Figure 3 shows the TGA curves and DSC thermograms
of the PVA/PAA films and PVA/PAA/glyoxal films. The
TGA curves show distinct weight loss regions. The first
stage represents the loss of weakly physisorbed water and
the second stage corresponds to the decomposition of the
side chain of PVA. The third stage indicates decomposition
of the main chain of PVA. As the PVA/PAA ratio
increased, the total weight loss of the PVA/PAA films
increased. The total weight loss of the PVA/PAA/glyoxal
films also decreased as the glyoxal weight percentage
increased. From the DSC thermograms, the melting temperature
(Tm) of the film was found to decrease with
increase in PVA/PAA ratio. Addition of glyoxal improved
the degree of crystallinity and lowered the Tm value of
PVA/PAA/glyoxal, resulting in better tensile properties.
Increased crosslinking is indicated by a left-shift (to lower
temperature) of the Tm value.2