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phr CBA loading was observed via optical microscopy as shown in
Figure 4. All samples showed the oval shape and homogeneous
closed-cell structure. In other words, each cell is surrounded by
connected faces with any ruptures. CBA started to decompose at
temperature higher than 135 ºC and released a gas in the
nanocomposite system, which can cause the bubble nucleation and
growth from the surface of CNFs used as a nucleant. [10,11] In addition,
to achieve the closed-cell system, the nanocomposite should have a
sufficient melt viscosity and strength not so as to break the cell wall. [12]
It thus can be thought that the presence of CNFs served as the
efficient nucleation sites, as well as contributed to produce a closed-
cell structure in foaming process. We also found that the average cell
size was prominently increased as the blowing time and temperature
increased. These two conditions facilitate the decomposition of blowing
agent.
In Table 2, we summarized the morphological parameters of PBS/2
wt% CNFs nanocomposite foaming for 5 min. Average cell size (d) was
calculated by measuring the maximum diameter of each cell
perpendicular to the skin from an OM micrograph, and cell density (Nc)
and mean cell-wall thickness (δ) are given by
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