Rheological Behaviour of PP/PET and Modified PP/PET Blends. I. Steady State Flow Properties

Abstract

Both polypropylene (PP) and polyethylene terephthalate (PET) constitute a significant portion of post-consumer waste. To improve the recycling of immiscible PP/PET blends, a compatibiliser should be utilised. The steady shear flow properties of unmodified and modified PP/PET blends having up to 50 wt.% PET were investigated and compared in this study. Three types of PPs with different flow properties were used to ascertain the influence of the matrix on the blend's rheology. The effect of modification on the rheological properties was evaluated in two ways - firstly, the addition of 1 wt.% of maleic anhydride (MA), and secondly, the use of already modified polypropylene. According to the morphological observations, an improvement in compatibility was found in both cases. The shear viscosity and the first normal stress difference were measured using a rotational cone and plate rheometer at 265°C (when both PET and PP are molten), and 245°C (when only PP has melted). Completely different behaviour was observed under these two temperature conditions. At 265°C, the shear viscosity decreases with PET content in the blend, while at 245°C it increases, thus recalling the behaviour of particle-filled systems. The addition of maleic anhydride affects the shear viscosity in various ways; a decrease, an increase, and some almost unchanged values were obtained. Concerning the first normal stress difference, an even more complex situation occurs, and the effect of modification by MA is also ambiguous. Furthermore, the deviations from the log-additivity rule were evaluated in terms of the shear viscosity and the first normal stress difference. From the results, it can be supposed that PP-X/PET samples were compatibilised successfully, and strong interphase interactions could be expected. Finally, the yield values of shear stress determined at 245°C showed a generally increasing tendency with increasing PET content.

Rheological Behaviour of PP/PET and Modified PP/PET Blends. II. Dynamic Viscoelastic Properties

“…Firstly, the morphological features are summarized based on the results from the electron scanning microscopy. As shown in Part I 28 , blends of PP and PET exhibited a phase structure typical of immiscible systems (large PET particles, poor interfacial adhesion). For compatibilised blends, in contrast, the particle size reduction and the improvement in the interfacial adhesion were recorded, especially for the PP-K/PET/MA and PP-X/PET specimens, i.e.…”

“…In addition, the first one differed from the others by having a significantly higher viscosity (melt flow rate 1.2 g/10 min); PP-K and PP-X, in contrast, showed similar values (50 g/ 10 min). More detailed material characterization was given in Part I 28 .…”

Rheology‐morphology correlation in PET/PP blends: Influence of type of compatibilizer

“…In the melt, the PP‐ g ‐MA may interact with the evolving PP droplets through van der Waals bonding between the PP chain and the olefinic segments of PP‐ g ‐MA. Its interaction with PET probably occurs as a result of a dipole–dipole interaction involving the PET carbonyl groups and the anhydride groups in the PP‐ g ‐MA . Above 5 wt%, which represents the saturation of the interface by the modifier, the particle size attains a steady‐state value.…”

“…Generally, the strength and stiffness of their blends increase almost linearly with higher PET content, but owing to their incompatibility, the blends exhibit very poor impact strength. Hence, appropriate compatibilization is needed to achieve better adhesion between the two phases and to overcome brittleness .…”

“…Several studies have been published on the compatibilization of blends containing PET and PP or polyethylene (PE). The most widely used reactive functional agents or groups for the compatibilization of PET with PO are acrylic acid , maleic anhydride (MA) , and epoxy groups , which react with the hydroxyl or carboxyl end groups of PET. These reactive groups result in a different extents of compatibilization and hence different properties are obtained.…”