Microwave irradiation of polypropylene surface: a study on wettability and adhesion

The effect of microwave irradiation on the surface characteristic of polypropylene (PP) was investigated in presence of potassium permanganate. Contact angle measurements, SEM and FTIR-ATR technique were employed to study the changes in the surface of the samples. The vertical pull-off test method was used to evaluate the adhesion strength of an acrylic lacquer on the treated PP samples. A relative increase in the surface free energy of the treated PP was observed. The surface became hydrophilic on exposure to microwave irradiation for 120 s. SEM revealed a slightly pitted structure on the surface of PP due to the treatment. FTIR-ATR analysis of treated surface showed some chemical changes evident from presence of carbonyl group and also formation of carbon double bonds. The adhesion measurement tests on bonded joints demonstrated an increase in performance as revealed by a change in the locus of failure from adhesive to cohesive failure within the bond line.