Investigation into the effect of Peel Ply surface preparation on adhesive bond performance

Abstract

An adhesive joint's strength is directly proportional to the quality of its bonding surface. One element influencing the quality of the bonding surface is the surface preparation before adhesive application. There are various methods to prepare a surface before a bond is applied, such as mechanical, chemical, and physical methods. The most-employed surface preparation method used in the industry involves sanding the surfaces with sandpaper by hand and wiping with solvent to remove contaminants. This process has several disadvantages: cost, time, dust, and limited repeatability in sanding quality. An alternative process which has become standard practice in many spheres is merely applying the adhesive to the bonding surface directly after the removal of the outer peel ply layer - with no additional surface preparation. This process eliminates all four of the previously mentioned disadvantages of the hand sanding method. An experimental investigation was initiated to examine the influence that the peel ply method has on the bonding strength and its ability to replace the hand sanding method. Double lap-shear loaded specimens were used to compare different types of peel plies with each other and with the benchmark, which was prepared using the hand sanding method. This study also investigated additional effects of surface degradation over time and surface contamination. Experimental data showed that the peel ply method outperformed the hand sanding method; however, only with certain types of peel ply. The experimental data also showed that the bonding strength decreases considerably when the bond surface is exposed to the atmosphere for more than eight hours before bonding. A similar decrease was observed when the peel ply was beforehand contaminated with carbon and glass fibre dust. Therefore, when employing the peel ply method, it is essential to control the time interval between the removal of the peel ply and adhesive application as well as the environment where the peel ply is stored.