This
work deals with the influence of the nature of a filler on the thermally
induced crystalline structure of polylactide (PLA)-based nanocomposites.
Particularly two types of silicated clay both having a platelet-like
shape, i.e., talc and kaolin, were melt compounded with PLA, and the
crystalline structure involved during isothermal crystallization was
followed in situ by means of both wide- and small-angle
X-ray scattering techniques. Results indicate that even if the two
types of clay are chemically similar, i.e., they both exhibit silicate
surfaces, only talc plays the role of nucleating agent on the PLA
crystallization. Moreover, structural analyses reveal that for PLA
nanocomposites filled with talc a transcrystallization process occurs
and that, in addition to the perpendicular growth of the PLA crystals
toward the clay surface, a well-ordered nanometer scaled structure
can be formed depending on the crystallization temperature. Particularly,
for the first time, an epitaxial growth process has been evidenced,
and crystallographic orientation relationships between the PLA crystals
and the talc platelets have been determined. In opposition, the same
behavior was not encountered for the kaolin-based nanocomposites.
From a fundamental point of view, this study shows that the existence
of favorable interactions between the polymer and the filler is not
the only parameter involving the nucleating effect process. Indeed,
the existence of crystallographic relationships between the filler
and the polymer crystalline structure is also a necessary condition
to observe a nucleating effect. Finally, this work also highlights
that incorporating a well-chosen filler into a polymer matrix can
be an efficient route to induce nanostructured materials.
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