140
6 Micromechanical Models of PVA-Based Bionanocomposite Films
nanotube (CNT) composites [3] and silk fibroin/graphene oxide (GO) nanocomposites [4], or underpredicted for polyamide 66 (PA66)/calcium carbonate (CaCO 3 )
nanocomposites [5]. Such drawbacks in modelling work for polymer nanocomposites are inevitably associated with the absence of interphase features and properties. Many recent attempts have been made by incorporating interphase regions
as the third phase within available micromechanical models like Mori–Tanaka
model [6] and Maxwell model [7] with little success. This can be attributed to
simple assumption that the interphase can be one-dimensional transitional material
phase surrounding nanofillers with uniform interphase thickness and regular shapes
while in reality three-dimensional (3D) irregular-shape interphase with non-uniform
thickness generally occurs in the material morphology of nanocomposites [8].
In order to consider the benefit of real interphase effect in nanocomposite
modelling work, interphase volume fraction is one of the key interphase material
parameters to be predetermined. For instance, with the addition of 5 vol% monodispersed spherical nanoparticles (particle diameter of 10 nm and interphase thickness of 0.5 nm), the volume fraction of interphase can be as high as 25 vol% [9].
More impressively, when particle diameter is reduced to less than 5 nm, the volume
fraction of interphase is increased by over 50 vol%, as compared to that of particles [9]. However, a full understanding for the effect of interphase volume fraction on elastic modulus of bulk nanocomposites still remains challenging owing
to complex interphase network structures and an overlapping potential to neighbouring interfacial layers. The main objective of this chapter is to investigate effect of
different nanofiller shapes and structures on nanomechanical properties of 3D interphase for finally prepared PVA-based bionanocomposites. Moreover, mechanical
properties of PVA-based bionanocomposite were predicted by considering experimentally measured dimensions and volume fraction of interphase. In particular,
polyvinyl alcohol (PVA) was selected as typical biopolymer after a great environmental concern associated with using conventional non-degradable petroleum-based
polymers. Additionally, three different types of nanoparticles including Cloisite 30B
clays, halloysite nanotubes (HNTs) and nanodiameter bamboo charcoals (NBCs)
were chosen as typical nanofillers in different shapes and sizes.
6.2 Theory
6.2.1 Micromechanical Models Based on Nominal
and Effective Volume Fractions
In general, the prediction of elastic modulus in case of unidirectional or randomly
distributed filler reinforced composites can be investigated by means of conventional
composite theoretical models such as Halpin–Tsai model. Such a model could also be
employed to estimate elastic moduli of PVA-based bionanocomposites with different
nanofiller orientation states, namely well-aligned and randomly oriented nanofillers,
6 Micromechanical Models of PVA-Based Bionanocomposite Films
nanotube (CNT) composites [3] and silk fibroin/graphene oxide (GO) nanocomposites [4], or underpredicted for polyamide 66 (PA66)/calcium carbonate (CaCO 3 )
nanocomposites [5]. Such drawbacks in modelling work for polymer nanocomposites are inevitably associated with the absence of interphase features and properties. Many recent attempts have been made by incorporating interphase regions
as the third phase within available micromechanical models like Mori–Tanaka
model [6] and Maxwell model [7] with little success. This can be attributed to
simple assumption that the interphase can be one-dimensional transitional material
phase surrounding nanofillers with uniform interphase thickness and regular shapes
while in reality three-dimensional (3D) irregular-shape interphase with non-uniform
thickness generally occurs in the material morphology of nanocomposites [8].
In order to consider the benefit of real interphase effect in nanocomposite
modelling work, interphase volume fraction is one of the key interphase material
parameters to be predetermined. For instance, with the addition of 5 vol% monodispersed spherical nanoparticles (particle diameter of 10 nm and interphase thickness of 0.5 nm), the volume fraction of interphase can be as high as 25 vol% [9].
More impressively, when particle diameter is reduced to less than 5 nm, the volume
fraction of interphase is increased by over 50 vol%, as compared to that of particles [9]. However, a full understanding for the effect of interphase volume fraction on elastic modulus of bulk nanocomposites still remains challenging owing
to complex interphase network structures and an overlapping potential to neighbouring interfacial layers. The main objective of this chapter is to investigate effect of
different nanofiller shapes and structures on nanomechanical properties of 3D interphase for finally prepared PVA-based bionanocomposites. Moreover, mechanical
properties of PVA-based bionanocomposite were predicted by considering experimentally measured dimensions and volume fraction of interphase. In particular,
polyvinyl alcohol (PVA) was selected as typical biopolymer after a great environmental concern associated with using conventional non-degradable petroleum-based
polymers. Additionally, three different types of nanoparticles including Cloisite 30B
clays, halloysite nanotubes (HNTs) and nanodiameter bamboo charcoals (NBCs)
were chosen as typical nanofillers in different shapes and sizes.
6.2 Theory
6.2.1 Micromechanical Models Based on Nominal
and Effective Volume Fractions
In general, the prediction of elastic modulus in case of unidirectional or randomly
distributed filler reinforced composites can be investigated by means of conventional
composite theoretical models such as Halpin–Tsai model. Such a model could also be
employed to estimate elastic moduli of PVA-based bionanocomposites with different
nanofiller orientation states, namely well-aligned and randomly oriented nanofillers,