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. 2025 Jun 3;17(11):1556.
doi: 10.3390/polym17111556.

Sustainable Polypropylene Blends: Balancing Recycled Content with Processability and Performance

Tatiana Zhiltsova  1   2 , Mónica S A Oliveira  1   2
Affiliations

Sustainable Polypropylene Blends: Balancing Recycled Content with Processability and Performance

Tatiana Zhiltsova et al. Polymers (Basel). .

Abstract

The increasing demand for sustainable materials has renewed interest in recycling polyolefins, particularly polypropylene (PP), due to its widespread use and environmental persistence. Post-consumer recycled polypropylene (PPr), however, often exhibits compromised properties from prior exposure to thermal, oxidative, and mechanical degradation. This study investigates the potential of using post-consumer PPr in melt-blended extrusion formulations with virgin PP (PPv), focusing on how different PPr contents affect processability, thermal stability, oxidative resistance, and mechanical performance. Blends containing 25%, 50%, and 75% PPr, as well as 100% PPr and virgin PP, were evaluated using melt flow index (MFI), differential scanning calorimetry (DSC), oxidation induction time (OIT), thermogravimetric analysis (TGA), and tensile testing. Results show that increasing PPr content improves polymer fluidity and thermal stability under inert conditions but significantly reduces oxidation resistance and ductility. However, the 25% PPr blend demonstrated a favourable balance between performance and recyclability, presenting 96% of the elastic modulus and 101% of the yield strength of PPv. Homogenization by extrusion improved the oxidative stability of recycled PP by 22% compared to its non-extruded form. These findings support the use of low-to-moderate levels of PPr in virgin PP for applications requiring predictable and tunable performance. contributing to circular economy goals.

Keywords: crystallinity; law of mixtures; mechanical properties; melt blending; oxidation stability; polymer recycling; recycled polypropylene; thermal degradation.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
MFI of PPv, PPr, and their blends at different recycled content levels. The dotted line represents the linear regression fit.
Figure 2
Figure 2
DSC thermograms of PPv, PPr, and their blends at different recycled content levels.
Figure 3
Figure 3
Oxidation induction time (OIT) of PPv and its blends with PPr: (a) Full dataset including virgin PP; (b) PPv/PPr blends at different PPr recycled content. The dotted line represents the linear regression fit.
Figure 4
Figure 4
Thermal properties of PPv, PPr, and their blends (a) TGA thermograms (b) Derivative thermogravimetry thermograms. The inset in (b) highlights the differences in peak degradation temperatures among the samples.
Figure 5
Figure 5
Tensile properties of PPv, PPr, and their blends: (a) Stress–strain curves; (b) normalized mechanical properties (%).
Figure 6
Figure 6
Elastic modulus of PPv, PPr, and their blends at different PPr recycled content. The dotted line represents the linear regression fit.
See this image and copyright information in PMC

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