In a previous article, we reported the preparation
and characterization of a nanocomposite of poly(Llactic
acid) (PLLA) and silica via the in situ melt polymerization
of L-lactic acid in the presence of acidic silica sol.
In this study, the isothermal crystallization and melting
behaviors of a PLLA/silicon dioxide (SiO2) nanocomposite
with 5 wt % well-dispersed SiO2 nanoparticles (PLLASN5)
and pure PLLA were comparatively studied with differential
scanning calorimetry and polarized optical microscopy.
The SiO2 nanoparticles acted as nucleation agents in
the PLLA matrix and enhanced its nucleation rate and
overall crystallization rate, especially at high crystallization
temperatures. However, no deleterious effect on the crystal
morphology or crystallinity was observed. The crystals
that formed at a low temperature were imperfect; therefore,
double melting peaks occurred during the second
heating scan because of melt recrystallization. With the
crystallization temperature increasing, the crystals became
increasingly perfect; as a result, the low melting peak
increased and shifted to a higher temperature. The existence
of SiO2 nanoparticles had no effect on the equilibrium
temperature of the PLLA matrix. Pure PLLA and
PLLASN5 have the same equilibrium temperature of
171.5
C. VVC