Epitaxial Crystallization of Linear Polyethylene in Blends with Isotactic Polypropylene

Abstract

The structure and morphology of extrusion oriented ribbons of polypropylene / polyethylene blends is described. The blends with 20, 30 and 40% of oriented isotactic polypropylene fibrils show homo-and hetero-epitaxial structures. Partial mutual solubility of the blend components influenced the melting and crystallization behavior.

Continuous Cooling Curve Diagrams of Isotactic-Polypropylene/Polyethylene Blends: Mutual Nucleating Effects under Fast Cooling Conditions

“…Thus, it can be already stated that there is a certain nucleating effect toward HDPE in the presence of PPn domains, while this effect is absent in the presence of PPp domains. A similar effect was already reported by Last in blends of low-density PE and PP, and by Rybnikar and Kaszonyiova for binary blends of linear PE and PP as major and minor components, respectively. Furthermore, in the work of Zhang and Ajji, a nucleating effect toward the PE phase at the interface in blends of LLDPE and PP was found and related to the difference in T c between LLDPE and the type of PP used.…”

“…1.7 °C was detected between the T c of neat and the T c of blended PPn. In previous studies, this effect of PE on the crystallization kinetics of PP, when melt-blended, was reported and explained as either a diluent effect of the PE phase (still molten at the temperatures at which PP crystallizes) on the crystallizing PP phase 7,13 or as a decrease in the number of heterogeneous nuclei in the PP phase due to their migration toward PE domains. 10,60 However, the first hypothesis seems not appropriate to explain this phenomenon for the present case study.…”

“…On the contrary, Rybnikár et al reported a higher crystallization rate of linear PE blended with PP, which was explained as changes in the concentration of nuclei of different types. However, in a more recent work of Rybnikár et al, the enhancement of the linear PE crystallization rate was attributed to the nucleating action of the previously crystallized PP phase upon cooling from the melt. Nevertheless, a thorough understanding of the crystallization behavior of PE/PP blends upon processing-relevant conditions is still lacking.…”

“…To unveil the complex crystallization behavior of recycled PE/PP blends, the first approach consists of studying crystallization of blends in different compositions, which have been prepared in a laboratory using different virgin materials. Several studies on PE/PP blends were carried out in the last decades to relate together the structure, properties, and processing conditions for academic and industrial purposes. − A point of agreement between different authors is that the presence of PE in a blend with PP reduces the nuclei density of the latter. However, the growth rate of PP was found unchanged in immiscible blends with high-density PE (HDPE) and low-density PE (LDPE), ,,,, while a significative decrease in growth rate was found for blends of PP and linear-low-density PE (LLDPE) .…”

Improving the Mechanical Performance of LDPE/PP Blends through Microfibrillation

“…It has been reported that in compatibilized PP/PET microfibrillated composites, the aspect ratio of microfibrils and mechanical properties improves only up to an optimum amount, above which the properties are not only not enhanced, but are actually diminished. ,, …”