Application and mechanism of amidoxime modification for flotation separation of recycled acrylonitrile-butadiene-styrene and recycled high impact polystyrene in WEEE

Recycled acrylonitrile-butadiene-styrene (rABS) and recycled high impact polystyrene (rHIPS) are two common types of plastics found in Waste Electrical and Electronic Equipment (WEEE). Due to their hydrophobic nature, separating these two plastics by flotation is a challenging task. This paper proposed a pioneering amidoxime modification for the flotation separation of rABS and rHIPS. In flotation experiments, the optimal modification conditions were determined to be a modification temperature of 70 ℃, a modification time of 75 min, and an NH 2 OH·HCl concentration of 0.18 mol/L. These conditions resulted in recovery of 96.54 % and purity of 98.16 % for rABS, and recovery of 98.15 % and purity of 96.65 % for rHIPS. To further investigate the mechanism of amidoxime modification for flotation separation of rABS and rHIPS, the surface chemical environment of the two plastics was analyzed through Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. The results showed that the nitrile groups in rABS reacted with NH 2 OH·HCl to form amidoxime groups, while rHIPS did not react with NH 2 OH·HCl. Scanning electron microscopy and contact angle results revealed that the surface morphology of rABS samples was changed and their hydrophilicity was significantly increased after amidoxime modification, resulting in a difference in hydrophilicity compared to rHIPS. This difference can be utilized to facilitate the efficient flotation separation of rABS and rHIPS.