1.4 Nanofillers for Bionanocomposites
17
system, stimulate acupuncture meridians of bodies, promote metabolism and balance
the body pH level and so on [115].
BCs, due to their carbon content, also possess certain electrical conductivity and
magnetic properties [115]. Electromagnetic pollution becomes a critical issue owing
to the excessive applications in electronic technologies. It has been reported that
in a range of 10–1000 MHz, composite materials reinforced with BCs (thickness:
3 mm) have electromagnetic shielding effect of 45–75 dB [115]. Additionally, BCs
have a special feature to prevent them from electromagnetic radiation, which can
motivate manufacturers to develop man-made boards for IT applications. BCs are
also considered as good materials in manufacturing supercapacitors and lithium-ion
batteries [115]. In a nanocomposite system, BC morphology displays a wide range
of pore distributions from less than 1 nm to 1 μm [110]. BC structure comprises
parenchyma, which is the basic unit inside bamboo with the characteristic of rough
wall surfaces, and with a large number of rough-walled pores inside BCs, polymeric
chains tend to easily penetrate into internal BC pores [117] to form strong mechanical
bonding in addition to the hydrogen bonding of pores. Hence, mechanical properties of resulting nanocomposites can be improved accordingly owing to the effective
interfacial bonding between fillers and polymer matrices. Nevertheless, the selection
of polymer matrices also plays a leading role in the preparation of nanocomposites in
addition to BCs. Polymeric behaviour in a porous medium is associated with capillary forces, which enables to prevent polymeric chains from entering into internal
pores [117]. According to the Laplace theory [117, 118], the strength of capillary
forces can depend on surface chemistry and physical properties of polymers. When
hydrophilic media are selected, applied positive capillary pressures drive polymeric
chains into BC pores to form both mechanical and chemical bondings, which is why
PVA has been chosen in this study. On the contrary, the surfaces of hydrophobic media
generate negative capillary pressures and thus hinder the entry of polymeric chains
into BC pores, leading to typical phase separation in a nanocomposite system. Such
a mechanism can be interpreted as the debonding effect in polymer/BC composites including PLA/BC composites [31], ultrahigh molecular-weight polyethylene
(UHMWPE)/BC composites [119] and polyaniline (PANI)/BC composites [120].
1.4.4 Other Popular Nanofillers
Other nanofillers worth mentioning include CNTs, nanocellulose and graphene
oxides (GOs). CNTs are one of the most interesting carbon allotropes in the form of
cylinders arranged by rolling graphene sheets [121], which results in the deformation of their sp
2 hybrid orbitals with the formation of a σ-π rehybridisation structure
[121]. The main feature of the rehybridisation structure is that the confinement of π
electrons offers unique and extraordinary properties of CNTs such as high Young’s
modulus at 1200 GPa and tensile strength at 150 GPa [122]. Enormous interest has
been shown on CNTs owing to their diverse potential for supercapacitors [123],
actuators in robotic manufacturing [124] and storage energy (e.g. hydrogen storage)
17
system, stimulate acupuncture meridians of bodies, promote metabolism and balance
the body pH level and so on [115].
BCs, due to their carbon content, also possess certain electrical conductivity and
magnetic properties [115]. Electromagnetic pollution becomes a critical issue owing
to the excessive applications in electronic technologies. It has been reported that
in a range of 10–1000 MHz, composite materials reinforced with BCs (thickness:
3 mm) have electromagnetic shielding effect of 45–75 dB [115]. Additionally, BCs
have a special feature to prevent them from electromagnetic radiation, which can
motivate manufacturers to develop man-made boards for IT applications. BCs are
also considered as good materials in manufacturing supercapacitors and lithium-ion
batteries [115]. In a nanocomposite system, BC morphology displays a wide range
of pore distributions from less than 1 nm to 1 μm [110]. BC structure comprises
parenchyma, which is the basic unit inside bamboo with the characteristic of rough
wall surfaces, and with a large number of rough-walled pores inside BCs, polymeric
chains tend to easily penetrate into internal BC pores [117] to form strong mechanical
bonding in addition to the hydrogen bonding of pores. Hence, mechanical properties of resulting nanocomposites can be improved accordingly owing to the effective
interfacial bonding between fillers and polymer matrices. Nevertheless, the selection
of polymer matrices also plays a leading role in the preparation of nanocomposites in
addition to BCs. Polymeric behaviour in a porous medium is associated with capillary forces, which enables to prevent polymeric chains from entering into internal
pores [117]. According to the Laplace theory [117, 118], the strength of capillary
forces can depend on surface chemistry and physical properties of polymers. When
hydrophilic media are selected, applied positive capillary pressures drive polymeric
chains into BC pores to form both mechanical and chemical bondings, which is why
PVA has been chosen in this study. On the contrary, the surfaces of hydrophobic media
generate negative capillary pressures and thus hinder the entry of polymeric chains
into BC pores, leading to typical phase separation in a nanocomposite system. Such
a mechanism can be interpreted as the debonding effect in polymer/BC composites including PLA/BC composites [31], ultrahigh molecular-weight polyethylene
(UHMWPE)/BC composites [119] and polyaniline (PANI)/BC composites [120].
1.4.4 Other Popular Nanofillers
Other nanofillers worth mentioning include CNTs, nanocellulose and graphene
oxides (GOs). CNTs are one of the most interesting carbon allotropes in the form of
cylinders arranged by rolling graphene sheets [121], which results in the deformation of their sp
2 hybrid orbitals with the formation of a σ-π rehybridisation structure
[121]. The main feature of the rehybridisation structure is that the confinement of π
electrons offers unique and extraordinary properties of CNTs such as high Young’s
modulus at 1200 GPa and tensile strength at 150 GPa [122]. Enormous interest has
been shown on CNTs owing to their diverse potential for supercapacitors [123],
actuators in robotic manufacturing [124] and storage energy (e.g. hydrogen storage)