Adhesion, wettability and mechanical properties of ammonia- and helium-plasma-treated polypropylene

The physicochemical modifications of ammonia-treated polypropylene (PP) films have been studied and characterized in terms of acid-base properties using the contact angle titration method and X-ray photoelectron spectroscopy in conjunction with a molecular probe technique using chloroform as a reference Lewis acid. These techniques have shown that PP surfaces that have been treated for between 0.7-1 s are basic in character. For longer treatment times, the basic character of the surfaces decreases, as shown by the above techniques and confirmed by time of flight-secondary ion mass spectroscopy (ToF-SIMS). On the other hand, for such treatment times, a degradation of the adhesion and mechanical properties was observed. The ageing of an ammonia-plasma-treated PP was limited by a helium (Ne) plasma pretreatment known to crosslink the surface, stabilizing in this way the wettability, adhesion and mechanical properties. ToF-SIMS was performed on helium treated High Density Polyethylene (HDPE) in order to point out the structural modifications.