Atmospheric pressure plasma treatment of polypropylene to improve the bonding strength of polypropylene/aluminum composites

The effect of atmospheric pressure plasma treatment of polypropylene (PP) on the peel strength and shear strength between PP and aluminum plates was studied. The optimal treatment number was determined by measuring the changes in the contact angle, paint adhesion strength, and Scotch tape peel strength as a function of treatment number. FTIR and AFM analyses were conducted to determine the chemical and physical changes on the surface of the PP due to the atmospheric pressure plasma treatment. T-peel and SLS tests were performed using untreated PP/aluminum and plasma-treated PP/aluminum specimens to determine the effect of treatment on the peel strength and shear strength of PP/aluminum composites. The results showed that eight plasma treatments were optimal, and the contact angle was reduced from ∼91° to ∼53°. The results also showed that peel and shear strengths improved by ∼42% and ∼44%, respectively, after eight times of treatment. The improved bonding strength was attributed to the increased surface roughness and newly created hydrophilic functional group (C=O) on the polypropylene surface caused by the atmospheric pressure plasma treatment.