Differences in the cellular morphology of neat PLA and
the three PLA/CNF composites are shown in Figure 6. The
SEM images revealed well interconnected foams of PLA
nanocomposites. Neat PLA exhibited cellular structures
with large cell diameters of 52.6 µm and a cell density of
0.56×109
cells/cm3
. As shown in Table II, the average cell
size of the PLA foams decreased with increasing CNF content
due to the increased viscosity which obstructed cell
growth in the polymer matrix. The solubility and diffusivity
of gas in semi-crystalline polymers influence the degree of
crystallinity because gas does not dissolve in the crystallites.
Increasing the mass fraction of crystallite in the polymer
PLA by dissolution of CO2 gas
the viscosity of the PLA/CNF (5 wt%) nanocomposite
decreased rapidly even from the highest initial viscosity,
which may have been cause by the tendency of the CNFs at
high content to agglomerate into larger aggregates and induce a