ROLE OF HELIUM PLASMA PRETREATMENT IN THE STABILITY OF THE WETTABILITY, ADHESION, AND MECHANICAL-PROPERTIES OF AMMONIA PLASMA-TREATED POLYMERS - APPLICATION TO THE AL-POLYPROPYLENE SYSTEM

The stability of a plasma-treated polymer surface is an important issu e, but very often a surface rendered wettable by the treatment is foun d to revert to a less wettable state with time. The purpose of this wo rk was to minimize the ageing phenomenon by stabilizing the surface la yer via crosslinking using an inert gas discharge. The stability of th e wettability, adhesion, and mechanical properties of treated polyprop ylene (PP) has been investigated by a comparative study of two differe nt plasma treatments (i.e. an NH3 plasma and a He plasma pretreatment carried out before the NH3 plasma; He plasma is well known to crosslin k polymer surfaces). The aluminium-polypropylene (Al-PP) interfaces pr esent very different features depending on the gas treatment. The role of the treatment time has been pointed out and under our experimental conditions, a treatment time of the order of a few seconds seems to b e an overtreatment leading to degradation of the adhesion and mechanic al properties. A broad interphase was obtained for an NH3-overtreated PP, in contrast to the abrupt one formed when pretreated with the heli um gas followed by NH3 treatment. Good correlations between wettabilit y and mechanical properties with adhesion measurements were establishe d.