Improvement of adhesive bonding of polypropylene and maleic anhydride grafted polypropylene blends to aluminium by means of addition of cyclic butylene terephthalate

In this work the adhesive bonding of polymeric blends based on polypropylene (PP), cyclic butylene terephthalate (CBT) and maleic anhydride grafted polypropylene (PP-g-MA) to aluminium was studied, with the aim of developing metal/polymer hybrid laminates for a multitude of applications among which the automotive and aeronautic sectors stand out. Different films with homogeneous compositions have been prepared and joined to aluminium (with any previous surface treatment) and the adhesive bonding has been characterized under the standard UNE-EN 1465. For binary blends, there is a critical PP-g-MA and CBT composition from which the shear strength declines. The combined presence of the PP-g-MA and CBT in the blend prevents this critical composition due to the possible Van der Waals forces and/or esterification/transesterification reactions created between the reactive chains. In addition, if the transformation from CBT to pCBT takes place at the same time as the joining process, the shear resistance of the laminated increases between 10% and 25%. The adhesive bonding between layers improves in two ways: the lower viscosity of the developed blends makes an easier substrate impregnation, and the active sites created during the ring opening polymerization (ROP) are capable of forming chemical bonds.