Significant Enhancement of the Adhesion Properties of Chemically Functionalized Polypropylene

Organosilicon compounds have been actively used with nano- and micro-fillers to improve the adhesion and mechanical properties. However, studies on the adhesion properties of polymeric materials, such as polypropylene (PP), functionalized with organosilicon compounds are limited. Here, we investigated the adhesion of organosilanized PP substrates, functionalized using (3-glycidoxypropyl)trimethoxysilane (GPTMS) and (3-aminopropyl)trimethoxysilane (APTMS) as coupling agents, with epoxy adhesives. The curing of epoxy-functionalized PP (PP-EPOXY) with triethylenetetramine (TETA) hardener led to the chemical crosslinking of TETA with PP-EPOXY, as determined by X-ray photoelectron spectroscopy and vacuum Fourier-transform infrared spectroscopy. Similarly, the curing of amine-functionalized PP (PP-NH₂) with bisphenol A diglycidyl ether (DGEBA) epoxy resin led to the chemical crosslinking of the resin with PP-NH₂. Finally, we measured the adhesion properties of the functionalized PP substrates using an adhesive composed of DGEBA and TETA based on ASTM D3163 and observed that the shear strength of PP-EPOXY and PP-NH₂ increased significantly up to 580% and 506% as compared with that of bare PP. These results strongly suggest that the functionalization of PP significantly contributes to the improvement of adhesion with an adhesive.