The dispersion of LS in PUR/NR (1/1) latex blend
differs considerably from that of the PUR. The TEM
picture in Figure 3 shows that NR and PUR are not
compatible. Note that particles from the sulfur prevulcanized
NR appear dark in these TEM images. Layered
silicate stacks can be located at the boundary of
the PUR (light) and NR (dark) phases. Pronounced
intercalation and possible exfoliation took place only
in the PUR phase [see Fig. 3(b)]. The silicate layers and
aggregates cover the NR particles, resulting in a skeleton
(house of cards) structure. This peculiar morphology
is rather specific for NR nanocomposites produced
by the latex route if the length of the LS is
commensurable with that of the rubber particle size inthe latex. Based on the TEM results, we can now
explain the difference in the XRD spectra of the PUR
and PUR/NR latices. Recall that LS is less intercalated
by NR than by PUR. So, in the case of the PUR/NR
blend, PUR should intercalate double the amount of
LS because the volume is excluded by NR. Bearing in
mind that there is an optimum in the LS content in
respect to intercalation/exfoliation phenomena, a substantial
increase in the LS may cause its reaggregation
(confinement). However, this does not necessarily
yield a deterioration in the mechanical properties. Recall
that the prevulcanized NR particles force the silicate
aggregates in the neighboring PUR phase to cover
their surface. This results in a skeleton morphology as
the length of the silicate layers is higher than those of
the diameter of the particles (Fig. 3). The formation of
this skeleton structure may yield improved mechanical
properties.