EFFECT OF ULTRASONIC WELDING PROCESS PARAMETERS ON THE CRYSTALLINITY OF GF/MWCNT/PP COMPOSITES

Abstract

Ultrasonic welding (USW) is a rapid and efficient joining method for thermoplastic polymer composites. This joining technique offers a high bonding strength between composite materials to form lightweight, durable structures in a costeffective way, compared to other traditional joining methods. Crystallinity at the bond line can influence mechanical properties and chemical resistance. However, despite technological development of the USW process, the underlying crystallization mechanisms at the welded interface are still insufficiently understood. This paper explores the use of polypropylene (PP) and multifunctional multi-walled carbon nanotube (MWCNT/PP) films to perform USW between glass fiber (GF)/PP adherends and the resulting effect of welding parameters on the crystallinity degree at the bonded interface. After the USW process, PP and MWCNT films were isolated from glass fiber laminates using Kapton tapes. The effect of MWCNT content (0, 5, 10, 15, 20, 25 wt.%) and welding parameters on the crystallinity of the films and the welded interface was analyzed using differential scanning calorimetry (DSC) and Scanning electron microscopy (SEM), respectively. It was found that increasing MWCNT percentage resulted in a lower degree of crystallinity (44-34%) for the films and for the welded composite interface (23-9%). Four sets of different parameters (welding force and vibration amplitude) were used in this experiment, (500N, 38.1μm), (500N, 54.0μm), (1500N, 38.1μm), and (1500N, 54.0μm), representing different welding times. It was found that increasing force and amplitude resulted in a higher and lower degree of crystallinity, respectively, at the welded interface. Thus, it is expected that the change of crystallinity during USW may be partially attributed to strain-induced crystallization mechanisms.