Graphene-loaded recycled PET: Exploring and enhancing electrical conductivity through processing and laser treatments near the electrical percolation threshold

The blend of polyethylene terephthalate (PET), among the most employed polymer, with graphene, among the most adopted conductive carbon materials, may represent a favorable and sustainable approach for the fabrication of value-added conductive composite materials. This work targeted on the fabrication of meltcompounded composites via injection molding process starting from homemade recycled PET (r-PET) and different loadings of graphene nanoplatelets (GnPs) with different lateral sizes (5 and 25 mu m, respectively), used as conductive fillers. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) investigations of the different r-PET/GnP-based compounds provided information about composition, textural and structural properties of the melt-compounded specimens, which were correlated with their DC electrical properties. Graphene loadings higher than ca. 9.5-10 wt% were found enough to achieve the electrical percolation within the two material types. With higher graphene loadings, electrical conductivity increased, due to the formation of a progressively developed percolation network. Notably, the effects of the different GnP loadings, GnP lateral sizes and crystallinity degree of the polymer on the conductivity of the of the melt-compounded specimens were investigated. Furthermore, the effect on the electrical properties of CO2 laser irradiation at different scribing speeds on r-PET/GnP composites with graphene loading below the percolation threshold, was verified. By altering locally the morphology and structure, the irradiation process impacted the electrical properties. Notably, the resulting low sheet resistance suggests potential applications in low-power electronics. In brief, the approach and methodology adopted in the present work, along with the results, can contribute to the development of future upcycling into more valuable and sustainable conductive materials and devices based on recycled PET with a reduced environmental footprint.