Laser-induced adhesion enhancement of polymer composites and metal alloys

Abstract

Proper surface treatment of an adherend is among the decisive factors concerning the final quality and durability of an adhesive joint. Various surface treatments are applied to plastic and metal adherends; among them are abrasive treatment, chemical treatment, and plasma etching. An alternative method is presented here which utilizes an excimer UV laser as a new technique for preadhesion surface treatment. Experimental results indicated that preadhesion laser surface treatment improved significantly the shear strength of adhesively bonded aluminum joints as compared with untreated or anodized substrates. Laser treatment also improved the adhesion strength of polycarbonate, polyetherimide, and composite adherends as compared with untreated or simply abraded substrates. Optimal laser treatment parameters (intensity, repetition rate, and number of pulses) depend on the substrate material and its chemical nature. As a result of laser treatment, the mode of failure changed from interfacial to cohesive as long as ablation did not occur. The adhesion enhancement resulted from morphological changes of the adherend surface caused by the laser irradiation as revealed by SEM (scanning electron microscopy), and from chemical modification and surface cleaning as indicated by ESCA (electron spectroscopy for chemical analysis) and FTIR (Fourier transform infrared spectroscopy). It can be concluded that the excimer laser has potential as a precise, clean, ecologically favorable, and simple preadhesion treatment for a wide variety of materials.