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Two-dimensional infrared for monitoring the structural variations of UV-aged recycled polypropylene straps used in the Ecuadorian banana industry

Abstract:

Mechanical stress, humidity, and prolonged UV radiation are the main degradation agents of plastics when exposed to environmental conditions. In Ecuador, besides its usage in the packaging industry, plastic straps are used in banana plantations to support growing crops. However, when straps suffer degradation, they become useless, transforming into tons of plastic waste. The plastic strapping industry seeks a more sustainable production model by incorporating recycled plastics without compromising product quality. For this study, industrial straps manufactured with virgin and recycled polypropylene (PP) were exposed to artificial UV radiation at 200, 400, 600, 800, and 1000-h intervals. Fourier transform infrared spectroscopy (FTIR) was applied to illustrate the effect of carbonyl peaks due to degradation. Nevertheless, as the carbonyl index proved unreliable for PP degradation monitoring, dynamic changes at the molecular level due to UV exposure were followed through two-dimensional correlation FTIR (2D COS FTIR) methodology. Also, thermo-mechanical properties were assessed to compare and verify variations in the UV-aged straps' crystallinity degree, melting temperature, and tensile strength with the spectra obtained with 2D COS FTIR. Morphological characterization via scanning electron microscopy confirmed the formation of a brittle surface due to the UV radiation effect. Results show that novel two-dimensional correlation tools could be used to correlate the physical properties with photodegradation of PP materials exposed to UV radiation in outdoor applications.