Different surface treatments to improve the adhesion of polypropylene

Injection-molded samples of polypropylene were exposed to oxygen plasma and SACO (SAndblasting and COating) treatments. The pretreated surfaces were successively adhesively bonded or lacquered. The adhesion strength and failure mode of these specimens were examined. The surfaces obtained after treatments were characterized by electron spectroscopy for chemical analysis (ESCA), contact angle measurements, and scanning electron microscopy (SEM). Both microroughness and chemical modification of the surface led to an increase in adhesion by up to a factor of 10. The stability of the surface changes generated during the plasma and SACO pretreatments was observed by different kinds of aging experiments in air and water. The aging of SACO-treated surfaces led to no significant change on the surface. In the case of plasma-treated surfaces, hydrophobic recovery during aging in air reduced the polarity of the surface layer. During aging in water, no hydrophobic recovery on the surface was observed.