Delaminating Metal–Polymer Composites through CO2 Bubble Nucleation and Crystallization for Material Recycle in Electric Vehicles

Recycling metal–polymer composites in electric vehicles (EVs) is a complex but crucial aspect of achieving sustainability in the automotive industry. To enable effective recycling of multimaterials in EVs, it is essential to ensure the thorough separation of all constituent materials. In this study, we demonstrated the effectiveness of bubble nucleation at higher saturation pressure, followed by subsequent heating, in achieving nearly complete delamination of the metal–polymer interface. A lap-shear assembly comprising aluminum alloy (Al) and 40 wt % glass fiber-reinforced polycarbonate (PCGF40) with a joined strength of 20 MPa as a test piece of EV part were impregnated with CO2 at a saturation pressure of 12.5 MPa and a temperature of 80 °C for 24 h. Subsequently, the impregnated samples were heated at different temperatures (110–150 °C) for 3 min to induce bubble nucleation at atmospheric pressure. The presence of crystallinity in the impregnated samples due to high saturation pressure was confirmed through differential scanning calorimetry (DSC) data. Tensile lap-shear strength tests were conducted on all samples to determine the maximum separation load, as per ISO19095-3 fixture standards. The results indicated a decrease in the maximum separation load with increasing the heating temperature, attributed to the presence of bubbles at the interface and fractures in the polymer matrix, as clarified by X-ray computed tomography (X-ray CT). Cohesive failure was observed at the temperature of 150 °C. The smallest maximum separation load and polymer residue were achieved for the sample heated at 140 °C. Through the crystallization of polycarbonate and bubble nucleation processes, the findings of this study demonstrate a successful reduction of approximately 95% in the maximum separation load compared to the control sample, showcasing an effective strategy for achieving nearly complete delamination of metal/semicrystalline polymers.