5.2 Interphase Characterisation of PVA-Based Bionanocomposites
131
suggests that interphases can play a more important role in enhancing mechanical
properties of PVA nanocomposites with better bonded matrix–filler interactions.
Moreover, it has also been demonstrated that the surface area of inner interface gives
rise to relatively high overall interphase modulus in contrast with corresponding
surface area of outer interface. As mentioned earlier by Liu et al. [13], the interphase
zone with modulus-gradient effect can be divided into two different regions, namely
Region 1 and Region 2 for a typical case in Fig. 5.10d, in which Region 1 is in contact
with nanoparticle zones with relatively high interphase density when compared with
Region 2. Additionally, Fan et al. [17] reported that increasing the interphase density
inevitably led to the modulus enhancement for the same type of materials, which
was in good accordance with high interphase modulus results obtained in case of the
surface area of inner interface. Apparently, the right boundary of Region 1 where
inner interface is located is adjacent to nanoparticles zones with higher density and
elastic modulus. The relationship between interphase modulus and interphase volume
is demonstrated in Fig. 5.10e, Fig. 5.11c, d in case of PVA/NBC bionanocomposites, PVA/HNT bionanocomposites and PVA/Cloisite 30B clay bionanocomposites,
respectively, on the basis of fully and partially embedded nanoparticles in PVA-based
bionanocomposites. It is clearly identified that the significant enhancement of interphase modulus takes place with increasing interphase volume, which is similar to the
case by increasing SA Interphase . The same applies to fully embedded nanoparticles,
resulting in much greater interphase modulus than partially embedded counterparts
in terms of interphase volume in PVA-based bionanocomposites.
Aspect ratio is used as an important factor to evaluate the reinforcement efficiency
of nanofillers within polymer matrices. The determination of aspect ratio can be much
easier when dealing with nanofillers in regular size and shape. However, in reality,
irregular nanofillers in different shapes often occur leading to the complexity of
aspect ratios due to the effect of multi-stage dispersion processing techniques used
in manufacturing nanocomposites [1]. In addition to aspect ratios of nanofillers,
interphase dimensions and properties can also be affected by the nanofiller dispersion. Liu and Brinson [1] and Alishahi et al. [18] suggested based on theoretical
modelling that an effective parameter in controlling the reinforcement efficiency of
nanofillers is the interphase volume per unit nanofiller volume (V interphase /V nanofillers )
instead of V interphase alone. In this work, V interphase /V nanofillers has been utilised in
PVA bionanocomposites for all three nanofillers used with corresponding results
being presented in Fig. 5.12. It is clearly observed that with increasing V nanofillers ,
V interphase /V nanofillers significantly decreases for PVA bionanocomposites reinforced
with NBCs and Cloisite 30B clays though this tendency becomes less pronounced for
PVA/HNT bionanocomposites. Overall, the inclusion of NBCs in PVA bionanocomposites induces the highest values of V interphase /V nanofillers when compared with those
of HNTs and Cloisite 30B clays. This finding suggests the most effective reinforcement efficiency of NBCs leading to the highest mechanical properties of PVA/NBC
bionanocomposites.
131
suggests that interphases can play a more important role in enhancing mechanical
properties of PVA nanocomposites with better bonded matrix–filler interactions.
Moreover, it has also been demonstrated that the surface area of inner interface gives
rise to relatively high overall interphase modulus in contrast with corresponding
surface area of outer interface. As mentioned earlier by Liu et al. [13], the interphase
zone with modulus-gradient effect can be divided into two different regions, namely
Region 1 and Region 2 for a typical case in Fig. 5.10d, in which Region 1 is in contact
with nanoparticle zones with relatively high interphase density when compared with
Region 2. Additionally, Fan et al. [17] reported that increasing the interphase density
inevitably led to the modulus enhancement for the same type of materials, which
was in good accordance with high interphase modulus results obtained in case of the
surface area of inner interface. Apparently, the right boundary of Region 1 where
inner interface is located is adjacent to nanoparticles zones with higher density and
elastic modulus. The relationship between interphase modulus and interphase volume
is demonstrated in Fig. 5.10e, Fig. 5.11c, d in case of PVA/NBC bionanocomposites, PVA/HNT bionanocomposites and PVA/Cloisite 30B clay bionanocomposites,
respectively, on the basis of fully and partially embedded nanoparticles in PVA-based
bionanocomposites. It is clearly identified that the significant enhancement of interphase modulus takes place with increasing interphase volume, which is similar to the
case by increasing SA Interphase . The same applies to fully embedded nanoparticles,
resulting in much greater interphase modulus than partially embedded counterparts
in terms of interphase volume in PVA-based bionanocomposites.
Aspect ratio is used as an important factor to evaluate the reinforcement efficiency
of nanofillers within polymer matrices. The determination of aspect ratio can be much
easier when dealing with nanofillers in regular size and shape. However, in reality,
irregular nanofillers in different shapes often occur leading to the complexity of
aspect ratios due to the effect of multi-stage dispersion processing techniques used
in manufacturing nanocomposites [1]. In addition to aspect ratios of nanofillers,
interphase dimensions and properties can also be affected by the nanofiller dispersion. Liu and Brinson [1] and Alishahi et al. [18] suggested based on theoretical
modelling that an effective parameter in controlling the reinforcement efficiency of
nanofillers is the interphase volume per unit nanofiller volume (V interphase /V nanofillers )
instead of V interphase alone. In this work, V interphase /V nanofillers has been utilised in
PVA bionanocomposites for all three nanofillers used with corresponding results
being presented in Fig. 5.12. It is clearly observed that with increasing V nanofillers ,
V interphase /V nanofillers significantly decreases for PVA bionanocomposites reinforced
with NBCs and Cloisite 30B clays though this tendency becomes less pronounced for
PVA/HNT bionanocomposites. Overall, the inclusion of NBCs in PVA bionanocomposites induces the highest values of V interphase /V nanofillers when compared with those
of HNTs and Cloisite 30B clays. This finding suggests the most effective reinforcement efficiency of NBCs leading to the highest mechanical properties of PVA/NBC
bionanocomposites.