The use of adhesives in place of traditional joining techniques as welding and riveting is becoming increasingly common in structural design. Compared to other conventional joining processes, adhesive bonding offers several advantages: including acoustic insulation, vibration attenuation, structure lightening, corrosion reduction and uniform stress distribution. These benefits can be offset if the surfaces to be bonded are not carefully cleaned, degreased and prepared. Many approaches to surface treatments based on physical or chemical modifications have been developed in the years in order to improve the surface activity. Although widely used and very efficient, these techniques present several disadvantages. Physical methods based on mechanical abrasion are supposed to extend bonding area as they increase the roughness, but cause an extensive degradation to the specimens and they are often not easy to reproduce. On the other hand, chemical treatments are typically used with the aim of modifying both morphology and chemical structure of the substrates layers, but they present serious environmental problems of waste disposal, which has moved investigations to an industrial alternative to these processes. According, the use of energetic methods of surface cleaning, such as laser and plasma cleaning processes have been recently consolidated since they are useful to modify the topmost layers of the substrates, increasing their reactivity, without affecting the bulk material properties. These treatments offer an effective and environment-friendly processing of different materials, providing strong and durable bonds with adhesives through modification of the surface morphology and functionalities. In this study, the effects of laser and low pressure plasma treatments on mechanical properties of adhesive bonded joints has been investigated and compared performing lap-shear tests

Polyolefins are considered among the most difficult polymeric materials to treat because they have poor adhesive properties and high chemical barrier responses. In this paper, an in-depth study is reported for the low pressure plasma (LPP) treatment of neutral polypropylene to improve adhesion properties. Changes in wettability, chemical species, surface morphology and roughness of the polypropylene surfaces were evaluated by water contact angle measurement, X-ray photoelectron spectroscopy and, furthermore, atomic force microscopy (AFM). Finally, the bonded joints were subjected to tensile tests, in order to evaluate the practical effect of changes in adhesion properties. The results indicate that plasma is an effective treatment for the surface preparation of polypropylene for the creation of bonded joints: contact angles decreased significantly depending on the plasma-parameter setup, surface morphology was also found to vary with plasma power, exposure time and working gas.