Application of froth flotation in the separation of polyvinyl chloride and polycarbonate for recycling of waste plastic based on a novel surface modification

摘要

The complicated stream of waste plastic impedes the recycling of polyvinyl chloride (PVC) and polycarbonate (PC), which can be settled by flotation separation. We proposed a novel chlorine dioxide (ClO_2) pretreatment to assist the separation of PVC and PC by froth flotation, and clarified possible surface reactions of hydrophilic PC by contact angles, scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The hydrolysis and further rearrangement of carbonic esters (O-(C=O)-O) may be deemed as the main reason for hydrophilic PC, introducing oxygenated functional groups, such as hydroxyl groups (C-OH), carboxyl groups (COOH), and tiny acyl chloride (Cl-C=0), on PC surfaces. The robustness of this process was proved by efficient flotation separation of PVC and PC under various conditions of size fractions, frother concentration, mass ratio, and flotation time. The optimal pretreatment conditions for flotation separation of PVC and PC are temperature of 70 °C, ClO_2 concentration of 0.5 g/L, and treatment time of 70 min. The optimal recovery and purity of PC in sunken plastic can stably maintain 97% and 99%, respectively. Compared with waste plastic, raw PC embraces a high floatability after ClO_2 pretreatment, revealing that ageing is conducive to surface modification.