3. Results and discussion
3.1. The effects of additives on the surface of PVC plastics
3.1.1. Surfaces of plastic particle in flotation systemBased on the determined data of contact angles, surface free energy of various surface were calculated and the results are shownin Table 2. It is observed that both the original and polished surfacesof PVC resin show similar surface properties, which can be ascribedto the uniformity of PVC resin. The difference in surface free energybetween PVC-Ca0and PVC resin may be owing to the effects oflow-surface-energy substances such as paraffins, while surface freeenergy of PVC-Ca50reflects the impacts of the stabilizers such a slead stearate. The surface free energy of the original surface of PVC-Ca0and that of PVC-Ca50are similar, but the surface free energy of