could not be foamed when rapidly depressurized at room
temperature. Consequently, cell nucleation could occur heterogeneously
at high energy regions such as the boundaries
between the solid LDPE and melt polysiloxane phases and
the boundaries between the solid microbead and melt polysiloxane
phases. Thus, it was expected that the addition of
LDPE would increase the cell density of the foamed body.
However, the opposite results were obtained. Thus, we surmised
from the results that a 10 wt.% addition of LDPE does
not make more nucleation sites per unit volume than a
4 wt.% addition of 20 μm-microbead. Note that the addition
of 10 wt.% LDPE decreased the content of microbeads from
40 % (SiOC1) to 36 % (SiOC2) (see Table 1). This means
that the size of the dispersed LDPE in the extruded blends
should be larger than the size of the microbead, i.e., ~20 μm.
A previous paper [12] confirmed that the microbead in
polysiloxane and microbead blends acted as a nucleating site
for the cells during foaming. Thus, the use of a smaller
microbead led to a higher population density of nucleation
sites per unit volume, resulting in a higher overall cell density.
The present results suggest that smaller microbead is a
more efficient nucleating agent than LDPE and larger microbead
in polysiloxane-LDPE-microbead blends.