a) b - École Polytechnique de Montréal

Addition of small amounts of HDPE to the binary blend of PS/PMMA results in a matrix/core-
shell dispersed phase morphology where the PS is the shell and HDPE is the core(point b in
Figure 6-12). Further increasing the concentration of HDPE leads to an increase in both the
number of core-shell dispersions and the core volume. At 33% HDPE, the continuity data shows
that HDPE forms its first connected pathway, the percolation threshold for HDPE. A further
increase of HDPE to 44% results in the formation of a tri-continuous (type I) morphology as
shown at point c where all phases, HDPE, PS and PMMA, are continuous. Figure 6-12 indicates
that, at the peak of the continuity diagram, a perfectly uniform and continuous layer of 10%PS
with a continuity of 97% situates at the interface of co-continuous HDPE and PMMA phases. In
a previous paper(J. Zhang, et al., 2007) from this laboratory, a PS continuity level of 69% was
observed for a 3%PS/50%HDPE/47%PMMA blend. Figure 6-12 suggests that the maximum
continuity for PS is obtained at a blend concentration of 10PS/43HDPE/47PMMA. Further
increasing the quantity of HDPE at point d, results in droplets of PMMA encapsulated in PS
shells. Finally, at 100%HDPE a matrix/droplet morphology of 90/10 HDPE/PS is observed(point
e in Figure 6-12).
6.4.8 Observations on the Effect of Viscosity on the Morphological State
It is well known that the viscosity ratio can have a significant effect on both the size and shape of
dispersed phases in a polymer blend(B. D. Favis, 2000). In this section it will be shown that
extreme changes in the viscosity of the PMMA phase (L-PMMA and H-PMMA) in a
HDPE/PS/PMMA blend of constant composition still results in morphological structures where
the PS separates HDPE and PMMA. Note that L-PMMA is the same PMMA used in all the rest
of this work. The viscosity of high molecular weight PMMA used here is almost 200 times that
of the viscosity of low molecular weight PMMA leading to a huge corresponding increase in the
PS/PMMA viscosity ratio. Two ternary blends comprised of 35/40/25 HDPE/PS/L-PMMA and
35/40/25 HDPE/PS/H-PMMA are prepared and the resulting morphology is shown in Figure 6-
13. Both blends using low molecular weight PMMA and high molecular weight PMMA
demonstrate a bi-continuous/PMMA droplet morphology, Figures 6-13a and 6-13b show that the
L-PMMA phase is present as numerous small droplets encapsulated in PS. In Figure 6-13a the L-
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