The variations in the degree of swelling (DS) and water
solubility (S) of the PVA/PAA/glyoxal film with glyoxal content are shown in Figure 4. The number of hydroxyl groups in the untreated PVA/PAA films decreased as
the weight ratio of glyoxal to PVA/PAA in the films
increased. Consequently, the DS decreased with increasing
weight percentage of glyoxal to PVA/PAA because
the free volume decreased owing to the crosslinking reaction
of PVA/PAA and glyoxal.7 The water solubility of the
PVA/PVA/glyoxal films decreased slightly with increasing
weight percentage of glyoxal to PVA/PVA. However,
the solubility of the PVA/PVA/glyoxal films was relatively
constant. A water durability test confirmed that indicated that the glyoxal improved the degree of crystallinity
and lowered the Tm of the PVA/PAA/glyoxal films
leading to better tensile properties. Increased crosslinking
was indicated by a left-shift of the Tm value. At a
PVA/PAA ratio of 85/15, a tensile strength of 48.6 N/mm2
was achieved for the PVA/PAA film. However, the introduction
of glyoxal into the crosslinked PVA/PAA/glyoxal
film (10 wt% glyoxal) increased the tensile strength by
55% relative to the pure PVA/PAA (85/15) film. The
degree of swelling (DS) and solubility(S) of the 10 wt%
(PVA/PAA = 85/15, wt%) film with 10 wt% glyoxal were
1.54 and 0.6, respectively