IR Spectroscopy as a Diagnostic Tool in the Recycling Process and Evaluation of Recycled Polymeric Materials

Driven by environmental concerns and aligned with the principles of a circular economy, urban plastic waste, such as packaging materials, disposable items, non-functional objects, and industrial plastic scrap is increasingly being collected, recycled, and marketed as a potential substitute for virgin polymeric materials. However, the use of recycled polymers introduces uncertainties that can significantly affect both the durability and the further recyclability of the resulting products. This paper demonstrates how spectroscopic analysis in the mid-infrared (MIR) and near-infrared (NIR) regions can be employed well beyond the basic identification of the main polymeric component—typically performed during the sorting stage of recycling processes. A detailed interpretation of spectral data, based on well-established correlations between spectroscopic response and material structure, enables the classification of recycled polymers according to specific physicochemical properties, such as chemical composition, molecular architecture, and morphology. In this context, infrared spectroscopy not only allows for a reliable comparison with the corresponding virgin polymer reference but also proves particularly effective in evaluating the homogeneity of recycled materials and the reproducibility of their properties—factors not inherently ensured due to the variability of input sources.