It was expected that the network structure obtained by introducing
PAA into the PVA would increase the thermal properties of pure
PVA by restricting the segmental motion of the pure PVA polymer
chains. To investigate how PAA affects the thermal properties of
the PVA/PAA blend films, DSC and TGA analyses were performed
under a nitrogen atmosphere. The results are shown in Figs 5 and
6 and summarized in Table 1.
The glass transition temperature (Tg) of pure PVA and pure PAA
are 77.1 ∘C and 122.7 ∘C (Fig. 5). At low PAA contents (1% and
5%) the Tg values decrease, but they increase significantly at high
PAA levels. These results indicate that the intermolecular bond in
the hydrogen bonding of PVA chains disturbed the interaction
between PVA and PAA at low amounts of PAA, while the effect of steric hindrance reduced the chain mobility leading to higher Tg
values at the high contents of 10% and 20%.27,28 Generally, the Tg
represents the amorphous regions of a polymer, as well as polymer
chain mobility.5 In this case, the PAA is crosslinked with PVA in
its amorphous regions through chemical condensation, restricting
the molecular chain mobility