy, thereby improving the wetting property of
the polymer matrix, resulting in a large interlayer spacing. 9
Consequently, layered silicate nanofillers are said to be indispensable in
PHA nanocomposites technology. 19 In general, the physico-mechanical
properties of nanocomposite materials are greatly influenced by the degree
of mixing between the two phases, and the quality of structure intercalation
depends on the extent to which the organic component and the inorganic
components are able to interact and thus be made compatible. In the
following sections, different methods of PHA nanocomposite production,
characterization and applications are discussed.

d n 2 r 4 n g | 8

5.2 Production of PHA Nanocomposites
A number of methods have frequently been employed in the production
of nanocomposite materials. These include solution intercalation, 11 melt
intercalation, 21 polymerization, 22 sol-gel, 23 deposition, 24 magnetron sput-
tering, 25 laser, 26,27 ultrasonication, 28 supercritical fluid, 29,30 etc.InPHA
nanocomposite fabrication, solution intercalation and melt intercalation
methods are the most widely explored procedures. 3,7 However, use of in situ
intercalative polymerization, supercritical fluids and electrospinning are
shown to be promising and emerging techniques. The performance and
quality of a nanocomposite depends on how well the nanofillers disperse or
blend into the matrix. Therefore, these methods constitute different strat-
egies to improve the composites' thermo-mechanical and physico-chemical
properties by enhancing ecient interactions between the nanofiller and the
polymer matrices.
When using nanofillers such as layered silicate, different morphologies
could be observed depending on how well the nanofillers were dispersed
in the matrix. Poor dispersion of nanofillers often results in aggregate
(tactoids) morphologies (Figure 5.1).
However, interactions between the nanofillers with some of the extended
polymer chains result in an intercalated nanocomposite with an alternate
arrangement of polymer and layered nanofiller (Figure 5.1). Absolute and
homogeneous dispersion of nanofillers in the polymer matrix gives a
nanocomposite with exfoliated morphological characteristics (Figure 5.1).
Previously, this ordered exfoliation was thought to be induced by steric
interactions. 10,31 However, some researchers, such as Zhang et al. 32 sug-
gested that the dispersion of the polymeric side chain into the nanofillers'
layered spaces was the main cause of exfoliation.
The surface of hydrophilic nanofillers is usually functionalized (modified)
so as to promote a homogeneous dispersion throughout the polymer, and to
enhance interactions within the polymeric matrix, resulting in improved

.