Interaction of Food-Packaging Plastic Residue and Bitumen: A Chemical and Mechanical Analysis

Abstract

This paper aims to analyze the chemical and mechanical effects of the interaction between recycled plastics, derived from food packaging and bitumen, in order to assess the potential use of the plastics as a component of bituminous mixtures. The growing difficulty in recycling multilayer food-packaging residues, typically composed of polyethylene, polypropylene, polyethylene terephthalate, cellulose, and aluminum, motivates the investigation of alternative high-volume reuse pathways such as asphalt applications. Chemical properties of plastics were assessed by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier-transform infrared (FTIR) spectroscopy. The interaction between bitumen and plastics was induced by mixing them at 150°C with different mixing speeds, durations, and proportions. Bitumen was then separated by sieving. The chemical and thermomechanical properties of bitumen before and after interaction with plastics were compared, considering the short-term aging effects caused by the mixing procedure. Chemical characterization was conducted by means of FTIR spectroscopy, while thermomechanical characterization was performed using a dynamic shear rheometer (DSR). TGA and DSC data suggest that the plastic is composed by a blend of different polymers and a residue of cardboard. From spectroscopic analysis, moderate variations in specific absorption bands were observed after mixing at 20% plastic content; however, these changes may be associated either with partial interaction phenomena or with finely dispersed inclusions passing through the sieve. The interaction between the two materials has effects on the thermomechanical properties of the bitumen, which presented similar characteristics as those observed in modified binders. In particular, at 20% plastic content and prolonged mixing, a reduction of the purely viscous (Newtonian flow) asymptote at high temperature was observed, together with variations in oxidation-related functional groups. The results indicate the potential use of the plastic as a material for asphalt mixtures.