Direct bonding mechanism of titanium and PET resin via heating and pressurization: Influence of bubble dynamics on bonding strength

• A positive correlation between the bubble area ratio and bonding strength was identified. • Bubbles were generated around 160 °C due to gas components derived from ethylene glycol in PET. • Pressure exerted by bubbles enhanced the adhesion of PET to Ti plate. • Formation of Ti-C compounds significantly improved bonding strength. In response to growing environmental concerns, the transportation industry, including automotive and aerospace sectors, has emphasized improving fuel efficiency and reducing carbon dioxide emissions. To achieve significant weight reduction, multi-material design strategies that strategically utilize different materials based on their properties are being adopted. This trend highlights the need for advanced joining technologies capable of bonding dissimilar materials, such as metals and polymers or resins, while maintaining structural integrity and lightweight performance. This study investigates the direct bonding mechanism between pure titanium (Ti) and polyethylene terephthalate (PET) resin using a simple heating and pressurization process. Bubble formation at the bonding interface, a critical factor influencing joint strength, was analyzed through in-situ observation. Results show that controlled bubble dynamics enhance bonding by creating localized pressure, while excessive bubbles act as defects. Optimal bonding conditions were identified at 200–300 °C with relatively high bonding shear stress. X-ray photoelectron spectroscopy revealed the formation of Ti-C bonds, confirming strong chemical interactions at the interface. Additionally, pyrolysis gas chromatography-mass spectrometry identified ethylene glycol as a key component in bubble generation during thermal decomposition of PET. The findings highlight the significance of surface preparation, thermal control, and bubble management in achieving high bonding strength. This research provides insights into sustainable and efficient methods of dissimilar materials that can improve recyclability and support the development of advanced lightweight structures.