A Study on Material Optimization for Polypropylene Nanocomposites Based On Layered Silicates Using Elongational Flow Devices

Over the last years, the use of nano-reinforced polymers increased due to their superior mechanical, thermal and
rheological properties. Polymer nanocomposites (PNCs) which are based on layered silicates feature a higher
Young’s Modulus and increased thermal conductivity.
The aim of this study was to increase the material properties for polypropylene PNCs based on layered silicates by
using elongational flow generating devices with super-imposed shear- and elongational flow and optimized nozzle
geometries. The experiments were carried out at the injection molding compounder (IMC) at the Institute of
Injection Molding at the Montanuniversität Leoben. Two different materials were tested. The first material used was
a lower viscous homopolymer and the second material a higher viscous block copolymer. The formulation of the
compounds was constant at 90 wt% polypropylene, 5 % organoclay and 5 %compatibilizer. Earlier works [1]
showed that there is a significant correlation between die geometries and mechanical properties of PNCs. In order to
gain a better understanding about the differences in influence for various nozzle geometries, five different
hyperbolical and conical nozzles were designed. The varying factors were the nozzle length, the exit diameter and
the injection speed which correlates with the elongation rate and shear rate. The influence of these parameters was
tested for two different materials with a full factorial 23 design (DoE) including two center-points. Additionally the
influence of the investigated factors on intercalation and exfoliation with SAXS-measurements was studied.
The results of the tensile tests showed, that there is more room for influencing the Young’s Modulus of the lower
viscous homopolymer (FIGURE 1), therefore better results for this material were achieved. On the opposite, it was
not possible to achieve satisfying results for the higher viscous block copolymer. This is possibly caused by an
inappropriate process window or the difference in viscosity of compatibilizer and block copolymer. In FIGURE 1
hLr describes a long hyperbolical nozzle with small exit diameter, and hlR describes a short hyperbolical with a big
exit diameter. The same notation was applied for conical dies which can be identified by the prefix k.
As displayed in FIGURE 1, the best results were
achieved with the short hyperbolical die
accompanied with a big exit diameter at the slow
injection flow rate. This indicates that with this
setting, the optimal level and balance between
intercalation and exfoliation was reached. In near
future, further intensive research, especially
concerning a flexible multi nozzle system, is
planned. Furthermore, the processing temperatures
for the block copolymer will be lowered and the
PP will be additivated with a stabilizer against
thermo-oxidative degradation.