18
1 Introduction to PVA-Based Bionanocomposite Films
[125]. In a nanocomposites system, CNTs have the capability to improve mechanical
and thermal properties, fire inflammability, moisture resistance and barrier properties due to their high-performance functionality [126]. It is worth noting that CNTs
possess the ability to reinforce both thermosets and thermoplastics [127] in order to
produce good mechanical properties and good affinity to chemical compounds [128].
Nevertheless, the critical issue currently being encountered is typical CNT agglomeration in the form of bundles when polymer/CNT nanocomposites are prepared.
Such a phenomenon arises from the high aspect ratio of CNTs together with their
strong Van der Waals interaction, particularly at the high CNT loadings.
Nanocellulose is the other popular nanofillers, which exhibits several excellent
properties such as high aspect ratio, low density at 1.6 g cm
−3 , very low coefficient of
thermal expansion and high tensile strength about 500 MPa [129]. Such unique properties induce numerous applications including antimicrobial films, transparent films,
drug delivery, fibres and textiles, supercapacitors and batteries [129]. Cellulose can
be classified as microfibrillated celluloses (MFCs), nanofibrillated celluloses (NFCs)
and CNCs. However, the hydrophilic nature of nanocellulose can limit its use as the
reinforcements in nanocomposite systems where hydrophobic polymers are generally
deemed as matrices. This is because blending nanocelluloses with hydrophobic polymers can yield weak interfacial bonding between polymer matrices and nanofillers,
resulting in increasing water uptake and filler aggregation with respect to hydrogen
bonding [130].
Graphene oxides (GOs) are two-dimensional nanomaterials synthesised from
natural graphite. Such nanosheets can be easily prepared from graphite flakes by
thermal oxidation, as recommended by Hummers [131]. GOs possess high mechanical properties (e.g. elastic modulus: 0.25 TPa), binding potential, high aspect
ratio, high flexibility and superior processibility [132]. Moreover, due to their good
hydrophilic characteristic, GOs can be easily exfoliated into monolayer nanosheets
stably dispersed in water, primarily due to plenty of hydrophilic oxygenated groups
[133]. These functional groups play a significant role in the improvement of GO
dispersion in solvents or within polymer matrices through covalent or non-covalent
bonding [133]. However, a high tendency of GO agglomeration can limit their use
at high nanofiller content levels. Recently, Chang et al. [134] examined the toxicity
and biocompatibility of GOs on A549 cells, which suggested that GOs induced the
oxidative stress and a slight decrease in cell viability at the high GO content.
1.5 Processing of Bionanocomposites
One of most common methods used for bionanocomposite preparation is solution
casting. Its first step involves nanoparticle dispersion in either water or organic
solvents by stirring or ultrasonic treatment. Subsequently, polymers and nanoparticles are mixed and stirred together in a solution. The final step is then to evaporate
the solvents in order to produce final nanocomposites. Solution casting has been
successfully employed in the manufacture of various bionanocomposites such as
1 Introduction to PVA-Based Bionanocomposite Films
[125]. In a nanocomposites system, CNTs have the capability to improve mechanical
and thermal properties, fire inflammability, moisture resistance and barrier properties due to their high-performance functionality [126]. It is worth noting that CNTs
possess the ability to reinforce both thermosets and thermoplastics [127] in order to
produce good mechanical properties and good affinity to chemical compounds [128].
Nevertheless, the critical issue currently being encountered is typical CNT agglomeration in the form of bundles when polymer/CNT nanocomposites are prepared.
Such a phenomenon arises from the high aspect ratio of CNTs together with their
strong Van der Waals interaction, particularly at the high CNT loadings.
Nanocellulose is the other popular nanofillers, which exhibits several excellent
properties such as high aspect ratio, low density at 1.6 g cm
−3 , very low coefficient of
thermal expansion and high tensile strength about 500 MPa [129]. Such unique properties induce numerous applications including antimicrobial films, transparent films,
drug delivery, fibres and textiles, supercapacitors and batteries [129]. Cellulose can
be classified as microfibrillated celluloses (MFCs), nanofibrillated celluloses (NFCs)
and CNCs. However, the hydrophilic nature of nanocellulose can limit its use as the
reinforcements in nanocomposite systems where hydrophobic polymers are generally
deemed as matrices. This is because blending nanocelluloses with hydrophobic polymers can yield weak interfacial bonding between polymer matrices and nanofillers,
resulting in increasing water uptake and filler aggregation with respect to hydrogen
bonding [130].
Graphene oxides (GOs) are two-dimensional nanomaterials synthesised from
natural graphite. Such nanosheets can be easily prepared from graphite flakes by
thermal oxidation, as recommended by Hummers [131]. GOs possess high mechanical properties (e.g. elastic modulus: 0.25 TPa), binding potential, high aspect
ratio, high flexibility and superior processibility [132]. Moreover, due to their good
hydrophilic characteristic, GOs can be easily exfoliated into monolayer nanosheets
stably dispersed in water, primarily due to plenty of hydrophilic oxygenated groups
[133]. These functional groups play a significant role in the improvement of GO
dispersion in solvents or within polymer matrices through covalent or non-covalent
bonding [133]. However, a high tendency of GO agglomeration can limit their use
at high nanofiller content levels. Recently, Chang et al. [134] examined the toxicity
and biocompatibility of GOs on A549 cells, which suggested that GOs induced the
oxidative stress and a slight decrease in cell viability at the high GO content.
1.5 Processing of Bionanocomposites
One of most common methods used for bionanocomposite preparation is solution
casting. Its first step involves nanoparticle dispersion in either water or organic
solvents by stirring or ultrasonic treatment. Subsequently, polymers and nanoparticles are mixed and stirred together in a solution. The final step is then to evaporate
the solvents in order to produce final nanocomposites. Solution casting has been
successfully employed in the manufacture of various bionanocomposites such as