4.1 Effect of glycerol content on morphology
PE/TPS blends display a discrete morphology where LDPE is the matrix, especially at low
TPS content. The combined effect of glycerol content and the elongational flow exerted on
PE/TPS blends (TPS concentration 30 wt%) during quenching can be observed in Figure 6.
PE1 blends prepared with TPS40 and TPS36 (Figures 6a and 6b) show a high level of
deformation in the machine direction. Conversely, blends compounded with TPS29 show
very little deformation (Figure 6c) and even less when prepared with PE2 (Figure 6d). The
singular morphologies displayed by PE/TPS blends are closely related to the differences in
viscosity of both TPS and PE. As mentioned in section 3, it was found that 30% glycerol is
required to effectively plasticize starch (Rodriguez-Gonzalez et al., 2004). From Figure 6, it
can be seen that below that limit, the viscosity and elasticity of TPS are too high to allow the
LDPE matrix to greatly deform the TPS dispersed phase. When the Low-viscosity PE2 is
used, it can be seen (Figure 6d) that the dispersed particles of TPS are of a spherical nature
and that the particle size has increased compared to those of PE2/TPS29 blends (Figure 6c).
These results clearly demonstrate that a high degree of morphological control is possible for
this system and that the full range from spherical dispersed phase to that of a highly
deformed fibrillar phase can be obtained at a given TPS concentration level. In fact, it is
apparent that the control of the glycerol concentration allows one to modify the state of the
starch from that of a solid particle to that of a quasi crosslinked dispersed phase to that of a
highly deformable material.