Combination of sodium hypochlorite pretreatment and flotation towards separation of polycarbonate from waste plastic mixtures.

This study developed a novel method, surface pretreatment using sodium hypochlorite along with flotation, to facilitate separation of waste polycarbonate from plastic mixtures for recycling. Surface pretreatment was observed that has an obviously negative effect on the floating ratio of polycarbonate and the floating ratio of poly-methyl-methacrylate, polystyrene, and polyvinylchloride was not affected in flotation, and this difference in floating ratio can be expected to separate polycarbonate from plastic mixtures. The optimum conditions obtained included sodium hypochlorite concentration of 0.05 M, pretreatment temperature of 70.0 °C, pretreatment time of 60.0 min, frother dosage of 10.8 mg/L, and flotation time of 4.0 min. Under optimum conditions, polycarbonate was separated effectively from multiple plastic mixtures, and the purity and recovery were 99.8% and 100.0%, respectively. The major mechanism of surface pretreatment was ascertained by the aid of Fourier transform infrared, scanning electron microscope, energy dispersive spectrometer, and X-ray photoelectron spectroscopy, and the hydrophilic groups, pitting, and protuberances introduced on polycarbonate surface caused the reduced floating ratio of polycarbonate. Accordingly, this method can be expected to improve the recycling quality of waste plastics, and provides technological insights in the environmentally friendly disposal of waste plastics.

Application of surface modification using sodium hypochlorite for helping flotation separation of acrylonitrile-butadiene-styrene and polystyrene plastics of WEEE.

Acrylonitrile-butadiene-styrene (ABS) and polystyrene (PS), as important fractions of Waste from Electric and Electronic Equipment (WEEE) plastics, show great significances to the recycling of WEEE. The objective of this study is to develop a simple, practical and efficient surface modification method using sodium hypochlorite (NaClO) for separation of waste ABS and PS plastics by the aid of froth flotation. After surface modification, more hydrophilic groups are introduced on ABS surface than that of PS, enhancing its surface hydrophilicity clearly and reducing its recovery in floated products. Single parameter experiments demonstrate NaClO concentration, treatment temperature, treatment time are key parameters in surface modification. Optimization of conditions for surface modification of ABS was conducted by Response Surface Methodology with a Box-Behnken design, and a predicting model was obtained also. The optimum conditions are NaClO concentration of 0.05 M/L, temperature of 67.50 °C, treatment time 59.50 min and stirring rate of 200 rpm. Under optimum conditions, ABS and PS with different particle sizes can be separated efficiently with recovery of 99.18% and 99.47%, and purity of 99.45% and 99.18% respectively. The application of surface modification using sodium hypochlorite can facilitate efficient flotation separation of waste ABS and PS plastics for the recycling of WEEE.