1.6 Bionanocomposite Properties and Characterisation
29
properties and bulk properties is not limited to PVA alone, but can be applied to
different polymers or composites. For instance, the storage modulus of epoxy was
measured to be 17 GPa via nanomechanical measurement as opposed to 3–4 GPa for
their bulk composites determined by tensile tests [184]. Moreover, elastic modulus
of bulk poly(ether sulfone) (PESU) membrane substrates was found to be only 151.7
± 7.9 MPa [197] when compared to 3.2 ± 0.3 GPa for PESU films at a nanoscaled
level [198].
1.6.4 Thermal Properties
The thermal properties of polymeric materials can be quantified by several techniques. Among these, thermogravimetric analysis (TGA) and DSC are the most
popular characterisation techniques. TGA is used to measure the weight loss resulting
from the formation of volatile products or chemical reactions as a function of temperature and/or time, while DSC is utilised to measure T g , crystallisation temperature (T c )
and T m of polymeric materials. In a polymer/clay nanocomposite system, the inclusion of layered silicates within polymer matrices can improve the thermal stability by
acting as an insulator and mass transport barrier to volatile products that are generated
through the degradation process [25]. For instance, the decomposition temperature
of PVA/5wt% MMT nanocomposites has increased to 354 °C as opposed to 337 °C
for pure PVA [13]. Moreover, the T g of PVA was also increased from 34 to 60 °C
when MMT content increased up to 10 wt%. Such a finding was related to uniform
dispersion of MMTs, which dissipated the applied heat through the polymer, thereby
leading to the enhanced heat resistance for final nanocomposites [13]. In addition,
Mallakpour et al. [139] reported that the degradation of PVA was promoted with the
inclusion of fluorohectorite or MMTs. The char yield of PVA at 800 °C was also
increased from 6% to 19% in case of PVA/5 wt% MMT nanocomposites, implying
the improvement of thermal stability at the higher temperature [139]. Another study
showed that the thermal decomposition temperature of PVA/OMLS nanocomposites
shifted to a marginally higher temperature compared with that of pure PVA [199].
This phenomenon was explained according to Stawhecker and Manias [140] that PVA
could supply oxygen by itself to initiate the thermal decomposition. Conversely, the
reduction in the thermal stability of nanocomposites has also been noted as stacklayered silicates can accumulate the heat at the early stages of decomposition [142].
Alkali ammonium cations existing in OMLS may experience subsequent decomposition by Hofmann elimination leading to the acceleration of polymer degradation
[4, 142]. Katti et al. [200] indicated that the addition of MMTs and hydroxyapatite (HAP) to chitosan improved the thermal stability of such new nanocomposites
with even higher onset temperature and the percentage residue left at 500 °C when
compared to chitosan/MMT nanocomposites.
29
properties and bulk properties is not limited to PVA alone, but can be applied to
different polymers or composites. For instance, the storage modulus of epoxy was
measured to be 17 GPa via nanomechanical measurement as opposed to 3–4 GPa for
their bulk composites determined by tensile tests [184]. Moreover, elastic modulus
of bulk poly(ether sulfone) (PESU) membrane substrates was found to be only 151.7
± 7.9 MPa [197] when compared to 3.2 ± 0.3 GPa for PESU films at a nanoscaled
level [198].
1.6.4 Thermal Properties
The thermal properties of polymeric materials can be quantified by several techniques. Among these, thermogravimetric analysis (TGA) and DSC are the most
popular characterisation techniques. TGA is used to measure the weight loss resulting
from the formation of volatile products or chemical reactions as a function of temperature and/or time, while DSC is utilised to measure T g , crystallisation temperature (T c )
and T m of polymeric materials. In a polymer/clay nanocomposite system, the inclusion of layered silicates within polymer matrices can improve the thermal stability by
acting as an insulator and mass transport barrier to volatile products that are generated
through the degradation process [25]. For instance, the decomposition temperature
of PVA/5wt% MMT nanocomposites has increased to 354 °C as opposed to 337 °C
for pure PVA [13]. Moreover, the T g of PVA was also increased from 34 to 60 °C
when MMT content increased up to 10 wt%. Such a finding was related to uniform
dispersion of MMTs, which dissipated the applied heat through the polymer, thereby
leading to the enhanced heat resistance for final nanocomposites [13]. In addition,
Mallakpour et al. [139] reported that the degradation of PVA was promoted with the
inclusion of fluorohectorite or MMTs. The char yield of PVA at 800 °C was also
increased from 6% to 19% in case of PVA/5 wt% MMT nanocomposites, implying
the improvement of thermal stability at the higher temperature [139]. Another study
showed that the thermal decomposition temperature of PVA/OMLS nanocomposites
shifted to a marginally higher temperature compared with that of pure PVA [199].
This phenomenon was explained according to Stawhecker and Manias [140] that PVA
could supply oxygen by itself to initiate the thermal decomposition. Conversely, the
reduction in the thermal stability of nanocomposites has also been noted as stacklayered silicates can accumulate the heat at the early stages of decomposition [142].
Alkali ammonium cations existing in OMLS may experience subsequent decomposition by Hofmann elimination leading to the acceleration of polymer degradation
[4, 142]. Katti et al. [200] indicated that the addition of MMTs and hydroxyapatite (HAP) to chitosan improved the thermal stability of such new nanocomposites
with even higher onset temperature and the percentage residue left at 500 °C when
compared to chitosan/MMT nanocomposites.