Thermal stabilities of PVA, PWA and PWA/PVA nanofiber were
analyzed through TG and DSC measurement and the results were
shown in Fig. 4. It could be observed in Fig. 4(A) that three main
degradation stages emerged in the TG curves of PVA and PWA/
PVA nanofiber. The first weight loss occurring around 100 C
was due to the removal of absorbed water molecules. The second
weight loss region between 110 and 300 C corresponded to the
dehydration from hydroxyl groups in PVA polymer between
intra- or inter-chains. The third weight loss appeared at about
400 and 420 C for PVA and PWA/PVA nanofiber, respectively.
This weight loss region was mainly correlated to the decomposition
of polymer main chains. This result suggested that the thermal
stability of PWA/PVA nanofiber was better than that of PVA
and this would be favorable for the long-term transesterification
to produce biodiesel production. The improved thermal stability
might be due to the interaction between PVA and PWA in PWA/
PVA nanofiber as analyzed in FTIR. The TG curves of PWA exhibited
one main weight loss stages below 600 C. This stage
occurred around 100 C, which was associated with the loss of
absorbed water molecules.
Fig. 4(B) shows the DSC curves of PVA, PWA and PWA/PVA
nanofiber. In the DSC curve of PVA, the two endothermic peaks
at 170 and 310 C were ascribed to the desolvation and dehydration
which were consistent with TG curves. Additionally, the peak
at 250 C in the DSC curve of PVA, which did not appear in the corresponding
TG curve, was the melting peak of PVA crystal. However,
no melting peaks, that is, no crystal existed in the PWA/PVA