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. 2025 Apr 16;30(8):1786.
doi: 10.3390/molecules30081786.

Influence of Partial Disentanglement of Macromolecules on the Rheological, Thermal, and Mechanical Properties of Polypropylene-Polyethylene Blends

Justyna Krajenta  1 , Magdalena Lipinska  2 , Andrzej Pawlak  1
Affiliations

Influence of Partial Disentanglement of Macromolecules on the Rheological, Thermal, and Mechanical Properties of Polypropylene-Polyethylene Blends

Justyna Krajenta et al. Molecules. .

Abstract

The properties of compatibilized blends of polyethylene (PE) and polypropylene (PP), having reduced macromolecular entanglements, were studied. The density of PP macromolecular entanglements was controlled by prior disentangling in solution. The polymer ratio in the blend was 4:1 or 1:4. An ethylene-octene copolymer was used as a compatibilizer. The melt blending process resulted in good dispersion of the minority component, with slightly larger inclusions when more disentangled PP was used. Rheological studies confirmed the achievement of different entanglement densities of PP macromolecules in the blends. The partial disentanglement did not affect the thermal stability of the blends. During the isothermal crystallization studies, faster growth of PP spherulites was observed in the blend with reduced entanglements, which also influenced the entire crystallization process. The recovery time of equilibrium entanglement was investigated and it turned out to be 45 min if the blend was annealed at 190 °C, which was shorter than in the analogous homopolymer. Studies of tensile properties showed that in blends with a majority share of polyethylene, the elongation at break increased with the disentanglement of the minority component, due to better bonding of the blend components and thus the reduction in microcavitation.

Keywords: crystallization; entanglements; polypropylene–polyethylene blends.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Morphologies of polymer blends: (a) PPe/PE (76:19), (b) PPe/PE (19:76), (c) PP1/PE (76:19), (d) PP1/PE (19:76), (e) PP05/PE (76:19), (f) PP05/PE (19:76). The bars show a size of 10 µm. Higher magnification photos show smaller inclusions of the dispersed phase in the blends: (g) PPe/PE (76:19), (h) PPe/PE (19:76). The bars here indicate a size of 1 µm.
Figure 2
Figure 2
The numerical frequencies of inclusions of dispersed polymer with specific diameters: (a) PPe/PE (76:19), (b) PP1/PE (76:19), (c) PP05/PE (76:19), (d) PPe/PE (19:76), (e) PP1/PE (19:76), (f) PP05/PE (19:76).
Figure 3
Figure 3
(a) The weight loss during heating of homopolymers in airflow as a function of temperature, (b) the derivative of the weight change of homopolymers as a function of temperature, (c) the weight loss during heating of blends in airflow as a function of temperature, (d) the derivative of the weight change of blends as a function of temperature.
Figure 4
Figure 4
The rheological properties measured by a frequency sweep test: (a) storage modulus of homopolymers and entangled blends, (b) loss modulus of homopolymers and entangled blends, (c) storage modulus of 76:19:5 wt.% blends, (d) loss modulus of 76:19:5 wt.% blends, (e) storage modulus of 19:76:5 wt.% blends, (f) loss modulus of 19:76:5 wt.% blends.
Figure 5
Figure 5
The heat flow during isothermal crystallization: (a) the crystallization of differently entangled PP at 135 °C; (b) the crystallization of PP in blends in which its content was 76 wt.%, carried out at a temperature of 135 °C; (c) the crystallization of PP in 76:19 blends at 137 °C; (d) the crystallization in blends with a composition of 19:76 carried out at a temperature of 125 °C; (e) melting samples of blends with a composition of 19:76 after crystallization at 125 °C.
Figure 6
Figure 6
The heat flow during isothermal crystallization: (a) the crystallization of PE in blends of composition 19:76 at 123 °C. The red curve almost overlaps the green curve. (b) The crystallization of PE in blends of composition 76:19 at 123 °C. (c) The melting of the PP1/PE (19:76) blend after isothermal crystallization at 123 °C.
Figure 7
Figure 7
(a) Morphology of PP05/PE (19:76) blend after crystallization at 123 °C, observed in a polarized optical microscope. A fine crystal structure is visible; (b) Spherulites of PP growing in the PP05/PE (76:19) blend at 135 °C. The polarizers in this case were not completely crossed in order to better show the boundaries of spherulites.
Figure 8
Figure 8
Growth rate of PP spherulites, measured at 135 °C as a function of the annealing time of the blends at 190 °C.
Figure 9
Figure 9
Typical stress–strain relationships for the tested blends: (a) blends containing 76 wt.% PP; (b) blends containing 19 wt.% PP.
Figure 10
Figure 10
Morphologies of highly deformed (i.e., shortly before breaking) samples of (a) PPe/PE (19:76), (b) PP1/PE (19:76), and (c) PP05/PE (19:76).
Figure 11
Figure 11
SAXS patterns recorded for the blends studied: (a) PPe/PE (76:19) before deformation, (b) PPe/PE (76:19) after deformation, (c) PP1/PE (76:19) after deformation, (d) PP05/PE (76:19) after deformation, (e) PPe/PE (19:76) before deformation, (f) PPe/PE (19:76) after deformation, (g) PP1/PE (19:76) after deformation, (h) PP05/PE (19:76) after deformation. The numbers near the scattering images show the ratio of the scattering intensity to the scattering intensity from the non-deformed, equilibrium entangled blend. Deformation direction was horizontal.
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