Investigation of tribo-electrostatic separation mechanism for thermoplastics in e-waste based on functional group distribution and surface potential

With the global dramatic increase in e-waste, recycling thermoplastics in e-waste through tribo-electrostatic separation has become essential. In this study, the internal and external functional group distribution of four typical thermoplastics including polyvinyl chloride (PVC), high impact polystyrene (HIPS), polypropylene (PP) and acrylonitrile–butadiene–styrene (ABS) were analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). A certain degree of oxidation, mainly exhibited as –OH, existed in all thermoplastics. For the first time, atomic force microscopy (AFM) was employed to assess surface potentials of thermoplastics, and their total electronegativity was calculated by integrating the content and electronegativity of various functional groups. The order of surface potential and total electronegativity in four thermoplastics is consistent: PVC (−4.08 V, 2.74) > HIPS (−8.36 V, 2.59) > PP (−9.18 V, 2.57) > ABS (−11.30 V, 2.56). Both content and electronegativity of functional groups in thermoplastics significantly influence surface potential levels. The variations in volume resistivity and relative dielectric constant (RDC) of thermoplastics under different environmental conditions suggested that low relative humidity and low temperature (particularly lower temperature) are more conducive to separation. Effective separation and recycling of binary mixed thermoplastics could be accomplished via tribo-electrostatic method. Thermoplastics with higher surface potential are more inclined to gain electrons and negatively charged, finally enriched in positive electrode. The greater the surface potential difference between two thermoplastics, the higher purity of their separation products. For instance, both positive and negative product purities of the ABS-PVC exceeded 97 % (surface potential difference of 7.22 V).