The same mechanical properties trends were obtained in the
case of CA/HEC blends (Table 3, Entries 11e14). The comparison
between the mechanical properties of CA/PVOH and CA/HEC blends of the same composition showed similar properties when the blend
composition CA/WSP is around 50/50 (Table 3, Entries 5 and 12). At
high composition of the water soluble polymer (PVOH and HEC),
the CA/PVOH blend has better mechanical properties (Table 3,
Entries 7 and 14).
Blends morphology was studied by scanning electron microscopy
(SEM) with a view to further investigate their mechanical
performances. As representative examples, SEM microphotographs
of cryofractured surfaces of the uncompatibilized and compatibilized
CA/PVOH blends with 48 and 69 wt% pPVOH are shown in
Fig. 2. A morphological analysis of the fracture surface evidences an
increase of adhesion between blend components on the compatibilized
blend, which is more evident on the PVOH-enriched blends.
Indeed, small CA domains dispersed in the uncompatibilized blend
can be easy recognized while they are almost not present in the
compatibilized composition. Confirmation of the transition from a
dispersed to a co-continuous-like morphology after blend compatibilization
was obtained after selective PVOH etching of both
compositions in water. Actually, the immersion of the uncompatibilized
composition in water led to a complete fragmentation and
the recovery of CA nodules dispersed in water. In contrast, the
compatibilized sample remained monolithic after PVOH removal as
expected for a co-continuous-like blend morphology (Fig. 3).