1.5 Processing of Bionanocomposites
21
successfully implemented to various nanocomposites systems such as PVA/HNT
nanocomposite fibres [156] and PVA/BC composite fibres [157]. In recent years,
electrophoretic deposition (EPD) method has also gained a particular attention for
the deposition of composite films with HNT inclusions. EPD involves the motion
of charged particles in suspension to an electrode leading to the formation of a
deposit on the electrode surface induced by uniform electrical-field effect [158]. The
main advantage of this method includes its potential to produce uniform films with
controlled thickness, as well as for the deposition on substrates with a complex shape
and high deposition rate. Such a procedure has been successfully used to fabricate
chitosan/HNT nanocomposites [159, 160].
1.6 Bionanocomposite Properties and Characterisation
1.6.1 Morphological Structure
It should be emphasised that mixing a polymer and inorganic nanofillers together
does not necessarily produce a nanocomposite. In an immiscible system, poor interfacial bonding between organic and inorganic components yields the separation of
nanocomposite constituents into discrete phases in final structures. This separation
induces the same properties in so-called nanocomposites as those of microcomposites
[142]. In the case of a miscible system, two types of nanocomposites, namely intercalated and exfoliated, (i.e. delaminated) nanocomposites can be achieved, as shown in
Fig. 1.13. The determination of final nanocomposite type in terms of intercalated or
exfoliated structures depends primarily on synthetic techniques and chemical nature
of nanocomposite constituents. In addition, intercalated structures are formed when
polymeric chains are penetrated into silicate layers, resulting in a multilayered structure of polymer matrices and inorganic fillers. In this case, polymeric chains expand
the interlayer spacing of layered silicates by 20–30 Å. In contrast, exfoliated structures occur when layered silicates are peeled apart and individually separated with an
increase in interlayer spacing up to 80–100 Å or above, which is most likely to be associated with the radius of gyration for polymers [142, 161, 162]. Exfoliated structures
are generally more favourable because clay dispersibility is significantly promoted as
individual particles/fillers leading to greatly enhanced mechanical properties of final
nanocomposites. However, it is more difficult to achieve such an ideal structure since
the majority of nanocomposites reported in the literatures possess either intercalated
or a mix of intercalated and exfoliated structures [136–138, 140]. The reason for this
phenomenon is that layered silicates are highly anisotropic with lateral dimensions
of 100-1000 nm. As a result, even when separated by the high interlayer spacing,
silicate layers cannot be completely and randomly dispersed within polymer matrices
[162]. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are the
21
successfully implemented to various nanocomposites systems such as PVA/HNT
nanocomposite fibres [156] and PVA/BC composite fibres [157]. In recent years,
electrophoretic deposition (EPD) method has also gained a particular attention for
the deposition of composite films with HNT inclusions. EPD involves the motion
of charged particles in suspension to an electrode leading to the formation of a
deposit on the electrode surface induced by uniform electrical-field effect [158]. The
main advantage of this method includes its potential to produce uniform films with
controlled thickness, as well as for the deposition on substrates with a complex shape
and high deposition rate. Such a procedure has been successfully used to fabricate
chitosan/HNT nanocomposites [159, 160].
1.6 Bionanocomposite Properties and Characterisation
1.6.1 Morphological Structure
It should be emphasised that mixing a polymer and inorganic nanofillers together
does not necessarily produce a nanocomposite. In an immiscible system, poor interfacial bonding between organic and inorganic components yields the separation of
nanocomposite constituents into discrete phases in final structures. This separation
induces the same properties in so-called nanocomposites as those of microcomposites
[142]. In the case of a miscible system, two types of nanocomposites, namely intercalated and exfoliated, (i.e. delaminated) nanocomposites can be achieved, as shown in
Fig. 1.13. The determination of final nanocomposite type in terms of intercalated or
exfoliated structures depends primarily on synthetic techniques and chemical nature
of nanocomposite constituents. In addition, intercalated structures are formed when
polymeric chains are penetrated into silicate layers, resulting in a multilayered structure of polymer matrices and inorganic fillers. In this case, polymeric chains expand
the interlayer spacing of layered silicates by 20–30 Å. In contrast, exfoliated structures occur when layered silicates are peeled apart and individually separated with an
increase in interlayer spacing up to 80–100 Å or above, which is most likely to be associated with the radius of gyration for polymers [142, 161, 162]. Exfoliated structures
are generally more favourable because clay dispersibility is significantly promoted as
individual particles/fillers leading to greatly enhanced mechanical properties of final
nanocomposites. However, it is more difficult to achieve such an ideal structure since
the majority of nanocomposites reported in the literatures possess either intercalated
or a mix of intercalated and exfoliated structures [136–138, 140]. The reason for this
phenomenon is that layered silicates are highly anisotropic with lateral dimensions
of 100-1000 nm. As a result, even when separated by the high interlayer spacing,
silicate layers cannot be completely and randomly dispersed within polymer matrices
[162]. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are the