2.3. Measurement of contact angle
Before the measurement of contact angle, different kinds of sur-faces were prepared to detect the contact angles. Plates of PVC resin and PVC plastics with different content of additives were tailo-red into 20 mm × 20 mm, and then put into tap water containing washing powder, tap water and distilled water in ultrasonic gen-erator (Shanghai Ultrasonic Co. Ltd., China) for 10 min in sequenceto clean, respectively. In order to study the impacts of additives,the polished surface of PVC resin and PVC plastics were prepared.Plates of PVC resin and PVC plastics were cut into 20 mm × 20 mm,lapped by hand using 400-mesh oil stone, polished through 800-mesh and 1200-mesh waterproof abrasive paper, and then washedin the same way demonstrated above.A JJC-I contact angle measuring instrument (Changchun Opti-cal Instrument Factory, China) is employed to measure the contact angle of liquid on the solid surface, and the measurement of contact angle is demonstrated in detail in our previous paper [13].