Oxygen cold plasma treatment on polypropylene: influence of process parameters on surface wettability

Polypropylene is one of the most versatile polymers. The wide range of physical properties and relative ease of processing make it an extremely attractive material capable of competing with more expensive resins in a number of demanding applications. Its key limitation is its poor adhesion towards paints. The low polarity of the molecules in polypropylene is the cause of the low surface energy of these plastics. Increasing the surface energy is one of the major purposes of pretreatment for such plastics. The cold plasma process represents a more efficient, cleaner and cheaper treatment than the flaming traditional treatment to activate polypropylene surfaces. The aim of this work has been to evaluate the influence of oxygen cold plasma parameters on wettability of polypropylene surfaces treated. The wettability aging time has been also assessed because it represents a fundamental step to plan the insertion of the plasma process inside an industrial system. A set of process variables ( voltage, time and pressure) has been identified and used to carry out some experimental tests on the basis of Design of Experiment techniques. The polypropylene wettability has been quantitatively characterised by the standard procedure detailed in ASTM D724 along the aging time.