Towards Sustainable Food Packaging: Mechanical Recycling Effects on Thermochromic Polymers Performance

Area of Science:

• Materials Science
• Polymer Recycling
• Food Packaging Technology

Background:

• Thermochromic pigments (TPs) enhance food packaging by indicating temperature, improving safety and reducing waste.
• The recyclability of TPs integrated into packaging materials is not well understood, especially concerning property retention.
• Polypropylene (PP) is a common food packaging material, making its blends with TPs relevant for industrial application.

Purpose of the Study:

• To investigate the impact of mechanical recycling on polypropylene (PP) blends containing thermochromic pigments (TPs).
• To evaluate changes in thermal stability, color transition, mechanical integrity, and surface morphology after multiple recycling cycles.
• To assess the feasibility of using TPs in sustainable and intelligent food packaging systems considering recyclability.

Main Methods:

• Three PP formulations with varying TP concentrations (0%, 2%, 8%) were prepared.
• Materials underwent five cycles of mechanical recycling.
• Properties analyzed included thermal stability, color transition behavior (ΔE*ab), mechanical strength, and surface morphology.

Main Results:

• Pure PP (PP100/TP0) showed minimal degradation (6% crystallinity loss, ΔE*ab = 1.45) after recycling.
• PP with 2% TPs (PP98/TP2) exhibited moderate property loss: -10.8% mechanical strength, ΔE*ab = 6.52.
• PP with 8% TPs (PP92/TP8) showed significant degradation: +3.8 °C activation temperature increase, 42.9% saturation loss, attributed to polymer breakdown and pigment aggregation.

Conclusions:

• Mechanical recycling negatively affects the properties of PP blends containing thermochromic pigments.
• Higher TP concentrations lead to more pronounced degradation, limiting their use in recyclable intelligent packaging.
• Further research is needed to improve TP stability during reprocessing for circular packaging applications.