Flotation separation of polyethylene terephthalate from waste packaging plastics through ethylene glycol pretreatment assisted by sonication

Abstract

The recycling of packaging plastics is hindered by the various plastic mixtures and their similar surface properties. Plastic separation is a key step to improve recycling efficiency of waste plastics. We proposed a simple and efficient protocol to separate polyethylene terephthalate (PET) from polycarbonate (PC), acrylonitrile-butadienestyrene copolymer (ABS), and polyvinyl chloride (PVC) by converting PET surface from hydrophobicity to hydrophilicity. PET surface was modified by potassiumhydroxide (KOH)and ethylene glycol ((CH₂OH)₂) with the aid of sonication. Contact angle, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to research the reactions on PET surface. It can be confirmed that the reaction of base-catalyzed transesterification occurs, leading to a hydrophilic PET plastic. We investigated the effects of ultrasonic power, ultrasonic time, (CH₂OH)₂ dosage, KOH dosage, flotation time, and frother concentration on the flotation separation. The flotation recovery and purity of PET are 98.8% and 100%, respectively when (CH₂OH)₂ dosage is 10 mL, KOH dosage is 2 g, ultrasonic time is 5 min, ultrasonic intensity is 160 W, flotation time is 4 min, and frother concentration is 52.7 mg/L. This study provided a novel surface modification with reliable mechanisms for the flotation of PET from plastic mixtures.

Keywords: Alcoholysis; Ethylene glycol; Plastic flotation; Surface modification; Transesterification.