Effects of additives on PVC plastics surface and the natural flotability

The polyvinyl chloride (PVC) plastics with calcium carbonate (CaCO3) or di-n-octyl phthalate (DnOP) serving as additive were chosen to investigate the effects of additives on the surface of PVC plastic, and flotation tests were conducted to study the natural flotability of PVC plastics. The surface free energy of the polished and original surface of PVC plastics demonstrates that the crushed or shredded particles in the flotation system present the true surface property of plastics, and the additives show significant impacts on the surface free energy of PVC plastics. The addition of CaCO3 results in an increase of the attraction force between plastic surface and water, and a decrease of the adhesion force between plastic surface and bubble, and thus the flotability is reduced. DnOP decreases the attraction force between plastic and water and increases the adhesion force between plastic and bubble, and thus the hydrophobicity of plastic is enhanced while the flotability rises. Flotation tests of PVC plastics and waste PVC plastics confirmed the above conclusions, and infrared spectra of the two waste plastics verified the influence of the additives. These conclusions provide some insights into flotation technique with respect to plastic separation, especially for the recovery of waste PVC plastics.