Insights on the use of PVB nanocomposites as energy directors in ultrasonic welding of epoxy composites

The selection of an adequate coupling film for welding thermoset composites (TSC) is primary for improving the degree of automation in the composite industry. Ultrasonic welding (UW) is a well-established technique for joining composites and has recently been utilized in the aerospace and automotive industries. To achieve an efficient joining, the use of a polymer-based material placed at the welding interface called an energy director (ED) is required. The choice of the coupling layer material is linked to several requirements, such as processing temperature, high adhesion to the TSC adherend and mechanical strength of the resulting welded joints. Most importantly, the viscoelastic dissipation of the ED influences the heating mechanism and the joint behaviour since the hysteresis loops generated during welding are dissipated into viscoelastic heat. In this work, the authors investigated the possibility of using Poly-vinyl-butyral (PVB) reinforced with graphite nanoplatelets (GNPs) as a coupling layer in UW of TSC adherents, showing that an improvement of lap shear strength (LSS) of 80% with respect to neat PVB.